37 votes
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Why did SpaceX choose to use Hydrazine over newer "green" propellants for Dragon 2?

TL;DR: The low technology readiness, the very, very low thrust, and the need for a catalyst bed means this was and still is the wrong technology for the intended purpose of a launch abort system and ...
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  • 62.8k
37 votes
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Challenger Shuttle: could the crew have survived?

One of the major errors in the Space Transportation System (STS) design was the lack of a crew escape system usable from launch to landing. Escape systems are costly, take up mass allowance that can ...
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31 votes
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Was the LES used in the MS-10 abort?

Yes, the launch escape system was used, contrary to earlier reports based on assumptions and ignorance of Soyuz hardware. However, it was not the tower that we are familiar with on Mercury and Apollo ...
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  • 1,157
29 votes

Could the Apollo lunar ascent stage have separated from the descent stage before touchdown in an emergency?

Yes. There is a lot of good information in this presentation from the June 1966 Apollo Lunar Landing Mission Symposium relative to landing flight design including abort planning. The crucial figure ...
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28 votes
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How hard is it on the crew to go through the 14+ g's of a launchpad abort of the Soyuz, or the Falcon system?

14G sounds like a lot. To put it in context: the acceleration you can endure depends on the force vector. The position in which we can withstand G-forces best is forward (using the directions from ...
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  • 121k
26 votes
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How did the attitude system of the uncrewed Soyuz 7K-OK No.1 fail on the launch pad in 1966, killing ground staff as LES was activated?

Rocket guidance systems generally use a fixed inertial platform based on gyroscopes to determine their orientation in space; an accelerometer solution would be useless to determine orientation (though ...
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20 votes
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Why didn't Saturn V have grid fins? Long March and Soyuz do!

The Apollo capsule was allowed to tumble after being pulled away by the LAS. This tumbling would continue until the first drogue parachute was deployed, which would stabilize the capsule. The LAS ...
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  • 121k
20 votes
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Why are launch escape towers jettisoned early?

Escape towers get jettisoned once they're no longer necessary, usually when the spacecraft can abort under its own power or using an intact upper stage. Using the Apollo abort modes as an example: ...
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  • 1,898
19 votes
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What exactly does it mean to human-rate a rocket? As opposed to the escape system?

While the launch escape system (LES) is important for getting the crew away on ascent there are other thing required for human-rating a craft/launch system (and you do need to pay attention to the ...
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  • 7,076
17 votes

Challenger Shuttle: could the crew have survived?

Similar systems certainly exist but not at this scale Some spherical cow approximations - a parachute for a 70kg human weighs 14kg, giving 0.2kg of parachute per kg of payload. The dry mass of the ...
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16 votes

Why were ejection seats used in Project Gemini instead of a tower escape system?

While a number of sources say the motivation for using ejection seats instead of LES is to save weight, a tower launch escape system can be jettisoned relatively early in flight, while ejection seats ...
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16 votes
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Has a pad abort ever been done on an actual launch?

Soyuz 10 used the launch escape tower from the pad.
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14 votes

Why was Dragon sent to the isolation room?

That is an anechoic chamber. An anechoic chamber ("an-echoic" meaning non-reflective, non-echoing or echo-free) is a room designed to completely absorb reflections of either sound or ...
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  • 9,886
12 votes

How hard is it on the crew to go through the 14+ g's of a launchpad abort of the Soyuz, or the Falcon system?

When I worked with Vladimir Titov on STS-86 he was fine after experiencing such an abort years earlier. If your question is could an injury happen, sure, anything can happen.
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11 votes

Has a pad abort ever been done on an actual launch?

You'll have to define 'pad abort' as you are talking about both Apollo, Soyuz and the Space Shuttle. Apollo/Soyuz and Space Shuttle are vastly different vehicles, hence they have vastly different ...
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  • 553
11 votes
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Does Soyuz LES take the service module?

The Soyuz LES takes only the orbital module and reentry module with it, in order to maximize acceleration away from the launch vehicle. The diagram you link to in the question implicitly confirms this;...
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11 votes
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When have astronauts been launched without launch escape system (tower)?

US Gemini capsules had ejection seats, not escape towers. Shuttle had ejection seats (commander and pilot only) for the first 4 flights (albeit with limited useful envelope: close to launch and ...
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10 votes

Could the Apollo lunar ascent stage have separated from the descent stage before touchdown in an emergency?

That maneuver was called "fire in the hole". See the wikipedia article. According to this NASA paper there was an extra "fire-in-the-hole shield". During Apollo 5, 9 and 10 there was a test of "fire-...
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9 votes

Why not turn off the main engines while using the launch escape system on liquid fuelled engines?

Great idea! The Apollo designers agreed. The Emergency Detection System / Abort Sequencer would indeed shut down the engines when the appropriate abort was called. Shutdown of the engines was ...
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8 votes

What kind of launch escape system (LES) does Dream Chaser have?

While Dream Chaser is, indeed, based on HL-20, one of the few significant changes was removing the launch abort adapter and replacing it with an integrated abort system. This was made possible by ...
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  • 180
7 votes

Why was Dragon sent to the isolation room?

Apparently, they also do electromagnetic interference testing inside what looks to be the same chamber, as just said by Elon Musk:
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7 votes
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Is a low-altitude, stable glide really absolutely needed to bail out of the space shuttle?

The escape pole / hatch jettison system was only certified to work in a controlled gliding flight situation. See Mode VIII Egress in the Crew Escape Workbook That doesn't mean that the crew couldn't ...
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6 votes
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Were ejection seats on the Space Shuttle a practical safety system?

The seats were ineffective above 80K feet on ascent due to the expansion of the SRB plumes - if you ejected after that, you would pass through the plumes making a bad day worse. A call was made at ...
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6 votes
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Are there any Pusher Launch Escape Systems in actual use?

No. Dragon V2 will likely be the first capsule with a built in "pusher" LES, an array of SuperDraco engines. The reason it has never been done is because the LES is usually considered dead weight once ...
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6 votes
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Does a launch escape system have any lateral propulsion?

Is there some form of lateral propulsion that moves the crew capsule out of the way of the booster? Yes. The Saturn-Apollo LES, for instance, has a solid rocket mounted sideways at the tip, the “...
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4 votes
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Will the EFT-1 mission for Orion carry an escape tower?

According to NASASpaceflight.com article from December 4, 2013, yes: Another element that will heading uphill on EFT-1 will be an inert Launch Abort System (LAS). Most of the LAS won’t be ...
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4 votes
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Why doesn't the BFR/Starship have a launch escape system?

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 ...
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  • 18.9k
4 votes

Why doesn't the BFR/Starship have a launch escape system?

You are not the first to raise this question! It's worth reviewing Tim Dodd's accessible and detailed evaluation of escape systems: https://everydayastronaut.com/starship-abort/ He draws attention to ...
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  • 333
4 votes

Launch escape trajectory

In the Apollo system the LES was comprised of three solid rocket motors. In an emergency two were used. These were solid motors so once started there was no LES control; only initiation. They did ...
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  • 1,989
4 votes
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Riding out an exploding rocket

This actually kind of happened during SpaceX CRS-7. The Falcon 9 booster exploded 136 seconds into the flight. The Dragon capsule was thrown from the disintegrating vehicle and plummeted back to the ...
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