18 November 2018

Near-Term and Long-Term Goals: Space Station and Lunar Base (1983-1984)

Homeward bound: an Orbital Transfer Vehicle (OTV) bearing a returning lunar base crew aerobrakes in Earth's atmosphere. After aerobraking it will rendezvous with the NASA space station. Image credit: Pat Rawlings/NASA
In December 1983, the National Science Foundation's Division of Policy Research and Analysis enlisted Science Applications Incorporated (SAI) of McLean, Virginia, to compare the science and technology research potential of an Earth-orbiting space station and a base on the moon. In its report, which was completed on 10 January 1984, SAI cautioned that, because its study was performed "in a very short two-week period," it could offer only "a preliminary indication" of the relative merits of a space station in low-Earth orbit (LEO) and a lunar base. Though SAI did not say so, its study had a short turnaround time because its results were meant to inform the White House ahead of President Ronald Reagan's planned announcement of a NASA space station program during his 25 January 1984 State of the Union Address.

SAI explained that its study had used a four-step approach. First, the study team had judged which science and technology disciplines could best be served by an LEO space station and which by a lunar base. Next, the team had developed a lunar base conceptual design capable of serving the disciplines it identified. It then had developed a transportation system concept for deploying and maintaining its base. Finally, the team had estimated the cost of developing, building, and operating its lunar base.

The team identified five science and technology disciplines that would best be served by a base on the moon. The first was radio astronomy. Bowl-shaped radio telescopes might be built in bowl-shaped lunar craters, SAI wrote. Radio astronomers might take advantage of the moon's Farside (the hemisphere turned permanently away from Earth), where up to 2160 miles of rock would shield their instruments from terrestrial radio interference. The 238,000-mile separation between lunar and terrestrial radio telescopes would enable Very Long Baseline Interferometry capable of detecting minute details of galaxies far beyond the Milky Way.

A bowl-shaped crater makes an ideal site for a bowl-shaped radio telescope. Visible stars are artist's license; the harsh glare of the Sun in lunar daylight would banish them from view. Image credit: NASA
High-energy astrophysics and physics was SAI's second lunar base discipline. The team noted that, because the moon offers "a large, flat area, a free vacuum, and a local source of refined material for magnets," it might serve as the site for a large particle accelerator.

Lunar geology (which SAI called "selenology") would obviously be better served by a lunar base than by a space station. SAI noted that, despite 13 successful U.S. robotic lunar missions and six successful Apollo landings, the moon had "barely been sampled and explored." Lunar base selenological exploration would focus on "understanding better the early history and internal structure of the Moon" and "exploring for possible ore and volatile deposits." Selenologists would rove far afield from the base to measure heat flow and magnetic properties, drill deep into the surface, deploy seismographs, and collect and analyze rock samples.

SAI's fourth lunar discipline was resource utilization. The study team noted that samples returned to Earth by the Apollo astronauts contained 40% oxygen by weight, along with silicon, titanium, and other useful chemical elements. Lunar oxygen could be used as oxidizer for chemical propulsion spacecraft traveling between Earth and moon and from LEO to geosynchronous Earth orbit (GEO). Silicon could be used to make solar cells. (SAI pointed out, however, that the two-week lunar night would make reliance on solar arrays for electricity "somewhat difficult.") Raw lunar dirt - known as regolith - could serve as radiation shielding. If water ice were found at the lunar poles - perhaps by the automated lunar polar orbiter that SAI advised should precede the lunar base program - then the moon might supply hydrogen rocket fuel as well as oxidizer.

SAI's fifth and final lunar base science discipline was systems development. The team expected that lunar base technology development would be "devoted to improving the efficiency and capabilities of systems that support the base," such as life support, with the goal of "reduced reliance on supplies sent from Earth." Transport system development might include research aimed at developing a linear electromagnetic launcher of the kind first proposed by Arthur C. Clarke in 1950. Such a device - often called a "mass driver" - might eventually launch bulk cargoes (for example, lunar regolith, liquid oxygen propellant, and refined ores) to sites around the Earth-moon system.

The SAI team noted that some disciplines might be served equally well by a lunar base or an Earth-orbiting space station. Large (100-meter) telescopes for optical astronomy, for example, might be equally effective on the moon or in Earth orbit. The moon, however, would offer a stable, solid surface that might enable the "pointing stability and optical system coherence" necessary in such a telescope.

SAI acknowledged that its report proposed "research and development activities. . .too numerous and often too difficult for a first-generation lunar base." It thus divided activities within the five lunar base disciplines into two categories: those suitable for its first-generation base and those that would need a more elaborate second-generation facility. First-generation radio astronomy, for example, would use two small dish antennas on Nearside (the lunar hemisphere facing Earth). In the second generation, a 100-meter-diameter antenna would operate on Farside.

Having defined its lunar base science program, the SAI team moved on to the second and third steps in its study. The team assumed that NASA's Space Shuttle, which at the time they wrote had just completed its ninth flight (STS-9/Spacelab 1, 28 November-8 December 1983), along with an LEO space station, would form part of the lunar base transportation infrastructure. The Shuttle would cheaply and reliably deliver lunar base crews, spacecraft, and cargo to the station, where they would be brought together for flight to the moon. SAI proposed reapplying hardware developed for the LEO station to the lunar base program.

An October 1984 paper for the first Lunar Bases and Space Activities of the 21st Century symposium provided additional details of SAI's Earth-moon transportation system and surface base design. Where these conflict with the December 1983 report, the description that follows defaults to information contained only in the December 1983 report (mostly).

SAI's lunar transportation system would include three types of spacecraft. The first, the reusable Orbital Transfer Vehicle (OTV), would be a two-stage spacecraft permanently based at the LEO station. SAI assumed that NASA would develop OTVs for moving cargoes between the LEO station and higher orbits (for example, GEO) and that this basic OTV design would then be modified for lunar base use. The OTV, which would operate as a piloted spacecraft through addition of a pressurized "personnel pod," would be capable of delivering up to 16,950 kilograms of crew and cargo to lunar orbit.

An OTV-derived four-legged lander would form the basis of two vehicles: the Logistics Lander and the Lunar Excursion Module (LEM). The former would include a removable subsystem module for automated lunar landings. The latter would carry a personnel pod for piloted flight. These were the second and third spacecraft in SAI's lunar transportation system, though one might argue that they were actually tricked-up OTVs.

SAI's one-way cargo lunar flight mode. Please click to enlarge. Image credit: Science Applications, Inc.
The three vehicle types would support two basic flight modes. One-way cargo missions would use Direct Descent. The OTV first stage would ignite and burn nearly all of its propellants, then would separate, turn around, and fire its engines to slow down and return to the LEO station for refurbishment. The OTV second stage would then ignite, burn most of its propellants, and separate from the Logistics Lander. The second stage would swing around the moon on a free-return trajectory, fall back to Earth, aerobrake in Earth's atmosphere, and rendezvous with the LEO station. The Logistics Lander, meanwhile, would descend directly to the lunar base site with no stop in lunar orbit.

For two-way crew sorties, the OTV first stage would operate as during a one-way cargo mission. After a three-day flight, the OTV second stage/personnel pod combination would capture into lunar orbit, where it would dock with a waiting LEM carrying lunar base astronauts bound for Earth. They would trade places with the new base crew. In addition to the new crew, 12,750 kilograms of propellants (sufficient for a round trip from lunar orbit to the surface base and back again) and up to 2000 kilograms of cargo would be transferred from the OTV second stage/personnel pod to the LEM.

SAI's roundtrip crew rotation lunar flight mode. Please click to enlarge. Image credit: Science Applications, Inc.
The OTV second stage/personnel pod and the LEM would then separate. The former would fire its engines to depart lunar orbit for Earth, and the latter would descend to a landing at the lunar base. The OTV second stage/personnel pod combination would subsequently aerobrake in Earth's atmosphere and return to the LEO station for refurbishment.

SAI's base buildup sequence would begin with a pair of Site Survey Mission flights. The first would see an unpiloted LEM with empty propellant tanks placed into lunar orbit through a variant of the crew sortie mode. An automated OTV second stage bearing the LEM in place of a personnel pod would enter lunar orbit, undock from the LEM, and return to Earth.

The second Site Survey Mission flight would employ another variant of the Crew Sortie mode. Five astronauts would arrive in lunar orbit in an OTV second stage/personnel pod and dock with the waiting LEM. The four astronauts of the base site survey team would transfer to the LEM along with propellants and supplies. They would then undock and land at the proposed base site, leaving the OTV pilot alone in lunar orbit. After completing their survey of the site, they would return to the OTV second stage/personnel pod, then would undock from the LEM and return to Earth orbit.

Assuming that the base site checked out as acceptable, Flight 3 would see the start of base deployment. A Logistics Lander would employ Direct Descent mode to deliver to the base site an Interface Module and a Power Plant. The Interface Module, which would be based on LEO space station hardware, would include a cylindrical airlock, a top-mounted observation bubble, and a cylindrical tunnel with ports for attaching other base modules. SAI's proposed Power Plant was a nuclear source capable of generating 100 kilowatts of electricity.

