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Graphite-Epoxy Motor

Graphite-Epoxy Motor
Delta II GEM 40 Booster.jpg
A GEM-40 is hoisted for attachment to a Delta II
Manufacturer Alliant Techsystems
Country of origin United States
Used on Delta II, Delta III, Delta IV
Launch history
Status Active
GEM-40
Length 11.4 m (449 in)
Diameter 1.0 m (40 in)
Gross mass 13,005 kg (28,671 lb)
Propellant mass 11,767 kg (25,942 lb)
Thrust 499 kN (112,200 lbf)
Specific impulse

245 s (sea level)

283 s (air-lit)
Burn time 63 seconds
Fuel HTPB
GEM-46
Length 12.6 m (495 in)
Diameter 1.2 m (46 in)
Gross mass 19,140 kg (42,196 lb)
Propellant mass 16,860 kg (37,180 lb)
Thrust 601 kN (135,200 lbf)
Specific impulse

242 s (sea level)

284 s (air-lit)
Burn time 77 seconds
Fuel HTPB
GEM-60
Length 13.2 m (518 in)
Diameter 1.5 m (60 in)
Gross mass 33,638 kg (74,158 lb)
Propellant mass 29,697 kg (65,471 lb)
Thrust 879 kN (197,500 lbf)
Specific impulse 245 s (sea level)
Burn time 91 seconds
Fuel HTPB

245 s (sea level)

242 s (sea level)

A Graphite-Epoxy Motor (GEM) is a solid-fuel rocket motor (SRM) produced by Orbital ATK (Formerly Alliant Techsystems) with an epoxy composite casing. GEM boosters have been used on the Delta II, Delta III, and Delta IV, and are planned for future use on the Atlas V and Vulcan.

On August 5, 1995, an air-lit GEM-40 failed to separate from a Delta II 7925 carrying Koreasat I. 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 (Delta 241) 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.


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