One of two NASA scientific laboratories launched aboard its Spacelab module to study the effects of microgravity (weak gravity causing weightlessness in space). Each USMG carried 14 experiments. USMG-1 was launched on the space shuttle Columbia on 25 June 1992 for a 14-day mission, and USMG-2 was launched on 20 October 1995 for a 16-day mission. Among the experiments on both flights were those to grow plants and protein crystals and to study how liquids react under microgravity conditions.