23 September 2016

The Eighth Continent

The northern hemisphere of the moon as viewed from the Jupiter-bound Galileo spacecraft. 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 size, 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 the surface area of a little more than four Australias, with 7.7 million square kilometers each, or a little less than three Antarcticas (14 million square kilometers each).

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

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.

The moon is close at hand. 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 Partners 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
Source

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.
 
Sources

"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

18 July 2016

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

The good ship Discovery from the classic 1968 motion picture 2001: A Space Odyssey. From right to left, we see the pressure sphere housing the crew; a train of six propellant modules; the communications complex; four more linked propellant modules; and the propulsion module. Image credit: Turner Entertainment/Metro Goldwyn Mayer
When I set out back in June to write about a pair of plans for accomplishing the space voyages portrayed in the classic 1968 film and novel 2001: A Space Odyssey, I assumed that I could get the job done in a single post. I should have known better; not only are the plans complex, there is much to say about the film and book that inspired them. Now I plan a total of three posts, of which this is the second.

This post deviates from my original intent in another way; it does not describe a real spaceflight plan inspired by and meant explicitly to reproduce a capability portrayed in the movie or book 2001. Instead, it describes how the spaceship Discovery, the setting for much of the action in the second half of the film 2001, was intended to propel itself between planets. This will lay useful groundwork for the third and final post in this little series.

Along the way, by way of explaining the details of the cinematic Discovery's propulsion system, I will sum up the state of advanced nuclear propulsion research at NASA Lewis Research Center (LeRC) in the early 1970s. During the same period, President Richard Nixon, the Congress, and NASA itself brought down the ax on the joint NASA/Atomic Energy Commission (AEC) nuclear-thermal propulsion development program.

The novel 2001 (written by Arthur C. Clarke) and the film 2001 (based on a screenplay jointly written by director Stanley Kubrick and Clarke) differ as to how Discovery is portrayed. There are in fact two different Discovery spacecraft.

Discovery in the novel 2001: A Space Odyssey measures more than 300 feet long from its forward-mounted spherical pressure hull to its aft-pointing plasma jet propulsion units. Immediately behind the pressure hull is a cluster of four cylindrical hydrogen propellant tanks and, behind them, a complex system of cooling fins. The fins form a "V" with the broad top of the "V" facing forward and a shielded nuclear reactor at its point.

The nuclear reactor would generate electricity for "focusing electrodes" in Discovery's plasma jets. These would heat the hydrogen and expel it to generate thrust. Judging by Clarke's description, the Discovery plasma jet design was apparently based on the same principle as the jets that propelled the Aries-1B moon shuttle I discussed in my last post.

The cooling fins, which Clarke described as "[v]eined with a delicate tracery of pipes for
. . .cooling fluid," were meant to radiate excess heat from Discovery's nuclear reactor into space. They would, he wrote, "glow cherry red" when the ship's plasma jets operated at full thrust, but become "dark and cool" after the jets were switched off.

Discovery of the film 2001 lacks any sign of cooling fins. Partly this is because Kubrick worried that his audiences would wonder why a spacecraft operating in the vacuum of space would need wings, but Kubrick's evolving aesthetic vision also played a part. Ultimately, he sought a frail-looking, skeletal Discovery.

The largest single component of the cinematic Discovery is the propulsion module at its aft end, with the roughly 40-foot-diameter pressure sphere at the spacecraft's forward end coming in a close second. In between is a train of linked propellant modules, each about 20 feet long. From a certain distance, these resemble vertebrae. About halfway along Discovery's "spinal column" is a communications complex with three Earth-pointing dish antennas, one large and two small.

Sadly, we never see Discovery's engines in action in the film 2001. We might have witnessed the slender spacecraft slowly turn to point its engines forward as it approached Jupiter, then watched in wonder as they lit up to slow Discovery so that the giant world's gravity could capture it into orbit.

Discovery's engines, 700 feet behind the pressure sphere bearing the crew. Image credit: Turner Entertainment/Metro Goldwyn Mayer
The timing for such a maneuver would, however, have been awkward from a story point of view; having just lobotomized the HAL 9000 computer, the "brain and central nervous system" of his ship, it seems doubtful that David Bowman, the sole surviving member of Discovery's five-person crew, could have had enough time to prepare for and carry out a successful deceleration maneuver. Kubrick opted instead to skip the Jupiter capture maneuver and proceed directly to his film's enigmatic, mind-bending climax.

