Launch VehiclesFor many years the United States has had a wide range of launch
Vehicles at its disposal for various space
programs. By the late 1970s, however, NASA planning had come to concentrate on the Space Shuttle as the bearer of orbital traffic. Other launch systems remained available, but their future was placed in doubt by pressure from NASA. Following the Challenger disaster, however, the old stable of boosters was revitalized and expanded, so that by the 1990s a large number of other launch vehicles would again be available for U.S. space needs. The boosters include the Scout, Delta, Atlas-Centaur, Titan 34, and Titan 4.At the smaller end of the scale, the
growing market in cheap, small satellites led to the development of several competing small booster systems, such as the air-launched Pegasus rocket. Many of these privately funded
projects encountered major technical difficulties and the growing threat of overseas competition. Meanwhile NASA settled on a strategy for developing rockets to replace the Space Shuttle by 2010 and initiated projects such as the X-33 and X-34 to examine the technology needed for single-stage-to-orbit (SSTO) vehicles.