totm nov 2023 SpaceX Discussion Thread

[Beccab]

Two Falcon 9s also took a barge to start their trip to Vandenberg yesterday

[JoeSchmuckatelli]

BFR.  Does that refer to the booster or only the booster / SS stack? 

[Beccab]

1 minute ago, JoeSchmuckatelli said:

BFR.  Does that refer to the booster or only the booster / SS stack? 

Neither, BFR is a different rocket. It's like calling SLS Ares V

[RealKerbal3x]

17 minutes ago, JoeSchmuckatelli said:

BFR.  Does that refer to the booster or only the booster / SS stack? 

BFR was essentially the placeholder name for the older proto-Starship designs. Officially it stood for Big Falcon Rocket, but it could also be interpreted as something a bit more rude

[tater]

Starship/Super Heavy is a BFR. They're all BFRs.

[sevenperforce]

20 hours ago, mikegarrison said:

On 3/26/2022 at 2:30 PM, sevenperforce said:

The fourth parachute is essentially a backup. It was designed to land optimally with three chutes. So a design which functions with three parachutes and then opens a backup afterward is fine…even if you don’t know which chute will act as the “backup” in advance. 

No, this is a bad take.

It's subtle, but the 4th chute is not a "backup". The system has no backup -- if it fails, you have a fatal event. But there is some redundancy -- only 3 of the 4 chutes need to work. However, filled chutes can fail. The system is not successful until the capsule is all the way down at a safe speed.

This is why I think that if they investigate this and discover that the 4th chute is still opening correctly, just slower, it's OK. But if they find that there is a serious risk of it not opening at all, this is a massive safety issue. Because at that point you no longer have redundancy, and your safety design was based on having redundancy.

I think you misapprehend. I didn’t say that the fourth chute didn’t need to open; I said that it is fine if the system “opens a backup afterward.” As you point out, it WOULD be a problem if the fourth chute never opened, but that’s not what we have seen so far.

There is a potential failure mode here. If three chutes open but the fourth chute has not opened yet, and then one of the three open chutes fails, what happens? Presumably this would accelerate the opening of the fourth chute (since it is no longer leeward of the chute that failed) and everything will be fine. It is possible that one of the three could fail in a way that causes it to become entangled with the fourth chute and prevent it from fully opening, but that’s really no different from a failed chute becoming entangled with one of the other filled chutes and causing it to fail in that fashion. So that’s a known failure mode anyway.

All the public data so far indicate that delay in the fourth chute opening happens if and when the first three chutes open properly. 

[mikegarrison]

1 hour ago, sevenperforce said:

If three chutes open but the fourth chute has not opened yet, and then one of the three open chutes fails, what happens?

This situation is something they need to test.

[Beccab]

17 minutes ago, mikegarrison said:

This situation is something they need to test.

A CRS splashdown would be a good way to try it given that the capsule is identical, but I doubt NASA would be on board with it

[tater]

Under the original Commercial Crew concept, Crew Dragon would only be flying once a year for NASA, then the CRS missions every 6 months or so. In the current situation, instead of ~3/year, they are at 4, and possibly more depending on Cygnus right now. At least this gives them loads of data on the actual chute deployment.

Wonder if altering the reefing might deal with it?

[sevenperforce]

1 hour ago, mikegarrison said:

This situation is something they need to test.

The trouble with testing it is that there are various failure modes for a chute and really no way of testing all of them. Like, how can you simulate all possible ways that a filled chute can fail AND then impact other chutes, let alone test it? Even if you found simulations where the failure of a filled chute would impact the other chutes, it would be prohibitively difficult to induce that exact interaction in a test scenario to see what would actually happen.

It should also be noted that they cannot conduct any test of this with a weighted frame as they have done in the past, because the chute-fill delay is the result of airflow interactions which depend not only on the other chutes but also on the shape (and presumably the COM) of the capsule. So you’d need a boilerplate capsule with sufficient fidelity to produce the same airflow interactions.

6 minutes ago, tater said:

Wonder if altering the reefing might deal with it?

What if they designated one chute as the “backup” and intentionally kept it reefed longer than the others? If I recall correctly, the fourth chute starts off inflated while reefed but then deflates when it is unreefed. A reefed chute needs less airflow to stay inflated than an unreefed one. 

[tater]

The reefing probably lets go mechanically, due to forces on the chute, not a control system, right?

they could pick 1, have the force required to break loose the reefing be such that it opens if the others are underperforming, I guess. Or just take loads of data, and watch how they work now.

