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Shuttle Thrust Augmentation

As the Advanced KEYHOLE satellite grew in weight, the need for shuttle thrust augmentation became apparent (NASA estimated that about 3 to 5 launches per year could use thrust augmentation beginning in the mid-1980s."(1))

The thrust augmentation program was a merry-go-round of different options - each one baselined at some point in a chaotic effort to assure DOD of boosting the KH-12 into polar orbit. The program was paid for by NASA, but its only purpose was to support the secret NRO project. The thrust augmentation program illustrates the extent to which the shuttle program served, and was affected by, the KH-12. The heavy-lift problem also testified to poor communication between DOD and NASA.

Although Air Force officials have bragged about "learning from all the mistakes" made at KSC, those in charge of VAFB development came up with a myriad of their own blunders and miscalculations.(2)

The KH-12 was initiated in 1977. Its original launch weight was set at 32,000. NASA had assured DOD that the shuttle would be able to boost this much; DOD had shuttle configured the KH-12 accordingly. But two things marred the planning: the KH-12 swelled in weight, due largely to additional fuel capacity, and the shuttle also became heavier than originally envisioned due to measures such as heat protection for the tiles [which were necessary because of DOD insistence on building the shuttle around the KH-12]. The combination was anathma to intelligence program managers who worried about getting the KH-12 into a polar orbit.

In 1978, the year that the VAFB IOC slipped from its original target of December 1982 to June 1983, was an eventful year.(3)

First, a system weight audit that NASA ordered in February identified a "performance deficit." By August, it had become clear that the shuttle would need some form of thrust augmentation if it was to meet its lift requirements for the KH-12.(4) General Stafford told Congress, "[S]pecific payload capabilities have not been realized principally due to heavier Orbiter weight resulting from design/equipment changes and weight growth....(T)he projected payload throw weight deficit following completion of Shuttle weight reduction programs is about 8000 pounds (from 32,000 pounds) for near polar missions flown from Vandenberg with the full capability Orbiters 103 and 104."(5)

Second, by August of 1978 the KH-12's mission pattern was changed from RM-3 to RM-4 which called for launch and retrieval in the same shuttle flight.(6) "Mission plans 3A and B have been dropped as a requirement by USAF for all practical purposes, as a result of a reevaluation of how to conduct launches and reconnaissance flights with the planned new strategic system. NASA believes, but not all USAF officials agree, that the new performance reference mission 4, requiring 32,000 lb launched from Vandenberg, represents a tougher profile that the earlier one-orbit missions."(7)

As Lieutenant Colonel Rivers, AF Directorate of Space, testified in 1978: "...[T]he most performance critical mission the DOD needs to fly out of Vandenberg is reference mission 4. To do it we must get 32,000 into orbit, and for economics, we must be able to retrieve 25,000 pounds on the same mission. The reason for retrieval is, we want to be able to bring the satellite back for refurbishments in reversion, and so we have to have a capability both ways."(8)

The DoD, in response to congressional questioning, stated in 1978 that "If the operational Shuttle were to be limited to the 100% thrust level planned for Orbital Flight Test (versus 109% required to operations) the DOD would not be able to launch the VAFB Reference Mission 4 without compensating weight reductions. It is planned to launch two of these payloads per year or 17 within the FY 1983 to the first quarter FY 1992 time period."(9)

Not only was the tougher profile adopted, the KH-12 was getting heavier. As the trade press reported that August, "The reconnaissance spacecraft has grown 5,000-6,000 lb. from its original planned weight. This, coupled with Shuttle weight increases and a more difficult launch profile, is forcing the Shuttle weight reduction and thrust augmentation to enable the launch of the high priority intelligence payload."(10) Therefore in August NASA advised USAF that the STS would need thrust augmentation.

Thus in January 1979, in response to these delays in DOD satellite development, the IOC again was revised to December 1983.

