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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

More Information

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)

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