Transtage, given the United States Air Force designation SSB-10A, was an American upper stage used on Titan III rockets, developed by Martin Marietta and Aerojet.

[2] Transtage used a pressure-fed two-chamber configuration, using Aerozine 50 fuel and nitrogen tetroxide as oxidizer; the thrust chambers were gimbaled for steering and each produced 8,000 lbf (36 kN) of thrust.

[3] The design specification required up to three restarts during the first six hours of a mission.

[6] The first launch, boosted by a Titan IIIA, occurred on 1 September 1964;[7] the Transtage failed to pressurize, resulting in premature engine cutoff, and a failure to reach orbit.

The last launch of a Transtage was on 4 September 1989, boosted by a Titan 34D rocket.