4 ms·

Comparing the Space-X explosion with the speed of the capsule abort system

24 points by CarolineW 10y ago

gus_massa 10y ago
Why can't they use the abort system also for unmanned flights too? They will get good PR and a "free" [1] test of the abort system. Does it reduce the maximal payload? Is it more expensive? Not enough testing? Some security risk for the people outside? [1] Free as in "if you buy the TV we will give the batteries for the remote control for free". [The video doesn't work in IE11, but it work in Chrome.]
- obi1kenobi 10y ago
  The launch escape system is part of the Crew Dragon spacecraft, which has not entered service yet, and would probably not be used to deliver satellites anyway because its crew-carrying capabilities add significant weight and cost. Rocket launches have gotten fairly reliable in recent years -- launch success rates have been hovering around ~95% since the 1970s. [1][2] A 5% chance of killing 7 astronauts is unacceptably high at essentially any cost, hence the launch escape system on the Crew Dragon. However, for an unmanned launch, the entire launch escape and recovery system would have to add little more than 5% extra cost on top of the satellite and launch vehicle for it to be a sound purchase. A Falcon 9 rocket costs about $62M. A very complex satellite can cost over $200M, so for easy math, let's say that the entire system costs $300M, 5% of which is $15M. Those $15M have to cover the following: - powerful launch escape engines (e.g. SuperDracos) that are not recovered if the satellite reaches orbit - hydrazine fuel for those engines (highly toxic and reactive, has to be handled with great care) - carrying all that extra weight to orbit - parachutes and their deployment systems - hardening the payload to survive the physical stresses experienced during landing - refurbishing the payload after it falls into corrosive salt water Given all this, I am skeptical that a launch escape system for unmanned payloads is economically feasible. [1] http://space.stackexchange.com/questions/1659/what-is-the-success-rate-of-nasa-launches/12319#12319 http://space.stackexchange.com/questions/1659/what-is-the-su... [2] http://planet4589.org/space/log/launchlog.txt http://planet4589.org/space/log/launchlog.txt
  - dTal 10y ago
    >A 5% chance of killing 7 astronauts is unacceptably high at essentially any cost Not that I disagree, but I find it interesting that this is "only" three times riskier than the Space Shuttle's empirical loss rate of ~1.5%
    - obi1kenobi 10y ago
      Indeed -- and the ~5% chance is averaged across all launches (manned and not) across many countries' launch systems. So that shows how "little" the billions of dollars' worth of redundancies and backups actually improved the safety bottom line, and also how far we are willing to go to prevent loss of life.
obi1kenobi 10y ago
This video by Scott Manley offers some interesting analysis, including a similar mash-up of the Dragon abort system and the explosion of the Falcon 9: https://www.youtube.com/watch?v=Ye0EOENUw0c https://www.youtube.com/watch?v=Ye0EOENUw0c

24 points by CarolineW 10y ago

Why can't they use the abort system also for unmanned flights too? They will get good PR and a "free" [1] test of the abort system. Does it reduce the maximal payload? Is it more expensive? Not enough testing? Some security risk for the people outside? [1] Free as in "if you buy the TV we will give the batteries for the remote control for free". [The video doesn't work in IE11, but it work in Chrome.]

obi1kenobi 10y ago
The launch escape system is part of the Crew Dragon spacecraft, which has not entered service yet, and would probably not be used to deliver satellites anyway because its crew-carrying capabilities add significant weight and cost. Rocket launches have gotten fairly reliable in recent years -- launch success rates have been hovering around ~95% since the 1970s. [1][2] A 5% chance of killing 7 astronauts is unacceptably high at essentially any cost, hence the launch escape system on the Crew Dragon. However, for an unmanned launch, the entire launch escape and recovery system would have to add little more than 5% extra cost on top of the satellite and launch vehicle for it to be a sound purchase. A Falcon 9 rocket costs about $62M. A very complex satellite can cost over $200M, so for easy math, let's say that the entire system costs $300M, 5% of which is $15M. Those $15M have to cover the following: - powerful launch escape engines (e.g. SuperDracos) that are not recovered if the satellite reaches orbit - hydrazine fuel for those engines (highly toxic and reactive, has to be handled with great care) - carrying all that extra weight to orbit - parachutes and their deployment systems - hardening the payload to survive the physical stresses experienced during landing - refurbishing the payload after it falls into corrosive salt water Given all this, I am skeptical that a launch escape system for unmanned payloads is economically feasible. [1] http://space.stackexchange.com/questions/1659/what-is-the-success-rate-of-nasa-launches/12319#12319 http://space.stackexchange.com/questions/1659/what-is-the-su... [2] http://planet4589.org/space/log/launchlog.txt http://planet4589.org/space/log/launchlog.txt
- dTal 10y ago
  >A 5% chance of killing 7 astronauts is unacceptably high at essentially any cost Not that I disagree, but I find it interesting that this is "only" three times riskier than the Space Shuttle's empirical loss rate of ~1.5%
  - obi1kenobi 10y ago
    Indeed -- and the ~5% chance is averaged across all launches (manned and not) across many countries' launch systems. So that shows how "little" the billions of dollars' worth of redundancies and backups actually improved the safety bottom line, and also how far we are willing to go to prevent loss of life.

obi1kenobi 10y ago

This video by Scott Manley offers some interesting analysis, including a similar mash-up of the Dragon abort system and the explosion of the Falcon 9: https://www.youtube.com/watch?v=Ye0EOENUw0c https://www.youtube.com/watch?v=Ye0EOENUw0c