NASA Marshall's 1966 NERVA-Electric Piloted Mars Mission

Image credit: NASA.

Through most of 1966, it was still reasonable to assume that NASA and the United States might enjoy an expansive post-Apollo future off the Earth. Manned missions beyond the Moon were expected to evolve from programs already in place; namely, the Apollo lunar landing program, the joint NASA/Atomic Energy Commission NERVA nuclear-thermal rocket program, and the Apollo Applications Program of advanced lunar missions and Earth-orbiting space stations.

With these programs in mind, in March 1966 the American Institute of Astronautics and Aeronautics and the American Astronautical Society jointly convened the Stepping Stones to Mars conference in Baltimore, Maryland. As it turned out, it would be the last major Mars-focused engineering meeting until the 1980s.

Attendees heard a team of engineers from NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, describe a piloted Mars mission based on both high-thrust NERVA-II nuclear-thermal rockets and low-thrust nuclear-electric (ion) propulsion. The study team's leader was veteran German-born rocketeer Ernst Stuhlinger, the director of MSFC's Research Projects Laboratory.

Stuhlinger had begun his work on electric propulsion in the 1930s. He earned a Ph.D. at age 23, then worked for Hitler's nuclear program. In spite of his science training, in 1941 he was drafted into the Wehrmacht and sent to the Russian front. After suffering wounds in the Battle of Moscow and surviving the Battle of Stalingrad, he was reassigned to Wernher von Braun's rocket team at the Baltic Sea rocket base of Peenemünde in 1943. There he worked on the guidance system for the V-2 missile.

Stuhlinger arrived in the United States courtesy of the U.S. Army. He resumed his electric propulsion work in Huntsville in the early 1950s, at which time von Braun's team was part of the Army Ballistic Missile Agency at Redstone Arsenal. He played a key role in the launch of the first U.S. satellite, Explorer 1, in January 1958. Under von Braun's leadership, the Peenemünde rocketeers became the nucleus around which NASA MSFC coalesced in July 1960.

Ernst Stuhlinger (left, holding slide rule) and Wernher von Braun during filming of the classic Walt Disney-produced documentary Mars and Beyond. The model Mars spacecraft shown, based on a Stuhlinger design, includes a disk-shaped thermal radiator, a bomb-shaped piloted Mars lander, and, at the end of a downward-pointing stalk, a nuclear reactor. The reactor would power thrusters mounted on the stalk opposite the lander. Crew quarters are in a torus near von Braun's hand. Image credit: NASA.

In the years before the Stepping Stones to Mars meeting, Stuhlinger had put forward several electric-propulsion spacecraft designs. His 1954 Sun Ship would have relied on concentrated sunlight for electrical power to drive its ion thrusters, but his other electric-propulsion designs — the 1957 Mars and Beyond crew and 1959 lunar freighter disc ships and his 1962 lunar freighter and spinning Mars crew spacecraft — would have employed large nuclear reactors.

The hybrid NERVA/nuclear-electric approach would, the MSFC engineers explained, magnify the benefits and mitigate the drawbacks of both propulsion methods. Efficient electric propulsion would slash the amount of the propellant required to reach and return from Mars. This would in turn reduce the number of costly rockets required to place a Mars spacecraft into Earth orbit for assembly. Five uprated two-stage Saturn V rockets would be sufficient to launch all the components making up a hybrid spacecraft into Earth orbit — about half as many as required to launch a Mars spacecraft propelled by NERVA nuclear-thermal rocket engines alone.

Nuclear-thermal rockets, for their part, would trim trip time and reduce crew radiation exposure. Nuclear-electric spacecraft could escape from Earth orbit only after spiraling outward for weeks or months. Because of this, they would linger in the Van Allen radiation belts for days or weeks. Nuclear-thermal spacecraft, on the other hand, could escape from Earth orbit in hours and race through the Earth-girdling radiation belts in minutes.

Stuhlinger and his colleagues scheduled their NERVA/nuclear-electric Mars expedition for launch in 1986, 20 years after they presented their paper, because in that year the amount of energy needed to travel from Earth to Mars and back would be relatively small and solar activity would be at an ebb. The MSFC team assumed (rather naively) that their expedition would encounter no solar flares, so they skimped on radiation shielding to reduce spacecraft weight.

They also anticipated that electric propulsion would be applied first to Earth-orbital satellite station-keeping in the late 1960s, and that enough electric propulsion research would be completed by 1974 to justify government approval of the NERVA/nuclear-electric Mars expedition. That would leave 12 years for spacecraft development and testing.

The hybrid Mars expedition would occur in three phases. Phase 1 would see nuclear-electric spacecraft components and propellant launched from Earth's surface. To enhance safety, four identical piloted spacecraft would undertake the Mars voyage. If one failed, its crew could find refuge on board the remaining three spacecraft. Each spacecraft would in fact be capable of returning all 16 crew members to Earth in cramped conditions.

For each Mars spacecraft, three uprated two-stage Saturn V rockets would launch a total of 388 tons of components and propellant into 485-kilometer-high assembly orbit. For the four-spacecraft expedition, 12 uprated Saturn Vs would launch a total of 1552 tons.

Ernst Stuhlinger displays models of the MSFC 1966 NERVA/nuclear-electric Mars spacecraft, an Apollo Saturn V rocket, and, at right, a Saturn V-launched payload module containing NERVA/nuclear-electric spacecraft truss components. The NERVA-II stage/propellant tank combination is not shown. The payload module, nuclear-electric spacecraft, and Saturn V are the same scale. On the wall in the background is an illustration of the 1962 diamond-shaped Mars spacecraft design Stuhlinger developed with MSFC engineer Joseph King, a member of the 1966 Mars spacecraft study team. Image credit: NASA.

The spacecraft would each include a central module containing the nuclear-electric propulsion system, a four-person, 57-ton Mars Excursion Module (MEM) lander, and space "taxis" for crew transport between the four spacecraft. The 123-ton propulsion system would include a 20-megawatt nuclear reactor, an electricity-generating turbine-generator, electric thrusters, and a cylindrical tank holding 153 tons of xenon or cesium propellant. Twin telescoping truss-like arms extending from either side of the central module would each carry four rectangular reactor radiator panels and, at its end, one two-deck drum-shaped pressurized crew module.

Phase 2 would see launch of four nuclear-thermal rocket stages and Mars expedition departure from Earth orbit. Shortly before the scheduled launch date, four uprated Saturn Vs would launch one NERVA-II nuclear-thermal propulsion module each, then four more uprated Saturn Vs would launch one liquid hydrogen tank module each. The NERVA-IIs and tank modules would dock in orbit to form four 54-meter-long, 10-meter-diameter nuclear-thermal stages, each with a mass of 309 tons. Of this mass, liquid hydrogen propellant would account for 226 tons. The nuclear-thermal stages would then each maneuver to dock with a nuclear-electric spacecraft's central module.

On 1 May 1986, the four NERVA-II engines would power up and operate for nearly 30 minutes. The spacecraft crews would, meanwhile, shelter in their MEMs. In the event of NERVA-II trouble during Earth departure, the MEM would serve as the crew's abort-to-Earth vehicle.

About 17 minutes after start-up, each NERVA-II engine would vent hot gas from its turbopump to spin its spacecraft once per minute, producing acceleration equal to 20% of Earth's surface gravity in the crew modules at the ends of the twin telescoping arms. Artificial gravity would ensure, among other things, that toilets and showers would operate much as they did on Earth.

The MSFC team noted, however, that "available evidence from the Gemini flight missions suggests that artificial gravity for long space missions may not be required physiologically." The longest two-man Gemini mission, Gemini VII, had lasted for just 14 days in December 1965, so the MSFC team in fact had very little basis for its opinion.

The NERVA-IIs would deplete their propellant at an altitude of 3450 kilometers, then Phase 3, the actual Mars expedition, would commence. The crews would leave their MEMs, climb down pressurized tunnels in the telescoping arms to their cabins, discard the spent NERVA rocket stages, and activate the nuclear-electric thrusters to complete spacecraft injection onto a trans-Mars trajectory. The astronauts would switch off the thrusters after an unspecified short period and the fleet would then coast around the Sun along a curving Mars-bound path.

One-hundred-and-forty-five days out from Earth, the four ships would reactivate their nuclear-electric thrusters to begin deceleration. Then, on 23 September 1986, Mars would capture them into a high orbit. Their nuclear-electric thrusters would continue to operate for 23.5 days so that they would spiral down to a 1000-kilometer circular Mars orbit.

During the spiral-down period, the four MEMs would undock and land on Mars, leaving the four ships unmanned. Relieved of the weight of the MEMs, the nuclear-electric ships could spiral inward toward Mars more rapidly.

