Flying the Shuttle - Abort Procedures Overview
| Space flight |
|---|
| in FlightGear |
| Space Shuttle |
| Vostok-1 |
| Note This article refers to the SpaceShuttle in the FGAddon repository. |
What are we trying to do?
As discussed in the article describing launch, the propellant load of the launch stack is such that a Shuttle with payload can be lifted into a higher inclination orbit, to an altitude of perhaps 600 km max, but there is usually no large margin for error. Also, during launch, not all energy is expended in actually bringing the Shuttle to orbital speed, a part is needed to keep it high enough outside the atmosphere during the acceleration phase.
It follows that if an engine is lost during ascent, the efficiency of the launch process drops. The Shuttle ends up with less acceleration, making the time to reach orbital speed longer, implying that more energy is needed to simply keep it at altitude while it increases velcoity. In fact, even with three engines, just after SRB separation the Shuttle has less than 1 g of acceleration and, till enough propellant is depleted, could not even hold itself against Earth's gravity. If one engine is lost at this phase, there is barely 0.6 g left and the Shuttle will inevitably fall for almost a minute.
In general, the loss of an engine will cause a certain underspeed as compared to the three-engine case when the propellant is depleted. Close to MECO this might not be serious at all - engines are throttled back to limit acceleration anyway, so if one engine is lost, the rest can be throttled up. Just after liftoff on the other hand, an underspeed will have severe consequences and the Shuttle might never be able to reach orbit.
Abort procedures are designed to manage the loss of a single or more engines during ascent. There are two different classes of procedures - performance aborts and contingency aborts. Performance aborts aim to bring the orbiter safely down onto a runway, i.e. they contain a focus on trajectory management and ranging. Contingency aborts aim to bring the orbiter in such a state that the crew can bail out before a crash landing and in general just focus on making the entry back into the atmosphere survivable.