Inertial Upper Stage - Development

Development

During the development phase of the Space Shuttle (1969–1974), NASA, with reluctant support from the Air Force, wanted an upper stage that can be used on the Space Shuttle, but at the same time, can be switched over to the Titan III rocket (then the most powerful unmanned rocket in the U.S. fleet, since the Saturn INT-21, a derivative of the Saturn V rocket, was only used once for the launch of Skylab in 1973), in the case the Shuttle ran into lengthy delays either from development or testing. Although NASA wanted to adopt a version of the Centaur upper stage for its planetary missions, the Air Force wanted to use the "Transtage," a hypergolic upper stage used on most Titan III launches in which the Centaur was not needed, and unlike the Centaur, used the same fuel and oxidizer used on the Shuttle Orbital Maneuvering System (OMS) and Reaction Control System (RCS) systems.

The solid-fueled IUS was created as a compromise between the Transtage, which was not powerful enough for most NASA payloads, and the Centaur, which was not needed for all military and intelligence payloads. The IUS upper-stage booster rocket design was based on he earlier on the Burner II upper-stage booster,

IUS was powerful enough to deliver two large DoD or NSA satellites into proper orbits over the former Soviet Union, or a single NASA payload (most notably the TDRS (Tracking and Data Relay Satellite) constellation into a geostationary orbit on either the Shuttle (STS), Titan III, or Titan IV.

IUS's first launch was in 1982 on a Titan 34D rocket from the Cape Canaveral Air Force Station shortly before the STS-6 mission. Boeing was the primary contractor for the IUS . Chemical Systems Division of United Technologies built the IUS solid rocket motors .