Author Topic: SpaceX Dragon 2 Updates and Discussion - Thread 2  (Read 547365 times)

Offline woods170

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1300 on: 05/31/2018 01:25 PM »
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?
« Last Edit: 05/31/2018 01:27 PM by woods170 »

Offline Semmel

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1301 on: 05/31/2018 02:22 PM »
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?

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.

Offline clongton

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1302 on: 05/31/2018 06:51 PM »
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.

Unless you can point to a document that says the Dragon will dump its propellant before landing then it already does carry it all the way down. I'm willing to be shown that I'm wrong. I'm not willing to dismiss a viable option that requires only a software command to execute.
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Offline whitelancer64

Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1303 on: 05/31/2018 07:59 PM »
I know that after the OMS de-orbit burn and re-orientation prior to re-entry, the Shuttle burned off all remaining fuel from the forward RCS tanks. This was done both to push the Shuttle's COG aft and to avoid having any hydrazine in the nose, the hottest area during re-entry. However, they did not burn off the rest of the hydrazine in the aft OMS / RCS tanks and also they did have to retain some hydrazine to power the Shuttle's APUs.

"The remaining propellants aboard the forward RCS are dumped by burning the propellants through the forward RCS yaw thrusters before entry interface"

https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-rcs.html

In principle, there's no reason why the remaining hydrazine on the Dragon couldn't be burned off (after the de-orbit burn, but prior to re-entry), but it's probably not necessary.
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Offline woods170

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1304 on: 06/01/2018 06:50 AM »
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?

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.

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.

Offline Semmel

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1305 on: 06/01/2018 07:54 AM »
- 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.

Offline mikelepage

Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1306 on: 06/09/2018 03:17 AM »
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).

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.

Offline AncientU

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1307 on: 06/09/2018 12:20 PM »
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).

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...
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Offline Johnnyhinbos

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1308 on: 06/09/2018 01:32 PM »
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).

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...
Except if you do the above then the one thing you can't do is land propulsively [/size]as you just consumed your landing fuel...
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Offline Nomadd

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1309 on: 06/09/2018 04:52 PM »
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).

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.

Online russianhalo117

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1310 on: 06/09/2018 06:34 PM »
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).

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.
I guess that they could do a post reentry depletion burn just before drogue deploy or just before landing but not apart of any officially stated plan.

Offline Semmel

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1311 on: 06/11/2018 01:47 PM »
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).

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.

Offline mikelepage

Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1312 on: 06/12/2018 08:47 AM »
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).

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.

Fair enough. It makes sense that they would keep the fourth chute just in case they have to land full, but I would have thought that every EDL would give them a chance to experiment with different landing procedures. Even a short burn following max-q would allow them to reduce the g-forces at chute-deploy and increase the landing zone precision.

Online gongora

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1313 on: 06/12/2018 02:40 PM »
I would have thought that every EDL would give them a chance to experiment with different landing procedures.

Every currently scheduled flight of Dragon 2 will be either a qualification mission or will be carrying people or cargo during descent.  This isn't like the boosters where they could play with it after it was done being part of the primary mission.

Offline RDMM2081

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1314 on: 06/12/2018 05:39 PM »
One of my hopes and dreams was that SpaceX would eventually take one of the recovered but not destined to be reused for a mission Dragons, and a recovered first stage and just huck that Dragon up as high as it could go with the first stage boost, leaving enough fuel to re-land the booster, and skip a second stage.  Isn't that basically free practice? 

I realize there are huge problems with that, biggest probably being that there is currently no known way to attach a Dragon directly to a first stage, much less release it reliably at any particular desirable point.  What kind of re-entry profile testing would that allow for the dragon capsule?  Would it simulate at all the type of landing performance that NASA needs to see to certify landing cargo (or astronauts) on thrusters?  I also accept that this must be a stupid idea, because SpaceX is obviously smart enough to recognize "free reused hardware + free reused hardware = free tests" so obviously the costs to do so outweigh whatever benefits they (I) would have hoped to achieve.

Or is it simply that they are halting development on F9/Dragon and focusing on BFR?

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1315 on: 06/12/2018 06:15 PM »
Or is it simply that they are halting development on F9/Dragon and focusing on BFR?
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Offline FutureSpaceTourist

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1316 on: 06/13/2018 12:10 AM »
NASA Kennedy has posted a bit higher-res pic of Dragon 2

Offline clongton

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1317 on: 06/13/2018 12:43 PM »
Or is it simply that they are halting development on F9/Dragon and focusing on BFR?

F9-Dragon will be flying for a few years. It wouldn't surprise me if SpaceX flew one or two test flights on its own dime. And I don't see BFS being used to bring persons or cargo to a Bigalow station. I don't think Falcon-Dragon will go away so quickly. After all both are reusable many, many times.
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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1318 on: 06/15/2018 07:11 PM »
The descriptions from the last few SpaceX CC contract updates:

MOD 46:  THE PURPOSE OF THIS MODIFICATION IS TO ADD REEF LINE CUTTER ENVIRONMENT SENSORS (RLCES) TO ATTACHMENT J-08, GOVERNMENT PROPERTY PROVIDED IN EXCHANGE FOR DEFERRED REDUCTION OF CONTRACT PRICE. AS A RESULT, ATTACHMENT J-08 PAGE 4 IS REPLACED.

MOD 45:  THE PURPOSE OF THIS MODIFICATION IS TO INCREASE FUNDING IN THE AMOUNT OF $110,463,653. THIS MODIFICATION CHANGES THE AMOUNT OBLIGATED UNDER THIS CONTRACT FROM $1,096,086,839 TO $1,206,550,492, AN INCREASE OF $110,463,653.

MOD 44: THE PURPOSE OF THIS BILATERAL MODIFICATION IS TO UPDATE ATTACHMENT J-07, GOVERNMENT PROPERTY TO ADD ITEMS 9.1 AND 9.2 TO TABLE J-07-2 GOVERNMENT PROPERTY IDENTIFIED IN SSP 50996 ISS/SPACEX CREW JOINT INTEGRATION, VERIFICATION AND TEST PLAN, APPENDIX G BILATERAL HARDWARE AND SOFTWARE EXCHANGE AGREEMENTS LIST AND SCHEDULE (BHSEALS). AS A RESULT, ATTACHMENT J-07, GOVERNMENT PROPERTY PAGE 5.1 IS ADDED.

MOD 43: THE PURPOSE OF THIS MODIFICATION IS TO ADD THE REQUIREMENT CHANGES FROM CR5, CHANGE MILESTONE DATES RESULTING FROM QUARTERLY PROGRAM REVIEWS (QPR) HELD IN NOVEMBER 2017 AND FEBRUARY 2018 AND ADD THREE NEW MILESTONES. CLIN 001 AMOUNT IS CHANGED FROM$1,206,115492 TO $1,206,550,492, AN INCREASE OF $435,000. CLIN 002 AND 003 REMAIN UNCHANGED.

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1319 on: 06/20/2018 04:10 PM »
SpaceX Nose Cone and Docking system inspection by CC flight crew members. The nose cone uses the docking systems Soft Capture and Hard Capture Systems as the primary means of securement to latch the Nose cone to the capsule during the non-docked phases of flight.

https://www.flickr.com/photos/nasakennedy/

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