introduction (1049407), страница 5
Текст из файла (страница 5)
Next, the report discusses what needs to be done to operate the Shuttle in themid-term, 3 to 15 years. Based on NASAʼs history of ignoring external recommendations, or making improvementsthat atrophy with time, the Board has no confidence that theSpace Shuttle can be safely operated for more than a fewyears based solely on renewed post-accident vigilance.Chapter 9 then outlines the management system changes theBoard feels are necessary to safely operate the Shuttle in themid-term. These changes separate the management of scheduling and budgets from technical specification authority,build a capability of systems integration, and establish andprovide the resources for an independent safety and missionassurance organization that has supervisory authority. Thethird part of the chapter discusses the poor record this nation has, in the Boardʼs view, of developing either a complement to or a replacement for the Space Shuttle.
The report iscritical of several bodies in the U.S. government that shareresponsibility for this situation, and expresses an opinion onhow to proceed from here, but does not suggest what the nextvehicle should look like.Chapter 10 contains findings, observations, and recommendations that the Board developed over the course of thisextensive investigation that are not directly related to theaccident but should prove helpful to NASA.Chapter 11 is a compilation of all the recommendations inthe previous chapters.PART FOUR: APPENDICESPart Four of the report by the Columbia Accident Investigation Board contains material relevant to this volumeorganized in appendices. Additional, stand-alone volumeswill contain more reference, background, and analysis materials.Report Volume IThis Earth view of the Sinai Peninsula, Red Sea, Egypt, Nile River,and the Mediterranean was taken from Columbia during STS-107.August 200313COLUMBIAACCIDENT INVESTIGATION BOARDAN INTRODUCTIONTO THEThe Space Shuttle is one of the most complex machines everdevised.
Its main elements – the Orbiter, Space Shuttle MainEngines, External Tank, and Solid Rocket Boosters – are assembledfrom more than 2.5 million parts, 230 miles of wire, 1,060 valves,and 1,440 circuit breakers. Weighing approximately 4.5 millionpounds at launch, the Space Shuttle accelerates to an orbitalvelocity of 17,500 miles per hour – 25 times faster than the speedof sound – in just over eight minutes.
Once on orbit, the Orbitermust protect its crew from the vacuum of space while enablingastronauts to conduct scientific research, deploy and servicesatellites, and assemble the International Space Station. At the endof its mission, the Shuttle uses the Earthʼs atmosphere as a brake todecelerate from orbital velocity to a safe landing at 220 miles perhour, dissipating in the process all the energy it gained on its wayinto orbit.SPACE SHUTTLEto the desired shape at very high temperatures.
The tiles, whichprotect most other areas of the Orbiter exposed to medium andhigh heating, are 90 percent air and 10 percent silica (similar tocommon sand). One-tenth the weight of ablative heat shields,which are designed to erode during re-entry and therefore can onlybe used once, the Shuttleʼs tiles are reusable. They come in varyingstrengths and sizes, depending on which area of the Orbiter theyprotect, and are designed to withstand either 1,200 or 2,300 degreesFahrenheit. In a dramatic demonstration of how little heat the tilestransfer, one can place a blowtorch on one side of a tile and a barehand on the other. The blankets, capable of withstanding either700 or 1,200 degrees Fahrenheit, cover regions of the Orbiter thatexperience only moderate heating.SPACE SHUTTLE MAIN ENGINESTHE ORBITERThe Orbiter is what is popularly referred to as “the Space Shuttle.”About the size of a small commercial airliner, the Orbiter normallycarries a crew of seven, including a Commander, Pilot, and fiveMission or Payload Specialists.
The Orbiter can accommodate apayload the size of a school bus weighing between 38,000 and56,300 pounds depending on what orbit it is launched into. TheOrbiterʼs upper flight deck is filled with equipment for flying andmaneuvering the vehicle and controlling its remote manipulatorarm.
The mid-deck contains stowage lockers for food, equipment,supplies, and experiments, as well as a toilet, a hatch for enteringand exiting the vehicle on the ground, and – in some instances – anairlock for doing so in orbit. During liftoff and landing, four crewmembers sit on the flight deck and the rest on the mid-deck.Each Orbiter has three main engines mounted at the aft fuselage.These engines use the most efficient propellants in the world– oxygen and hydrogen – at a rate of half a ton per second. At 100percent power, each engine produces 375,000 pounds of thrust,four times that of the largest engine on commercial jets. The largebell-shaped nozzle on each engine can swivel 10.5 degrees up anddown and 8.5 degrees left and right to provide steering controlduring ascent.EXTERNAL TANKDifferent parts of the Orbiter are subjected to dramatically differenttemperatures during re-entry.
The nose and leading edges of thewings are exposed to superheated air temperatures of 2,800 to 3,000degrees Fahrenheit, depending upon re-entry profile. Other portionsof the wing and fuselage can reach 2,300 degrees Fahrenheit. Stillother areas on top of the fuselage are sufficiently shielded fromsuperheated air that ice sometimes survives through landing.To protect its thin aluminum structure during re-entry, the Orbiteris covered with various materials collectively referred to as theThermal Protection System. The three major components of thesystem are various types of heat-resistant tiles, blankets, and theReinforced Carbon-Carbon (RCC) panels on the leading edge ofthe wing and nose cap.
