Author Topic: Should Crew Dragon have ability to use SuperDracos for landing emergency? (Read 62968 times)

Spindog · « **on:** 03/04/2019 01:44 pm »

Ok I dont know if anyone has ever asked this. In the unlikely event of a parachute deployment problem, let's say something like 1 or 2 chutes becoming tangled, is there a system to jettison the chutes and use the super dracos to 'propulsively land' on the water to save the crew? It would seem like another failsafe but I think it would 1) require human eyes on the chutes to make the call, and 2) would introduce some risk by adding a system to jettison the main chutes quickly under load. Or is this already the plan? Thoughts?

kevinof · « **Reply #1 on:** 03/04/2019 02:17 pm »

Nope. No testing done, no altimiter on the Dragon to control the dracos and no software on-board to kick it all off. Add in that the Dragon Will be over water when the chutes deploy so can't divert back to land.

OnWithTheShow · « **Reply #2 on:** 03/04/2019 02:29 pm »

If there is no altimeter how does it decide when to fire the chutes?

kevinof · « **Reply #3 on:** 03/04/2019 02:34 pm »

No high definition altimeter (radar/lidar) for judging when to fire the superdracos and when to shut them off.

Quote from: OnWithTheShow on 03/04/2019 02:29 pm

If there is no altimeter how does it decide when to fire the chutes?

JohnLloydJones · « **Reply #4 on:** 03/04/2019 02:54 pm »

Quote from: kevinof on 03/04/2019 02:17 pm

Nope. No testing done, no altimiter on the Dragon to control the dracos and no software on-board to kick it all off. Add in that the Dragon Will be over water when the chutes deploy so can't divert back to land.

Maybe I have it all wrong, but I imagined that the Dracos and Super Dracos share the same propellant tanks. If you need the Super Dracos for an abort, you won't need the Dracos; likewise for a normal launch, the Super Dracos are just along for the ride. Anyone able to correct me?

CorvusCorax · « **Reply #5 on:** 03/04/2019 03:01 pm »

Quote from: kevinof on 03/04/2019 02:34 pm

No high definition altimeter (radar/lidar) for judging when to fire the superdracos and when to shut them off.

Quote from: OnWithTheShow on 03/04/2019 02:29 pm
If there is no altimeter how does it decide when to fire the chutes?

That would not be needed for a splashdown. GPS + barometric altimeter would be enough for a water landing.

The goal would not be to make a perfect landing with 0 damage, the goal would be to limit impact G-forces to prevent pressure vessel rupture and to give the crew a survival chance in the event of a catastrophic parachute failure.

This doesnt need an exact altitude estimate, it would be enough to limit vertical speed to max 5m/s for any altitude under 50m above sea level. Well within the abilities of available sensors ( including auto-activation if the capsule is in freefall at that stage ). And engine shutdown on impact will be easy too. At those speeds the splashdown will have a clear signal to noise ratio.

You would not need to certify such a contingency program, only the decision tree that makes sure it never ever gets activated under normal conditions.

You would not want to rely on it, ever. But if the parachutes do fail, it might save lifes.

Spacenick · « **Reply #6 on:** 03/04/2019 03:08 pm »

Or even easier, have a manual trigger that says "Slow to < 4 m/s vertical descent and keep upright until propellant runs out". That would work even with damaged chutes, manual should always be fine by NASA and the astronauts eye on the GPS altimeter should be enough to time it. Even with no chutes at all a Dragon shouldn't fall much faster than a human sky diver.

mn · « **Reply #7 on:** 03/04/2019 03:18 pm »

Quote from: kevinof on 03/04/2019 02:17 pm

Nope. No testing done, no altimiter on the Dragon to control the dracos and no software on-board to kick it all off. Add in that the Dragon Will be over water when the chutes deploy so can't divert back to land.

I don't think anybody said anything about diverting back to land.

Oersted · « **Reply #8 on:** 03/04/2019 03:21 pm »

To me it would be a shocking breach of due diligence if they did NOT program the spacecraft to land with Superdracos in case of parachute failure.

Back in the day I seem to remember that Musk mentioned that they could have saved the Dragon capsule when its booster blew up. That alone would indicate to me that they have thought this through.

CorvusCorax · « **Reply #9 on:** 03/04/2019 03:21 pm »

Quote from: Spacenick on 03/04/2019 03:08 pm

Or even easier, have a manual trigger that says "Slow to < 4 m/s vertical descent and keep upright until propellant runs out". That would work even with damaged chutes, manual should always be fine by NASA and the astronauts eye on the GPS altimeter should be enough to time it. Even with no chutes at all a Dragon shouldn't fall much faster than a human sky diver.

ThInk: blaring alarm, a big warning message on all screens:

!!!MASTER CAUTION!!!
Alt: 2780ft. Rate: -12391 ft/min ! ( red flashing)
!!!Vertical speed exceeds critical limits!!!
Time to impact: 13 sec !!!

With an equally large button:

Emergency Landing Sequence Suggested:
<<< OVERRIDE THRUSTER INHIBITION >>>

Oersted · « **Reply #10 on:** 03/04/2019 03:48 pm »

...Also, let's just remember that this is a company that has perfected automated, retro-propulsive landings... They would never forgive themselves if they could have saved lives. Apollo 13 taught us that Failure is not an Option, and that every option must be explored.

Jarnis · « **Reply #11 on:** 03/04/2019 04:05 pm »

While we don't know if they have this done and set up, I would suggest that they probably have or at least should.

Hypothetical (unlikely, hopefully never going to happen) scenario:

Parachutes fail, Crew Dragon hits water at high speed and the crew is lost. Superdracos are never fired because there was no option, no manual override, nothing. They were dumb pieces of metal as soon as launch escape system was disarmed.

