In a USAF centrifuge at Brooks Air Force Base, Texas. U.S. Sen. John H. Glenn Jr. is strapped in by the Johnson Space Center's Carlous Gillis (left). The STS-95 mission specialist completed two nine-minute sessions in the centrifuge, reaching a threshold of three G-forces, or three times his own body weight. (USAF photograph by Staff Sgt. Steve Thurow).