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I have a hard time understanding this reasoning. There are two ways to do it. You can load the fuel first, then have the astronauts board a rocket full of stuf

I have a hard time understanding this reasoning. There are two ways to do it. You can load the fuel first, then have the astronauts board a rocket full of stuff ready to go boom. Or you can load the astronauts first, and load the fuel once they’re strapped in and ready to go. In the first scenario, there’s a large window where an exploding rocket results in dead crew. The launch escape system doesn’t do them any good if they’re still on the walkway or the elevator. In the second scenario, there is no such window. At all times, either the rocket is unloaded or the launch escape system can save the crew. If I were flying on Dragon, I’d really want to be in the scenario where I can always be saved.

cdibona 9y ago
Can the launch escape system work during fueling? Would the gantry/service tower be in the way? I suspect if the les were to fire off during fueling it'd be .... pretty dramatic.
- CarVac 9y ago
  Fuel is added from the sides, there's no gantry/service tower to be in the way. The gantry would only be there while loading the crew, which would take place with an inert rocket.
extrapickles 9y ago
That is my thinking too. The launch abort system can get the capsule away faster than the rocket blows up from a leak catching on fire. Several people have overlaid the launch abort test video with the one that caught fire on the launch pad to roughly confirm this. This is more of the current culture of being so risk adverse that you end up with more risky behavior with the ‘mitigation’ than the original risk.
- eesmith 9y ago
  What's the failure rate of the abort system? What's the failure rate during fuel loading? That is, if we assume 0% failure rate of the abort system then your scenario works. If we assume (for argument's sake) a 50% failure rate in the abort system, and a 10% chance during fueling, then there's a 5% failure leading to human deaths. Without those numbers, it's hard to draw a conclusion.
  - mikeash 9y ago
    That’s a good point. I suspect the abort system is much less likely to kill you, since it’s fairly simple, but it would be good to actually quantify that.
  - greglindahl 9y ago
    The observed failure rate during fuel loading is 2% with a big error bar, based on one accident. And the cause of that accident has been mitigated. The expected failure rate for the LAS is pretty high, high enough that the loss of crew/mission statistic computation doesn't include the LAS.
    - mikeash 9y ago
      A bit of a nitpick: the observed failure rate is quite a bit lower. Each launch involves at least two fuelings, since they do a static fire before every launch (which is when the accident occurred). Every booster also gets tested at their facility in Texas, and there have been a lot of scrubs after fueling, so the average number of fuelings per launch is probably 3 or so. That’s around 150 total fueling events for the Falcon 9, or around 100 if you only count the ones with densifier propellants, making the failure rate so far around 0.6-1%.
aqme28 9y ago
I think the logic is that the chance of an explosion is a lot higher during the loading of the fuel, but is pretty stable once it is loaded. But I still like your reasoning a lot.
- mikeash 9y ago
  I’d rather take a higher chance of survivable failure than a lower chance of certain death. Fault tolerance is better than being brittle and trying to never fail. But I’m just a software guy so this is just uninformed opinion!
  - loeg 9y ago
    I think it really depends on the actual numbers for both "chance" and "survivable." You want to minimize something like the product of "chance of occurrence" (frequency) times "chance of death, if event occurs" (severity). The numbers really matter.
    - mikeash 9y ago
      Right, but those numbers aren’t really known. You can estimate, but that’s always error-prone. (NASA famously estimated the Shuttle’s loss of crew risk at 1 in 100,000, when the actual rate was about 1 in 70, for example.) Still, I’d be really interested in seeing the estimated numbers here.
      - afterburner 9y ago
        There was poor math and methodology behind that 1 in 100,000 estimate though. I don't think that level of error should be held against an estimate made with rigourous and scientifically valid methodology. https://science.ksc.nasa.gov/shuttle/missions/51-l/docs/rogers-commission/Appendix-F.txt https://science.ksc.nasa.gov/shuttle/missions/51-l/docs/roge...
      - loeg 9y ago
        > Right, but those numbers aren’t really known. We agree! :) I was just pointing out that your first comment expressing a preference for one style over another presupposes the relative magnitude of those numbers. I would also be interested in actual data.
ChuckMcM 9y ago
There isn't anything wrong with your reasoning, it just isn't the reasoning that NASA came up with. NASA has the entire history of US Spaceflight in its collective memory. It has many memories of accidents occurring during fueling that resulted in the loss of the spacecraft. It has no memories of a crew being saved by the crew abort systems because it has only happened once[1] and that was with a Russian rocket. Thus, going by what they "know", NASA knows that rockets can blow up when they are being fueled and they know that SpaceX blew up one of their rockets while fueling it, but they do not know if a launch escape system would save astronauts in that situation. Therefore SpaceX's plan is "risky" because they are exposing the crew to a "known" danger and relying on an "unknown" system to protect them from that danger. It is this kind of thinking that keeps NASA moving slowly and carefully. SpaceX has essentially said, "Trust us, if anything went wrong the crew escape system would save them." Unfortunately they don't have a launch pad they can blow up on purpose to demonstrate that for NASA (it would help if they could). The last time they blew up a rocket while fueling it, it took months to recondition the pad for launches again. [1] In 1983, an escape rocket pulled the three cosmonauts of Soyuz T-10-1 to safety when its booster exploded on the launch pad. As of 2015, this is the only case where an abort system saved a crew from a launchpad accident. -- https://www.space.com/29260-how-spacecraft-launch-aborts-work-infographic.html https://www.space.com/29260-how-spacecraft-launch-aborts-wor...
- mikeash 9y ago
  “It has many memories of accidents occurring during fueling that resulted in the loss of the spacecraft.” Does it? I did a brief search and only found SpaceX’s explosion and an old Soviet ICBM accident where the engines ignited during fueling. I certainly may have missed something.
  - jccooper 9y ago
    It's not really NASA, but Atlas D and similar early vehicles did have fueling failures. But they also failed sitting empty on the pad and a hundred other ways. Propellant loading is a state change, and so it's theoretically more dangerous. But examples of real problems are rare.
wafflebear 9y ago
We don't know how effective the launch escape system is in a pad explosion. It might only save the crew 50% of the time, or 10% of the time. If we assume the launch escape system is unreliable, then the numbers strongly point towards loading the crew after the rocket has been fuelled. The crew avoid the riskiest part of the process, and they are on the rocket for a shorter amount of time.
- xenadu02 9y ago
  One of SpaceX’s stated reasons for using the same thrusters for maneuvering as for launch escape is to give the system many more flight hours. Every unmanned Dragon flight is also a test of the launch abort system.
Robotbeat 9y ago
Not only that, but there's also a bunch of ground crew that are at risk if there's a rocket explosion while crew are being loaded. So two or three times as many people can die, none of which will have access to a LAS for a while.