Flight 4 would deliver two "mass mover" rovers, two 2000-kilogram mobile laboratory trailers, and a 1000-kilogram lunar resource utilization pilot plant. The rovers would tow the mobile labs up to 200 kilometers from the base on selenologic excursions lasting up to five days. The mobile labs would carry instruments for microscopic imaging, elemental and mineral analysis, and subsurface ice detection. They would also carry a radio sounder for exploring beneath the lunar surface, stereo cameras, and a soil auger or core tube for drilling up to two meters deep. The first-generation lunar resource utilization Pilot Plant would process 10,000 kilograms of regolith per year to yield oxygen, silicon, iron, aluminum, titanium, magnesium, and calcium.

Flight 5 would deliver the Laboratory Module, the first 14-foot-diameter, 40-foot-long cylindrical base module based on the pressurized module design used on the LEO station. Flight 6 would deliver the Habitat Module, which would provide living quarters for the seven-person base crew, and Flight 7 would deliver the Resources Module, which would include a pressurized control center and an unpressurized section containing water and oxygen tanks and equipment for life support, power conditioning, and thermal control. The final base deployment flight, a duplicate of Flight 1, would deliver a backup LEM to lunar orbit.

Long-term occupation of the moon would begin with Flight 9, a crew sortie mission that would deliver a four-person construction team. A three-person construction team would join them on Flight 10, bringing the total base population to seven. The OTV pilots for these flights would return to Earth alone after the construction teams undocked and landed at the base in their respective LEMs.

Using the mass mover rovers, the base crew would unload the Logistics Landers and join together the base components. The completed base would provide seven astronauts with 2000 cubic feet of living space per person. They would attach the Lab, Hab, and Resource Modules to the Interface Module, then would link the resource utilization pilot plant to the Lab Module.

The Power Plant would be placed a safe distance away from the base and linked by a cable to the base power conditioning system. The crew would link the Power Plant and base thermal control system by hoses to a heat exchanger/heat sink, then would activate the Power Plant. Finally, the astronauts would use bulldozer scoops on the rovers to cover the pressurized modules with regolith radiation shielding.

Flight 11, the first base crew rotation flight, would see the four-person construction team that arrived on Flight 9 lift off in a LEM and return to lunar orbit, where they would dock with an OTV second stage/personnel pod combination just arrived from Earth. The Flight 9 lunar base team would trade places with them and, following LEM refueling and cargo loading, would descend to a landing at the base. The first construction team and the Flight 11 OTV pilot would then return to the LEO station. On Flight 12, a three-person base team would replace the Flight 10 team.

Lunar base teams of three or four astronauts would rotate every two months. The typical base complement would include a commander/LEM pilot, an LEM pilot/mechanic, a technician/mechanic, a doctor/scientist, a geologist, a chemist, and a biologist/doctor, SAI wrote.

Mass mover rover in the field with advanced power cart and deep drill rig. Image credit: NASA
SAI then estimated the cost of its lunar base and three years of operations based on NASA's cost estimates for the Space Shuttle and the LEO station. At the time SAI conducted its study, NASA placed the cost of its proposed LEO station at between $8 billion and $12 billion. This was in fact an underestimation calculated to make the station more politically palatable. NASA placed the total cost of LEO station Logistics, Habitat, Laboratory, and Resource Modules and other structures at $7.1 billion, so SAI estimated the total cost of the lunar base Resource, Habitat, Laboratory, and Interface Modules at $5.8 billion.

Although the OTV would find uses in LEO and GEO, SAI charged all of its development and procurement costs (a total of $7.2 billion) to the lunar base. The expendable Logistics Lander and reusable LEM would cost $6.6 billion and $4.8 billion, respectively. The LEM, though structurally beefier and more complex, would cost less because the Logistics Lander would bear the development cost of systems common to both landers.

Based on optimistic NASA pricing, the SAI team assumed that a Shuttle flight would cost $110 million in 1990. The 89 Shuttle flights in the lunar base program would thus cost a total of $9.8 billion. The LEO station, by contrast, would need only 17 Shuttle flights at a cost of $1.9 billion. SAI placed total LEO station cost plus three years of operations at $14.2 billion. Lunar base cost plus three years of operations came to $54.8 billion.

To conclude its report, SAI noted that both the LEO station and the lunar base could be completed in about a decade. The LEO station would, however, serve a broader science user community and would provide an OTV base in LEO for eventual lunar base use. The SAI team argued that the LEO station was a reasonable near-term (for the next 10 years) objective, while the lunar base would yield obvious benefits in a long-term (50 years) space program. It added that the
Space Program will function best if it has both near-term objectives and long-range goals. The near-term objectives assure [sic] that we progress with each year that passes. The long-range goals provide direction for our annual progress. The Space Station and Lunar Base appear to serve these respective roles at the present time.

A Manned Lunar Science Base: An Alternative to Space Station Science? A Brief Comparative Assessment, Report No. SAI-84/1502, Science Applications, Inc., 10 January 1984

"Preliminary Design of a Permanently Manned Lunar Surface Research Base," S. Hoffman and J. Niehoff, Science Applications International Corporation; published in Lunar Bases and Space Activities of the 21st Century, "papers from a NASA sponsored, public symposium hosted by the National Academy of Sciences in Washington, D.C., Oct[ober] 29-31, 1984," W. W. Mendell, editor, Lunar and Planetary Institute, 1985, pp. 69-75

More Information

There's a Helluva Good World Next Door

Chronology: Space Station 1.0

As Gemini Was to an Apollo Lunar Landing by 1970, So Apollo Would Be to a Permanent Lunar Base by 1980 (1968)

"A Vision of the Future": Military Uses of the Moon and Asteroids (1983)

09 November 2018

Another Look at Staged Reentry: Janus (1962-1966)

The M2-F1 lifting-body glider (left) and its successor, the M2-F2. Of the experimental lifting bodies NASA built and flew, the Janus spacecraft would have most resembled these pioneering aircraft. Image credit: NASA
In 2013, while spending a gleeful Sunday afternoon searching through old patent applications (don't judge me), I stumbled upon an intriguing design for a piloted spacecraft using "staged reentry." I wrote about it on my old Beyond Apollo blog on the WIRED website.

In 2017, I expanded that post with more context details on the history of lifting body research and better illustrations and posted it on this blog (see the link at the end of this post). At the time, the patent application, filed in January 1964 by TRW engineers C. Cohen, J. Schetzer, and J. Sellars and granted in December 1966, remained my only source of information on the staged reentry concept.

No longer. One benefit of working at a university is that journal articles formerly locked up behind paywalls, out of reach of independent scholars on a budget, are now readily accessible. Last month, while spending a gleeful Sunday afternoon searching through the 1965 volume of The Journal of Spacecraft & Rockets, I stumbled upon a staged reentry design named for Janus, the two-faced Roman god of endings and beginnings. Closer examination confirmed that the Janus spacecraft was indeed the unnamed spacecraft of the 1966 patent.

Janus is an apt name for the proposed spacecraft design, because its most unique features are related to launch and (especially) landing - that is, the beginning and ending of its mission. The name was first used in a confidential May 1962 TRW Space Technology Labs report by I. Spielberg and C. Cohen.

Spielberg, whose name does not appear on the patent application, presented the staged reentry concept at the first conference of the American Institute of Aeronautics and Astronautics in Washington, DC (29 June-2 July 1964) along with Cohen, whose name was the only one to appear on the 1962 report, the 1964 presentation, the 1965 Journal of Spacecraft & Rockets paper based on the presentation, and the 1966 patent. It seems likely, given his continuous involvement, that Cohen originated and championed the Janus staged reentry concept.

Patent applications are not engineering papers; or, perhaps, one may say that lousy is the engineering paper that reads like a patent application. In addition to being more readable, the 1965 Spielberg and Cohen paper provides considerably more detail than the patent application.

The TRW engineers explained the rationale behind the staged reentry concept:
A manned system should provide precision and flexibility in its landing characteristics. It should be capable of routine launch and routine return without a large recovery task force. Moreover, these criteria must be satisfied without curtailing payload volume or weight or reducing the reliability of reentry protection. In general, these requirements conflict, since efficient entry vehicles (e.g., blunt lifting bodies) have poor landing characteristics, whereas vehicles that land well (winged configurations) tend to have low volumetric efficiency and serious reentry design problems. The staged reentry concept. . . circumvents the difficult design compromises that otherwise must be made to ensure good landing qualities, high volumetric efficiency, and desirable reentry characteristics.
The Janus spacecraft comprised two parts that would separate in flight. The largest part was a 26.8-foot-long, 16-foot-wide, 10-foot-deep "pod." Designed to carry three astronauts, it was an 11,660-pound half-cone lifting body with flat aft and top surfaces and a curved, blunt nose.

