This Week in NASA History: The First Use of Transfer Orbit Stage – Sept. 25, 1992

This week in 1992, the Transfer Orbit Stage, or TOS, a single-stage, solid propellant upper stage vehicle used to propel a spacecraft from low-Earth orbit on journeys to geostationary orbit or toward interplanetary destinations, was used for the first time with the launch of the Mars Observer aboard a Titan III launch vehicle.

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