Single-Orbit Trajectory

If one of the core stage engines failed after T + 3m10s, Buran could still reach orbit, but the exact scenario depended on when the failure occurred and how much propellant Buran’s DOM engines needed to achieve that orbit, something that was calculated by the on-board computers. If the failure happened late in the launch, Buran’s DOM engines could have boosted the vehicle to its nominal orbit or to a lower but still usable orbit (in NASA parlance the latter scenario is called “Abort to Orbit’’, performed once by Challenger on STS-51F in July 1985). If it occurred much earlier, the remaining propellant in the core stage would have been burned to depletion, with Buran then firing its DOM engines to reach a very low orbit and somewhat later re-igniting those engines to initiate re-entry. Excess DOM propellant would have been expended prior to entry interface to meet center-of-gravity require­ments. This “Single-Orbit Trajectory” (OT) abort is the same as an Abort Once Around (AOA) on Shuttle launches [31].