explore (Раздаточные материалы), страница 10

Others were launchedmuch later on ELVs or were never launched.74The Reagan administration and Congress moved relatively quickly to replace the lostorbiter. NASA was able to proceed promptly with construction because, in April 1983, theagency had awarded Rockwell International a contract to construct long-lead-time structural spares, which were to have been completed by 1987. In part, the 1983 decision wasprompted by the concern that eventually a fifth orbiter would be needed to handle theexpected demand for Space Shuttle launch services.

NASA officials also wanted to havecrucial replacement parts on hand in case of a major failure of the Shuttle system. Theadministration requested funding to build a replacement orbiter in mid-1986. In anunusual move, Congress approved the entire package of funding of $2.1 million as part ofa supplemental appropriations for fiscal year 1987.75 The new vehicle (OV-105) was delivered to Kennedy Space Center in May 1991 and made its first flight in May 1992.76Congress had directed NASA to establish a contest to name the orbiter, involving elementary and secondary school students. In May 1989, President George Bush announcedthat the vehicle would be named Endeavour, after Captain Cook’s famous ship.On September 29, 1988, the Shuttle Discovery lifted off Pad 39B at the Kennedy SpaceCenter, conveying a crew of five into orbit (STS-26).

[II-44] Discovery also carried thereplacement for NASA’s Tracking and Data Relay Satellite (TDRS), one of the payloadslost when Challenger exploded in January 1986. The successful flight of Discovery andlaunch of TDRS held special significance because it marked the return of the SpaceShuttle program to flight status and the end of a painful reevaluation of U.S. access tospace. As an editorial in Aviation Week & Space Technology opined, “The launch, witnessedby the largest gathering of spectators and press since the Apollo 11 launch to the Moonin 1969, was balm to the wounds remaining from the Challenger accident. It was a long timecoming.

. . . It was a moment worth waiting for. . . . The Discovery mission should be savoredas a triumph for NASA, the U.S. space program and the nation.” The article also quoted73. Cited in U.S. Congress, Office of Technology Assessment, Launch Options for the Future: A Buyer’s Guide,OTA-ISC-383 (Washington, DC: U.S. Government Printing Office, July 1988), p. 23.74. Most of the payloads eventually launch on ELVs had to be reconfigured, as the support points hadbeen configured for horizontal integration into the Shuttle, rather than the vertical configuration required forELV launch.

This shift sometimes imposed substantial additional costs.75. Normally, Congress is reluctant to fund an entire project in one appropriation because of the impacton the budget of any one year. However, proponents of the fifth orbiter successfully argued that full fundingwould result in lower overall costs. In fact, the funds for the fifth orbiter were taken from excess Air Forceappropriations.76. This first flight of OV-105 was used to rescue the Intelsat VI satellite, which had been left stranded in LEO.****EU4 Chap 2 (161-192)4/2/0112:45 PMPage 187EXPLORING THE UNKNOWN187Kennedy Space Center Director Forrest McCartney, who observed that “[it] was a greatday for America . .

. today we stand tall.”77The second and last Shuttle flight of 1988 (STS-27) took place nine weeks later onDecember 2, during which the orbiter Atlantis carried a classified DOD satellite into highinclination orbit.78 The success of this flight added to NASA’s (and DOD’s) confidence inthe revised launch procedures.The loss of Challenger had forced NASA to reexamine the risks of human spaceflight,to examine more closely the methods used to evaluate and reduce such risks, and to bemore forthcoming with the American public about them. Some NASA officials had inadvertently slipped into thinking that the Space Shuttle was nearly as reliable as a commercial aircraft. However, aircraft typically have empirically derived reliabilities (successfulflights divided by attempts) approaching 99.9999 percent, based on many thousands offlights of essentially identical vehicles.

Prior to the Shuttle’s first launch, NASA had facedthe difficulty of estimating flight risks based on detailed estimates of previous experiencewith subsystems, extensive testing of new subsystems, and the amount of redundancy builtinto critical systems.