The TRW engineers described the pod's double-walled structure. Its inner hull, the pressure vessel, would be manufactured from aluminum sheet. The outer hull would be made of aluminum honeycomb with aluminum alloy plates for added strength. Aluminum frames with "I" and "Z" cross-sections would link the two hulls. An ablative heat shield (that is, one that chars and erodes to carry away heat) would cover the aluminum honeycomb, and low-density insulation would fill the space between the inner and outer hulls.

Cutaway view of the Janus spacecraft. Image credit: U.S.Patent Office
The other part of the Janus spacecraft was a 4000-pound delta-wing jet aircraft measuring 21 feet long, 13.3 feet across its wings, and 5.33 feet tall. It would include twin downward facing rudder fins and a belly-mounted air intake feeding a Continental 356-23 turbojet engine. The engine could be started at 18,000 feet of altitude using ambient air or at up to 45,000 feet with supplemental oxygen. Cruise speed at 30,000 feet was about Mach 0.6 (370 knots) and range with a full load of 77 gallons (500 pounds) of jet fuel was 200 nautical miles.

The flat top of the small jet would form the largest part of the top of the lifting body. The jet's underside would form the "ceiling" of the lifting body's 860-cubic-foot pressurized internal volume; that is, the plane's belly, including its air intake, would protrude into the main crew living and working space. Ceiling height, though variable, would measure no less than seven feet.

The jet would ride on three rod-like "pneumatic/explosive actuators" attached to the pod. Latches would link the actuators to holes in the plane's nose and on the underside of its wings. Other latches would anchor the jet's wing leading edges.

Spielberg and Cohen recognized that creating an air-tight seal between jet and pod would pose significant design challenges. They proposed an inflatable or "fluted" (grooved) gasket, presumably made of a rubberized fabric. They admitted that their seal system, though "feasible," was not yet "optimized."

Atop a booster on the launch pad, jet and lifting body would point their noses at the sky. Spielberg and Cohen envisioned that the flat aft surface of the pod would sit atop a launch vehicle adapter that would measure 10 feet in diameter where it linked to the pod. The bottom of the adapter would match the larger diameter of the launch vehicle upper stage.

Just before launch, the astronauts would pass through a hatch in the side of the adapter. Overhead they would see the flat aft surface of the pod, which would include a round hatchway. The hatchway would lead into a cylindrical airlock just large enough to hold one space-suited astronaut. A round hatch in the airlock would in turn lead into the pod. In the near-vacuum of low-Earth orbit, the airlock would permit astronauts to spacewalk without depressurizing the pod.

Forward-facing crew couches would be arranged single-file, one behind the other, in a line beneath the jet fuselage. This would place the astronauts one above the other on the launch pad.

The pod would contain the Janus spacecraft main control console. Intended for use in orbit, it would be mounted on the pod's aft interior wall next to the inner airlock hatch. This would place it out of reach of the reclining astronauts. Critically important controls would be mounted on couch arms.

The patent application said nothing about possible launch vehicles, but in their paper Spielberg and Cohen specified two candidates: Titan III (probably the Titan IIIC variant) and Saturn C-1 (otherwise known as Saturn I). The former could boost 28,000 pounds into the 140-nautical-mile orbit required to forestall orbital decay long enough to carry out a two-week Janus mission; the latter, 20,000 pounds. The total weight of the Janus spacecraft (crew, pod, and jet) was 15,660 pounds, so in theory it could transport 12,340 pounds of unspecified payload if launched on a Titan III and 4340 pounds if launched on a Saturn C-1.

It is worth noting that Janus included no docking mechanism, and that was it not designed to perform significant maneuvers in space (apart from a deorbit burn). This ran against the grain of NASA requirements in the first half of the 1960s, when both Gemini and Apollo were under development. Though it could carry a hefty payload, it could not deliver it anywhere. Presumably, this meant that its payload would always take the form of equipment that would remain inside the pod. It is conceivable, however, that small payloads could be tossed out its airlock and larger ones assembled outside by spacewalkers - Spielberg and Cohen did not, however, suggest these possibilities.

A successful mission would begin with launch from Cape Kennedy on Florida's east coast. The launch vehicle would ascend vertically, then roll toward the southeast on a course that would avoid Caribbean islands and South America. About 10 minutes after liftoff, Janus would reach its operational orbit and separate from the upper stage of its launch vehicle. The crew would then unstrap from their couches and begin work in the pod's large pressurized volume.

They would also work in the jet cockpit. The jet's glass canopy, which would stand higher than most of the Janus spacecraft's mostly flat top, would make the cockpit the prime spot for conducting Earth and astronomy observations.

Spielberg and Cohen proposed a novel method for entering and leaving the cockpit. The crew couches would each be mounted on a pair of rails, and the underside of the jet's fuselage would include automatic doors. Operating controls on the couch arms would cause the doors to open and the couch to ride the rails from pod to cockpit and vice versa. The TRW engineers explained that a single set of couches shared between the pod and the jet would save weight, though with the large Janus payload capability this would probably have been a minor concern.

The crew would breathe a 47% oxygen/53% nitrogen air mix at a pressure of 7.5 pounds per square inch. Water for crew needs would come from fuel cells, the primary task of which would be to generate 2.5 kilowatts of continuous electricity by combining liquid hydrogen and liquid oxygen. Fluid circulating in pipes in the pod walls would gather and carry waste heat from the pressurized volume and the fuel cells to a radiator mounted on the pod's aft surface.

For return to Earth, the astronauts would sit in their couches in the pod, turn the Janus spacecraft using small thrusters so that its aft end pointed in its direction of motion, and ignite its 1100-pound solid-propellant retrorocket. After burnout, the retrorocket casing would be cast off and Janus reoriented with its nose aimed forward. Descent toward 400,000-foot reentry altitude would last 14 minutes. At start of reentry, the Janus spacecraft would be moving at about 250 feet per second (fps).

Reentry would be a balancing act. The lifting-body pod would need trim flaps for stability and steering; however, four trim flaps attached in pairs to the bottom edge of its flat aft surface would tend to tip its nose down (that is, give it a negative angle of attack). This would permit hot reentry plasma to course over the pod's top surface, destroying the jet canopy. At the same time, the pod would be tail-heavy, raising its nose and making it aerodynamically unstable.

Spielberg and Cohen proposed a two-part solution: cautiously reshaping the pod's nose and packing its triangular nose volume with heavy subsystems (for example, the fuel cells and their reactants). The former would tend to level its angle of attack and the latter, they calculated, would shift its center of gravity forward to a point 54% of its length (about 11 feet) aft of the pod's nose, yielding a slightly "nose up" angle of attack. The pod's nose would thus bear the brunt of reentry heating, and no reentry plasma would reach the jet canopy.

The Janus spacecraft would reenter at a very shallow angle (just 2°). It would thus shed speed gradually in a low-density atmosphere, preventing maximum deceleration from exceeding 1.9 gravities. An automated attitude control system would operate the trim flaps and small thrusters to maintain stability as the pod descended.

During reentry, the outer hull, safe behind its heat shield, would maintain a temperature below 600° Fahrenheit (F). The inner hull would remain at 70° F throughout the mission. The hot outer hull would tend to expand. If the aluminum frames linking the inner and outer hulls were rigidly attached at both ends, differential expansion would tear them apart. To avoid this, Spielberg and Cohen proposed that the frames be attached to the outer hull by flexible connections and to the inner hull by rigid ones.

A little less than 12 minutes after reentry start, at an altitude of about 120,000 feet, the Janus spacecraft would slow to a velocity of about 50 fps. Deprived of lift, its angle of descent would increase in a little over a minute to about 55°.

At 50,000 feet of altitude, the Janus spacecraft would slow to subsonic speed and begin to lose stability. The mission commander would activate the motors that would raise the three couches into the jet cockpit. Beneath the astronauts' feet, the fuselage doors would close and seal. At 45,000 feet, the spacecraft would slow to Mach 0.9, and jet separation from the pod could occur.

Separation would begin with a command to fire explosive bolts. This would release the latches linking the jet to the pod so that the three rod-like pneumatic actuators could extend, pushing the jet away from the pod with a jolt. The pressure seal would be breached, exposing the pod's interior to the outside environment.

The commander would ignite the jet's engine and fly at a cruise altitude of 30,000 feet to a waiting airfield up to 200 nautical miles away. The jet would land on a nose wheel and skids on the ends of its rudder fins. The pod, meanwhile, would deploy parachutes from its aft surface and descend to a landing on its nose.

In the event of an abort on the launch pad or during first-stage operation, a pair of solid-propellant abort rocket motors mounted on the pod's aft surface outside the adapter linking it to the launch vehicle would ignite to boost the Janus spacecraft up and away. The motors would propel it to an altitude of 6600 feet in 19 seconds. If no first-stage abort took place, the abort motors would eject after second-stage ignition so that the launch vehicle would not need to carry their weight to orbit.

