NASA Jet Propulsion Laboratory California Institute of Technology JPL HOME EARTH SOLAR SYSTEM STARS & GALAXIES SCIENCE & TECHNOLOGY JPL Email News RSS Mobile Video
Follow this link to skip to the main content
JPL banner - links to JPL and CalTech
left nav graphic Overview Science Technology The Mission People Spotlights Events Multimedia All Mars
Mars for Kids
Mars for Students
Mars for Educators
Mars for Press
+ Mars Home
+ Rovers Home
image link to mission page
image link to summary page
image link to rovers update
Where are they now?
month in review
image link to mission team
link to launch vehicle page
Stage I
Solid Rocket Motors
Payload Fairing
Stage II
Stage III
image link to spacecraft
link to mission timeline page
communications to earth
Launch Vehicle: Solid Rocket Motors

Summary | Stage I | Solid Rocket Motors | Payload Fairing | Stage II | Stage III

Nine strap-on rocket motors are used to increase the main engine thrust. They use a solid rocket fuel called hydroxyl-terminated polybutadiene (HTPB) propellant. HTPB is a hard rubbery material that binds together the fuel and oxidizer.

The rocket motors are made of a graphite-epoxy shell that is about 4 to 5 times lighter than metals. These shells provide the outer structure for the solid rocket motor fuel. The rocket motors are familiarly known as graphite-epoxy motors, or "GEMs."

Six of the nine GEMs are ignited at the time of lift-off. The remaining three, with extended nozzles, are ignited shortly after the initial six GEMs burn out and when the spacecraft is lighter due to the burning of fuel from Stage I.

image of solid rocket motorsSize, Weight, and Power of the GEMs

For the Rover A mission, which used the standard Delta II 7925 launch vehicle, the GEMs are 1016 mm (40 in) in diameter and are fueled with approximately 12,000 kg (26,400 lbs) of hydroxyl-terminated polybutad Each GEM provides an average thrust of 498,000 N (112,000 lbs).

For the Rover B mission, which used the Delta II 7925H, the GEMs are 1168 mm (46 in) in diameter. The GEMs for the Delta II 7925H are also longer than the GEMs used on the Delta II 7925. The Delta II 7925H GEMs provide approximately 25 percent more thrust than the standard Delta II GEMs.

See also the reasons for the differences.
PRIVACY    |     FAQ    |     SITEMAP    |     CREDITS