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5. Contingency abort 

Space Shuttle Directive number S01660, signed February 5, 1975, added contingency aborts to the Space Shuttle design. Software and crew procedures were implemented to provide flight techniques (mostly manual) for response to contingent situations resulting in the loss of multiple SSME thrust during first stage ascent. Most cases result in an Orbiter water ditching.

6. FAST-SEP

First stage Orbiter abort is referred to as FAST-SEP because many of the time delays required for nominal reconfiguration of the Space Shuttle systems for separation of the Orbiter from the ET are either bypassed or are drastically shortened. Nominal shutdown of SSME's reconfiguration of fluid valves, separation of umbilicals, deadfacing and separation of electrical connectors, and charging and firing of separation pyrotechnics require 18 seconds. Such a long timeline is not consistent with any hypothesized first stage time critical failure scenario. The genesis of FAST-SEP occurred at the Space Shuttle Configuration Design Review with the review item discrepancy (RID) number 03.00.151 which stated the requirement to separate the Orbiter from the ET at any time. The resulting actions, directives, and revised directives detailed in table C1 occurred in order to resolve the conflict between the requirement to separate "as quickly as possible" and to separate "safely." To perform these separation functions "quickly" was not a "safe" thing to do. For example, fast shutdown of the SSME's could cause catastrophic failure of all three engines. The final resolution was to compromise and accept some risk in order to achieve approximately a 3.0-second sequence. As discussed later in this report, the dynamics of the execution of FAST-SEP during first stage will most likely result in the structural failure of the Orbiter in several modes; therefore, it was not reasonable to expend a large quantity of resources to analyze the detailed flight dynamics of the vehicle. This particular fact was the rationale that was behind the directives to implement the software but not the performance analyses. 

FAST-SEP is not without utility, however. There exists a collection of contingency abort cases that are time critical and need every fraction of a second that can be trimmed out of the Orbiter-ET separation sequence. In general, contingency aborts are executed by lofting the vehicle, post SRB burnout and separation, to a point where aerodynamic pressures are low enough not to interfere with safe separation without recontact. However, the vehicle has experienced the loss of two SSME's and is in a bad situation with respect to the thrust-to-weight ratio such that it is "falling out of the sky." The resulting high rate of descent means that very little time is available for the separation to be executed and for the vehicle to be maneuvered from separation attitude to entry flight attitude before the aerodynamic pressures build up to hazardous levels that may exceed structural limits. FAST-SEP has been incorporated into the flight techniques for contingency aborts to help alleviate this problem.

-C6-

Transcription Notes:
Has already been reviewed. This document was reopened for transcribing to account for spelling errors.