The deorbit rocket motor would play two possible abort roles: in an abort off the launch pad, it could be ignited after the twin abort rocket motors burned out to boost the Janus spacecraft higher and farther downrange, providing more time for successful jet separation; it would also become the primary abort rocket motor after the twin abort motors ejected.

An abort within 200 nautical miles of Cape Kennedy would see the commander separate the jet from the pod as during a normal descent, then fly back to the launch site. The jet could also remain attached to the pod throughout the abort, in which case the entire Janus spacecraft would descend nose down on parachutes to a landing or splashdown at 25 feet per second. Spielberg and Cohen included 1030 pounds of recovery gear in the Janus spacecraft mass budget.

Down-range aborts - for example, during second stage flight - would occur over open ocean, placing land - never mind suitable airports - outside the jet's 200-nautical-mile range. Spielberg and Cohen noted that the lifting body would during second-stage flight be high enough to use its trim flaps and steering thrusters to maneuver closer to land. This would, they judged, permit jet separation within 200 miles of airfields on Caribbean islands or in northeastern South America.

Here is the link to my staged reentry post based only on the Cohen, Schetzer, and Sellars patent of December 1966. In addition to a summary history of lifting body development in the United States, the post contains detailed labeled drawings from the patent application.


"Janus: A Manned Orbital Spacecraft with Staged Re-Entry," I. N. Spielberg and C. B. Cohen, The Journal of Spacecraft & Rockets, Volume 2, Number 4, July-August 1965, pp. 531-536

Patent No. 3,289,974, "Manned Spacecraft With Staged Re-Entry," C. Cohen, J. Schetzer, and J. Sellars, TRW, 6 December 1966

Related Links

X-15: Lessons for Reusable Winged Spaceflight (1966)

Where to Launch and Land the Space Shuttle? (1971-1972)

What if a Shuttle Orbiter Struck a Bird? (1988)

NASA Johnson Space Center's Shuttle II (1988)

24 October 2018

Preparing for Patreon

Apollo 7 launch, 11 October 1968. Image credit: NASA
It has taken me a while, but I now have worked out how I want to treat my Patreon patrons. By that, I mean what incentives to offer and how folks should expect to be charged.

I've learned that I can charge my patrons by new blog post. I like that idea, because I don't post on a regular schedule, and in the past year I've not posted often because of a new job, new home city, and new health problems. I'd hate to automatically charge people on a monthly basis and then miss posting in any given month.

In addition, I am working on two ebooks, publication date TBD. I like the idea of being my own publisher. I've published print works, so this will be something new for me. I expect I can earn more money this way than by publishing through a print publisher. I can also use access to the ebooks as an incentive.

I imagine it would go something like this - lowest-level patrons get the blog. More wealthy and/or generous patrons get a 25% markdown on the price of the ebooks. Even more wealthy and/or generous patrons get a 50% markdown. Insanely wealthy patrons get a 75% markdown. And the MegaPowerBall winner patrons get a 75% markdown, plus the second ebook for free!

I expect I'll also offer extras related to the ebooks. You know the drill: the more you contribute, the more extras you get. I'm not sure yet what the extras will be. I'd be happy to receive suggestions.

There'll be a Wall of Fame page. Not sure of the details yet, but it might go like this: lowest-level patron name is listed. Next up the scale, name with a link. Then name, image - avatar, picture, whatever - and link. Next up, the same but higher up the page. Then, for the top-level patrons, top of the page and perhaps some "advertising" text if they have a blog, podcast, or other project they want to promote. Of course, your image could be your advertising. No rule against that, but your placement would improve if you pledged more.

As for patron levels - my research indicates that most folks are more frugal than I am. By the same token, they pledge to more creators. I have to take into account the "per post" pledge structure, which I've noticed some folks don't understand. I'd hate for someone to think they were pledging $50 per month, then get a $150 charge if I post three posts in a month. I think that argues for lower pledge levels to avoid painful misunderstandings.

So, I think the maximum would be $20 per post, with lower levels of $15, $10, $5, and $1. I'd feel better about telling someone "You should've read the fine print" at those levels than at higher levels.

I seek a $2500 monthly income. At that level of income, I could live comfortably, freeing me to devote all my attention to the blog and ebooks, and add blog improvements (paid original art and posts based on research at costly archives being the first that leap to mind). That doesn't seem impossible, given the number of people who check out this blog. Most seem to be serious, intelligent people, which might imply that $5 per post would not break the bank.

If I posted twice per month, a $5 per pledge patron would get a $10 charge in that month. If I could do that for a year, they would pay me $120. If I could get just 20 people to post at that level, I would hit my goal.

That doesn't mean that $1 pledges would not be welcome. Change only that parameter in the example above, and they would pay in $2 in a month, or $24 in a year. I'd only need 105 people to pledge at $1 per post to reach my goal - and that's far fewer than visit the blog each day when I post frequently.

I invite discussion of these ideas, especially from prospective patrons and experienced Patreon creators. My plan is to start this at the beginning of 2019, which, being the start of the Apollo 11 50th anniversary year, seems to me to be an auspicious time to call on folks to support this blog.

12 September 2018

Keep My Memory Green: Skill Retention During Long-Duration Spaceflight (1968)

All piloted space missions end with Earth-atmosphere reentry. For short-duration missions - for example, an Apollo voyage to the Moon - the period of time between reentry training using simulators on Earth and actual reentry would be short enough that pilot skills retention would be unlikely to become a problem. For longer missions, years might separate simulator training on Earth from actual reentry, almost certainly leading to degradation of critical pilot skills. Image credit: NASA
Serious plans for astronaut space activities take into account human frailties. Long stays in the space environment on board Earth-orbiting space stations have revealed some: for example, loss of calcium in load-bearing bones in microgravity. Other frailties have been part of human experience for many millennia: for example, forgetfulness over time.

In July 1968, when J. R. Birkemeier, with Bellcomm, NASA's advance planning contractor, performed a preliminary assessment of astronaut skills retention during long space missions, the longest human spaceflight had lasted just 13 days, 18 hours, and 35 minutes. During the Gemini VII mission, launched on 4 December 1965, astronauts Frank Borman and James Lovell experienced no obvious degradation of skills as they orbited Earth 206 times. They splashed down just 11.9 kilometers off target in the Atlantic Ocean between Bermuda and the north coast of the Dominican Republic on 18 December 1965.

Astronauts James Lovell (left) and Frank Borman stand on the deck of the aircraft carrier U.S.S. Wasp after a safe splashdown. They orbited Earth for nearly 14 days in the cramped confines of the Gemini VII capsule to demonstrate that humans could survive in space long enough to reach and return from the Moon during the Apollo Program. Their record would not be broken until the Soyuz 9 flight in 1970, which lasted 17 days, 16 hours, and 58 minutes. Image credit: NASA
No Apollo mission was expected to last longer than Gemini VII, so Birkemeier looked beyond Apollo to possible longer-duration missions of the 1970s and 1980s. Bellcomm had since 1962 studied piloted lunar and planetary missions for the NASA Headquarters Office of Manned Space Flight. The studies were useful for Birkemeier's analysis because they included plausible long-duration mission timelines.

Birkemeier pointed to U.S. Navy regulations, which drew the line at three months for pilot skills retention. Navy rules specified that, in the interest of safety, a pilot should be allowed to land a jet on an aircraft carrier only if they had flown high-performance aircraft for five hours in the previous three months. He assumed that critical space mission events - for example, a piloted Mars landing - would all be at least as challenging as landing a jet on a carrier at sea.

The enormous distances between worlds and the limitations of the propulsion systems expected to exist in the 1970s and 1980s meant that, much more often than not, critical space mission events could not occur within three months of a training session on Earth. A typical Mars landing mission, for example, would see astronauts reach Mars about six months after launch from Earth. High-speed Earth-atmosphere reentry at the end of a Venus-Mars-Venus triple-flyby mission would occur 25 months after departure from Earth orbit.

Birkemeier also considered mission activities unlikely to affect safety, but which might determine whether a mission could be considered successful. Mars Surface Sample Return (MSSR) probe operations, for example, had become the centerpiece of piloted Mars flyby mission planning in 1966. The crew would prepare and release the robotic MSSR probe and other probes five months after Earth-orbit departure. The probes would capture into Mars orbit or enter the martian atmosphere a month after that, just before the piloted flyby spacecraft passed Mars.

After the MSSR probe soft-landed on Mars, the flyby crew would remotely examine its landing site via a television camera on the probe and direct operation of its sample collection devices. They would then pack samples into a capsule and initiate MSSR ascent stage launch.

The ascent stage would boost the sealed sample capsule toward the piloted flyby spacecraft. As their spacecraft sped past Mars, the crew would capture the capsule, transfer it to a sealed glove box, open it, and quickly (but carefully) examine the dirt and rocks inside for signs of living organisms - all while attending to other Mars flyby scientific and navigational tasks.

