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Flying the Shuttle - Abort Procedures Overview: Difference between revisions
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Flying the Shuttle - Abort Procedures Overview (view source)
Revision as of 08:57, 26 April 2016
, 26 April 2016→We're going to Africa! - a TAL tutorial
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This would of course never be done in reality - but the point is that we need the engine to cut out at a well-defined time. The failure time is the most important parameter used to determine what needs to be done during an abort, so we can't use a random failure scenario for this tutorial because if the engine fails too early, a TAL abort may be flat-out impossible, and if it fails late it may not be necessary. | This would of course never be done in reality - but the point is that we need the engine to cut out at a well-defined time. The failure time is the most important parameter used to determine what needs to be done during an abort, so we can't use a random failure scenario for this tutorial because if the engine fails too early, a TAL abort may be flat-out impossible, and if it fails late it may not be necessary. | ||
Take a moment to watch the predictors of the Shuttle future state change to realize what is now happening: There are three things that keep the Shuttle from falling down during all flight phases - a thrust component pointed downward during powered flight, centrifugal force during orbital flight and lift during entry and aerodynamical flight. | |||
We're nearly outside of the atmosphere, so there's no lift, and we're not fast enough to feel significant centrifugal force - so at this stage only lift is keeping us up. Now look at the acceleration - it's actually below 1 g. Even if we'd point all thrust we have downward now, with all the mass of the ET, two engines are not enough to keep the Shuttle from falling down. Well - the ET will get lighter as we keep burning fuel, so eventually we'll be okay, but we need to cope for the next few minutes till this happens. | |||
But - the SRBs gave us a good 1000 m/s upward velocity, so it'll be some time till we actually start falling. Nevertheless, currently guidance assumes we have the thrust of three engines, so if we have only two, we'll have to pitch up and point more thrust downward to get onto the same trajectory. | |||
That is to say, we need to declare an abort and tell guidance that the plan has changes. | |||
* Type <b>SPEC 51 PRO</b> to get to the override display | |||
[[File:TAL-tutorial03.jpg|600px|TAL tutorial 3]] | |||
Then do <b>ITEM 1 EXEC</b> to arm a TAL abort, followed by <b>ITEM 3 EXEC</b> to call it. | |||
== Further reading == | == Further reading == | ||
[http://spaceflight.nasa.gov/shuttle/reference/shutref/events/aborts/ NASA human spaceflight page on abort modes] | [http://spaceflight.nasa.gov/shuttle/reference/shutref/events/aborts/ NASA human spaceflight page on abort modes] | ||