NASA Glenn Research Center's 2001 Plan to Land Humans on Mars Three Years Ago

August 2014. Image credit: NASA.

In October 2001, at the 52nd International Astronautical Congress in the European aerospace center of Toulouse, France, nuclear propulsion engineers at NASA's Glenn Research Center (GRC) in Cleveland, Ohio, led by Stanley K. Borowski, Advanced Concepts Manager in GRC's Space Transportation Project Office, described a variant of NASA's 1998 Mars Design Reference Mission (DRM) based on Bimodal Nuclear-Thermal Rocket (BNTR) propulsion. The BNTR DRM concept, first described publicly in July 1998, evolved from nuclear-thermal rocket mission designs Borowski and his colleagues had developed during President George H. W. Bush's abortive Space Exploration Initiative (SEI), which got its start with a July 1989 presidential speech commemorating the 20th anniversary of Apollo 11, the first piloted moon landing mission.

This post contains more than its share of significant acronyms. As an aid to the reader, these are grouped alphabetically and defined at the bottom of the post, just ahead of the list of sources.

NASA's first Mars DRM, designated DRM 1.0 in 1997, was developed by a NASA-wide team during the 1992-1993 period. It was based on Martin Marietta's 1990 Mars Direct mission plan. SEI's demise temporarily halted NASA Mars DRM work in 1994.

The civilian space agency resumed its Mars DRM studies after the announcement in August 1996 of the discovery of possible microfossils in martian meteorite ALH 84001. This enabled NASA planners to release their baseline chemical-propulsion DRM 3.0 in 1998. There was no official DRM 2.0, though a "scrubbed" (that is, mass-reduced) version of DRM 1.0 bears that designation in at least one NASA document.

Shortly thereafter, NASA's Johnson Space Center (JSC) in Houston, Texas, which led the DRM study effort, was diverted from DRM work by the in-house COMBO lander study (more on this below). Left largely to its own devices, NASA GRC developed a pair of DRM 3.0 variants: a solar-electric propulsion (SEP) DRM 3.0 and the BNTR DRM 3.0 discussed here.

In BNTR DRM 3.0, two unpiloted spacecraft would leave Earth for Mars during the 2011 low-energy Mars-Earth transfer opportunity, and a third, bearing the crew, would depart for Mars during the corresponding opportunity in 2014. Components for the three spacecraft would reach Earth orbit on six Shuttle-Derived Heavy-Lift Vehicles (SDHLVs), each capable of launching 80 tons into 220-mile-high assembly orbit, and in the payload bay of a winged, reusable Space Shuttle Orbiter, which would also deliver the Mars crew.

The SDHLV, often designated "Magnum," was a NASA Marshall Space Flight Center conceptual design. The Magnum booster would burn liquid hydrogen (LH2)/liquid oxygen (LOX) chemical propellants in its core stages and solid propellant in its side-mounted boosters. Magnum drew upon existing Space Shuttle hardware: its core stages were derived from the Space Shuttle External Tank and its twin solid-propellant rocket boosters were based on the Shuttle's twin Solid-Rocket Boosters.

The mighty Magnum was the conceptual ancestor of the equally conceptual Ares V and the Space Launch System, now under development. Image credit: NASA.

SDHLV 1 would launch BNTR stage 1 with 47 tons of LH2 propellant on board. Each BNTR DRM mission would need three 28-meter-long, 7.4-meter-diameter BNTR stages. The BNTR stages would each include three 15,000-pound-thrust BNTR engines developed as part of a joint U.S./Russian research project in 1992-1993.

SDHLV 2 would boost an unpiloted 62.2-ton cargo lander into assembly orbit. The cargo lander would include a bullet-shaped Mars aerobrake and entry heat shield (this would double as the cargo lander's Earth launch shroud), parachutes for landing, a descent stage, a 25.8-ton Mars surface payload including an in-situ resource utilization (ISRU) propellant factory, four tons of "seed" LH2 to begin the process of manufacturing propellants on Mars, and a partly fueled Mars Ascent Vehicle (MAV) made up of a conical Earth Crew Return Vehicle (ECRV) capsule and an ascent stage. The cargo and habitat lander engines would burn liquid methane fuel and LOX.

SDHLV launch 3, identical to SDHLV launch 1, would place into assembly orbit BNTR stage 2 containing 46 tons of LH2 propellant. SDHLV launch 4 would place the unpiloted 60.5-ton habitat lander into assembly orbit. The habitat lander would include a Mars aerobrake & entry shield/launch shroud identical to that of the cargo lander, parachutes, a descent stage, and a 32.7-ton payload including the crew's Mars surface living quarters.

The BNTR stage forward section would include chemical thrusters. These would provide maneuvering capability so that the stages could dock with the habitat and cargo landers in assembly orbit. During flight to Mars, the thrusters would provide each stage/lander combination with attitude control.

2011: the unmanned BNTR 1 stage/cargo lander and BNTR 2 stage/habitat lander spacecraft orbit the Earth prior to departure for Mars. Image credit: NASA.

The BNTR 1/cargo lander combination would have a mass of 133.7 tons, while the BNTR 2/habitat lander combination would have a mass of 131 tons. Both combinations would measure 57.5 meters long. As the 2011 launch window for Mars opened, the BNTR stages would fire their engines to depart assembly orbit for Mars.

Each BNTR engine would include a nuclear reactor. When moderator elements were removed from its nuclear fuel elements, the reactor would heat up. To cool the reactor so that it would not melt, turbopumps would drive LH2 propellant through it. The reactor would transfer heat to the propellant, which would become an expanding very hot gas and vent through an LH2-cooled nozzle. This would propel the spacecraft through space.

Following completion of Earth-orbit departure, the BNTR engine reactors would switch to electricity-generation mode. In this mode, they would operate at a lower temperature than in propulsion mode, but would still be capable of heating a working fluid that would drive three turbine generators. Together the generators would make 50 kilowatts of electricity. Fifteen kilowatts would power a refrigeration system in the BNTR stage that would prevent the LH2 it contained from boiling and escaping.

Much like the LH2 propellant in BNTR propulsion mode, the working fluid would cool the reactor; unlike the LH2, however, it would not be vented into space. After leaving the turbine generators, it would pass through a labyrinth of tubes in radiators mounted on the BNTR stage to discard leftover heat, then would cycle through the reactors again. The cycle would repeat continuously throughout the journey to Mars.

2012: Cargo lander/Mars Ascent Vehicle Landing. Image credit: NASA.

As Mars loomed large ahead, the turbine generators would charge the lander batteries. The BNTR stages would then separate and fire their engines to miss Mars and enter a safe disposal orbit around the Sun. The landers, meanwhile, would aerobrake in the martian upper atmosphere. The habitat lander would capture into Mars orbit and extend twin solar arrays to generate electricity. The cargo lander would capture into orbit, then fire six engines to deorbit and enter the atmosphere a second time.

After casting off its heat shield, it would deploy three parachutes. The engines would fire again, then landing legs would deploy just before touchdown. The GRC engineers opted for a horizontal landing configuration; this would, they explained, prevent tipping and provide the astronauts with easy access to the lander's cargo.

As illustrated in the cargo lander image above and the MAV launch image below, the four MAV engines would serve double-duty as cargo lander engines. In addition to saving mass by eliminating redundant engines, this would test-fire the engines before the crew used them as MAV ascent engines.

2012: Automated propellant manufacture for MAV ascent begins. Image credit: NASA.

