F9 Second Stage Reusability

[Cheapchips]

Will the nozzel survive this type of entry and bouncy landing?  It uses strengthening rings for launch.  Can they keep those in place instead of discarding them at S2 ignition?

I'd imagine that the nozzel is one of the more extensive and difficult to manufacture element of the 2nd stage, next to the rest of the Mvac.

The nozzle *extension* is a very simple thing. Remember when they sent an engineer into the interstage to cut it short with some tin snips?
If they can reliably jettison it, they can easily fit a new one.

My thought was around cost and ease of manufacture.  Niobium alloy isn't cheap or easy to work with.

[speedevil]

My thought was around cost and easy of manufacture.  Niobium alloy isn't cheap or easy to work with.

In principle, if engine cost was very significant, using F9S1 engines would drop the payload of a ASDS F9 by something like 4-5 tons, assuming no modifications other than any required for vacuum start, and that those modifications were trivial.
However, it's been stated it's only 'some fraction' of a million dollars.

[Bananas_on_Mars]

Will the nozzel survive this type of entry and bouncy landing?  It uses strengthening rings for launch.  Can they keep those in place instead of discarding them at S2 ignition?

I'd imagine that the nozzel is one of the more extensive and difficult to manufacture element of the 2nd stage, next to the rest of the Mvac.

The nozzle *extension* is a very simple thing. Remember when they sent an engineer into the interstage to cut it short with some tin snips?
If they can reliably jettison it, they can easily fit a new one.

My thought was around cost and easy of manufacture.  Niobium alloy isn't cheap or easy to work with.

I found a price of 40$/kg for ferroniobium(60-70% Nb). SpaceX might use an alloy that's 10% Hafnium, 1%Titanium, rest Niobium. That alloy was used on the Apollo Service Module.

So it's definitely an expensive material, but not THAT expensive, compared to the rest of the stage. If you estimate the cost of the second stage at 8 million $, at 4t that's an average of 2000$/kg. So I don't think they would mind getting the rest of the stage back even if they loose the nozzle extension ;-)

[Darkseraph]

Off the wall prediction about S2 reuse but here we go:

SpaceX will eventually land F9 second stages back at the launch site or on a droneship using cradle-landing. This will allow them to test this technique for the BFR on a cheaper platform and remove the additional weight of landing legs for S2 recovery.

[john smith 19]

Another cross connection - someone noticed crates from Airtech International Inc. at the BFR manufacturing site. I just checked their website and they offer vacuum bagging for composite manufacture. They offer bagging(Polyimide) that is resistant to 426°C, has great tensile strength etc.
Its intended for vacuum...

Well spotted.  What a remarkable operating temp for a plastic (assuming that's in air, not vacuum).

If it's true that it's mainly a case of being thin enough to radiate the heat away then this does sound exactly what you'd need to make this work.

Keep in mind the air pressure at these heights is very low. A couple of psi absolute could be all that's needed to make this thing as stiff as a truck tire inner tube.

It could be an annular ballute fitted around the engine, which then hangs the stage nose first. The engine would then be largely protected. Annular ballutes have I believe mass and volume advantages over a sphere.

This would change everything Protecting the engine was always the challenge for US recovery given either stages tendency to orientate engine first.  You're not quite home and dry as it's unclear if you could get away with just what's on the outside of the stage walls and just put the TPS on the nose, but it'd be a good start.

[Bananas_on_Mars]

Another cross connection - someone noticed crates from Airtech International Inc. at the BFR manufacturing site. I just checked their website and they offer vacuum bagging for composite manufacture. They offer bagging(Polyimide) that is resistant to 426°C, has great tensile strength etc.
Its intended for vacuum...

Well spotted.  What a remarkable operating temp for a plastic (assuming that's in air, not vacuum).

If it's true that it's mainly a case of being thin enough to radiate the heat away then this does sound exactly what you'd need to make this work.

It should be similar or identical to Kapton, which is a Dupont trademark for polyimide foils...

Kapton is used in, among other things, flexible printed circuits (flexible electronics) and thermal blankets used on spacecraft, satellites, and various space instruments.

The James Webb Space Telescopes Sunshield is made from Kapton.

[AncientU]

Maybe what they really want back is the dispensers they will be using for Starlink deployment... might be worth considerably more than the Merlin Vac.  Cannot mention it because of the steep competition for constellation deployment.

[corrodedNut]

[LouScheffer]

Will the nozzle survive this type of entry and bouncy landing?  It uses strengthening rings for launch.  Can they keep those in place instead of discarding them at S2 ignition?

I'd imagine that the nozzel is one of the more extensive and difficult to manufacture element of the 2nd stage, next to the rest of the Mvac.

