for these upgrades—most of which have been or are being implemented—was approximately $1.5 billion. (The health monitoring system for the main engine is still in the early research and development (R&D) stage.)

While these safety and reliability improvements were under development, the shuttle program was undergoing substantial cuts in contractors and civil service personnel and was implementing many changes to reduce the program's operational budget. In a five-year period, the shuttle budget was cut from $3.5 billion per year to $2.9 billion per year (in real-year dollars), while the flight rate of six to eight shuttle launches per year was maintained.

Three events in 1993 resulted in additional upgrades to the space shuttle system. A new program in which the shuttle would rendezvous and dock with the Mir space station required several modifications to the orbiter, including the development of a new payload bay airlock/docking system. The ASRM program was canceled, depriving the shuttle of approximately 5,000 kg of additional payload capacity. Finally, the planned orbit for the newly restructured International Space Station (ISS) was moved to a 51.6 degree inclination. The new orbit was compatible with Russian launch facilities but reduced the amount of payload the shuttle could deliver to the ISS by more than 5,000 kg.

In order to address these decrements, the shuttle program embarked on a campaign to improve the shuttle's payload capability significantly so that it could meet the ISS program requirements. The largest upgrade was a super lightweight tank, a $200 million program that increased the payload the shuttle could deliver to the ISS by 3,500 kg. Additional upgrades, including lightweight crew seats, adjustments to trajectory and propellant reserves, and many minor weight reductions throughout the orbiter, increased payload capacity by approximately another 4,000 kg.

The national policy debate about the possible replacement of the shuttle took another step forward with the National Space Transportation Policy of August 5, 1994 (White House, 1994). This policy charged NASA to “provide for the improvement of the space shuttle system, focusing on reliability, safety, and cost-effectiveness” and also to “be the lead agency for technology development and demonstration for next-generation reusable space transportation systems, such as the single-stage-to-orbit concept.” Following the release of this policy statement, NASA initiated the X-33 and X-34 prototype demonstration programs to test technologies for low-cost, highly reliable access to space. To free its scarce resources for the new programs, NASA decided to further reduce the cost of the shuttle program where possible, consistent with flight safety.

In February 1995, the Space Shuttle Management Independent Review Team issued a report (known as the Kraft report) recommending a freeze of the space shuttle configuration to cut costs (NASA, 1995). According to the report, “freezing the current vehicle configuration, hardware, and software will stabilize the program and allow reductions in cost.” The Kraft report also recommended that “future changes should be minimized and [should] concentrate on making the

Front Matter (R1-R10)

Executive Summary (1-8)

1 Background (9-13)

2 Shuttle Upgrades Program (14-20)

3 Choosing Upgrades (21-37)

4 Assessments of Proposed Upgrades (38-56)

Appendix A: Statement of Task (57-59)

Appendix B: Biographical Sketches of Committee Members (60-63)

Appendix C: Shuttle Upgrades Presented to the Committee (64-65)

Apendix D: List of Recommendations (66-70)

acronyms (71-72)