Based on such considerations, NASA designed each orbiter to have a97-percent probability of lasting 100 flights, which leads to a requirement that each individual Shuttle flight have a reliability of at least 99.97 percent. Actual Shuttle reliability wasuncertain, but one NASA-funded study estimated that it lies between 97 and 99 percent.79After operations begin, estimations of reliability can also be based on statistical analysis of observed successes and failures, although with most launch vehicles such analysisinvolves the statistics of small numbers.80 For example, using a simple statistical analysis,the congressional Office of Technology Assessment estimated for illustrative purposes thatif STS reliability were assumed to be 98 percent, NASA would face a fifty-fifty chance oflosing an orbiter within thirty-four flights.81 [II-45] Whatever the actual reliability, thisanalysis led to the conclusion that reducing, rather than enhancing, the flight rate wouldbe a prudent way to reduce Shuttle losses over time.

The 1986 policy that encouraged federal agencies to launch on commercial ELVs when possible helped reduce the pressureon Space Shuttle launches. It also increased the resilience of the launch fleet because itmade it possible to recover from a launch failure of a single vehicle more quickly than wastrue prior to January 1986—a concern of great importance to military planners who musthave the greatest possible access to space.82 However, too few Shuttle flights might increaseflight risks, because the skill level of Shuttle launch crews might degrade between launches. Since 1988, NASA has kept the rate of Shuttle flights relatively low (five to seven per77.

“Back to Space!,” Aviation Week & Space Technology, October 3, 1988, p. 7.78. According to news sources, Atlantis carried a Lacrosse imaging radar satellite, a supposition that isstrengthened by the fact that Atlantis entered a 57-degree orbit. See Craig Covault, “Atlantis’ Radar SatellitePayload Opens New Reconnaissance Era,” Aviation Week & Space Technology, December 12, 1988, pp. 26–28.79.

L-Systems, Inc., Shuttle/Shuttle—Cooperations, Risks, and Cost Analyses, LSYS-88-008 (El Segundo, CA:L-Systems, Inc., 1988).80. Most statistical analyses of launch system reliability are further hampered by the changes that aremade in the system after a failure to improve it; this introduces new unknowns into the analysis. Furthermore,for the STS, each of the four orbiters are somewhat different, and many upgrades and other changes are madein the subsystems between flights. Therefore, each launch can in many respects be considered as nearly the firstof its kind.

Nevertheless, one can obtain a rough statistical estimate of reliability by assuming that all Shuttlelaunches are roughly identical.81. U.S. Congress, Office of Technology Assessment, Round Trip to Orbit: Human Spaceflight Alternatives(Washington, DC: U.S. Government Printing Office, August 1989), pp. 6, 25.82.

Resilience is a measure of the ability to recover from a launch failure. High resilience can be accomplished by repairing the failure quickly and employing a launch surge strategy to catch up on waiting launchesor by using other launch vehicles (assuming launch vehicles are relatively interchangeable). Before the development of the Titan IV, heavy payloads could only be launched on the Shuttle.****EU4 Chap 2 (161-192)1884/2/0112:45 PMPage 188DEVELOPING THE SPACE SHUTTLEyear) and improved its on-time launch performance, suggesting that such a rate providesa good balance between safety and costs.The Soviet ShuttleBefore NASA officials were able to savor fully the return of the Space Shuttle to flightstatus, the Soviet Union demonstrated its capacity to build and launch its own shuttle.

Ina move that mirrored the increasing openness of Soviet society during the regime ofGeneral Secretary Mikhail Gorbachev, early in 1988, Soviet officials released drawings anddescriptions of their space shuttle.83 Later in the year, on November 15, rocket engineerssuccessfully launched the shuttle Buran (meaning “snowstorm”) into orbit, attached to theall-liquid Energiya heavy-lift launch vehicle.84 The flight was automated; no crew memberswere aboard (Figure 2–7). After two orbits, flight controllers landed Buran on a runwayabout ten kilometers from the Baikonur Cosmodrome launch pad.Although Buran superficially resembledthe U.S.

Shuttle orbiter, in detail its conceptwas rather different. For one thing, in keeping with the Russian approach to newhuman spaceflight undertakings, the firstflight was fully automatic—no cosmonautswere aboard, although the orbiter wasreportedly capable of carrying ten crewmembers. Second, Buran carried no rocketengines. Finally, unlike the integrated SRBs,external tank, and SSMEs of the U.S.Shuttle, Energia was a stand-alone vehiclecapable of launching up to 220,000 poundsto LEO, including the Buran orbiter.Although it lasted only two orbits, the flightwas an impressive achievement, but one thatwas not followed up either with additionalflights or the crafting of other orbiters.While the weakness of the Soviet space program had not yet become fully apparent inthe United States, the program was past itszenith.