If the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.
If the first stage had an engine failure or two and would be unable to make orbit could the the entire rocket (w/ payload) land on the ASDS or RTLS.I assume the weight on the legs would be the first obvious thing to consider.Would the grid fins have less control?Too top heavy?Since they were able to program the dragon to survive a rare case, perhaps it'd be worth programming to save f9 in an engine out?
Quote from: R7 on 04/11/2016 08:08 amIf the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.
Quote from: su27k on 04/11/2016 12:20 pmQuote from: R7 on 04/11/2016 08:08 amIf the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.Save a $40 million stage vs a $200 million spacecraft.Any ways the launch vehicle doesn't know it is doomed.
It must know if all its engines are still running. If it knows that then it would know if there is enough thrust to make orbit. If there isn't, does it just just destruct, or could decide to stage itself, separate from the second stage, (if carrying Dragon, eject the Dragon as well for parachute landing - we know it can do that), try and land the first stage, crashing the second stage? I certainly cannot see any way of saving the second stage, but 1stage and Dragon might be possible.Of course, reliability of the first stage and its redundant engines make this a very unusual circumstance.
Quote from: Jim on 04/11/2016 01:45 pmQuote from: su27k on 04/11/2016 12:20 pmQuote from: R7 on 04/11/2016 08:08 amIf the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.Save a $40 million stage vs a $200 million spacecraft.Any ways the launch vehicle doesn't know it is doomed.It must know if all its engines are still running. If it knows that then it would know if there is enough thrust to make orbit. If there isn't, does it just just destruct, or could decide to stage itself, separate from the second stage, (if carrying Dragon, eject the Dragon as well for parachute landing - we know it can do that), try and land the first stage, crashing the second stage? I certainly cannot see any way of saving the second stage, but 1stage and Dragon might be possible.Of course, reliability of the first stage and its redundant engines make this a very unusual circumstance.
Quote from: JamesH65 on 04/11/2016 02:11 pmQuote from: Jim on 04/11/2016 01:45 pmQuote from: su27k on 04/11/2016 12:20 pmQuote from: R7 on 04/11/2016 08:08 amIf the engine-out situation is so severe it endangers the mission the logical thing is to forfeit S1 recovery and keep burning to depletion to ensure successful payload delivery.I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.Save a $40 million stage vs a $200 million spacecraft.Any ways the launch vehicle doesn't know it is doomed.It must know if all its engines are still running. If it knows that then it would know if there is enough thrust to make orbit. If there isn't, does it just just destruct, or could decide to stage itself, separate from the second stage, (if carrying Dragon, eject the Dragon as well for parachute landing - we know it can do that), try and land the first stage, crashing the second stage? I certainly cannot see any way of saving the second stage, but 1stage and Dragon might be possible.Of course, reliability of the first stage and its redundant engines make this a very unusual circumstance.Propellent used for recovery, especially for RTLS, would provide enough fuel for a crazy long burn. Depending when the engine loss occurred I suspect it could lose more than one engine and still eventually make up most the delta-v.
I actually thought that this topic, from its title, might be speculating about performing a recovery of the first stage when the centre engine is lost. To which, admittedly unasked, question I would suggest- yes, it might just be within a whisker of the possible to switch to using two opposing engine instead and land with a more aggressive hoverslam. It all comes down to the minimum impulse and start/shutdown transients of the Merlins, none of which are public information.
One point is that a two-engine suicide burn conserves fuel far better than a single-engine burn without being nearly so aggressive as a three-engine landing. They'll need 2-3 engines for the high-velocity returns, so if they get those down to a science then I can see them using that arrangement for even low-velocity landings to save propellant and to extend the life of the central engine.
I wonder if there're cases where the mission is doomed even with burn to depletion, in these cases maybe it's better to try S1 recovery as planned, since at least you can (hopefully) get the S1 back.
For their engine out on landing procedure, I think we hear it in the audio of the landing. The FTS was safed after the rocket was on the ship. IRRC they used to safe it soon after separation from the 2nd stage. Perhaps this give the rocket a chance to use the FTS in the event of bad landing burn. They would rather have falcon rain than falcon lawn dart.
Quote from: sevenperforce on 04/11/2016 03:56 pmOne point is that a two-engine suicide burn conserves fuel far better than a single-engine burn without being nearly so aggressive as a three-engine landing. They'll need 2-3 engines for the high-velocity returns, so if they get those down to a science then I can see them using that arrangement for even low-velocity landings to save propellant and to extend the life of the central engine.I believe this has been discussed elsewhere, but there may be an issue with gimbal or throttle range if you don't use the centre engine.
Quote from: sewebster on 04/11/2016 04:39 pmQuote from: sevenperforce on 04/11/2016 03:56 pmOne point is that a two-engine suicide burn conserves fuel far better than a single-engine burn without being nearly so aggressive as a three-engine landing. They'll need 2-3 engines for the high-velocity returns, so if they get those down to a science then I can see them using that arrangement for even low-velocity landings to save propellant and to extend the life of the central engine.I believe this has been discussed elsewhere, but there may be an issue with gimbal or throttle range if you don't use the centre engine.Do the SL-optimized Merlin 1Ds gimbal?Definitely an issue with throttle range; a much hotter suicide burn.
Quote from: sevenperforce on 04/11/2016 07:20 pmDo the SL-optimized Merlin 1Ds gimbal?Definitely an issue with throttle range; a much hotter suicide burn.Yes. That's how the first stage is controlled.
Do the SL-optimized Merlin 1Ds gimbal?Definitely an issue with throttle range; a much hotter suicide burn.
Quote from: Kaputnik on 04/11/2016 07:42 pmQuote from: sevenperforce on 04/11/2016 07:20 pmDo the SL-optimized Merlin 1Ds gimbal?Definitely an issue with throttle range; a much hotter suicide burn.Yes. That's how the first stage is controlled.I had assumed it was controlled with cold gas RCS.
Unless the other engines have extra starter-fluid tanks over and above the boost-back burn then no it can't recover with the center engine out. Unless they've changed the design significantly each engine has it's own tank and only the center engine has more than two 'starts' worth of fluid.Randy
SES9 did a 3-engine landing burn (not successfully).
If the center engine is out, it seems plausible that a 2 engine landing could be possible. It would take modelling that scenario in the landing software, and maybe require a hardware mod. Probably a low priority since the Merlin 1D is proving to be quite reliable.
With any other engine out, the landing may still be forced to use less fuel, which could mean coming in hotter and using a 2-3 engine landing burn.
More, not less propellant since you're running more engines. Any other engine out on launch won't be an issue, they only use three engines for everything after staging. Landing shouldn't be effected by any failure of an engine that are not the three used for boost-back, retro-burn and landing unless it damages those engines and then you're probably looking at a LOV situation rather than any attempt at landing.Randy