The MSFC team cited data from the Mariner IV Mars probe when they proposed an "Apollo-shaped" conical MEM design. Mariner IV had flown past Mars in July 1965, returning data that indicated that the planet's atmosphere was about 10 times thinner than had been expected. Because of this, winged and lifting-body Mars landers, which would rely on aerodynamic lift to reduce the amount of landing and liftoff propellants they would need, were no longer considered feasible. The Apollo-shaped MEM design had been the subject of special study by Gordon Woodcock, a member of the MSFC study team (see "more Information" below).

Atmospheric drag would slow the 10-meter-wide MEM, then its heat shield would eject to expose chemical-propellant landing retro-rockets. These would slow the MEM to a halt 400 meters above Mars; the MEM pilot would then have 60 seconds to select a landing spot before he exhausted the MEM's descent propellants.

After a month on Mars, the four 27-ton MEM ascent stages would blast their crews back to Mars orbit, where they would dock with their respective nuclear-electric Mars ships. The crews would transfer, then the ascent stages would be cast off. Because the Mars spacecraft would no longer carry the weight of the MEMs, outward spiral from Mars would last just 17.5 days, with Mars escape taking place on 12 November 1986.

Mars-Earth crossing would need 255 days. About halfway through, the spacecraft would begin deceleration. Earth-orbit capture would occur on 25 July 1987. A five-day inward spiral would place the fleet in 30,000-kilometer-high Earth parking orbit, where the electric thrusters would be turned off for the final time. A chemical-propulsion "commuter rocket" would then arrive to retrieve the Mars explorers and ferry them home to Earth. The Mars expedition ships would remain in distant Earth orbit as permanent monuments to the early days of space exploration.

The 1966 study was among the last to look in detail at nuclear-electric propulsion until the late 1980s. Just seven years earlier, Stuhlinger had concluded his 1959 nuclear-electric freighter paper by predicting that a nuclear-electric cargo ferry would serve a U.S. Moon base "from 1965-70 on." When he retired from NASA in 1975, however, the U.S. had abandoned the Moon and nuclear-electric propulsion was little closer to flight than it had been in 1959. Stuhlinger died at age 94 in May 2008.

Sources

"Possibilities of Electrical Space Ship Propulsion," E. Stuhlinger, Bericht über den V Internationalen Astronautischen Kongreß, Frederich Hecht, editor, 1955, pp. 100-119; paper presented at the Fifth International Astronautical Congress in Innsbruck, Austria, 5-7 August 1954.

"Lunar Ferry with Electric Propulsion System," Ernst Stuhlinger, First Symposium (International) on Rockets and Astronautics, Tokyo, 1959, Proceedings, M. Sanuki, editor, 1960, pp. 224-234.

"Concept for a Manned Mars Expedition with Electrically Propelled Vehicles," Ernst Stuhlinger and Joseph C. King, Progress in Astronautics, Vol. 9, pp. 647-664, 1963; paper presented at the American Rocket Society Electric Propulsion Conference in Berkeley, California, 14-16 March 1962.

"Study of a NERVA-Electric Manned Mars Vehicle," Ernst Stuhlinger, Joseph King, Russell Shelton, and Gordon Woodcock, A Volume of Technical Papers Presented at the AIAA/AAS Stepping Stones to Mars Meeting, pp. 288-301; paper presented in Baltimore, Maryland, 28-30 March 1966.

"Ernst Stuhlinger: Rocket Scientist Crucial in Space Race, is Dead at 94," John Noble Wilford, New York Times, 28 May 2008 (http://www.nytimes.com/2008/05/28/us/28stuhlinger.html - accessed 18 December 2016).

More Information

The Challenge of the Planets, Part Two: High Energy

Gumdrops on Mars (1965)

The Last Days of the Nuclear Shuttle (1971)

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

Image credit: U. S. Department of Defense.

On the evening of 23 March 1983, U.S. President Ronald Reagan addressed the people of the United States from the Oval Office. Citing aggressive moves on the part of the Soviet Union, he defended proposed increases in U.S. military spending and the introduction of new missiles and bombers. He then called for a revolution in U.S. strategic doctrine.

"Let me share with you a vision of the future," Reagan began. He then summed up that vision in the form of a two-part question replete with the Cold War language of his Presidency: "What if free people could live secure in the knowledge that their security did not rest upon the threat of instant U.S. retaliation to deter a Soviet attack, that we could intercept and destroy strategic ballistic missiles before they reached our own soil or that of our allies?"

Reagan acknowledged that his vision represented "a formidable technical task, one that may not be accomplished before the end of this century." He then called on U.S. scientists — "those who gave us nuclear weapons" — to direct their talents "to the cause of Mankind and world peace, to give us the means of rendering these nuclear weapons impotent and obsolete."

President Ronald Reagan shares his missile-defense vision with the American people. The image on the easel is a declassified satellite view of Soviet MiG aircraft stationed in Cuba. Image credit: The Reagan Library.

Thus was born the Strategic Defense Initiative (SDI), which is perhaps better known by its cinema-inspired nickname "Star Wars." This post is not meant to discuss the origins, geopolitics, or technical feasibility of SDI. It will instead focus on one of the lesser-known aspects of SDI planning: the potential use of space resources.

The Reagan White House appointed James Fletcher, NASA Administrator from 1971 until 1977 under Presidents Nixon and Ford, to head up a panel to propose an SDI experiment and development program. Fletcher tasked the California Space Institute (Calspace) at the University of California-San Diego (UCSD) with organizing a workshop to consider whether exploitation of the resources of the Moon and asteroids might help to give substance to Reagan's vision. The Defense Applications of Near-Earth Resources Workshop took place in La Jolla, California, on 15-17 August 1983.

That Fletcher should have asked Calspace to assist with his SDI report is not too surprising. In February 1977, James Arnold, a UCSD chemistry professor, had spoken with NASA Administrator Fletcher about making the exploitation of near-Earth space resources a major new focus for NASA. He subsequently summed up his thoughts in a detailed two-page letter to Fletcher. Three years later, Arnold became the first director of Calspace, which had its origins in California Governor Jerry Brown's enthusiasm for technological development in his state.

Arnold's deputy in 1983-1984, young planetary scientist Stewart Nozette, organized the La Jolla workshop, which brought together 36 prominent scientists and engineers from aerospace companies, national laboratories, NASA centers, the Department of Defense, and defense think-tanks to weigh in on the potential use of Moon and asteroid resources in SDI. Nozette also edited the workshop report, a draft of which Arnold submitted to Fletcher on 18 August 1983. A revised final version of the workshop report was completed on 31 October 1983. This post is based upon the latter version.

In the cover letter to the La Jolla workshop report, Nozette described how, in the late 1970s, NASA, aerospace companies, and universities expended a great deal of time and effort on planning large structures — for example, Solar Power Satellites — which would be assembled in space. Some of these plans relied on space resources. Nozette explained that these studies, though conducted "in an unfocused and low priority vein," had laid the groundwork for SDI exploitation of Moon and asteroid resources. The La Jolla workshop was, he added, the first to consider the defense implications of the 1970s concepts.

Lunar prospector: Apollo 16 astronaut Charles Duke collects geologic samples in the Descartes region of the Lunar Highlands in April 1972. The Lunar Roving Vehicle is just visible among rocks and boulders in the background. Image credit: NASA.

At the time of the La Jolla workshop, relatively little was known of near-Earth space resources. Five Lunar Orbiter spacecraft had imaged much of the Moon at modest resolution and selected areas of it — mostly corresponding to potential Apollo landing sites — at higher resolution. NASA had landed Apollo astronauts at six sites between 1969 and 1972 and scientists had analyzed many of the more than 2400 geologic samples they collected. In addition, Apollo astronauts had surveyed the Moon from lunar orbit using remote sensors. These provided low-resolution data on the composition of perhaps 10% of the lunar surface.

Scientists had hypothesized since 1961 that permanently shadowed craters at the lunar poles might contain ice deposited by comet impacts. The lunar poles, far from the "Apollo Zone" — the near-equatorial region where orbital mechanics dictated the Apollo Lunar Modules could land — nevertheless remained unexplored.

In 1983, only 75 near-Earth asteroids (NEAs) had known orbital paths; the rate of discovery in the late 1970s/early 1980s suggested a population of sizable NEAs numbering many thousands, of which perhaps 20% would be readily accessible to prospecting spacecraft (these early gross estimates have been revised downward over the years). Meteorites collected on Earth were assumed (correctly) to have originated among the NEAs, but for the most part they could not yet be traced to specific asteroids.

