Graphite-Epoxy Motor

Graphite-Epoxy Motor
	A GEM 40 solid rocket motor being prepared for integration with a Delta II launch vehicle
Manufacturer	Hercules (1990‍–‍1995); Alliant Techsystems (1995‍–‍2015); Orbital ATK (2015‍–‍2017); Northrop Grumman (2017‍–‍present);
Country of origin	United States
Used on	Ground-Based Interceptor; Delta II; Delta III; Delta IV; Atlas V; Vulcan Centaur; OmegA (Cancelled);
Associated stages
Comparable	AJ-60A; Castor;
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 currently used on the Atlas V and Vulcan Centaur launch vehicles operated by United Launch Alliance (ULA), as well as the Ground-Based Interceptor missile, and were previously flown on the Delta II, Delta III, and Delta IV. The motor names include numerals that denote the diameter of the booster in inches.