totm nov 2023 SpaceX Discussion Thread

[mikegarrison]

45 minutes ago, tater said:

Marginal weather at Vandy, maybe 2 the same day tomorrow?

Do they have any redundancy in mission control? Can they do two F9 launches at the same time? Have they ever before?

[Beccab]

8 minutes ago, mikegarrison said:

Do they have any redundancy in mission control? Can they do two F9 launches at the same time? Have they ever before?

The only SpaceX mission control is at hawthorne, though I'm not sure how large it is - considering that with the current launch dates there's a separation of 22 hours and that with a delay at Vandy it will go down to only a little more than a hour, it's going to be interesting how this plays out. The current record between F9 launches is 14 hours iirc, so I'm personally betting on a delay of 2 days at vandemberg

[RCgothic]

Apparently the logic behind a small door is pressure stabilization of the nose cone:

Might work for Starlink, but not sure about any larger payload.

 

[Beccab]

25 minutes ago, RCgothic said:

Apparently the logic behind a small door is pressure stabilization of the nose cone:

Might work for Starlink, but not sure about any larger payload.

 

Looks like we're gonna have to wait for tomorrow for more info on this

[darthgently]

41 minutes ago, RCgothic said:

Might work for Starlink, but not sure about any larger payload.

Maybe there will be pricing incentives for customers to fit their sat into a Pez format that works, otherwise they'll pay extra for a more standard solution where the payload capacity will be less because fairing will weigh a lot more as bigger doors, or hinged clamshell will require a lot more internal structure taking away from payload capacity.   Guessing of course

Edited May 13, 2022 by darthgently

[tater]

 

1 hour ago, mikegarrison said:

Do they have any redundancy in mission control? Can they do two F9 launches at the same time? Have they ever before?

Answered above, dunno what the minimum gap between launches is for them. I seem to recall they had a few times when 2 launches in a day was possible, but it didn't end up happening—perhaps because they can't.

[JoeSchmuckatelli]

49 minutes ago, tater said:

Answered above, dunno what the minimum gap between launches is for them. I seem to recall they had a few times when 2 launches in a day was possible, but it didn't end up happening—perhaps because they can't.

That's an interesting thing... We are right to be amazed at the rapidity of the launches that SX is delivering... But if they remain so manpower intensive w/r/t control teams - that right there is a price barrier. 

Perhaps in 10 years we see 5-person teams managing each launch? 

[zolotiyeruki]

In the video clip, Elon is talking about pressure stabilizing the fairing.  And I'm confused, because I think of a fairing as a (historically) disposable aerodynamic cover that is not pressurized.  Can someone enlighten me?

[CatastrophicFailure]

16 minutes ago, zolotiyeruki said:

In the video clip, Elon is talking about pressure stabilizing the fairing.  And I'm confused, because I think of a fairing as a (historically) disposable aerodynamic cover that is not pressurized.  Can someone enlighten me?

IIRC it needs to be pressurized during launch & maybe reentry for extra strength & rigidity. It would be vented once in orbit to deploy payloads. 

[Terwin]

So for the first few prototype launches they are using as small of a door as they can manage because that makes it easier to seal while they continue to iterate on the design.

Once they have a more final design it will likely be more worth-while to spend the design time needed to have a larger opening.

[RealKerbal3x]

53 minutes ago, zolotiyeruki said:

In the video clip, Elon is talking about pressure stabilizing the fairing.  And I'm confused, because I think of a fairing as a (historically) disposable aerodynamic cover that is not pressurized.  Can someone enlighten me?

At least in my understanding, 'fairing' is colloquially used in the context of spaceflight to mean the disposable aerodynamic cover that surrounds payloads, but the general definition means just any aerodynamic covering. So I think Starship's nosecone still counts as a fairing, though I think referring to it as a 'payload bay' would probably still make more sense.

[RCgothic]

1 hour ago, zolotiyeruki said:

In the video clip, Elon is talking about pressure stabilizing the fairing.  And I'm confused, because I think of a fairing as a (historically) disposable aerodynamic cover that is not pressurized.  Can someone enlighten me?

Most fairings are vented to external pressure to avoid internal pressure blowing the fairing open prematurely as external pressure reduces.

But with a small door it can be built to resist internal pressure.

Internal pressure adds rigidity which allows mass reduction by deletion of otherwise necessary stringer reinforcements. This is particularly necessary for Starship because it has to survive lateral aero loads during re-entry.

However, some way or another starship is going to have to cope with a larger payload door. Payloads as small as individual starlinks are not typical.

[obnox twin]

19 hours ago, tater said:

 

Nooo

[Beccab]

19 minutes ago, RCgothic said:

However, some way or another starship is going to have to cope with a larger payload door. Payloads as small as individual starlinks are not typical

Yep, plus there's also the problem of stacking the payload in the fairing and all. We're still at least a year away from the first non-starlink payload so it makes for a good interim solution, but seeing how it transitions to larger doors will be interesting. Does anyone have a size comparison between an F9 fairing and Starship payload bay?

[magnemoe]

9 minutes ago, RCgothic said:

Most fairings are vented to external pressure to avoid internal pressure blowing the fairing open prematurely as external pressure reduces.

But with a small door it can be built to resist internal pressure.

Internal pressure adds rigidity which allows mass reduction by deletion of otherwise necessary stringer reinforcements. This is particularly necessary for Starship because it has to survive lateral aero loads during re-entry.

However, some way or another starship is going to have to cope with a larger payload door. Payloads as small as individual starlinks are not typical.

It makes sense, normally fairing has openings to equalize pressure but you could seal it off, perhaps have safety valves if you just want .5 bar over pressure. 
You can also do this during decent but then you need to fill it with gas, and neither oxygen nor methane sounds smart. 
You could use an inert gas, co2 would be solid next to the header tank until you heat it, assume flip and landing it the main constrains outside of max q? 

[cubinator]

That looked like a pretty short entry burn. Maybe I just zoned out.

[tater]

Landed, apparently (had audio on in car)

[tater]

 

 

And in 19 hours:

 

[Beccab]

 

[Beccab]

Expendable F9 looks extremely weird for some reason

[tater]

 

[tater]

Stack will have ~1.5 TWR.

Minimizes propellant use/cost.

Design optimization for cost per ton to orbit.

Current cost to the surface of Mars per useful ton is about a billion dollars (ballpark). SpaceX wants that under $100,000/ton.

Forward flaps are gonna change a lot.

[JoeSchmuckatelli]

10 minutes ago, tater said:

Forward flaps are gonna change a lot

Speculation about why? 

[StrandedonEarth]

2 minutes ago, JoeSchmuckatelli said:

Speculation about why? 

My guess is mass vs effectiveness vs complexity (part count)

[JoeSchmuckatelli]

47 minutes ago, StrandedonEarth said:

My guess is mass vs effectiveness vs complexity (part count)

I'm wondering if it is about payload deployment.  I don't know enough about airframes but I do know that sport convertibles lack the rigidity of sports cars with a full roof - so by extension - absent a deployment method that uses only the nose cone, deployment strategies that break the cylinder of the main part of the craft likely bring additional design challenges