Despite never seeing it operate, we have at our disposal information about how the cinematic Discovery's propulsion system was meant to work. The individual most responsible for this was Frederick Ordway.

Ordway was born in 1927. He graduated Harvard in 1949 with a Bachelor of Science degree, then earned certificates in physics and geosciences at the Sorbonne. In 1950, while studying in Paris, he attended the first International Astronautical Congress, where he met Clarke, whose six-decade writing career was just taking off.

In the 1950s, Ordway worked for New York-based aviation companies, generally in the area of rocketry. Toward the end of the decade, at the urging of Wernher von Braun, he relocated to Huntsville, Alabama, to work at the Army Ballistic Missile Agency (ABMA). Ordway became a NASA employee in July 1960, when ABMA became the nucleus around which NASA Marshall Space Flight Center crystallized.

In 1963, Ordway published the first of more than 20 books he would author in his lifetime. Titled Conquering the Sun's Empire, it was a popular-audience vision of humankind's future in the Solar System illustrated by his friend and collaborator, the artist Harry Lange.

In January 1965, Clarke introduced Ordway and Lange to Kubrick, who hired them both in mid-February to provide him with technical advice. The Discovery design in the novel 2001, known informally as the "dragonfly," was based on Lange pre-production illustrations developed during early discussions between Ordway, Lange, Clarke, and Kubrick.

A major part of Ordway's contribution to 2001: A Space Odyssey involved visiting aerospace companies and NASA centers, where he interviewed experts in spaceflight-related fields and collected advance-planning documents in an effort to ensure that Kubrick's film would present a believable vision of spaceflight at the turn of the millennium. He also became a spokesperson for the film, which had aroused intense interest in the aerospace community.

25 September 1965: Frederick Ordway (left, in white) joins a few notables for a tour of the British studio where 2001: A Space Odyssey was filmed. From left to right, they are: Donald "Deke" Slayton, NASA Director of Flight Crew Operations; Arthur C. Clarke; Stanley Kubrick; and George Mueller, NASA Associate Administrator for Manned Space Flight. Image credit: The Stanley Kubrick Archives
Ordway's formal involvement with 2001 production ended after nearly two years, in December 1966, 15 months ahead of the film's world-wide release in April 1968. Ordway's time on Kubrick's payroll coincided with NASA's peak funding year.

In 1965-1966, it was still reasonable to assume that the U.S. space agency would in the 1970s, 1980s, and 1990s expand upon the achievements of the 1960s Apollo Program. Thirty-five years seemed to be plenty of time to build a giant artificial-gravity Earth-orbital space station, establish a moon base, land humans on Mars, and launch humans and intelligent, talking computers into the outer Solar System.

According to Ordway, the cinematic Discovery was meant to have a "Cavradyne" gas-core nuclear-thermal propulsion system. He described it in a 1970 Spaceflight magazine article on the spacecraft of 2001. His description subsequently appeared as design notes in a set of Discovery blueprints drawn by graphic artist Shane Johnson. Ordway himself excerpted his 1970 description of Discovery's propulsion system in a 1982 paper. I will describe the fictional Cavradyne system shortly; before that, though, I will provide for it some "real world" context.

At the time Ordway published his 1970 article, NASA and the Atomic Energy Commission (AEC) had for more than a decade worked together to develop nuclear-thermal rockets. NASA and the AEC emphasized solid-core nuclear-thermal propulsion; gas-core nuclear engines of the type envisioned for Discovery of the film were widely seen as exotic and perhaps impossible.

Nuclear rocketry had ceased to be a national priority as early as 1963-1964, when Presidents John F. Kennedy and Lyndon Baines Johnson grounded the Reactor In-Flight Test (RIFT) project, which had optimistically aimed to launch a solid-core nuclear rocket engine into Earth orbit on a Saturn V rocket in 1967. Nevertheless, many within NASA remained hopeful in 1970 that solid-core nuclear rocket stages might navigate the Earth-moon system in the mid-to-late 1970s, as described in NASA's 1969 Integrated Program Plan (IPP). I discuss the IPP elsewhere in this blog - please see the "More Information" links at the end of this post.

During the 1960s, low-level gas-core engine studies took place under the aegis of the Advanced Reactor Concepts Section at NASA Lewis Research Center (LeRC) in Cleveland, Ohio. Robert Ragsdale, chief of the Section, performed gas-core research and analysis with his LeRC colleagues and supervised small contractual studies at more than a dozen corporations and universities across the United States. It is possible that Ordway contacted Ragsdale or researchers his Section funded as he gathered information for Kubrick, though no record of such a meeting is known to exist.