The cargo lander would touch down on Mars with virtually empty tanks. After touchdown, a teleoperated cart bearing a nuclear power source would lower to the ground and trundle away trailing a power cable. Controllers on Earth would attempt to position it so that the radiation it emitted would not harm the astronauts (for example, behind a sand dune or boulder pile). The reactor's first job would be to power the lander's ISRU propellant plant, which over several months would react the seed hydrogen brought from Earth with martian atmospheric carbon dioxide in the presence of a catalyst to produce 39.5 tons of liquid methane fuel and LOX oxidizer for the MAV ascent engines.

SDHLV launch 5, identical to SDHLV launches 1 and 3, would mark the start of launches for the 2014 Earth-Mars transfer opportunity. It would place BNTR stage 3 into assembly orbit with about 48 tons of LH2 on board. Because it would propel a piloted spacecraft, its BNTR engines would require a new design feature: each would include a 3.24-ton shield to protect the crew from the radiation it produced while in operation. The shields each would create a conical radiation "shadow"; the radiation shadows would overlap to create a safe zone in which the crew would remain while they were inside or close to their spacecraft.

2013: the BNTR 3 stage and the first Crew Transfer Vehicle components dock automatically in Earth orbit. Image credit: NASA.

Thirty days after SDHLV launch 5, SDHLV launch 6 would place into assembly orbit a 5.1-ton spare Earth Crew Return Vehicle (ECRV) attached to the front of an 11.6-ton truss. A 17-meter-long tank with 43 tons of LH2 and a two-meter-long drum-shaped logistics module containing 6.9 tons of contingency supplies would nest along the truss's length. BNTR stage 3 and the truss assembly would rendezvous and dock, then propellant lines would automatically link the truss tank to BNTR stage 3.

A Shuttle Orbiter carrying the Mars crew and a 20.5-ton deflated Transhab module would rendezvous with the BNTR stage 3/truss combination one week before the crew's planned departure for Mars. Following rendezvous, the spare ECRV would undock from the truss and fly automatically to a docking port in the Space Shuttle payload bay. Astronauts would then use the Orbiter's robot arm to hoist the Transhab from the payload bay and dock it to the front of the truss in the spare ECRV's place.

2014: Crew and a deflated Transhab arrive on board a Space Shuttle Orbiter to complete Crew Transfer Vehicle assembly. Image credit: NASA.

The Mars astronauts would enter the spare ECRV and pilot it to a docking at a port on the Transhab's front, then enter the cylindrical Transhab's solid core and inflate its fabric-walled outer volume. The inflated Transhab would measure 9.4 meters in diameter. Unstowing floor panels and furnishings from the core and installing them in the inflated volume would complete assembly. Transhab, truss, and BNTR stage 3 would make up the 64.2-meter-long, 166.4-ton Crew Transfer Vehicle (CTV).

The CTV's truss-mounted tank and BNTR stage 3 would hold 90.8 tons of LH2 at the start of CTV Earth-orbit departure on 21 January 2014. The truss tank would provide 70% of the propellant needed for departure. In the most demanding departure scenario, the BNTR engines would fire twice for 22.7 minutes each time to push the CTV out of Earth orbit toward Mars.

2014: Crew Transfer Vehicle departs Earth orbit. Image credit: NASA.

Transhab cutaway (weightless design). Floor and ceiling would be reversed in the NASA Glenn artificial-gravity design. "Down" would thus be toward the top of this image, where the airlock and Earth Crew Return Vehicle capsule would be located. Image credit: NASA.

Following Earth-orbit departure, the crew would jettison the empty truss tank and use small chemical-propellant thrusters to start the CTV rotating end over end at a rate of 3.7 rotations per minute. This would create acceleration equal to one Mars gravity (38% of Earth gravity) in the Transhab module. Artificial gravity was a late addition to BNTR DRM 3.0; it made its first appearance in a June 1999 paper, not in the original July 1998 paper describing BNTR DRM 3.0.

In artificial-gravity mode, "down" would be toward the spare ECRV on the CTV's nose; this would make the Transhab's forward half its lower deck. Halfway to Mars, about 105 days out from Earth, the astronauts would stop rotation and perform a course-correction burn using the attitude-control thrusters. They would then resume rotation for the remainder of the trans-Mars trip.

The CTV would arrive in Mars orbit on 19 August 2014. The crew would halt rotation, then three BNTR engines would fire for 12.3 minutes to slow the spacecraft for Mars orbit capture. In its loosely bound elliptical Mars orbit, the spacecraft would circle the planet once per 24.6-hour martian day.

2014: Crew Transfer Vehicle arrival in Mars orbit. Image credit: NASA.

The crew would pilot the CTV to rendezvous with the habitat lander waiting in Mars orbit, taking care to place it in the CTV's radiation shadow. If the cargo lander on the surface or the habitat lander in Mars orbit malfunctioned while awaiting the crew's arrival, then the crew would remain in the CTV in Mars orbit until Mars and Earth aligned for the flight home (a wait time of 502 days). They would survive by drawing upon contingency supplies in the drum-shaped logistics module attached to the truss.

If the orbiting habitat lander and landed cargo lander checked out as healthy, however, then the crew would fly the spare ECRV to a docking port on the habitat lander's side. After discarding the spare ECRV and the habitat solar arrays, they would fire the habitat lander's engines, enter the martian atmosphere, and land near the cargo lander.

The habitat lander's horizontal configuration would provide the astronauts with ready access to the martian surface. After the historic first footsteps on Mars, the astronauts would inflate a Transhab-type habitat attached to the side of the habitat lander, run a cable from the habitat lander to the nuclear power source cart, unload at least one unpressurized crew rover, and commence a program of Mars surface exploration that would, if all went as planned, last for nearly 17 months.

In case of hardware failure or other emergency, the crew could retreat to the MAV and return early to the orbiting CTV. They would, however, have to wait in Mars orbit until Mars and Earth aligned to permit a minimum-energy Mars-Earth transfer (that is, until the originally planned end of their stay at Mars).

2014-2015: The first Mars campsite. In the foreground is the habitat lander with inflated Transhab surface habitat; in the background, the nuclear power source cart and the cargo lander with Mars Ascent Vehicle. Image credit: NASA.

2014-2015: Exploring Mars with a crew rover and two teleoperated robot rovers, one small and one large. Image credit: NASA.

2014-2015: Drilling for water, geologic history, and, just possibly, life. Image credit: NASA.

2015: Mars Ascent Vehicle liftoff. Image credit: NASA.

Near the end of the surface mission, the unmanned CTV would briefly fire its nuclear engines to trim its orbit for the crew's return. The MAV bearing the crew and about 90 kilograms of Mars samples would then lift off. Taking care to remain within the the radiation shadows of the CTV's BNTR engines, it would dock at the front of the Transhab, then the astronauts would transfer to the CTV. They would cast off the spent MAV ascent stage, but would retain the MAV ECRV for Earth atmosphere reentry.

The CTV would leave Mars orbit on 3 January 2016. Prior to Mars orbit departure, the astronauts would abandon the contingency supply module on the truss to reduce their spacecraft's mass so that the propellant remaining in BNTR stage 3 would be sufficient to launch them home to Earth. They would then fire the BNTR engines for 2.9 minutes to change the CTV's orbital plane, then again for 5.2 minutes to escape Mars and place themselves on course for Earth.

Soon after completion of the second burn, the crew would fire attitude-control thrusters to spin the CTV end-over-end to create acceleration equal to one Mars gravity in the Transhab. About halfway home they would stop rotation, perform a course correction, then resume rotation. Flight home to Earth would last 190 days.

2016: Return to the Earth-Moon system. Image credit: NASA.

Near Earth, the crew would stop CTV rotation for the final time, enter the MAV ECRV with their Mars samples, and undock from the CTV, again taking care to remain in the BNTR engine radiation shadows as they moved away. The abandoned CTV would fly past Earth and enter solar orbit. The MAV ECRV, meanwhile, would re-enter Earth's atmosphere on 11 July 2016.