cdibona 9y ago

Can the launch escape system work during fueling? Would the gantry/service tower be in the way? I suspect if the les were to fire off during fueling it'd be .... pretty dramatic.

CarVac 9y ago
Fuel is added from the sides, there's no gantry/service tower to be in the way. The gantry would only be there while loading the crew, which would take place with an inert rocket.

extrapickles 9y ago

That is my thinking too. The launch abort system can get the capsule away faster than the rocket blows up from a leak catching on fire. Several people have overlaid the launch abort test video with the one that caught fire on the launch pad to roughly confirm this. This is more of the current culture of being so risk adverse that you end up with more risky behavior with the ‘mitigation’ than the original risk.

eesmith 9y ago
What's the failure rate of the abort system? What's the failure rate during fuel loading? That is, if we assume 0% failure rate of the abort system then your scenario works. If we assume (for argument's sake) a 50% failure rate in the abort system, and a 10% chance during fueling, then there's a 5% failure leading to human deaths. Without those numbers, it's hard to draw a conclusion.
- mikeash 9y ago
  That’s a good point. I suspect the abort system is much less likely to kill you, since it’s fairly simple, but it would be good to actually quantify that.
- greglindahl 9y ago
  The observed failure rate during fuel loading is 2% with a big error bar, based on one accident. And the cause of that accident has been mitigated. The expected failure rate for the LAS is pretty high, high enough that the loss of crew/mission statistic computation doesn't include the LAS.
  - mikeash 9y ago
    A bit of a nitpick: the observed failure rate is quite a bit lower. Each launch involves at least two fuelings, since they do a static fire before every launch (which is when the accident occurred). Every booster also gets tested at their facility in Texas, and there have been a lot of scrubs after fueling, so the average number of fuelings per launch is probably 3 or so. That’s around 150 total fueling events for the Falcon 9, or around 100 if you only count the ones with densifier propellants, making the failure rate so far around 0.6-1%.