A solid-core nuclear-thermal rocket, the most basic kind, can be seen as a nuclear reactor with an open-cycle cooling system. A reflector focuses neutrons radiated from solid uranium fuel elements back into the reactor core, causing nuclear fission to occur. The fuel elements grow hot. Left to themselves, they would melt catastrophically; however, a turbopump drives propellant (typically cryogenic liquid hydrogen) into the reactor. The propellant turns to hot plasma upon contact with the fuel elements and vents into space through a bell-shaped nozzle, generating thrust.

A major advantage of a nuclear-thermal rocket engine over a chemical-propellant rocket engine (for example, the Space Shuttle Main Engine) is in the area of specific impulse, or the ratio of a unit of propellant expended to a unit of thrust generated. Specific impulse, abbreviated Isp, is expressed in seconds. The best Isp attainable using liquid hydrogen/liquid oxygen chemical propellants is in the neighborhood of 450 seconds, while the best solid-core nuclear Isp is in theory roughly twice that - on the order of 800 to 1000 seconds.

Nuclear-thermal Isp is dependent on the temperature of the fuel elements. Achieving an Isp much greater than about 1000 seconds using a solid-core nuclear-thermal engine rapidly becomes infeasible because the propellant can no longer cool the fuel elements enough to prevent them from melting. Supplemental cooling - for example, coolant flowing through plumbing within the engine to pick up its excess heat and then through large cooling fins to radiate that heat into space - becomes increasingly necessary, boosting spacecraft weight. The NASA LeRC team found that, for really high Isps, the heaviest gas-core engine system would be its cooling system. Increased weight would mean more costly heavy-lift rockets to place the spacecraft's components into space for assembly as well as reduced engine performance.

Gas-core nuclear-thermal propulsion promised a way around the "temperature barrier." In a gas-core engine, uranium would take the form of an incandescent ball of plasma in which nuclear fission would take place. The uranium fuel element (the plasma ball) would operate at a temperature far above the point at which a solid-core uranium fuel element would vaporize - and that would be exactly as it should be.

Ragsdale's group emphasized open-cycle gas-core propulsion over closed-cycle gas-core propulsion. The open-cycle plasma ball would "float" in a "stagnant region" that would fill about 40% of a spherical engine chamber about a dozen feet across. Hydrogen propellant would flow around the plasma ball, be heated until it also became a plasma, and then vent through a nozzle into space.

No physical wall would separate the uranium plasma from the hydrogen, an omission meant to reduce engine mass and complexity. A thin uranium wire would feed slowly into the plasma ball to make up for the small amount of uranium plasma - about 0.25% of the propellant flow at any particular moment - that would escape the open-cycle gas-core engine with the hydrogen propellant. As the open-cycle engines was shut down, the entire uranium plasma ball, diluted by hydrogen, would gradually vent from the nozzle into space.

A closed-cycle gas-core system - sometimes called a "nuclear lightbulb" - would include a physical barrier between the uranium plasma ball and the hydrogen propellant. The barrier would add weight and complexity, and might create temperature limitations; it would, however, also prevent uranium plasma from escaping into space. Presumably it would also make engine start-up - hydrogen flow initiation for cooling followed by creation of a stable uranium plasma ball in which fission would occur - a simpler task.

Using mathematical models, Ragsdale's group studied open-cycle gas-core engines with Isps of between 1500 and 3000 seconds. These could, they determined, operate without supplemental cooling.

To reach Isps beyond 3000 seconds, the plasma ball would need to become so hot that surrounding structure would melt and fail without supplemental cooling. Even with supplemental cooling, seemingly insurmountable temperature barriers would soon be reached. For an Isp of 5000 seconds, for example, the core temperature would run at about 22,000 K (about 39,000° F, or 21,700° C); that is, about four times the temperature of the Sun's surface and well above the melting point of all known materials.

Ragsdale's group found a surprisingly simple partial solution to the melting problem. The hydrogen propellant would enter the spherical chamber containing the uranium plasma ball through pores or slots. Seeding the propellant with tungsten particles, each roughly the size of those making up cigarette smoke, would help it to absorb heat, preventing all but about 0.5% of the plasma ball's thermal radiation from reaching the inner chamber wall. The resulting increased hydrogen temperature would also mean increased engine thrust.

