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If Superheavy fails during launch (or even fails to launch in an unsafe way) the Starship itself might well be able to just light its engines and fly a suitable suborbital trajectory to a safe landing spot (assuming it wasn't hit by too much shrapnel).

https://space.stackexchange.com/a/46080/36625

Is it normal for upper stages to survive having a lower stage go boom beneath them? Are there any recorded instances of sn upper stage emerging unharmed (only to be destroyed by the fall/range safety)?

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    $\begingroup$ A fail of a lower stage is not necessarily an explosion. $\endgroup$
    – Uwe
    Commented Apr 16, 2023 at 17:45
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    $\begingroup$ Starship is a special case because its upper stage is designed to work at sea level as well as in vacuum. Most upper stages could only pull this trick off if it were already very near to the end of the first stage burn already. Then they have to worry about where they'd escape to. $\endgroup$
    – Infinite_Maelstrom
    Commented Apr 16, 2023 at 21:48
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    $\begingroup$ There is another big problem here--most rockets can't survive a fire in the hole ignition. The upper stage exhaust hits the lower stage and bounces back. The only space rocket that I'm aware of that could survive this is the Apollo lunar lander--and that was done by arranging things so there wasn't much in the way of the upper stage exhaust. $\endgroup$
    – Loren Pechtel
    Commented Apr 17, 2023 at 0:17
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    $\begingroup$ A loss-of-mission failure of the lower stage is propbably going to leave it tumbling or exploding, or most likely both. LES usually takes the crew capsule away at 10+ g acceleration, while an upper stage might not even be able to produce 1 g at ignition (though obviously Starship could). A relatively benign failure might be survivable for an upper stage, but that's going to be a rare case. $\endgroup$
    – Russell Borogove
    Commented Apr 17, 2023 at 4:37
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    $\begingroup$ @LorenPechtel many Soviet boosters use(d) fire-in-the-hole ignition as did some US Titans. space.stackexchange.com/q/5187/6944 $\endgroup$
    – Organic Marble
    Commented Apr 17, 2023 at 13:25

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Other than "upper stages" in the form of launch escape systems, I'm not aware of any actual cases of a rocket firing an upper stage in response to a lower stage failing. However, there have been cases, most notably the fourth attempt at launching the N-1, where post-failure analysis noted that activating an upper stage in response to a lower stage failing could have salvaged the mission.

It's important to note that most "rocket blowing up" pictures you see aren't showing the actual failure. The actual failure would have been something much smaller (such as a guidance-system failure or an engine catching fire), and the bigger explosion is a deliberate rupture of the fuel tanks to prevent them from crashing down somewhere.

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  • $\begingroup$ Missed Apollo 6. Third stage failed to ignite. SM engine was used to make orbit. It's kind of like another stage. $\endgroup$
    – Joshua
    Commented Apr 26, 2023 at 1:42
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    $\begingroup$ @Joshua, according to the Wikipedia article, it was the second ignition of the third stage (to perform the trans-lunar injection) that failed. The SPS engine was used to put the spacecraft into an orbit that would complete some but not all of the mission objectives. $\endgroup$
    – Mark
    Commented Apr 26, 2023 at 2:43
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I believe most upper stages that rely on supercooled liquid fuels perform a pre-chill of the fuel/oxidizer pumps before firing to keep them from overheating when spinning up. This is based on every Falcon 9 launch mentions the precool of the upper stage engine taking place quite a few seconds before stage separation and 2nd stage ignition. I would guess that if there were a catastrophic failure of the 1st stage, there wouldn't be time to initiate the precool for proper firing. If it were a solid fuel upper stage, I suppose this could be possible, but I believe solid fuel upper stages are pretty uncommon for a variety of reasons.

I'm pretty confident (though don't have the data handy to back it up) that all emergency escape systems are solid-fuel for instant firing capability to get the important cargo (i.e. humans) away as quickly as possible and not have to wait for any prechill.

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  • $\begingroup$ Solid-fuel escape systems are the most common, but there are several capsules that use hypergolic engines instead. There are also non-cryogenic upper stages (hypergolic or otherwise) that don't need pre-chilling, and upper stages that start pre-chill on the ground. $\endgroup$
    – Mark
    Commented Apr 26, 2023 at 2:31

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