A Mars Surface Sample Return (MSSR) ascent stage (right) bearing a sample of martian dirt and rocks approaches a piloted Mars flyby spacecraft. Image credit: NASA
Birkemeier proposed methods of space mission "skills maintenance." He wrote that "crew members could preserve some degree of proficiency simply by reading instruction manuals, watching training films, studying the controls, and reviewing specific procedures."

More complex tasks - which tended also to be the ones most crucial to mission safety and success - "could not be maintained by bookwork alone," but neither could they be practiced by actual replication of maneuvers. The latter would, for one thing, expend valuable propellants. Birkemeier explained that "an aircraft pilot can make realistic practice landings on cloud banks," but that "no analogous opportunity [existed] for an astronaut wishing to practice Mars landing or an Earth entry while. . .in space."

The obvious solution would be to provide opportunities for inflight mission simulation. Birkemeier suggested that the actual spacecraft control panels could be designed to serve double-duty as simulators, especially if they were also designed to be periodically tested using actual control inputs. The control panels would be temporarily disconnected from the systems they were designed to control and tied to a computer that would simultaneously provide responses to crew actions and monitor control system health.

The Apollo Command Module (CM) simulator at the Manned Spacecraft Center in Houston, Texas in 1966. The CM hatch, with its round window, is visible at the top of the ladder. Light brown cabinets house (among other things) projection equipment that provides a realistic view through the CM windows. At the time Birkemeier wrote his report (July 1968), the simulator used 88,000 words of memory on three computers to simulate six-degree-of-freedom maneuvers in real time. Fifty thousand words on a single UNIVAC 1108 computer was sufficient to simulate three-degree-of-freedom maneuvers. Image credit: NASA
Birkemeier assumed that 1970s and 1980s computers would be at least an order of magnitude more capable than the computers of 1968, and that "simplifying assumptions" might be used to reduce memory requirements. He estimated that a program using 4000 words of memory on a computer with a solution rate of 25 cycles per second could adequately simulate an Apollo Command Module Earth-atmosphere reentry.

Such a simulation would not, however, be capable of generating "out the window" views. Birkemeier urged more study of whether visual cues would in fact be a requirement for adequate in-flight simulation.

Birkemeier estimated that extended Earth-orbital space station missions would need to devote only 4000 words of computer memory to simulations because the only critical task a station crew would need to simulate would be Earth-atmosphere reentry. Extended lunar surface missions would need 4000 words of memory to simulate liftoff from the lunar surface and 4000 words for Earth-atmosphere reentry.

Piloted Mars/Venus flyby missions, which would need to simulate automated probe operations and Earth-atmosphere reentry, would also use 8000 words of computer memory. Planetary landing mission simulations would be memory hogs: they might need as many as 20,000 words of memory.

Birkemeier concluded his report by proposing other ways that computer simulation could be used during long space missions. If a crewmember with critical skills died or became ill, for example, simulators could be used to train a replacement. Similarly, if a substantial change in planned procedures became necessary - for example, if the Apollo Command Module heat shield became damaged so that a new Earth-reentry profile became necessary - then the crew could practice the new procedures ahead of reentry.

Finally, behavioral scientists could monitor simulator performance to obtain information on crew state of health as the mission progressed. Birkemeier wrote that simulation monitoring could be used to assess astronaut psychomotor functions (for example, control of fine and gross physical movements) and cognitive processes (for example, problem solving).


The first part of the post title is a play on a line in Charles Dickens' Christmas ghost story "The Haunted Man and the Ghost's Bargain," published in 1848. 

"Inflight Maintenance of Crew Skills on Long Duration Manned Missions," J. R. Birkemeier, Bellcomm, July 1968

More Information

Astronaut Sally Ride's Mission to Mars (1987)

Starfish and Apollo (1962)

After EMPIRE: Using Apollo Technology to Explore Mars and Venus (1965)

Triple-Flyby: Venus-Mars-Venus Piloted Missions in the Late 1970s/Early 1980s (1967)

28 May 2018

Lunar Viking (1970)

NASA's lunar soft-landers: in the background, the Apollo 12 Lunar Module Intrepid; in the foreground with Apollo 12 Commander Charles Conrad, Surveyor 3. Image credit: NASA
In the 1960s, U.S. space assets included two spacecraft designed to soft-land on the Moon. These were automated three-legged Surveyor, of which seven were launched on Atlas-Centaur rockets between June 1966 and January 1968 (five Surveyors landed successfully), and the piloted four-legged Apollo Lunar Module (LM), which landed at six sites between July 1969 and December 1972.

Even as Surveyor 7 successfully soft-landed near the great ray crater Tycho, NASA, science advisory groups, Congress, and President Lyndon Baines Johnson considered plans for a project to soft-land spacecraft on Mars. Originally conceived in late 1967/early 1968 as "Titan Mars 1973," Project Viking, as it became known, received new-start funding in the Fiscal Year (FY) 1969 budget.

NASA's Langley Research Center (LaRC) managed Viking. LaRC, located in Hampton, Virginia, contracted with Martin Marietta in Denver, Colorado, to build two new-design Viking Landers. Meanwhile, the Jet Propulsion Laboratory (JPL) in Pasadena, California, began work on two Viking Orbiters based on its Mariner flyby spacecraft design first flown in 1962. The twin Viking spacecraft would each comprise a Lander and an Orbiter, and each Lander-Orbiter combination would leave Earth atop a Titan rocket with a Centaur upper stage.

NASA at first planned to launch the Vikings in July 1973, when an opportunity for a minimum-energy Earth-Mars transfer would occur. In January 1970, however, tight funding planned for FY 1971 forced a slip to the August-September 1975 minimum-energy Earth-Mars transfer opportunity.

For NASA's piloted space program, 1970 was eventful even though only a single mission took place. The mission, Apollo 13 (11-17 April 1970), was intended to build on the experience gained through the Apollo 11 (16-24 July 1969) and Apollo 12 (14-24 November 1969) landings. The Apollo 11 LM Eagle landed long, but the Apollo 12 LM Intrepid set down close by derelict Surveyor 3 on the Ocean of Storms, demonstrating that the LM could successfully reach a predetermined target.

Landing accuracy was important for planning geologic traverses, the first of which was to have taken place at Fra Mauro during Apollo 13. An explosion in the Service Module of the Apollo 13 Command and Service Module (CSM) Odyssey scrubbed the landing and put off the first lunar geologic traverse to Apollo 14 (31 January-9 February 1971), which also was directed to Fra Mauro.

The Apollo 13 accident and postponement of subsequent missions meant that much of the activity in NASA's piloted program in 1970 concerned planning and budgets. President Richard Nixon saw no cause for a large-scale Apollo-type goal in the 1970s; NASA Administrator Thomas Paine begged to differ. Nixon appointed the Space Task Group (STG) in February 1969 - less than a month after his inauguration - and made his Vice President, Spiro Agnew, its chair. Paine, a Washington neophyte, misjudged Agnew's importance in the Nixon White House, so believed that he had scored big when Agnew declared at the Apollo 11 launch that he believed NASA should put a man on Mars before the end of the 20th century.

Paine took Agnew's statement as an endorsement of the Integrated Program Plan (IPP), NASA's proposal for its future after Apollo. The IPP included a large Earth-orbital "Space Base," nuclear rockets, lunar orbital and surface bases, a piloted Mars landing mission, and Mars orbital and surface bases. At Paine's insistence, the STG's September 1969 report The Post-Apollo Space Program: Directions for the Future offered the White House only the IPP with three different timetables for carrying it out. Nixon's aides, more cognizant of their boss's thoughts on spaceflight, added an introduction outlining a future with no major goals and no target dates.

This NASA Marshall Space Flight Center illustration from 1970 displays Integrated Program Plan hardware elements planned to be operational in the 1990s. 
Paine largely ignored this clear message, instead focusing his efforts on making a permanent Earth-orbiting Space Station NASA's 1970s goal. In addition to a host of Earth-focused uses, the Station would permit astronauts to live and work in space for long periods. This would enable aerospace physicians to certify that humans could remain in space long enough to reach and return from Mars, a voyage that might last three years. A reusable piloted logistics resupply & crew rotation spacecraft - a Space Shuttle - would economically service the Station.

Paine expected that NASA would use a two-stage version of the Saturn V rocket to launch the core Station and other large IPP hardware elements. In January 1970, however, he found himself obliged to announce that Saturn V production would end with the fifteenth rocket in the series. Apollo missions through Apollo 19 would occur at six-month intervals, ending in 1974, and Apollo 20 would be canceled so that its Saturn V, the last of the original Apollo buy, could launch the Skylab Orbital Workshop. Skylab was the last remnant of President Johnson's post-Apollo piloted program, the Apollo Applications Program (AAP), which aimed to apply successful Apollo technology to new space goals; that is, to squeeze the U.S. investment in Apollo for all it was worth.