How about a simple and brute force solution?  Let the stage land engine first in a net, such as on Mr. Stevens.  The thin nozzle extension crumples, so you take it off and bolt on another.  If material cost is a big concern you recycle the old one.

The question is whether that puts too much strain on the regenerative part of the nozzle.   It's not obvious it would, since that part has to be quite strong to deal normal thrust, and the extension will serve as a crumple zone.   And even if you need to strengthen the nozzle, it might be a worthwhile tradeoff.  Finally, you can test this all you want with drop tests from airplanes/helicopters, so it's not crazy expensive to try.

[Steve G]

Second stage re-usability would likely incorporate re-using the fairings. Which essentially, we're looking at a mini BFS in configuration. The weight penalty would be enormous for the F9, but Falcon Heavy could handle the payload penalty. If re-usability centers around capturing the fairings with the seaborne net, then the second stage would have to have a heat shield at the front of the stage, protection for the nozzle, and superdrakos for landing. My bet would be the mini BFS, if they even pursue this option.

[speedevil]

Second stage re-usability would likely incorporate re-using the fairings. Which essentially, we're looking at a mini BFS in configuration.

This is at least unclear.
For some configurations, it seems at least plausible that carrying the fairings to orbit is going to weigh considerably more than ballute recovery, perhaps even plus parachute.
The mass of S2 is really quite close indeed to the mass of the fairings, and it's quite plausible they could just reuse wholly the landing solution for the fairings, though it is not optimal.

[nacnud]

If re-usability centers around capturing the fairings with the seaborne net, then the second stage would have to have a heat shield at the front of the stage, protection for the nozzle, and superdrakos for landing. My bet would be the mini BFS, if they even pursue this option.

I don't think there will be super dracos involved

Elon Musk
‏@elonmusk
12h12 hours ago

This is gonna sound crazy, but …

SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon

And then land on a bouncy house.

[hallmh]

My thought was around cost and easy of manufacture.  Niobium alloy isn't cheap or easy to work with.

Even if the nozzle is crushed by the recovery process, they'll still have the alloy to re-work into a replacement - or at the least, for exchange with the supplier as scrap.

[wannamoonbase]

There is another reason, which is that they discovered they still had the bandwidth to do it despite the pivot to BFR.

Another reason would be that the F9/FH family have a long future ahead of them. I think it’s at least 5 years before BFR flys a paying payload. 

The US would likely only be reuseable on low energy, small payload missions, at best.  But that’s enough to make it worth while. Especially if you get the US back then smaller payload launch costs can be even lower than now.

Maybe they get the fairing figured out before jumping to this step. 

Edit: imagine the launch cost for smaller or LEO payloads if they can recover the booster, fairing and US.  My gosh, it could eventually be maybe $20 million or less with time. 

Edit 2: It's likely fair to think that for chance of US reuse that RTLS would give way to ASDS recovery.  Make the booster do as much work as possible and give the US as much margin as possible.  I think this whole idea is marginal at best, but it would be great fun to try.

[yokem55]

There is another reason, which is that they discovered they still had the bandwidth to do it despite the pivot to BFR.

Another reason would be that the F9/FH family have a long future ahead of them. I think it’s at least 5 years before BFR flys a paying payload. 

The US would likely only be reuseable on low energy, small payload missions, at best.  But that’s enough to make it worth while. Especially if you get the US back then smaller payload launch costs can be even lower than now.

Maybe they get the fairing figured out before jumping to this step. 

Edit: imagine the launch cost for smaller or LEO payloads if they can recover the booster, fairing and US.  My gosh, it could eventually be maybe $20 million or less with time. 

Edit 2: It's likely fair to think that for chance of US reuse that RTLS would give way to ASDS recovery.  Make the booster do as much work as possible and give the US as much margin as possible.  I think this whole idea is marginal at best, but it would be great fun to try.

I think even for larger payloads it should be recoverable. Echo 2 (40 meter diameter mylar) only weighed 256 kg with the pressurant. Granted, adding all the attachment bits to the balloon, some tps on the body of the stage, and a parafoil for final descent adds to that mass, but I can't see it totalling to more than a ton.

[Space Ghost 1962]

As to why attempt this, suggest you notice that it seems to be an extension of the fairing recover scheme, down to the "bouncy castle/house" part.

Sector leaders of an industry often demonstrate "command of the sector" by going beyond the present need. (Intel, for example, has gone from the Andy Grove days of "being beyond the best in sector" to going to "uh, who cares about Spectre/Meltdown, you'll mostly use our processors or not, we'll be 'good enough' as budget/market/yeild requires" - which is why some analysts as well as me are slowly suggesting to sell off and diversify.)