What would be the first "WTF?" question afterwards once everyone realizes that the capsule had 8 high power thrusters and a ton of propellant for them that could have slowed down that plunge and possibly saved the crew?

How would NASA and SpaceX survive the fallout from the unavoidable public outcry? "Who was the bureaucrat that decided it was a great idea to not be able to even try to do emergency water landing with the thrusters if chutes fail?"

You can explain away not doing certification & testing and not making the superdracos the primary landing method. You cannot explain away a decision to basically make it impossible to try in an emergency if primary (chutes) fail.

So, an educated guess: They do have some kind of procedure for trying to pull of a decisively uncertified maybe-survivable emergency landing with the thrusters. Based on above hypothetical scenario alone. If they do not, they are betting the farm, literally, on parachutes never failing - because the public opinion would crucify everyone involved if it ever happened.

cbarnes199 · « **Reply #12 on:** 03/04/2019 04:08 pm »

Quote from: Oersted on 03/04/2019 03:21 pm

To me it would be a shocking breach of due diligence if they did NOT program the spacecraft to land with Superdracos in case of parachute failure.

Back in the day I seem to remember that Musk mentioned that they could have saved the Dragon capsule when its booster blew up. That alone would indicate to me that they have thought this through.

Elon was referring to the fact that they could have deployed the chutes for the Dragon capsule not suggesting the use of the Dracos.

But when certain death is the outcome of the current situation (chute failure) trying something risky becomes an option to consider. I doubt the Dracos could divert the capsule very far from the ballistic target it was on when the chutes failed but they could slow the landing speed.

Have failed chutes ever caused a fatality?

Negan · « **Reply #13 on:** 03/04/2019 04:17 pm »

Quote from: Jarnis on 03/04/2019 04:05 pm

What would be the first "WTF?" question afterwards once everyone realizes that the capsule had 8 high power thrusters and a ton of propellant for them that could have slowed down that plunge and possibly saved the crew?

Not to nitpick your points, but I as I recall there were some good reasons to purge the propellant before Dragon 2 hits the water. I assume the original propulsive landing design should have been able to land with the propellant since the chutes were backup so this might not matter.

Mongo62 · « **Reply #14 on:** 03/04/2019 04:18 pm »

Quote from: cbarnes199 on 03/04/2019 04:08 pm

Quote from: Oersted on 03/04/2019 03:21 pm
To me it would be a shocking breach of due diligence if they did NOT program the spacecraft to land with Superdracos in case of parachute failure.

Back in the day I seem to remember that Musk mentioned that they could have saved the Dragon capsule when its booster blew up. That alone would indicate to me that they have thought this through.

Elon was referring to the fact that they could have deployed the chutes for the Dragon capsule not suggesting the use of the Dracos.

But when certain death is the outcome of the current situation (chute failure) trying something risky becomes an option to consider. I doubt the Dracos could divert the capsule very far from the ballistic target it was on when the chutes failed but they could slow the landing speed.

Have failed chutes ever caused a fatality?

Vladimir Komarov

Lar · « **Reply #15 on:** 03/04/2019 04:19 pm »

Quote from: Spindog on 03/04/2019 01:44 pm

Ok I dont know if anyone has ever asked this. In the unlikely event of a parachute deployment problem, let's say something like 1 or 2 chutes becoming tangled, is there a system to jettison the chutes and use the super dracos to 'propulsively land' on the water to save the crew? It would seem like another failsafe but I think it would 1) require human eyes on the chutes to make the call, and 2) would introduce some risk by adding a system to jettison the main chutes quickly under load. Or is this already the plan? Thoughts?

The thinking among some is that they do have not entries in the error tree for propulsive use. Too far away from normal and too untested. Unlike when they wished they'd put something in the D1 error tree to deploy chutes when it might be helpful.

Jarnis · « **Reply #16 on:** 03/04/2019 04:25 pm »

Quote from: Negan on 03/04/2019 04:17 pm

Quote from: Jarnis on 03/04/2019 04:05 pm
What would be the first "WTF?" question afterwards once everyone realizes that the capsule had 8 high power thrusters and a ton of propellant for them that could have slowed down that plunge and possibly saved the crew?

Not to nitpick your points, but I as I recall there were some good reasons to purge the propellant before Dragon 2 hits the water. I assume the original propulsive landing design should have been able to land with the propellant since the chutes were backup so this might not matter.

We know they do not dump the propellant. There was a forum post that Hans confirmed it just gets offloaded and re-used.

Alexphysics · « **Reply #17 on:** 03/04/2019 04:31 pm »

Quote from: Spindog on 03/04/2019 01:44 pm

Ok I dont know if anyone has ever asked this.

It's been literally asked a thousand times

Alexphysics · « **Reply #18 on:** 03/04/2019 04:35 pm »

I only wish some reporter to ask this on the post-splashdown conference so some SpaceX official could close that damn discussion that's been going around for years even after the cancellation of propulsive landings.

Star One · « **Reply #19 on:** 03/04/2019 04:49 pm »

Quote from: Alexphysics on 03/04/2019 04:35 pm

I only wish some reporter to ask this on the post-splashdown conference so some SpaceX official could close that damn discussion that's been going around for years even after the cancellation of propulsive landings.

Not helped by articles like this.

Quote

Crew Dragon will remain latched to the ISS until Thursday, when it will embark on a journey back to Earth. It's expected to land on a SpaceX drone ship in the Atlantic ocean, close to Kennedy Space Center.

https://www.popularmechanics.com/space/rockets/a26625114/spacex-manned-mission-iss/