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

All piloted space missions end with Earth-atmosphere reentry. For short-duration missions — for example, an Apollo voyage to the Moon — the period of time between reentry training using simulators on Earth and actual reentry would be short enough that pilot skills retention would be unlikely to become a problem. For longer missions, years might separate simulator training on Earth from actual reentry, almost certainly leading to degradation of critical pilot skills. Image credit: NASA.

Serious plans for astronaut space activities take into account human frailties. Long stays in the space environment on board Earth-orbiting space stations have revealed some: for example, loss of calcium in load-bearing bones in microgravity. Other frailties have been part of human experience for many millennia: for example, forgetfulness over time.

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

Astronauts James Lovell (left) and Frank Borman stand on the deck of the aircraft carrier U.S.S. Wasp after a safe splashdown. They orbited Earth for nearly 14 days in the cramped confines of the Gemini VII capsule to demonstrate that humans could survive in space long enough to reach and return from the Moon during the Apollo Program. Their record would not be broken until the Soyuz 9 flight in 1970, which lasted 17 days, 16 hours, and 58 minutes. Image credit: NASA.

No Apollo mission was expected to last longer than Gemini VII, so Birkemeier looked beyond Apollo to possible longer-duration missions of the 1970s and 1980s. Bellcomm had since 1962 studied piloted lunar and planetary missions for the NASA Headquarters Office of Manned Space Flight. The studies were useful for Birkemeier's analysis because they included plausible long-duration mission timelines.

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

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

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

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

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

A Mars Surface Sample Return (MSSR) ascent stage (right) bearing a sample of martian dirt and rocks approaches a piloted Mars flyby spacecraft. Image credit: NASA.

Birkemeier proposed methods of space mission "skills maintenance." He wrote that "crew members could preserve some degree of proficiency simply by reading instruction manuals, watching training films, studying the controls, and reviewing specific procedures."

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

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

The Apollo Command Module (CM) simulator at the Manned Spacecraft Center in Houston, Texas in 1966. The CM hatch, with its round window, is visible at the top of the ladder. Light brown cabinets house (among other things) projection equipment that provides a realistic view through the CM windows. At the time Birkemeier wrote his report (July 1968), the simulator used 88,000 words of memory on three computers to simulate six-degree-of-freedom maneuvers in real time. Fifty thousand words on a single UNIVAC 1108 computer was sufficient to simulate three-degree-of-freedom maneuvers. Image credit: NASA.

Birkemeier assumed that 1970s and 1980s computers would be at least an order of magnitude more capable than the computers of 1968, and that "simplifying assumptions" might be used to reduce memory requirements. He estimated that a program using 4000 words of memory on a computer with a solution rate of 25 cycles per second could adequately simulate an Apollo Command Module Earth-atmosphere reentry.

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

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

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

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

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

Sources

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

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

More Information

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

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

Chronology: Failure Was an Option 1.0

Image credit: NASA.

Periodically, I write a post in which I list in chronological order links to posts in this blog which I originally presented in no particular order. History is, after all, in large measure about chronology, so these omnibus posts are meant to aid understanding. This post brings together posts with the label "failure was an option" and is offered as a memorial to the 17 persons who have died on board NASA spacecraft.

The end of January and beginning of February is a time of remembrance for NASA piloted spaceflight. On 27 January 1967, astronauts Gus Grissom, Edward White, and Roger Chaffee lost their lives in the Apollo 1 fire. On 28 January 1986, the crew of Space Shuttle mission STS-51L (Dick Scobee, Michael Smith, Ellison Onizuka, Judith Resnik, Ron McNair, Gregory Jarvis, and Christa McAuliffe) perished after the Orbiter Challenger disintegrated 73 seconds after launch. On 1 February 2003, the STS-107 crew (Rick Husband, William McCool, Michael Anderson, Kalpana Chawla, David Brown, Laurel Clark, and Ilan Ramon) died when the Orbiter Columbia broke up during reentry after a nearly 16-day mission in Earth orbit.

Piloted spaceflight has never been routine, though sometimes, for reasons that have little to do with best practices in space engineering, it has been unwisely treated as such. Throughout the history of U.S. piloted spaceflight, however, NASA and its contractors typically have tried to anticipate possible malfunctions and, where possible, develop procedures for dealing with them.

What If an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

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

North American Aviation's 1965 Plan to Rescue Apollo Astronauts Stranded in Lunar Orbit

What If an Apollo Lunar Module Ran Low on Fuel and Aborted Its Moon Landing? (1966)

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

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

A CSM-Only Back-Up Plan for the Apollo 13 Mission to the Moon (1970)

What If a Crew Became Stranded On Board the Skylab Space Station? (1972)

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

George Landwehr von Pragenau's Quest for a Stronger, Safer Space Shuttle (1984)

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

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

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

Final approach: the Shuttle Orbiter Discovery lands on the Shuttle Landing Facility at Kennedy Space Center, Florida, at the end of its longest mission (STS-131, 5-20 April 2010). Image credit: NASA.

The first NASA astronaut to die in the line of duty was U. S. Air Force Captain Theodore Freeman. Little known today, Freeman was a member of the third astronaut selection group, which NASA introduced to the world on 18 October 1963. The group included 10 astronauts who would become famous — Michael Collins, Edwin Aldrin, Alan Bean, David Scott, Russell Schweickart, William Anders, Eugene Cernan, Walter Cunningham, Donn Eisele, and Richard Gordon — and three besides Freeman who would perish before reaching orbit — Clifton Williams, Roger Chaffee, and Charles Bassett. Of the seven pre-Shuttle NASA astronaut groups, Group 3 experienced more pre-flight astronaut deaths than any other.

The astronauts had at their disposal Northrop T-38 Talon supersonic training aircraft. They used them in two basic ways: for training sorties to accumulate flight time so that they could keep their piloting skills well honed and retain their flight status, and as readily available, speedy transportation to NASA and contractor facilities and training sites across the United States. Transportation flights also contributed to the flight time requirement.

On 31 October 1964, 34-year-old Freeman took off alone in a T-38 from Ellington Air Force Base, located between downtown Houston, Texas, and NASA's Manned Spacecraft Center (MSC). He began his training sortie by flying over MSC, then out over Clear Lake and Galveston Bay.

NASA's Third Astronaut Group. Theodore Freeman is in the back row, fourth from left. Image credit: NASA.

As he returned to Ellington, a flock of Canadian geese took wing to one side of his flight path. As he made a turn, the flock rose up around his T-38, and one bird struck and shattered the plane's plexiglass forward canopy. Plexiglass shards entered the jet's twin engines through their air intakes. Moments later, the engines began to fail.

The eight-pound goose did not enter the T-38's intakes, though some sources report that it did. In fact, after striking the canopy, it struck the plane's rear seat, then spun away along the jet's upper fuselage.

Freeman tried to line up with an Ellington runway, but the engines flamed out and his plane began a steep dive at low altitude. He ejected, but before his parachute had time to open he struck the ground and was killed.

In October 1983, nearly 20 years after Freeman's untimely death, The Christian Science Monitor published a puff piece on NASA's efforts to keep wild pigs and alligators off the 15,000-foot-long, 300-foot-wide Shuttle Landing Facility (SLF) runway at Kennedy Space Center (KSC) in Florida. The story was timely because NASA aimed to achieve its first Orbiter landing at the SLF in January 1984. The space agency had planned to land Challenger at the SLF at the end of mission STS-7 on 24 June 1983, but had to divert it to Edwards Air Force Base (EAFB) in California after KSC became fogged in.

The north end of the SLF is about a mile from the Visitor Center for the Merritt Island National Wildlife Refuge (MINWR). MINWR and KSC both owe their origin to President John F. Kennedy's 25 May 1961 "Moon Speech." In 1962-1963, NASA acquired more than 140,000 acres of orange groves, swamp, and beaches to create a safety buffer around its Apollo Saturn V launch pads and other facilities. As landowners moved out, sometimes grudgingly, wildlife moved in.