The La Jolla workshop report thus urged more exploration as an early step toward exploitation of near-Earth resources. An automated prospecting spacecraft that would pass over both lunar poles during each orbit — a Lunar Polar Orbiter (LPO) — topped the Workshop's list of "projects to be started immediately." A spacecraft in lunar polar orbit could pass over the entire lunar surface in daylight every month.

In addition, the La Jolla workshop report recommended that efforts to discover and perform initial analyses of NEAs using Earth-based telescopes should be stepped up dramatically. It noted that, in terms of NEAs accessible to spacecraft, "the most promising targets very likely have not, as yet, been detected." The workshop report then urged NASA to carry out a series of automated NEA rendezvous missions.

In 1983, NASA's piloted spaceflight focus was on working the bugs out of the Space Shuttle, which, despite a minimal flight record (the eighth Shuttle mission flew between the La Jolla workshop and completion of the Fletcher Report), already had an extensive manifest of planned missions. Many within the space community hoped that President Reagan would soon green-light a NASA Space Station that would be launched in pieces in the payload bays of Shuttle Orbiters and assembled in low-Earth orbit (LEO). They expected that auxiliary spacecraft, including piloted Orbital Transfer Vehicles (OTVs) for reaching beyond Shuttle/Station orbit, would be based permanently at the Station.

An Orbital Transfer Vehicle (left) maneuvers in lunar orbit near a tank farm and a Moon lander. This 1983 concept art by Pat Rawlings illustrates a lunar oxygen mining infrastructure: SDI-related facilities and vehicles in lunar orbit would no doubt have appeared very similar. Image credit: NASA.

The La Jolla workshop participants saw in the OTVs the potential for carrying out piloted mining missions to the Moon and NEAs. The key upgrade that would make such missions possible, the workshop report explained, was a reusable heat shield that would enable OTVs to use Earth's atmosphere to slow down and capture into LEO using very little propellant. The report also recommended a lunar base feasibility study and studies of lunar and NEA mining and raw materials processing techniques.

Participants in the La Jolla workshop proposed more than a dozen SDI applications for lunar and asteroid resources. What follows is a description of the top three applications in terms of the mass of lunar and asteroid materials required.

Much of the wide-ranging prospecting, mining, and processing the La Jolla workshop advocated would lead to in-space manufacture of spacecraft "armor" made of lunar aluminum, asteroid iron, and aluminum and iron alloys created by adding small amounts of metals launched from Earth. The workshop report noted that military space systems launched from Earth tended to be made as lightweight as possible to reduce launch costs; this made them fragile and thus vulnerable if attacked.

"On the other hand," the workshop report continued, "if a relatively inexpensive (500-1000 dollars per kilogram) supply of construction materials became available high above Earth, defensive systems would likely be designed very differently, with greater capabilities and greater survivability." Layered armor for an SDI missile-defense platform with a cross-sectional area of 20 square meters would have a mass of about 400 metric tons; 100 such platforms would thus require about 40,000 metric tons of armor.

Layered metal armor would blunt attacks by kinetic-energy weapons (that is, systems that fired solid projectiles); for defense against particle beams or nuclear explosions, however, radiation shielding would be needed. The La Jolla workshop proposed using water from asteroids or (if any existed) from the lunar poles as neutron shielding for vulnerable electronic systems. Water would, of course, also have life support uses, and could be split into liquid oxygen and liquid hydrogen chemical rocket propellants.

After armor, the most important application of space resources in terms of mass was what the La Jolla workshop report dubbed "stabilizing inertia.” An enemy attack might cause a missile-defense platform to spin out of control even if its armor shielded it from damage. Mounting the platform on a chunk of raw asteroid would greatly increase its mass, making it much harder to shove around.

Third after armor and stabilizing inertia were heat sinks. The La Jolla workshop anticipated that missile-defense systems — for example, missile-destroying lasers powered by exploding nuclear bombs — would generate a great deal of waste heat very rapidly. Without places for the heat to go, they could easily destroy themselves. A heat sink might take the form of a large tank of water or large block of metal.

The Fletcher Panel submitted its hefty seven-volume final report to the Reagan White House on 4 November 1983. More than three decades later, most of the Fletcher Report remains classified, so the degree to which the La Jolla workshop influenced its findings is unclear.

Fifteen years into the 21st century, SDI has yet to match Reagan's vision, in no small part part because the Soviet Union — which Reagan dubbed "the evil empire" — collapsed in 1991. Instead of leading to a shield against massive Soviet nuclear attack, SDI became the most important space technology development program since Apollo. Neither the ongoing Discovery Program of cheap, relatively frequent automated lunar and planetary missions nor the low-cost automated Mars missions of the 1996-2008 period would have been possible without the technology infusion from SDI.

Image credit: NASA/USGS.

The pioneer for these missions was Clementine, a joint project of the SDI Organization (later renamed the Ballistic Missile Defense Organization — BMDO), the U.S. Air Force, Lawrence Livermore National Laboratory, the Naval Research Laboratory, and NASA. Stewart Nozette led the Clementine mission. The octagonal 227-kilogram Clementine spacecraft, intended mainly as a BMDO technology demonstrator, lifted off atop a repurposed Titan II missile from Vandenberg Air Force Base on 25 January 1994.

The Clementine spacecraft entered lunar polar orbit on 19 February 1994, where it carried out the first U.S. lunar exploration mission since Apollo 17 in December 1972. It surveyed almost the entire lunar surface for two months. In collaboration with Deep Space Network antennas on Earth, it prospected for ice in the permanently shadowed lunar polar craters. Clementine researchers interpreted data they collected as evidence for large deposits of water ice.

Almost as soon as it was announced at a Department of Defense press conference on 4 December 1996, this interpretation was questioned. Subsequent lunar spacecraft (Lunar Prospector, Chandrayaan-1, LCROSS, and the currently operational Lunar Reconnaissance Orbiter) have, however, confirmed the existence of hundreds of millions of tons of water ice at the lunar poles.

Permanently shadowed areas at the Moon's south pole stand out as a cluster of dark gray voids at the center of this Clementine image mosaic. Image credit: NASA/USGS.

On 5 May 1994, Clementine departed lunar orbit bound for the near-Earth asteroid 1620 Geographos. Geographos, discovered in 1951, is an S-type asteroid, meaning that it is composed mainly of nickel-iron. Radar images of Geographos show it to be extremely elongated (5.1 kilometers long, 1.8 kilometers wide) with pointed ends.

Unfortunately, just two days into its four-month journey, the spacecraft suffered a computer malfunction that caused it to expend all of its attitude-control propellant. The flyby had, incidentally, been the mission's primary goal when spacecraft and mission design began in March 1992; Clementine had been named in reference to the song "Oh, My Darling Clementine" because it would be "lost and gone forever" after it flew past Geographos. The lunar phase of the Clementine mission was added later.

A Clementine 2 asteroid-flyby spacecraft was proposed and studied, but did not receive development funding. Clementine 2 would have flown past near-Earth asteroids 433 Eros and 4179 Toutatis. During the flybys, it would have released impactors, the design of which would have been based on proposed missile interceptors. Instruments on board Clementine 2 based on missile-detection sensors would have recorded the impacts to enable scientists to determine asteroid surface properties. Work on Clementine 2 ceased in 1997.

The fate of Stewart Nozette forms a strange, sad denouement to this story. He was widely celebrated for his work on Clementine: among other awards, he received the NASA Exceptional Achievement Medal. He went on to play roles in the Lunar Reconnaissance Orbiter and Chandrayaan-1 missions. In 2006, 49-year-old Nozette left government service to head up the not-for-profit Alliance for Competitive Technology, which received NASA funding.

Nozette, who had "top secret" security clearance from 1989 to 2006, soon came under Justice Department scrutiny for misappropriation of NASA funds and tax evasion; he was then charged with espionage after attempting to sell classified information to an FBI agent posing as an Israeli spy. In 2011, he was sentenced to 13 years in Federal prison.

Sources

"Ex-White House Scientist Pleads Guilty in Spy Case Tied to Israel," S. Shane, The New York Times, 8 September 2011, p. A22.

"The Clementine Satellite," Energy & Technology Review, Lawrence Livermore National Laboratory, June 1994.

"Reagan is Urged to Increase Research on Exotic Defenses Against Missiles," C. Mohr, The New York Times, 5 November 1983, p. A32.

Defense Applications of Near-Earth Resources, Workshop Held at the University of California, San Diego, Hosted by the California Space Institute, 15-17 August 1983, S. Nozette, editor/workshop organizer, 31 October 1983.

Address to the Nation on Defense and National Security, President Ronald Reagan, 23 March 1983.

