24 October 2016

Talking to the Farside: A 1963 Proposal to Use the Apollo Saturn V S-IVB Stage as a Radio Relay

The moon's Farside hemisphere: a mosaic of Lunar Reconnaissance Orbiter images. Image credit: NASA 
A Saturn S-IVB stage awaits shipment from the Douglas Aircraft plant in California. Various red protective covers would be removed before flight. Image credit: NASA
The S-IVB rocket stage played several important roles in NASA's 1960s and 1970s piloted space programs. The 58.4-foot-long, 21.7-foot-wide stage, which comprised a single restartable J-2 rocket engine, a forward liquid hydrogen tank, and an aft liquid oxygen tank, served as the second stage of the two-stage Apollo Saturn IB rocket and the third stage of the three-stage Apollo Saturn V.

The Saturn IB S-IVB's J-2 engine would ignite at an altitude of about 42 miles and burn until it placed a roughly 23-ton payload into low-Earth orbit. After that, it would shut down and the spent stage would separate. The Saturn V S-IVB's J-2, on the other hand, would ignite twice to accelerate the stage and its payload: once for 2.5 minutes at an altitude of about 109 miles and again for six minutes about two and a half hours later. The first burn would place the S-IVB and payload into a low parking orbit between 93 and 120 miles above the Earth; the second would place the S-IVB and payload onto a path that would intersect the moon, about 238,000 miles away, about three days after Earth launch. Departure for the moon was called Translunar Injection (TLI).

During Apollo moon landing missions, the payload was a three-man Command and Service Module (CSM) and a Lunar Module (LM) moon lander. The astronauts would separate the CSM from the four-segment shroud linking it to the S-IVB about 40 minutes after TLI. They would then maneuver it clear of the S-IVB and turn it end-for-end so that its nose pointed back at the top of the stage. The shroud segments, meanwhile, would hinge back and separate to reveal the LM spacecraft mounted atop the S-IVB. The crew would guide the CSM to a docking with the LM; then, about 50 minutes after docking, the joined CSM and LM would move away from the S-IVB. The stage would then vent residual propellants and ignite auxiliary rocket motors to place itself on a course away from the CSM-LM combination.

Schematic representation of Apollo 8 mission events (not to scale). Apollo 8 was the first mission to inject the Saturn V S-IVB stage into orbit around the Sun. Image credit: NASA 
Roughly 60 hours after launch from Earth, the docked CSM and LM would enter the moon's gravitational sphere of influence. About 12 hours later, they would pass behind the moon over the Farside, the lunar hemisphere that is turned always away from Earth. There, out of visual, radar, and radio contact with Earth, the astronauts would ignite the CSM's Service Propulsion System (SPS) main engine to slow the CSM and LM so that the moon's gravity could capture them into lunar orbit. This critical maneuver was called Lunar Orbit Insertion (LOI). Orbital mechanics dictated that LOI should occur more or less over the center of the Farside.

A few hours later, two astronauts would separate from the CSM in the LM. They would fire the moon lander's throttleable descent stage engine - again over Farside, as dictated by orbital mechanics - to begin their descent toward their pre-selected landing site on Nearside, the lunar hemisphere that is turned always toward Earth. Following a safe landing and a period of surface exploration (about one Earth day for the earliest Apollo landing missions), the LM ascent stage would lift off.

About two hours later - again over the moon’s hidden hemisphere – the CSM would rendezvous and dock with the LM. The lunar landing crew would rejoin the CSM pilot, the astronauts would cast off the LM ascent stage, and preparations would begin to ignite the SPS to depart lunar orbit for Earth. The critical lunar-orbit departure maneuver, also carried out over Farside, was called Trans-Earth Injection (TEI).

The S-IVB stage would, meanwhile, swing past the moon and enter orbit around the Sun. Although it would travel to the moon and beyond, as of early 1963 no one had identified any further role for the S-IVB after the CSM and LM separated from it.

The silhouette at left shows the position of the S-IVB third stage in the Saturn V stack. The cutaway illustration (right) shows the interstage faring that linked the S-IVB to the Saturn V S-II second stage and the relative sizes of the liquid oxygen and liquid hydrogen propellant tanks. Helium stored in spherical tanks push propellants into the J-2 engine. Image credit: NASA
For six months in 1963, engineers at The Bissett-Berman Corporation in Santa Monica, California, working on contract to NASA Headquarters, studied another use for the Apollo-Saturn V S-IVB stage. In a series of "Apollo Notes" prepared beginning in March of that year, they identified a need for a relay satellite to enable Earth-based radar tracking of the Apollo CSM and LM while they carried out crucial maneuvers over the Farside. They then proposed that the spent S-IVB be outfitted to serve as a relay.

The first note, authored by H. Epstein and based on a concept suggested by L. Lustick, proposed a radar relay satellite for tracking the Apollo CSM during LOI and CSM rendezvous and docking with the LM ascent stage. Epstein and Lustick's satellite would include an omnidirectional antenna for near-lunar operations and, for "deeper phase operation," a steerable four-foot parabolic dish antenna.

The relay satellite, Epstein wrote, would separate from S-IVB stage along with the Apollo LM and CSM after TEI, then separate from the CSM-LM combination before LOI. It would fly past the moon on a path that would keep both Earth and most of the Farside in view during LOI and CSM-LM rendezvous and docking. The omni antenna would relay radar from Earth until the satellite was 40,000 kilometers beyond the moon, then the dish would take over.

The second Bissett-Berman Apollo Note, dated 16 April 1963, raised the possibility of placing a "special purpose relay package" on the S-IVB stage. The package would either remain attached to the stage or would eject from it when activated. The Apollo Note's author, L. Lustick, attributed the S-IVB relay concept to one Dr. Yarymovych, whose organizational affiliation was not stated.

For his analysis, Lustick assumed that the S-IVB would retain enough propellants for its J-2 engine to restart a third time shortly after CSM-LM separation, raising its speed by 160 feet per second. He calculated that, at the time of CSM-LM LOI, the S-IVB or ejected relay package would have in view simultaneously both Earth and more than three-quarters of the Farside hemisphere. At the time of CSM docking with the LM ascent stage, about 100 hours after Earth launch, the relay would have in view Earth and a little more than two-thirds of the Farside. Throughout the approximately 28-hour period between LOI and CSM rendezvous with the LM ascent stage, the S-IVB or ejected relay package would remain within 143,000 miles of the moon.

The S-IVB would rely for attitude control guidance on the ring-shaped Instrument Unit (IU), the Saturn V's "electronic brain." The IU, located on top of the S-IVB during launch, encircled the LM descent stage and provided attachment points for the four separable shroud segments. It was not intended to operate for more than a few hours, so would need modifications to ensure that it could reliably stabilize the S-IVB throughout the relay period.

The ring-shaped Instrument Unit (IU) rode atop the S-IVB stage on both Saturn IB and Saturn V rockets. Image credit: NASA
The Instrument Unit assembly line at the IBM plant in Huntsville, Alabama. Image credit: NASA
In an addendum to Lustick's 16 April Apollo Note dated 18 April, engineer H. Epstein looked at simplifying the S-IVB Farside Relay concept by assuming that the stage would lack attitude control while it acted as a data relay. Replacing steerable dish antennas – one for Earth-S-IVB communication and one for S-IVB-Apollo CSM communication – with two passive omnidirectional antennas would permit data relay no matter how the S-IVB stage became oriented, he wrote.

The use of relatively low-power omni antennas would produce few problems as far as Earth-S-IVB communication was concerned, for NASA could call into play large antennas on Earth to ensure reception of the weak signal. Epstein proposed increasing from four feet to five feet the planned diameter of the dish antenna on the CSM to enable it to receive data from Earth relayed through the S-IVB-CSM omni antenna. He noted, however, that, even with a larger CSM dish antenna, radio interference from the Sun might stymie the omni antenna relay concept.

An undated Apollo Note by Lustick and C. Siska explored the S-IVB Farside Relay concept in yet greater detail, and included evidence of NASA interest in the scheme: for the first time, the authors cited NASA Headquarters-imposed study requirements. The space agency told Bissett-Berman to assume that the S-IVB could increase its speed by up to 1000 feet per second for up to about seven hours after TLI, and that the maximum range between the S-IVB Farside Relay and the CSM should not exceed 40,000 nautical miles throughout the relay period.

NASA, Lustick and Ciska explained, sought to learn whether relay of voice (not only data or radar) would be possible using an S-IVB Farside Relay during the roughly 30-hour period between LOI (a "particularly important" time to have voice relay capability, NASA asserted) and CSM-LM ascent stage rendezvous and docking. The authors found that boosting the S-IVB's speed by 1000 feet per second 7.6 hours after TLI would place it on a path to relay voice between Earth and Farside from 72 hours after Earth launch until 102 hours after Earth launch, at which time the S-IVB would reach NASA's 40,000-nautical-mile operational limit. In fact, they found that the S-IVB would have Farside in view as early as 60 hours after Earth launch (this was of purely academic interest, however, because the Apollo spacecraft would not be orbiting over the Farside at that time).

Lustick and Ciska also noted that the S-IVB would pass out of sight behind the moon (that is, become occulted by the moon) as viewed from Earth 102 hours after Earth launch. They added, however, that slight adjustments in S-IVB boost direction would postpone loss of Earth contact with the S-IVB Farside Relay for long enough to ensure that voice communication could continue during CSM rendezvous with the LM ascent stage.

In Bissett-Berman's penultimate examination of the S-IVB Farside Relay concept, author Ciska noted that a 1000-foot-per-second boost could be planned for as early as TLI. This would, however, leave no propellant margin for later correction of S-IVB boost aim errors. On the other hand, S-IVB attitude control was expected to "drift" over time, making accurate boost pointing later than TLI increasingly unlikely. Furthermore, boil-off of liquid hydrogen from the S-IVB stage would rapidly reduce the amount available to fuel a later boost. Both of these factors favored an "all-or-nothing” early boost.

Ciska noted also that, regardless of the S-IVB boost aim point selected, the stage would pass out of sight behind the moon as viewed from Earth for roughly half an hour at some point along its curved path during the voice relay period. For a 1000-foot-per-second boost applied 7.6 hours after TLI with an aim point slanted 100° relative to a line linking the Earth and moon, for example, the half-hour occultation would occur about 99 hours after Earth launch.

