Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!wuarchive!zaphod.mps.ohio-state.edu!samsung!uunet!world!ksr!clj@ksr.com From: clj@ksr.com (Chris Jones) Newsgroups: sci.space.shuttle Subject: Re: Shuttle question Message-ID: <1126@ksr.com> Date: 27 Nov 90 12:41:15 GMT References: <37200@nigel.ee.udel.edu> <1990Nov19.140100@alazif.cxo.dec.com> <3795@cuisun.unige.ch> <40040@ut-emx.uucp> <1990Nov26.113837@alazif.cxo.dec.com> Sender: news@ksr.com Reply-To: clj@ksr.com (Chris Jones) Organization: Kendall Square Research Corp Lines: 106 In-reply-to: wherry@alazif.cxo.dec.com (bradley g wherry) In article <1990Nov26.113837@alazif.cxo.dec.com>, wherry@alazif (bradley g wherry) writes: >***Warning Potential Botched Nasa speak*** > >types of aborts (that I can recall off hand) > >RTLS -- Return to Launch Site (KSC) >TAO -- Transatlantic abort (not sure where the o comes from) > (Dakar, Madrid any more?) TAL -- Trans Atlantic Landing >AOA -- Abort to Orbit (not sure where the a comes from) ATO -- Abort to Orbit AOA -- Abort Once Around Extract from Space Link BBS (heavily abridged): 6.2.3.14.5 ASCENT ABORT MODES There are two basic types of ascent abort modes for space shuttle missions: intact aborts and contingency aborts. An intact abort would provide a safe return of the orbiter to a planned landing site, while a contingency abort is designed to permit the crew to survive following more severe failures when an intact abort is not possible. A contingency abort would generally result in a ditch operation. There are four types of intact abort modes: return to launch site, transatlantic landing, abort to orbit and abort once around. There is a definite order of preference for the various abort modes. The type of failure and the time of the failure would determine which type of abort is selected. In cases where performance loss is the only factor, the preferred modes, in order, would be ATO, AOA, TAL and RTLS. The mode chosen would be the highest one that could be completed with the remaining vehicle performance. For certain support system failures, such as cabin leaks or vehicle cooling problems, the preferred mode might be the one that would end the mission most quickly. In these cases, TAL or RTLS might be preferable to AOA or ATO. A contingency abort would never be chosen if another abort option existed. RETURN TO LAUNCH SITE. The RTLS abort mode is designed to allow the return of the orbiter, crew and payload to the Kennedy Space Center launch site, approximately 25 minutes after lift-off. The RTLS profile would accommodate the loss of thrust from one main engine between lift-off and approximately four minutes and 20 seconds, at which time not enough MPS propellant remains to return to the launch site. TRANSATLANTIC LANDING. In a TAL abort, the vehicle would continue on a ballistic trajectory across the Atlantic Ocean, landing on a predetermined runway approximately 45 minutes after launch. The landing site, which is located near the nominal ascent ground track of the orbiter in order to make the most efficient use of main engine propellant, must have the necessary runway length and U.S. State Department approval. Weather conditions must also be nominal. The three landing sites that have been identified for a due-east launch are Moron, Spain; Dakar, Senegal; and Ben Guerir, Morocco (on the west coast of Africa). ABORT TO ORBIT. The ATO would be used to boost the orbiter to a safe orbital altitude if performance has been lost and it is impossible to reach the planned altitude. If a main engine fails in a region that results in a MECO underspeed, the Mission Control Center would determine that an abort mode is necessary and would inform the crew. In addition, the crew can verify the nominal OMS burn solutions on the OMS-1 maneuver execute display and burn them instead of the nominal targets. Similarly, they would load the ATO OMS-2 burn targets and use them for OMS-2. This results in the orbiter being placed in a circular orbit. ABORT ONCE AROUND. The AOA abort mode would be used when vehicle performance has been lost to such an extent that either it is impossible to achieve a viable orbit or not enough OMS propellant is available to accomplish the OMS-1, OMS-2 and deorbit burns. AOA would also be used in cases in which a major system problem (cabin leak, loss of cooling) made it necessary to land quickly. In this abort, one OMS burn would be made to adjust the post-MECO orbit so that a second OMS burn would cause the vehicle to deorbit and land at the AOA landing site (Northrup, Edwards Air Force Base or Kennedy Space Center). Thus, in an AOA, the orbiter would circle the Earth once and land approximately 90 minutes after lift-off, CONTINGENCY ABORT. Contingency aborts are caused by loss of more than one main engine or failures in other systems. Loss of one main engine while another is stuck at a low thrust setting may also necessitate a contingency abort. Such an abort would maintain orbiter integrity for in-flight crew escape if a landing cannot be made at a suitable landing site. Contingency aborts due to system failures other than those involving the main engines would normally result in an intact recovery of vehicle and crew. Loss of more than one main engine may, depending on engine failure times, result in a safe runway landing. However, in most three-engine-out cases during ascent, the orbiter would have to be ditched. The in-flight crew escape system would be used before ditching the orbiter. -- Chris Jones clj@ksr.com {world,uunet,harvard}!ksr!clj