The authors compared their Mars plan with the baseline chemical-propulsion DRM 3.0 and with the NASA GRC SEP DRM 3.0. They found that their plan would need eight vehicle elements, of which four would have designs unique to BNTR DRM 3.0. The baseline DRM 3.0, by contrast, would need 14 vehicle elements, 10 of which would be unique, and SEP DRM 3.0 would need 13.5 vehicle elements, 9.5 of which would be unique. BNTR DRM 3.0 would require that 431 tons of hardware and propellants be placed into Earth orbit; the baseline DRM 3.0 would need 657 tons and SEP DRM 3.0, 478 tons. Borowski and his colleagues argued that fewer vehicle designs and reduced mass would mean reduced cost and mission complexity.

The BNTR DRM 3.0 variant became the basis for DRM 4.0, which was developed during NASA-wide studies in 2001-2002 (though NASA documents occasionally back-date DRM 4.0 to 1998, when BNTR DRM 3.0 was first proposed). DRM 4.0 differed from BNTR DRM 3.0 mainly in that it adopted a "Dual Lander" design concept developed as part of JSC's 1998-1999 COMBO lander study. COMBO was the brainchild of William Schneider, NASA JSC Engineering Directorate boss.

Dual Lander concept. The lander in the foreground is the habitat; the background lander is the Mars Descent/Ascent Vehicle. Image credit: NASA.

The Dual Lander concept grew from COMBO's main design guideline, which was to develop a low-mass "Apollo-style" piloted Mars landing mission. A major change from past Mars DRMs was no reliance on ISRU. As in BNTR DRM 3.0, two cargo missions would leave Earth one minimum-energy Earth-Mars transfer opportunity ahead of the crew; in DRM 4.0, however, these would take the form of a Mars lander that would also include an ascent vehicle for returning the crew to the CTV in Mars orbit and a cargo lander with an inflatable donut-shaped habitat. The former could by itself support a short-stay (~30-day) Mars surface mission; the latter would enable a Mars surface stay of more than 400 days.

In 2008, a decade after BNTR DRM 3.0 first was made public, NASA released a version of DRM 4.0 modified to use planned Constellation Program hardware (for example, the Ares V heavy-lift rocket in place of the Magnum and the Orion Multi-Purpose Crew Vehicle in place of the ECRVs). The space agency dubbed the new DRM Design Reference Architecture (DRA) 5.0.

The DRA 5.0 Mars plan acknowledged that, largely as a result of the 1 February 2003 Columbia accident, the Space Shuttle would be retired after the remaining Orbiters — Endeavour, Discovery, and Atlantis — completed their part of the task of building the International Space Station. The last Space Shuttle mission, STS-135, took place in July 2011.

DRA 5.0 also saw the return of ISRU. A Descent/Ascent Vehicle (DAV) and a Surface Habitat (SHAB) would capture into Mars orbit in the first minimum-energy Earth-Mars transfer opportunity. The DAV would descend, land, and begin making propellants for its ascent stage. The SHAB would loiter in orbit awaiting arrival of a crew on board a Mars Transfer Vehicle (MTV) launched from Earth during the second Earth-Mars transfer opportunity of the mission. The crew would transfer to the SHAB in an Orion/service module and land on Mars near the DAV. After a stay on Mars lasting more than 400 days, they would lift off in the DAV ascent stage, dock with the waiting MTV, and return to Earth.

Though DRA 5.0 exerts influence on current NASA planning, the precise form a piloted Mars mission will eventually take remains unclear at this writing. NASA increasingly has shifted its attention toward finding low-cost stepping stones that could lead to a piloted Mars landing in 2033. A crew-tended — that is, not permanently staffed — Deep Space Gateway space station in cislunar space, for example, could be established by 2026 through a series of Orion missions launched using the Space Launch System (SLS) heavy-lift rocket (SLS replaced Ares V in 2010). Other possible interim steps toward Mars include an SLS-launched robotic Mars sample return mission in the mid-2020s and a piloted mission to Mars orbit in 2030 using a Deep Space Transport based partly on Deep Space Gateway hardware.

Acronyms

BNTR = Bimodal Nuclear Thermal Rocket
CTV = Crew Transfer Vehicle
DAV = Descent/Ascent Vehicle
DRA = Design Reference Architecture
DRM = Design Reference Mission
ECRV = Earth Crew Return Vehicle
GRC = Glenn Research Center
ISRU = In-Situ Resource Utilization
JSC = Johnson Space Center
LH2 = liquid hydrogen
LOX = liquid oxygen
MAV = Mars Ascent Vehicle
MTV = Mars Transfer Vehicle
SDHLV = Shuttle-Derived Heavy-Lift Vehicle
SEI = Space Exploration Initiative
SEP = Solar-Electric Propulsion
SHAB = Surface Habitat
SLS = Space Launch System

Sources

"Bimodal Nuclear Thermal Rocket (NTR) Propulsion for Power-Rich, Artificial Gravity Human Exploration Missions to Mars," IAA-01-IAA.13.3.05, Stanley K. Borowski, Leonard A. Dudzinski, and Melissa L. McGuire; paper presented at the 52nd International Astronautical Congress in Toulouse, France, 1-5 October 2001.

"Vehicle and Mission Design Options for the Human Exploration of Mars/Phobos Using 'Bimodal' NTR and LANTR Propulsion," AIAA-98-3883, Stanley K. Borowski, Leonard A. Dudzinski, and Melissa L. McGuire; paper presented at the 34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit in Cleveland, Ohio, 13-15 July 1998.

"Artificial Gravity Vehicle Design Option for NASA's Human Mars Mission Using 'Bimodal' NTR Propulsion," AIAA-99-2545, Stanley K. Borowski, Leonard A. Dudzinski, and Melissa L. McGuire; paper presented at the 35th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit in Los Angeles, California, 20-24 June 1999.

NASA Exploration Team (NEXT) Design Reference Missions Summary, NASA, 12 July 2002 [draft].

"Enabling Human Deep Space Exploration with the Deep Space Gateway," Tim Cichan, Bill Pratt, and Kerry Timmons, Lockheed Martin; presentation to the Future In-Space Operations telecon, 30 August 2017.

More Information

Humans on Mars in 1995! (1980-1981)

Bridging the Gap Between Space Station and Mars: The IMUSE Strategy (1985)

The Collins Task Force Says Aim for Mars (1987)

Sally Ride's Mission to Mars (1987)

Footsteps to Mars (1993)

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. The Sun is behind and below the viewer; hence the rings cast shadows on the planet's northern hemisphere clouds. 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 the year 1968, when the film 2001: A Space Odyssey had its debut and the novel by the same name first saw print, it was clear that the Saturn system is home to some intriguing space oddities which Clarke could put to good use 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 that is very dark on one side (its leading hemisphere as it orbits Saturn) and very bright on the other. 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 of the planet.

Stanley Kubrick, who directed the film 2001, co-authored its screenplay, and received co-author credit on 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 Saturn actually appears up close, Kubrick and the production crew might have cut 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-to-Moon transport system and a 1997 NASA Lewis Research Center (now called NASA Glenn Research Center) plan to partially replicate 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 version of 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 which they name 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, of course, the signal was beamed at Jupiter.