The last Bissett-Berman Apollo Note devoted to the S-IVB Farside Relay concept, also by Ciska and dated 20 August 1963, was an extension of his earlier note. In it, he examined an S-IVB boost 4.15 hours after TLI and considered further the impact of boost direction. Ciska did not attempt to plot S-IVB attitude drift or liquid hydrogen boiloff rates; nevertheless, he proposed as realistic a 700-foot-per-second boost 4.15 hours after TLI with an aim point slanted 100° relative to the Earth-moon line. Following this maneuver, the S-IVB Farside Relay would pass out of view of Earth for about 30 minutes a little more than 83 hours after Earth launch and would pass beyond NASA’s 40,000-nautical-mile limit about 103 hours after launch.

The S-IVB stage converted into the Skylab Orbital Workshop retained its IU and liquid oxygen tank - the latter launched dry and used as a dumpster - but lost its J-2 engine and saw its liquid hydrogen tank converted into a large habitable volume (note astronaut on lower deck for scale). Image credit: NASA
Though the Bissett-Berman S-IVB relay proposal was not taken up, S-IVB stages did play key non-propulsive roles in NASA's manned space program. NASA converted Saturn IB S-IVB 212 into the Skylab 1 Orbital Workshop. Skylab was launched into low-Earth orbit on the last Saturn V to fly and staffed by three three-man crews in 1973-1974. Saturn V S-IVB 515, originally intended to boost the Apollo 20 mission to the moon, was converted into the Skylab B workshop, but was not launched and became a walk-through display in the National Air and Space Museum in Washington, DC.

Of the 10 Apollo Saturn V S-IVBs that departed low-Earth orbit between 1968 and 1972, half reached orbit about the Sun and half were intentionally crashed into the moon. The Apollo 8, Apollo 9, Apollo 10, Apollo 11, and Apollo 12 S-IVBs departed the Earth-moon system, while those that boosted Apollo 13, 14, 15, 16, and 17 out of low-Earth orbit toward the moon were intentionally impacted on the moon's Nearside. The impacts were part of a science experiment: the seismic waves their impacts generated registered for hours on seismometers left behind on the lunar surface by earlier Apollo crews, helping to reveal to scientists the structure of the moon's deep interior.

The irregular ray crater blasted out by the impact of the Apollo 13 S-IVB stage in 1970 as imaged by NASA's Lunar Reconnaissance Orbiter in 2010. Image credit: NASA
The Apollo 12 S-IVB, launched on 14 November 1969, flew past the moon too fast to receive a gravity-assist boost into orbit about the Sun, so circled the Earth in a loosely bound distant orbit until 1971, when, through gravitational perturbations from Earth, Sun, and moon, it finally escaped into solar orbit. It orbited the Earth again for about a year in 2002-2003, during which time it was observed and mistakenly identified as a near-Earth asteroid. Spectral analysis revealed the presence of titanium-based paint, however, confirming the object's identity as Apollo 12's errant S-IVB.


Apollo Note No. 35, Lunar Far Side Relay Technique – Some Basic Radar Considerations, H. Epstein, The Bissett-Berman Corporation, 21 March 1963

Apollo Note No. 44, Back of Moon Relay Trajectories, L. Lustick, The Bissett-Berman Corporation, 16 April 1963

Addendum to Apollo Note No. 44, Communications Capability of Unstabilized S-4-B Satellite Relay System, H. Epstein, The Bissett-Berman Corporation, 18 April 1963

Apollo Note No. 87, Section 7, Far-Side Relay, L. Lustick and C. Ciska, The Bissett-Berman Corporation, no date

Apollo Note No. 90, Further Examination of Far-Side Relay Trajectories, C. Ciska, The Bissett-Berman Corporation, 6 August 1963

Apollo Note No. 97, Minimum Boost Velocity Requirement for Far-Side Relay, C. Ciska, The Bissett-Berman Corporation, 20 August 1963

More Information

Reviving & Reusing Skylab in the Shuttle Era: NASA Marshall's November 1977 Pitch to NASA Headquarters

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)

Solar Flares and Moondust: The 1962 Proposal for an Interdisciplinary Science Satellite at Earth-moon L4

15 October 2016

"A Continuing Aspect of Human Endeavor": Bellcomm's January 1968 Lunar Exploration Program

Lunar Exploration Program candidate landing sites. Of these, the Apollo Program would reach only Fra Mauro; Apollo astronauts would, however, visit five other sites not labeled here. Please click on image to enlarge. Image credit: NASA/Arizona State University/DSFPortree
Bellcomm, Inc., based near NASA Headquarters in Washington, DC, was carved out of Bell Labs in 1962 to provide technical advice to NASA's Apollo Program Director. NASA rapidly expanded Bellcomm's bailiwick to take in nearly all NASA Office of Manned Space Flight planning.

In a January 1968 report, Bellcomm planners N. Hinners, D. James, and F. Schmidt proposed a lunar mission series designed to bridge a gap in NASA plans they believed existed between the first piloted "Early Apollo" moon flights and sophisticated Apollo Applications Program (AAP) lunar expeditions. They declared that their Lunar Exploration Program was "based upon a reasonable set of assumptions regarding hardware capability and evolution, an increase in scientific endeavor, launch rates, budgetary constraints, operational learning, lead times, and interaction with other space programs," as well as "the assumption that lunar exploration will be a continuing aspect of human endeavor."

Hinners, James, and Schmidt envisioned a series of 14 lunar missions in four phases. Phase 1 would span the period from 1969 through 1971. The five Phase 1 missions were approximately equivalent to the Early Apollos. They would launch at least six months apart to give engineers and scientists adequate time to learn from each mission's successes and failures and enable them to apply their new knowledge to subsequent missions. Phase 1 would begin with Lunar Landing Mission (LLM)-1, the historic first Apollo moon landing.

The LLM-1 Lunar Module (LM) would alight on one of the moon's flat, relatively smooth basaltic plains. Called since the 17th century "maria" (Latin for "seas" - the singular is "mare"), they appear as mottled gray areas on the moon's white face. They cover about 20% of the moon's Earth-facing Nearside hemisphere, but are scarce on the hemisphere the moon turns always away from Earth (its Farside). LLM-1 and the other Phase 1 missions would each have several back-up near-equatorial Nearside mare landing sites, enabling them to land in safe places regardless of how their planned launch dates might slip.

Almost any mare would do for LLM-1, Hinners, James, and Schmidt argued, because the first piloted landing mission would emphasize engineering, not science. LLM-1 would test the LM, lunar space suits, and other Apollo systems ahead of more ambitious Phase 1 missions. If all went as planned, the LLM-1 crew would stay on the moon for 22 hours and carry out two short moonwalks.

LLM-1 would follow a "free-return" flight path that would guarantee that the Apollo Command and Service Module (CSM) could loop around the moon and return to Earth without propulsion in the event that its Service Propulsion System (SPS) main engine failed en route to the moon. The SPS was meant to adjust the CSM/LM combination's course during flight to and from the moon, slow the CSM and LM so that the moon's gravity could capture them into lunar orbit, and boost the CSM out of lunar orbit to return to Earth. The Bellcomm planners noted that use of the free-return trajectory would greatly limit the percentage of the moon's surface a lunar mission could reach.

The LMs constructed for Phase 1 missions would each be capable of delivering two astronauts. their space suits, and up to 300 pounds of payload to the lunar surface. This would include geologic tools for collecting up to 50 pounds of lunar rock and dust samples for return to Earth. Missions LLM-2 through LLM-5 would, in addition, each include an Apollo Lunar Scientific Experiment Package (ALSEP) – a cluster of geophysical experiments – for deployment on the moon. The ALSEPs would monitor the moon and return data after the astronauts returned to Earth.

LLM-2 through LLM-5 would see astronauts perform geological traverses on foot to spots up to several kilometers from the LM. Meanwhile, the CSM Pilot, alone in lunar orbit, would photograph the moon's surface through the CSM's small windows.

LLM-2, like LLM-1, would follow a free-return trajectory and remain for 22 hours at a mare landing site. It would, however, add a third moonwalk.

LLM-3 would abandon the free-return trajectory so that it could reach a fresh crater on a mare. The crater, the Bellcomm planners explained, would serve as a natural "drill hole." Studies of both natural and human-made craters on Earth had shown that the LLM-3 astronauts would find the oldest rocks – those excavated from deepest beneath the surface – on the crater's rim. The astronauts would explore the lunar surface for longer than 22 hours but less than 36 hours.

LLM-4 would be similar to LLM-3, but would be targeted to land at one of the many widely scattered mare "wrinkle ridges." In 1968, some scientists (notably, Nobel Laureate Harold Urey) still attributed these sinuous raised features to salty water escaping from reservoirs beneath the moon's surface, but today we know that they formed when lava that filled the mare nearly 4 billion years ago buckled as it cooled. Some may link or follow traces of ancient landscape drowned when the lava welled up from within the moon.

LLM-5, the final Phase 1 flight, would see an LM land at a mare site bordering a Highlands region. The Highlands of the moon, the light-colored areas on the moon's disk, are ancient cratered terrain. The LLM-5 astronauts would squeeze four moonwalks into their 36-hour mission.

The Bellcomm planners' four Lunar Exploration Program Phase 2 missions would commence about two years after LLM-5 and span 1972-1973. Upgrades to Apollo hardware and operations in Phase 2 would permit in-depth exploration of specific unique landing sites selected primarily for scientific interest. Among the upgrades that Hinners, James, and Schmidt proposed was variable Earth-to-moon flight time or time spent in lunar orbit prior to landing. This operational flexibility was intended to permit an Extended LM (ELM) spacecraft to reach its pre-planned target site even if launch from Earth were delayed for several days.

The Phase 2 lunar-surface astronauts would perform six moonwalks at each landing site. The ELM would land 1300 pounds of payload. Phase 2 CSMs would carry prototype remote sensors to test their feasibility ahead of their operational use in Phases 3 and 4.

The first Phase 2 mission, LLM-6, would see an ELM spend three days at Tobias Mayer in the extensive Oceanus Procellarum ("Ocean of Storms") mare region. Its crew would deploy an ALSEP and explore on foot a sinuous rille (canyon), a dome (possible volcano), and a fresh crater with a surrounding dark halo (possible volcanic vent). LLM-7 would be similar to LLM-6, but would land at a linear rille site designated I-P1.

