One thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.
Quote from: Patchouli on 06/07/2017 06:00 pmOne thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.More difficulty yes, but not THAT much more.
The perigee is what matters for re-entry delta-v, and that is very low also in GTO. Just very slight burn in apogee makes the perigee drop to low enough that atmosphere does the rest.
Quote from: Patchouli on 06/07/2017 06:00 pmOne thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.Creating a third stage so that you can recover the second stage misses the point I think? The idea is to reuse everything possible (the trunk is tossed, some rings are tossed but minimize the disposables/consumables other than fluids...)
Quote from: Lar on 06/07/2017 09:10 pmQuote from: Patchouli on 06/07/2017 06:00 pmOne thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.Creating a third stage so that you can recover the second stage misses the point I think? The idea is to reuse everything possible (the trunk is tossed, some rings are tossed but minimize the disposables/consumables other than fluids...)How much spare mass does Dragon usually come down with? I think that some of the trunk could possibly be brought back down in Dragon (maybe solar panels?). Anyway, I think that stage 2 recovery would probably be based on their Dragon recovery expertise.
Creating a third stage so that you can recover the second stage misses the point I think?
At this point, it would still have fully a pressurised LOX tank, right? (I'm assuming LOX is always in excess to RP-1) Also, you still have Helium in COPVs inside the LOX tank, right?
Quote from: mikelepage on 06/12/2017 08:34 amAt this point, it would still have fully a pressurised LOX tank, right? (I'm assuming LOX is always in excess to RP-1) Also, you still have Helium in COPVs inside the LOX tank, right? SOP is to exhaust the heaviest propellant first, which is normally LOX, it also ensures the engine won't run LOX rich, which will normally damage the engine, unless it's been designed for it.
Quote from: john smith 19 on 06/12/2017 08:42 pmQuote from: mikelepage on 06/12/2017 08:34 amAt this point, it would still have fully a pressurised LOX tank, right? (I'm assuming LOX is always in excess to RP-1) Also, you still have Helium in COPVs inside the LOX tank, right? SOP is to exhaust the heaviest propellant first, which is normally LOX, it also ensures the engine won't run LOX rich, which will normally damage the engine, unless it's been designed for it. Ah okay, that makes sense. But don't you at least have the LOX tank full of pressurised Helium? Could that be released in ordered to inflate some structure?
Well assuming the tank pressure is 2x or 3x atmospheric pressure you could use the excess to fill something provided you did not need it to resist bending and other loads (F9 is a "semi pressure stabilized structure"). The questions would be a) At this stage in the flight are the loads low enough to not need that stiffening and b)What would you fill with the "excess" Helium? and c) How would you deploy this structure?
The main problem with re-using the second stage in a similar way as the first stage, is that it compromises the payload to much.The only way I see you could really deal with this fundamentally is to re-fuel the second stage in orbit.
Quote from: hkultala on 06/07/2017 08:19 pmThe perigee is what matters for re-entry delta-v, and that is very low also in GTO. Just very slight burn in apogee makes the perigee drop to low enough that atmosphere does the rest.Also critically important is where that perigee will occur, for the cost/possibility of recovery/reuse and flight frequency. Which is not so easy given orbital dynamics, for efficient GTO.
Envy. You forgot the fact that it delays the development of the next generation vehicle. You also forgot that a reusable second stage might just not work. I would think it's bad investment. But we are again on the wrong thread for this discussion and should defer to not continuing.
Delaying the next vehicle goes against Musk's Mars goal. He has only so many years of life to achieve his colony dream. BIG opportunity cost.And the opportunity cost analysis does not allow for the loss of payload mass, i.e. number of satellites per launch that a Falcon class re-useable upper stage would penalize. So the cost of Falcon class re-useability is higher than stated.
SpaceX is going through a lot of effort to catch a bloody fairing, since it's a "pallet full of cash".With rapid reuse of S1, S2 becomes a very large pallet of cash - the largest such pallet on the rocket.For LEO launch, even doubling the mass of S2 is perfectly acceptable.The constellation will require tens of identical LEO launches per year.Why would they not bother? Especially when this constellation is what is financing the Mars drive?The only reason is if they think that a new vehicle will take over completely, and then why bother. But that would be good news from my perspective...
Quote from: Semmel on 07/18/2017 05:21 pmEnvy. You forgot the fact that it delays the development of the next generation vehicle. You also forgot that a reusable second stage might just not work. I would think it's bad investment. But we are again on the wrong thread for this discussion and should defer to not continuing.That's only relevant if the new vehicle reduces operating costs, and that is what I described as the " opportunity cost of the delay".A reuse solution specific to the constellation would be worthwhile IMO, if it minimized development costs with mostly existing hardware.
Quote from: philw1776 on 07/18/2017 05:32 pmDelaying the next vehicle goes against Musk's Mars goal. He has only so many years of life to achieve his colony dream. BIG opportunity cost.And the opportunity cost analysis does not allow for the loss of payload mass, i.e. number of satellites per launch that a Falcon class re-useable upper stage would penalize. So the cost of Falcon class re-useability is higher than stated.The lost payload mass could be irrelevant if F9 is volume limited and the recovery hardware takes up volume not otherwise available for payload. And there may be additional capital cost to manufacture an additional 15 upper stages per year.Delaying the Mars vehicle is an issue. But getting the constellation up faster, cheaper, and earning more revenue for the Mars vehicle could actually accelerate its development.Posting from here: https://forum.nasaspaceflight.com/index.php?topic=36552.msg1703515