More Information

Earth-Approaching Asteroids as Targets for Exploration (1978)

Energy from Space: The 1970s DOE/NASA Solar Power Satellite Studies

An Apollo Landing Near the Great Ray Crater Tycho (1968)

Starfish and Apollo (1962)

Victory Lap

Image credit: NASA

Bob was a legend, or so he had read in the newspaper this morning. He didn't feel like a legend; he felt like he was playing hooky from his real job as NASA's Director of Space Shuttle Booster Operations. Then he reminded himself that this was an "inspection flight," so technically he was still flying a desk.

Of course, his desk for today was much more interesting than usual. Instead of wood grain and a pen set, he had a wide window above a complex console. A web-work and metal ejection seat replaced his leather desk chair, and an orange and white flight suit and helmet replaced his customary gray suit and light blue tie.

At the moment, a little more than seven million pounds of thrust pushed him back into his seat at the regulation 3.3 gravities of acceleration. The view out the window was a blue band shading to black and, above that, looking frankly enormous, the forward third of the Space Shuttle Orbiter Adventure.

"Booster 004, this is Houston. Bob, we are reading excess temperature on engine nine. Can you confirm that for us? Over." That was Danny in Mission Control.

Bob glanced at the computer screens. "Affirmative, Houston, we see that. Over."

"Flight Director says take no action," Danny said. "Modeling shows temp will stay within limits until shutdown. Over."

"We'll keep an eye on number nine. Thanks for the heads up. Over." Bob said, looking over at Ellen, his Commander on this flight.

She smiled, reached over, toggled Houston out of the mike loop. "That one always runs hot," she explained, "and they know it."

"The press corps wants to hear me talk, right?"

Ellen nodded vigorously, grinning. Then she toggled Houston back in and spoke. "Houston, we are 20 seconds from engine shutdown at my mark. Mark."

"Roger, Booster 004. Over," Danny said.

"Hey, Ellen," came another voice. It was Jim, Adventure's Commander for this Space Station mission. "Thanks for the lift. We're standing by for separation here. Over."

"Roger that, Adventure. We wish you smooth sailing. Over."

As Bob listened to the routine, relaxed conversation, he also listened to the noises from Booster 004. As liquid oxygen and liquid hydrogen ran past anti-slosh baffles and down drains that led to turbopumps, engine bell cooling channels, and thrust chambers, the Booster's big tanks emptied and gradually became echo chambers. They picked up and magnified the rumble of its 10 J2-B engines. The sound rapidly grew louder, as though a roaring dragon were struggling to climb against the acceleration through the nearly empty tanks toward the forward-facing cockpit.

"Houston here," Danny said. "Booster shutdown in 5, 4, 3, 2, 1 - "

The roar became a rapidly diminishing whine, and Bob felt himself tipping forward against his shoulder straps. "Houston," said Ellen, sounding loud in the sudden quiet, "we confirm shutdown. Over."

"Confirmed here, too," said Danny. "Adventure, separation in 5, 4, 3, 2, 1 -"

A clunk shook the cockpit. Bob looked down for a second, taking in the mass of data on the three computer screens, then looked back up and exclaimed, "Holy sh-, I mean, cow." He heard someone laugh, realized it was Cal in the observer's seat.

Adventure had looked huge before, when it was attached to Booster 004 and he could only see part of its underside. Now the delta-winged Orbiter moved slowly forward, up, and away. He'd seen Orbiter sep a thousand times on video, but that hadn't captured the graceful enormity of it. Then he saw the Orbiter's four rear-mounted engine bells and the tip of its swept-back vertical stabilizer.

Ellen leaned forward against her straps to get a better view of Adventure's underside. "Clean separation. Attachment fixture doors are closed. Over."

"Adventure confirms, over."

Danny spoke. "We see a good separation. Time to come back to Earth, Bob. Over."

Back to Earth. He was aware of Ellen's momentary glance, then she returned to scanning the computer screens. "Roger that, Danny. Over."

It was the fifth time he'd come back to Earth, and it was almost certainly the last time. The unofficial retirement age for Commanders and Pilots was 50, and he would turn 56 next month. Hell, he wore bifocals. His knees creaked. His top-level management job had let him finagle a Booster run as Pilot at his advanced old age - after all, he was Booster boss, he'd never done a run, and he was - at least on paper - still a member of the Astronaut Corps. That's what he'd told the Administrator; and, after letting him hang for a year, that damned political hack had finally granted him permission.

The first time he returned to Earth, it was in an Apollo Command Module with Jerry and Paul and nearly a hundred kilos of moon rocks. He'd been Command Module Pilot on Apollo 22, back in '73, which included the first week-long lunar surface mission. Jerry and Paul had landed in Marius Hills and he'd kept busy as a one-armed paper hanger operating a suite of instruments in lunar orbit. He didn't expect he'd fly again beyond low-Earth orbit, and he was thinking of finding a job in industry. Then President Rockefeller had pushed to extend Apollo again, and he'd opted to stay in.

The second time, just two years later, he was Commander on Apollo 26. He would never forget the feeling of stepping out onto the moon the first time. No Earth in the sky - his was the first Farside landing.

The third time he'd commanded Apollo 30. That launch was unique - they'd put an S-IVB stage, LM, and CSM on the back of an almost-new Space Shuttle Booster. NASA needed all its Saturn V S-IC and S-II stages to launch Space Station Cores to build up the Space Base, and someone had suggested that it should be possible to substitute a Shuttle Booster for the first two stages of the Apollo Saturn V. Turned out that they were right.

He'd landed with Ed next to the sprawling Webb Array in the Sea of Ingenuity. The multi-billion-dollar teleoperated science complex had gone silent almost as soon as it was completed, so NASA, under a lot of pressure from an angry President and Congress, cobbled together a rapid-response repair mission. By then he was the only Farside explorer left in the Astronaut Corps, so they'd tapped him for the job. At 47 years of age, he was as old as Al Shepard had been when he'd stepped out onto the moon during Apollo 14 in 1971.

The Array wasn't built for astronaut servicing. Nevertheless, they'd managed to untangle a couple of robots from some poorly placed cables, tighten connectors, cycle the breakers - they'd had to twist the "hand" off a hapless robot to use it as a tool to manipulate the breakers since they weren't designed for fat gloved human fingers - and heard cheers in Mission Control as the Array came back to life.

The fourth time was Orbiter Flight Test-5 in '80. He'd visited the Space Station for two weeks to give the new Orbiter Endurance a good long soak in the near-Station Earth-orbital environment and to serve as a biomed guinea pig. ("Space and the Aging Astronaut," they'd called the experiment program, until he threw a fit. Looking back, he felt foolish for objecting to the name. It was accurate.) He knew that it was his final flight.

Then that old Russian cosmonaut, desk-bound for 20 years and so fat that they had to build a custom couch so he could ride Soyuz, flew an "inspection tour" mission to the Zarya Station. That planted the seed, and now here he was again, returning to Earth for the last time.

"Booster, this is Houston, please verify completion of your avoidance turn," said Danny, making him jump a little and bringing him back to the here and now. "Booster here," said Ellen. "Turn completed. Over."

"Adventure, second stage ignition in 5, 4, 3, 2, 1 -," Danny said.

"Roger, Houston, Adventure here, we have ignition. Four good engines."

Bob had nearly lost sight of the Orbiter as he mused about his space career. However, as the four engines came on, pulling liquid hydrogen/liquid oxygen propellants from Adventure's internal tanks, he saw it right away even though it wasn't dramatic. Just four round white lights set against the blue-black background. The Orbiter disappeared behind the upper edge of the window.

"Roger that," Danny said. "Woo-hoo!" said Jim. "We are headed uphill."

"Booster 004, this is Houston. We have you at the top of your parabola at 231,121 feet. Please run through reentry checklist. Over." "We're on it, Houston. Over," Ellen said.

The checklist included checking the switch settings for the ABES - the Air-Breathing Engine System. Everything was in its place, ready for jet engine deploy and activation at 23,000 feet.

"Ellen, now descending past 220,000 feet. Please check attitude for reentry," Danny said.

"Roger, Houston. We're seeing some glow outside," Ellen reported. A few moments later, a series of distant pops sounded. "Thrusters firing to auto-trim attitude," she added.

The glow outside grew in intensity, and Bob could feel himself growing heavy. Then he felt the big Booster perform a stately bank and turn, shedding energy. A minute later, with the glow fading, it banked again, then its nose slowly dropped. The blue sea and the hazy east coast of Florida spread out before them. He thought that he could make out the Gulf of Mexico on the far side of the Florida peninsula. He saw Ellen grin. She toggled Houston out of the loop. "I never get tired of that view. Orbiters don't see it, since they mostly come in from the west."

"When are you going to orbit, Ellen?" Bob asked. Ellen had flown more Booster flights than anyone; by now she should have been an Orbiter Commander.