LLM-8 would see the introduction of the Lunar Flying Unit (LFU), a one-person rocket flyer. Bellcomm targeted LLM-8 to the Flamsteed Ring, an ancient crater mostly submerged by lava during the formation of Oceanus Procellarum. At the time Hinners, James, and Schmidt selected it, the Flamsteed Ring was suspected of being an extrusive volcanic feature called a "ring dike."

LLM-9, similar to LLM-8, would visit Fra Mauro, a site known for its domes and rilles, which geologists interpreted as signs of recent volcanism. Fra Mauro would later come to be seen (correctly) as a large geologic unit made up of ejecta from the enormous impact that blasted out Mare Imbrium, the right "eye" of the "Man in the Moon." Cone crater, a natural drill hole in the Fra Mauro Formation, would become the target of Apollo 13 (and, after that mission failed to land on the moon, Apollo 14).

Phase 3 of Bellcomm's Lunar Exploration Program would comprise a single lunar-orbital survey mission in 1974. Because it would include no lunar landing, it received no LLM number. The mission would, for all practical purposes, mark the start of advanced AAP lunar flights. A solar-powered sensor module based on a planned AAP Earth-resources observation module design would replace the LM. By spending 28 days (one lunar day-night period) in lunar polar orbit, the mission's augmented CSM could pass over the entire lunar surface in daylight, enabling the crew to conduct global high-resolution film photography. When time came to return to Earth, the astronauts would load exposed film into their CSM, then undock from the sensor module and leave it behind in lunar orbit to function as an independent satellite.

Hinners, James, and Schmidt explained that Lunar Exploration Program Phases 1 and 2 missions would gather "ground truth" data on the composition and structure of the moon's surface. These data would enable scientists to interpret Phase 3 mission results in preparation for Lunar Exploration Program Phase 4, which would span 1975-1976.

Phase 4 would see two "Dual Launch" Lunar Surface Rendezvous and Exploration Missions. Each Dual Launch mission would require two Saturn V rockets, two augmented CSMs, an LM-derived unmanned Lunar Payload Module (LPM), and an augmented ELM bearing one LFU.

LLM-10 and LLM-11 together would make up the first Dual Launch mission. LLM-10 would deliver an unmanned LPM to either Hyginus Rille or the Davy crater chain. The LLM-10 crew, orbiting the moon in their augmented CSM, would remotely pilot the LPM's final approach to the landing site to help to ensure that it would set down within 100 meters of a predetermined target point. Before returning to Earth, the LLM-10 astronauts would "photo locate" the landed LPM from lunar orbit to aid the follow-on LLM-11 crew in finding it. They would also release a science subsatellite into lunar orbit.

LLM-11 would see two astronauts wearing advanced "hard" (mostly non-fabric) space suits land their augmented ELM near the pre-landed LPM for a two-week stay. They would draw on the LPM's 8000-pound payload to conduct in-depth exploration of their complex landing site.

The LPM payload would include lunar surface transportation systems: specifically, one LFU and a one-man, 2000-pound Local Scientific Survey Module (LSSM) moon rover. Other LPM cargo would include: a spare hard suit; a core drill attached to the LPM for obtaining a 100-foot drill core; an LSSM-transportable core drill for obtaining 10-foot cores at scattered sites; life support consumables for replenishing those on board LLM-11's ELM; and an advanced lunar-surface geophysical station with a 10-year design life.

Hinners, James, and Schmidt selected the Marius Hills as the landing site for LLM-12 and LLM-13, their second Dual Launch mission pair and the final missions of their Lunar Exploration Program. The Marius Hills were popular with planners for their many domes and other features of possible volcanic origin.

The Bellcomm planners anticipated that, after the LLM-13 crew returned to Earth, even more ambitious AAP moon missions would commence. These might lead to establishment of a lunar surface outpost. They were, of course, incorrect; it became clear soon after they completed their report that lunar exploration would not become "a continuing aspect of human endeavor."

This NASA map, published at the time of the Apollo 17 mission in December 1972, shows the six Apollo landing sites. All landings occurred within an area the size of the western United States between the Mississippi River and the Rocky Mountains (on a world with about as much surface area as Europe and North America combined). If Apollo 17 had landed in St. Louis, Missouri, Apollo 16 would have landed in northeastern Texas; Apollo 15 on the Kansas-Nebraska border; Apollo 14 and Apollo 12 in New Mexico; and Apollo 11 in Oklahoma.
The earliest Apollo landing missions (Apollo 11, Apollo 12, and Apollo 14) were roughly equivalent to Bellcomm's LLM-1, LLM-2, and LLM-3, though their crews performed fewer moonwalks. Apollos 15, 16, and 17, by contrast, were mainly shaped by the certain knowledge that Apollo lunar exploration would soon conclude. They became unlike any of Bellcomm's proposed missions as NASA sought to accomplish as much lunar exploration as possible at minimal cost before political support for the Apollo Program ran out.

The final Apollo lunar mission, Apollo 17 (December 1972), saw astronauts Eugene Cernan and Harrison Schmitt explore the Highlands-bordering Taurus-Littrow mare site for about three days. They drove an electric-powered Lunar Roving Vehicle (LRV). Meanwhile, Ron Evans, on board the Apollo 17 CSM in lunar orbit, used a suite of sensors to map a broad swath of the moon's surface and released a science subsatellite.


"A Lunar Exploration Program – Case 710," N. Hinners, D. James, and F. Schmidt, TM-68-1012-1, Bellcomm, 5 January 1968

To a Rocky Moon: A Geologist's History of Lunar Exploration, D. Wilhelms, University of Arizona Press, 1993

The Geologic History of the Moon, U.S. Geological Survey Paper 1348, D. Wilhelms, J. McCauley, and N. Trask, USGS, 1987

More Information

Apollo's End: NASA Cancels Apollo 15 & Apollo 19 to Save Station/Shuttle (1970)

Rocket Belts and Rocket Chairs: Lunar Flying Units

"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (1967)

Harold Urey and the Moon (1961)

23 September 2016

The Eighth Continent

The northern hemisphere of the moon as viewed from the Jupiter-bound Galileo spacecraft during an Earth gravity-assist flyby. Parts of the spectrum invisible to the human eye are rendered as green and bluish tints; these provide hints to the complex, barely understood mineralogy of lunar features. Image credit: NASA
Earth's moon is for most people just a light in the sky. Many of us who have followed the course of spaceflight know that it is in fact a place we have barely explored.

I like to think of our planet's moon as its eighth continent. In terms of extent, Asia is, at 44.6 million square kilometers, the largest continent. The moon is next in order, with 37.9 million square kilometers. Africa comes in third with 30.4 million square kilometers.

Another way to look at this is, the moon has more area than North America (24.7 million square kilometers) and Europe (10.2 million square kilometers) combined. Or one could say that the moon has about the same surface area as five Australias (7.7 million square kilometers each) or three Antarcticas (14 million square kilometers each).

South America, at 17.8 million square kilometers fifth in area after Asia, the moon, Africa, and North America, has a little less area than one lunar hemisphere. When we look up at the hemisphere the moon holds forever turned toward Earth, the Nearside, we view a surface area that could comfortably encompass Brazil, Argentina, Colombia, Venezuela, Peru, Chile, Ecuador, Bolivia, Uruguay, Suriname, French Guiana, Guyana, and Paraguay, plus the nations of Central America and the Caribbean. Half a billion people call those countries home.

If there's one hemisphere we can see from Earth, it follows that there's a hemisphere we cannot see. Called the Farside, we have observed it only from lunar-orbiting spacecraft or more distantly, from interplanetary spacecraft flying through the Earth-moon system (see image at top of post). No lander, rover, or astronaut has explored there. The Farside is home to the South Pole-Aitken Basin, the largest impact basin on the moon and one of the top five largest impact basins in the entire Solar System. Its full extent and depth were not confirmed until the last years of the 20th century.

Many people - including space enthusiasts, who really should know better - look at the moon and say, "been there, done that." The fact is, we have examined up close far less than 1% of the moon's surface. All the territory that the Surveyor and Luna robot landers, Apollo astronauts, and Lunokhod robot rovers of the 1960s and 1970s explored could fit within a smallish city.

All of this unexplored territory is close at hand - on average just 385,000 kilometers away, a distance approximately equal to 10 times Earth's circumference. There exist automobiles and many ships and aircraft that have racked up more kilometers than that. If we still possessed Saturn rockets and Apollo spacecraft, in three days you could climb a ladder down to the surface of the moon. That compares favorably with the travel time to remote places on Earth, such as Antarctica or the ocean abyss.

The eighth continent. The phrase makes the moon seem more real, more like a place, more like a part of Earth. That's how it should be. Earth and moon form a unique system. When we see the Earth as everything and its moon as separate, remote, and insignificant, we are only a step removed from ancient peoples who thought the Earth was flat. It's time we stopped that nonsense and gave our eighth continent its due consideration.

15 September 2016

Naming the Space Station (1988)

The 1982 "Space Platform" was the Station design President Ronald Reagan displayed to leaders of prospective Space Station International Partner nations in 1984. Image credit: NASA
On 12 April 1988, James Odom, NASA's Associate Administrator for Space Station, sent out a memorandum with two attachments to a long distribution list. Recipients included NASA Administrator James Fletcher, Deputy, Associate, and Assistant Administrators at NASA Headquarters, the NASA Inspector General, the NASA Chief Scientist, the nine NASA field center Directors, Public Affairs Officers across the agency, the six field center Space Station Project Offices, and representatives of the Space Station International Partners (Canada, the European Space Agency, and Japan). The memo's subject line summed up its purpose succinctly: it was called "Naming the Space Station."

Odom explained that the Space Station President Ronald Reagan had called upon NASA to build in his State of the Union Address of 25 January 1984 was about to enter its "development phase," so the time was ripe to decide on a name for it. He attached a NASA Management Instruction laying out guidelines for naming NASA projects and, more interestingly, a list of 16 names suggested by a Space Station Name Committee he had appointed. Each name included a brief rationale.