On 28 August 1963, the space agency and the U.S. Fish and Wildlife Service agreed that the latter would manage the roughly 90% of KSC that NASA did not actively use. The interagency agreement assumed that KSC activities would increase over the course of the 1960s and 1970s and that its facilities would steadily expand. Apollo-era construction leveled off in 1966-1967, however.

Major facilities expansion did not begin again at KSC until April 1974, when the Morrison-Knudsen Company began work on the $22-million-dollar SLF. The facility, modeled on flight research runways at EAFB, was completed in 1976. It became KSC's airport, supporting astronaut T-38s, Gulfstream II Shuttle Training Aircraft, and other planes and helicopters. The first space-worthy Orbiter, Columbia, arrived at the SLF atop a 747 carrier aircraft in March 1979.

The Shuttle Landing Facility. Image credit: NASA.

A NASA spokesman told The Christian Science Monitor's reporter that KSC and MINWR played host to "all kinds of bald eagles, vultures, lots of brown pelicans, and ducks in winter." This was, however, not of great concern; the Shuttle Orbiter was a glider, he explained, so lacked air intakes that might ingest birds.

The Christian Science Monitor reporter wrote that the Orbiter had "triple-strength windows." This was a reference to the design of the six windows making up the flight deck windshield; each was three panes thick, with empty spaces between the panes. The outermost pane, the "thermal" pane, was attached to the fuselage structure; the innermost pane, the "pressure" pane, was attached to the crew cabin structure. Between these, also attached to the crew cabin structure, was a thick "redundant" pane.

The article affected an almost humorous tone as it described measures aimed at keeping alligators and wild pigs off the SLF. It seemed impossible that the Space Shuttle, a pinnacle of U.S. technological know-how, could ever be harmed by mere animals. Its author did suggest, however, that running over alligators basking in the Sun on the SLF runway might damage the Orbiter's "delicate landing gear."

On its second try, at the end of mission STS 41-B in February 1984, Challenger glided to a safe landing on the SLF runway. NASA hailed the landing, little more than five miles from the launch pad Challenger had left just eight days before, as a major step toward routine Shuttle flights and Shuttle launch rates of up to 25 per year.

A little less than two years later, on 28 January 1986, Challenger disintegrated 73 seconds after liftoff from KSC's Pad 39B, killing its seven-person crew. The disaster revealed that the Shuttle stack — twin reusable Solid Rocket Boosters, expendable External Tank, and reusable delta-winged Shuttle Orbiter — was much less robust than many had assumed.

Under intense scrutiny, NASA commenced a wide-ranging examination of Space Shuttle systems and operations. The U.S. civilian space agency soon found that many of its comfortable assumptions were incorrect.

Shuttle windshield: the Orbiter Endeavour during mission STS-123 (11-27 March 2008). Image credit: NASA.

Karen Edelstein, with NASA's Johnson Space Center, and Robert McCarty of the Wright Aeronautical Laboratories at Wright-Patterson Air Force Base in Ohio, reported on results of their study of bird impacts on the Orbiter windshield. They determined that, far from being triple-strength, it was "a poor barrier to bird impacts."

In fact, computer modeling using a refined version of the U. S. Air Force Material and Geometrically Nonlinear Analysis (MAGNA) program showed that, in every case, a four-pound bird — for example, a typical turkey vulture — would penetrate all three windshield panes in less than a second and enter the flight deck if the Orbiter were moving above an indeterminate speed between 150 knots (172 miles per hour) and 175 knots (201 miles per hour). They noted that the Orbiter traveled at up to 355 knots (408 miles per hour) as it fell past 10,000 feet and 195 knots (224 miles per hour) as its rear wheels touched the SLF runway.

This meant that at no time during descent through altitudes where birds fly did the Orbiter's windshield provide protection from bird strikes. In fact, the crew on the flight deck remained vulnerable until about the time the Orbiter's nose gear touched concrete.

Edelstein and McCarty did not examine in detail a bird impact leading to a partial window failure; for example, broken thermal and redundant panes and an intact pressure pane. This scenario was expected to occur at speeds as low as 150 knots. One may speculate that at the very least a partial failure would make the affected window essentially opaque; it might also create extra drag, altering the handling characteristics of the Orbiter.

A turkey vulture. Its wingspan is about six feet. Image credit: Wikipedia.

They noted that, short of a major redesign, there was little NASA could do to beef up the Orbiter windows. They urged designers of future space planes to seek materials more sturdy than glass when designing their windshields.

The Edelstein and McCarty paper did not lead to a major Orbiter redesign or new Orbiter window materials; NASA's allotted budget would not extend that far. Instead, the space agency redoubled its efforts to scare birds away from the SLF. Mostly it relied on loud noises.

For a time in the mid-1990s, however, KSC seriously considered putting falconers on its payroll. A June 1994 study noted that falcons had been used intermittently since the 1940s to kill or scare away birds at airfields in the U.K., the Netherlands, Spain, France, Canada, and the United States.

The study determined, however, that most of the more than 300 bird species that spent at least part of the year in MINWR had little experience with falcons, so were unlikely to be frightened by them. Falcons, for their part, were likely to be confused by wading birds such as herons and egrets.

The birds most threatening to Orbiters and other aircraft at the SLF, the 1994 study found, were various species of vulture. These were too large and numerous for falcons to tackle. It noted that groups of up to 30 individuals were frequently found around a single roadkill and that a "roost" of about 300 vultures had become established on the SLF runway's southern approach path.

The vultures, which weighed up to five pounds, took to the skies to ride thermals over KSC beginning in mid-morning. Mostly they glided lazily between 150 and 1800 feet above the ground. The air currents rising off the 526-foot-tall Vehicle Assembly Building were especially attractive to them. If the birds smelled a carrion buffet, however, they could fly rapidly, thwarting efforts to track and deter them. Loud noises, effective in driving away most other birds, were of little concern to vultures.

During the mid-morning launch of the Orbiter Discovery at the start of mission STS-114 on 26 July 2005, a vulture collided with the External Tank before the Shuttle stack cleared the Pad 39A launch tower. The bird probably weighed more than twice as much as the 1.7-pound chunk of External Tank foam insulation that had struck and breached Columbia's left wing leading edge on 16 January 2003, 82 seconds into mission STS-107. The foam chunk was estimated to have been moving at about 525 miles per hour when it hit the wing.

During Earth-atmosphere reentry on 1 February 2003, hot gases entered Columbia's left wing through the breach and rapidly destroyed its aluminum internal structure. NASA's oldest Orbiter broke up, killing the seven-member STS-107 crew.

Though the low-speed bird impact caused no obvious damage to the External Tank, NASA took notice because it occurred during launch of the first Shuttle mission since STS-107. The vulture might easily have struck a more vulnerable part of the Shuttle stack, or have struck it at a higher altitude, after the Shuttle had gained speed. KSC managers decided to apply SLF bird control techniques to the twin Shuttle launch pads. They also adopted a launch-day vulture "trap-and-release" policy.

By 2009, KSC's Bird Abatement Program relied on quick removal of roadkill to eliminate a major scavenger food source and pare down vulture numbers, bird detection radar and cameras, sirens, shotguns firing blanks and whistlers, and 25 liquid-propane-fueled "cannons." Installed along the SLF in 2007, the noise-producing cannons could be set off from the SLF runway control tower or by bird observers on the ground. They could also be set to fire automatically at random times and in random directions. Despite these measures, the risk to the Shuttle from bird strikes persisted until the Orbiter Atlantis rolled to a stop on the SLF runway at the end of STS-135, the final Shuttle mission, in July 2011.

Sources

"Space Shuttle Orbiter Windshield Bird Impact Analysis," ICAS-88-5.8.3, K. Edelstein and R. McCarty, Proceedings of the 16th International Council on Aeronautical Sciences Congress held in Jerusalem, Israel, 28 August-2 September 1988, Volume 2, pp. 1267-1274.

