# Graphite-Epoxy Motor

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American solid rocket booster

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](/source/Solid_rocket_booster) developed in the late 1980s and first flown in 1990. The motors use casings made from [carbon-fiber-reinforced polymer](/source/Carbon-fiber-reinforced_polymers) and a propellant consisting of [ammonium perchlorate composite propellant](/source/Ammonium_perchlorate_composite_propellant), formulated with [hydroxyl-terminated polybutadiene](/source/Hydroxyl-terminated_polybutadiene) as a binder, [ammonium perchlorate](/source/Ammonium_perchlorate) as an oxidizer, and [aluminum powder](/source/Aluminum_powder) as a fuel.

Production of GEM motors has passed through several companies due to [mergers and acquisitions](/source/Mergers_and_acquisitions). They were manufactured by [Hercules](/source/Hercules_Inc.) from 1990 to 1995, [Alliant Techsystems](/source/Alliant_Techsystems) from 1995 to 2015, and [Orbital ATK](/source/Orbital_ATK) from 2015 to 2017, before being taken over by [Northrop Grumman](/source/Northrop_Grumman) in 2017.

GEM boosters are used on the [Atlas V](/source/Atlas_V) and [Vulcan Centaur](/source/Vulcan_Centaur) launch vehicles operated by [United Launch Alliance](/source/United_Launch_Alliance) (ULA), as well as the [Ground-Based Interceptor](/source/Ground-Based_Interceptor) missile, and were previously flown on the [Delta II](/source/Delta_II), [Delta III](/source/Delta_III), and [Delta IV](/source/Delta_IV). Motor designations include numerals indicating booster diameter in inches.[1]

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](/source/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. Current variants include the GEM 63 for the Atlas V and the GEM 63XL for the Vulcan Centaur.[1]

## Active variants

### GEM 63

The GEM 63 is a 63.2-inch-diameter (1,610 mm) solid motor used on the Atlas V. It was developed by Orbital ATK as a "drop-in" replacement for the [AJ-60A](/source/AJ-60A) solid rocket booster built by [Aerojet Rocketdyne](/source/Aerojet_Rocketdyne). Its dimensions are similar to those of the AJ-60A. The Atlas V first flew with the GEM 63 on the NROL-101 mission in 2020.[2] According to ULA, the GEM 63 provides higher performance at about half the cost of the AJ-60A.[3]

### GEM 63XL

The GEM 63XL, developed by Northrop Grumman, is an extended version of the GEM 63, approximately 73 inches (190 cm) longer.[4] Each booster has a mass of about 117,000 pounds (53 metric tons).[5] Static test firings began in 2020, and the booster entered service with the Vulcan Centaur launch vehicle on its first flight on January 8, 2024.[6][7][8] Up to six GEM 63XLs can be mounted on a Vulcan core, depending on mission requirements.[9]

A variant equipped with a [thrust-vectoring](/source/Thrust_vectoring) nozzle, the GEM 63XLT, was under development for the cancelled [OmegA](/source/OmegA) launch vehicle.[10]

#### Anomalies

On October 4, 2024, a GEM 63XL experienced a partial failure about 35 seconds after liftoff during the Vulcan Centaur Cert-2 mission. change in the motor's exhaust plume and debris falling from the vehicle were observed. Analyses indicated damage or structural failure of the nozzle. Despite the anomaly, the mission reached orbit after burnout and separation of the two boosters at about 2 minutes 10 seconds into flight.[11] The nozzle failure was later attributed to manufacturing defects.[12]

In February 2026, another Vulcan mission experienced a performance anomaly affecting one of four solid rocket motors. A ULA vice president stated that "early during flight, the team observed a significant performance anomaly on one of the four solid rocket motors".[13]

## Retired variants

### GEM 40

A GEM 40 is hoisted for attachment to a [Delta II](/source/Delta_II)

The GEM 40 was a 40.4-inch-diameter (1,030 mm) solid rocket motor developed for the 7000-series [Delta II](/source/Delta_II) launch vehicle beginning in 1987 by [Hercules](/source/Hercules_Inc.).[14] Its first flight took place in 1990 on the USA-66 mission,[15] when 9 boosters were used on a Delta II 7925 launcher. The use of composite materials allowed for casings lighter than the steel casings of the [Castor 4](/source/Castor_(rocket_stage)) SRMs they replaced. The reduction in weight was used to extend the GEM 40 by 5.9 feet (1.8 m) compared to the Castor 4 used on 6000-series Delta II.[14][16] Delta II vehicles could be configured with three, four, or nine GEM 40 boosters. When using three or four boosters, all GEM 40s were ignited on the ground. On nine-booster Delta II, six were ignited on the ground; the remaining three were ignited in flight after burnout of the first six.[17]

