3 ms·

If one engine starts even a fraction of a second too late, it will suck up the exhaust from the other engines with predictably mission ending consequences. I m

by smegel 9y ago

If one engine starts even a fraction of a second too late, it will suck up the exhaust from the other engines with predictably mission ending consequences. I might totally wrong, but I don't think the engine are brought up to full throttle in a normal launch while it is still strapped down. In a hold down test, they are. I am just wondering if they are going to to risk possible synchronization issues in a hold down test, which effectively doubles the chance they will encounter a problems vs doing it once at launch.

nkoren 9y ago
Falcons are held down at full throttle for three seconds prior to launch, to ensure that everything is working perfectly before letting go. (They've aborted during this period in the past, although that was a long while ago.) As far as I know, this is unique among launch vehicles. I presume (but do not know for certain) that they will do the same for the heavy.
- JshWright 9y ago
  Well, they're held down as they are throttling up. They aren't at full throttle the whole time.
- JshWright 9y ago
  Additionally... Many liquid fueled rockets can abort on the launch pad after ignition, but before the clamps release. The shuttle, for instance, had 5 aborts after main engine start (once the SRBs lit though, the shuttle was going up, one way or another).
JshWright 9y ago
> If one engine starts even a fraction of a second too late, it will suck up the exhaust from the other engines with predictably mission ending consequences. It's even more precise than that. The engines will be started in pairs, a few dozen ms apart, in order to minimize the risk of sympathetic vibrations tearing the rocket apart.
yborg 9y ago
>suck up the exhaust Wat. It's a rocket, it doesn't 'suck up' anything except what's coming through the turbopumps. The engine starts are staggered to minimize stresses on the thrust structure. For the Saturn V: "At 8.9 seconds before launch, the first stage ignition sequence started. The center engine ignited first, followed by opposing outboard pairs at 300-millisecond intervals to reduce the structural loads on the rocket. When thrust had been confirmed by the onboard computers, the rocket was "soft-released" in two stages: first, the hold-down arms released the rocket, and second, as the rocket began to accelerate upwards, it was slowed by tapered metal pins pulled through dies for half a second."
- smegel 9y ago
  Maybe "blown" is a better word, but the point is the only thing stopping exhaust going up another nozzle is it's own pressure. I read about it here I think: https://www.space.com/38016-spacex-falcon-heavy-rocket-maiden-launch-success-chances.html https://www.space.com/38016-spacex-falcon-heavy-rocket-maide... > If one engine doesn't ignite internally as it should, you will get a flame front that travels back into the engine." > "That creates a pressure spike, and that can cause what we call 'rapid unscheduled destruction' — and that's bad,"

by smegel 9y ago

nkoren 9y ago

Falcons are held down at full throttle for three seconds prior to launch, to ensure that everything is working perfectly before letting go. (They've aborted during this period in the past, although that was a long while ago.) As far as I know, this is unique among launch vehicles. I presume (but do not know for certain) that they will do the same for the heavy.

JshWright 9y ago
Well, they're held down as they are throttling up. They aren't at full throttle the whole time.
JshWright 9y ago
Additionally... Many liquid fueled rockets can abort on the launch pad after ignition, but before the clamps release. The shuttle, for instance, had 5 aborts after main engine start (once the SRBs lit though, the shuttle was going up, one way or another).

JshWright 9y ago

> If one engine starts even a fraction of a second too late, it will suck up the exhaust from the other engines with predictably mission ending consequences. It's even more precise than that. The engines will be started in pairs, a few dozen ms apart, in order to minimize the risk of sympathetic vibrations tearing the rocket apart.

yborg 9y ago

>suck up the exhaust Wat. It's a rocket, it doesn't 'suck up' anything except what's coming through the turbopumps. The engine starts are staggered to minimize stresses on the thrust structure. For the Saturn V: "At 8.9 seconds before launch, the first stage ignition sequence started. The center engine ignited first, followed by opposing outboard pairs at 300-millisecond intervals to reduce the structural loads on the rocket. When thrust had been confirmed by the onboard computers, the rocket was "soft-released" in two stages: first, the hold-down arms released the rocket, and second, as the rocket began to accelerate upwards, it was slowed by tapered metal pins pulled through dies for half a second."

smegel 9y ago
Maybe "blown" is a better word, but the point is the only thing stopping exhaust going up another nozzle is it's own pressure. I read about it here I think: https://www.space.com/38016-spacex-falcon-heavy-rocket-maiden-launch-success-chances.html https://www.space.com/38016-spacex-falcon-heavy-rocket-maide... > If one engine doesn't ignite internally as it should, you will get a flame front that travels back into the engine." > "That creates a pressure spike, and that can cause what we call 'rapid unscheduled destruction' — and that's bad,"