The guardians of the KH-12 wanted to be sure its growing weight could be accommodated. "Thrust augmentation is not required for DOD payloads scheduled for launch through fiscal year 1984. However, we believe, based on our experience, that these payloads will grow in weight with time, and that Shuttle thrust augmentation will be needed to fully utilize the Shuttle's capabilities. DOD currently has payload design concepts which, if approved will require full Shuttle capability."(11)

After evaluating six possible thrust augmentation approaches, NASA selected a single strap-on solid rocket motor (SSR) to the Solid Rocket Boosters. It was believed that the SSRs would enable launch of 32,000 pounds, while analysis continued on a later option for increasing capability up to a total of about 45,000 pounds for a polar/near polar payload. Related design modifications of the launch pad were underway, although General Stafford stated that the RDT&E program for the SSRs did not have to be initiated until FY 1981 "to meet a first flight date of June 1984 at Vandenberg."(12) This was another change from the (initial) VAFB IOC of December 1982 (12/83).

However, in December 1979, a liquid propulsion system (or liquid boost module -LBM) was chosen. NASA apparently had concluded that with small solid motors "it would have been difficult to remain within the 650-psf. maximum dynamic pressure desired at launch...."(13) The Two Aerojet engines, identical to those used on the Titan launch vehicle, were to be mounted under the external tank with four clustered propellent containers.

As AW&ST reported: "Primary requirement for the system is for launch and retrieval of an improved version of the KH-11 imaging reconnaissance spacecraft. Without the thrust augmentation, shuttle orbiter 103 could achieve only a 24,000-lb. payload launch from Vandenberg even with main engines rated at 109% thrust and a lightweight external tank." The liquid propulsion system reportedly would allow the shuttle to put up to 38,000 pounds into low 98% inclined orbit, and to retrieve 24,000 pounds on the way back - in other words, to assure DRM4 for a heavy KH-12.(14) Moreover, argued engineers from the LBM manufacturers Martin Marietta and Aerojet, "[b]ecause the LBM augmented STS shows such a generous performance margin over the [DR] Mission 4 requirements, considerable mission planning flexibility will be available."(15) (In case the KH-12 should grow larger still?) In March 1980 Martin Marietta stated that the "projected first launch of a Space Shuttle with additional thrust augmentation provided by a liquid boost module in June, 1985."(16) [what of this?]

By mid-1981, the IOC was slipped until October 1985.(17) It was reported in August that NASA was having doubts about the cost and complexity of the LBM enterprise and was considering other options to enhance shuttle performance NASA needed FY83 funding, "for launch program enhancements if the 32,000-lb capability is to be on line by December, 1987, as desired by the Defense Dept. The extra payload capability will allow launch of improved imaging reconnaissance spacecraft into low earth orbit.".(18)

And that August, in response to a reported engineer shortage, the IOC was set as October in 1985, slipping 14 months from its previous IOC of August 1984. The delay to October 1985 "will not have a major impact on payloads already scheduled" a USAF spokesman said.(19)

In March 1982, NASA announced its plans to replace eight of the eleven metal segments of the Solid Rocket Booster motor cases with four segments made of composite filament material. The plan to reduce shuttle weight with filament wound casing (FWC) - plastic rather than metal motor cases - aimed to reduce liftoff weight by 65,000 lbs, thereby increasing the Shuttle's payload capability by up to 6,000 pounds.(20) First launch of the components was planned for late 1985.(21)

In March 1983, during congressional hearings, the Undersecretary of Defense for R&E noted major concerns about the shuttle's deficient lift capacity. "We have some national security payloads being developed which are close to the latest maximum Shuttle payload capability projections provided by NASA. Reductions in orbiter payload weight capability could cause significant problems and result in major delays and cost increases for some of the nation's most critical space systems," Richard DeLauer told a Senate subcommittee.(22)

By August 1985, the first West Coast Shuttle launch was set for March 1986. But even with FWC boosters and an increase of Shuttle main engine power to 109% of rated thrust, the shuttle could only lift a maximum of 28,000 pounds into polar orbit. It was clear that on its first flight, the shuttle would be unable to meet performance requirements upon which the Air Force had depended - i.e unable to deliver 32,000 pounds or to provide a 1,100 mile cross range.(23)

Yet in October 1985, a structural test of a FWC solid rocket booster revealed that the booster could not withstand a 20% increase of its load, while it is required to withstand additional loads 40% higher.(24) An ensuing NASA Aerospace Safety Advisory Panel investigation advised the Air Force not to use the FWC boosters, but the Air Force continued to stack them on the SLC-6 pad in preparation for the first military polar orbit. The Air Force promised to pay attention to the panel's recommendation, and further tests were planned.(25) Some astronauts reportedly were unwilling to participate in a mission using the untested new boosters.(26)