#### Failures

On August 5, 1995, an GEM 40 failed to separate from a Delta II 7925 carrying [Koreasat 1](/source/Koreasat_1). The excess mass of the booster resulted in the satellite reaching a lower orbit than intended. The satellite was able to correct for the error using on-board propellant.[18]

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](/source/Self-destruct) function 13 seconds after ignition. An Air Force investigation determined that the motor's casing had been damaged prior to launch, causing the case to split open soon after ignition.[18]

### GEM 40VN

The GEM 40VN, a thrust-vectoring variant of the GEM 40, was developed for the [Ground-Based Midcourse Defense](/source/Ground-Based_Midcourse_Defense) (GMD) [anti-ballistic missile](/source/Anti-ballistic_missile) program.[19] It uses the same basic motor configuration as the GEM 40, with a modified nozzle assembly providing up to ±6-degree thrust vector control. The motor can be configured for in-line or strap-on applications, and an extended nozzle is available for air ignition. A version was qualified for use on the Boost Vehicle/Boost Vehicle Plus (BV/BV+) configurations of the GMD interceptor program.[1] The program later switched to an [Orion 50](/source/Orion_(rocket_stage))-based missile.

### GEM 46

The GEM 46 was a 45.1-inch-diameter (1,150 mm) solid rocket motor originally developed for [Delta III](/source/Delta_III) by [Alliant Techsystems](/source/Alliant_Techsystems). This solid motor variant included thrust vector control (TVC) to help steer the vehicle. After the discontinuation of the Delta III, GEM 46 motors (without TVC)[17] were used on the Delta II to create the Delta II Heavy, which could only be launched from a modified pad at [Cape Canaveral Air Force Station](/source/Cape_Canaveral_Space_Force_Station), [SLC-17B](/source/Cape_Canaveral_Space_Launch_Complex_17).[20] Both Delta III and Delta II Heavy used nine GEM 46s, with six ignited on the ground and three .[21]

#### Failures

On August 27, 1998, the GEM 46 boosters on the first Delta III, carrying the Galaxy 10 satellite, depleted their hydraulic fluid used to control the thrust-vectoring nozzle. This was due to guidance issues with the rest of the rocket, which forced the solid rocket motors to make rapid adjustments to compensate, using up the supply of hydraulic fluid before burnout. The nozzles were then stuck in a position that turned the rocket over, triggering the vehicle's self-destruct function 70 seconds after ignition.[22][23]

### GEM 60

A GEM 60 being prepared for integration onto a [Delta IV](/source/Delta_IV)

The GEM 60 was a 60-inch-diameter (1,500 mm) solid motor used on the [Delta IV](/source/Delta_IV) family of launch vehicles, used with and without thrust vector control.[17] Developed for the [EELV](/source/Evolved_Expendable_Launch_Vehicle) program, its first flight was on November 20, 2002, boosting the first launch of the Delta IV.[24] Delta IV Medium+ launchers were built with either two or four GEM 60.[25] The added performance from the solid rocket motors allowed variants of the Delta IV Medium+ to accommodate a larger second stage. The motor was retired in 2019 after the final Delta IV Medium launch.[26] Throughout its lifetime, 64 GEM 60 boosters were flown; there were no failures.[26]

## Version comparison

*Data from* Northrop Grumman catalog[1]