A Review of Falconry as a Bird Control Technique With Recommendations for Use at the Shuttle Landing Facility, John F. Kennedy Space Center, Florida, U.S.A., NASA Technical Memorandum 110142, V. Larson, S. Rowe, D. Breininger, and R. Yosef, June 1994.

"History of the Shuttle Landing Facility at Kennedy Space Center," E. Liston and D. Elliot; paper presented at The (40th) Space Congress in Cocoa Beach, Florida, 28 April-2 May 2003.

Fallen Astronauts: Heroes Who Died Reaching for the Moon, Revised Edition, C. Burgess and K. Doolan with B. Vis, University of Nebraska Press, 2016, pp. 1-45.

"NASA Tries To Keep The Hogs and 'Gators Off the Shuttle's Runway," G. Klein, The Christian Science Monitor, 12 October 1983 (https://www.csmonitor.com/1983/1012/101225.html - accessed 17 December 2017).

"It's a Jungle Out There!" L. Herridge, 26 June 2006 (https://www.nasa.gov/mission_pages/shuttle/behindscenes/roadkill.html - accessed 14 December 2017).

"Bye, Bye, Birdies," C. Mansfield, 30 June 2006 (https://www.nasa.gov/mission_pages/shuttle/behindscenes/avian_radar.html - accessed 16 December 2017).

"Bird Team Clears Path for Space Shuttles," L. Herridge, 12 August 2009 (https://www.nasa.gov/mission_pages/shuttle/behindscenes/clearbirds.html - accessed 14 December 2017).

More Information

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

What If a Shuttle Orbiter Had to Ditch? (1975)

What Shuttle Should Have Been: NASA's October 1977 Space Shuttle Flight Manifest

A CSM-Only Back-Up Plan for the Apollo 13 Mission to the Moon (1970)

The Apollo 13 crew of Commander James Lovell (left), Command Module Pilot John "Jack" Swigert (center), and Lunar Module Pilot Fred Haise (right). Image credit: NASA.

Launch of Apollo 13, the planned third Apollo Moon landing, was just two months in the future when NASA Manned Spacecraft Center (MSC) engineer Rocky Duncan proposed an alternate plan for the mission. He noted that Apollo 13 would mark the first flight of the Hycon Lunar Topographic Camera (LTC), a modified U.S. Air Force KA-74 aerial reconnaissance camera, which would be mounted in the Command and Service Module (CSM) crew hatch window for high-resolution overlapping photography of candidate future Apollo landing sites.

In Apollo Program parlance, this was dubbed "bootstrap photography." It took advantage of the piloted CSM, which had to loiter in lunar orbit anyway to collect the lunar surface crew after they completed their mission, to collect data useful for planning future Apollo missions.

Duncan noted that previous Apollo lunar missions had followed a "free-return" path that would enable them to loop behind the Moon and fall back to Earth if their CSM Service Propulsion System (SPS) main engine failed. The Apollo 13 CSM, on the other hand, would fire its engine during the voyage to the Moon to leave the free-return trajectory. This was necessary so that the mission's Lunar Module (LM) could reach its target landing site at Fra Mauro.

The Apollo 13 Saturn V rocket clears the tower. Image credit: NASA.

A day after launch from Earth, the Apollo 13 crew ignited the CSM Odyssey's Service Propulsion System (SPS) main engine to leave the free-return trajectory that would automatically return them to Earth in the event of an SPS failure. This was required to permit the mission to reach its destination, the scientifically significant Fra Mauro landing site. Image credit: NASA.

The MSC engineer then described a scenario in which the Apollo 13 LM was judged to be "NO-GO" soon after Trans-Lunar Injection (TLI), the maneuver that would boost them from low-Earth orbit and place them on course for the Moon. TLI would occur about two hours after launch; it would use the Saturn V S-IVB third stage with its single J-2 engine.

Following TLI, the CSM would separate from the segmented shroud — the Spacecraft Launch Adapter — linking it to the S-IVB stage; the shroud would then peel back to reveal the LM. The crew would dock their CSM with the port on top of the LM and separate it from the S-IVB stage. Presumably soon after maneuvering away from the S-IVB they would discover the fault that would render their LM unable to land on the Moon.

Apollo 13 would then become a "CSM-only lunar alternate photographic mission." The CSM would remain on a free-return path until it reached the Moon, then its crew would perform a standard two-impulse lunar orbit insertion (LOI) maneuver; that is, they would fire the SPS to slow their CSM so that the Moon's gravity could capture it into an elliptical lunar orbit, then would fire the engine again at perilune (the low point of its lunar orbit) to circularize its orbit.

Duncan noted that some "desirable photographic orbits with high inclinations. . .require a three-impulse LOI." He argued, however, that "since the crew has not been trained for this type of LOI. . .this type of profile [should] not be flown."

In Duncan's alternate mission, Apollo 13 would capture into a lunar orbit that would take it over the craters Censorinus and Mösting C. These were, respectively, ranked first and eleventh in priority on the Apollo 13 list of targets for lunar-orbital photography.

Censorinus was the leading landing site candidate for Apollo 15, which at the time Duncan wrote his memo was planned as an H-class mission similar to Apollo 13 (that is, its LM would not carry a Lunar Roving Vehicle and would remain on the Moon for only about a day and a half). Apollo 12 in November 1969 had been the first H-class mission, so had been designated H-1; Apollo 13 was H-2, Apollo 14 would be H-3, and Apollo 15 would be H-4, the final H-class flight.

Duncan advocated delaying the crew's scheduled sleep period by two lunar revolutions to enable them to photograph Censorinus and Mösting C. The photographic program would begin during Revolution 3 with vertical stereo photography using window-mounted Hasselblad cameras.

Revolution 4 would see the first high-resolution vertical Hycon LTC photography, then the astronauts would conduct high-resolution oblique (side-looking) LTC photography during Revolution 5. They would perform "landmark tracking" using the CSM's wide-field scanning telescope (a part of its navigation system) during Revolutions 6 and 7, then would begin their delayed sleep period.

The Apollo 13 crew would awaken during Revolution 12 and fire the SPS to change their spacecraft's orbital plane (that is, the angle at which its orbit crossed the Moon's equator). They would do this so that, beginning with Revolution 14, they would pass over Descartes, a suspected volcanic site in the Moon's light-colored central Highlands, and Davy Rille, a chain of small craters of suspected volcanic origin. The astronauts would repeat the five-revolution photography sequence they used to image Censorinus and Mösting C. Duncan noted that Descartes ranked second on the Apollo 13 list of photographic targets, while Davy was fourth.

Duncan briefly considered a scenario in which the Apollo 13 LM was incapable of landing yet had a working descent engine which the crew could use to perform plane-change maneuvers in lunar orbit. He noted that the LM would block some CSM windows while it was docked. The astronauts might undock the CSM from the LM for photography and dock again for additional plane changes, or they might discard the LM after only a single plane change. Duncan favored a simpler approach: jettison the LM as soon as it was judged to be incapable of landing whether its descent engine was functional or not and use only the CSM SPS.

The astronauts would perform "target of opportunity" photography during Revolutions 18 and 19, then would sleep. They would wake during Revolution 24 and perform a plane change during Revolution 25 so that they could fly over Alphonsus crater, Gassendi West, and Gassendi East beginning with Revolution 27 and again carry out the five-revolution photography sequence. Alphonsus, where surface color changes and luminescence have been reported, was ranked ninth on the Apollo 13 target list, while the two sites in dark-floored Gassendi crater were ranked thirteenth and fourteenth, respectively.

Duncan estimated that, by the time the astronauts finished photographing the Alphonsus and Gassendi crater candidate landing sites, Apollo 13's cameras would likely have run out of film. He recommended that the crew fire the SPS to leave lunar orbit and return to Earth during Revolution 32 or two revolutions after the film ran out, whichever came first.