"Oh, not all of us want to go uphill," she said. She laughed. "I want to be the very best Booster pilot NASA has. Besides, I like having you for a boss." Before Bob could reply, she toggled in Houston again.

"Houston, this is Booster 004, we are in gliding descent, awaiting ABES deploy. Rudder and ailerons active. Minor buffeting. Can you give me a weather report? Over."

"Booster, we have you right on course. Weather at Strip 01 is fine. Mild crosswinds - five to eight knots. Light rain," said Danny.

"Roger that," she said.

A minute later, as Bob scanned the computer screens, Cal spoke. Bob kept forgetting he was sitting back there. "I'd like to do three or four Booster flights and then do Orbiter flights after that. Not that I mind having you as a boss, Bob."

"I have reports on your sim runs. I think you'll be out of my hair pretty quick," said Bob. Cal laughed.

"OK, boys," Ellen said, "we are passing 27,000 feet. Prepare for ABES deploy at 23,000, brake-flaps at 22,500." Eight ABES were folded up in compartments in the thickest parts of the Booster's delta wings and two in its belly, between its main landing gear doors. As a fail-safe, the jet engines were designed to drop and lock with gravity doing the work.

"Booster, this is Houston. Good news - Adventure is in orbit," Danny said. A long pause. "We have you at 23,500 feet, good descent angle and speed. ABES deploy on my mark - 3, 2, 1 - mark."

There was a series of clunks, and for a moment Ellen looked alarmed - a look Bob hadn't seen on her face before. He didn't like it.

"Houston, please confirm ABES deploy. Also brake-flaps. Over," she said, keeping her voice level.

There was a pause. "Uh, Booster, we're looking at the data. Stand by," Danny said.

There was another pause, longer this time. Ellen turned to Bob, opened her mouth - then Danny interrupted.

"Ellen, we see eight engines deployed. Numbers 5 and 6 are not deployed, as best we can tell. You're coming in fast, which supports that hypothesis. Less drag with just eight ABES hanging. We have no data on the brake-flaps. Seems we have some dead sensors. Do you want to have a second try at 5 and 6? Over."

Ellen was checking computer screens. "Standby on that, Houston. Request permission to commence ABES start."

"You know best, Booster. Over." Ellen toggled Houston out of the loop.

Image credit: NASA

"OK, Bob, Cal, we have a situation," Ellen said, pressing buttons and flipping switches. "We are now two ABES out. Booster is certified for safe descent and landing with one ABES out. Five and six - the belly ABES -  are not deployed, so we don't have their drag, and we're coming in hot, putting too much pressure on the wings and the deployed engine connections as we get deeper into the atmosphere. Plus, maybe no brake-flaps. This could get messy."

As she spoke, the deployed ABES whined. The Booster shook. "Good, we have all eight deployed ABES running normally. I can control our descent so we don't melt our wings. Bob, watch the ABES temps for me. Cal, stay sharp. Tell me if you see or hear anything peculiar. Got that?"

"Affirmative," Cal and Bob said simultaneously.

Bob looked at the computer screens. He didn't like what he saw. "Ellen, we have over-temps on 1, 10, 9, and 2."

"All the outboard engines, as you'd expect. Tell me when they exceed safe limits."

"They exceed safe limits."

Ellen grimaced. She toggled Houston in. "OK, Houston, we've slowed some, but we're still too fast, and the outboard ABES are overheating. I want to try to deploy 5 and 6 now to get some more drag. Over."

"Roger that, Booster. Uh, Ellen, Flight Director has activated emergency teams. Over," Danny said, his voice shaking a little.

Ellen swore under her breath. "Thank you, Danny." As she spoke she flipped the switches to deploy ABES 5 and 6.

"Computer 1 is down," Bob said. Long pause. "But so are ABES 5 and 6."

"Hot-damn," said Ellen. She thumbed the activation button. A new whine began.

"Booster, your descent is off-nominal for KSC Strip 01. We need you to reset for contingency landing in Orlando," Danny said. "Teams there are activating."

Bob said, "We have 10 good ABES. I think. One and 10 still exceed temp limits. Five is running slow." He looked again. "Or maybe not at all. Make that nine good ABES."

"Houston, acknowledge Orlando landing. I have one ABES out and two at risk. Brake flaps read open, but it doesn't feel like it. You might want to activate Tampa and the Coast Guard," Ellen said.

A pause. "And Coast Guard. Roger, Ellen."

Ellen toggled out Houston. "So, boss, Cal, I just said we might ditch in the Gulf."

Bob grinned. "I got that. I've lived through some splashdowns."

Ellen smiled back, glad for his attempt at humor. "You're the last guy left in the Astronaut Corps who can say that. But you splashed in Apollo gumdrops. I don't have to tell you that a Booster ditch is officially unsurvivable. I believe the book on that. With all our big tankage, we're too fragile to hold together if we belly flop. Dammit. Right now our landing point is drifting past Orlando." She cycled a switch. "Where are those damned brake flaps? It's like they fell off."

The cabin shook. Ellen shook her head, toggled Houston back into the com loop. "We're finally subsonic, Houston. Over."

Danny spoke. "Ellen, we've told Tampa to expect you. Coast Guard and Air Force assets are moving into position for sea recovery, but we advise against water landing. Over." Ellen rolled her eyes.

Bob looked closely at the computer screens. "Computer 2 is down," he said quietly.

"Oh, this is not fair," said Cal.

"So now we can't rely on on-board data for our landing point. Houston, do you see we are minus two computers? Over." Ellen sounded exasperated, but otherwise in control.

"Affirmative, Booster 004, we see that. Still have you targeted for Tampa. Over."

"But Tampa has no alignment circle," Bob muttered, too softly for anyone to hear.

"But Tampa has no alignment circle," Danny said a moment later. "Flight Director recommends you eject over water. Over."

Cal coughed and smiled weakly. "I cannot eject. It's the risk the observer runs."

"Oh, hell," said Ellen. "Houston, we are trying for Tampa. It's that or lose Cal."

Bob cleared his throat. "Excuse me - Ellen, Danny, Cal, anyone else who's listening - I am pulling rank here. We cannot land in Tampa without putting the local population at risk. Ellen and Cal will eject over water. No - no time for debate," he said, louder, overriding their objections. He began to unbuckle his straps. "Cal, get your ass over here. I'm observer now."

Bob stood, turned, and began to unbuckle Cal, who, after a few stunned moments, helped him. Then Cal took Bob's seat. Bob waited to see if Cal could get himself buckled in, saw that despite his shaking hands he could, then sat in the observer seat. He buckled in, then looked around. "You know, for an observer seat, this is a crap view."

Ellen drew a deep breath, let it out, and turned back to her controls. "OK, let's do this," she said. She toggled out Houston. "Like in those drills we never thought we'd actually need."

She checked and readied her suit and helmet and armed her seat, calling out each action as she performed it. Cal followed along. Then she confirmed that Cal was ready.

When that was finished, she said, "You can help me, guys. Just tell me if you hear or see anything unusual. I trust you more than the one computer we have left."

Bob knew there was really nothing left for them to do. He admired Ellen for trying to distract them from that fact, however.

"There's a grinding noise aft," Cal said. "I can feel the vibration of it when I put my hand on the console."

"Yes, that's ABES 5's turbofan free-spinning in the air-flow - saw it just before the second computer went down," said Bob. "We might've had a fire in there."

Ellen looked puzzled. "If we had a fire, why no alarm?"

"Houston here." It was a new voice. Ellen worked the coms toggle. "This is Gene Kranz. We confirm no Tampa landing. As I understand it, Cal and Ellen are in ejection seats. You will eject at 4000 feet in" - a long pause - "about 90 seconds. Bob?"

"Yes, Gene?"

"Godspeed. Over."

"Thank you, Flight Director. Over."

Ellen and Cal's faces were ashen. Now it was his turn to give his shipmates something new to think about. He made a sign for Ellen to toggle out Houston. She complied.

"Kids, listen. Be sure you keep your heads down when your seats light off. We're low enough to breathe, so disconnect your breather, mask, and hoses so they don't catch on something or hit you in the face. Crappy design - I kept trying to get that changed. You don't need that junk, so leave it here. On the floor. Got it?"

"Yes, boss," said Ellen. Cal nodded as he began to dismantle his breathing gear.

As they took off their breathing apparatus, Bob continued. "When they do the post-mortem on this flight, tell them I said to look into the electrical system. I think the alarm shorted in the ABES 5 compartment and started this mess. Three wiring trunks cross right over 5 and 6. Probably melted some wires. Tell them I fixed the damned Webb Array, so I know all about electricity. Got that?"