NASA advance planning developed a split personality in 1970. Some planners assumed that Saturn V rockets would be available indefinitely; others, that the Space Shuttle would launch all IPP hardware.

For example, even as Paine announced the end of Saturn V production, NASA piloted spaceflight planners studied a versatile reusable chemical-propellant Space Tug which could double as a Saturn V fourth stage. As early as 1980, a four-stage Saturn V would launch a Lunar Orbit Space Station (LOSS). The Saturn V S-IVB third stage would boost the LOSS/Space Tug toward the Moon and detach; the Space Tug would then correct the LOSS's course en route to the Moon and slow it so that the Moon's gravity could capture it into lunar orbit.

Subsequent Saturn V missions would build up a propellant farm and fleet of Space Tugs in lunar orbit. Astronauts in Space Tugs with crew cabins and landing legs would then descend from the LOSS to resume piloted lunar surface exploration and build a Lunar Surface Base (LSB).

Space Tug outfitted for piloted lunar landings. Image credit: NASA
In June 1970, five planners with Bellcomm, the NASA Headquarters planning contractor, completed a multi-part memorandum in which they bemoaned the "prolonged gap in the lunar program. . .of at least six years" that NASA's Space Tug/LOSS/LSB plans would create. They argued that the gap would threaten the multidisciplinary community of lunar scientists Apollo and its robotic precursors had created. The gap also meant that Apollo exploration would make discoveries that could not be followed up until at least 1980. Construction of the LSB could not proceed immediately after the LOSS was established; piloted Space Tug missions to check out prospective LSB sites would need to take place first.

The Bellcomm team proposed a novel method of filling the gap after Apollo 19 and hastening construction of the LSB. They sought to repurpose spacecraft designs expected to become available in 1975: namely, the robotic Orbiter and Lander of the Viking Mars exploration program.

At the time they wrote, neither the Viking Orbiter nor Viking Lander designs were final. The Lander, for example, would eventually carry three biology experiments and two scanning cameras, but the Bellcomm team assumed only two biology experiments and one camera. They saw this as an advantage, for it meant that the Mars Viking design was not so far along that it could not to some degree take into account anticipated Lunar Viking needs.

Lunar Viking Lander. Image credit: NASA/Russell Arasmith
The most obvious modification to the Mars Viking design for lunar missions would be replacement of the Lander aeroshell, heat shield, and parachutes with a solid-propellant landing rocket. The Lunar Viking Orbiter would expend liquid propellants to slow itself and the Lunar Viking Lander so that the Moon's gravity could capture the combination into lunar orbit, then would perform maneuvers to adjust its orbit ahead of Lander release. The Lander would then detach and, at the proper time for a landing at its target site, ignite the solid-propellant rocket.

After its propellant was expended, the motor casing would fall away. The Lunar Viking Lander would then complete descent and soft-landing using liquid-propellant vernier rockets.

The Bellcomm team outlined six basic Lunar Viking missions; some included several variants. For example, the first Lunar Viking mission, the Orbital Survey Mission, would have three variants. None would include a Lander and all would use only instruments planned for the Mars Viking Orbiter. All three would complete their main objectives a month after capture into lunar orbit.

The Orbital Survey Mission variant #1 would see a Viking Lunar Orbiter map the entire Moon in visual wavelengths at eight-meter resolution from 460-kilometer-high lunar polar orbit. Variant #2 would map the entire lunar surface in stereo at 12-meter resolution. For variant #3, a Lunar Viking Orbiter would operate in 100-kilometer orbit. This, the Bellcomm planners explained, would enable it to image potential Lunar Viking Lander and Space Tug landing sites at two-meter resolution.

The Mars Viking Orbiter was meant to transmit data at a rate of just 1000 bits per second over a distance ranging from tens of millions to hundreds of millions of kilometers (that is, from Mars to Earth). The Lunar Viking Orbiter, on the other hand, would transmit from only about 380,000 kilometers (that is, from the Moon), so in theory could transmit about 75,000 bits per second. The Viking Orbiter data recorder could, Bellcomm estimated, store up to 100 images. The Lunar Viking Orbiter would use these capabilities to image the Moon while it was out of radio contact over the Farside hemisphere and transmit the Farside images to Earth while it passed over the Nearside hemisphere.

A Titan III-C rocket would be sufficient to place the Lunar Viking Orbiter into a 100-kilometer circular lunar polar orbit with plenty of propellant remaining on board for additional maneuvers. An Atlas-Centaur SLV-3C rocket would suffice if after lunar-orbit capture no other maneuvers were planned.

The second type of Orbiter-only Lunar Viking mission would use a Titan III-C-launched Orbiter outfitted with a scientific instrument suite tailored specifically for lunar investigations. The Bellcomm team modeled their specialized Lunar Viking Orbiter science payload on instruments expected to be mounted in the Service Module of the advanced Apollo 16, Apollo 17, Apollo 18, and Apollo 19 CSMs.

The Bellcomm team's third Lunar Viking mission would establish twin Farside Geophysical Observatories. A Titan III-D/Centaur rocket - the rocket intended in 1970 to launch the 1975 Mars Vikings - could, they calculated, place a stripped-down Lunar Viking Orbiter with two Lunar Viking Landers attached into a 600-kilometer circular equatorial orbit. The twin Landers would then detach and land at two different Farside sites, out of direct radio contact with Earth. The Orbiter would serve as a communications satellite for retransmitting radio signals from the twin Landers. Landing site selection would be based on Orbital Survey Mission images.

The Farside Geophysical Observatory payload on the twin Landers would comprise instruments similar to those in the Apollo Lunar Scientific Experiment Package (ALSEP) the Apollo astronauts first deployed during Apollo 12. This would extend the exclusively Nearside Apollo seismic monitoring network to the Farside hemisphere.

Unfortunately, a Lunar Viking Orbiter in 600-kilometer equatorial orbit could receive signals from each Lunar Viking Lander only about 10% of the time. The Bellcomm planners noted that an Orbiter in a 5000-kilometer circular equatorial orbit could communicate with a Lander at Tsiolkovskii crater (23° south latitude) 26% of the time. Launching on the Titan III-D/Centaur would, they explained, enable the stripped-down Lunar Viking Orbiter to carry enough propellants to capture into 600-kilometer orbit and, after it released the Landers, maneuver to a 5000-kilometer communications orbit for the remainder of the mission.

Bellcomm's fourth Lunar Viking mission, the Farside Geochemical Mission, would see a Lunar Viking Orbiter/augmented Lunar Viking Lander combination leave Earth atop a Titan III-D/Centaur and capture into a 2000-kilometer circular equatorial orbit. The augmented Lunar Viking Lander would detach and ignite its chemical-propellant motors to place itself into a 2000-kilometer-by-100-kilometer elliptical orbit, then would ignite them again to reach a 100-kilometer circular equatorial orbit.

Finally, it would use its solid-propellant motor to deorbit and chemical-propellant verniers to soft-land at a geologically interesting Farside site. The Bellcomm team proposed that it transport to the surface a rover weighing up to 2000 pounds. Neither the augmented Lunar Viking Lander nor the rover was described. The Orbiter, again stripped down to serve mainly as a communications satellite, would remain in its initial 2000-kilometer orbit throughout the mission.

The Polar Mission, fifth on Bellcomm's list, would see the Lunar Viking Orbiter and Lander perform science together much as the Mars Viking Orbiter and Lander were meant to do. The Orbiter would again serve as a relay, but would also carry a suite of scientific instruments. The Lunar Viking Orbiter would capture into a 100-kilometer lunar polar orbit. As it passed over the Moon's poles, it would search permanently shadowed polar craters for ice deposits.

If ice were found, the Orbiter would release the Lander and maneuver to a higher orbit to improve communications. The Lander, meanwhile, would touch down in cold darkness and use an arm-mounted scoop or perhaps a drill to collect surface material for analysis in an on-board automated lab.

The sixth and most complex Lunar Viking mission, the Transient Event Mission, would aim to find and study Transient Lunar Phenomena (TLP). The Bellcomm team, which devoted an entire appendix of their report to TLP studies, noted that TLP had been recorded for decades at many sites on the Moon by telescopic observers. Appearing as bright spots, color changes, and hazes, TLP were generally interpreted as volcanic gas releases tied, perhaps, to the tides Earth raises in the solid crust of the Moon.

According to the Bellcomm planners, about half of all TLP recorded by 1970 had occurred in and around 40-kilometer-wide Aristarchus crater, located just west of Mare Imbrium in one of the most geologically diverse areas of the Moon. The Lunar Viking Orbiter would thus spend as much time as possible within sight of Aristarchus. This requirement would, along with the need for good image resolution, dictate Lunar Viking Orbiter altitude and maneuvers.

