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being representative of actual water landing cases. Thus, it is generally assumed that actual ditching is far more hazardous than as determined in the test program. This issue was reviewed by the Crew Safety Panel and by the Flight Techniques Panel, and the consensus of the panels was that the probability of surviving an Orbiter water ditching was low. C. FAST-SEP 1. Functional Description Functionally, FAST-SEP is available anytime after SRB ignition. The crew functions required to initiate the sequence are to place the "ET-SEP AUTO/MAN" switch in the MAN position and push the "ET-SEP INITIATE" pushbutton. The software will initiate the ET SEP sequence, shut down the SSME's, close the main propulsion system prevalves, wait for the SSME thrust to decay and the pyrotechnic initiators to charge, fire the separation pyrotechnics, and configure the flight control system for glide return to launch site (GRTLS) flight control mode. 2. Performance The discussion of Orbiter performance is divided into two regimes, separation and glide flight. The primary forces acting on the Orbiter after separation are the reaction force from the SRB thrust acting at the aft attach point on the Orbiter, and the aerodynamic forces. Although the RCS will be fired during this time period, the RCS forces are negligible as compared to the other two forces. As a result of these forces, the Orbiter pivots on the aft attach because of the application of the force substantially below the center mass of the Orbiter and the Orbiter quickly achieves very high angles of attack because of angular acceleration on the order of 40 to 60 deg/sec^2. If it can be assumed that the Orbiter can be recovered from this initial upset, the performance of the GRTLS flight is as follows. • Mission elapsed time (MET) < 50 seconds (alt = 25 kft, Mach = 1.1): The Orbiter has insufficient energy and altitude to recover to wings-level equilibrium flight and/or glide back to the launch site. • 50 < MET < 70 seconds: The Orbiter has sufficient energy and range to glide back to a landing at the launch site. • MET > 70 seconds: (alt = 45 kft, Mach = 1.7): The Orbiter is too far downrange to be capable of flying back to the launch site and, therefore, is committed to a water ditching. Therefore, a 20-second window between MET of 50 and 70 seconds exists in which the Orbiter and crew may be recovered. After 70 seconds, there is an additional 50-second window in which there exists potential to recover the crew, but the Orbiter will be lost because of ditching. -C11-
Transcription Notes:
This document has been thoroughly reviewed and was reopened for editing to correct the following mistakes:
Document read fore instead of fire in 2nd paragraph
Document read tow instead of two in 3rd paragraph
Document read aft instead of kft under the bullet point Mission elapsed time
