totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

21 minutes ago, Nefrums said:

I highly doubt that it would be possible to reenter the second stage top first.   All the mass is at the bottom.  It would be very aerodynamically unstable.

It would require huge fins, mounted behind CoM, And CoM for an empty stage is probably not that far above the engine.

 

 

Depends on the mass of the recovery assembly. The MVac only masses 500 kg or so.

[kerbiloid]

Or they can put the propulsion unit of the stage on a horizontal bar (with heatshield hidden inside the stage between the tank and the engine), and make re-entry workout, setting heatshiel prograde.

Spoiler

Ninja'd

Edited June 14, 2017 by kerbiloid

[wumpus]

5 hours ago, KSK said:

Cheap (relatively speaking) and light apparently. I'm not sure how expensive the original PICA material was but PICA-X, the SpaceX version is about 10 times cheaper. Source. It's an old article but an interesting one. I thought this paragraph was particularly prescient:

"Many of Lindenmoyer’s NASA colleagues remain skeptical—even some who have visited SpaceX. “There’s quality control in development, and then there’s quality control in production,” says one agency senior manager who asked not to be named. “The history of launch vehicle development suggests that design issues might crop up in the first or second launch, but it’s the process problems that start to show up on the sixth, the seventh, and the eighth launch.” Noting that so far Musk’s team has launched only two Falcon 9s, this skeptic asks, “How does he ever get to a rate—you know, he’s talking about flying a dozen, two dozen times a year? And as they fly their vehicle, how long before they have a major accident? And are they able to sustain a major accident and still be a viable company?”
 

Emphasis added. Yes, yes they did show up. And happily yes, yes they are still a viable company.

NASA (and the space industry in general) has really weird ideas about "development" vs. "production".  I wonder how long it takes Elon to go from "Tesla mode" (they have produced and sold even tens of thousands of model  "X") to Spacex mode (where 8 is a long production run).

[Rakaydos]

2 hours ago, sevenperforce said:

Remember that whatever is used for recovery has to fit inside the payload fairing, with the possible exception of fold-flush grid fins. 

Since the outer mold line of the recovery module is clean sheet, why not have it mount the fairing?

[sevenperforce]

5 minutes ago, Rakaydos said:

Since the outer mold line of the recovery module is clean sheet, why not have it mount the fairing?

The outer mold line of the vehicle needs to remain the same during ascent, or the qualification is moot.

[CatastrophicFailure]

The payload fairing flares out at the base. There's your room for the heatshield's "shadow:" make it slightly wider so it fits the cross section of the fairing, or nearly enough. Again, would still easily fit inside and remain modular using the existing fairings. 

With most of the fuel gone and just the very light MVac engine out back, the recovery module alone (and that heat shield) should move the COM far enough forward to make it stable with simple re-use of existing F9 grid fins out back. 

[sevenperforce]

34 minutes ago, CatastrophicFailure said:

The payload fairing flares out at the base. There's your room for the heatshield's "shadow:" make it slightly wider so it fits the cross section of the fairing, or nearly enough. Again, would still easily fit inside and remain modular using the existing fairings. 

With most of the fuel gone and just the very light MVac engine out back, the recovery module alone (and that heat shield) should move the COM far enough forward to make it stable with simple re-use of existing F9 grid fins out back. 

Agreed. Ideally, you'd have the entire recovery module couple onto the existing (or the upgraded) payload adapter, with a second payload adapter mounted to the recovery module.

[tater]

The TEL apparently moved into the HIF, but I have not seen anything about it coming out yet for a static fire.

[magnemoe]

32 minutes ago, sevenperforce said:

Agreed. Ideally, you'd have the entire recovery module couple onto the existing (or the upgraded) payload adapter, with a second payload adapter mounted to the recovery module.

Not sure if they will use an real payload adapter, rather make the frame of the recovery module use the payload adapter fastenings, it makes more sense, then put an shortened adapter on top of heat shield. 

The orginal idea for the upper stage was also nose first for reentry, then flipover and landing using an retractable nozzle for upper stage. 

[Skylon]

Judging by some estimates I've seen of weight increase, I'd say it would only be worth making the second stage reusable on the FH, partly because of structural limitations that already limit the mass it can carry to orbit. 

[blowfish]

Inflatable heatshields exist.  This would (1) Allow the heat shield to be large enough to provide stability while still fitting within the fairing and (2) Protect the rest of the stage more from what is likely a very high energy re-entry (probably GTO for most missions)

[Steel]

18 minutes ago, blowfish said:

Inflatable heatshields exist.  This would (1) Allow the heat shield to be large enough to provide stability while still fitting within the fairing and (2) Protect the rest of the stage more from what is likely a very high energy re-entry (probably GTO for most missions)

Two things:

1) Inflatable heatshields (to the best of my knowledge) have never actually been tested in flight.