Fateful decisions are made at the highest level of the United States government. The ancient Tycho monolith and the signal aimed at Saturn are to be kept secret, ostensibly 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's signal, Discovery's Jupiter mission is changed into a one-way Saturn mission with a gravity-assist flyby at Jupiter to gain speed. (I describe the early 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" travels to Saturn in hibernation; they 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, 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. Extending the limits of hibernation is, they are told, a major goal of their mission; 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 conundrum for HAL 9000. Deep in its programming is a directive never to distort information, yet it has been commanded to do just that. Though an 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 its 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 sharp line between the dark and light hemispheres is 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 shortcut through space-time leading into a galactic transit system. The lone survivor of Discovery's crew 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 rocket technology when I started work on this post, but I think after much study I have managed to accurately describe 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 will focus on the Saturn version of 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 heliocentric curve of a minimum-energy Hohmann transfer.

At present, nuclear fusion occurs mainly inside stars. Human effort toward harnessing star power since the 1940s has emphasized fusion bombs. The U.S. exploded the first such weapon in 1952; a nuclear-fission bomb 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 rocket 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 spacecraft's spheromak fusion reactor, four slush hydrogen tanks, and magnetic rocket nozzle. Image credit: NASA.

Discovery II's 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 high-temperature plasma filling. Discovery II's compact "spheromak" reactor would instead be shaped like a cored apple. Because it would be smaller, it would need less structure and fewer heavy components, such as electromagnets. The spheromak could thus be made much lighter than an equivalent Tokamak.

Though the NASA Glenn team took pains to make her fusion reactor as light as possible, at an estimated 310 metric tons it was still the most massive single hardware element of 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 needed 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's reactor would "burn" 11 metric tons of D/He-3 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 erode away and mix with the swirling plasma.

The NASA Glenn team envisioned that heavy element and wall debris plasma (informally known as "ash") would form 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 generate thrust.

The NASA Glenn team proposed to increase thrust by augmenting the ash plasma 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. The divertor and magnetic nozzle would together have a mass of only six metric tons, the 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.

To place its Discovery II fusion rocket 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 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, creating challenges in the areas of HLLV assembly and launch operations.

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 piloted space pods portrayed in the book and film 2001, which might have made 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 truss 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 took place in the payload bay of the Space Shuttle Atlantis. Discovery II central truss assembly would apparently occur in open space.

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

The HLLV's 250-metric-ton weight limit dictated 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, in addition to the truss and attached components, spacewalking astronauts would need to piece together 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 insight into how 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 each to maneuver gingerly into place near Discovery II's tail.

Discovery II with selected components and dimensions indicated. Please 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.

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 its only docking port, located on the front of the central hub crew module, and transfer to their interplanetary spacecraft.

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 would require weeks. The magnets and reactor structure would need to be thoroughly cooled using liquid helium; the chief reason for the long preparation period, however, 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 in the form of one-gram, 2.2-centimeter cube-shaped "pellets" accelerated at 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, the NASA Glenn engineers explained, help to preserve the stability of the swirling plasma flow. Pellets would need to be injected into the reactor once per second to maintain steady 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 also place strain on the central truss, as would operation of various turbines and movement of coolant and working fluids through pipes and pumps. The D/He-3 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 experience, 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 surface 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 three 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 take place.

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

Discovery II would arrive in Saturn sub-parabolic orbit with nearly empty cryogen 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 only 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 for the trip back to Earth.

No indication was given as to how D/He-3 mining machinery would reach Saturn's atmosphere ahead of Discovery II. Nor did the NASA Glenn team explain how D/He-3 mined from Saturn's atmosphere would reach the automated Saturn-orbiting refueling station they assumed would be in place when Discovery II arrived.

NASA Glenn envisioned that Discovery II's empty self-propelled hydrogen tanks would separate and dock autonomously with the refueling station. Identical full tanks would, meanwhile, undock from the station, rendezvous with Discovery II, and take the place of the depleted ones. How the hydrogen would reach the station was left to the imagination.

Discovery II would carry no auxiliary craft, so would need vehicles pre-deployed at Saturn if her crew was to leave the ship and land on any of the ringed planet's many moons. The NASA Glenn team did not explain how such 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 Discovery in the book and film 2001: A Space Odyssey? 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. Those advanced non-propulsion systems meant that a round-trip Jupiter mission could be re-planned as a one-way Saturn mission with eventual crew retrieval by a separately launched spacecraft.

Though it promises an impressive fusion rocket capability, the NASA Glenn Discovery II design is incomplete. It fails to account for the existence at Saturn of extensive pre-deployed assets essential to Discovery II's mission. Furthermore, it emphasizes propulsion to the exclusion of other potentially groundbreaking, 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.

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.

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

"A True Gateway": Robert Gilruth's June 1968 Space Station Presentation

Artist concept of Gilruth's 1968 "million-pound" artificial-gravity space station. Visible in this image are the habitat module (left), the hub with space-facing instruments on top and the hangar below, and, in the distance on the right, the S-II stage counterweight linked to the hub by a truss structure. Also visible are a small module maneuvering toward the hangar opening, a small piloted servicing vehicle approaching a free-flying 120-inch telescope, and a docked Gemini-derived crew rotation/logistics resupply vehicle. Image kindly provided by Carmine Rossi. Image credit: NASA.

Engineers often make the mistake of assuming that the course of spaceflight should be logical. Perhaps this is a quirk of the engineer personality (if such a thing exists). In any case, it is an unrealistic expectation. Human enterprise does not follow a logical path. History is about expediency and contingency, rarely do engineers see eye to eye, and, in any case, engineers do not comprise the majority of players in spaceflight decision-making.

In reading various proposals for NASA's post-Apollo future, one often has the sense that engineers wanted earnestly to take back the planning process and put the space agency on a logical track. They understood as well as most people the international and domestic political drivers behind Apollo, but viewed the Moon program as a step out of turn. They were proud of their Apollo accomplishments; as the lunar program's culmination approached, however, many seemed eager for the opportunity to leave the Moon alone in favor of a logical build-up of experience and capabilities back in low-Earth orbit.

At the cutting edge: Robert Gilruth in 1958. Image credit: NASA.

In few places is this as apparent as in Robert Gilruth's 25 June 1968 presentation to the Fourth International Symposium on Bioastronautics and the Exploration of Space. The Symposium took place in San Antonio, Texas, just a few hours' drive from the Houston-based NASA Manned Spacecraft Center (MSC), where Gilruth was director. Gilruth titled his presentation "Manned Space Stations: Gateway to Our Future in Space."

A native of Minnesota, Gilruth had gone to work at the Langley Memorial Aeronautical Laboratory in Hampton, Virginia, in 1937, directly out of graduate school. The National Advisory Committee for Aeronautics (NACA) had established Langley, its first research lab, in 1917, in part to ensure that the United States would not be left behind as the First World War drove aviation advancement in Europe.

Gilruth was no raging conservative when it came to technology. In the 1940s and 1950s he had worked at the cutting edge of high-speed aviation, where conventional aeronautics shaded into the arcane world of rockets and vehicles shaped to endure the pressures and temperatures of hypersonic speeds. He was instrumental in the creation of the rocketry range at Wallops Island, located across Chesapeake Bay from Langley near the tip of the Delmarva Peninsula. His talents were noticed early on; in 1952, before he turned 40, he became Langley's assistant director.

Gilruth's work took on new significance when the Soviet Union launched the first Sputnik satellite into Earth orbit on 4 October 1957. Though President Dwight Eisenhower downplayed the significance of the Sputniks, political pressure orchestrated in large part by Senate Majority Leader and Presidential aspirant Lyndon Baines Johnson forced his hand.

Within a year of Sputnik's launch, NACA became a part of the newly established NASA, Langley was renamed the NASA Langley Research Center (LaRC), and Gilruth became director of the Space Task Group (STG), an ad hoc organization within LaRC dedicated to human spaceflight. He remained director as the STG was elevated in 1962 to the status of a new NASA center, renamed the Manned Spacecraft Center, and transplanted to Vice President Johnson's home state of Texas.

