When is SpaceX's DragonFly propulsive landing technique likely to be demonstrated as part of a real landing, rather than the simple test shown below (from here)?
What will be the key objectives for the test?
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1$\begingroup$ Propulsive landing for the Dragon has been indefinitely postponed. $\endgroup$– David HammenApr 10, 2018 at 9:37
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$\begingroup$ See SpaceX and propulsive landing on Mars — what just happened? (and why?) for more on this. $\endgroup$– uhohApr 10, 2018 at 11:59
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$\begingroup$ So up till now, all we have seen publicly is the Dragon V2 with those 8 SuperDraco engines. If they are not going to use those, will they remove them and change the shape and structure of the existing Dragon V2 prototype? Does that mean that all the efforts put into designing and manufacturing the SuperDraco engines is in vain? $\endgroup$– JayApr 10, 2018 at 14:25
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2 Answers
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Probably never.
NASA was not comfortable with the idea of legs that went through holes in the heat shield, and thus SpaceX reverted to water landings for Dragon Crew vehicles.
Once that choice was made, and with BFR on the horizon, they decided not to spend the money on developing a feature for which they had no paying customers.
This also meant the Red Dragon mission (Dragon v2 sent to Mars by a Falcon Heavy) went by the wayside as well.
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$\begingroup$ This is discussed more fully already in the answers to SpaceX and propulsive landing on Mars — what just happened? (and why?) $\endgroup$– uhohApr 10, 2018 at 12:00
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$\begingroup$ So up till now, all we have seen publicly is the Dragon V2 with those 8 SuperDraco engines. If they are not going to use those, will they remove them and change the shape and structure of the existing Dragon V2 prototype? Does that mean that all the efforts put into designing and manufacturing the SuperDraco engines is in vain? $\endgroup$– JayApr 10, 2018 at 14:25
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$\begingroup$ They still plan on using the engines for abort. Maybe to slow down during landing to make it safer by parachute/softer water landing. $\endgroup$– geoffcApr 10, 2018 at 14:30
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I agree with the other answer that this will not happen. I think the causes vary slightly, though --
The legs are an oft-repeated bit of fan speculation. We have a few real world examples of openings in heat shields, though, that don't indicate any particular problems. Shuttle had multiple openings, and while it had heat shield problems none were related to openings. A Gemini was flown with a circular hatch in it's heatshield, to enable MOL missions. This was never manned or ramped up to actual use, but it was tested successfully in flight.
There are several major factors in dropping propulsive flight. For one thing, NASA never requested it. They are currently the sole customer of Dragon and while they may find some uses of propulsive landings it isn't among the features they signed for, so they aren't likely to pay anything additional for it.
It needs qualification, and the only Dragon customer doesn't provide any post-mission opportunities for testing, like customers provided with F9 propulsive landings. NASA is nearly as concerned with cargo downmass from the station as cargo up, and won't risk contractually obligated deliveries for propulsive landing tests.
It has little benefit for SpaceX's future plans. Capsules don't scale up well - they need to get wider as they get taller in order to keep a stable shape for entry, and keep the side walls away from the hot plasma flows around the shield. Long/tall cylinders can't hide behind a small shield at the base. Because of this, their next returning cargo/crew vehicle (BFR) is intended to enter in a different way, with a side heat shield and bottom mounted engines (opposite of Dragon's arrangement).
It also isn't likely to reduce costs for SpaceX in the long run. They can't rely solely on propulsive landings and must plan for a water/parachute touch down zone in case of an abort to parachutes after high altitude engine test failure. This means having a recovery ship prepositioned off the coast while the capsule approaches.
No extra revenue, no cost savings, no R&D useful to future vehicles, and expensive out-of-pocket testing process. That's why the landings were cut.
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$\begingroup$ So up till now, all we have seen publicly is the Dragon V2 with those 8 SuperDraco engines. If they are not going to use those, will they remove them and change the shape and structure of the existing Dragon V2 prototype? Does that mean that all the efforts put into designing and manufacturing the SuperDraco engines is in vain? $\endgroup$– JayApr 10, 2018 at 14:26
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2$\begingroup$ Not at all - they serve an important role in launch abort/crew escape. Without the built-in Super Dracos they would need a traditional launch escape tower. These are traditionally solid fueled, which goes against SpaceX's general "test like you fly" philosophy in that you cannot test your flight articles. They're also disposed of, which is wasteful. Reusable abort motors that come home on the capsule are a better solution, especially when they already exist. $\endgroup$– SaibooguApr 10, 2018 at 14:31
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$\begingroup$ Oh, alright. Although their main function was Propulsive landing. And with the provision of attitude cold gas thrusters, they won't be much of use. Plus, keeping the launch abort system, which is only useful for mission abort during launch phase, will be a huge chunk of additional mass to the spacecraft. SuperDraco thrusters along with it's propellants account for about 2500kg mass within the 6000kg spacecraft. $\endgroup$– JayApr 11, 2018 at 10:34
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$\begingroup$ Henceforth, an expendable external launch abort tower or other such system would have been more profitable economically and fuel-wise. $\endgroup$– JayApr 11, 2018 at 10:35
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1$\begingroup$ They've not yet succeeded at that, plus abort motors released near orbital speeds are a very different recovery challenge than big lightweight fairings released just after booster MECO. Mass from Dragon is a good point, but everyone always makes the mistake of viewing that item in a vacuum - it isn't waste if it serves an important purpose while allowing them to meet design goals. Dragon is already volume limited, an extra 2.5T mass budget isn't that useful. I'm not privy to internal SpaceX accounting, but I suspect the fact they're keeping them means that is the more economical option. $\endgroup$– SaibooguApr 11, 2018 at 13:51