2) If anything, an inflatable heatshield makes thing less stable, because it's essentially like deploying a giant parachute and so makes the spacecraft want to flip around.

[tater]

The tests in Hawaii of inflatable heat shields have both failed, right? Or was that just the chute?

 

Edited June 14, 2017 by tater

[Steel]

12 minutes ago, tater said:

The tests in Hawaii of inflatable heat shields have both failed, right? Or was that just the chute?

 

I'd forgotten about the HIAD tests! I think it was just the chute, the actually inflatable bit was fine I think

Edited June 14, 2017 by Steel

[tater]

Yeah, it was the chute that failed, my bad.

[RedKraken]

1 hour ago, Skylon said:

Judging by some estimates I've seen of weight increase, I'd say it would only be worth making the second stage reusable on the FH, partly because of structural limitations that already limit the mass it can carry to orbit. 

Yep. We are talking about 3 to 4 tonnes of kit. Eats a big chunk of Falcons GTO capabilities. A much smaller part of FH's GTO payload. Or Falcon LEO.

[blowfish]

1 hour ago, Steel said:

Two things:

1) Inflatable heatshields (to the best of my knowledge) have never actually been tested in flight.

2) If anything, an inflatable heatshield makes thing less stable, because it's essentially like deploying a giant parachute and so makes the spacecraft want to flip around.

1. Yes, still emerging technology.
2. For the same CoM on a blunt-nosed re-entry vehicle, widening the aerodynamic surface makes it more stable (because the ratio of aerodynamic diameter to CoM offset increases).

[Steel]

22 minutes ago, blowfish said:

1. ...
2. For the same CoM on a blunt-nosed re-entry vehicle, widening the aerodynamic surface makes it more stable (because the ratio of aerodynamic diameter to CoM offset increases).

This is true, so long as the CoM and CoD are in the correct place so that the vehicle is aerodynamically stable with a heatshield deployed. You'd have to have an inflatable heatshield that was pretty large to achieve this I'd imagine (something like this perhaps)

Edited June 14, 2017 by Steel

[tater]

Bulgariasat-1 launch pushed to NET Monday. Weather was looking bad, anyway.

[blowfish]

25 minutes ago, Steel said:

This is true, so long as the CoM and CoD are in the correct place so that the vehicle is aerodynamically stable with a heatshield deployed. You'd have to have an inflatable heatshield that was pretty large to achieve this I'd imagine, so that the shape approaches that of a capsule without the sloping sides.

Yep, it would have to be pretty wide when inflated.  But I'm skeptical that there's another solution for keeping the second stage stable during re-entry.  Grid fins might be fine for the first stage's suborbital re-entry, but the second stage is going to get much, much hotter, so having something like that exposed to the airstream could be rather problematic.  I guess maybe you could cover the fins with some sort of ablative coating...

[CSE]

On 13/06/2017 at 7:56 PM, KSK said:

It's a close run thing though. I don't think HTP is quite monomethylhydrazine levels of nasty but it's not exactly safe or easy to handle either. Also SpaceX would need to build the pad infrastructure for handling HTP as well as their other hypergolics and as well as RP1 and LOX. I doubt it's going to happen, given that this is the company that deliberately uses the same propellant combo on both stages of their workhorse booster in the interests of keeping costs down.

Again, I think @Rakaydos has the right answer here.

Is there any info on when and where the payloads' integral propellant is loaded in the current process? Before integration? Just before the fairing is closed? On the pad?

[CatastrophicFailure]

31 minutes ago, CSE said:

Is there any info on when and where the payloads' integral propellant is loaded in the current process? Before integration? Just before the fairing is closed? On the pad?

IIRC, payloads are fueled before integration. The AMOS satellite that went poof was fully fueled, hence the bigger poof when it hit the ground. 

 

45 minutes ago, tater said:

Bulgariasat-1 launch pushed to NET Monday. Weather was looking bad, anyway.

Well, poop. 

Any word as to why?

[tater]

None that I saw. The weather prediction for Saturday gave a 60% chance of a violation, though.

[kerbiloid]

Isn't inflatable heatshield single-use?
Is it cheaper than an aluminium can if return only the propulsion unit?

Perfect 2nd stage:
 

Spoiler

 

[tater]

According to NSF, static fire window opens at 6pm eastern today.