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|
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.
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