Graphite-Epoxy Motor

A GEM-40 Solid rocket booster 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
Length 449 in (11.4 m)
Diameter 40 in (1.0 m)
Gross mass 28,671 lb (13,005 kg)
Propellant mass 25,942 lb (11,767 kg)
Engines Solid
Thrust 112,200 lbf (499 kN)
Specific impulse 245 s (sea level)

283 s (air-lit) [1]

Burn time 63 seconds
Length 495 in (12.6 m)
Diameter 46 in (1.2 m)
Gross mass 42,196 lb (19,140 kg)
Propellant mass 37,180 lb (16,860 kg)
Engines Solid
Thrust 135,200 lbf (601 kN)
Specific impulse 242 s (sea level)

284 s (air-lit) [2]

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

A Graphite-Epoxy Motor (GEM) is a solid rocket motor (SRM) produced by Alliant Techsystems with an epoxy composite casing, used as boosters for the Delta II, Delta III, and Delta IV launch vehicles. The use of composite materials allowed for booster casings several times lighter than the steel casings of the Castor 4 SRMs they replaced.[3] The first flight of a GEM-40 occurred in 1990 on a Delta II 7925.[4]


A Boeing Delta IV launching with two GEM-60 solid motors.
The GEM-40 is a 40-inch-diameter (1,000 mm) SRM used on Delta II beginning in 1990. 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.[5]
The GEM-46 was a lengthened 46-inch-diameter (1,200 mm) solid motor originally developed for Delta III. This solid motor variant also included thrust vector control (TVC), which helped to steer the vehicle by changing (or vectoring) the direction of the thrust. With the discontinuation of the Delta III, the GEM-46 motors (without TVC)[5] were also used on the Delta II Heavy variant, where they could only be launched from a modified pad at Cape Canaveral.[6] Both Delta III and Delta II-Heavy used nine GEM-46s, with six ignited on the ground and three air-lit.[7][8]
The GEM-60 is a 60-inch-diameter (1,500 mm) solid motor used on the Delta IV family of launch vehicles. These motors are available with and without TVC.[5] A Delta IV can have two or four GEM-60s, and a Delta IV with these motors is classified as a Delta IV Medium+ launch vehicle.[9]


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.[10]

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.[10]

External links

  • Alliant Techsystems

See also


  1. ^ "GEM 40". Retrieved 24 July 2014. 
  2. ^ "GEM 46". Retrieved 24 July 2014. 
  3. ^ "Launch Vehicle: Solid Rocket Motors". JPL. Retrieved July 2014. 
  4. ^ "GEM 40". Astronautix. Retrieved July 2014. 
  5. ^ a b c "ATK Product Catalog". ATK. Retrieved July 2014. 
  6. ^ "ULA Delta II successfully lofts OCO-2 to orbit". Retrieved July 2014. 
  7. ^ "Delta II 7920H-10". Spaceflight 101. Retrieved July 2014. 
  8. ^ "Delta III Data Sheet". Space Launch Report. Retrieved July 2014. 
  9. ^ "Delta IV Medium+ (4,2)". Spaceflight 101. Retrieved July 2014. 
  10. ^ a b "Delta 2 Productive Years". Space Launch Report. Retrieved July 2014.