The Symposium held six years later in San Antonio was a high-profile venue for putting across Gilruth's vision of the logical course of post-Apollo spaceflight. Arthur C. Clarke, screenwriter with Stanley Kubrick of the landmark film 2001: A Space Odyssey, was on hand to talk about exotic biology in the clouds of Jupiter. 2001 was released just three months before the Symposium. National Aeronautics and Space Council Executive Secretary Edward Welsh delivered the keynote address. In it, he called upon Congress to cease slashing NASA funding aimed at giving the agency a post-Apollo future.

Planning and building an Earth-orbiting space station would be challenging, Gilruth told his audience, in part because engineers had proposed so many different designs and justifications for space stations. In his presentation, he emphasized designs from MSC in-house and contractor studies. In fact, to prepare for his talk, Gilruth in April 1968 had tasked his engineers with designing a "million-pound station" based on 1966 MSC designs.

A 1966 NASA Manned Spacecraft Center station design with the same general layout as the 1968 "million-pound" design at the top of this post. At upper right is the habitat module. Telescoping arms link it to the zero-gravity hub, to which an Apollo Command and Service Module piloted spacecraft is docked. A spent Saturn V S-II second stage (left) serves as an artificial-gravity counterweight for the habitat. The solar-powered station would permanently point its solar arrays at the Sun as it orbited the Earth so that the spin axis would pass through the center of the cylindrical hub and through the long axis of the docked Apollo. Image credit: NASA.

Gilruth's 1968 station would need three Saturn V rocket launches to get started and two more to reach its full potential as a "location in space. . .developed to support men and equipment on a permanent basis. . .to take advantage of the economies of size, centralization, and permanency." He likened the space station to a base in Antarctica.

He declared that "development of the Saturn V. . .had provided one of the major building blocks for space station design." Gilruth then discussed how the Apollo Applications Program (AAP), NASA's only approved successor to Apollo, would compliment his station program. As its name implied, AAP would apply hardware developed for the Apollo Moon program, including the Saturn V rocket, to new missions on the Moon and in Earth orbit.

In early 1966, as AAP's NASA Headquarters office drew up a roster of more than 30 AAP Earth-orbital and lunar flights after minimal consultation with MSC and the other NASA centers, Gilruth had frank discussions with George Mueller, NASA Associate Administrator for Manned Space Flight, via letter, telephone, and telex. He argued that finding new uses for Apollo spacecraft and rockets was no basis for a post-Apollo space program. This ignored the fact that President Johnson had in 1965 called for a low-cost post-Apollo program based on Apollo technology.

NASA's piloted spaceflight organizations, Gilruth wrote, should aim instead for a "next big program" after Apollo. He mentioned the possibility of casting AAP as a precursor to a piloted Mars/Venus flyby, a class of piloted Apollo-derived mission under active investigation in 1964-1967. While engaged in discussions with Mueller, however, Gilruth initiated the 1966 in-house MSC station studies, thus revealing the form he believed the next big program should take.

In his San Antonio talk, Gilruth explained that AAP would explore the advantages of Earth-orbiting space stations "in a modest way." In particular, the AAP "wet launched" workshop, a modified Saturn IB S-IVB second stage, would enable NASA to study station habitability, biomedical effects of long spaceflights, and, through the addition of a separately launched solar observation module, the ability of humans to perform "a really complex scientific experiment" in Earth orbit.

Cutaway of the AAP Wet Workshop showing the Apollo Lunar Module-derived solar observatory (center left) attached to the docking adapter. The solar observatory would reach Earth orbit atop a Saturn IB rocket, the Saturn V's smaller cousin, which was intended as AAP's workhorse launcher. Image credit: NASA.

The AAP workshop would play the role for which it was intended — that of rocket stage — until it reached orbit. During ascent to orbit, a streamlined launch shroud on top of the stage would separate, revealing a docking module mounted atop the S-IVB stage liquid hydrogen fuel tank.

Ground controllers would command the orbiting stage to open vents in its liquid hydrogen and liquid oxygen tanks to enable residual propellants to escape. They would then close the vents and fill the hydrogen tank with a breathable air mixture from tanks in the docking module. Meanwhile, twin solar arrays would unfold from the workshop's sides. These would generate a total of about six kilowatts of electricity.

A three-man crew would then arrive in a Saturn IB-launched Apollo Command and Service Module (CSM) spacecraft. They would dock at the front of the docking adapter, enter it, and move furnishings stowed inside through a "manhole" hatch into the hydrogen tank. They would, for example, install a grid-work floor, fabric walls, and a galley module. After completing their orbital program, which might last weeks or months, the astronauts would return to Earth in the CSM. Subsequent crews would live on board the AAP workshop for successively longer periods.

Gilruth concluded his discussion of the AAP workshop by noting that it would "neglect what may be one of the major requirements for successful operation of a space station" — namely, artificial gravity. He believed that a practical space station would need to provide its inhabitants with "a high level of artificial gravity."

Artificial gravity would, he explained, enable comfortable movement, easy handling of fluids, and Earth-like "general man/machine interfaces." Because they could move more or less as they did on Earth, with their hands free to hold objects and to work, station crew members would need little special training to move about. Fluids would move as they did on Earth, which would make familiar the basics of personal hygiene, station cleaning, and food preparation. Equipment on the station could be identical to equipment on Earth, improving efficiency.

Artificial gravity would allow many types of researchers to live and work on the station, Gilruth told his San Antonio audience; basically, any who were eager to explore and exploit the economic and scientific benefits the space station would offer. "I, personally, look forward to the day when our space station crews will contain representatives from all the nations of the world," he added.

Gilruth described briefly an intermediate step between the zero-gravity AAP workshop and his large artificial-gravity station. He envisioned that a Saturn IB might launch an Apollo CSM. A drum-shaped multipurpose experiment module Boeing had designed on contract to MSC would ride in the streamlined adapter between the CSM engine bell and the top of the Saturn IB second stage.

Upon reaching orbit, the CSM would detach from the adapter, the four petal-like segments of which would fold back to expose the experiment module. The CSM crew would turn their spacecraft end for end and dock with the top of the experiment module, then would open latches linking the module to the rocket stage. Using the CSM's attitude-control thrusters, they would then pull the experiment module away from the stage.

Artificial-gravity experiment: the counterweight (upper right) is the S-IVB second stage of the Saturn IB rocket that boosted the CSM and experiment module into Earth orbit. Image credit: NASA

The module would, however, remain attached to the spent stage by an "extension mechanism," which might be as simple as a reel and cable. As the CSM/experiment module combination backed away from the stage, the crew would carefully fire the CSM's attitude-control thrusters, causing the CSM/experiment module/cable/stage assemblage to slowly spin end over end. The cable would draw taut and the crew would feel artificial gravity pressing them down into their couches. Separating from the module would end the experiment.

The 1966 MSC station study had looked at three classes of artificial-gravity space station, designated "Y," "O," and "I." The "Y" station would be approximately Y-shaped, with at least three arms. (The Project Olympus station — see the 1963 "Space Station Resupply. . ." link under "More Information" at the end of this post — is a good example of this station type.) The "O" station would take the form of a rotating wheel. The "I" station, which Gilruth favored and described in his San Antonio talk, would be a long cylindrical assemblage. He likened it to a "baton."

Assembling Gilruth's spinning baton (left to right): Saturn V launch 1 boosts the habitat module with its twin telescoping arms into Earth orbit. Saturn V launch 2 places the hub into orbit; the hub then docks with the habitat module. Saturn V launch 3 launches a deployable truss which turns the Saturn V S-II second stage into a counterweight. The station crew then fires rocket motors to spin the station end over end 3.5 times per minute to produce about one Earth gravity in the section of the habitat module farthest from the center of rotation. Image credit: NASA.