About 7% of the uranium plasma ball's energy would, however, emerge as gamma and neutron radiation, pass unimpeded through the hydrogen/tungsten propellant mix, and heat the chamber wall and surrounding structures. Research had found that, because of this, some level of supplemental cooling would inevitably be required to prevent destruction of the gas-core engine.

Simplified cutaway of an open-cycle gas-core nuclear rocket engine. A pressure vessel provides structural strength and a beryllium oxide (BeO) moderator absorbs neutrons radiated from the uranium plasma, limiting pressure shell and adjacent spacecraft structure heating. Coolant moves through passages in the moderator to provide supplemental cooling. After passing through the moderator, the coolant flows through a space radiator then returns to the moderator to pick up more heat. A turbopump drives hydrogen propellant through the inner, "porous" wall. Uranium enters the plasma ball in the form of a "wire" roughly the diameter of a pencil lead to make up for the small amount carried off by the hydrogen plasma, which vents into space through the nozzle at right to generate thrust. Not shown is the system for introducing tungsten particles into the hydrogen. An engine of this basic design could in theory yield Isps of between 3000 and 5000 seconds. Image credit: NASA
Citing more than a decade of research, Ragsdale predicted confidently that open-cycle gas-core nuclear-thermal propulsion would be confirmed to be feasible within just a few years. It is important to note, however, that the gas-core studies explored in this post were of necessity preliminary due to limited research funding. One consequence of this is that some study results are inconsistent and many are perhaps optimistic.

Ragsdale pointed to planned 56-day astronaut stays on board Skylab in Earth orbit when he proposed a 60-day round-trip piloted Mars mission with a spacecraft mass of 2250 tons in Earth orbit at mission start. Of this, the gas-core engine would account for from 50 to 250 tons and hydrogen propellant about 1500 tons. He noted that, if it were determined that astronauts could remain healthy for up to 80 days in space, then extending the Mars voyage duration accordingly would cut in half the quantity of hydrogen propellant the gas-core Mars spacecraft would expend during its round-trip journey.

NASA LeRC researchers envisioned 80-day gas-core "courier" Mars missions. These would travel to Mars in 40 days and then return to Earth in 40 days. The spacecraft would linger near Mars only long enough to "jettison" a forward-mounted payload.

Like so many advanced concepts, NASA LeRC gas-core propulsion never got the conceptual artwork it deserved - until now. This illustration, kindly provided by artist William Black/http://william-black.deviantart.com/, is based on a crude line drawing that appears in early 1970s NASA LeRC gas-core propulsion reports. It shows the 80-day "courier" spacecraft early in its Earth-departure burn. The NASA LeRC line drawing indicated a need for radiator fins, but did not show their shape or extent; Black has made them resemble the "V"-shaped radiator configuration of the dragonfly Discovery in the novel 2001. Doing so places them within the conical radiation shadow created by the shield at the front of the gas-core engine (see image below) so that they do not reflect radiation toward the crew. Please click on image to enlarge.
Closeup of an open-cycle gas-core nuclear-thermal rocket engine based on NASA LeRC design concepts as envisioned by artist William Black/http://william-black.deviantart.com/. The large disc at left is a shadow shield for protecting the spacecraft crew from radiation from the engine. The cage-like truss structure surrounds the uranium storage and feed system and tungsten particle feed, hydrogen feed, and coolant circulation lines. Liquid hydrogen cools the silver part of the engine bell, becoming a hot gas; it then drives turbopumps (colored gold) that pump hydrogen into the spherical gas-core engine chamber. In Black's interpretation, turbobump hydrogen gas then vents aft into space through a pair of pipes. He also includes a gimbal system for pivoting the engine off its center line and an uncooled rocket nozzle extension (colored black).
Ragsdale wrote that the Space Shuttle, with its planned ability to routinely and cheaply launch payloads to Earth orbit, would help to make possible piloted interplanetary spacecraft with gas-core engines. This observation is ironic because, in testimony before a February 1971 Congressional hearing on the future of U.S. nuclear rocketry, NASA Acting Administrator George Low had used the need to fund Shuttle development as an excuse for slashing nuclear propulsion funds in Fiscal Year 1972 to a level barely sufficient to close out the program.

In his January 1972 article, Ragsdale wrote that his group had big plans for gas-core development in the 1972-1975 period. As it turned out, however, the Nixon White House and NASA officials announced while his article was still current that they had slashed all funding for nuclear rocket research from the Fiscal Year 1973 NASA budget. NASA and the AEC backed out of the nuclear-thermal propulsion business by the end of 1973.

