Project 7969 Bell Credit - © Mark Wade

Bell's preferred concept for the Air Force initial manned space project was the boost-glide vehicle they had been developing for the Dynasoar program.

When pressed they considered briefly a minimum vehicle, spherical in shape, weighing about 1,400 kg. But their baseline was the Dynasoar approach - 'anything else would be a stunt'. It was expected that a first manned orbital flight of the boost-glide vehicle could be achieved five years after a go-ahead at a cost of $ 889 million.

Mass: 8,200 kg (18,000 lb). Associated Launch Vehicle: Titan 2.

• Grimwood, James M., Project Mercury: A Chronology, NASA Special Publication-4001.

• Baker, David, The History of Manned Spaceflight, Crown, New York, 1981. The best overview of America's manned space programs up to Skylab. Information and details not available anywhere else. Unfortunately out of print and difficult to locate.