The naming rules were straightforward. Candidate names were to be simple and easily pronounced, not refer to living persons, neither duplicate nor closely resemble other NASA or non-NASA space program names, be translatable into the languages of the International Partners, and have neither ambiguous nor offensive meanings in the International Partner languages. In addition, acronyms were to be avoided. The naming process was not to be revealed to the public; if, however, members of the public happened to submit names that followed the rules, the Name Committee would consider them.

NASA's 1985 "Power Tower" Space Station configuration included hangars for space tugs and satellite servicing, a laboratory, a free-flyer providing an enhanced microgravity environment, and zenith- and nadir-pointing truss-type platforms for instruments. Image credit: NASA
Several of the Name Committee's 16 names sought a return to the Greco-Roman mythology naming tradition of the Mercury, Gemini, and Apollo programs. Hercules was, its rationale explained, an appropriate name for the Space Station because the mythical hero was "a symbol of extraordinary strength. . . who won immortality by performing 12 labors." Minerva was the Roman goddess of wisdom and learning; Aurora, the Roman goddess of the dawn. Jupiter, the greatest Roman god, was a candidate name; the Name Committee explained, however, that it was meant to refer to the Solar System's largest planet, and that it was "symbolic of mankind's greatest adventure, the exploration of space."

Pegasus was suggested because the Space Station would "dwell among the stars" like "the winged horse who ascended into Heaven." Olympia referred to the sacred grove where ancient Greece held its Olympic Games; the name was meant to invoke the spirit of international cooperation.

Another proposed 1985 NASA Space Station design provided ample room for hangars and attached payloads, as well as a simplified track arrangement for the Station's mobile platform-mounted robot arm. The Station's electricity-generating solar arrays, steerable only by moving the entire Station, cover its zenith-facing side. Image credit: NASA
Two names, Earth-Star and Starlight, referred to the Station's likely bright star-like appearance in the skies of Earth, while another, Skybase, was said to build on "the tradition of Skylab," the first U.S. space station, which had reached orbit in May 1973. Landmark was suggested because the Space Station Program would constitute a "landmark" in the history of the NASA spaceflight. Pilgrim referred to outer space settlement, and the rationale for Prospector declared that the Space Station would "serve as a base for exploration of space for natural deposits."

This last Station function must have come as a surprise to many on Odom's distribution list, for the Space Station was meant to serve as a laboratory; before 1988 it had lost essentially all of its transportation node capabilities, so had little hope of ever playing a significant role in the development of space resources. NASA planners, meanwhile, had moved toward the concept of a separate transportation node space station. They believed (with good reason) that separating transportation and laboratory functions would result in two stations with optimized designs.

Other names – Freedom, Independence, Liberty, and Unity – advertised U.S. political values, and thus followed Soviet convention. ("Soyuz," for example, means "Union," which refers to the multi-modular nature of the Soyuz spacecraft, but also to the Union of Soviet Socialist Republics.) Liberty also referred to breaking "the bond of Earth's gravitational pull," Unity to international cooperation, and Independence to “man’s first permanent step to be 'independent' of Earth."

Freedom, the Name Committee explained, was appropriate because the Space Station would "provide scientific and technological 'freedom' to explore avenues of research," as well as freedom "from the confines of gravity." In addition, freedom was "a political value central to all of the Space Station's international partners."

In his memorandum, Odom explained that names submitted to the Space Station Name Committee would be given to the NASA Administrator, who would make the final selection. In the end, though, the list of candidate names landed on President Reagan's desk. On 18 July 1988, NASA announced that he had selected the name Space Station Freedom.

Space Station Freedom - sometimes referred to as Space Station "Fred" due to its much-reduced size and capabilities - in 1991. Image credit: NASA
Despite Odom's assertion that it would soon enter development, Space Station Freedom underwent repeated redesigns to reduce cost and complexity and narrowly dodged cancellation. In mid-1993, new President William Clinton ordered a comprehensive review of the U.S. space station program, a management overhaul, and a redesign based on one of three options, designated A, B, and C. In November 1993, Clinton selected Option A, a pruned-back version of Freedom that became known as Alpha. (One might speculate, none too seriously, that had Option B been selected, the station would have been called Beta.)

During his single term in office, President George H. W. Bush, Clinton's predecessor, had concluded agreements first with Soviet leader Mikhail Gorbachev and then with Russian President Boris Yeltsin that called for, among other things, use of the Soyuz spacecraft as a Space Station Freedom lifeboat. Bush had stopped short of giving the Russians a central role in the NASA station; nevertheless, he laid groundwork for things to come.

President Clinton's decision to accept the Russian invitation to combine Alpha and Mir-2 had its critics. Nevertheless, the move created a geopolitical rationale that ensured broad Congressional support for the station for the first time. The combined space station would keep Russian rocketeers occupied so that they would not peddle their missile-manufacturing services internationally. In terms of space operations, the merger amounted to what was probably the first instance of Earth-orbital barter: the Russian segment would provide orbit-maintenance propulsion and early staffing in exchange for abundant electricity from the U.S. segment's enormous truss-mounted steerable solar arrays.

The International Space Station in August 2005. Image credit: NASA
For a time, the combined U.S.-Russian station was jokingly referred to as "Ralpha," for "Russian Alpha," which at least had the advantage of being distinctive. Ultimately, however, NASA and its partners settled on the prosaic name International Space Station (ISS).

Following (mainly) Russian tradition, individual ISS modules have received names. The Mir-2 core module, a small independent space station NASA referred to as the "Service Module," was named Zvezda ("Star"), while the first U.S. component, Node 1 – a module designed as an attachment point for other modules – was dubbed Unity for reasons similar to those given by the 1988 Name Committee. Other names include Zarya ("Dawn") for the FGB propulsion and storage module, the first ISS component launched; Destiny for the U.S. Lab Module; Kibo ("Hope") for the Japanese lab; and Columbus for the European lab.

The International Space Station in 2011. Image credit: NASA

Memorandum with attachments, S/Associate Administrator for Space Station to Distribution, Naming the Space Station, 12 April 1988

More Information

NASA's 1992 Plan to Land Soyuz Space Station Lifeboats in Australia

Skylab-Salyut Space Laboratory (1972)

He Who Controls the Moon Controls the Earth (1958)

10 September 2016

Dreaming A Different Apollo, Part Four: Naming Names

A lunar outpost near an abandoned Apollo Lunar Module descent stage (left). Image credit: European Space Agency
The names we give to places on and off Earth and to vessels of sea and space have long fascinated me. The moon is one of my favorite places because it is covered with names of scientists and engineers, each of whom has an intriguing biography. At the insistence of Carl Sagan, Mercury bears the names of artists, musicians, poets, and the like, so is also interesting.

Other worlds have other themes assigned to them. The Uranian moon Miranda, for example, draws names from Shakespeare's The Tempest and locations in Shakespeare's plays.

The Royal Navy in the Age of Fighting Sail is a great source for picturesque ship names, and science fiction seldom disappoints. The late, great Iain M. Banks had a particular talent for irreverent names, which he applied to the intelligent starships of his The Culture setting: I Blame the Parents is one of my favorites.

In Part One of this series (see link below), I described a world in which Apollo did not die; one in which U.S. taxpayers opted to squeeze our $24-billion Apollo investment for all it was worth instead of (as President Lyndon Baines Johnson put it) pissing it all away. I did not give the Apollo Command and Service Module (CSM) and Lunar Module (LM) spacecraft in that post names for fear of making more confusing an already complicated series of missions. In this post, I mean to rectify that omission.

In Apollo as flown, we saw the following spacecraft names (or, perhaps more properly, call-signs): Apollo 7, none; Apollo 8, none; Apollo 9, CSM Gumdrop and LM Spider; Apollo 10, CSM Charlie Brown and LM Snoopy; Apollo 11, CSM Columbia and LM Eagle; Apollo 12, CSM Yankee Clipper and LM Intrepid; Apollo 13, CSM Odyssey and LM Aquarius; Apollo 14, CSM Kitty Hawk and LM Antares; Apollo 15, CSM Endeavour and LM Falcon; Apollo 16, CSM Casper and LM Orion; and Apollo 17, CSM America and LM Challenger. Apollo 7 and Apollo 8 were CSM-only missions, so their spacecraft did not need names to distinguish them from their LMs in radio communications. Their CSMs were thus known by their mission designations alone.

Part One of this post series continued the Apollo series with the first Saturn V launch of the Olympus 1 space station in late 1971. My alternate-history NASA designated the uncrewed station launch Apollo 18. Olympus is, of course, the name of the lofty home of the Greek Gods. It was a favorite name among 1960s space station planners - for example, Edward Olling - at NASA's Manned Spacecraft Center (since 1973, Johnson Space Center) in Houston.

The first Apollo CSM to reach Olympus 1 was Apollo 19. It was another CSM-only mission, so bore no spacecraft name - much as the Skylab CSMs in our timeline had only numbers (Skylab 2, Skylab 3, and Skylab 4 - Skylab 1 was the launch of the Skylab station). Apollo 20, nearly identical to Apollo 19 apart from its duration (its crew lived on board Olympus 1 for 56 days in early 1972, twice as long as the Apollo 19 crew) also bore no name.
After that, though, NASA had a change of heart. It developed and retroactively applied an alphanumeric designation system for flights and encouraged crews to name their spacecraft, much as it had during Project Mercury (but not Project Gemini). The alphanumeric system pleased NASA bureaucrats; naming piloted spacecraft in single-spacecraft missions was a public-relations ploy meant to point up the distinctive qualities of the individual CSM-only missions to the Olympus stations.

NASA called it Skylab; I call it Olympus. Image credit: NASA
The Apollo 19 mission, which flew the first K-class CSM with modifications for long-duration space station missions, became O-1/K-1/R1 (Olympus 1/K-class CSM 1/Olympus 1 Resident Crew 1). Apollo 20 became O-1/K-2/R2.