"You know all about electricity," Ellen said. "Got it." Bob winked.

Then he reached under the observer seat. "I'm going to use this seat cushion to protect myself from the blast when you guys go. I plan to live through this. If I don't, though, please tell the Administrator that I said he's a useless hack."

Cal's eyes went wide. Ellen nodded in solemn agreement and Bob couldn't help but smile.

"You can be the very best Orbiter Commander NASA has," he told Ellen.

"Not if I tell the Administrator that," she said. Then they both laughed. Ellen's laugh was only a little forced.

"This is Houston. Please confirm your ejection seats are armed. Over."

Ellen toggled in Houston, checked Cal's seat again. "This is Booster 004 - seats armed."

"Eject on my mark." Ellen and Cal grasped their loud handles and Bob brought up his improvised shield. "5, 4, 3, 2, 1 - mark!"

Booster 004's cabin became the inside of a tornado, and despite his headphones and helmet Bob was deafened. He felt a wave of intense heat. The seat cushion was torn from his hands - he saw it spin away out the now-open roof of the cabin. Glass broke somewhere in the cabin, and the Booster lurched as the open roof panel increased drag.

Then there was relative calm. Bob looked out the window. The view was better with the ejection seats gone, he mused.

"Houston, this is Booster 004. Please be advised that Ellen and Cal are away. Over." Before anyone could say anything, Bob unplugged his mike and headphones. Out the window, he saw the glint of Sun off water.

"I'm returning to Earth for the last time," he said to the empty cabin. "And this time I mean it."

Sources

"Space Shuttle Descriptions for Operations Support Systems Study - Case 900," D. Cassidy, Bellcomm, 31 December 1970.

"The Space Shuttle Booster," R. Lynch, General Dynamics/Convair Aerospace; paper presented at the 8th Space Congress in Cocoa Beach, Florida, 1 April 1971.

Space Shuttle Booster Air Breathing Engine System, Report No. 76-115-0-505, Rockwell/IBM/American Airlines/Honeywell/General Dynamics, no date (1971).

More Information

An Alternate Station/Shuttle Evolution: The Spirit of '76 (1970)

McDonnell Douglas Phase B Space Station (1970)

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

What if a Space Shuttle Orbiter Had to Ditch? (1975)

Rube Goldberg's Space Shuttle

By mid-1971, this was one of the two leading Space Shuttle design configurations. The first stage, bearing the letters "USA" and a single stabilizing oversized tail fin, might have been derived from the Saturn V S-IC first stage. Image credit: NASA.

For Americans above a certain age, the phrase "Rube Goldberg Machine" elicits a chuckle or perhaps a sneer, depending on the context of its use. Rube Goldberg (1883-1970) was an award-winning cartoonist. His most famous drawings were of whimsical machines that accomplished a simple task in the most complex way possible.

It is not too unkind, given that most of the factors that led to its complexity were outside of NASA's control, to place the Space Shuttle in the category of a Rube Goldberg Machine. It began as a simple idea — economically deliver crews, supplies, and equipment to an Earth-orbiting Space Station — and, through conflicting, expanding demands placed on it, unwise cuts in funding for its development, and deferral of the Space Station it was meant to serve, grew into something large, complex, and costly.

Throughout the Space Shuttle design process, NASA fought a rearguard action to preserve reusability. In 1969, the U.S. civilian space agency sought a fully reusable Shuttle design with a piloted Booster and a piloted Orbiter, each carrying liquid propellants for placing the Orbiter into Earth orbit. Inadequate funding support from the Nixon White House and Congress coupled with a U.S. Air Force requirement that the Orbiter include a payload bay at least 60 feet long and 15 feet wide soon made that design untenable, however.

NASA and its contractor teams took a rapid series of cost-cutting steps during 1970-1972. The design process became messy and almost untrackable, with concepts proposed, abandoned, and proposed again in rapid succession or even simultaneously by different contractor and NASA teams.

The piloted Booster shrank after engineers tacked a pair of reusable solid-propellant rocket motors onto its tail. Then it ceased to be piloted, becoming part of what amounted to a three-stage rocket. Riding bolted to the top or side of the Booster's expendable second stage, the piloted Orbiter became in effect a reusable third stage that would complete its climb to Earth orbit by burning liquid hydrogen (LH2) fuel and liquid oxygen (LOX) oxidizer carried in tanks inside its streamlined fuselage.

In part to prevent the Orbiter from growing out of all proportion as its payload bay grew, NASA moved low-density LH2 out of the Orbiter fuselage into cheap expendable drop tanks. The move also ended worries about safe containment within the Orbiter of volatile LH2, which is prone to slow seepage even through solid metal.

The Orbiter carried LOX for its ascent to orbit inside its fuselage for a little while longer. By August 1971, however, the delta-winged Orbiter contained only enough propellants to maneuver in orbit and to slow itself so that it could deorbit and reenter Earth's atmosphere. At first, its orbital maneuvering engines were expected to burn LH2/LOX, but then NASA substituted hypergolic (ignite-on-contact) propellants.

During the same period, the preferred Shuttle stack design flip-flopped between two candidates. One (image at top of post) had two LH2/LOX stages stacked one atop the other. The first-stage engines were mounted directly beneath their stage, as on a conventional rocket. The engines for the second stage were built into the tail of the Orbiter mounted on its side. They would ignite at altitude after the first stage separated and, owing to their position on the side of the second stage, would thrust off center.

The first stage would be reusable; after depleting its propellants and separating from the second stage, it would deploy parachutes and lower to a gentle landing at sea, where it would bob with its engines pointed at the sky. A specially designed ship would then recover it and tow it to port for refurbishment. The second stage would reach orbit attached to the Orbiter, then would separate, reenter, and break up over the ocean.

The other candidate design (image below) featured a reusable Orbiter and a pair of reusable LH2/LOX boosters mounted on the sides of a single large expendable External Tank (ET). The lightweight ET's interior would be split between a small tank for LOX and a large one for LH2. Both the twin boosters and the tail-mounted Orbiter engines would ignite on the launch pad. The side-mounted boosters would expend their propellants and fall away about two minutes after liftoff. They would each deploy parachutes and descend to a gentle ocean landing to await recovery. Pipes leading from the ET tanks would feed propellants to the Orbiter's engine cluster throughout ascent to orbit.

That looks familiar: the other Space Shuttle stack design leading the pack by mid-1971. Note off-center thrust plumes from the delta-winged Orbiter's tail-mounted engines (lower left). Image credit: NASA.

In a final cost-cutting move, NASA replaced the reusable liquid-propellant boosters with reusable solid-propellant boosters. The liquid-propellant boosters could be turned off in the event of a major malfunction; the solid-propellant boosters could not.

Mounting engines on the reusable Orbiter meant that they would be returned to Earth for refurbishment and reuse. The resulting off-center thrust troubled many engineers, however, because it meant that thrust forces would be transmitted through the Orbiter to the second stage (in the case of the first Shuttle design alternative) or the ET (in the case of the second). This would place added stress on the Orbiter, its links to the second stage or ET, and the second stage or ET. Links between the second stage/ET and the Orbiter would include propellant pipe connections, which engineers expected would be prone to leaks even without the added stress of off-center thrust.

Off-center thrust also meant that the short LOX tank, when full the heaviest part of the second stage or ET, had to be situated atop the long LH2 tank, the lightest part of the second stage or ET. Putting the dense LOX on top helped the Shuttle stack to remain stable in flight as the Orbiter's engines rapidly emptied the second stage or ET and the stack's center of gravity shifted, but it also placed added stress on the second stage or ET structure. Because the LOX at the top of the second stage/ET needed a long pipe to reach the engines on the Orbiter's tail, the arrangement also increased the risk of propellant pipe rupture.

During the 1970-1972 Shuttle design evolution, several engineers proposed and re-proposed a novel alternative to off-center thrust: a cluster of reusable engines that would operate attached to the bottom of the expendable second stage or ET. After the Orbiter reached Earth orbit and its main engines shut down, the engine cluster would be detached from the second stage or ET and, using an armature system of booms or struts, be swung into a storage compartment inside the aft end of the Orbiter fuselage.

The second stage or ET would then be cast off. In the case of the ET, vented residual propellants would cause it to tumble, rapidly reenter the atmosphere, and break up. When the astronauts on board the Orbiter completed their mission in Earth orbit, the engine cluster would return to Earth with them, where it would be removed from the compartment, refurbished, and mounted on a new second stage or ET.

The NASA Manned Spacecraft Center — renamed the Lyndon B. Johnson Space Center (JSC) in February 1973 — managed Space Shuttle development. Shuttle engineers were quick to reject the swing-engine design. They did this mainly because its armature system seemed overly complex and thus prone to malfunctions.