Aristarchus is the largest and brightest crater in this Apollo 15 image. Image credit: NASA
In June 1970, the Mars Viking Orbiter was expected to operate during a six-month Earth-Mars cruise and then for at least three months in Mars orbit. This meant that - in theory - the Lunar Viking Orbiter could be expected to seek TLP for nine months in lunar orbit. In practice, the spacecraft would pass in and out of night several times each day as it orbited the Moon from very near the beginning of its mission, placing added stress on its solar arrays, batteries, and temperature-sensitive systems.

The Bellcomm team expected that the Lunar Viking Orbiter might not last for nine months, but that it would last long enough to detect a pattern in the occurrence of TLP events. Based on this pattern, the Lunar Viking Lander would be directed to a site where it would be likely to witness a TLP event up close.

If the Lunar Viking Orbiter could not spot enough TLP events to enable scientists to detect a pattern, the Lander would be dispatched to Aristarchus. There it would seek evidence of past TLP and stand by in the hope that it might witness a TLP event.

The Bellcomm planners lamented an expected six-year gap in U.S. lunar landings. One wonders how they would have greeted the news that NASA would soft-land no spacecraft on the Moon after Apollo 17 in December 1972 - that after almost 50 years, Apollo 17 remains the last U.S. lunar soft-lander. Three automated soft-landers followed Apollo 17: the Soviet Union's Luna 21, which delivered the eight-wheeled Lunokhod 2 rover (1973); Luna 24, which collected and launched to Earth a small sample of lunar surface material (1976); and China's Chang'e 3 lander (2015), which delivered the small Yutu rover.

20 August 1975: Viking 1 launch atop a Titan III-E/Centaur rocket. Image credit: NASA
The Viking 1 and Viking 2 spacecraft exceeded all expectations. Viking 1 reached Mars orbit on 19 June 1976. The Viking 1 Lander separated from its Orbiter and soft-landed on 20 July 1976. Viking 2 reached Mars on 7 August 1976, and its Lander touched down on 3 September 1976. The Viking Landers performed multiple life-detection experiments (with equivocal results). Together, the four spacecraft of Viking 1 and Viking 2 transmitted to Earth more than 100,000 images.

The Viking 2 Orbiter suffered a propulsion system leak and was turned off on 25 July 1978; the Viking 2 Lander suffered battery failure and was switched off on 11 April 1980. The Viking 1 Orbiter depleted its attitude-control gas supply and was turned off on 17 August 1980. Though designed to operate on Mars for 90 martian days (Sols), the Viking 1 Lander transmitted from Mars until 13 November 1982 - a total of 2245 Sols. It might have lasted longer, but a faulty command caused it to break contact with Earth.

NASA and its contractors proposed many Viking-derived missions for the late 1970s and early 1980s. These included rover and dual-rover missions, sample-returners, and landers and rovers for the martian moons Phobos and Deimos. Their planning efforts in some ways resembled those of Apollo planners in AAP and its successor/remnant, the Skylab Program. The Earth-orbiting Skylab Orbital Workshop was staffed three times in 1973-1974. There was, however, no Viking Applications Program; despite Viking's success, its spacecraft designs saw no further application.

Mariner-based Viking Orbiter with attached Viking Lander capsule. Image credit: NASA

Schematic of Viking Lander as it would appear on Mars with all appendages deployed. Image credit: NASA

The Post-Apollo Space Program: Directions for the Future, Space Task Group Report to the President, September 1969

America's Next Decades in Space: A Report for the Space Task Group, NASA, September 1969

Internal Note: Integrated Space Program - 1970-1990, IN-PD-SA-69-4, T. Sharpe & G. von Tiesenhausen, Advanced Systems Analysis Office, Program Development, NASA Marshall Space Flight Center, 10 December 1969

"U. S. Space Pace Slowed Severely," W. Normyle, Aviation Week & Space Technology, 19 January 1970, p. 16

"Presentation Outline [Space Tug]," NASA Manned Spacecraft Center, 20 January 1970

"NASA Budget Hits 7-Year Low," W. Normyle, Aviation Week & Space Technology, 2 February 1970, pp. 16-18

"Viking Spacecraft for Lunar Exploration - Case 340," R. Kostoff, M. Liwshitz, S. Shapiro, W. Sill, and A. Sinclair, Bellcomm, Inc., 30 June 1970

On Mars: Exploration of the Red Planet, 1958-1978, NASA SP-4212, E. Ezell and L. Ezell, NASA, 1984, pp. 128-153, pp. 185-201, pp. 245-284

More Information

"Assuming That Everything Goes Perfectly Well In The Apollo Program. . ." (1967)

The Russians are Roving! The Russians are Roving! A 1970 JPL Plan for a 1979 Mars Rover

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

A Bridge from Skylab to Station/Shuttle: Interim Space Station Program (1971)

Prelude to Mars Sample Return: the Mars 1984 Mission (1977)

04 May 2018

Saturn-Apollo Applications: Combining Missions to Save Rockets, Spacecraft, and Money (1966)

This cutaway illustration of the Saturn V rocket configured for Apollo lunar missions needs some explanation. "Apollo Capsule" is a label almost never applied to the Apollo Command and Service Module (CSM) spacecraft. "LOX" is liquid oxygen. In the top two stages of the three-stage rocket, fuel tanks hold liquid hydrogen; the first stage fuel tank contains RP-1 aviation fuel similar to kerosene. Image credit: NASA
Long before NASA reached the Moon, the U.S. civilian space agency's managers and engineers began to look at ways of using Apollo lunar hardware in non-lunar and advanced lunar missions. In April 1963, for example, the Manned Spacecraft Center (MSC) in Houston awarded North American Aviation (NAA), prime contractor for the three-man Apollo Command and Service Module (CSM) spacecraft, a contract to study modifying the CSM to serve as a six-man crew transport and logistics resupply vehicle for a 24-man Earth-orbiting space station.

In early 1964, President Lyndon Baines Johnson asked NASA Administrator James Webb to plan a future space program based on Apollo hardware. The primary goal was to squeeze the Apollo investment for all it was worth. NASA began to study options for using Apollo hardware for new missions. Progress in 1964 was minimal in part because the space agency was oversubscribed. In addition to creating Apollo spacecraft, launchers, and infrastructure, NASA was preparing Project Gemini, a series of 10 piloted missions meant to teach American astronauts rendezvous and docking and spacewalk techniques required for Apollo Moon flights and to confirm that astronauts could live in space long enough (up to two weeks) to accomplish a lunar mission.

On 18 February 1965, George Mueller, NASA Associate Administrator for Manned Space Flight, told the U.S. House of Representatives Committee on Science and Astronautics that repurposing Apollo hardware would enable NASA "to perform a number of useful missions. . .in an earlier time-frame than might otherwise be expected" and at a fraction of the cost of developing wholly new spacecraft. He explained that NASA's program for applying Apollo hardware to new missions "would follow the basic Apollo manned lunar landing program and would represent an intermediate step between this important national goal and future manned space flight programs." At the time he testified, the first manned lunar landing attempt was slated for late 1967 or early 1968.

Six months later, in August 1965, Mueller established the Saturn-Apollo Applications (SAA) Office at NASA Headquarters. The new organization quickly began efforts to define the SAA Program's hardware requirements and mission manifest. At about the same time, SAA began to be referred to as the Apollo Applications Program (AAP), the name by which it is best known today.

In late January 1966, Mueller wrote to the directors of the three main NASA facilities dedicated to piloted spaceflight - MSC, the Marshall Space Flight Center (MSFC) in Huntsville, Alabama, and Kennedy Space Center (KSC), Florida - to sum up SAA's evolving objectives. He told Robert Gilruth (MSC), Wernher von Braun (MSFC), and Kurt Debus (KSC) that, in addition to readying NASA for its next Apollo-scale space goal - no one knew what that would be in early 1966, though a large Earth-orbiting space station stood near the top of the list - SAA should provide immediate benefits to the American public in areas as diverse as air pollution control, Earth-resources remote sensing, improved weather forecasting, materials science, and communications satellite repair.

Apollo spacecraft and rockets in 1966. The "Uprated Saturn I" rocket at lower right, used for Earth-orbital missions, would soon be renamed the Saturn IB. Image credit: NASA
By March 1966, the SAA Program Office had compiled a list of potential new missions for Apollo hardware. From MSC and NAA came proposals for CSM missions in low-Earth orbit (LEO), geosynchronous orbit, and lunar orbit. MSFC proposed that the spent S-IVB second stages of Saturn IB rockets be outfitted in LEO to serve double-duty as pressurized "workshops."

Apollo Lunar Module (LM) prime contractor Grumman suggested that LMs without legs or ascent engines might serve as Earth-orbital and lunar-orbital scientific instrument carriers and mini-laboratories. The company also proposed manned and unmanned LM variants - respectively the LM Taxi and the LM Shelter - for 14-day lunar surface stays. The LM Shelter design took several forms; most carried surface transportation systems (rovers or flyers).