Sources

1. Hearings by Joint Subcommittees on Department of Defense Appropriations for 1980, p.439

2. "Air Force Shows off SLC-6," Space Business News, December 2, 1985 p.1

3. Sasser, p.19

4. Hearings by Joint Subcommittee on Department of Defense Appropriations for 1980, pp. 438

5. Hearings by Joint Subcommittee on Department of Defense Appropriations for 1980, p.438

6. Mission 3A was just a satellite launch while Mission 3B was just retrieval. As 3A and 3B were to be executed within one orbit, neither DRM would have involved overflight of the USSR.

7. "New Payload Could Boost Shuttle Cost," AW&ST 14 August, 1978, pp.16,17 (check quote and page*)

8. U.S. House Committee on Armed Services, Hearings on H.R. 11167, 95th, 2nd, p.244

9. U.S. Congress, 95th, 2nd session, Hearings before Subcommittees of the House Committee on Appropriations, Space Shuttle Appropriations for FY 1979, p.351

10. "New Payload Could Boost Shuttle Cost," Aviation Week & Space Technology, 14 August, 1978, pp. 16

11. Hearings by Joint Subcommittee on Department of Defense Appropriations for 1980, p.439

12. Hearings by Joint Subcommittee on Department of Defense Appropriations for 1980, p.438,439

13. The report also stated that the SSRs could have provided up to a 10,000-lb increase in lift capacity versus the 12,000-lb minimal increase possible with the liquid concept. Nor would further pad modifications be necessary with the liquid augmentation. "Liquid Engine Picked to Augment Shuttle," AW&ST, December 10, 1979, p.66

14. "Liquid Engine Picked to Augment Shuttle," Aviation Week & Space Technology, December 10, 1979 p.66 See also "Shuttle Performance Augmentation with the Titan Liquid Boost Module," Arthur E. Inman and John G. Muehlbauer, for Proceedings of the Seventeenth Space Congress, April 20, May 1,2, 1980, Cocoa Beach Florida. p.1-66, 1-67.

15. The authors also specify that the LBM would provide an increase in the anticipated DRM4 capability of over 17,000 pounds, bringing the STS to a total lift capability of over 41,000 pounds. (p.1-67) "Shuttle Performance Augmentation with the Titan Liquid Boost Module," Arthur E. Inman and John G. Muehlbauer, for Proceedings of the Seventeenth Space Congress, April 20, May 1,2, 1980, Cocoa Beach Florida. p.1-67

16. "Martin Marietta Wins Space Shuttle Liquid Boost Module Contract," Martin Marietta Aerospace News Release #2347, March 3 1980

17. Sasser, p. 19

18. "Decision Near on Shuttle Payload Boost," Aviation Week & Space Technology, August 10, 1981, p.51

19. "Defense Role for Space Shuttle Lags," NYT August 7, 1981

20. The FWC actually would have allowed the Shuttle to carry only an additional 4,600 into space."Filament Wound Casing Readied For Tests," NASA News Release No. 84P-83, October 9, 1984

21. "Shuttle Booster Modification Proposed," NASA News, March 2, 1982, p. 1; "NASA Presses Filament-Wound Shuttle Solids," Aviation Week & Space Technology, March 8, 1982, p.95

22. "AF Concerned that Shuttle May Not be able to Lift Some Payloads," Aerospace Daily, August 5, 1983, p.196

23. "Shuttle Still Short 4,000 Pounds for VAFB Launches," Defense Daily, August 15, 1985, p. 253

24. "Filament-Wound Booster Case Ruptures During Test," Aviation Week & Space Technology, October 14, 1985, p.23

25. "DOD's SRBs Also Blow Up," Military Space, February 17, 1986, p.? Meanwhile the cost for the FWC was estimated to be $16-$17 million per flight - over 50% of the marginal cost of Pentagon missions. "Premium Price," Aerospace Daily, January 6, 1986, p.17

26. Deep Black, p.309


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