The Rube Goldbergian swing-engine concept would not die, however. In March 1974, in fact, JSC chief of engineering Maxime Faget (co-designer of the Mercury capsule and a 1969 all-reusable Shuttle) and JSC engineers William Petynia and Willard Taub filed an application to patent the swing-engine design. By then, the decision to settle on the second stack configuration described above was two years old (NASA Administrator James Fletcher announced the choice on 16 March 1972).

The JSC engineers proposed three swing-engine design approaches. The U.S. Patent Office granted their patent on 30 December 1975.

All of their design approaches would, they argued, eliminate stress on the Shuttle stack caused by off-center thrust, enable transposition of the ET LOX and LH2 tanks, and improve stack flight characteristics during ascent through Earth's atmosphere. The results would, they explained, include a lighter Orbiter and ET, more payload, and greater safety.

As a bonus, the swing-engine system would enable the Orbiter to adjust its center of gravity after it released or took on an orbital payload, thus improving its reentry and atmospheric gliding flight characteristics. It would do this by shifting the engine cluster forward toward the back of the Orbiter payload bay using the same mechanical armature system that would swing the engines away from the bottom of the ET. The armature system would also serve to gimbal (swivel) the engines to steer the Orbiter/ET stack during ascent to orbit.

Other benefits would spring from the swing-engine design. The ET and engine cluster could be tested together without an Orbiter attached. All piping linking the Orbiter and the ET would be eliminated. Separable links between the ET and the engine cluster would be required, of course. The engine cluster would, however, be quite small and light compared to the Orbiter; this meant that it could be easily mounted on the ET, tested for leaks, and (if necessary) removed and repaired before flight.

First method for transferring engine cluster from aft end of the ET to storage in the Orbiter aft fuselage. 1 = ET; 2A = mounting ring for four engines (in thrust position on ET); 2B = mounting ring for four engines (in stored position in Orbiter aft fuselage); 3 = joint linking lower armature to engine ring (1 of 2); 4 = lower armature strut (1 of 2); 5 = upper armature strut (1 of 2); 6 = joint linking upper armature to Orbiter aft fuselage (1 of 2); 7 = trailing edge of wing (1 of 2); 8 = opening in aft fuselage for engine cluster storage; 9 = solid-propellant ascent abort rocket (1 of 2); 10 = vertical stabilizer. Image credit: NASA/U.S. Patent Office.

The JSC engineers' first swing-engine design, illustrated above, assumed a quartet of Shuttle engines, a single vertical stabilizer, and an aft-pointing fuselage opening. The armature system would swing the engines into the fuselage so that their engine bells pointed aft.

The second design, illustrated below, assumed three Space Shuttle engines in a vertical row and an Orbiter with twin out-splayed vertical stabilizer fins. The armature system would swing the engines up and over the aft end of the Orbiter fuselage and lower them into a rectangular slot between the fins. After a horizontal landing on Earth, their engine bells would point skyward.

Second method for transferring the Space Shuttle engine cluster from the aft end of the ET to the storage space in the Orbiter aft fuselage. 1 = Orbiter payload bay; 2 = LOX tank in aft end of ET; 3 = ET; 4 = vertical stabilizer (1 of 2); 5A = engine cluster in thrust position on aft end of External Tank; 5B = engine cluster in stowed position in Orbiter aft fuselage; 6A = centerline of engine cluster in thrust position; 6B = centerline of engine cluster in stowed position; 7A = armature strut for transferring engine cluster (thrust position) (1 of 2); 7B = armature strut for transferring engine cluster (stowed position) (1 of 2); 8 = center armature joint (1 of 2); 9 = path of center armature joint (8) during engine cluster transfer to stowed position. Image credit: NASA/U.S. Patent Office.

The JSC engineers' third swing-engine design also assumed three engines arranged in a vertical row, but could be used with either single or double vertical stabilizer Orbiter configurations. The armature system would tilt the engine cluster 45° and slide it on rails into a rear-facing opening in the aft fuselage. As with their second design, the engine bells would point upward after the Orbiter glided to a landing.

Orbital Flight Test-1 (OFT-1), also known as Space Transportation System-1 (STS-1), the first flight of the Space Shuttle. Columbia lifted off from Launch Complex 39A at Kennedy Space Center, Florida, on 12 April 1981, and landed at Edwards Air Force Base, California, two days later. Veteran astronaut John Young was Commander and rookie Robert Crippen was Pilot. Image credit: NASA.

The swing-engine concept had, of course, become a mere curiosity well before the U.S. Patent Office granted Faget, Petynia, and Taub their December 1975 patent. Following the March 1972 selection of the Shuttle stack configuration, NASA awarded Rockwell International the contract to build Space Shuttle Orbiters on 26 July 1972. The company built a total of five space-worthy Orbiters, each with three Space Shuttle Main Engines mounted in a triangle on their aft fuselages, over a span of more than 20 years.

The Orbiters functioned admirably, though they needed far more costly refurbishment and maintenance than NASA envisioned when it proposed its all-reusable Space Shuttle design in 1968-1969. Booster system malfunctions claimed two Orbiters and their seven-person crews, however. Challenger was destroyed on 28 January 1986 when a solid-propellant booster field joint burned through, leading to ET structural failure and Orbiter break-up 73 seconds after launch. Columbia, the first Orbiter to orbit Earth (12-14 April 1981), was lost after foam insulation on the ET it rode broke loose during ascent and struck and damaged its wing leading edge. This led to wing structural failure and Orbiter breakup during reentry on 1 February 2003, at the end of a 16-day mission.

Sources

Patent No. 3,929,306. Space Vehicle System, Maxime A. Faget, William W. Petynia, and Willard M. Taub, NASA Johnson Space Center, 5 March 1974 (filed), 30 December 1975 (granted).

Space Shuttle: The History of the National Space Transportation System, the First 100 Missions, Dennis R. Jenkins, 3rd Edition, 2008.

Wikipedia: Rube Goldberg Machine (https://en.wikipedia.org/wiki/Rube_Goldberg_machine — accessed 28 November 2016)

More Information

George Landwehr von Pragenau's Quest for a Stronger, Safer, Better Space Shuttle

Series Development: A 1969 Plan to Merge Saturn V and Shuttle to Spread Out Space Program Cost

One Space Shuttle, Two Cargo Volumes: Martin Marietta's Aft Cargo Carrier (1982)

An Apollo Landing Near the Great Ray Crater Tycho (1969)

Splat! Tycho crater (lower center) is the the most prominent bright surface feature in this NASA image of the full Moon. Linear rays originating at the crater can be traced outward for hundreds of kilometers.

Of the seven automated Surveyor spacecraft NASA launched to the Moon between May 1966 and January 1968, only the last, Surveyor 7, aimed for a target selected specifically for its scientific value. Surveyors 2 and 4 failed, while Surveyors 1, 3, 5, and 6 soft-landed at flat mare (basalt plain) sites in the "Apollo Zone," the near-equatorial band readily accessible to piloted Apollo Lunar Module (LM) spacecraft. The successful Apollo Zone Surveyors performed valuable scientific investigations, but their main purpose was to image their landing sites and test surface bearing strength to help assure mission planners that the lunar terrain was smooth and stable enough to permit Apollo astronauts to land safely.

Surveyor 7, by contrast, aimed for the rugged northern flank of Tycho crater, one of the most prominent features on the Moon's Earth-facing nearside hemisphere. The 85-kilometer-wide asteroid impact scar, centered at 43° south latitude in heavily cratered highlands terrain, is surrounded by an extensive system of bright rays best viewed when the Moon is full. The rays are made up of ejecta blasted out when Tycho formed about 110 million years ago. As ejecta fell back onto the Moon, it stirred up more material, generating a ray cascade extending up to 1500 kilometers from Tycho.

Surveyor 3 (above) served as a pinpoint landing target for Apollo 12 astronauts Charles Conrad and Alan Bean in November 1969. During their second moonwalk, they stopped by the derelict lander to collect parts and take pictures for engineering analysis. Surveyor 7 resembled Surveyor 3, but included noticeable differences; most obvious was the addition of the deployable alpha-scattering instrument. Image Credit: NASA.

Hand-laid mosaic of images from Surveyor 7 illustrating the rocky, rolling nature of the terrain north of Tycho. Image credit: NASA/USGS.

Surveyor 7 lifted off from Cape Kennedy atop an Atlas-Centaur rocket on 7 January 1968. It landed on 10 January at 40.9° south latitude, 11.4° west longitude, just 2.5 kilometers from its intended target and 30 kilometers from Tycho's rim, on the ejecta blanket surrounding the crater.

