Can the Space Shuttle abort and return to Earth before reaching orbit?
Can the Space Shuttle return to Earth even before it leaves our atmosphere? How difficult is that?
Yes, the Shuttle can abort during the ascent to orbit, although this has never been tried before. There are two types of ascent abort modes, which are described in the events section of the Shuttle Reference Manual. There are four intact abort modes where the crew can fly the orbiter someplace, and a contingency abort option if the orbiter needs to be evacuated (this was developed after Challenger). Which of these they use depends on when they decide to abort and what caused the decision to abort.
Of the four intact ascent abort modes, only two allow landing before the Shuttle reaches some kind of orbit. The first intact abort mode allows the crew to land the orbiter at Kennedy approximately 25 minutes after launch. This mode would be used if one of the Shuttle's main engines stopped functioning between launch and 4 minutes 20 seconds. The second mode involves taking the orbiter on a ballistic trajectory across the Atlantic and landing in a predetermined location in Spain, Gambia or Morocco. This would be used if the orbiter need to land quickly but did not have enough fuel left to land at Kennedy. The third abort mode is abort to orbit. In this case the orbiter would go into a low circular orbit if it was not able to reach the planned altitude because of an engine failure. The fourth option is to orbit once, and then land at Edwards Air Force base or back at Kennedy. This could be used if the craft could not be placed in a proper orbit, or needed to land shortly after entering space.
The contingency option basically involves using the crew escape system in the orbiter so that the crew can bail out of the orbiter at a safe altitude and parachute to safety. More details about all these plans can be found at the sites above, or at this older press kit, which also has some diagrams.
Even though these plans have never been used before, NASA takes them very seriously. For example, if the trans-atlantic site that they plan to use as backup has bad weather, they might not launch the Shuttle because they would be unable to use that abort option.
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