Inertial Upper Stage - Applications

Applications

The IUS was a two-stage rocket launched by either a Titan family booster or as a "cargo" by the Space Shuttle. On Titan launches, the Titan booster would launch the IUS, carrying the payload into low earth orbit where it was separated from the Titan and ignited its first stage, which carried it into an elliptical "transfer" orbit to higher altitude. On Shuttle launches, the cargo bay was opened, the IUS and its payload raised to a 50° angle, and released. After the Shuttle separated from the payload to a safe distance, the IUS first stage ignited and, as on a Titan booster mission, entered "transfer orbit". Upon reaching apogee, the first stage and an interstage structure were jettisoned. The second stage then fired to circularlize the orbit, after which it released the satellite and, using its attitude control jets, began a retrograde maneuver to enter a lower orbit to avoid any possibility of collision with its payload.

In addition to the Communication and Reconnaissance missions described above, which placed the payload into stationary (24 hour) orbit, the IUS was also used to boost Planetary spacecraft. For these missions, the second IUS stage was separated and ignited immediately after first stage burnout. Igniting the second stage at low altitude provided the extra velocity the spacecraft needed to escape from earth orbit.

The final flight of the IUS occurred in February 2004.