Apollo 13 left Earth on 11 April 1970. The LM Aquarius checked out as "GO" for a landing on the Moon, and on 12 April the crew performed the SPS burn to leave the free-return trajectory. The next day, CSM Odyssey suffered an oxygen tank explosion in its Service Module (SM).

Because the extent of the internal damage to the CSM was unknown, NASA wrote off Odyssey's SPS and looked to the LM for salvation. Astronauts James Lovell, Jack Swigert, and Fred Haise used Aquarius's descent engine to get back onto a free-return trajectory.

During their lunar flyby, the crew photographed the Moon through Aquarius's windows using hand-held cameras. The Hycon camera was not used. Odyssey blocked part of their field of view, but there could be no thought of discarding it: the crew needed the conical Command Module (CM), with its bowl-shaped heat shield, to re-enter Earth's atmosphere at the end of their voyage. With help from the world-wide Apollo mission team, the crew safely reentered Earth's atmosphere and splashed down in the Pacific Ocean in the Odyssey CM on 17 April 1970.

Inside the lifeboat: after the explosion in the Apollo 13 CSM Odyssey, the Apollo 13 crew shut down Odyssey's systems and relocated to the still-functional LM Aquarius. The LM was designed to support two men for 36 hours, not three for four days. This meant that exhaled carbon dioxide built up in the cabin air. With assistance from engineers on Earth, the crew built a system (image above) that allowed the CSM's carbon dioxide-absorbing lithium hydroxide canisters to be used in the LM. CSM Pilot Jack Swigert, who would have performed "bootstrap photography" in lunar orbit had the third lunar landing attempt gone ahead as planned, is visible at right. Image credit: NASA.

As Apollo 13 swung around the Moon and began its fall back to Earth, its crew used handheld cameras to photograph the lunar surface through windows in the LM Aquarius. This image, captured through one of the ceiling-mounted rendezvous and docking windows, shows parts of the Nearside and Farside hemispheres. Dominating the top half of the image is the crippled CSM Odyssey. To conserve electricity, its internal lights are off, making its windows dark. The out-of-focus lines on the rendezvous window were meant to enable the LM crew to gauge distance during rendezvous and docking with the CSM. Image credit: NASA.

Apollo 14 (31 January-9 February 1971) became the first (and last) lunar mission to use the Hycon LTC. By the time it flew, NASA had cancelled Apollo 15 and 19 as part of its efforts to preserve its proposed Space Station/Space Shuttle Program. It had renumbered the remaining Apollo flights so that they ended with Apollo 17. Apollo 14, H-3, became the last H-class mission. The camera's chief target was Descartes, which had moved to the top spot among Apollo 16 landing site candidates. Apollo 16, planned as a J-class mission, would include a two-seat Lunar Roving Vehicle, an LM capable of remaining on the Moon for three days, and a CSM with an ejectable subsatellite and a pallet of sophisticated sensors and cameras in its SM.

The Hycon camera captured 192 images, but malfunctioned while imaging the lunar surface about 70 kilometers east of Descartes. Though Apollo 14 returned no images of the site, Apollo 16 (J-2) landed at Descartes in April 1972.

Sources

Memorandum with attachment, FM5/Lunar Mission Analysis Branch to various, “Lunar alternate missions for Apollo 13 (Mission H-2),” Rocky Duncan, 13 February 1970.

"Scientific Rationale Summaries for Apollo Candidate Lunar Exploration Landing Sites – Case 340," J. Head, Bellcomm, Inc., 11 March 1970.

"Significant Results from Apollo 14 Lunar Orbital Photography," F. El-Baz and S. Roosa, Proceedings of the 1972 Lunar Science Conference, Vol. 2, pp. 63-83, 1972.

More Information

North American Aviation's 1965 Plan to Rescue Apollo Astronauts Stranded in Lunar Orbit

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

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

Safeguarding the Earth from Martians: The Antaeus Report (1978-1981)

The Viking 2 landing site in Utopia Planitia, a northern plain where water frost is seen on winter mornings. The lander touched down on 3 September 1976. A three-meter arm with a scoop on the end dug into the martian surface near the lander, collecting dirt to feed into its three biology experiments. The arm was also used to push rocks and dig trenches that enabled scientists on Earth to study the top 20 centimeters or so of the martian surface. Had the arm been able to dig down deeper — perhaps as little as 30 centimeters deeper — it would have encountered water ice and the history of Mars exploration could have been very different. Image credit: NASA.

In the summer of 1978, 16 university professors from around the United States gathered at NASA's Ames Research Center near San Francisco to spend 10 weeks designing an Earth-orbiting Mars sample quarantine facility. It was one of a series of similar Ames-hosted Summer Faculty Design Studies conducted since the 1960s.

At the time, NASA actively considered Mars Sample Return (MSR) as a post-Viking mission. Agency interest flagged as it became clear that no such mission would receive funding, so publication of the 1978 design study, titled Orbiting Quarantine Facility: The Antaeus Report, was delayed until 1981.

The Summer Fellows noted that the three biology experiments on the Viking landers had found neither organic carbon nor clear evidence of ongoing metabolic processes in the soil they tested on Mars. Furthermore, the Viking cameras had observed no obvious signs of life at the two rather dull Viking landing sites.

Nevertheless, the Summer Fellows argued, "the limitations of automated analysis" and the fact that "the landers sampled visually only a small fraction of one percent of the planet's surface" meant that there could be "no real certainty" about whether Mars was lifeless. This, they argued, meant that, "in the event that samples of Martian soil are returned to Earth for study, special precautions ought to be taken. . .the samples should be considered to be potentially hazardous to terrestrial organisms until it has been conclusively shown that they are not."

Their report listed three options for attempting to ensure that samples would not accidentally release martian organisms on Earth. The MSR spacecraft might sterilize the sample en route from Mars to Earth, perhaps by heating it. Alternately, the unsterilized sample might be quarantined in a "maximum containment" facility on Earth or in Earth orbit, outside our planet's biosphere.

The Summer Fellows noted that each of these three options would have advantages and disadvantages; sterilizing the sample, for example, might ensure that no martian organisms could reach Earth, but would likely also damage the sample, diminishing its scientific utility. The scientists explained that the Antaeus study emphasized the third option because it had not been studied in detail previously.

The Summer Fellows explained the significance of the name they had selected for their Orbiting Quarantine Facility (OQF) project. Antaeus was a giant in Greek mythology who forced passing travelers to wrestle with him and killed them when he won. The Earth was the source of Antaeus's power, so the hero Hercules was able to defeat the murderous giant by holding him above the ground. "Like Antaeus," they explained, a martian organism "might thrive on contact with the terrestrial biosphere. By keeping the pathogen contained and distant, the proposed [OQF] would safeguard the Earth from possible contamination."

Five 4.1-meter-diameter cylindrical modules based on European Space Agency Spacelab module hardware would form the Antaeus OQF. The Summer Fellows assumed that the modules and many of the other components needed to assemble and operate the OQF would become available during the 1980s as the Space Shuttle Program evolved into a Space Station Program.

OQF assembly in 296-kilometer-high circular Earth orbit would need two years. It would begin with the launch of drum-shaped Docking and Logistics Modules together in a Space Shuttle Orbiter's payload bay.

The 2.3-ton Docking Module, the OQF's core, would measure 4.3 meters long. It would include six 1.3-meter-diameter ports with docking units derived from the U.S. version of the 1975 Apollo-Soyuz "neuter" design. Outward-splayed guide "petals" and a system of shock absorbers and latches would enable identical docking units to link together.

The Antaeus Orbital Quarantine Facility. Image credit: NASA.

