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I would have thought de-orbiting by power would be excluded due to the high fuel load required ie higher for first AND second stages. I've never heard of plans to recover second stage- sounds amazing. Parachutes sound pretty cool
dunno if it's possible, though!
There is an extensive discussion on the Facebook SpaceX group about how a second stage could be recovered. Elon tweeted (if I remember correctly, can't find the tweet) that the goal was to do it "like the Dragon". Currently the Dragon capsule uses chutes and lands in the ocean but we know the goal is to return it to a solid surface (land or ASDS) using retropropulsion like the F9 1st stage.
So...is Elon saying that he wants to work toward landing the 2nd stage like the 1st stage? I think so. Fiendishly difficult. 2nd stage makes it to orbit so is traveling very very fast. De-orbiting it through the atmosphere produces a lot of heat and it only has a single engine to use, an engine optimized for vacuum operation, an engine that is not steerable. And of course the 2nd stage would need side thrusters, grid fins, and lots of heat shielding. Making it much heavier.
The only good news is that since the 2nd stage is in orbit you can de-orbit it at a point that will bring it back to land at a location of your choosing.
So...is Elon saying that he wants to work toward landing the 2nd stage like the 1st stage? I think so. Fiendishly difficult. 2nd stage makes it to orbit so is traveling very very fast. De-orbiting it through the atmosphere produces a lot of heat and it only has a single engine to use, an engine optimized for vacuum operation, an engine that is not steerable. And of course the 2nd stage would need side thrusters, grid fins, and lots of heat shielding. Making it much heavier.
The only good news is that since the 2nd stage is in orbit you can de-orbit it at a point that will bring it back to land at a location of your choosing.
Ulmo
Active Member
I find Facebook extremely hard to use. However, there is a short discussion of it on Reddit.
I agree that the Facebook discussion format is poor. But reddit can be a cesspool of angry commentary. The SpaceX Facebook I referred to is very well moderated so discussions are civil and generally constructive. And there are SpaceX employees who participate. But they are circumspect about what they say, as they should be.
Spaceflight 101 has specs for 1st and 2nd stage. 2nd stage is 'only' 30 feet long. The specs don't breakdown F-9 launch mass between 1st and 2nd stage, so I can't calc total weight of empty 2nd stage. Fully fueled the stage is carrying 45,000 liters of RP-1 and LOX.
The Merlin weights only 630 Kg. Bottom line is empty stage 2 isn't all that heavy.
So let's consider a straw man recovery plan. Bringing an orbital velocity capsule down using heat shield and parachutes is well understood, adjusting for the larger size and different shape of stage 2 should be feasible. It can be brought out of orbit to the desired land recovery area. Given all the exact location tracking now employed for stage 1 landings, is it really that difficult once the stage is floating down the last two or three miles, to intercept it with a heavy lift helicopter? A Chinook CH-47 can handle 20,000 lbs. The new Sikorsky King Stallion can do 27,000 lbs with range of 110 nautical miles even in hot weather.
Finally the second stage if it retains 5% of its fuel appears to have some ability to maneuver if necessary. Spaceflight 101 shows
the Merlin is Gimbaled to move and there are 4 Draco engines for reaction control. Those are likely unnecessary to enable mid air capture,
just mentioning in case they might contribute somehow. Heavy lift helicopter flys it to landing zone and sets it down gently with no exposure to salt water.
Are you referring to the F9 2nd stage? Then my apologies, I didn't realize that.
So then it seems at least possible that Elon is thinking about a retropropulsive landing for the 2nd stage. But it would certainly need a lot of modifications (adding mass) to survive re-entry without incurring significant damage. And extra fuel, which adds mass.
Fiendishly difficult, in my completely inexpert opinion.
nwdiver
Well-Known Member
LOL... I love some of Elons non-response responses.
Q: What's the cost of the second stage?
A: A lot.
Yes, that was my point. Unnecessarily difficult. Every extra pound of fuel added to the 2nd stage to make a retropropulsive landing possible, requires allocating many times more pounds in the first stage to get that extra fuel up to orbital speed. That would seem to make no sense when there is a much simpler and less costly way to accomplish the exact same thing.
Gwynne Shotwell speaking at the 33rd Space Symposium today had a lot of information to impart:
SpaceX gaining substantial cost savings from reused Falcon 9 - SpaceNews.com
Major points:
The cost of refurbishing 1021 (CRS-8 booster) for the SES-10 launch was “substantially less than half the cost of new first stage."
“We did way more on this one than we’re doing on future ones, of course,” she said.
She mentioned that they recovered one fairing intact and that they expect to get it down before the end of the year.
SpaceX gaining substantial cost savings from reused Falcon 9 - SpaceNews.com
Major points:
The cost of refurbishing 1021 (CRS-8 booster) for the SES-10 launch was “substantially less than half the cost of new first stage."
“We did way more on this one than we’re doing on future ones, of course,” she said.
She mentioned that they recovered one fairing intact and that they expect to get it down before the end of the year.
The fundamental problem with a propulsive landing for S2 is a vacuum nozzle has flow separation problems at sea level, that prevents safe usage for that. For that reason the ITS SpaceShip has 2 sets of engines, a bunch of vacuum engines for normal high altitude/vacuum flight and a set a sea level engines for landing.
