That is big news indeed, that they will try for 2nd stage recovery.I recall the video shown a few years back where the first stage landed, the 2nd stage deployed a Dragon, then deorbited with heat shielding material covering part of the stage, then the 2nd stage landing on a land landing pad. Would SpaceX still plan it this way, or have they come up with something else in the intervening years? If they do land the 2nd stage would they need extra barges, or try to land at a landing pad somewhere away from populated areas (like say at Vandenberg AFB)?Edited to add: how much would second stage recovery eat into the payload mass? Would SX have to use Falcon Heavy as its "go to" launcher for most payloads because of this?
Quote from: Bubbinski on 03/31/2017 01:23 amThat is big news indeed, that they will try for 2nd stage recovery.I recall the video shown a few years back where the first stage landed, the 2nd stage deployed a Dragon, then deorbited with heat shielding material covering part of the stage, then the 2nd stage landing on a land landing pad. Would SpaceX still plan it this way, or have they come up with something else in the intervening years? If they do land the 2nd stage would they need extra barges, or try to land at a landing pad somewhere away from populated areas (like say at Vandenberg AFB)?Edited to add: how much would second stage recovery eat into the payload mass? Would SX have to use Falcon Heavy as its "go to" launcher for most payloads because of this?I seem to recall that 10 Kg of recovery gear on S1 costs 1 Kg of payload, N (>1, <10) Kg of recovery gear on the fairing costs 1 Kg of payload1Kg of recovery gear on S2 costs 1 Kg of payload(gear is anything other than fuel, fuel is a slightly different calculation)but I can't remember where I saw this or who did the analysis or if 10 is the right number or what N is.... And that these were rough/typical, that the numbers differ for LEO and GEO...
But then the only thing left is the upper stage, which we didn't originally intend for Falcon 9 to have a reusable upper stage, but it might be fun to try like a hail mary, and you know. What's the worst thing that can happen? It blows up. You know, it blows up anyway. [Martin Halliway chimes in humorously. "We need to discuss this."]
Since this is a new topic on second stage reusability, I'm copying my reply from the other thread so people can easily find the a copy of the presser and the particular part at issue, which is right after he talks about the fairing (after a guy walks in and shows him the photo):Quote from: Elon Musk from the presser at 14:23But then the only thing left is the upper stage, which we didn't originally intend for Falcon 9 to have a reusable upper stage, but it might be fun to try like a hail mary, and you know. What's the worst thing that can happen? It blows up. You know, it blows up anyway. [Martin Halliway chimes in humorously. "We need to discuss this."]
I should add, I think landing vertically is not the right approach for S2.Since it can orbit multiple times, it takes negligible dV to make sure the deorbit pass is near the launch site. Then deorbit, re-entry (possibly ballistic, since there's nobody on board), parachute deployment, and helicopter capture.All the factors that make helicopter capture difficult for the fairing (range, duration, etc) are non-issues with S2.
Quote from: meekGee on 03/31/2017 12:59 amI should add, I think landing vertically is not the right approach for S2.Since it can orbit multiple times, it takes negligible dV to make sure the deorbit pass is near the launch site. Then deorbit, re-entry (possibly ballistic, since there's nobody on board), parachute deployment, and helicopter capture.All the factors that make helicopter capture difficult for the fairing (range, duration, etc) are non-issues with S2.I had this thought as well after the "hail mary" comment. "Hail mary" doesn't sound like the type of commitment it would take to add legs, deal with the nozzle ratio somehow, perform a flip maneuver, and perform a propulsive landing as in the old video, and definitely rules out a raptor S2. A natural extension of the fairing recovery system("bouncy castle" seems more likely than helicopter to me though) does seem to fit the bill in my mind. But I remember a discussion here which concluded that the first stage is nowhere near terminal velocity by the time it performs it's landing burn, something like mach 2-3 IIRC. I wonder what that figure would be for a second stage that only uses TPS to re-enter, and whether that would preclude parachute landings. I know drogues can help with this, but does it work out? As it is there is surprisingly little time between S1's entry burn and it's landing burn on these GTO missions, if that window gets even shorter for a faster S2 then I for one would be pretty impressed if they could get chutes deployed and bleed it all off.Edit: Having thought about this a bit more, I realized that the second stage could come in at a much more shallow angle, so perhaps there's no need to speculate about this.
If they can reenter from LEO they can do it without much more weight penalty from GTO. How? Aerocapture. We've been doing it already on many missions at Mars with flimsy satellites. S2 with a nice sturdy heatshield wouldn't take many passes at perigee before the reentry would be the same as LEO. But, but, but this is much different you say than the Mars application. I say the SpaceX engineers will find a way to make it work.
Quote from: ppb on 03/31/2017 06:07 amIf they can reenter from LEO they can do it without much more weight penalty from GTO. How? Aerocapture. We've been doing it already on many missions at Mars with flimsy satellites. S2 with a nice sturdy heatshield wouldn't take many passes at perigee before the reentry would be the same as LEO. But, but, but this is much different you say than the Mars application. I say the SpaceX engineers will find a way to make it work.Sorry to be a pedant but you mean aerobraking. Aerocapture refers to an object travelling higher than escape velocity, and is something that has never been done to date, strictly speaking.
Quote from: ppb on 03/31/2017 06:07 amIf they can reenter from LEO they can do it without much more weight penalty from GTO. How? Aerocapture. We've been doing it already on many missions at Mars with flimsy satellites. S2 with a nice sturdy heatshield wouldn't take many passes at perigee before the reentry would be the same as LEO. But, but, but this is much different you say than the Mars application. I say the SpaceX engineers will find a way to make it work.Oh I don't think it's that much different, I'm just wondering:A) how much DeltaV it takes to lower the perigee of the GTO so that it's low enough to rapidly de orbitB) How accurately you can do it?570m/s delta V equates to roughly an extra 1t of fuel, which is 1t less of GTO payload at least, assuming the upper stage weighs about 4.5t (that's the number I'm using but I don't know how accurate that is) and your reentry/landing hardware is only 1t extra on top of that. GTO payload starts disappearing rapidly when you add mass to the second stage. Also it needs to be accurate to several hundred square kilometres at least. If you can't bring it down in a reliably accurate way, it's useless.
How slow would it already have to move under parachutes for a helicopter to grab it?Assuming you can get it that slow... how much slower can you get it?Why not a jumbo bouncy castle? And, of course... how much does all this equipment weigh vs a couple of SuperDracos and their fuel?For TPS perhaps you can eject the remains of the payload adapter and have Pica-X underneath it, like Dragon jettisons the trunk? Trying to go nose first with the payload adapter still there seems rather difficult, it would probably melt/mangle and damage the TPS on the way in, leading to loss of vehicle.