Early astronauts sustained high "G forces" from acceleration during launch, and deceleration during reentry because they were launched on modified ICBMs and reentered on steep trajectories. In order to make these forces more tolerable, the astronauts had special form-fitting couches during Project Mercury, the first U.S. human spaceflight program. The two-person Gemini spacecraft had ejection seats, which made a full form-fitting couch infeasible. Instead Gemini astronauts had two pieces made specially for them, the contour backboard, and the "pelvic block" in which they sat.

This pelvic block may have flown with Virgil I. "Gus" Grissom, who commanded the first Gemini mission with astronauts, Gemini 3, on March 23, 1965. McDonnell-Douglas Corporation gave it to the Smithsonian in about 1971 on behalf of NASA.