Less than an hour after touchdown, the three-legged, solar-powered lander returned the first of more than 21,000 images it would beam to Earth. Some of these were stereo pairs, enabling scientists to precisely locate the many varied rocks and boulders visible in the field of view of Surveyor 7's scanning camera. Other images were assembled into panoramic mosaics that show lunar landscape features up to 13 kilometers away from the lander.

Among the features most intriguing to lunar scientists were so-called "lakes" of relatively dark material. They lay in depressions and had relatively flat surfaces. Curving, branching trenches etched many of these small dark plains. Some scientists interpreted the lakes as signs of recent volcanic activity, the "holy grail" of 1960s lunar exploration.

Tycho, its ejecta blanket, and the Surveyor 7 landing site as imaged by NASA's Lunar Reconnaissance Orbiter (LRO). The spacecraft entered lunar polar orbit in June 2009. The ejecta surrounding the crater partly covers and "blurs" lunar surface features that existed before Tycho was formed. Image credit: NASA.

In keeping with its science-focused mission, Surveyor 7 carried more scientific apparatus than any of its predecessors. Besides its camera, the lander carried an alpha-scattering device for determining the composition of rocks and dirt and an arm-mounted digger. The former had flown previously on Surveyor 5 and Surveyor 6; the latter on Surveyor 3.

At first, the alpha-scattering device failed to deploy, but flight controllers were able to direct the digger to push it down into contact with the lunar surface. They later used the arm/digger to position the alpha-scatterer on a rock and in a trench the digger had excavated. They found that the surface material at Surveyor 7's highlands landing site contained more aluminum than did that at the mare sites the other Surveyors explored.

Controllers were unable to place the alpha-scatterer in contact with boulders on a low ridge near Surveyor 7, some of which might have been blasted from kilometers below the lunar surface by the Tycho impact. They were far beyond the digger's 1.52-meter maximum reach. Nor were controllers able to move the instrument to the dark material of the lakes, the nearest of which lay about a kilometer from the lander. When the Surveyor 7 mission ended on 21 February 1968, much was known about its complex landing site, but much else remained mysterious.

Lunar Orbiter image of the Surveyor 7 landing area. The two dotted lines originating at the Surveyor 7 ("S.VII") touchdown point indicate the limits of the field of view of the lander's scanning camera. North is toward the top. Prominent in the right half of the image is a dark lake-like feature, the "shore" of which is located about a kilometer away from Surveyor 7. Image credit: NASA.

The lakes and the tantalizing variety of rocks near Surveyor 7 caused some lunar scientists to call for an Apollo mission to the site. It was far outside the Apollo Zone, but could be reached during certain times of year if conservative Apollo mission rules were relaxed.

In August 1969, less than a month after Apollo 11, the first piloted Moon landing mission, U.S. Geological Survey (USGS) scientists worked with Bellcomm, NASA's Apollo planning contractor, to rough out the surface portion of an Apollo Tycho mission. It would begin with a pinpoint LM landing a kilometer southeast of Surveyor 7.

The pinpoint landing would be required if the astronauts were to follow the geologic traverse routes the Bellcomm/USGS team planned. The LM descent stage would carry enough propellants to enable the Tycho mission crew to at least partly compensate if their LM missed its designated touchdown point. This was deemed an especially important capability because the Apollo 11 LM Eagle had landed off course at the edge of its landing ellipse.

On the basis of Surveyor 7 and Lunar Orbiter V images, the Bellcomm/USGS team judged that the Tycho site was too rocky for a jeep-like lunar rover to navigate. They suggested that the astronauts explore on foot within an operational radius of about 2.5 kilometers centered on their LM.

Proposed new "constant volume" hard suits tougher and more flexible than the mostly fabric Apollo suits would, they anticipated, make possible speedy hikes over rugged terrain. The new suits would also permit the astronauts to operate on the surface for up to seven hours at a stretch. They would spend 54 hours at the Tycho landing site, providing enough time for three seven-hour traverses.

LRO image of the Surveyor 7 landing area. Please refer to the previous image for a scale bar. The arrow points to the derelict lander, which is just visible because of the shadow it casts on the surface. Technology advancement means that the image is sharper than the previous Lunar Orbiter image: individual boulders about the size of the lander are clearly seen, as are details of the lake-like melt "pond" and small impact craters. Image credit: NASA.

The Bellcomm/USGS team planned that, during Traverse I, one astronaut would deploy an Apollo Lunar Scientific Experiment Package (ALSEP) about 1.1 kilometers east of the LM. The ALSEP would include a passive seismometer. In addition to establishing a "far southern" station in the Apollo seismic network, the instrument would exploit natural moonquakes and asteroid impacts to chart Tycho's subsurface structure. The ALSEP might also include a heat-flow experiment to help scientists determine whether volcanism had occurred recently at the site, a laser retroreflector, a magnetometer, and a gravimeter.

The other astronaut, meanwhile, would walk along the low ridge visible from Surveyor 7 and sample the boulders there. The two moonwalkers would then meet up and return to the vicinity of the LM. Traverse I would total about 3.5 kilometers.

During Traverse II, at about 6.25 kilometers the longest of the Tycho mission moonwalks, the astronauts would strike north together to the "shore" of a prominent kilometer-wide dark lake. They would photograph and sample the branching trenches, then walk to a point 2.6 kilometers from their LM to sample "dark flow dome material." On the way back to the LM, they would visit Surveyor 7 to collect samples of lunar materials it had examined and salvage parts of the robot lander for engineering analysis.

The final traverse of the Apollo Tycho mission would see the astronauts walk south about 1.3 kilometers to sample another dark lake, then travel a further 1.4 kilometers to sample subsurface material exposed by a small fresh impact crater. They would then hike half a kilometer to a raised "flow levee" surrounded by "late smooth flow materials." Traverse III would total 5.25 kilometers. In all, the astronauts would walk 15 kilometers and collect between 100 and 200 pounds of samples during their three moonwalks.

The Bellcomm/USGS team acknowledged that the Tycho site presented challenges beyond its position outside the Apollo Zone. It was rugged and undulating, so the astronauts were likely to lose line-of-sight contact with the radio antennas on their LM as they walked. The LM would relay signals from their space suit radios, so they might temporarily lose radio contact with Earth. In addition, the site had not been imaged from orbit at the same high resolution as other candidate Apollo sites.

The team suggested that, if no high-resolution orbital images of the site could be obtained and if this continued to be considered a major drawback, then the Apollo Tycho mission could land closer to Surveyor 7. Though doing so would enable a landing in a well-characterized area, it would create its own problems. The most serious of these would be to place much of the Traverse III loop beyond the planned 2.5-kilometer operational radius of the mission's moonwalks.

This map of the landing sites of all the successful Surveyors shows how far south Surveyor VII landed. No other spacecraft has soft-landed so far from the lunar equator. Image credit: NASA.

During 1970, in the aftermath of the near-disastrous Apollo 13 mission, NASA engineers, mission planners, managers, and astronauts, never enthusiastic about the Tycho site proposal, rejected the region as too rugged for a safe Apollo landing. Some scientists were, however, not easily deterred: they continued to sing the site's praises as late as 1972.

They pointed to the fact that Surveyor 7 had successfully landed without the precise terminal guidance an astronaut would provide. They hoped that Apollo 16 or 17 might be diverted to Tycho. In the end, however, no Apollo mission visited Surveyor 7, leaving to it the honor of the highest-latitude/farthest-south landing site of any spacecraft that has soft-landed on the Moon.

The dark lake-like features observed near Tycho are known today to be patches of melt material that flowed and was thrown outward from Tycho during its explosive formation, not signs of recent volcanic activity. Impact melt flows are found inside and around many large young impact craters. Melt flow features are rare close to older craters because the steady rain of micrometeoroids and small asteroids that strikes the Moon splinters them into dust and boulders and gradually renders them indistinct.

Sources

Surveyor VII: A Preliminary Report, NASA SP-173, NASA Surveyor Program Office, May 1968.

Surveyor Program Results, NASA SP-184, Surveyor Program, NASA, 1969.

"Tycho - north rim," H. Masursky, G. Swann, D. Elston, and J. Slaybaugh, 14 August 1969 (revised 15 August 1969).

Memorandum, J. Slaybaugh to J. Llewellyn, "Tycho Rim Engineering Evaluation - Case 320," Bellcomm, Inc., 28 August 1969.

To A Rocky Moon: A Geologists' History of Lunar Exploration, Don E. Wilhelms, The University of Arizona Press, 1993, pp. 242, 287, 312.

More Information

"Essential Data": A 1963 Pitch to Expand NASA's Robotic Exploration Programs

If an Apollo Lunar Module Crashed on the Moon, Could NASA Investigate the Cause? (1967)

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