In addition to the Logistics Module, Power, Habitation, and Laboratory Modules would link up with Docking Module ports. When completed, they would form what the Fellows called a "pinwheel" design. The remaining two Docking Module ports would enable Shuttle dockings, spacewalks outside the OQF with the Docking Module serving as an airlock, and attachment of additional modules if necessary.

The 4.3-meter-long Logistics Module would weigh 4.5 tons loaded with a one-month supply of air, water, food, and other supplies. After a crew took up residence on board the OQF, a Shuttle Orbiter would arrive each month with a fresh Logistics Module. Using twin robot arms mounted in the Orbiter payload bay, the Shuttle crew would remove the spent Logistics Module for return to Earth and berth the fresh one in its place.

The second OQF assembly flight would see the Shuttle crew link the 13.6-ton Power Module to the Docking Module's aft port. The Power Module would then deploy two steerable solar arrays capable of generating between 25 and 35 kilowatts of electricity. Spinning momentum wheels would provide OQF attitude control and small thrusters would fire periodically to counter atmospheric drag, which would otherwise over time cause the quarantine station to reenter. The Power Module would also provide OQF thermal control and communications.

The OQF's five-person crew would live in the 12.4-meter-long, 13.6-ton Habitation Module, which would arrive on the third assembly flight. The OQF's "command console," five crew sleep compartments, and workshop, sickbay, galley, exercise, and waste management/hygiene compartments would be arranged on either side of a central aisle. The Hab Module would provide life support for all the OQF's modules except the Laboratory Module.

The Lab Module, delivered during the fourth and final OQF assembly flight, would measure 6.9 meters long and, like the Hab and Power Modules, would weigh 13.6 tons. Not surprisingly, the Ames Faculty Fellows devoted an entire chapter of the Antaeus report to the Lab.

Spacelab pressurized modules included a central corridor running their entire length. Experiment equipment lined their walls. The Spacelab-based OQF Lab Module, on the other hand, would have a central experiment area running most of its length with corridors along its walls. Most of the experiment area would be located within glass-walled "high-hazard" "Class III" biological containment cabinets similar to those at the Centers for Disease Control in Atlanta, Georgia.

The Antaeus OQF Lab Module included an independent life support system to help prevent contamination of adjoining modules. Grills in the floor and ceiling lead to air filters. The Mars Sample Return sample canister would enter the central experiment area from above. Visible are at least three microscopes. Image credit: NASA.

Analysis equipment within the cabinets would include a refrigerator, a freezer, a centrifuge, an autoclave, a gas chromatograph, a mass spectrometer, incubation and metabolic chambers, scanning electron and compound light microscopes, and challenge culture plates. The crew would operate the equipment from outside the cabinets using sleeve-like arms with mechanical grippers.

The Summer Fellows provided no obvious aids for crew positioning. In the illustration of the Lab module above, scientists are shown floating without hand-grips or feet or body restraints. Given the delicate and sensitive nature of the work they were meant to perform, this would probably turn out to be a significant omission.

The Lab Module would include an independent life support system with "high efficiency particle accumulator" (HEPA) filters. Experimenters would enter and exit the Lab Module through a decontamination area, where they would don and doff respirator masks and protective clothing. If a mishap contaminated the Lab Module, the module could be detached from the OQF and boosted to a long-lived 8000-kilometer circular orbit using a Laboratory Abort Propulsion Kit delivered by a Shuttle Orbiter.

Following the two-year assembly period, a rehearsal crew would board the OQF to test its systems and try out the Mars sample analysis protocol using biological samples from Earth. The Summer Fellows set aside up to two years for these practice activities. At about the time the rehearsal crew boarded the OQF, a robotic MSR spacecraft would depart Earth on a one-year journey to Mars.

Two years later and four years after the start of OQF assembly, a small Mars Sample Return Vehicle (MSRV) containing one kilogram of martian surface material and atmosphere samples would fire rocket motors to enable Earth's gravity to capture it into a high orbit. The sample would ride within a sample canister, the exterior of which would have been sterilized during Mars-Earth transfer.

Meanwhile, a Shuttle Orbiter would deliver to the OQF the first five-person sample-analysis crew. It would comprise a commander (a career astronaut with engineering training) and four scientists with clinical research experience (a medical doctor, a geobiologist, a biochemist, and a biologist).

A Shuttle-launched remote-controlled Space Tug would collect the sample canister from high-Earth orbit and deliver it to a special "docking cone" on top of the Lab Module. This is not shown in the illustration of the completed OQF; in its place, one finds a cylindrical "Sample Acquisition Port." The canister would then enter the experiment area through a small airlock.

The first sample analysis crew would cut open the canister using "a mechanism similar to a can opener." They would immediately place 900 grams of the sample into "pristine storage." Over the next 60 days, they would execute an analysis protocol that would expend 100 grams of the sample. Twelve grams each would be devoted to microbiological culturing and challenge cultures containing living cells from more than 100 Earth species; six grams each to metabolic tests and microscopic inspection for living cells and fossils; 10 grams to chemical analysis; and 54 grams to "second-order" follow-up tests.

If the 60-day analysis protocol yielded no signs of life in the test sample, a Shuttle Orbiter would carry the 900-gram pristine sample from the OQF to Earth's surface for distribution to laboratories around the world. Based on highly optimistic 1970s NASA estimates of Shuttle, Spacelab, and Station costs, the Summer Fellows placed the total cost of OQF assembly and operations for this "minimum scenario" at only $1.66 billion.

If, on the other hand, OQF scientists detected life in the Mars sample, then analysis on board the OQF could be extended for up to six and a half years. Throughout that period, Shuttle Orbiters would continue to deliver a steady stream of monthly Logistics Modules; they would also change out OQF crews at unspecified intervals. In all, about 80 Logistics Modules would reach the OQF by the time its mission ended. The cost of this "maximum scenario" might total $2.2 billion, the Ames Summer Faculty Fellows optimistically estimated.

Source

Orbiting Quarantine Facility: The Antaeus Report, D. DeVincenzi and J. Bagby, editors, NASA, 1981.

More Information

Clyde Tombaugh's Vision of Mars (1959)

Peeling Away the Layers of Mars (1966)

What Shuttle Should Have Been: NASA's October 1977 Space Shuttle Flight Manifest

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

The Space Shuttle Challenger and its booster system moments before they were destroyed. The plume of flame emerging from the side of its malfunctioning SRB is clearly visible. Image credit: NASA.

The Space Shuttle Orbiter Challenger was minding its own business on 28 January 1986, working hard to get its seven-member crew and its large satellite payload to low-Earth orbit, when its booster stack betrayed it and everything began to go badly wrong. First, hot gas within its right Solid Rocket Booster (SRB) began to burn through a seal meant to contain it. Soon, a fiery plume gushed from the side of the SRB, robbing it of thrust, and reached out menacingly toward the side of the brown External Tank (ET) and the strut linking the lower end of the SRB to the ET (image at top of post). The plume broke though the ET's foam insulation and aluminum skin, then the strut pulled free of the weakened ET.

Challenger fought back as the ET began to leak liquid hydrogen fuel. It swiveled (the aerospace term is "gimballed") the three Space Shuttle Main Engines (SSMEs) in its tail as it struggled to stay on course. The plume from the SRB, meanwhile, glowed brighter as it began to burn hydrogen leaking from the ET. At the same time, the SRB began to rotate around the single strut left holding it to the ET. That strut was located not far from the Orbiter's gray nose, near the conical top of the errant SRB.

Throughout these events, Challenger's last crew remained oblivious to the technological drama taking place around them. This was just as well, since they had no way to escape what was about to happen to them.

When Challenger at last lost its struggle against its own booster stack, significant events were separated by tenths or hundredths of seconds. Immediately after the right SRB's lower strut came free, the entire Shuttle stack lurched right. Mike Smith, in Challenger's pilot seat, had time for a startled "Uh-oh" less than a second after the lurch. The ET's dome-shaped bottom then fell away, freeing all the hydrogen fuel it contained. The right SRB's pointed nose slammed into and crushed the top of the ET, freeing liquid oxygen oxidizer. The escaped hydrogen blossomed into a fireball that encompassed Orbiter, rapidly disintegrating ET, and SRBs.

