Lotsa discussion here about what happens with the hypergolic fuel on-board Crew Dragon when it is NOT used in a launch abort (now that propulsive landing is out the window).Well, here are few indicators to steer the discussion in the right direction:- Fuel supply for both the abort system (SuperDraco) and RCS (Draco) is the same set of tanks.- Full fuel load on Crew Dragon is substantially larger than what is needed for RCS and de-orbit requirement, courtesy of the requirements of the integrated abort system.- Crew Dragon WAS to perform a short "test-burn" of the SuperDracos prior to doing a propulsive landing. The health of the SuperDracos would be determined from this "test-burn". When a problem with the SuperDracos was found, landing would have switched to parachutes (back-up). That meant: landing under chutes with a very substantial load of fuel on-board.- With deletion of propulsive landing the back-up landing mode (parachutes) became the primary landing mode.- NASA requested that SpaceX add a FOURTH parachute to increase safety margin. This is because Crew Dragon, upon landing, is substantially heavier than the three-chuted Cargo Dragon.- Pad-abort Crew Dragon test article had mass simulators on-board to simulate the presence of a full crew complement. Yet, it landed very gently, under just three parachutes.Now, given the above, WHY is Crew Dragon substantially heavier than Cargo Dragon, upon landing?Why is a nominal Crew Dragon substantially heavier than aborted Crew Dragon, upon landing?Answer: nominal Crew Dragon is carrying a substantial amount of fuel on-board, upon landing, courtesy of NOT having performed a propulsive landing.Some consider this to be a hazard. But ask yourself: how much more is this a hazard compared to a shuttle landing with several thousands of pounds of hypergolic fuels still remaining in its OMS pods and RCS tankage?
You’re saying you think NASA and ASAP will be fine carrying enough extremely volatile hypergolic fuel aboard a capsule carrying humans - enough to light four extremely thirsty super Draco’s to slow the D2 from freefall to standstill - in the event of a third level failure.
Quote from: woods170 on 05/31/2018 01:25 pmLotsa discussion here about what happens with the hypergolic fuel on-board Crew Dragon when it is NOT used in a launch abort (now that propulsive landing is out the window).Well, here are few indicators to steer the discussion in the right direction:- Fuel supply for both the abort system (SuperDraco) and RCS (Draco) is the same set of tanks.- Full fuel load on Crew Dragon is substantially larger than what is needed for RCS and de-orbit requirement, courtesy of the requirements of the integrated abort system.- Crew Dragon WAS to perform a short "test-burn" of the SuperDracos prior to doing a propulsive landing. The health of the SuperDracos would be determined from this "test-burn". When a problem with the SuperDracos was found, landing would have switched to parachutes (back-up). That meant: landing under chutes with a very substantial load of fuel on-board.- With deletion of propulsive landing the back-up landing mode (parachutes) became the primary landing mode.- NASA requested that SpaceX add a FOURTH parachute to increase safety margin. This is because Crew Dragon, upon landing, is substantially heavier than the three-chuted Cargo Dragon.- Pad-abort Crew Dragon test article had mass simulators on-board to simulate the presence of a full crew complement. Yet, it landed very gently, under just three parachutes.Now, given the above, WHY is Crew Dragon substantially heavier than Cargo Dragon, upon landing?Why is a nominal Crew Dragon substantially heavier than aborted Crew Dragon, upon landing?Answer: nominal Crew Dragon is carrying a substantial amount of fuel on-board, upon landing, courtesy of NOT having performed a propulsive landing.Some consider this to be a hazard. But ask yourself: how much more is this a hazard compared to a shuttle landing with several thousands of pounds of hypergolic fuels still remaining in its OMS pods and RCS tankage?Nice hints, but unfortunately not valid. See the bolted part. The original Dragon 2 already was designed to land with substantial fuel (minus the test burn) under 3 parachutes.
Quote from: Semmel on 05/31/2018 02:22 pmQuote from: woods170 on 05/31/2018 01:25 pm- Crew Dragon WAS to perform a short "test-burn" of the SuperDracos prior to doing a propulsive landing. The health of the SuperDracos would be determined from this "test-burn". When a problem with the SuperDracos was found, landing would have switched to parachutes (back-up). That meant: landing under chutes with a very substantial load of fuel on-board.On the contrary, it is valid.In case the "test-burn" failed the back-up landing system (parachutes) was to be used. A 3-parachute landing was a contingency scenario, back when propulsive landing was still the baseline.Margins for contingency landing scenario's are accepted a whole lot thinner than for nominal landings. Purpose is to have the crew survive the landing, not necessarily do so unharmed.A 3-parachute landing, with a load of fuel on-board, can be done just fine, but without any margin for parachute failure. When parachute landing, with a load of fuel on-board, became the new baseline, NASA wanted margin put back into the parachute system. Hence the fourth parachute having been added.Ok, that makes vastly more sense. I didnt got THAT train of thought from your original post. Thanks.
