Graphite-Epoxy Motor
 A GEM 40 solid rocket motor being prepared for integration with a Delta II launch vehicle | |
| Manufacturer |
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|---|---|
| Country of origin | United States |
| Used on | |
| Associated stages | |
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| Launch history | |
| Status | Active |
| First flight | November 26, 1990 |
The Graphite-Epoxy Motor (GEM) is a family of solid rocket boosters developed in the late 1980s and first flown in 1990. The motors use casings made from carbon-fiber-reinforced polymer and a propellant consisting of ammonium perchlorate composite propellant, formulated with hydroxyl-terminated polybutadiene as a binder, ammonium perchlorate as an oxidizer, and aluminum powder as a fuel.
Production of GEM motors has passed through several companies due to mergers and acquisitions. They were manufactured by Hercules from 1990 to 1995, Alliant Techsystems from 1995 to 2015, and Orbital ATK from 2015 to 2017, before being taken over by Northrop Grumman in 2017.
GEM boosters are used on the Vulcan Centaur launch vehicle operated by United Launch Alliance (ULA), as well as the Ground-Based Interceptor missile, and were previously flown on the Delta II, Delta III, Delta IV, and Atlas V. Motor designations include numerals indicating booster diameter in inches.
The series originated with the GEM 40 for the Delta II, followed by the larger GEM 46 for the Delta III and Delta II Heavy, which increased length and diameter and introduced optional thrust vectoring nozzles. The GEM 60 was subsequently developed for the Delta IV, providing additional liftoff thrust for Medium+ configurations with fixed or vectorable nozzles. The GEM 63 was a replacement for the older AJ-60A in order to reduce costs and increase performance on Atlas V. The GEM 63XL for the Vulcan Centaur is the only current GEM motor in use.