Apollo 21 (I-1), the one and only I-class piloted CSM-only lunar polar orbiter mission, was dubbed Endurance by its two-man crew, who orbited the moon for 28 days to image potential landing sites for advanced L-class Apollo lunar landing missions planned to begin in late 1974. An automated imaging orbiter was considered for the mission, but was rejected because it would have required costly new development (for example, a complicated Earth-return capsule system for exposed film) as well as a unique Saturn IB upper stage configuration.
The crew of Apollo 22 (O-1/K-3/R3) named their CSM Discovery. They docked with Olympus 1 in June 1972 for a 112-day stay. Ninety days into their flight, the two-person crew of Apollo 23 (O-1/K-4/V1), the first space station short-stay visitor crew, docked at Olympus 1's radial port to check on the health of the Apollo 22 crew and certify continuation of their mission. In a poetic reference to their short stay of only 10 days, they named their CSM Hummingbird.

Apollo 24 (J-3), launched in October 1972, was a J-class mission resembling our Apollo 15, Apollo 16, and Apollo 17 missions. In fact, it carried the original Apollo 17 crew of Eugene Cernan, Joseph Engle, and Ronald Evans. In our timeline, Apollo 17 was the last crewed mission to the moon of the 20th century and geologist Harrison Schmitt, the only professional scientist to reach the moon, replaced Engle as LM Pilot. Cernan, Engle, and Evans named their CSM America and their LM Challenger, just as Cernan, Schmitt, and Evans did in our timeline.

Schmitt was one of six scientist-astronauts selected as part of Group 4 in June 1965. He would fly Apollo 17, and three others - Joseph Kerwin, Owen Garriott, and Edward Gibson - would fly as Science Pilots on the three Skylab missions. Garriott also flew a Space Shuttle mission. In our timeline, Schmitt was originally assigned to fly Apollo 18; after it was cut, he was moved to Apollo 17.

It would be different in the alternate timeline. Schmitt would not be the first Group 4 scientist-astronaut to fly; several would reach Olympus stations before he set out for the moon. He would become the first Group 4 astronaut to reach the moon, but not (as was the case in our timeline) the only one. He would also fly to the moon a second time and never run for U.S. Senator from New Mexico.

NASA selected the 11 scientist-astronauts of Group 6 in August 1967, just as Congress slashed President Johnson's request for funds to begin major work on the Apollo Applications Program (AAP). AAP shrank rapidly and morphed into Skylab. Of the eleven Group 6 scientists, seven eventually flew Space Shuttle missions. In the alternate timeline, most would fly Apollo missions before 1976.

This is a good place to consider how astronaut selection would unfold in the alternate timeline. Seven refugees from the cancelled U.S. Air Force Manned Orbiting Laboratory would join NASA in August 1969 as Group 7, just as they did in our timeline. In our timeline, they were the last astronauts selected until January 1978, when Group 8 - which included among its 35 members the first minority and women astronauts - was selected to crew Space Shuttles.

In the alternate timeline, NASA would select new astronaut groups of about 10 members every three or four years to bring in new skills and make up for attrition. Group 8 would, as in our timeline, include the first U.S. women and minority spacefarers, but they would join NASA in January 1971, not January 1978.

Older astronauts of our timeline's Group 8 might join Group 9 (1974) and younger ones might join Group 10 (1977) or Group 11 (1981). In general, though, NASA would need fewer astronauts. Because of this, many individuals who flew in space in our timeline would never join the space agency.

Given the "morality" and prejudices of the 1970s, it seems likely that NASA would find excuses not to fly women as members of Resident or lunar crews, though several would reach Olympus 3 as members of Visitor crews. One would serve as Visitor crew Commander. In an era when the proposed Equal Rights Amendment to the Constitution was struck down, however, mixed crews on long-duration and minimal-privacy lunar missions would make many American taxpayers uncomfortable.

In the early 1980s, however, this would change. Once the spaceflight "glass ceiling" was shattered, many women would fly in space in many roles, just as in our timeline.

Apollo 25 (J-4) was an engineering/technology-development mission to the Apollo 24 site meant to prepare NASA for L-class missions and eventual lunar outposts. In addition to accomplishing a precision landing almost exactly one kilometer from the Apollo 24 LM descent stage, which they inspected in considerable detail, the Apollo 25 crew collected materials-exposure cassettes and meteoroid, dust, and solar-particle capture cells the Apollo 24 crew had left behind. They also collected geologic samples scientists studying Apollo 24 photos had determined to be of special interest. They named their CSM Franklin and their LM Edison for the famed American inventors.

Journey to a lava tube cave. Image credit: NASA
Apollo 26 (O-2) was the uncrewed launch of the Olympus 2 station. Apollo 27 (O-2/K-5/R1) saw three astronauts live in orbit for 224 days. They named their CSM Freedom, which led one stand-up comedian to quip that it should have been named "Incarceration."

The crew received the Apollo 28 (0-2/K-6/V1) CSM Athena, Apollo 29 (O-2/K-7/V2) CSM Amity, and the Apollo 30 CSM (O-2/K-8/V3) Liberty. Apollo 28 included the first American woman in space, Apollo 29 the first non-U.S./non-Soviet astronaut in space, and Apollo 30's Visitor crew returned to Earth in the Apollo 27 CSM, leaving their CSM for the Apollo 27 Resident crew.

The uncrewed Apollo 31 Saturn V launched a pair of Radio/TV Relay Satellites to Earth-moon L2 and the uncrewed Apollo 32 (O-3) Saturn V launched Olympus 3, first of the "long-life" stations. The Apollo 33 (O-3/K-9/R1) crew, the first to stay on board a space station for what became the "routine" interval of 180 days, arrived in the CSM Eos, which was named for the Greek goddess of the dawn.
Apollo 34 (J-5) in February 1974, the last of the J-class missions, landed in dark-floored Tsiolkovskii in the moon's Farside hemisphere. Harrison Schmitt was the mission's LM Pilot and the first geologist on the moon. They named their CSM Infinity and their LM for the red-golden star Arcturus, long seen as a harbinger of springtime.

The Apollo 35 (O-3/K-10/V1) CSM Hermes delivered the first drum-shaped Cargo Carrier (CC-1) to Olympus 3 and the Apollo 36 (O-3/K-11/V2) CSM Independence caused it to reenter after the Apollo 33 crew unloaded it. Hermes was, among other things, the Greek God of Commerce, The Messenger of the Gods, and the half-brother of Apollo. The Apollo 37 (O-3/K-12/R2) CSM Celeste (a feminine name meaning "heavenly") delivered the large Argus telescope module to Olympus 3.
The uncrewed Apollo 38 (L-1A) mission saw the LM-derived Lunar Cargo Carrier-1 (LCC-1) launched on a Saturn V on a direct path to the planned landing site of the Apollo 40 (L-1B) mission. Apollo 38 included no CSM. The Apollo 39 (O-3/K-13/V3) CSM Shenandoah was the first of more than a dozen Earth-orbital CSM spacecraft named for U.S. national parks and monuments.

The Apollo 40 CSM was the first L-class Advanced CSM (ACSM) and its LM was the first L-class Advanced LM (ALM). The Apollo 40 crew named their ACSM Aquila, for the constellation The Eagle, and their ALM Altair, for its brightest star. The lunar surface crew used Aquila as their base camp to explore a complex landing site for one week. This more than doubled the three-day J-class lunar stay-time.
The Apollo 41 (O-3/K-14/R3) CSM Constitution delivered the Olympus 3 station's third Resident crew while its second Resident crew was still on board, marking the beginning of continuous station occupation. The Apollo 42 (O-3/K-15/V4) CSM was named Adventure.

The Apollo 43 (O-3/K-16/V5) crew named its CSM Yosemite, and the Apollo 44 (O-3/K-17/R4) crew named its CSM Acadia. Yosemite is, of course, a famous national park in California; Acadia, the first eastern national park, is on the other side of the country, in the Mission Commander's home state of Maine.
My first Dreaming a Different Apollo post ended with the launch of Apollo 44 in December 1975. The timeline could, of course, continue (and, I suspect, probably will). One can imagine an ACSM called Draco paired with an ALM named Thuban, Draco's rather faint brightest star. I am sure that we will see an Enterprise at some point. 

Direct Ascent moon lander with Apollo-style Earth-reentry module (top) from NASA's 1991-1994 First Lunar Outpost (FLO) study. Image credit: NASA
I expect that the Apollo series would continue into the late 1980s or early 1990s. By the beginning of the 1990s decade, the Lunar-Orbit Rendezvous Apollo mission scheme would give way to Direct-Ascent missions, in which a single spacecraft would launch from Earth and travel directly to a lunar base. Opportunities for naming spacecraft would become fewer, but almost certainly would continue.

More Information

Dreaming a Different Apollo, Part One

Space Station Resupply: The 1963 Plan to Turn the Apollo Spacecraft Into a Space Freighter

Apollo's End: NASA Cancels Apollo 15 & Apollo 19 to Save Station/Shuttle (1970)

26 August 2016

Catching Some Comet Dust: Giotto II (1985)

Giotto 1 liftoff. Image credit: European Space Agency
On the overcast morning of 2 July 1985, the eleventh Ariane 1 rocket to fly lifted off from the Centre Spatial Guyanais in Kourou, French Guiana, an outpost of the European Community located a few degrees north of the equator on the northeast coast of South America. The last Ariane 1 to fly, it bore aloft Giotto, the first European Space Agency (ESA) interplanetary spacecraft. Giotto's destination was Comet Halley.

A "dirty snowball" containing materials left over from the birth of the Solar System 4.6 billion years ago, Halley needs about 76 years to revolve around the Sun once. Its elliptical orbit takes it from the cold emptiness beyond Neptune to the space between the orbits of Venus and Mercury. Halley travels around the Sun in a retrograde orbit, meaning that it orbits "backwards" relative to the eight planets and most other objects making up the Solar System.

Comet Halley has passed through the inner Solar System 30 times since its first verified recorded apparition in 240 B.C. In 837 A.D., it passed just 5.1 million kilometers from Earth; during that apparition, its dust tail must have spanned nearly half the sky, and its bright coma – the roughly spherical dust and gas cloud surrounding its icy nucleus – may have appeared as large as the full moon.

Shortly after its bright apparition in the year 1301, Italian artist Giotto di Bondone was inspired to add Comet Halley to his painting The Adoration of the Magi. The Giotto spacecraft was named for him.

Comet Halley appears near the top of Giotto di Bondone's The Adoration of the Magi. 
Throughout most of its known apparitions, Comet Halley was not understood to be one comet repeatedly passing through the inner Solar System. Not until 1705 did English polymath Edmond Halley determine that comets seen in 1531, 1607, and 1682 were probably one comet orbiting the Sun. He predicted that, if his hypothesis were correct, the comet should reappear in 1758 (which it subsequently did).