One million pounds, the mass Gilruth gave for his station, is equal to 500 tons. Probably this underestimates the likely mass of the station, which he hoped would house 50 people and 100,000 pounds (50 tons) of experiment equipment after its first three assembly launches.

The station would measure 240 feet from the center of rotation at its hub to the farthest part of the multi-deck, 50,000-cubic-foot habitat module and 375 feet from the center of rotation to the engine bells of the spent Saturn V S-II second stage that would serve as an artificial-gravity counterweight for the habitat. Total station length thus would come to about 615 feet.

These dimensions would enable the station to spin at 3.5 rotations per minute (rpm) without any ill effects for the crew, Gilruth explained. Spinning the station at 3.5 rpm would produce artificial gravity in the habitat module about equal to Earth's gravity. He noted that small-radius, fast-spinning systems could, based on Earth-surface studies of rotating rooms, cause crews to become ill and disoriented and produce other undesirable effects: water pouring from a faucet would, for example, curve. Setting his 500-ton baton twirling would require a one-time expenditure of 7000 pounds of propellants, Gilruth added.

The 45,000-cubic-foot drum-shaped hub would include electric motors that would cause it to rotate "backwards," canceling out the station's spin so that it would appear motionless. This would preserve zero-gravity conditions there. Gilruth envisioned that the hub would serve as a laboratory for exploring potential applications of zero gravity and as a hangar.

The hub hangar would receive self-propelled co-orbiting automated modules. Astronauts would service the modules in the hangar; they might collect and replace film, change out experiment equipment, and transfer propellants before releasing them to resume their zero-gravity work near the spinning station. Larger automated modules that could not fit within the hub hangar — for example, a 120-inch telescope — might be visited by astronauts, not returned to the station.

The station would operate in an orbit inclined 50° relative to the equator, enabling its Earth-pointing instruments, mounted on the lower sides of the hub, to survey a large fraction of Earth's lands and seas. Gilruth, an avid sailor, gave special attention to oceanographic observations in his San Antonio presentation. 

Space-pointing instruments would ride on top of the hub. Gilruth explained that many types of astronomical instruments would benefit from a position high above "Earth's dirty and shimmering atmosphere." 

Gilruth was not specific about the station's means of generating electricity, though he expected that it would need "20 or 50 or even 100 kilowatts" if it was to accomplish a wide range of experiments. The station's large size would permit mounting of proportionately large solar arrays; equally, it could enable use of "large nuclear systems" with extensive heat radiator panels, a large separation distance between the crew and the power source, and ample radiation shielding. 

Gilruth envisioned that, some time after the initial 50-person station was complete in Earth orbit, two more Saturn V launches would add another habitat module and a second S-II stage counterweight, bumping the station population up to at least 100. The large number of people would do away with the need for extensive cross-training in multiple skills and would enable specialization impossible in small crews. It would also reduce the amount of time any one station resident would spend performing maintenance and housekeeping chores, thus increasing time available for productive work.

Interestingly, Gilruth barely mentioned the need for a vehicle for transporting supplies and crews to and from his station, let alone any specific vehicle design. He mentioned "flexible crew rotation patterns," but did not explain how they would be accomplished. He did, however, note that the station could serve as a "logistic center" — a kind of warehouse — which would enable "efficient launch schedules for operational and experiment support supplies." He argued that the station's permanency would enable reuse and modification of equipment, reducing the quantity that would need to be shipped up from Earth.

The illustration of Gilruth's million-pound station at the top of this post — sent my way by reader Carmine Rossi — helps to clear up some of the mystery. Visible on either side of the hub are twin "Big Gemini" crew/cargo vehicles. These would have "backed up" to dock with ports on the sides of the non-spinning hub.

Proposed by contractor McDonnell Douglas in 1967, Big Gemini represented a continuation of Gemini contractor McDonnell's efforts to sell NASA and the U.S. Air Force Gemini-derived spacecraft and modular space stations. McDonnell had begun to pitch a broad range of Gemini variants as early as 1962, the year Gemini became the "bridge" program linking Mercury and Apollo.

Each Big Gemini might have launched nine astronauts (12 in its advanced version) and several tons of supplies. The design would have been familiar to many in his audience, so perhaps Gilruth felt no need to call it out specifically in his presentation.

Even in its advanced form, however, Big Gemini was a small crew/cargo spacecraft for a big space station. The concept, spelled out in a detailed eight-volume report submitted to MSC in August 1969, fueled awareness that large stations such as MSC's 1968 design would need sophisticated crew/cargo vehicles. This bolstered plans for reusable winged "Space Shuttle" vehicles.

Gilruth ended his presentation by declaring that a large space station would provide "tens of thousands of hours of operational experience. . .in the space environment." This would, he said, make it "a true gateway into the exciting space programs of the more distant future."

Sources

Letter, Robert Gilruth to George Mueller, 25 March 1966.

Letter, Robert Gilruth to George Mueller, 15 April 1966.

Preliminary Technical Data for Earth Orbiting Space Station, Volume 1, Summary Report, MSC-EA-R-66-1, NASA MSC, 7 November 1966.

Status Report: Earth Orbiting Space Station Artificial Gravity Experiment, MSC Internal Note 68-ET-1, NASA MSC, January 1968.

Manned Space Stations: Gateway to Our Future in Space, Robert Gilruth; presentation to the Fourth International Symposium on Bioastronautics and the Exploration of Space in San Antonio, Texas, 25 June 1968.

Astronautics and Aeronautics, 1968: Chronology on Science, Technology, and Policy, NASA, 1969, pp. 141-142.

A Summary of NASA Manned Spacecraft Center Advanced Earth Orbital Missions Space Station Activity from 1962 to 1969, Maxime Faget and Edward Olling, NASA MSC, February 1969, pp. 17-18, 27-28.

Skylab: A Chronology, NASA SP-4011, R. Newkirk, I. Ertel, and C. Brooks, NASA, 1977, pp. 172-174.

NASA Press Release, "Dr. Robert Gilruth, An Architect of Manned Space Flight, Dies," Bob Jacobs, NASA Headquarters, 17 August 2000.

More Information

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

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

McDonnell Douglas Phase B Space Station (1970)

A Forgotten Rocket - The Saturn IB

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

President John F. Kennedy messes up NASA's carefully wrought long-range plans, 25 May 1961. Image credit: NASA.

When first proposed in 1959, the spacecraft that would come to be known as the Apollo Command and Service Module (CSM) was envisioned as an Earth-orbital "advanced manned spacecraft" capable of being uprated for circumlunar or lunar-orbital flights. On 15 November 1960, NASA awarded six-month feasibility study contracts for just such an Apollo spacecraft to three contractors: the Martin Company; the Convair Division of General Dynamics; and the General Electric Company Defense Electronics Division, Missile and Space Vehicle Department.

In 1960, the three-man Apollo spacecraft was expected to be the second U.S. piloted spacecraft after the Mercury capsule. It would include a Command Module (CM), a Service Module (SM), and an Orbital Module; the last of these would augment the work and living space available to the crew, in effect making the spacecraft into a mini-space station.

NASA expected that its piloted program in the 1960s would proceed down one or both of two "logical" paths, and that Apollo would be crucial for both. The first path would have Apollo spacecraft transport crews to a temporary "orbiting laboratory." The Orbital Module would be used to transport supplies to the lab in space. The other path would see an Apollo perform a piloted flight around the moon. What might come after 1970 was anybody's guess, though NASA expected that the orbiting lab path would lead to a permanent Earth-orbiting space station and the circumlunar path would trend toward to a piloted Moon landing, piloted Mars and Venus flybys, and a piloted Mars landing.