That's not a significant issue. Adding grid fins and cold gas thrusters is a given and those aren't that heavy. The big deal is thermal shielding and how to land (or get retrieved in the air by a helicopter or jet).
In fact the hail Mary attempt likely means just keeping the stage in one piece then using the M1D vacuum to try to land it even if it blows up at low altitude.
Remember the S1 recovery saga in early F9 Block II days. The first massive accomplishment was hovering a few ft above the sea until fuel depletion. Loosing the stage wasn't a big deal. Then advance on step at a time until success.
Most FH launches will have something like 8 tons of payload capacity left over.
FH can do 22 tons to GTO expendable with Block II figures. With Block V that will likely be 30 tons to GTO expendable. Currently booked missions are up to 10 tons to GTO. Side booster RTLS and center booster ASDS doesn't even requires 50% of performance, that leaves something like 5 tons margin on S2. There are several 7-8 ton GTO missions, so even if the experimental hardware weighs 6 tons, SX might be able to test experimental S2 recovery in every launch except when going to the Moon/Mars and beyond.
As long as S2 reuse hardware can be removed and doesn't interfere until payload deployment, we'll just get exciting successes and failures until they perfect recovery.
My understanding is that seawater contamination is the big bugaboo in retrieval parts reusability. To the extent that is the case, does anyone know if it is considered a factor both in rockets - from nozzles all the way up to the giggle and the match - AND in the more structural elements of a stage? Is it possible there are easily salvageable, significant components of Stage 2s?
"We started with 'Flight Proven' components for your ease of mind, Mr Satellite Maker. And now, we can also offer you 'Dunk Proven' parts as well!"
"We started with 'Flight Proven' components for your ease of mind, Mr Satellite Maker. And now, we can also offer you 'Dunk Proven' parts as well!"
My (admittedly limited) understanding is that the difference in a vac Merlin and a atmospheric Merlin is nozzle size. It also is of note that the larger nozzle is in two pieces (the separate extension being the larger pieces, as shown in the pic in the above reference).
So in one early case, a nozzle developed some cracks at the end, so they simply cut that section off., although that only represented about 1.3M. So there's some variability in the criticality of that nozzle length. It also appears that extension is not actively cooled.
So... what if they found some way to vary the nozzle size? Or discarded the extension?
While the engine might not be running at optimum during the landing effort, would it be sufficient to do so?
There are more differences than the nozzle. But yeah bigger nozzle = higher expansion ratio. That's the sole purpose of the nozzle. Instead of letting the exhaust gas expand into air/vacuum and waste a lot of its thrust, the nozzle acts as a reaction area that converts more of the exhaust into thrust.
At sea level an over expanded (way too large) nozzle produces bubbles as air enters the nozzle and produces flow problems.
In a vacuum a nozzle can be as large as the designer wants the sole limit is mass and size. A theoretically 100% efficient vacuum nozzle would be infinitely big. So every vacuum nozzle is somewhat under expanded (smaller than it could be for practical issues).
The ITS booster nozzle is 1:40 expansion ratio limited by the available space to tuck 42 engines on.
The ITS spaceship/tanker is 1:50 expansion ratio on the SL raptors and 1:200 expansion ratio on the vacuum raptors.
Operating a 1:200 nozzle at sea level is asking for trouble. The stage could be destroyed due to vibration.
One alternative is to use a bunch of Dragon Draco or Dragon 2 SuperDracos trained towards the upper side and land the 2nd stage upside down. Re-enter going forward and land going forward with the dracos firing retrograde.
We have the second reuse flight next month with BulgariaSat and we have a number of major players saying they are willing to use flight proven boosters. We have SES and the Air Force announcing that they would consider using flight proven boosters and, now, after a very successful launch we have Inmarsat willing to do so as well. That's two of the largest players in the satellite industry. Which guarantees that everyone else will be willing as well.
We Will Launch on Reuseable Rocket After Exceptional SpaceX Performance - Inmarsat CEO Tells Universe Today - Universe Today
“This has obviously been an absolutely exceptional performance from SpaceX," Inmarsat CEO Rupert Pearce told Universe Today in a post launch interview at the Kennedy Space Center on Monday, May 15.
“They have now earned themselves an immensely loyal customer.”
We Will Launch on Reuseable Rocket After Exceptional SpaceX Performance - Inmarsat CEO Tells Universe Today - Universe Today
“This has obviously been an absolutely exceptional performance from SpaceX," Inmarsat CEO Rupert Pearce told Universe Today in a post launch interview at the Kennedy Space Center on Monday, May 15.
“They have now earned themselves an immensely loyal customer.”
Oops. I posted this article in satellite contracts but missed that this will be another flight proven booster launch.
Indonesia to use SpaceX to Launch Next Satellite | Good News from Southeast Asia
So this will make a minimum of three contracted reuse flights. This is supposed to launch in 2018 so I doubt it will be numerically the third reuse flight. I expect two or three more flight proven launches for this year.
Indonesia to use SpaceX to Launch Next Satellite | Good News from Southeast Asia
So this will make a minimum of three contracted reuse flights. This is supposed to launch in 2018 so I doubt it will be numerically the third reuse flight. I expect two or three more flight proven launches for this year.
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