The boosters can produce 371.5K pounds of maximum thrust and were developed in partnership with United Launch Alliance to equip the Atlas V launch vehicle with additional lift capability, Northrop said Friday.
Aside from GEM 63, Northrop produced eight retro motors to handle the rocket's first and second stage separation and propellant tanks for the Atlas V reaction control system.
Atlas V flew Nov. 13 from Cape Canaveral Air Force Station in Florida carrying a national security payload from NRO.
Northrop is currently developing the GEM 63XL motor for ULA's Vulcan Centaur spacecraft.
GEM 40, which is the first unit in the GEM family of strap-on boosters, supported 132 Delta II missions in the 1980s.