Now we return to the world of 2001: A Space Odyssey. Ordway's conjectural Cavradyne engine, a closed-cycle gas-core system, was a "cavity reactor only several feet across." A uranium plasma ball with a temperature of about 11,400 K (about 20,000° F, or 11,100° C) would float at the center of a graphite inner container that would pass heat but not neutrons. Hydrogen would flow between the graphite container and the inner wall of the cavity reactor outer shell, then would vent as high-temperature plasma through a nozzle into space.

Nuclear-propulsion spacecraft designs are usually shaped at least in part by the need to keep astronauts well away from sources of radioactivity. The cinematic Discovery's length of 700 feet reflected the presence - judging from the external configuration of its propulsion units - of at least three and possibly six Cavradyne engines. One can speculate that each engine was meant to have a shield at its forward end, creating overlapping radiation shadows that would encompass the pressure sphere bearing the crew.

Neither Ordway nor Clarke provided detailed performance data for their Discovery spacecraft. The voyage durations they mention do, however, imply high-performance propulsion. In a late 1965/early 1966 draft of the 2001 screenplay, for example, Discovery's trip time to Saturn with a gravity-assist at Jupiter is given as 257 days. In Clarke's novel, Discovery reaches Jupiter in about six months and then proceeds onward to Saturn. In a draft of the novel which has Jupiter as Discovery's goal, excerpted in Clarke's 1972 book The Lost Worlds of 2001, the one-way trip-time is given as 219 days. These trip times are consistent with the Earth-Mars trip times in NASA LeRC conference papers and reports.

Sources

2001: A Space Odyssey, draft screenplay by Stanley Kubrick and Arthur C. Clarke, p. c15d, 11/1965

Kubrick, Stanley, and Arthur C. Clarke, 2001: A Space Odyssey, directed by Stanley Kubrick, Metro Goldwyn Mayer, April 1968

The Lost Worlds of 2001: The Ultimate Log of the Ultimate Trip, Arthur C. Clarke, New York: Signet, January 1972, pp. 130-132

"Part B: 2001: A Space Odyssey in Retrospect," Frederick I. Ordway, III; Science Fiction and Space Futures, Eugene E. Emme, editor, AAS History Series, Volume 5, San Diego: Univelt, 1982, pp. 47-105

2001: A Space Odyssey, Arthur C. Clarke, New York: New American Library, October 1999, pp. 98-99, 105, 190-191

The 2001 File: Harry Lange and the Design of the Landmark Science Fiction Film, Christopher Frayling, London: Rare Art Press, 2015, pp. 210-211, 217, 226, 228-231

U.S.S. Discovery: Manned Nuclear Exploration Vessel (Registry XD-1) Spacecraft Interior Blueprints and Exterior Plans, Shane Johnson, no date (c. 1985), Sheets 1, 3, and 5

"Crew Radiation Dose from a Gas-Core Nuclear Rocket Plume," NASA TM X-52832, C. Masser, NASA Lewis Research Center; paper presented at the Sixteenth Annual Meeting of the American Nuclear Society in Los Angeles, California, 28 June-2 July 1970

"Gas-Core Rocket Reactors - a New Look," NASA TM X-67823, R. Ragsdale and E. Willis, NASA Lewis Research Center; paper presented at the Seventh AIAA Joint Specialist Conference in Salt Lake City, Utah, 14-18 June, 1971

"To Mars in 30 Days by Gas-Core Nuclear Rocket," R. Ragsdale, Astronautics & Aeronautics, January 1972, pp. 65-71

"Reactor Moderator, Pressure Vessel, and Heat Rejection System of an Open-Cycle Gas-Core Nuclear Rocket Concept," NASA TM X-2772, M. Taylor, C. Whitmarsh, P. Sirocky, and L. Iwanczyk, NASA Lewis Research Center, July 1973

Humans to Mars: Fifty Years of Mission Planning, 1950-2000, NASA SP-2001-4521, Monographs in Aerospace History #21, David S. F. Portree, Washington: NASA, February 2001, pp. 33-52

More Information

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

The Last Days of the Nuclear Shuttle (1971)

Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

On the Moons of Mighty Jupiter (1970)

Touring Titan by Blimp & Buoy (1983)

The Challenge of the Planets, Part Three: Gravity