[sevenperforce]

52 minutes ago, tater said:

The reefing probably lets go mechanically, due to forces on the chute, not a control system, right?

they could pick 1, have the force required to break loose the reefing be such that it opens if the others are underperforming, I guess. Or just take loads of data, and watch how they work now.

 No, the reefing line is cut specifically by pyrotechnics or some other mechanism; it doesn’t open automatically. 

[tater]

1 minute ago, sevenperforce said:

 No, the reefing line is cut specifically by pyrotechnics or some other mechanism; it doesn’t open automatically. 

Oh, interesting. Course then those pyros are another failure mode, lol.

If commanded, then release the reefing if needed.

[JoeSchmuckatelli]

Tried looking this up but... figured it would be easier just asking here.  B7 has a new design over B4, and presumably with the different layout and use of R2s is the more capable craft.  I know there was talk of changing the flight control surfaces on SS - but I haven't seen if they've implemented those as yet.

So do we think S20 will fly?  Or will it go the way of B4 with the new delay in the environmental review granting time to iterate?

[darthgently]

The general buzz is that S20 will not fly.  But who knows

[darthgently]

I learned a few things about the old and the newer Florida Starship sites in this vid:

 

[RealKerbal3x]

3 hours ago, JoeSchmuckatelli said:

So do we think S20 will fly?  Or will it go the way of B4 with the new delay in the environmental review granting time to iterate?

S20 is incompatible with Raptor 2, and changes to the stage separation design make it incompatible with B7+ boosters as well.

There's a small chance that it could conduct a solo suborbital flight, but I wouldn't count on that. It's an old design now, SpaceX probably wants to move on.

Edited March 28, 2022 by RealKerbal3x

[JoeSchmuckatelli]

7 hours ago, RealKerbal3x said:

SpaceX probably wants to move on.

Which is their signal, organizational strength.  Love it! 

[Beccab]

On the topic about moving on to newer stuff:

 

[Guest]

Just now, Beccab said:

On the topic about moving on to newer stuff:

 

[RCgothic]

One thing about ending production of Dragon is that there won't be enough Dragons to service multiple commercial stations as well as ISS, as well as free flights, plus downtime and refurbishment.

They say they can always build more, but in reality their preference will be to use Starship.

And the thought of Starship serving commercial stations that are generously half its habitable volume is a bit ridiculous. The alternative at this point is the vastly more expensive option of Starliner.

So I think one effect will be that commercial stations will need to get a bit more ambitious.

 

[Minmus Taster]

1 hour ago, Beccab said:

On the topic about moving on to newer stuff:

 

[tater]

Seems reasonable. They need to be able to fly 2/year for NASA—1/year once Starliner is flying. Cargo Dragon is separate (dunno how many they need). Presumably they have good data on wear and tear, maybe they can fly many times.

[darthgently]

8 minutes ago, tater said:

Seems reasonable. They need to be able to fly 2/year for NASA—1/year once Starliner is flying. Cargo Dragon is separate (dunno how many they need). Presumably they have good data on wear and tear, maybe they can fly many times.

Not only that, it is also fairly reasonable to assume that about the time any more are needed (given current fleet, reusability, wear and tear, projected demand), a fairly major makeover of the design would probably make sense anyway as materials, electronic tech,  niche requirements, etc advance.   I think Musk sees these as space taxis and space delivery vans, and if you don't see needing additions for 5 or 8 years or more then you don't get extra of this year's model and mothball them, you plan on getting the current vehicle at that future date and he doesn't see the current Dragon as that future vehicle.  I don't think he is imagining Starship necessarily, but who knows?  Given the SpaceX team history, I'd like to think Musk and his team are already thinking of a better replacement, and given that history, it will probably be better.  If not, they can always dust off Dragon and tool back up

[Terwin]

59 minutes ago, RCgothic said:

And the thought of Starship serving commercial stations that are generously half its habitable volume is a bit ridiculous. The alternative at this point is the vastly more expensive option of Starliner.

No worse than a multi-passenger buss dropping families off at specific bungalows at a resort.

envision this:

Starship docks, old residents board starship, maid-service works to clean/refresh habitat, then new residents board the mini-station, starship un-docks.

Those with a stay of greater than (LS refresh duration) get 'maid-service' part way through their stay.

With enough habitats, you can have daily flights that can also address any urgent issues for habitats that are not yet scheduled for return...

(I would expect most holiday stays to be 1-2 days under this approach, because there is not a lot to do in a mini-habitat besides look out the window, but corporate/research teams could stay a week or two for micro-g research/production)