4 ms·
It depends on the target orbit. For launches to the ISS, you have to launch at the correct instant because even a few minutes later means the ISS is so far ahea
by lutorm 6y ago
It depends on the target orbit. For launches to the ISS, you have to launch at the correct instant because even a few minutes later means the ISS is so far ahead it will take much longer, and use more propellant, to rendezvous.
I think they could probably delay a few seconds without too much trouble, but I guess the extra complication of recalculating the rendezvous isn't worth it because most of the time a few seconds won't matter anyway.
- dmurray 6y agoCan you delay the launch window 90 minutes until the next ISS orbit? Maybe you then run into the next on the long list of reasons.
- NikolaeVarius 6y agoThe orbit moves because the earth is moving, so it will not be in the same trajectory as planned. This requires a change in fuel requirements as well as programming
- skykooler 6y agoNo, because in 90 minutes the cryogenic liquid oxygen would have warmed up too much. The Falcon doesn't have an onboard refrigeration unit; it relies on loading the propellant shortly before launch. However, "shortly" is also relative, and 90 minutes is not long enough to purge all the fuel from the rocket and refuel it with cold oxygen (it took close to an hour today to de-fuel the rocket), so it can't be cycled in that window.
- jamesmontalvo3 6y agoIn 90 minutes the space station is back at the same point in its orbit, but Kennedy Space Center has rotated ~1500 miles east.
- lutorm 6y agoJohn Insprucker just talked about this on the webcast and pointed out that with the chilled propellants used by the F9, it's also not possible to wait after prop load has started because the propellants will warm up and change engine performance.