The problem is that you need to know what the pressure was in order to estimate how much of a delay you need. In other words, you need some sort of measurement. You can't just do the math without a measurement. And Elon's point was that with ambient pressure, it screwed up the measurements enough that it was hard to get a real number that you could use in those equations. Also, the big fireball was due to the fact that you have a fuel rich exhaust that's shooting into air, which down where we live provides a lot more oxidizer than up at 35km altitude. Once again, it isn't entirely obvious that they had enough data to really know. Sure, I agree in hindsight that with the fact that the shutdown transients were qualitatively different, that the fact they didn't have detailed data should still have led them to conservatism, but I don't think this is as much a case of ameteurism as you're claiming.I respect what you're saying, but have to disagree.
At some point SpaceX changed the fuel, that is a big hardware/requirements change. Several years later the software was still trying to burn the original fuel.
Quote from: Lee Jay on 08/07/2008 02:28 amShould this type of "burp" happen during engine shut down? What I mean is, is this type of engine behavior considered acceptable industry practice, or should things have been changed in the shutdown sequence to eliminate this behavior?All engines have a shutdown transient. The process is to wait until things settle down.
Should this type of "burp" happen during engine shut down? What I mean is, is this type of engine behavior considered acceptable industry practice, or should things have been changed in the shutdown sequence to eliminate this behavior?
Quote from: Jim on 08/07/2008 12:30 amQuote from: StuffOfInterest on 08/07/2008 12:26 amI know there are some pretty big vacuum chambers out there. Is there any which could handle the test of shutting down an engine the size of the F1 (after a second or two of burn) to measure any residual thrust or reactions in a near vacuum environment? My first thought is that even one or two seconds of firing would put enough pressure in the chamber to negate any testing.not needed. other first stage engines are not tested in vacuum chambers. Also it is not just the engine, it is the propulsion system, which includes the stage.I thought these big engine test stands were capable of simulating low pressure environments using some method involving water that I don't understand.
Quote from: StuffOfInterest on 08/07/2008 12:26 amI know there are some pretty big vacuum chambers out there. Is there any which could handle the test of shutting down an engine the size of the F1 (after a second or two of burn) to measure any residual thrust or reactions in a near vacuum environment? My first thought is that even one or two seconds of firing would put enough pressure in the chamber to negate any testing.not needed. other first stage engines are not tested in vacuum chambers. Also it is not just the engine, it is the propulsion system, which includes the stage.
I know there are some pretty big vacuum chambers out there. Is there any which could handle the test of shutting down an engine the size of the F1 (after a second or two of burn) to measure any residual thrust or reactions in a near vacuum environment? My first thought is that even one or two seconds of firing would put enough pressure in the chamber to negate any testing.
Quote from: Herb Schaltegger on 08/07/2008 12:29 amYou don't need to measure it in a vacuum. As noted in my post above, ambient conditions are just part of the equations used in the design process, and those conditions change with every millisecond of flight. Experienced designers realize this without even really thinking about it. They know cutoff conditions for any kind of trajectory will be different from launch conditions and design accordingly.The problem is that you need to know what the pressure was in order to estimate how much of a delay you need. In other words, you need some sort of measurement. You can't just do the math without a measurement. And Elon's point was that with ambient pressure, it screwed up the measurements enough that it was hard to get a real number that you could use in those equations. Also, the big fireball was due to the fact that you have a fuel rich exhaust that's shooting into air, which down where we live provides a lot more oxidizer than up at 35km altitude. Once again, it isn't entirely obvious that they had enough data to really know. Sure, I agree in hindsight that with the fact that the shutdown transients were qualitatively different, that the fact they didn't have detailed data should still have led them to conservatism, but I don't think this is as much a case of ameteurism as you're claiming.I respect what you're saying, but have to disagree.~Jon
You don't need to measure it in a vacuum. As noted in my post above, ambient conditions are just part of the equations used in the design process, and those conditions change with every millisecond of flight. Experienced designers realize this without even really thinking about it. They know cutoff conditions for any kind of trajectory will be different from launch conditions and design accordingly.
Ok so between MECO and second stage engine start the F1 is unguided, as i suspect most rockets are.
Delta II and Atlas I used vernier motors.
Falcon 1 Flight 3 Liftoff image from SpaceX. - Ed Kyle
nacnud Quote Ok so between MECO and second stage engine start the F1 is unguided, as i suspect most rockets are. Jim Quote Delta II and Atlas I used vernier motors. Big difference, isn't it ?