Yet the Orbiter Challenger did not explode. Instead, it broke free of what was left of the ET and began a tumble. The aerodynamic pressures the Orbiter experienced as its nose pointed away from its direction of flight were more than sufficient to snap it into several large pieces: the crew cabin, the satellite payload, the wings, and the SSME cluster emerged from the fireball more or less intact. The SRBs, still firing, flew out of the fireball, tracing random trails across the blue Florida sky until a range safety officer commanded them to self-destruct. The Orbiter's wreckage, meanwhile, plummeted into the Atlantic within sight of the Florida coast.

NASA recovered the bodies of the crew and portions of the wreckage, including the section of the right SRB that had leaked hot gas. The wreckage was turned over to accident investigators.

This 1975 NASA illustration depicts the basic components of the Space Shuttle system. The Orbiter includes three Space Shuttle Main Engines (left). Two Solid Rocket Boosters, one of which is mostly hidden behind the External Tank, provide thrust during liftoff and the early part of ascent. The tank includes (from right to left) a small tank for dense liquid oxygen, a drum-shaped structural support ring/tank separator below the Orbiter's nose, and a large tank for low-density liquid hydrogen.

During a Shuttle launch, the three SSMEs ignited first. This caused the twin SRBs, the bases of which were mounted to the launch pad by explosive bolts, to flex along their entire length away from the SSMEs, then straighten out again just as they ignited. O-ring seals between the cylindrical segments making up the SRBs often became unseated during flexure, then had to reseat to contain hot gases after SRB ignition. Accident investigators concluded that failure of one of those seals doomed Challenger. Even more damning, they found that partial seal failures followed by hot exhaust leaks had occurred on pre-Challenger flights — and had been disregarded by NASA managers.

After Challenger, NASA and its contractors redesigned the SRB joints and seals, added crew pressure suits and a limited crew escape capability, and banned potentially unsafe practices and payloads from Shuttle missions. Yet the U.S. civilian space agency might have gone much farther when it sought to enhance Space Shuttle safety after Challenger.

Even before the accident, NASA had at its disposal redesign proposals that could have made the Shuttle stack stronger and safer. In 1982, for example, George Landwehr von Pragenau, a veteran engineer at NASA's Marshall Space Flight Center, filed a patent application — granted in 1984 — for a Shuttle stack design that would have made the Challenger accident impossible.

Born and educated in Austria, von Pragenau joined the von Braun rocket team in Huntsville, Alabama, in 1957. He became a U.S. citizen in 1963. He specialized in rocket stability and flight effects on rocket behavior. He had, for example, been part of the team that found the cause of the "pogo" oscillations that crippled Apollo 6, the second unmanned Saturn V-launched Apollo test mission (4 April 1968).

In the conventional Shuttle stack, von Pragenau explained, SRB thrust was transmitted through the forward SRB attachment points to a reinforced intertank ring between the ET's top-mounted liquid oxygen tank and its liquid hydrogen tank.  He considered this "indirect routing" of thrust loads to be perilously complex. SSME thrust loads, for their part, passed through the Orbiter to its twin aft ET attachment points on the large, fragile liquid hydrogen tank.

By the time he filed his 1982 patent application, von Pragenau had spent almost a decade thinking about how the Shuttle stack might be rearranged to reduce weight and aerodynamic drag, increase stability, simplify thrust paths, and provide greater structural strength. His 1984 patent was, in fact, not his first aimed at Shuttle improvement.

Von Pragenau's 1974 alternative Shuttle stack. Image credit: U.S. Patent Office.

In 1974, von Pragenau had filed a patent — granted the following year — in which he proposed a more slender, more vertically oriented Shuttle stack; that is, one that would mimic conventional rocket designs in which stages are stacked one atop the other. He linked the twin SRBs side by side. Moving the tank for dense liquid oxygen from the ET's nose to its tail placed its concentrated mass nearer the base of the stack, improving in-flight stability. He then mounted the SRBs to the Orbiter's belly and perched the ET atop the SRB/Orbiter combination. SRB and SSME thrust loads were conveyed through struts to meet at the ET's flat, reinforced base.

Von Pragenau's 1982 Shuttle stack design was in some ways a less radical departure from the existing Shuttle design than was his 1974 design. He left the SRBs, ET, and Orbiter in their normal positions relative to each other, but made other significant changes. As in his 1975 patent, he moved the liquid oxygen tank from the ET's nose to its tail and brought the SRBs closer together to improve stability. The liquid oxygen tank became skinny, cylindrical, and almost as long as the Orbiter and SRBs attached to it. The liquid hydrogen tank, fat with low-density fuel, von Pragenau mounted atop the oxygen tank, partially overhanging the Orbiter and SRBs.

Von Pragenau's 1982 Shuttle stack redesign. The numeral "15" points to the rigid thrust structure framework. "34," "35," "36" are Solid Rocket Booster attachment fixtures. These would link to slide rails ("31" and "32") that would run the length of the liquid oxygen tank ("20"). "19" is the liquid hydrogen tank. Image credit: U.S. Patent Office. 

Von Pragenau could not tolerate flexing SRBs. He proposed to mount a slide rail on either side of the liquid oxygen tank. Three attachment fixtures on each SRB would link to the slide rails, helping to ensure rigidity. When the SRBs depleted their propellant, pyrotechnic bolts would fire, freeing them to slide backwards down the rails and fall neatly away from the Orbiter/ET stack.

The most important feature of von Pragenau's redesign was a rigid framework – a thrust structure – that would link the bottom of the SRBs just above their rocket nozzles. In addition to holding the SRBs rigidly in place, the thrust structure would transmit SRB thrust loads to the bottom of the ET oxygen tank, which would rest atop the center of the thrust structure. When the spent SRBs slid away from the Orbiter/ET stack, they would take the thrust structure with them.

Side view of Von Pragenau's 1982 Shuttle stack concept. Image credit: U.S. Patent Office.

Von Pragenau's concepts apparently exerted little influence on NASA's post-Challenger recovery effort. A likely explanation is that neither of his proposals — if they were known to decision-makers at all — was deemed affordable. In addition to extensive changes in manufacturing tooling, both proposals would have required modifications to the Vehicle Assembly Building, the twin Complex 39 Shuttle pads at Kennedy Space Center (KSC), and even the barge that delivers ETs to KSC. Instead of beefing up the existing Shuttle, NASA studied designs for new shuttles which, for lack of funding, remained firmly in the low-cost realm of CAD drawings, conference papers, and conceptual artwork.

On 1 February 2003, the Space Shuttle claimed another crew. The oldest Orbiter, Columbia, was heavier than her sisters Atlantis, Discovery, and Endeavour, which limited the amount of cargo she could deliver to the International Space Station (ISS). For this reason, NASA largely relegated to Columbia the few remaining non-ISS missions — for example, Hubble Space Telescope servicing.

As they began Earth-atmosphere reentry at 8:44 a.m. Eastern Standard Time after a nearly 16-day life sciences mission, the seven STS-107 astronauts on board Columbia were unaware that, during ascent, a piece of ice-impregnated insulating foam nearly a meter wide had broken free from the ET and impacted their spacecraft's left wing. Ice and foam had broken free from ETs before, but the damage they caused was, after cursory examination, deemed acceptable by Shuttle Program managers. This time, however, the impact opened a hole up to 10 inches wide in the Orbiter's left wing leading edge.

Hot plasma generated during reentry entered the hole and began to destroy Columbia's left wing from the inside out. Observers along the Orbiter's flight path, which cut across the southern tier of U.S. states, reported unusual flashes. Meanwhile, members of the STS-107 crew on Columbia's Flight Deck observed and recorded on video flashes visible outside their windows. In the recovered video, the astronauts appear to realize that the flashes were unusual but show no signs of panic.