All of these spacecraft would reach space atop Apollo Saturn IB and Saturn V rockets, some of which might be uprated for increased payload capacity. In its early SAA planning, NASA referred to missions by their launch vehicle designations. The second, third, and fourth Saturn V-launched SAA missions were thus called AS-511, AS-512, and AS-513 because they would use the 11th, 12th, and 13th of 15 Saturn V rockets purchased for Apollo. SAA planners assumed that, the moment Apollo achieved its goal of a man on the Moon, all remaining Apollo hardware would be released to the SAA Program.

The image above shows an Apollo Command and Service Module (CSM) spacecraft docked with a proposed Lunar Module (LM) variant meant to serve as a telescope mount for an SAA Workshop in Earth orbit. The AS-511 LM Lab would have shared many features with this design. Image credit: Grumman/NASA
The SAA Program Office envisioned AS-511 as a CSM-LM Lab mission that would map the Moon from lunar polar orbit. Its three-man crew would operate mapping cameras and sensors mounted on the LM Lab as the Moon revolved beneath their spacecraft, then would cast off the LM Lab and ignite their CSM's single Service Propulsion System (SPS) main engine to leave lunar orbit and return to Earth.

AS-512 would see a three-man CSM deliver an uncrewed LM Shelter to near-equatorial lunar orbit. The LM Shelter would undock and descend automatically to a preselected landing site. The three astronauts would then return to Earth.

AS-513, the first SAA piloted lunar landing mission, would launch less than three months after AS-512. Two astronauts would land near the LM Shelter in an LM Taxi while a third astronaut remained in lunar orbit on board an Extended Capability CSM (XCSM) with an independent space endurance of 45 days. The surface astronauts would place their LM Taxi in "hibernation" and use the LM Shelter as their base of operations for 14 days of exploration. A lunar day-night period lasts about 28 days at most sites, so if they landed at local dawn they would leave the lunar surface at local dusk.

The SAA Program Office solicited comment on its plans from Bellcomm, NASA Headquarters' Washington, DC-based Apollo planning contractor. On 4 April 1966, Bellcomm engineer P. W. Conrad (not to be confused with astronaut Charles "Pete" Conrad) wrote a brief memorandum in which he proposed that the AS-511 and AS-512 missions be merged.

Conrad wrote that AS-511 did not need an LM Lab: its CSM could carry the cameras, film, sensors, and magnetic tape it would need for lunar-orbital mapping. He noted also that, in the SAA Program plan, the AS-512 CSM would be a mere "escort" for the LM Shelter, leaving its crew with relatively few meaningful duties. A mission in which a CSM bearing mapping instrumentation carried the LM Shelter to the Moon would keep its crew productively occupied, Conrad argued, and would free up a Saturn V, a CSM, and an LM Lab for other SAA missions.

He examined two possible profiles for the combined mission. In the first, which Conrad called "direct descent," the CSM would release the unmanned LM Shelter immediately following the last SPS course-correction burn en route to the Moon. The LM Shelter would fall toward the Moon's nearside without entering orbit. Fifty thousand feet above its target landing area, it would automatically ignite its Descent Propulsion System (DPS) engine to decelerate, hover until it found a safe spot, and land.

The piloted CSM, meanwhile, would pass over one of the lunar poles and fire its SPS behind the Moon to perform Lunar Orbit Insertion (LOI); that is, it would slow down so that the Moon's gravity could capture it into polar mapping orbit.

As the CSM orbited, the Moon would revolve beneath it. If it were a Block II CSM with 14-day endurance, it would orbit the Moon for from five to eight days. After about seven days, the CSM would pass over half the Moon's surface and map about one quarter in daylight.

If it were an XCSM, it would orbit for about 28 days. After 14 days, it would pass over the entire lunar surface and map half in daylight. At the end of 28 days, it would pass over the entire lunar surface twice and map the entire surface in daylight. At the planned end of its time in lunar polar orbit - or sooner, if some fault developed that required an early Earth return - the XCSM would ignite its SPS behind the Moon to depart lunar polar orbit for Earth.

Conrad's second combined mission profile would see the LM Shelter remain docked to the CSM until some time after LOI. The CSM would ignite its SPS to slow itself and the LM Shelter so that the Moon's gravity could capture the docked spacecraft into polar orbit, then the crew would turn CSM-mounted cameras and sensors toward the moon.

As the CSM and LM Shelter orbited over the lunar poles, the Moon would revolve beneath them, so that within a few days of LOI the LM Shelter's nearside target landing site would move into position for descent and landing. The LM Shelter would then undock from the CSM and automatically ignite its DPS to begin descent over the Moon's farside hemisphere about 180° of longitude from its landing site. It would fire the DPS again close to the landing site to carry out powered descent, hover, and landing. The CSM astronauts, meanwhile, would continue their lunar-orbital mapping mission.

Conrad acknowledged that both scenarios had their advantages and disadvantages. Direct descent would require that the LM Shelter carry extra landing propellants, which might limit the mass of exploration equipment and life support consumables it could place on the Moon. This might in turn limit the scope of the two-week exploration it was meant to support. In addition, the LM Shelter's DPS would not be available as an SPS backup or supplement if an abort were declared before LOI or in lunar orbit.

On the plus side, relieving the CSM of the LM Shelter's mass ahead of LOI would reduce the quantity of propellants the SPS would need to expend to accomplish LOI. The mass freed up by reducing the CSM's propellant load could be applied to additional CSM cameras, film, sensors, magnetic tape, and life support consumables.

Retaining the LM Shelter until after LOI would maximize its payload mass, but would also require that the CSM carry more LOI propellants. This might lead to a reduction in the mass that could be devoted to cameras, film, sensors, tape, and life support consumables on board the CSM. On the other hand, the LM Shelter DPS would remain available as a backup or supplement to the SPS at least through LOI and, in almost all cases, for several days thereafter.

The SAA Program evolved rapidly. Conrad's proposal appears, however, not to have exerted much influence on SAA planners.

More consequential by far was the AS-204/Apollo 1 fire (27 January 1967), which killed astronauts Gus Grissom, Ed White, and Roger Chaffee. The fire, which revealed fundamental flaws in Apollo Program quality-control and contractor oversight, undermined support in Congress for NASA and, along with LM development delays, put off the first piloted lunar landing until July 1969. All six piloted Moon landings took place within the Apollo Program, and neither an Apollo lunar polar orbit mission nor a surface stay longer than about three days was accomplished.

The Saturn V rocket designated AS-511 in Conrad's memo launched the Apollo 16 lunar landing mission in April 1972. By then, NASA had changed its designation to SA-511. The SA-512 Saturn V launched Apollo 17, the final lunar landing mission, in December 1972, and SA-513 launched the Earth-orbital Skylab Orbital Workshop, the sole surviving remnant of what had been the SAA Program, in May 1973.

A lunar polar orbiter would have to wait until 1994, when the Ballistic Missile Defense Organization launched the 424-kilogram Clementine spacecraft (25 January 1994). The U.S. Department of Defense spacecraft followed a circuitous route to the Moon, at last arriving in mapping orbit on 19 February 1994. Though it accomplished a science mission, Clementine was conceived as a test of sensors and other technologies that would be used to detect and intercept nuclear-tipped missiles launched against the United States.

In an experiment using Earth-based radar, Clementine found the first indications of hydrogen concentrations in permanently shadowed craters near the Moon's poles. These were widely interpreted as signs of water ice, though the quantity of ice and its exact location could not be reliably determined. Clementine mapped the Moon until 3 May 1994, when it left lunar polar orbit bound for the near-Earth asteroid 1620 Geographos. A malfunction on 7 May 1994 caused Clementine to expend its propellant, however, scrubbing the asteroid flyby.

Japan's SELENE/Kaguya lunar polar orbiter with one of its two sub-satellites (center right). The spacecraft orbited the Moon from 3 October 2007 through 10 June 2009. Image credit: JAXA
NASA had sought to launch a robotic lunar polar orbiter since the 1960s. Not until 7 January 1998, however, did the Lunar Prospector mission begin. Lunar Prospector reached lunar polar orbit on 11 January 1998 and mapped the Moon until it was intentionally deorbited on 31 January 1999. The spacecraft crashed near the Moon's south pole, where it had detected more signs of water ice in permanently shadowed craters.

Since Lunar Prospector, the United States, Europe, Japan, China, and India have all launched automated spacecraft into lunar polar orbit. As of May 2018, however, only one (NASA's Lunar Reconnaissance Orbiter, launched 18 June 2009) still operates. New lunar polar orbiters are, however, in the planning and development stages: for example, the Republic of Korea (South Korea) plans to launch the Korean Pathfinder Lunar Orbiter in 2020.


"Combining Lunar Polar Orbit Mission with an Unmanned Landing, Case 218," P. W. Conrad, Bellcomm, Inc., 4 April 1966

Living and Working in Space: A History of Skylab, NASA SP-4298, W. David Compton and Charles Benson, NASA, 1983

Korea Aerospace Research Institute: Lunar Exploration (accessed 5 May 2018)

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