Apollo as a fork in the road: NASA's plans for piloted spaceflight in 1959. Image credit: NASA.

Martin, General Dynamics, and General Electric submitted their final study reports to NASA on 15 May 1961. Ten days later, new President John F. Kennedy wreaked havoc on NASA's logical plans when he opted to proceed directly to a lunar landing before 1970.

Stinging from the failed Bay of Pigs invasion of Cuba and the first piloted spaceflight by Soviet cosmonaut Yuri Gagarin (12 April 1961), Kennedy had asked Lyndon Baines Johnson, his Vice President and National Space Council chair, to propose a space goal that the U.S. might reach ahead of the Soviet Union. The apparent Soviet advantage in launch vehicle capability would, it was believed, give communist rocketeers a head-start if the goal was anything as modest as the establishment of an Earth-orbiting space station. Landing a man on the Moon, on the other hand, was a goal audacious enough that the U.S. and Soviet Union would start out more or less evenly matched.

Model of the Apollo Command and Service Module atop a conceptual Landing Propulsion Module. Image credit: NASA.

On 28 November 1961, NASA awarded North American Aviation (NAA) the contract to build the Apollo CSM, the design of which included two modules: the conical CM and the drum-shaped SM. The method by which NASA would carry out President Kennedy's bold lunar mandate remained uncertain, though it was widely assumed that the space agency would soon award a contract for a third Apollo spacecraft module: a Landing Propulsion Module for lowering the CSM to a gentle touchdown on the Moon. NAA went so far as to specify in its April 1962 subcontract with Aerojet General Corporation that the CSM's Service Propulsion System (SPS) main engine be capable of generating enough thrust to launch the CSM off of the lunar surface and place it on course for Earth.

As it turned out, however, the Apollo CSM would never land on the moon. On 11 July 1962, as part of an ongoing debate that was not finally settled until November of that year, NASA selected the Lunar-Orbit Rendezous (LOR) mode for accomplishing the Apollo mission. A contract for a third Apollo module was indeed awarded (to Grumman Aircraft Engineering Corporation, 7 November 1962), but it was for the Lunar Excursion Module (LEM), a bug-like two-man spacecraft that would undock from the CSM in lunar orbit and lower to a landing on the Moon. The Apollo CSM thus became the mother ship for delivering astronauts and LEM to lunar orbit and returning astronauts and Moon rocks to Earth.

Despite President Kennedy's new high-priority moon landing goal, space station studies within NASA did not cease. In fact, some believed that NASA might launch its first station into Earth orbit before an astronaut stepped onto the Moon. They reasoned that lunar landing program development costs would peak two or three years before NASA launched its first lunar landing attempt (as in fact they did). If NASA's portion of the Federal purse remained near its peak as Moon program costs declined, then funds might become available for a station in Earth orbit as early as 1968.

At the newly established NASA Manned Spacecraft Center (MSC) in Houston, Texas, engineer Edward Olling headed up space station planning. He informally named MSC's first proposed station program Project Olympus.

In April 1962, Olling circulated a draft planning document within MSC for comment; then, on 16 July 1962, he unveiled to top-level MSC managers his "Summary Project Development Plan" for the Project Olympus space station program. Olling envisioned a series of four 24-man stations launched and continuously staffed over a period of from five to seven years.

Olling explained that the Project Olympus space stations would provide NASA with enough astronauts, scientific equipment, pressurized volume, and electrical power to carry out wide-ranging basic and applied science research in space. Early station research would, however, seek to answer important questions about the efficacy of humans in space; for example, could astronauts work safely and effectively in orbit for long periods?

Image credit: NASA.

Each 138,600-pound Project Olympus station would consist of a 15,000-cubic-foot central hub from which would radiate three evenly spaced arms with a total of about 35,000 cubic feet of volume. The hub would include a hangar for crew and supply spacecraft. Each arm would include a pressurized crew module of oval cross-section with two cylindrical access tunnels. The Project Olympus station would launch atop a two-stage Saturn V rocket with its hub on top and its three radial arms folded below. Once in orbit, the station would separate from the Saturn V second stage and the three arms would hinge upward and lock into place. Pressurized tunnels would link each arm to the station hub.

Small rocket motors at the ends of the arms would ignite to spin the station. The 150-foot-wide Project Olympus station would revolve four times per minute to create acceleration in its arms which the crew inside would feel as gravity. "Down" would be away from the hub.

The crew decks farthest from the hub would experience the greatest acceleration: the equivalent of one-quarter of Earth's gravitational pull, or about midway between lunar and martian surface gravity. Decks closer to the hub would experience less acceleration, so might be used mainly for storage. Olling hinted that the different levels of acceleration experienced at varying distances from the hub might be useful for scientific research, though he did not explain how.

Cutaway drawing of a Project Olympus-type space station. The centrifuge in lower part of the hub would support variable gravity experiments. Not shown is a station power system; NASA MSC proposed both solar- and nuclear-powered station designs. Image credit: North American Aviation/NASA.

New research objectives would be added over time as old stations were retired and new ones launched. The Project Olympus stations would become space-environment research facilities, "national laboratories" for research into meteorology, geophysics, radio communications, navigation, and astronomy, as well as "orbital operations" platforms (that is, shipyards for preparing spacecraft bound for points beyond space station orbit).

Olling advised MSC management that Project Olympus stations should operate in circular 300-nautical-mile-high orbits inclined 28.5° relative to Earth's equator — what he called a "Mercury orbit" because it matched the orbital inclination of the one-man Mercury capsules. Astronaut Scott Carpenter orbited Earth for nearly five hours in the Aurora 7 capsule on 24 May 1962, while Olling prepared his project plan. Olling later lowered his recommended altitude to 260 nautical miles.

The 28.5° latitude of the launch pads at Cape Canaveral, Florida, determined the orbital inclination of the Project Olympus stations. Matching launch-site latitude and station orbital inclination would maximize both station mass and the mass of the payload that could be delivered to the station. Olling also mentioned (albeit briefly) the possibility of a polar-orbiting Project Olympus station that would pass over all points on Earth.

In April 1963, MSC awarded NAA a contract for a seven-month study of a Modified Apollo (MODAP) logistics spacecraft for delivering astronauts and cargo to Project Olympus space stations. The Apollo CSM design had yet to reach its final form. No docking unit design had been selected, for example, though the probe-and-drogue system eventually chosen was already the leading candidate. The overall CSM layout was, however, firmly in place, giving NAA a meaningful point of departure for its MODAP study.

Apollo 15 Command and Service Module Endeavor in lunar orbit. Image credit: NASA.

The Apollo CM included three astronaut couches, control consoles, small windows at strategic locations, a side-mounted hatch with a window, a docking tunnel and parachutes in its nose, thrusters for orienting it for atmosphere reentry, and, at its base, a bowl-shaped reentry heat shield. Umbilicals and cables in a hinged housing linked the CM to the SM.

The Apollo SM included seven major internal bays. A central cylindrical bay housed tanks of helium pressurant for pushing rocket propellants into the SPS main engine. Arrayed around the central compartment were six triangular bays containing tanks of fuel and oxidizer for the SPS and for four attitude-control thruster quads, electricity- and water-making fuel cells, and tanks of liquid oxygen and liquid hydrogen reactants for supplying the fuel cells.

The MODAP CSM would comprise a stripped-down SM and a beefed-up CM. Because it would spend a limited amount of time in free flight before it docked with an Earth-orbiting station, the MODAP SM could dispense with or minimize many Apollo lunar SM systems. Batteries would replace fuel cells, for example, and a compact LEM descent engine could replace the SPS. The LEM engine would draw its propellants from a pair of spherical tanks in the MODAP SM's central cylindrical compartment. These deletions and additions would free up four of the MODAP SM's triangular bays for cargo transport.

