Everything you never knew you wanted to know about the Mercury Project
Astronaut support couch
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Managing The G-Force Loads
One of the problems which needed to be solved in the design and development of the Mercury Spacecraft was how to best equip the astronaut to withstand the g-forces which would be imposed on his body during the ascent and descent portions of the mission.
The problems of high-g on the human body had been known at least since World War II. Fighter pilots in high-g maneuvers were familiar with the experience of red-out when negative g-forces during maneuvers such as an outside loop forced blood to pool in the brain and eyeballs, as well as black-out when positive g-forces drained blood from the head.
Another concern was how much exposure to several hours of weightlessness would have on the astronaut's tolerance of the deceleration forces during re-entry.
The g-forces expected during a Mercury mission were higher than those which could be generated by the airplanes of the time, so two other devices were used to study the effects of acceleration, the centrifuge which could simulate the gradual build up of g-forces, and the rocket sled which could produce the rapid onset of both positive and negative g-forces and therefore simulate more violent events, such as an escape tower abort or a hard landing. The rocket sled was made famous by U.S. Air Force Colonel John Stapp.
Centrifuge tests in the early fifties indicated that the body could best withstand g-forces which were applied transversely, that is along the front-back axis, and that "eyeballs-in" acceleration was preferable to "eyeballs-out".
This led to further experimental designs for couches which would rotate so as to always orient the g-load in the preferred "eyeballs-in" direction. Another alternative pursued was immersing the astronaut in water. The US Navy had been experimenting with this idea sporadically. Tests were actually performed at the Navy's NADC center in Pennsylvania in which a capsule which could hold a man in water was fitted to the Johnsville centrifuge. Although this provided the ability to withstand 31g of transverse acceleration force, the complication, space requirements and weight of such systems ruled out their use in Project Mercury. Changing the flight design so that the spacecraft would reenter with the pilot facing backwards also obviated the need for dealing with eyeballs-out forces by rotating the seat.
Another approach was a couch constructed of nylon netting. The problem here was that such a couch would tend to "bounce" the astronaut as g-forces diminished. Such a couch design was considered again late in the program and was fitted to spacecraft 15 and would have flown on the MA-10 mission, but since this mission was canceled at the termination of the program after MA-9 no Mercury spacecraft flew with such a couch design.
As was so much else of the Mercury spacecraft design, the couch design came from the aerodynamic designers at the NASA Langley laboratory, and the team headed up by Max Faget. Faget had the idea of building "a lightweight, stationary couch that a man would lie not on but in.[1]" Testing in the Johnsville centrifuge showed that a subject could withstand more than 20g in a contour couch in a semi-supine position. This allowed Faget to disregard an Air Force ground rule that 12g was the design limit for reentry, and that a tower abort need not endanger the astronauts safety.
"The procedure ultimately used for protecting the Mercury astronauts from the g loads of acceleration to orbital velocity and deceleration during reentry represented a combination of the advantages gained from many experiments by military and other specialists in flight physiology, as well as from the ingenuity of the aeronautical engineers in NACA and NASA. Although the idea of using a hammock either for the basic support or in combination with the contour couch was perennially attractive to the human-factors experts in Project Mercury, all Mercury astronauts sat in essentially the same couch designed by Faget and his coworkers in the spring of 1958. But added to this basic technique were restraining straps, a semi-supine posture, frontward application of acceleration loads, and the reversal of the spacecraft attitude during orbit to permit frontward imposition of reentry loads as well. The final elements in the NACA-NASA campaign to minimize the effects of insertion-reentry g buildups was the use as astronauts of experienced test pilots provided by the military services. During the centrifuge experiments of the fifties such men had consistently proved capable of withstanding higher g forces than nonpilots[2]."
The Mercury Astronaut Couch
The original design (Fig. 1), shown here in a drawing from the December 1959 edition of SEDR-104, comprised a formfitting shell which suppported the astronauts head, back, and buttocks; thigh extensions; and a section which supported the lower legs.
The couch was constructed of fiberglass molded to closely conform to the back of the individual astronaut. This was done to avoid pressure points, both for the comfort of the astronaut, and to avoid damage to the pressure suit. The seat was lined with foam for the comfort of the pilot. This foam liner is not shown in the diagrams.
Minor Modifications through MA-7
The form of the couch was unchanged through the manned flights through MA-7
MR-4
More foam padding was added to the head area of the couch in Gus Grissom's spacecraft 14 [3].
MA-6
It appears that the couch in John Glenn's spacecraft 13 was identical to the one used by Grissom.
MA-7
The couch in Scott Carpenter's spacecraft 18 had a more resilient liner installed[4].
Changes for MA-8
For Wally Schirra's MA-8 flight in spacecraft 16 the leg supports were removed to save weight and improve pilot comfort for the longer flight. Restraints for the astronauts feet (toe, and heel) and knees replaced the leg supports. The knee restraints could be loosened while on-orbit[5].
MA-9
Because of the severe weight restriction program for Gordon Cooper's one-day flight in spacecraft 20 the use of an entirely new web mesh seat design was considered.
"Manned Spacecraft Center engineers almost discarded the fiber-glass couch in favor of a new hammock to shave away 17 more pounds, but that change did not materialize because the engineers feared the material might stretch and the astronaut bounce [6]."
So, despite the quest for a lighter spacecraft, the couch used in MA-9 was similar to that in Schirra's spacecraft, only marginally lighter than that used in earlier missions because of the deletion of the leg supports.
MA-10
The unflown spacecraft 15 has a web mesh support chair instead of the contour couch. Such a design was considered throughout the Mercury development program but was never flown.
See Also
References
- Note: This New Ocean (NASA) From NACA to NASA - NACA Makes Ready [7]
- Note: This New Ocean (NASA) Exploring The Human Factor - Multiple G [8]
- Note: This New Ocean (NASA) Suborbital Flights into Space - Second Suborbital Trial [9]
- Note: This New Ocean (NASA) Mercury Mision Accomplished - Preparations for MA-7 [10]
- Note: This New Ocean (NASA) Climax of Project Mercury - Preparations for MA-8 [11]
- Note: This New Ocean (NASA) Climax of Project Mercury - Redevelopment for MA-9 [12]
