I would think it could get to ISS fast without the ISS having to maneuver.. would also use up some of those nasty hypergols.
Quote from: rockets4life97 on 07/17/2017 12:06 AMMy expectation is NASA will have SpaceX burn off the hypergol fuel before re-entry. It will be another event (like removing an LAS tower), but would be less risky then landing with the fuel as you say.What's the best use of the fuel if not for landings? Can they decelerate enough to take stress off the heat shield?Or should they reboost ISS before undocking? Can D2 do reboosts?
My expectation is NASA will have SpaceX burn off the hypergol fuel before re-entry. It will be another event (like removing an LAS tower), but would be less risky then landing with the fuel as you say.
Quote from: starsilk on 07/17/2017 05:46 PMI would think it could get to ISS fast without the ISS having to maneuver.. would also use up some of those nasty hypergols.Launch provides the fast ascent and not so much maneuvering propellant.
Quote from: Norm38 on 07/17/2017 01:24 PMQuote from: rockets4life97 on 07/17/2017 12:06 AMMy expectation is NASA will have SpaceX burn off the hypergol fuel before re-entry. It will be another event (like removing an LAS tower), but would be less risky then landing with the fuel as you say.What's the best use of the fuel if not for landings? Can they decelerate enough to take stress off the heat shield?Or should they reboost ISS before undocking? Can D2 do reboosts?This may be a silli question, Can it be designed to transfer the access fuel to the ISS?I mean, apart from the effect on the Dragon's CoG
seems like plentiful maneuvering propellant should make it possible to overcome an uncooperative target.
Quote from: starsilk on 07/17/2017 08:46 PMseems like plentiful maneuvering propellant should make it possible to overcome an uncooperative target.It has nothing to do with uncooperative target. And there is a limit to what propellant can do. Like I said, fast ascent is a launch targeting issue and not maneuvering propellant
Quote from: dror on 07/17/2017 08:26 PMQuote from: Norm38 on 07/17/2017 01:24 PMQuote from: rockets4life97 on 07/17/2017 12:06 AMMy expectation is NASA will have SpaceX burn off the hypergol fuel before re-entry. It will be another event (like removing an LAS tower), but would be less risky then landing with the fuel as you say.What's the best use of the fuel if not for landings? Can they decelerate enough to take stress off the heat shield?Or should they reboost ISS before undocking? Can D2 do reboosts?This may be a silli question, Can it be designed to transfer the access fuel to the ISS?I mean, apart from the effect on the Dragon's CoGno, it would have to dock to the russian segment for that
There's a limit to what propellant can do? That's an odd statement. A lot of propellant can do all sorts of things in orbit... And dragon 2 will have a LOT to burn off.
Uncooperative = political games.
revision to the International docking standard and a subsequent upgrade to the ISS US segment docking adapters could allow for water, fuel, oxidizer and pressurant transfer.
Quote from: starsilk on 07/18/2017 04:09 AMThere's a limit to what propellant can do? That's an odd statement. A lot of propellant can do all sorts of things in orbit... And dragon 2 will have a LOT to burn off. Not really "a lot" in the true scheme of thing.
Not when the spacecraft has limited orbital life.
Quote from: starsilk on 07/18/2017 04:09 AMUncooperative = political games.And wrong about that. ISS maneuvering means more propellant has to be brought up.
Quote from: soltasto on 07/18/2017 09:32 AMrevision to the International docking standard and a subsequent upgrade to the ISS US segment docking adapters could allow for water, fuel, oxidizer and pressurant transfer.Not feasible to plumb the ISS US segment for el, oxidizer and pressurant transfer. It would still have to go to the Russian segment.
Quote from: Jim on 07/18/2017 02:39 PMQuote from: soltasto on 07/18/2017 09:32 AMrevision to the International docking standard and a subsequent upgrade to the ISS US segment docking adapters could allow for water, fuel, oxidizer and pressurant transfer.Not feasible to plumb the ISS US segment for el, oxidizer and pressurant transfer. It would still have to go to the Russian segment.Jim, wasn't there some discussion about an interim propulsion module a couple of years back, when Russia was considering pulling their segment of the ISS out to form their own space station complex?
random internet speculators out there say 400-450 m/s. that seems like a lot.superdracos can apply all of that in < 10 seconds. not that they would want to, but there will be more than enough capability to apply the delta-v quickly.
Quote from: starsilk on 07/18/2017 03:35 PMrandom internet speculators out there say 400-450 m/s. that seems like a lot.superdracos can apply all of that in < 10 seconds. not that they would want to, but there will be more than enough capability to apply the delta-v quickly.Neither are going to make rendezvous quicker.If the Dragon is not launched at the proper time, it will take many more days for it to catch up with the ISS. 2 day rendezvous provides for launch opportunities every 24 hours - 23 minutes.Fast transfer does not allow for 24hr scrub turnaround, the next opportunity is too soon and a day will have to be skipped.The amount of Dragon propellant does not change this.
Quote from: Jim on 07/18/2017 04:35 PMQuote from: starsilk on 07/18/2017 03:35 PMrandom internet speculators out there say 400-450 m/s. that seems like a lot.superdracos can apply all of that in < 10 seconds. not that they would want to, but there will be more than enough capability to apply the delta-v quickly.Neither are going to make rendezvous quicker.If the Dragon is not launched at the proper time, it will take many more days for it to catch up with the ISS. 2 day rendezvous provides for launch opportunities every 24 hours - 23 minutes.Fast transfer does not allow for 24hr scrub turnaround, the next opportunity is too soon and a day will have to be skipped.The amount of Dragon propellant does not change this.This is true with the current method of fast rendezvous, where you adjust the phase of ISS so it's in the right place when you launch in-plane.But a different approach is certainly possible. You launch when the ISS *phase* is right, then you do a plane correction to get into the ISS plane. This is the approach used on Gemini 11, which achieved a 1.5 hour rendezvous. Compared to the existing approach, this needs additional delta-V, to be provided by some combination of excess booster performance and payload maneuvering. With this approach you get two opportunities each day.Falcon 9 easily has enough raw performance to do this, if run expendable. But if the booster does RTLS, then the margin is less and the booster may not be able to do all of the plane change needed. In this case the amount of Dragon propellant may determine if this approach is possible.This seems pretty unlikely, though. It's a very different procedure, SpaceX does not currently offer yaw steering, two day rendezvous for cargo seems fine, phasing for crewed missions only is not too much of burden, and so on.