Quote from: woods170 on 05/31/2018 01:25 pm- Crew Dragon WAS to perform a short "test-burn" of the SuperDracos prior to doing a propulsive landing. The health of the SuperDracos would be determined from this "test-burn". When a problem with the SuperDracos was found, landing would have switched to parachutes (back-up). That meant: landing under chutes with a very substantial load of fuel on-board.On the contrary, it is valid.In case the "test-burn" failed the back-up landing system (parachutes) was to be used. A 3-parachute landing was a contingency scenario, back when propulsive landing was still the baseline.Margins for contingency landing scenario's are accepted a whole lot thinner than for nominal landings. Purpose is to have the crew survive the landing, not necessarily do so unharmed.A 3-parachute landing, with a load of fuel on-board, can be done just fine, but without any margin for parachute failure. When parachute landing, with a load of fuel on-board, became the new baseline, NASA wanted margin put back into the parachute system. Hence the fourth parachute having been added.
- Crew Dragon WAS to perform a short "test-burn" of the SuperDracos prior to doing a propulsive landing. The health of the SuperDracos would be determined from this "test-burn". When a problem with the SuperDracos was found, landing would have switched to parachutes (back-up). That meant: landing under chutes with a very substantial load of fuel on-board.
Lotsa discussion here about what happens with the hypergolic fuel on-board Crew Dragon when it is NOT used in a launch abort (now that propulsive landing is out the window).
Quote from: woods170 on 05/31/2018 01:25 pmLotsa discussion here about what happens with the hypergolic fuel on-board Crew Dragon when it is NOT used in a launch abort (now that propulsive landing is out the window).Must admit I never thought they would try to land with hypergolics onboard.I had been assuming they would use the SuperDracos for an entry interface burn.1) Remove mass of hypergolic fuels from parachute landing requirements.2) Remove risk of toxic hypergolic fuel leaks to occupants upon landing.3) Increase accuracy of landing ellipse.4) Reduce peak-heating/wear on Dragon v2 heat shield.5) Decrease peak g-forces on occupants/payload.
Quote from: mikelepage on 06/09/2018 03:17 amQuote from: woods170 on 05/31/2018 01:25 pmLotsa discussion here about what happens with the hypergolic fuel on-board Crew Dragon when it is NOT used in a launch abort (now that propulsive landing is out the window).Must admit I never thought they would try to land with hypergolics onboard.I had been assuming they would use the SuperDracos for an entry interface burn.1) Remove mass of hypergolic fuels from parachute landing requirements.2) Remove risk of toxic hypergolic fuel leaks to occupants upon landing.3) Increase accuracy of landing ellipse.4) Reduce peak-heating/wear on Dragon v2 heat shield.5) Decrease peak g-forces on occupants/payload.Might as well land it propulsively if you are going to assume/use all those engineering benefits.Oh, wait...
Quote from: mikelepage on 06/09/2018 03:17 amQuote from: woods170 on 05/31/2018 01:25 pmLotsa discussion here about what happens with the hypergolic fuel on-board Crew Dragon when it is NOT used in a launch abort (now that propulsive landing is out the window).Must admit I never thought they would try to land with hypergolics onboard.I had been assuming they would use the SuperDracos for an entry interface burn.1) Remove mass of hypergolic fuels from parachute landing requirements.2) Remove risk of toxic hypergolic fuel leaks to occupants upon landing.3) Increase accuracy of landing ellipse.4) Reduce peak-heating/wear on Dragon v2 heat shield.5) Decrease peak g-forces on occupants/payload. I'm not sure it works that way. If you slow down too much you're going to come in at a steeper angle right? The optimum angle to hit the atmosphere to minimize stress and wear and tear might be what they're using even if it's not the one that dissipates the minimum amount of energy. Just guessing, I really don't have any idea.
Quote from: mikelepage on 06/09/2018 03:17 amQuote from: woods170 on 05/31/2018 01:25 pmLotsa discussion here about what happens with the hypergolic fuel on-board Crew Dragon when it is NOT used in a launch abort (now that propulsive landing is out the window).Must admit I never thought they would try to land with hypergolics onboard.I had been assuming they would use the SuperDracos for an entry interface burn.1) Remove mass of hypergolic fuels from parachute landing requirements.2) Remove risk of toxic hypergolic fuel leaks to occupants upon landing.3) Increase accuracy of landing ellipse.4) Reduce peak-heating/wear on Dragon v2 heat shield.5) Decrease peak g-forces on occupants/payload.I am certain they wouldnt do this. Hypergol residuals will remain in tanks. Only less of them but the danger would be the same. Also, if the parachute system requires the reduced mass to land safely, a failure of running the engines for any reason could be fatal. No point in adding failure modes.
I would have thought that every EDL would give them a chance to experiment with different landing procedures.
Or is it simply that they are halting development on F9/Dragon and focusing on BFR?
Crew Dragon is at @NASA’s Plum Brook Station testing facility in Ohio, home to the largest thermal vacuum chamber in the world, to demonstrate its capability to withstand the extreme temperatures and vacuum of space. instagram.com/p/BkQ8w0mFoxa