The Ariane 1's third stage injected 980-kilogram Giotto into a 198.5-by-36,000-kilometer orbit about the Earth. Thirty-two hours after launch, as it completed its third orbit, flight controllers in Darmstadt in the Federal Republic of Germany commanded drum-shaped Giotto to ignite its French-built Mage solid-propellant rocket motor. The motor burned 374 kilograms of propellant in 55 seconds to inject the spinning 2.85-meter-tall, 1.85-meter-diameter spacecraft into orbit about the Sun.
Two months before Giotto's launch, Americans P. Tsou (Jet Propulsion Laboratory), D. Brownlee (University of Washington), and A. Albee (California Institute of Tech) proposed in a paper in the Journal of the British Interplanetary Society that a second Giotto mission be launched to fly close by one of 13 candidate comets between 1988 and 1994. They proposed that the new spacecraft, which they dubbed Giotto II, might launch on an Ariane 3 or in the payload bay of a Space Shuttle. Giotto II's "free-return" trajectory would take it as close as 80 kilometers from the target comet's nucleus, then would return it to Earth.

Near the comet, Giotto II would expose sample collectors to the dusty cometary environment. Near Earth, it would eject a sample-return capsule based on the proven General Electric (GE) Satellite Recovery Vehicle (SRV) design. The capsule would enter Earth's atmosphere to deliver its precious cargo of comet dust to eager scientists.
Tsou, Brownlee, and Albee pointed out that the Mage solid-propellant motor had not been required to boost Giotto into interplanetary space; that is, that the Ariane 1 could have done the job itself. Giotto was, however, based on a British Aerospace-built Geos magnetospheric satellite design, which included the Mage motor. Re-testing the design without the motor would have cost time and money, so ESA elected to retain it for Giotto. After noting that the GE SRV could fit comfortably in the space reserved for the Mage, they proposed that, in Giotto II, the reentry capsule should replace the motor.

Giotto included on its aft end a "Whipple bumper" - named for its inventor, planetary astronomer Fred Whipple - to protect it from hypervelocity dust impacts. During approach to Comet Halley, the spacecraft would turn the bumper toward its direction of flight. The bumper comprised a one-millimeter-thick aluminum shield plate designed to break up, vaporize, and slow impactors, a 25-centimeter empty space, and a 12-millimeter-thick Kevlar sheet to halt the partially vaporized, partially fragmented impactors that penetrated the aluminum shield.
In the case of Comet Halley, dust would impact the bumper at up to 68 kilometers per second. Tsou, Brownlee, and Albee noted that the 13 candidate Giotto II target comets were all less dusty and would have lower dust impact velocities than Halley. Because of this, Giotto II would need less shielding than Giotto.

Comet dust would, nevertheless, create challenges for Giotto II. Tsou, Brownlee, and Albee devoted much of their paper to a description of how the spacecraft might successfully capture dust for return to Earth. One proposed capture system, based on the Whipple bumper design, would use a shield made from ultrapure material to vaporize and slow impacting dust particles. The vapor from the impactor and the impacted part of the bumper would then be captured as it condensed. Scientists would disregard the bumper material when they analyzed the condensate.
Tsou, Brownlee, and Albee also noted that thermal blankets from the Solar Maximum Mission (SMM) satellite, launched into Earth orbit on 14 February 1980, had demonstrated that intact capture of high-velocity particles was possible. The multilayer Kapton/Mylar blankets, which were returned to Earth on board the Space Shuttle Orbiter Challenger at the end of mission STS 41-C (6-13 April 1984), were found to have collected hundreds of intact meteoroids and human-made orbital debris particles.

The three scientists described preliminary experiments in which gas guns were used to fire meteoroid and glass fragments at "underdense materials," such as polymer foams and fiber felts. The experiments suggested that such materials could capture at least partially intact comet dust particles.

Giotto's encounter with Comet Halley spanned 13-14 March 1986. At closest approach the spacecraft passed just 596 kilometers from Halley's nucleus. The comet's 15-by-eight-by-eight-kilometer heart turned out to be extremely dark, with powerful jets of dust and gas blasting outward into space.

Artist's concept: Giotto at Halley. Image credit: European Space Agency
Halley's hot heart as imaged by ESA's Giotto spacecraft. 
The intrepid probe suffered damage from dust impacts – one large particle sheered off more than half a kilogram of its structure – but most of its instruments continued to operate after the Comet Halley flyby. ESA thus decided to steer Giotto toward another comet.

On 2 July 1990, five years to the day after its launch, Giotto flew past Earth at a distance of 16,300 kilometers, becoming the first interplanetary spacecraft to receive a gravity-assist boost from its homeworld. The gravity-assist flyby put it on course for Comet Grigg-Skjellurup, which it passed at a distance of 200 kilometers on 10 July 1992.
After determining that Giotto had less than seven kilograms of hydrazine propellant left on board, ESA turned it off on 23 July 1992. The inert spacecraft flew past Earth a second time at a distance of 219,000 kilometers on 1 July 1999.
By that time, a comet coma sample return mission was under way with two of the Giotto II proposers playing central roles. In late 1995, Stardust became the fourth mission selected for NASA's Discovery Program of low-cost robotic missions. Brownlee and Tsou, respectively Stardust Principal Investigator and Deputy Principal Investigator, designed the mission's sample capture system.

Artist's concept of the NASA Stardust spacecraft at Wild 2. Image credit: NASA
The 380-kilogram Stardust spacecraft left Earth on a free-return trajectory on 7 February 1999, and flew past Comet Wild 2 (one of the 13 Giotto II candidates) at a distance of about 200 kilometers on 2 January 2004. Stardust captured dust particles in aerogel, a silica-based material of extremely low density that was invented in the 1930s. Tsou, Brownlee, and Albee had apparently been unaware of aerogel when they proposed Giotto II in 1985.

Stardust returned to Earth on 15 January 2006. Its sample capsule streaked through the pre-dawn sky over the U.S. West Coast before parachuting to a landing on a salt pan in Utah.

When opened on 17 January 2006 at NASA's Johnson Space Center, in the same lab that received the Apollo moon rocks, Stardust's 132 aerogel capture cells were found to contain thousands of intact dust grains captured from Wild 2. Subsequent analysis indicated that some probably formed close to other stars before our Solar System was born.

"Comet Coma Sample Return via Giotto II," P. Tsou, D. Brownlee, and A. Albee, Journal of the British Interplanetary Society, Volume 38, May 1985, pp. 232-239

ESA Remembers the Night of the Comet, European Space Agency, 11 March 2011 (accessed 26 August 2016)

Stardust: NASA's Comet Sample Return Mission, NASA Jet Propulsion Laboratory (accessed 26 August 2016)

More Information

A 1974 Plan for a Slow Flyby of Comet Encke

Cometary Explorer (1973)

Missions to Comet d'Arrest and Asteroid Eros in the 1970s (1966)

12 August 2016

Could the Space Voyages in the Film and Novel "2001: A Space Odyssey" Really Happen? (Part 3)

The glory that is Saturn. The Cassini spacecraft was crossing the plane of the rings as it captured this image, so they are visible only as a sharp thin line running across the center of the image and a complex play of shadows on the planet's northern hemisphere. Image credit: NASA
One can hardly blame Arthur C. Clarke for stubbornly insisting that the spaceship Discovery travel to Saturn. Even with the minimal knowledge of the Saturn system we possessed in 1968, when the film and novel 2001: A Space Odyssey had its debut, it was clear that Saturn is home to some intriguing space oddities which Clarke could put to work in his narrative.

There are, of course, the rings. They make Saturn an austere work of art wrought in ice and orbital mechanics. Clarke attributed their creation to the same advanced aliens who uplifted humankind at the beginning of the book and film 2001, three or four million years before Discovery's launch.

There is also peculiar Iapetus - which Clarke called Japetus (the German spelling) - a 1500-kilometer-diameter moon very dark on one side (its leading hemisphere as it orbits Saturn) and very bright on the other. The arrangement of the dark leading and bright trailing hemispheres mean that Iapetus, Saturn's second-largest moon after Titan, is very bright to Earth-based observers when its 79-day orbit puts it on one side of Saturn and very faint roughly 40 days later, when it moves into view on the other side.

Stanley Kubrick, who directed the film 2001, co-authored its screenplay, and received co-author credit on early editions of the novel, also sought to send Discovery to Saturn, but had to settle for Jupiter. The film's overtaxed art department rebelled - Kubrick, ever the perfectionist, was given to demanding quick-turnaround changes which he subsequently threw away. Perhaps more important, a portrayal of Saturn convincing to 1968 film audiences proved too great a challenge for 2001's pioneering special-effects technology and skilled artisans. Had they known how improbable-seeming Saturn really appears, Kubrick and the production crew might have given themselves a bit of slack.

A raging storm in Saturn's northern hemisphere imaged by the Saturn-orbiting Cassini automated explorer 10 years after 2001. In 1968, observers using Earth-based telescopes believed Saturn's atmosphere to be practically featureless. Image credit: NASA
This is the third and last of a series of posts I have written this summer on real-world proposals for spacecraft and supporting infrastructure meant to emulate the spacecraft and infrastructure portrayed in the film and novel 2001. In the first installment, I described 2001's Earth-moon transport system and a 1997 NASA Lewis Research Center (now called NASA Glenn Research Center) plan to partially duplicate it using the International Space Station, nuclear-thermal rockets, and oxygen mined from the moon.

In the second installment, I described two versions of Discovery, the "hero ship" of 2001. I emphasized the film Discovery; that is, the open-cycle gas-core nuclear-fission design the film's technical consultant, Frederick Ordway, described in the British Interplanetary Society magazine Spaceflight in 1970.

This post picks up the 2001 story where my first post left off, then I will conclude the series by discussing a paper NASA Glenn researchers Craig Williams, Leonard Dudzinski, Stanley Borowski, and Albert Juhasz first presented in July 2001 and subsequently published as a NASA Technical Memorandum (TM) in March 2005. They describe a fusion-powered spacecraft meant to emulate 2001's Discovery spacecraft. They named it Discovery II.