Much as Challenger had before it, Columbia fought bravely against the forces destroying it. Onboard computers took account of increased drag on the left side of the Orbiter and sought to compensate to keep it on the flight path. At 8:59 a.m. Eastern Standard Time, however, Columbia tumbled and disintegrated over northeast Texas.

Both of von Pragenau's design concepts placed all or part of the ET above the Orbiter, so one might argue that they would not have prevented a failure resembling that which killed the STS-107 crew. On the other hand, one can be forgiven for speculating that a U.S. civilian space agency provided with the means after Challenger to rebuild the Shuttle system to make it safer might also have evolved an organizational culture more prone to investigating and less prone to tolerating recurring flight anomalies.

Von Pragenau retired from NASA in 1991 after more than 30 years of service. He remained involved in engineering efforts at NASA Marshall Space Flight Center during his retirement. He died two years after the Space Shuttle's final flight (STS-135, 8-24 July 2011), on 11 July 2013, at the age of 86.

Sources

Patent No. 4,452,412, Space Shuttle with Rail System and Aft Thrust Structure Securing Solid Rocket Boosters to External Tank, George L. von Pragenau, NASA Marshall Space Flight Center, 15 September 1982 (filed), 5 June 1984 (granted).

Patent No. 3,866,863, Space Vehicle, George L. von Pragenau, NASA Marshall Space Flight Center, 21 March 1974 (filed), 18 February 1975 (granted).

Hampton Cove Funeral Home Obituaries: George Landwehr von Pragenau (http://www.hamptoncovefuneralhome.com/fh/obituaries/obituary.cfm?o_id=2150841&fh_id=13813 — accessed 27 October 2016).

NASA History: Columbia Accident Investigation Board (http://history.nasa.gov/columbia/CAIB.html — accessed 29 October 2016).

NASA History: Challenger STS 51-L Accident (https://www.hq.nasa.gov/office/pao/History/sts51l.html — accessed 29 October 2016).

More Information

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

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

What If Galileo Had Fallen to Earth? (1988)

What If Galileo Had Fallen to Earth? (1988)

Galileo awaits its chance to fly. Image credit: NASA.

The U.S. Congress authorized new-start funding for the Jupiter Orbiter and Probe (JOP) on 19 July 1977, early in the Administration of President Jimmy Carter. When JOP development began officially on 1 October 1977, at the start of Fiscal Year 1978, NASA planned to launch the new robot explorer in January 1982 on STS-23, the 23rd operational flight of the Space Transportation System (STS). At the time, NASA still maintained the hopeful fiction that the STS could begin a series of six Orbital Test Flights in early 1979 and become operational in May 1980. Until 1986, the STS — the centerpiece of which was the Space Shuttle — was intended to replace all other U.S. launch vehicles.

At liftoff, the Shuttle stack comprised twin reusable Solid Rocket Boosters (SRBs), a reusable piloted Orbiter with a 15-by-60-foot payload bay and three Space Shuttle Main Engines (SSMEs), and an expendable External Tank (ET) containing liquid hydrogen and liquid oxygen propellants for the SSMEs. The STS also included upper stages for boosting spacecraft carried in the Orbiter payload bay to places beyond its maximum orbital altitude. Until the mid-1980s, many in NASA hoped that a reusable Space Tug — perhaps incorporating a propellant-saving aerobrake — would eventually replace the expendable upper stages.

At the start of STS-23 (and, indeed, at the beginning of all STS missions), the three SSMEs mounted on the aft end of Orbiter fuselage and the twin SRBs bolted to the side of the ET would ignite in sequence to push the Shuttle stack off the launch pad. SRB separation would then take place 128 seconds after liftoff at an altitude of about 155,900 feet and a speed of about 4417 feet per second.

The three SSMEs would operate until 510 seconds after liftoff, by which time the Orbiter and its ET would be moving at about 24,310 feet per second at an altitude of 362,600 feet above the Earth. The SSMEs would then shut down and the ET would separate, tumble, and break up as it fell back into dense atmospheric layers over the Indian Ocean.

The Orbiter, meanwhile, would ignite its twin Orbital Maneuvering System (OMS) engines at apogee (the high point in its Earth-centered orbit) to raise its perigee (the low point in its orbit) above 99.99% the Earth's atmosphere. By the time it completed its OMS maneuvers, the STS-23 Shuttle Orbiter would circle the Earth in a 150-nautical-mile-high low-Earth orbit (LEO).

The STS-23 crew would next open the Orbiter payload bay doors and release JOP and its three-stage solid-propellant Interim Upper Stage (IUS). After they maneuvered the Orbiter a safe distance away, the IUS first-stage motor would ignite to begin JOP's two-year direct voyage to Jupiter.

Early days: artist concept of Jupiter Orbiter and Probe. Image credit: NASA.

In February 1978, NASA gave JOP the name Galileo. Largely because of its reliance on the STS, Galileo suffered a series of costly delays, redesigns, and Earth-Jupiter trajectory changes. The first of these was, however, not the fault of the STS. As Galileo's design firmed up, it put on weight, and was soon too heavy for the three-stage IUS to launch directly to Jupiter.

In January 1980, NASA decided to split Galileo into two spacecraft. The first, the Jupiter Orbiter, would leave Earth in February 1984. The second, an interplanetary bus carrying Galileo's Jupiter atmosphere probe, would launch the following month. They would each depart LEO on a three-stage IUS and arrive at Jupiter in late 1986 and early 1987, respectively.

In late 1980, under pressure from Congress, NASA opted to launch the Galileo Orbiter and Probe out of LEO together on a liquid hydrogen/liquid oxygen-fueled Centaur G' upper stage. Centaur, a mainstay of robotic lunar and planetary programs since the 1960s, was expected to provide 50% more thrust than the three-stage IUS. Modifying it so that it could fly safely in the Shuttle Orbiter payload bay would, however, delay Galileo's Earth departure until April 1985. The spacecraft would arrive at Jupiter in 1987.

Another delay resulted when David Stockman, director of President Ronald Reagan's Office of Management and Budget, put Galileo on his "hit list" of Federal government projects to be scrapped in Fiscal Year 1982. The planetary science community campaigned successfully to save Galileo, but NASA lost the Centaur G' and three-stage IUS.

In January 1982, NASA announced that Galileo would depart Earth orbit in April 1985 on a two-stage IUS with a solid-propellant kick stage. The spacecraft would then circle the Sun and fly past Earth for a gravity-assist that would place it on course for Jupiter. The new plan would add three years to Galileo’s flight time, postponing its arrival at Jupiter until 1990.

In July 1982, Congress overruled the Reagan White House when it mandated that NASA launch Galileo from LEO on a Centaur G'. The move would postpone its launch to 20 May 1986; however, because the Centaur could boost Galileo directly to Jupiter, it would reach its goal in 1988, not 1990. NASA designated the STS mission meant to launch Galileo STS-61G.

Artist concept of Galileo on a Centaur G' stage. Image credit: NASA.

There matters rested until 28 January 1986, when, 73 seconds into mission STS-51L, the Orbiter Challenger was destroyed. A joint between two of the cylindrical segments making up the Shuttle stack's right SRB leaked hot gases that rapidly eroded O-ring seals. A torch-like plume formed and impinged on the ET and the lower strut linking the ET to the SRB. The plume breached and weakened the ET's liquid hydrogen tank, causing the strut to separate. Still firing — the SRBs were not designed to be turned off once ignited — the right SRB pivoted on its upper attachment and crushed the ET's liquid oxygen tank. Hydrogen and oxygen mixed and ignited in a giant fireball.