The RCC panels most closely resemble ahi-tech fiberglass – layers of special graphite cloth that are molded14Report Volume IThe three main engines burn propellant at a rate that would drainan average-size swimming pool in 20 seconds. The ExternalTank accommodates up to 143,351 gallons of liquid oxygen and385,265 gallons of liquid hydrogen. In order to keep the super-coldpropellants from boiling and to prevent ice from forming on theoutside of the tank while it is sitting on the launch pad, the ExternalTank is covered with a one-inch-thick coating of insulating foam.This insulation is so effective that the surface of the External Tankfeels only slightly cool to the touch, even though the liquid oxygenis stored at minus 297 degrees Fahrenheit and liquid hydrogenat minus 423 degrees Fahrenheit. This insulating foam alsoprotects the tankʼs aluminum structure from aerodynamic heatingduring ascent. Although generally considered the least complexof the Shuttleʼs main components, in fact the External Tank is aremarkable engineering achievement.
In addition to holding over1.5 million pounds of cryogenic propellants, the 153.8-foot longtank must support the weight of the Orbiter while on the launch padand absorb the 7.3 million pounds of thrust generated by the SolidRocket Boosters and Space Shuttle Main Engines during launch andascent.
The External Tanks are manufactured in a plant near NewAugust 2003COLUMBIAACCIDENT INVESTIGATION BOARDTHE SHUTTLE STACKThe first step in assembling a Space Shuttle for launch is stackingthe Solid Rocket Booster segments on the Mobile LaunchPlatform. Eight large hold-down bolts at the base of the SolidRocket Boosters will bear the weight of the entire Space Shuttlestack while it awaits launch. The External Tank is attached tothe Solid Rocket Boosters, and the Orbiter is then attached to theExternal Tank at three points – two at its bottom and a “bipod”attachment near the nose. When the vehicle is ready to move out ofthe Vehicle Assembly Building, a Crawler-Transporter picks up theentire Mobile Launch Platform and carries it – at one mile per hour– to one of the two launch pads.Orleans and are transported by barge to the Kennedy Space Centerin Florida. Unlike the Solid Rocket Boosters, which are reused, theExternal Tank is discarded during each mission, burning up in theEarthʼs atmosphere after being jettisoned from the Orbiter.SOLID ROCKET BOOSTERSDespite their power, the Space Shuttle Main Engines alone are notsufficient to boost the vehicle to orbit – in fact, they provide only 15percent of the necessary thrust.
Two Solid Rocket Boosters attachedto the External Tank generate the remaining 85 percent. Together,these two 149-foot long motors produce over six million pounds ofthrust. The largest solid propellant rockets ever flown, these motorsuse an aluminum powder fuel and ammonium perchlorate oxidizerin a binder that has the feel and consistency of a pencil eraser.A Solid Rocket Booster (SRB) Demonstration Motor being testednear Brigham City, Utah.Each of the Solid Rocket Boosters consists of 11 separate segmentsjoined together. The joints between the segments were extensivelyredesigned after the Challenger accident, which occurred when hotgases burned through an O-ring and seal in the aft joint on the leftSolid Rocket Booster. The motor segments are shipped from theirmanufacturer in Utah and assembled at the Kennedy Space Center.Once assembled, each Solid Rocket Booster is connected to theExternal Tank by bolts weighing 65 pounds each.
After the SolidRocket Boosters burn for just over two minutes, these bolts areseparated by pyrotechnic charges and small rockets then push theSolid Rocket Boosters safely away from the rest of the vehicle. Asthe boosters fall back to Earth, parachutes in their nosecones deploy.After splashing down into the ocean 120 miles downrange from thelaunch pad, they are recovered for refurbishment and reuse.Report Volume IAugust 200315COLUMBIAACCIDENT INVESTIGATION BOARDAN INTRODUCTION“An Act to provide for research into the problems of flight withinand outside the Earthʼs atmosphere, and for other purposes.” Withthis simple preamble, the Congress and the President of the UnitedStates created the National Aeronautics and Space Administration(NASA) on October 1, 1958.
Formed in response to the launch ofSputnik by the Soviet Union, NASA inherited the research-orientedNational Advisory Committee for Aeronautics (NACA) and severalother government organizations, and almost immediately beganworking on options for manned space flight. NASAʼs first highprofile program was Project Mercury, an early effort to learn if humans could survive in space. Project Gemini followed with a morecomplex series of experiments to increase manʼs time in space andvalidate advanced concepts such as rendezvous. The efforts continued with Project Apollo, culminating in 1969 when Apollo 11landed the first humans on the Moon. The return from orbit on July24, 1975, of the crew from the Apollo-Soyuz Test Project begana six-year hiatus of American manned space flight.
The launch ofthe first Space Shuttle in April 1981 brought Americans back intospace, continuing today with the assembly and initial operations ofthe International Space Station.In addition to the human space flight program, NASA also maintains an active (if small) aeronautics research program, a spacescience program (including deep space and interplanetary exploration), and an Earth observation program. The agency also conductsbasic research activities in a variety of fields.NASA, like many federal agencies, is a heavily matrixed organization, meaning that the lines of authority are not necessarily straightforward.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