My first post ended with United States Astronautics Agency (USAA) bureaucrat-astronauts accidentally triggering an ancient alarm system. Radio waves blast from an alien black monolith in the moon's great ray crater Tycho. The film 2001 then skips ahead 18 months, and we get our first look at Discovery, her crew, and their daily routine.

As always, Clarke fills in missing details. The novel describes a host of robotic monitors scattered across the Solar System. Each in turn detects the radio signal from the Tycho monolith. Later we learn that data from the monitors enabled scientists on Earth to determine that the signal was directed at Saturn. In the movie, the signal was, of course, beamed at Jupiter.

Fateful decisions are made at the highest level of the United States government. The ancient Tycho monolith and the signal it aimed at Saturn are to be kept secret, allegedly to prevent cultural shock and mass hysteria.

Preparations for Project Jupiter, the first piloted round-trip journey to the Solar System's largest planet, are by this time well advanced; this provides an opportunity. In search of those who received the Tycho monolith signal, the Jupiter ship Discovery will instead travel one-way to Saturn with a gravity-assist flyby at Jupiter to gain speed. I describe the development of gravity-assist spaceflight in my "The Challenge of the Planets" post series; please see the "More Information" links at the bottom of this post.

Discovery's crew of six is split up. A separately trained three-man "survey crew" will travel to Saturn in hibernation; they will thus remain safely incommunicado, ensuring that the mission's true purpose does not slip out during radio communications with Earth. Mission Commander David Bowman and his deputy, Frank Poole, will remain awake. The pair form a minimal caretaker crew during the interplanetary phase of the Saturn mission.

Bowman and Poole are told that their mission aims to expand knowledge of the Solar System and to extend space technology capabilities, and that the survey crew has been placed aboard Discovery in hibernation to conserve life support resources. Hibernation development is a major goal of their mission, for after 100 days of scientific exploration at Saturn the entire human crew is scheduled to hibernate for more than five years. Eventually, the as-yet-unbuilt spacecraft Discovery II will arrive to take them home.

The NASA Glenn Discovery II has no connection with the Discovery II crew-retrieval spacecraft of the novel 2001. Clarke barely describes the latter. I encourage readers to speculate on the shape and capabilities of the Discovery II in the 2001 universe.

The sixth member of the Discovery crew, the HAL 9000 computer, is an artificial intelligence (AI). HAL 9000 knows the true purpose of the trip to Saturn; it is, however, programmed not to tell Bowman and Poole. The secrecy order creates a terrible behavioral conundrum for HAL 9000. Deep in its programming is a directive never to distort information, yet it has been commanded to do just that. This weighs heavily on the advanced AI. HAL 9000 is an innocent being, unable to tamp down what amounts to its conscience. The conflicting directives drive HAL 9000 to neurotic behavior which exacerbates the internal conflict, leading to psychosis and murder between Jupiter and Saturn.

Following the deaths of Poole and the three hibernating crewmen, Bowman is left alone aboard Discovery with HAL 9000. For his own safety, he disconnects the AI. When he finishes, he is the only conscious being within a billion kilometers.

Mission Control belatedly tells Bowman the true purpose of Discovery's mission. He begins a program of study to prepare himself for whatever he will encounter at Saturn. Without HAL 9000 to monitor him in hibernation, his has become a true one-way mission. Increasingly intrigued (and not a little daunted) by the prospect of contact with highly advanced aliens, Bowman is, however, able to put aside thoughts of a lonely death far from home. He even sympathizes with HAL 9000's plight.

The real thing: cylindrical projection of Iapetus image mosaic. The Cassini spacecraft captured images of Iapetus during flybys at different distances and under different lighting conditions; hence some are blurred and others are sharp. The leading hemisphere is at right. Image credit: NASA
Bowman uses Discovery's telescopes to observe the Saturn system. He determines that Iapetus is his goal; the line between the dark and light hemispheres is sharp and obviously artificial. Guided by Earth-based computer control, Discovery of the book successfully fires her plasma jet propulsion system to place herself first into orbit about Saturn and then, with her last drops of hydrogen propellant, into orbit about Iapetus. Bowman then descends in a one-man space pod with the aim of landing atop a giant ("at least a mile high") black monolith standing at the exact center of the white hemisphere of Iapetus. Bowman calls it the Tycho monolith's "big brother."

The big monolith has plans for Bowman; it is, among other things, a Stargate, a space-time shortcut leading into a galactic transit system. He is soon whisked across the Milky Way Galaxy to meet an enigmatic fate. I do not feel qualified to describe the intricacies of Stargate technology, so here I will conclude my overview of the second half of the novel 2001.

Discovery II: this forward view highlights the artificial-gravity section and the spacecraft's lone docking port. Image credit: NASA
Neither did I feel qualified to describe nuclear fusion propulsion technology when I started work on this post, but I think I stand a good chance now of accurately describing the NASA Glenn nuclear-fusion spacecraft Discovery II. If, however, you detect what you believe is an error, it probably is, so please let me know so that I can correct it.                                    

In their documents, the NASA Glenn team describes Jupiter and Saturn versions of its Discovery II. As shown by their estimated weights, only minor differences distinguish the two versions; at 1690-metric-tons, the Jupiter-bound Discovery II would weigh only nine metric tons less than the Saturn-bound version. In keeping with my already-established emphasis on Saturn in this post, I have opted to focus on the Saturn version of NASA Glenn's Discovery II.

The Discovery II design was hatched while an obscure NASA study group called the Decadal Planning Team (DPT) was active. A creation of President William Clinton's Office of Management and Budget, the DPT aimed to articulate a philosophical foundation for NASA advance planning in the 21st century. It did this to prepare the way for new space initiatives during the Presidency of Clinton's Vice President and "space czar," Albert Gore.

"Go anywhere, any time" was an oft-repeated DPT slogan that seems on the face of it to apply well to NASA Glenn's Discovery II. The spacecraft's fusion rocket could in theory propel it to Saturn in 212 days when the planet was at opposition - that is, when Saturn was as close to Earth as it could be. The NASA Glenn team found that, all else being equal, a Saturn voyage at conjunction - that is, when Saturn was on the far side of the Sun and thus as distant from Earth as it could be - would last only 15% longer. Discovery II's course to Saturn in both instances would follow nearly a straight line, not the graceful rising curve of a minimum-energy Hohmann transfer.

At present, nuclear fusion occurs mainly inside stars. Human efforts toward harnessing star power since the 1940s have emphasized fusion bombs. The U.S. exploded the first such weapon in 1952; a nuclear-fission device served as the "spark plug" for triggering the fusion explosion.

Development of electricity-generating fusion reactors, by contrast, has turned out to be more difficult than once assumed. The international ITER project, based in southern France, now hopes to test a prototype commercial fusion reactor in the 2030s.

Earth-based fusion electricity-generation technology would need to advance and considerable additional investigation into almost all engineering aspects of fusion rocketry would be necessary before a fusion engine could become part of NASA's spaceflight tool kit. Nevertheless, the NASA Glenn engineers optimistically predicted that Discovery II's maiden voyage might take place 30 years after they completed their NASA TM - that is, in the year 2035.

Discovery II: this aft view highlights the spheromak fusion reactor, four slush hydrogen tanks, and magnetic rocket nozzle. Image credit: NASA
Discovery II's proposed propulsion fusion reactor would be of a modified Tokamak design. The original Tokamak, a 1970s Russian invention, was a normal torus - the proverbial doughnut - with a magnetically contained high-temperature plasma filling. Discovery II's "spheromak" propulsion reactor, by contrast, would be shaped like a cored apple. Plasma would swirl inside a relatively compact torus with an approximately "D"-shaped cross section. Because it would be compact, it would need less structure and fewer heavy components, such as electromagnets. The spheromak could thus be made much lighter than an equivalent doughnut Tokamak.

Though the NASA Glenn team took pains to make her propulsion reactor as light as possible, at an estimated 310 metric tons it was still the most massive single hardware element of the Discovery II. The reactor weight estimate did not include support systems such as the fission reactor and battery bank that would supply the electrical power necessary for fusion reactor startup.

Tokamak vs. spheromak. Image credit: Culham Centre for Fusion Energy
The NASA Glenn researchers opted for a deuterium/helium-3 (D/He-3) reactor fuel mix, partly because it is relatively well understood and partly because deuterium and helium-3 are relatively plentiful in the outer Solar System. The spacecraft would arrive at Saturn with an empty reactor fuel tank and refuel with deuterium and helium-3 mined from its icy moons and tawny cloud bands. Discovery II would "burn" 11 metric tons of D/He-3 reactor fuel to travel one-way to Saturn.

Nuclear fusion brings together atomic nuclei at high temperatures and pressures. Lightweight nuclei, such as those of various isotopes of helium and hydrogen, yield the most energy per unit, so are generally favored as reactor fuel. When atomic nuclei fuse, they release prodigious energy and create heavier elements. The heavier elements would, over time, build up in Discovery II's fusion plasma, gradually reducing the reactor's performance. In addition, some small portion of the spheromak interior walls would sputter away and mix with the swirling plasma.

Heavy element and wall debris plasma (informally known as "ash") would congregate in a "halo" against the outer wall of the plasma torus through skillful management of interlaced "toroidal" and "poloidal" magnetic fields, then a gutter-like magnetic "divertor" would vent the ash plasma from the aft end of the torus. The vented ash plasma would produce thrust.

The NASA Glenn team proposed increasing that thrust by augmenting the vented ash plasma flow with hydrogen. Contact with ash plasma and passage through a constricted "throat" would heat the hydrogen until it also became plasma. A skeletal "magnetic nozzle" would then expel the plasma mix into space to generate thrust. The divertor and magnetic nozzle would together have a mass of only six metric tons, the NASA Glenn team estimated.

Discovery II would include four cylindrical 37-meter-long propellant tanks containing a total of 861 metric tons of "slush" hydrogen. Chilling the hydrogen until it became slush using an on-board refrigeration system would increase its density, reducing the size and number of hydrogen tanks required.

Two authors of the 2001 and 2005 Discovery II documents - Borowski and Dudzinski - proposed in 1997 a different kind of propulsion plasma augmentation. I described this in the first post of this three-part series (see "More Information" below). Their system had lunar liquid oxygen, or LUNOX, augmenting hydrogen plasma expelled from a nuclear-fission reactor. The hydrogen plasma and LUNOX would burn as in a chemical-propellant rocket engine, increasing thrust and making possible 24-hour Earth-moon "commuter" flights.