Name Application Length Diameter Mass Thrust Specific impulse Burn time (sec.) First flight Final flight Gross Propellant GEM 40 Delta II 11 m (435 in) 1.03 m (40.4 in) 12,962 kg (28,577 lb) 11,770 kg (25,940 lb) 643.8 kN (144,740 lbf) 274 s (2.69 km/s) 63.3 November 26, 1990 September 15, 2018 GEM 40 (air‑lit) 11 m (449.1 in) 13,101 kg (28,883 lb) 665.7 kN (149,660 lbf) 283.4 s (2.779 km/s) 63.3 GEM 40VN Ground-Based Interceptor 11 m (425.1 in) 13,102 kg (28,886 lb) 478.74 kN (107,625 lbf) 265.3 s (2.602 km/s) 64.6 GEM 46 Delta II Heavy, Delta III 12.59 m (495.8 in) 1.15 m (45.1 in) 18,860 kg (41,590 lb) 16,860 kg (37,180 lb) 611 kN (137,300 lbf) 277.8 s (2.724 km/s) 75.9 August 26, 1998 September 10, 2011 GEM 46 (air‑lit) 12.92 m (508.6 in) 19,069 kg (42,039 lb) 920 kN (206,000 lbf) 284 s (2.79 km/s) 75.9 GEM 46 (vectorable) Delta III 12.48 m (491.5 in) 19,140 kg (42,196 lb) 875 kN (196,600 lbf) 279.8 s (2.744 km/s) 76.9 August 23, 2000 GEM 60 Delta IV M+ 13.2 m (518 in) 1.5 m (60 in) 33,183 kg (73,156 lb) 29,698 kg (65,472 lb) 1,248.9 kN (280,767 lbf) 275 s (2.7 km/s) 90.8 November 20, 2002 August 22, 2019 GEM 60 (vectorable) 33,650 kg (74,185 lb) 1,235.9 kN (277,852 lbf) 274 s (2.69 km/s) GEM 63 Atlas V 20.1 m (792 in) 1.62 m (63.7 in) 49,342 kg (108,781 lb) 44,087 kg (97,195 lb) 1,649.6 kN (370,835 lbf) 279.06 s (2.737 km/s) 97.6 November 13, 2020 —N/a GEM 63XL Vulcan Centaur 22 m (865.3 in) 53,030 kg (116,920 lb) 47,853 kg (105,497 lb) 2,061 kN (463,249 lbf) 280.3 s (2.749 km/s) 87.3 January 8, 2024 —N/a

## Gallery

		- A GEM 46 motor prior to mating to a Delta II 7925H

		- Technicians prepare a GEM 46 booster

		- GEM 40 booster is towed to the integration facility

		- A Delta IV M+ (4,2) lifts off with 2 GEM 60 boosters

		- A Delta II 7920H ignites 9 GEM 46 boosters

		- An Atlas V 541 lifts off with 4 GEM 63 boosters

## See also

- [Solid rocket](/source/Solid_rocket)

- [Spacecraft propulsion](/source/Spacecraft_propulsion)

## References

1. ^ [***a***](#cite_ref-NG_Propulsion_Products_Catalog_1-0) [***b***](#cite_ref-NG_Propulsion_Products_Catalog_1-1) [***c***](#cite_ref-NG_Propulsion_Products_Catalog_1-2) [***d***](#cite_ref-NG_Propulsion_Products_Catalog_1-3) [*Propulsion Products Catalog*](https://www.prd.ngc.agencyq.site/wp-content/uploads/NG-Propulsion-Products-Catalog.pdf) (PDF). [Northrop Grumman](/source/Northrop_Grumman). pp. 29–39. Retrieved October 24, 2024.

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1. **[^](#cite_ref-10)** Northrop Grumman [@northropgrumman] (November 21, 2019). ["We've started winding our first GEM 63XLT!"](https://twitter.com/northropgrumman/status/1197536657798520833) ([Tweet](/source/Tweet_(social_media))). Retrieved May 9, 2022 – via [Twitter](/source/Twitter).

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1. ^ [***a***](#cite_ref-:2_14-0) [***b***](#cite_ref-:2_14-1) Vlahakis, Nick; Va, Darryl (1989), ["Graphite epoxy motors (GEM) for the Delta II launch vehicle"](https://arc.aiaa.org/doi/abs/10.2514/6.1989-2313), *25th Joint Propulsion Conference*, American Institute of Aeronautics and Astronautics, [doi](/source/Doi_(identifier)):[10.2514/6.1989-2313](https://doi.org/10.2514%2F6.1989-2313), retrieved May 7, 2022

1. **[^](#cite_ref-15)** McDowell, Jonathan (May 7, 2022). ["Launch Log"](https://planet4589.org/space/gcat/data/derived/launchlog.html). *Jonathan's Space Report*. [Archived](https://web.archive.org/web/20220507204819/https://planet4589.org/space/gcat/data/derived/launchlog.html) from the original on May 7, 2022. Retrieved May 7, 2022.