Despite appearances, Challenger did not explode. Instead, the Orbiter began a tumble while moving at about twice the speed of sound in a relatively dense part of Earth's atmosphere. This subjected it to severe aerodynamic loads, causing it to break into several large pieces. The pieces, which included the crew compartment and the tail section with its three SSMEs, emerged from the fireball more or less intact. The mission's main payload, the TDRS-B data relay satellite, remained attached to its two-stage IUS as Challenger's payload bay disintegrated around it.

The pieces arced upward for a time, reaching a maximum altitude of about 50,000 feet, then fell, tumbling, to crash into the Atlantic Ocean within view of the Shuttle launch pads at Kennedy Space Center, Florida. The crew compartment impacted 165 seconds after Challenger broke apart and sank in water about 100 feet deep.

NASA grounded the STS for 32 months. During that period, it put in place new flight rules, abandoned potentially hazardous systems and missions, and, where possible, modified STS systems to help improve crew safety. On 19 June 1986, NASA canceled the Shuttle-launched Centaur G' for reasons of safety. On 26 November 1986, it announced that a two-stage IUS would launch Galileo out of LEO. The Jupiter spacecraft would then perform gravity-assist flybys of Venus and Earth. On 15 March 1988, NASA scheduled Galileo's launch for October 1989, with arrival at Jupiter to follow in December 1995.

One month after NASA unveiled Galileo's newest flight plan, Angus McRonald, an engineer at the Jet Propulsion Laboratory (JPL) in Pasadena, California, completed a brief report on the possible effects on Galileo and its IUS of a Shuttle accident during the 382-second period between SRB separation and SSME cutoff.

McRonald was not specific about the nature of the "fault" that would produce such an accident, though he assumed that the Shuttle Orbiter would become separated from the ET and would tumble out of control. He based his analysis on data provided by NASA Johnson Space Center in Houston, Texas, where the Space Shuttle Program was managed.

The Space Shuttle was by far the largest spacecraft to launch with astronauts on board. It was immensely capable — but with capacity came complexity, making it vulnerable. Image credit: NASA.

McRonald also examined the effects of aerodynamic heating on Galileo's twin electricity-generating Radioisotope Thermoelectric Generators (RTGs). The RTGs would each carry 18 General Purpose Heat Source (GPHS) modules containing four iridium-clad plutonium dioxide pellets each. The GPHS modules were encased in graphite and housed in protective aeroshells, making them unlikely to melt following an accident during Shuttle ascent. In all, Galileo would carry 34.4 pounds of plutonium.

McRonald assumed that both the Shuttle Orbiter and the Galileo/IUS combination would break up when subjected to atmospheric drag deceleration equal to 3.5 times the pull of gravity at Earth's surface. Based on this, he determined that the Orbiter and its Galileo/IUS payload would always break up if a fault leading to "loss of control" occurred after SRB separation.

The Shuttle Orbiter would not break up immediately after loss of control occurred, however. At SRB separation altitude, atmospheric density would be low enough that the spacecraft would be subjected to only about 1% of the drag that tore apart Challenger. McRonald determined that the Shuttle Orbiter would ascend unpowered and tumbling, attain a maximum altitude, and fall back into the atmosphere, where drag would rip it apart.

He calculated that, for a fault that occurred 128 seconds after liftoff — that is, at the time the SRBs separated — the Shuttle Orbiter would break up as it fell back to 101,000 feet of altitude. The Galileo/IUS combination would fall free of the disintegrating Orbiter and break up at 90,000 feet, then the RTGs would fall to Earth without melting. Impact would take place in the Atlantic about 150 miles off the Florida coast.

For an intermediate case — for example, if a fault leading to loss of control occurred 260 seconds after launch at 323,800 feet of altitude and a speed of 7957 feet per second — then the Shuttle Orbiter would break up when it fell back to 123,000 feet. Galileo and its IUS would break up at 116,000 feet, and the RTG cases would melt and release the GPHS modules between 84,000 and 62,000 feet. Impact would occur in the Atlantic about 400 miles from Florida.

A fault that took place within 100 seconds of planned SSME cutoff — for example, one that caused loss of control 420 seconds after launch at 353,700 feet of altitude and at a speed of 20,100 feet per second — would result in an impact far downrange because the Shuttle Orbiter would be accelerating almost parallel to Earth's surface when it occurred. McRonald calculated that Orbiter breakup would take place at 165,000 feet and the Galileo/IUS combination would break up at 155,000 feet.

McRonald found (somewhat surprisingly) that, in such a case, Galileo's RTG cases might already have melted and released their GPHS modules by the time the Jupiter spacecraft and its IUS disintegrated. He estimated that the RTGs would melt between 160,000 and 151,000 feet about the Earth. Impact would occur about 1500 miles from Kennedy Space Center in the Atlantic west of Africa.

Impact points for accidents between 460 seconds and SSME cutoff at 510 seconds would be difficult to predict, McRonald noted. He estimated, however, that loss of control 510 seconds after liftoff would lead to wreckage falling in Africa, about 4600 miles downrange.

McRonald summed up his findings by writing that Galileo's RTG cases would always reach Earth's surface intact if an accident leading to loss of control occurred between 128 and 155 seconds after liftoff. If the accident occurred between 155 and 210 seconds after launch, then Galileo's RTG cases "probably" would not melt. If it occurred 210 seconds after launch or later, then the RTG cases would always melt and release the GPHS modules.

STS flights resumed in September 1988 with the launch of the Orbiter Discovery on mission STS-26. A little more than a year later (18 October 1989), the Shuttle Orbiter Atlantis roared into space at the start of STS-34. A few hours after liftoff, the Galileo/two-stage IUS combination was raised out of the payload bay on an IUS tilt table and released. The IUS first stage ignited a short time later to propel Galileo toward Venus.

Free at last: Galileo and its two-stage IUS shortly after release from the Space Shuttle Orbiter Atlantis, October 1989. Image credit: NASA.

Galileo passed Venus on 10 February 1990, adding nearly 13,000 miles per hour to its speed. It then flew past Earth on 8 December 1990, gaining enough speed to enter the Main Belt of asteroids between Mars and Jupiter, where it encountered the asteroid Gaspra on 29 October 1991.

Galileo's second Earth flyby on 8 December 1992 placed it on course for Jupiter. The spacecraft flew past the Main Belt asteroid Ida on 28 August 1993 and had a front-row seat for the Comet Shoemaker-Levy 9 Jupiter impacts in July 1994.

Flight controllers commanded Galileo to release its Jupiter atmosphere probe on 13 July 1995. The spacecraft relayed data from the probe as it plunged into Jupiter’s atmosphere on 7 December 1995. Galileo fired its main engine the next day to slow down so that the giant planet's gravity could capture it into orbit.

Artist concept of Galileo in communication with its Jupiter atmosphere probe. Blue dots linking the low-gain antenna and Jupiter represent radio signals. After the spacecraft's large main antenna jammed partly open (left), the low-gain antenna, much less powerful, became Galileo's link with Earth. Image credit: NASA.

Galileo spent the next eight years touring the Jupiter system. It performed gravity-assist flybys of the four largest Jovian moons to change its Jupiter-centered orbit. Despite difficulties with its umbrella-like main antenna and its tape recorder, it returned invaluable data on Jupiter, its enormous magnetosphere, and its varied and fascinating family of moons over the course of 35 orbits about the giant planet.

As Galileo neared the end of its propellant supply, NASA decided to dispose of it to prevent it from accidentally crashing on and possibly contaminating Europa, the ice-crusted, tidally warmed ocean moon judged by many to be of high biological potential. On 21 September 2003, the venerable spacecraft dove into Jupiter's turbulent, banded atmosphere and disintegrated.

Sources

Galileo: Uncontrolled STS Orbiter Reentry, JPL D-4896, Angus D. McRonald, Jet Propulsion Laboratory, 15 April 1988.

Mission to Jupiter: A History of the Galileo Project, NASA SP-2007-4231, Michael Meltzer, NASA History Division, 2007.

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