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XXIII. PRELIMINARY FINDINGS - TAL CONSIDERATIONS

The findings for the TAL considerations are presented and are further discussed as appropriate.

1. TAL EXPOSURE FOR A SINGLE SSME FAILURE MANY NOT BE AVOIDABLE FOR A FEW PAYLOADS.

2. THE TAL ABORT MODE PROVIDES INTACT ABORT COVERAGE BETWEEN RTLS AND AOA FOR SINGLE SSME FAILURES AND PROVIDES EXCELLENT COVERAGE FOR LESS LIKELY MULTIPLE SSME FAILURES AND A RANGE OF SYSTEM FAILURES.

3. TAL ABORTS PROVIDE A REASONABLE PROGRAM TRADE BETWEEN MISSION PERFORMANCE CAPABILITY AND EXTENDED TURNAROUND IN THE EVENT OF A TAL LANDING.

4. THE STS 61-C BRAKE STATOR FAILURE HAS RENEWED CONCERN THAT THE LANDING/DECELERATION SYSTEMS ON THE ORBITER AND THE CURRENT BRAKE ENERGY LIMITS FOR TAL COUPLED WITH CURRENT ALLOWABLE WIND LIMITS PUSH THE ORBITER'S ABILITY TO REMAIN ON THE RUNWAY TO THE DESIGN LIMITS OF THE PARTICULAR SYSTEMS.

PROGRAM ACTION: COMPLETE ANALYSIS OF STS 61-C STATOR FAILURE, REEVALUATE HEADWIND/TAILWIND, CROSSWIND, AND BRAKE ENERGY LAUNCH COMMIT LIMITS FOR TAL LANDINGS. CONSIDER REVISING THESE PLACARDS CONSISTENT WITH REALISTIC EXPECTED MAXIMUM PERFORMANCE FROM THE LANDING/DECELERATION SYSTEM AND/OR CONSIDER MINIMIZING ABORT GAPS UNTIL THE LANDING DECELERATION SYSTEM IS UPGRADED TO PROVIDE REASONABLE MARGINS.

The real concern is the uncertainty in the landing deceleration system margins. In the KSC landing case, actual low performance conditions with the braking system still provided adequate rollout protection using worst case scenarios. This is not true for the TAL case. Clearly, TAL landings will be heavy landings and available brake energy will be the issue. Today, with the stator failures observed, the entire community is concerned about the ability of the Orbiter to stop on the DAKAR runway (or Easter Island, etc.). The program obviously recognizes this same concern as evidenced by the recent decision to add runway rollout barriers at key sites. The program must move to improve the landing/deceleration system margins so that the TAL intact abort mode offers the same surviveability [[survivability]] as the RTLS. In all probability, the same improvements that would make routine KSC operations acceptable would also go a long way towards making the TAL landing/rollout situation acceptable.

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