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1. ^ [***a***](#cite_ref-atkp_17-0) [***b***](#cite_ref-atkp_17-1) [***c***](#cite_ref-atkp_17-2) ["ATK Product Catalog"](https://web.archive.org/web/20180730082316/http://www.ltas-vis.ulg.ac.be/cmsms/uploads/File/DataSheetSolidATK.pdf) (PDF). *ATK*. Archived from [the original](http://www.ltas-vis.ulg.ac.be/cmsms/uploads/File/DataSheetSolidATK.pdf) (PDF) on July 30, 2018. Retrieved July 24, 2014.

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v t e Rocket engines and solid motors for orbital launch vehicles Comparison of orbital rocket engines Liquid fuel Cryogenic Hydrolox (LH2 / LOX) China YF-73 YF-75 YF-75D YF-77 YF-79 YF-90 Europe HM7B Vinci Vulcain India CE-7.5 CE-20 Japan LE-5 LE-7 LE-9 Russia KVD-1 (RD-56) RD-0120 RD-0146 United States BE-3U BE-7 J-2 RL10 RS-2200 RS-25 RS-68 RS-83 TR-106 XRS-2200 Methalox (CH4 / LOX) China BF-20 Lingyun Longyun TQ-11 TQ-12 TQ-15A YF-209 YF-215 United States BE-4 Raptor Archimedes Aeon 1 Aeon R Russia RD-0169 Europe Prometheus M10 Semi- cryogenic Kerolox (RP-1 / LOX) China TH-11 TH-12 YF-100 YF-102 YF-115 YF-130 Welkin India SCE-200 Russia NK-15 NK-33, 44 RD-58 RD-0105, 0109 RD-0107, 0108, 0110 RD-0110R RD-0124 RD-107, 108, 117, 118 RD-120 RD-170, 171 RD-180 RD-191, 151, 181 RD-193 S1.5400 Spain TEPREL Ukraine RD-8 RD-801 RD-810 United States AR1 F-1 H-1 Kestrel LR-79 LR89 LR105 LR70-NA , S-3D Merlin Miranda RS-27 RS-27A RS-56 RS-84 S-3D Rutherford TR-107 XLR50 Storable Hypergolic (Aerozine, UH 25, MMH, or UDMH / N2O4, MON, or HNO3) China YF-1, 2, 3 YF-20, 21, 22, 24, 25 YF-23 YF-40 YF-50D Europe Aestus Astris Vexin Viking India PS4 Vikas Israel LK-4 North Korea Paektusan LRE along other LREs Russia 17D61 RD-0202 to 0206, 0208 to 0213 RD-0207, 0214 RD-0216, 0217, 0235 RD-0233, 0234 RD-0236 RD-0237 RD-0243 to 0245 RD-0255 to 0257 RD-215 to 219 RD-250 to 252, 261, 262 RD-253, 275 RD-263, 268, 273 RD-270 S5.92 S5.98M Ukraine RD-843 RD-854, 861 RD-855 RD-856 RD-864, 869 United States AJ10 LR-87 LR-91 RS-88* TR-201 VTR-10 XLR81* Other Russia RD-0410 RD-109, 119 RD-211 to 214 UK Gamma United States Curie Kiwi A, Kiwi B NERVA RS-88* XLR81* Solid fuel China FG-02 FG-36 FG-46 FG-47 SpaB-65 SpaB-140C Europe Mage 1 P-4 P-6 PAP P80 P120C P230 Topaze Waxwing Zefiro 9 Zefiro 23 Zefiro 40 India S7 S9 S12 S139 S200 Iran Salman Rafe Israel LK-1 RSA-3 Japan KM-V1 KM-V2b M-14 M-24 M-34 M-34c SRB-A United States AJ-60A Algol Castor 30 GEM Orbus-6 Orbus-21 Orion Space Shuttle SRB Star 37 Star 48 UA120 SRMU X-248 X-254 * Different versions of the engine use different propellant combinations Engines in italics are/were under development

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Adapted from the Wikipedia article [Graphite-Epoxy Motor](https://en.wikipedia.org/wiki/Graphite-Epoxy_Motor) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Graphite-Epoxy_Motor?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.