 The Titan IIID was the Vandenberg Air Force Base version of the Titan IIIC, without a Transtage, that was used to place members of the Key Hole series of reconnaissance satellites into polar low Earth orbits.The Titan IIIE, with a high-specific-impulse Centaur upper stage, was used to launch several scientific spacecraft, including both of NASA's two Voyager space probes to Jupiter, Saturn and beyond, and both of the two Viking missions to place two orbiters around Mars and two instrumented landers on its surface.The Titan IV was an extended length Titan III with solid rocket boosters on its sides.