Graphite-Epoxy Motor


The Graphite-Epoxy Motor is a series of solid rocket boosters fueled by HTPB and produced by Northrop Grumman Innovation Systems with a carbon-fiber-reinforced polymer casing. GEM series boosters were previously used on the Delta II, Delta III, and Delta IV. They will fly on Atlas V, Vulcan, and the proposed OmegA.

Active variants

GEM-63

The GEM-63 is being developed as a drop-in replacement for the Aerojet Rocketdyne AJ-60A booster used on the Atlas V. The Atlas V will begin flying with the GEM-63 in 2020 with the STP-3 launch.

GEM-63XL

The GEM-63XL is about 5 feet longer than the regular GEM-63 and will be used on the Vulcan, OmegA launch vehicles starting in 2021.
GEM-63XL offers higher performance at almost half the cost of the AJ-60A boosters currently being used on the Atlas V.

Version comparison

Retired variants

GEM-40

The GEM-40 is a SRM used on Delta II beginning in 1990. The use of composite materials allowed for booster casings lighter than the steel casings of the Castor 4 SRMs they replaced. The first flight of a GEM-40 occurred in 1990 on a Delta II 7925. Delta II vehicles can use three, four, or nine GEM-40s. When using three or four boosters, all GEM-40s ignite on the ground, while on Delta IIs using nine boosters six are ignited on the ground, and the remaining three are ignited in the air when the first six burn out.

Failures

On August 5, 1995, an air-lit GEM-40 failed to separate from a Delta II 7925 carrying Koreasat 1. The excess mass of the booster resulted in the satellite reaching a lower than intended transfer orbit, which it was able to compensate for using on-board propellant.
On January 17, 1997, a Delta II exploded due to a catastrophic failure in a GEM-40. The failure triggered the launch vehicle's self-destruct function 13 seconds after ignition. An Air Force investigation determined that the motor's casing had been damaged prior to launch, resulting in the casing splitting open soon after ignition.

GEM-46

The GEM-46 was a lengthened solid motor originally developed for Delta III. This solid motor variant also included thrust vector control to help steer the vehicle. After the discontinuation of the Delta III, GEM-46 motors were used on the Delta II to create the Delta II Heavy, which could only be launched from a modified pad at Cape Canaveral. Both Delta III and Delta II-Heavy used nine GEM-46s, with six ignited on the ground and three air-lit.

GEM-60

The GEM-60 was a solid motor used on the Delta IV family of launch vehicles, available with and without Thrust Vector Control. A Delta IV Medium+ can use two or four GEM-60s, and was retired after the launch of a GPS-III satellite which launched on 22 August 2019.