aqme28 9y ago

I think the logic is that the chance of an explosion is a lot higher during the loading of the fuel, but is pretty stable once it is loaded. But I still like your reasoning a lot.

mikeash 9y ago
I’d rather take a higher chance of survivable failure than a lower chance of certain death. Fault tolerance is better than being brittle and trying to never fail. But I’m just a software guy so this is just uninformed opinion!
- loeg 9y ago
  I think it really depends on the actual numbers for both "chance" and "survivable." You want to minimize something like the product of "chance of occurrence" (frequency) times "chance of death, if event occurs" (severity). The numbers really matter.
  - mikeash 9y ago
    Right, but those numbers aren’t really known. You can estimate, but that’s always error-prone. (NASA famously estimated the Shuttle’s loss of crew risk at 1 in 100,000, when the actual rate was about 1 in 70, for example.) Still, I’d be really interested in seeing the estimated numbers here.
    - afterburner 9y ago
      There was poor math and methodology behind that 1 in 100,000 estimate though. I don't think that level of error should be held against an estimate made with rigourous and scientifically valid methodology. https://science.ksc.nasa.gov/shuttle/missions/51-l/docs/rogers-commission/Appendix-F.txt https://science.ksc.nasa.gov/shuttle/missions/51-l/docs/roge...
    - loeg 9y ago
      > Right, but those numbers aren’t really known. We agree! :) I was just pointing out that your first comment expressing a preference for one style over another presupposes the relative magnitude of those numbers. I would also be interested in actual data.

ChuckMcM 9y ago

There isn't anything wrong with your reasoning, it just isn't the reasoning that NASA came up with. NASA has the entire history of US Spaceflight in its collective memory. It has many memories of accidents occurring during fueling that resulted in the loss of the spacecraft. It has no memories of a crew being saved by the crew abort systems because it has only happened once[1] and that was with a Russian rocket. Thus, going by what they "know", NASA knows that rockets can blow up when they are being fueled and they know that SpaceX blew up one of their rockets while fueling it, but they do not know if a launch escape system would save astronauts in that situation. Therefore SpaceX's plan is "risky" because they are exposing the crew to a "known" danger and relying on an "unknown" system to protect them from that danger. It is this kind of thinking that keeps NASA moving slowly and carefully. SpaceX has essentially said, "Trust us, if anything went wrong the crew escape system would save them." Unfortunately they don't have a launch pad they can blow up on purpose to demonstrate that for NASA (it would help if they could). The last time they blew up a rocket while fueling it, it took months to recondition the pad for launches again. [1] In 1983, an escape rocket pulled the three cosmonauts of Soyuz T-10-1 to safety when its booster exploded on the launch pad. As of 2015, this is the only case where an abort system saved a crew from a launchpad accident. -- https://www.space.com/29260-how-spacecraft-launch-aborts-work-infographic.html https://www.space.com/29260-how-spacecraft-launch-aborts-wor...

mikeash 9y ago
“It has many memories of accidents occurring during fueling that resulted in the loss of the spacecraft.” Does it? I did a brief search and only found SpaceX’s explosion and an old Soviet ICBM accident where the engines ignited during fueling. I certainly may have missed something.
- jccooper 9y ago
  It's not really NASA, but Atlas D and similar early vehicles did have fueling failures. But they also failed sitting empty on the pad and a hundred other ways. Propellant loading is a state change, and so it's theoretically more dangerous. But examples of real problems are rare.

wafflebear 9y ago

We don't know how effective the launch escape system is in a pad explosion. It might only save the crew 50% of the time, or 10% of the time. If we assume the launch escape system is unreliable, then the numbers strongly point towards loading the crew after the rocket has been fuelled. The crew avoid the riskiest part of the process, and they are on the rocket for a shorter amount of time.

xenadu02 9y ago
One of SpaceX’s stated reasons for using the same thrusters for maneuvering as for launch escape is to give the system many more flight hours. Every unmanned Dragon flight is also a test of the launch abort system.

Robotbeat 9y ago

Not only that, but there's also a bunch of ground crew that are at risk if there's a rocket explosion while crew are being loaded. So two or three times as many people can die, none of which will have access to a LAS for a while.