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SpaceX NASA returning human spaceflight to United States today (canceled)

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Re: SpaceX NASA returning human spaceflight to United States today (canceled)

#311

Post by dmurray »

jacquesm wrote: post #284

It looks like the launch will be scrubbed due to the weather, lightning risk during propellant loading is too high. edit: yep, launch scrubbed. Too bad! But better safe than sorry, especially today with a crewed vehicle. Does anybody know if the crew dragon comes with different weather restrictions for LOX loading?

According to the stream, the crewed mission has stricter weather requirements for launch and further along the ascent path, in case of an abort. I didn't hear them mention stricter conditions for LOX loading.

Re: SpaceX NASA returning human spaceflight to United States today (canceled)

#312

Post by dmurray »

lutorm wrote: post #304
elliekelly wrote: post #290

Earlier quoted context omitted.

Can someone ELI5 why they sometimes need to have an “instantaneous launch window” that can’t be pushed even by a few minutes?

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 secon…

Can 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.

Re: SpaceX NASA returning human spaceflight to United States today (canceled)

#313

Post by NikolaeVarius »

dmurray wrote: post #312
lutorm wrote: post #304

Earlier quoted context omitted.

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 secon…

Can 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.

The 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

Re: SpaceX NASA returning human spaceflight to United States today (canceled)

#314

Post by dmoy »

NiceWayToDoIT wrote: post #202
TrainedMonkey wrote: post #188

Here is pretty accurate in terms of spacecraft UI docking simulator: https://iss-sim.spacex.com/ Astronauts will be using similar for manual piloting demo before docking.

I have tried and barely succeeded, I just hope those are not real controls. Those should be either automated or they should consult someone from gaming industry. Sorry to say UX controls are terrible (saying from gaming position).

Counterpoint, I found it really easy to control, but I've also played a lot of KSP and am terrible at building balanced rockets, so my docking maneuvers always have imbalanced RCS thrusters (so correcting one axis knocks another one off).

Plus they start you at 200m out with no relative movement, so it's pretty easy to just zero out one axis at a time and go from there

Re: SpaceX NASA returning human spaceflight to United States today (canceled)

#316

Post by gpm »

jacquesm wrote: post #306
mauvehaus wrote: post #291

Earlier quoted context omitted.

As I understand the timing, they scrubbed around T-15:00, and the first stage propellant loading started at T-35:00. https://www.spacex.com/launches/

So is that lightning strike concern limited to the second stage?

I believe that the lightning strike concern is lightning strikes during flight not on the ground. They've got plenty of lightning towards around the rocket on the ground, and if it would be useful they could have easily added more taller ones. They just don't want to load the propellant if there is no chance of launching.

Re: SpaceX NASA returning human spaceflight to United States today (canceled)

#317

Post by lutorm »

lutorm wrote: post #304
elliekelly wrote: post #290

Earlier quoted context omitted.

Can someone ELI5 why they sometimes need to have an “instantaneous launch window” that can’t be pushed even by a few minutes?

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 secon…

John 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.

Re: SpaceX NASA returning human spaceflight to United States today (canceled)

#318

Post by ceejayoz »

fanf2 wrote: post #131
martythemaniak wrote: post #27

Earlier quoted context omitted.

Similar - about 18-19hrs before docking. You should be able to watch it live tomorrow morning. It's funny that it takes that long, since they could theoretically make it up there in like half an hour or so. Here's a good overview of what's gonna happen today: https://www.youtube.com/watch?v=Lr_zfpzGxQQ

Half an hour is very optimistic! The Soyuz expedited rendezvous takes hours. https://space.stackexchange.com/questions/21819/how-did-soyu...

It's possible physics-wise, I believe.

They do a couple orbits gentle approach first because a) it's not a great idea to barrel towards the ISS at speed and b) it gives an opportunity to check for things like "did our solar panels deploy" and "do we need to land because the air is leaking out".

Re: SpaceX NASA returning human spaceflight to United States today (canceled)

#319

Post by skykooler »

dmurray wrote: post #312
lutorm wrote: post #304

Earlier quoted context omitted.

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 secon…

Can 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.

No, 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.

Re: SpaceX NASA returning human spaceflight to United States today (canceled)

#320

Post by bhhaskin »

mariushn wrote: post #46
imshashank wrote: post #3

Love the new "Space" suits and the touch screen panel inside the capsule. This is going to be amazing. My prayers with the brave astronauts.

Is the touch screen usable during lift-off / landing? I'm thinking gravity (4+g?) and trepidations is making it hard to touch a specific spot. Or, maybe there isn't much to do manually during this phase, and for the little things there are some classic controls.

There really isn't a whole lot you can do during lift-off/landing anyways. Main thing is the abort handle and that is pre-programmed.
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