The Apollo SM had six roughly triangular bays arrayed around a cylindrical core. The bays contained propellants, fuel cells, and liquid hydrogen and liquid oxygen tanks, among other systems necessary for a lunar mission. For its Earth-orbital station logistics missions, the MODAP SM needed fewer systems and tanks, so could devote four of the six triangular bays to cargo. The section image at right displays the cargo and equipment bays and a possible arrangement for four cargo doors. Image credit: North American Aviation/NASA.

A two-stage Saturn IB rocket capable of placing 32,500 pounds into a 105-nautical-mile circular parking orbit at 28.5° of inclination would launch the MODAP CSM. Pre-launch preparation, launch operations, and ascent to parking orbit would need from five to 10 days, from five to eight hours, and 11 minutes, respectively.

The MODAP CSM would remain in parking orbit for less than five hours before its crew ignited its LEM descent engine to place it into an elliptical transfer orbit with a 260-mile apogee (highest point above the Earth). Upon reaching apogee 45 minutes later, its crew would again ignite the engine to circularize its orbit. Subsequent station rendezvous and docking maneuvers might need up to 17.5 hours.

The company calculated that a 24-man station with crew stays lasting six months would need to receive a MODAP CSM bearing six astronauts and 5855 pounds of supplies eight times per year — that is, every 45 days. The typical cargo manifest would include 1620 pounds of food, 1035 pounds of oxygen, 505 pounds of nitrogen, 1450 pounds of propellants, and 1245 pounds of spare parts. The Project Olympus station would recover and reuse all water launched with it, so would have no need of water resupply.

These cutaway drawings of the Project Olympus hangar display internal (right) and external palletized cargo transfer methods. The internal method assumes that the entire MODAP CSM can fit into the hangar. The drawing at left shows how the protruding MODAP SM would separate from the MODAP CM and pivot into cargo-unloading position. MODAP CMs for Earth-return are docked radially on the dome-shaped docking hub near the floor of the hangar. Image credit: North American Aviation/NASA.

Supplies would reach the Project Olympus station in drum-shaped Cargo Modules, or CAMs, packed in the four empty triangular MODAP SM bays. The mass of the empty CAMs would total 1970 pounds. Liquid and gaseous cargo would fill small CAMs, while solid cargoes would ride on disc-shaped pallets in large CAMs. In all, a MODAP CSM could transport 9127 pounds of cargo and CAMs.

The MODAP CSM would dock with the Project Olympus station via an axial docking unit at the bottom of the station hangar. NAA envisioned that the station would include either a tall hangar for the entire MODAP CSM or a short hangar for the MODAP CM alone (in which case the MODAP SM would protrude into space). If the former, then CAM transfer could occur entirely within the hangar. If the latter, then CAM transfer would occur external to the station. In both cases, after all cargo was transferred, the MODAP SM would be cast off and the hangar closed to protect the MODAP CM.

These cutaway drawings of the Project Olympus station hangar show CAM internal (right) and external transfer methods. Compare with palletized transfer drawings above. Image credit: North American Aviation/NASA.

To free up the single axial docking port for the next MODAP CSM, a manipulator arm inside the hangar would pivot the MODAP CM to one of three radial berthing ports. It would remain parked there, undergoing periodic inspection and maintenance but otherwise dormant, for up to six months.

Discarding the MODAP SM with its LEM descent engine meant that the MODAP CM would need to carry a separate de-orbit propulsion module. NAA proposed a cluster of six solid-propellant retrorockets, any five of which could deorbit the MODAP CM. The retro package would include batteries for powering the MODAP CM during free-flight prior to reentry. NAA expected that, in normal circumstances, the MODAP CM would need 30 minutes for checkout and undocking. The MODAP CM's crew would ignite its retrorockets immediately after it maneuvered clear of the hangar.

The MODAP CM with solid-propellant retropack. Image credit: North American Aviation/NASA.

Twenty-five minutes after retrofire and shortly after retropack separation, the MODAP CM would reenter Earth's atmosphere. Because the MODAP CM would encounter the atmosphere moving at about half the speed of the Apollo lunar CM, its heat shield could be about half as thick. Descent and splashdown would need 11 minutes. With six astronauts on board, the MODAP CM would be heavier than the lunar CM, so would lower on four parachutes; that is, one more than the lunar CM. Its crew could splash down safely if one parachute failed.

Under normal circumstances, the MODAP CM would splash down in the Gulf of Mexico not far from Houston, so crew recovery would take place within a few hours. NAA acknowledged, however, that emergencies might occur. Because of this, the MODAP CM could fly free of the space station for up to 10.5 hours while its inclined orbit and Earth's rotation put it on course for reentry and splashdown at any of three sites. These were the prime site in the Gulf of Mexico, a site near Okinawa in the western Pacific Ocean, and one near Hawaii. To trim costs, fleets of recovery ships would not remain on standby at the landing sites; because of this, the astronauts might need to wait for up to 24 hours for rescue following an emergency splashdown near Okinawa or Hawaii.

An abort during ascent to Earth orbit could cause the Apollo and MODAP CMs to land in southern Africa; that is, to touch down on land. To protect its three-man crew during a land landing, the lunar CM would include shock absorbers in its supporting seat struts. These would enable the crew couches to move vertically up to five inches to dissipate the force of impact.

A tight fit: six-man MODAP Command Module seating arrangement. Image credit: North American Aviation/NASA.

Because the MODAP CM would carry six men arrayed in two rows of three couches each, with one row above the other, NAA found that vertical couch movement would not be an option. The three-man lunar CM would also rely on crushable material behind its heat shield to absorb the force of land impact; this would be inadequate for the greater mass of the six astronauts in the MODAP CM.

NAA proposed to solve the emergency land-landing problem by in effect moving the shock absorbers from the seat struts to the MODAP CM's heat shield and by adding four solid-propellant landing rockets. In the event of a land landing, the bowl-shaped heat shield would deploy downward on shock-absorbing struts and the landing rockets would ignite and pivot out from behind the shield.

NAA envisioned a MODAP CSM design & test program spanning from early 1964 to mid-1968. Operational MODAP CSMs would deliver crews and supplies to 24-man Project Olympus stations between mid-1968 and the end of 1973. The company anticipated that five MODAP CSMs would be used in ground tests and unmanned test flights, and that 40 MODAP CSMs would support the station program. Of these, perhaps two would fail, requiring assembly of at least two backup MODAP CSMs. NAA placed the total cost of the MODAP CSM program including $861 million for Saturn IB rockets at $1.881 billion.

A significant outcome of Olling's Project Development Plan and NAA's MODAP study was the realization that space station crew rotation and resupply would dominate total space station program cost. Summing up his findings, Olling wrote that a "reusable launch vehicle could contribute large economies" (that is, ensure large cost savings) for the station program. Even if four space stations were launched on expendable Saturn V rockets during the Project Olympus program, station cost would total only $1.273 billion; that is, about $600 million less than the MODAP CSM flights.

The Project Olympus and MODAP CSM study teams were not alone in reaching these conclusions; thus, as early as 1963, a reusable logistics spacecraft came to be seen as a desirable component of a large space station program. By 1968, this led to calls by high-level NASA management for a 1970s Space Station/Space Shuttle program.

Sources

Final Technical Presentation: Modified Apollo Logistics Spacecraft, Contract NAS 9-1506, North American Aviation, Inc., Space and Information Systems Division, November 1963.

"Project Olympus: Proposed Space Station Program," Edward H. Olling, NASA Manned Spacecraft Center, 16 July 1962.

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