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to 15 years old.) The ASRM system weighed approximately 100 000 [[100,000]] pounds and generated 300 000 [[300,000]] pounds of thrust each. The function of the system was to provide an escape path for the Orbiter and crew during the first stage ascent from 4.5 seconds to 30 seconds. The ASRM's would input enough energy into the Orbiter to permit a glide return to the launch site. Without this extra boost, the Orbiter either did not have enough energy to glide back to the launch site or, in the first few seconds, to recover to wings level flight. After 30 seconds, the range and energy of the launch configuration was sufficient for the Orbiter to glide back to the launch site without the need for an additional boost from the ASRM's; therefore, at this point, the ASRM's were jettisoned. After 90 seconds of ascent, the Orbiter was too far downrange to be able to glide back to the launch site and was committed to a water ditching for first stage contingencies occurring from 90 seconds to SRB burnout (120 seconds).

The ASRM's were deleted on August 9, 1972, by Space Shuttle Directive number SS00015. The rationale given at the Level I Configuration Control Board (CCB) was that many first stage failures were non-time critical and could be postponed until after SRB burnout, that the highest risk for SRB burnthrough [[burn-through]] was late in first stage flight where no protection was available (i.e., loss of Orbiter due to water ditching), and that premature attach separation could be prevented by other means. Key charts from that presentation are included as figures C3 and C4. The key decision parameters were that the ASRM system provides little protection for the highest risk area and that the program must accept that risk and design to preclude failures for that latter portion of first stage ascent; therefore, with that philosophy, the ASRM's had even less value. (NOTE: Today's analyses of system performance show that glideback is not available at the 30-second point but at the 50-second point, and that the downrange point-of-no-return occurs at 70 seconds rather than 90 seconds. These new data further constrain the utility of ASRM's and support the decision to delete.)

2. Thrust Termination

Thrust termination (or thrust neutralization) was a concept proposed for the Titan III-M manned booster for the Air Force's Manned Orbiting Laboratory Program. This system was proposed for the original Space Shuttle design. The objective of TT was to either greatly reduce SRB thrust or to completely extinguish the motor burn. Without the SRB thrust, several options are available for emergency action, such as crew ejection or complete Orbiter "ejection." Concepts for TT had the principal drawback that the action of TT introduced significant dynamic loads into the vehicle which caused failure of several structural components as designed at that time, and the weight impact to strengthen the vehicle summed with the TT systems was on the order of 19 600 [[19,600]] pounds.

TT was deleted on April 27, 1973, by Space Shuttle Directive number SS00040. The arguments for deletion were similar to those presented for ASRM deletion. The charts presented at the Systems Integration

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Transcription Notes:
Has been reviewed. Editing opened back up for minor spelling errors.