Why would you want to be a sector leader right now? Well, the former sector leader was ULA, and they don't appear to be competitive on price/frequency/futures, plus they are seen as possessing the joint advantages of Lockheed Martin and Boeing, but have no advantage to show for it, only apparent disadvantage. So the beginnings of a great comic book story, like a Marvel action pic. (Musk has been cast before as Tony Stark.)

Let me talk about how Uber got it's immense valuation. New York taxi medallions have long went for large sums, and San Francisco decided to try to market price them as a tulip industry, expecting wild rises in valuation. Because they could briefly construct a valuation model of large scale, built off of New York's base/history, Uber could similarly value spot drivers in cars with a smartphone equally. By integrating this as a global value (all those drivers possible), they got a huge number that they could show analysts had a reality, and then show that they could grab 5-10% of those drivers in five years, with the potential to get 51% in 10-20 years.

For SX, one can use ULA's economics of Atlas V 551 and Delta IVH as a similar basis, then have the long term economies projected for BFR/BFS, and claim the early Boeing model to dominate civil aviation as space based transport as it's application.

But the problem is how do you connect the dots, to get that huge valuation? You need to go from a current business to that final business, and that you can "command the sector" until you're the only game in town, like Uber.

All they need to do at the moment is demonstrate that they could recycle all the parts of a launch system, such that the theory of "airliner like" reuse could be done. (They don't have to prove economics or practicality - because none of their rivals are within ten years of reaching them in a provable way, and it is reasonable to conclude to analysts that in ten years they stand the best chance of making practical/economical the theory as real.

The space category has always thought of itself as an industry within margins, and Musk as a carney barker.  What if someone erases the margins, and oversells this as a future? (And isn't a Kalanick idiot about it.)

They underestimated their sector, and his scope and sales target. Note - it doesn't have to be real, which is what aerospace engineers always obsess on.

Back to F9US reuse. If he shows a crisped,wet US to park next to the booster out in front of SX in Hawthorne, the analysts will trot by for pics with Musk and them, chat up an insane valuation, and his ability to raise $40-50T goes online at that point. It is SX's equivalent to "Boeing Model 200", while BFS is more like the Model 247. Who needs NASA HSF exploration contracts at that point?

Watch for it.

[rst]

Second stage re-usability would likely incorporate re-using the fairings. Which essentially, we're looking at a mini BFS in configuration. The weight penalty would be enormous for the F9, but Falcon Heavy could handle the payload penalty. If re-usability centers around capturing the fairings with the seaborne net, then the second stage would have to have a heat shield at the front of the stage, protection for the nozzle, and superdrakos for landing. My bet would be the mini BFS, if they even pursue this option.

Elon's recent tweets on the subject say that they'll be trying to get F9 S2 back from orbit by using "a giant party balloon" (presumably a ballute), and then "land on a bouncy house". No sign of a similar strategy for BFS recovery yet...

[speedevil]

Back to F9US reuse. If he shows a crisped,wet US to park next to the booster out in front of SX in Hawthorne, the analysts will trot by for pics with Musk and them, chat up an insane valuation, and his ability to raise $40-50T goes online at that point.

That valuation seems unlikely - I can sort-of-see >>>50B, but going from that to 50T (All stocks are worth around 70T) seems perhaps a reach.
Even if for the reason that basically all investors would need to sell most of their assets to go in.

[ChrisWilson68]

I'm not sure why everyone seems to take it as a given that this upper stage recovery is only for LEO missions.

When SpaceX launches a satellite destined for GEO, it doesn't do a direct GEO insertion.  It releases the satellite in GTO.  So the upper stage is in a highly elliptical orbit with its low point pretty close to Earth.  If it inflates a giant balloon of some shape, it can do many passes grazing the atmosphere to lose speed and slow down until it's in a circular low-Earth orbit, and then go for re-entry.

This assumes both the stage and the balloon can last a while in space.  Maybe that's realistic, maybe not, but I wouldn't discount it out-of-hand as impossible.

Edit: fix GEO for LEO typo in first sentence, thanks Kaputnik.

[Kaputnik]

I'm not sure why everyone seems to take it as a given that this upper stage recovery is only for GEO missions.

When SpaceX launches a satellite destined for GEO, it doesn't do a direct GEO insertion.  It releases the satellite in GTO.  So the upper stage is in a highly elliptical orbit with its low point pretty close to Earth.  If it inflates a giant balloon of some shape, it can do many passes grazing the atmosphere to lose speed and slow down until it's in a circular low-Earth orbit, and then go for re-entry.

This assumes both the stage and the balloon can last a while in space.  Maybe that's realistic, maybe not, but I wouldn't discount it out-of-hand as impossible.

I take it you meant to say LEO in your first sentence?
Your basic point stands, though. A longer lived stage could aero brake into a low circular orbit prior to a de orbit burn. Requires some non trivial mods to the stage of course.