To place its Discovery II fusion ship into space, the NASA Glenn team postulated the existence of a Heavy Lift Launch Vehicle (HLLV) capable of boosting 250 metric tons into a circular assembly orbit between 140 and 260 nautical miles above the Earth. They argued that 250 tons would be very near the practical maximum payload for an HLLV. Placing Discovery II components into assembly orbit would require that seven of the monster rockets launch in rapid succession. This would create challenges in the areas of HLLV assembly, pad installation, and launch operations, among others.

The Discovery spacecraft of the book and film 2001 included large-diameter propulsion and crew modules. The latter was a sphere a little over 12 meters in diameter and the former was even longer and wider. The NASA Glenn team looked upon these with skepticism; such modules would likely be too large to launch intact, so would need to be at least partly built in space by spacewalking astronauts or through complex teleoperations.

They ignored the versatile space pods portrayed in the book and film 2001, which might have made orbital assembly easier, opting instead for pre-assembled launch packages that would fit within a 10-meter-diameter, 37-meter-long streamlined HLLV payload fairing. The self-propelled launch packages would, they explained, rendezvous and dock automatically in assembly orbit.

EASE assembly experiment, 1985. Image credit: NASA
Having said that, they then contradicted themselves by describing a series of HLLV payloads that would in fact require extensive in-space assembly. The first would include Discovery II's 203-meter-long, six-metric-ton central truss. The NASA Glenn team explained that it would be based on the Experimental Assembly of Structures in EVA (EASE) Space Station truss concept tested during STS-61B spacewalks in late 1985.

The Discovery II truss, hexagonal in cross section, would comprise 58 "bays," each built from 97 separate struts, nodes, and other parts. EASE assembly occurred in the payload bay of the Space Shuttle Atlantis. Discovery II central truss assembly would apparently take place in open space.

Following truss assembly, spacewalking astronauts would install a wide variety of systems inside and outside the truss. Most obvious were 20 rectangular 25-meter-long radiator panels for cooling Discovery II's electricity-generation systems. Each would reach orbit folded like an accordion.

Most important for the six remaining HLLV flights of the assembly phase would be communications, avionics, and reaction control systems. The avionics system, linked to controllers on Earth through the communications system, would use the hydrogen-fueled reaction control system to keep the truss and its attached payloads stable in orbit so that subsequent payloads could dock with it.

The HLLV's 250-metric-ton weight limit required that the 310-metric ton reactor reach space in two launches. The NASA Glenn engineers proposed launching part of the fusion reactor - its poloidal magnetic coils - with the truss payload. This meant that spacewalking astronauts would need to piece together in space Discovery II's most complex and important hardware element.

The second HLLV payload would include the remainder of the fusion reactor and the magnetic rocket nozzle. The third - the 172-metric-ton "artificial gravity crew payload" - would comprise seven pressurized crew modules. The NASA Glenn team offered no information as to how the crew modules would join together automatically in assembly orbit. The fourth through seventh payloads would each comprise a filled slush hydrogen propellant "cryo-tank." Thrusters and avionics would permit them to maneuver into place near Discovery II's tail.
Discovery II with selected components and dimensions indicated. Click on image to enlarge. Image credit: NASA
The NASA Glenn team had Discovery II saving reactor fuel and propellant by departing the Earth-moon system from a loose, distant, "sub-parabolic" orbit, but gave no indication as to how she would reach her departure orbit from her assembly orbit. Presumably the spacecraft would be moved using space tugs.

The NASA Glenn engineers stated that an air-breathing space plane would deliver a six-to-12-person crew to a space station in low-Earth orbit. There they would board a taxi vehicle for the journey to the waiting Discovery II. They would dock with Discovery II's only docking port, located on the front of her central hub crew module, and transfer to Discovery II.

Crews returning from Saturn would park the spacecraft in sub-parabolic orbit and await retrieval. Discovery II would be designed for reuse, though how she would be refueled, resupplied, and refurbished in sub-parabolic orbit after each flight was left to the reader's imagination.

Preparation for departure, much of which could occur before the crew arrived, would require weeks. The magnets and reactor structure would need to be thoroughly cooled using liquid helium, though the chief reason for the long preparation period would be the need to charge a five-metric-ton nickel-hydrogen battery bank. A two-megawatt, 10-metric-ton auxiliary fission reactor inside the central truss would slowly charge the batteries in preparation for the roughly one-gigawatt burst of radio-frequency energy needed to start fusion in the reactor. The NASA Glenn team called this start-up technique "high harmonic fast wave heating."

D/He-3 fuel would enter the reactor rather spectacularly as one-gram, 2.2-centimeter cube-shaped "pellets" accelerated at a rate of 27,580 gravities inside a 185-meter-long electromagnetic rail-gun. How the long, complicated rail-gun would be assembled in space within the central truss was not described. The solid-deuterium/liquid-helium-3 pellets would enter the reactor moving at 10 kilometers per second, so would deeply penetrate the dense plasma torus. This would help to preserve the stability of the swirling plasma flow. Pellets would need to be injected into the reactor once per second to maintain reactor energy output.

Swirling plasma in the fusion reactor torus would at start-up torque (twist) the central truss. Discovery II's maximum acceleration would reach 1.9 milligravities as she closed in on her target planet, when her cryo-tanks would be nearly empty. This acceleration, though minute, would place strain on the central truss, as would operation of various turbines and the movement of coolant and working fluids through pipes and pumps. The reactor fuel injector would generate a four-gravity load each time it fired a pellet. The NASA Glenn team suggested that a flywheel might absorb some of the forces Discovery II would place on herself, but provided little information as to how this would function.

The revolving crew section would also place strain on the truss. Though they noted that data concerning a healthful level of artificial gravity do not yet exist, NASA Glenn team opted to provide Discovery II's astronauts with artificial gravity one-fifth as strong as Earth gravity. Three arms 17 meters long would each connect a 5.6-meter-tall, 7.5-meter-diameter lab/hab module to a 7.5-meter-diameter central hub where weightless conditions would prevail. The artificial-gravity system would spin 3.25 times per minute. The two-deck lab/hab modules would contain accommodations for four astronauts each. Opting for separate lab/hab modules connected only through a hub would mean that the "hamster wheel" jogging routine demonstrated in the film 2001 could not occur.

All crew modules would include a layer of water between two layers of graphite epoxy hull material for radiation protection and to serve as a heat dump for crew module thermal control. The central hub would also contain a solar-flare storm shelter with augmented shielding.

Discovery II would arrive at Saturn - more accurately, Saturn sub-parabolic orbit - with nearly empty cryo-tanks. Her crew would carefully shut down her fusion reactor and begin charging her battery bank for another start-up in several weeks' time.

The NASA Glenn team offered a vague vision of how their ship might refuel for the trip home to Earth. Robotic fuel-gathering systems, perhaps suspended from balloons, might be placed into Saturn's atmosphere. They would need to process hundreds of kilograms of gas to obtain a single gram of helium-3 or deuterium and tens of thousands of tons to collect the 11 metric tons required to refuel Discovery II.

No indication was given as to how or when the refueling infrastructure would have been established. Similarly mysterious was how the collected D/He-3 would reach Discovery II.

Hydrogen propellant would be more plentiful than either deuterium or helium-3. The NASA Glenn team envisioned that Discovery II's self-propelled hydrogen cryo-tanks would separate and maneuver to an automated refueling station; meanwhile, identical full tanks would rendezvous with Discovery II and replace the depleted ones. How and when the hydrogen refueling station would have been established and how it would collect hydrogen at Saturn was left to the imagination.

Discovery II would carry no auxiliary craft, so would need vehicles pre-deployed at Saturn if her crew was meant to leave the ship and land on any of the ringed planet's many moons. The NASA Glenn team did not explain how auxiliary craft might reach Saturn ahead of Discovery II, nor how they would be maintained after they became based in Saturn's neighborhood.

Could NASA Glenn's Discovery II replicate the capabilities of 2001's Discovery? As detailed in the second part of this three-part post series, the film Discovery differed from the Discovery of Clarke's novel. The cinematic and literary spacecraft had different propulsion systems, though both relied on nuclear fission. Discovery of the film was a gas-core nuclear-thermal rocket; Discovery of the book employed electromagnetic "plasma jets" that drew electricity from a fission reactor.

Both of 2001's Discovery spacecraft - admittedly fictional, but designed with great concern for realism - could travel round-trip to Jupiter without reliance on pre-deployed assets. Both were adaptable enough that they could be diverted from Jupiter to Saturn when the need arose. That adaptability was based on advanced crew support (hibernation) and automation (HAL 9000) systems. Because of those advanced non-propulsion systems, the round-trip Jupiter mission could be re-planned as a one-way Saturn mission with eventual crew retrieval by a second spacecraft.

Though it promised fusion rocket capability, the NASA Glenn Discovery II design study is in fact incomplete. Among other things, its failure to account for the existence at Saturn of extensive pre-deployed assets essential to Discovery II's mission plan makes it hard to take seriously. Furthermore, it emphasizes propulsion to the exclusion of other potentially ground-breaking, mission-shaping technologies. For these reasons, NASA Glenn's Discovery II cannot be said to replicate the capabilities of the Discovery spacecraft portrayed in the book and film 2001: A Space Odyssey.

Saturn viewed by the Cassini spacecraft from an orbital position north of the planet's equator. The gray north polar region and peculiar spinning hexagonal polar vortex at its center are just visible. Image credit: NASA
More Information

Could the Space Voyages in the Film and Novel "2001: A Space Odyssey" Really Happen? (Part 1)

Could the Space Voyages in the Film and Novel "2001: A Space Odyssey" Really Happen? (Part 2)

The Challenge of the Planets, Part Three: Gravity

Sources (please also see Part 1 and Part 2 Sources)

Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion, NASA/TM-2005-213559, C. Williams, L. Dudzinski, S. Borowski, and A. Juhasz, NASA Glenn Research Center, March 2005

2001: A Space Odyssey, Arthur C. Clarke, New York: New American Library, October 1999, pp. 80-82, 85-101, 120-203