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In this SpaceX promotional video, they indicate their plans to land a crewed capsule without a parachute, using landing thrusters. I know that Soyuz does this too, though in combination with a landing chute.

Why, in either case, but especially the no-chute-at-all configuration, is it desirable to replace a (apparently) hyper-reliable and inexpensive chute system with an (apparently) expensive and complex landing thruster system? What's the advantage?

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    $\begingroup$ Possible duplicate of Is powered descent from orbit a viable method of reentry on bodies with an atmosphere? $\endgroup$ – Russell Borogove Dec 2 '15 at 17:22
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    $\begingroup$ Just realized this is a duplicate of space.stackexchange.com/questions/7718/… $\endgroup$ – Brian Lynch Dec 2 '15 at 18:02
  • $\begingroup$ Yeah, there were some differences between this and the current duplicate, but that one is EXACTLY the same question. $\endgroup$ – Chris B. Behrens Dec 2 '15 at 18:03
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    $\begingroup$ Actually no, the second linked question asks about first stage recovery, this one asks about crewed capsule landing. The first link is closer to being a dupe, but not quite either IMO (tho it does hint at an additional advantage of powered landing vs parachuted one - i.e. that it works also on bodies with no or too tenuous atmospheres, something that Elon Musk is constantly repeating, e.g. in the interview for the MIT Centennial Symposium, if a source is needed) $\endgroup$ – TildalWave Dec 2 '15 at 18:11
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    $\begingroup$ @LocalFluff Not sure which is more reliable; after all rockets have quite a history of catastrophic failure even to the present day. At least with a parachute you can't run out of fuel. Doesn't help on Mars though. $\endgroup$ – D_Bester Dec 3 '15 at 2:29
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Note that this answer refers to the final flight version of the Dragon V2. The first powered landings will be using parachutes before the system is validated for powered-only landing (see this article, thanks to Mark Adler for pointing this out).

Parachutes are passive devices that slow the vehicle but do not steer it (some parachutes can steer a bit, others more, but not the kind used for spacecraft entry, descent, and landing). So if you want to precisely land the vehicle at a designated target then you need an active system like what you are describing.

It could be possible to add parachutes to assist with the descent but the added mass and complexity is likely not worth it since the vehicle itself is already outfitted with a propulsion system that can be leveraged for descent and landing.

Also keep in mind that a parachute landing is not the softest, whereas a powered landing allows you to make a much cleaner touchdown.

It would seem that it was a design decision to build the system so that it reliably used a powered landing alone, that way the same vehicle could possibly be used for other missions (such as to Mars or the Moon).

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    $\begingroup$ The cargo Dragon already does land (splash) using parachutes, and it is reported that the initial versions of the crewed Dragon will use parachutes as well, with a final assist by the Super Dracos for land landing. The early attempts of Falcon 9 1st stage recoveries had parachutes. $\endgroup$ – Mark Adler Dec 3 '15 at 1:17
  • $\begingroup$ Of course! I completely overlooked that fact while getting caught up in the hype about the fully reusable future plans. I will edit my answer to add that aspect of the initial chute/thruster landing tests for the Dragon V2. It would have surprised me to hear there was no consideration for at least testing with both before moving on to powered-only. $\endgroup$ – Brian Lynch Dec 3 '15 at 1:27
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If you're just looking at it as a mass trade, then yes, you will definitely get a mass savings by replacing a portion of your propellant with a bag full of nylon. Depending on your speed, the nylon can have a much higher "Isp" than the rockets.

However at the system level, there are other things to consider besides mass. First, parachutes are not "hyper-reliable". You need to consider the consequences of parachute failure, which is why you usually see three of them in a cluster on crewed vehicles. (Soyuz is an exception with one large parachute, though there is a smaller backup parachute you don't see. The single Soyuz 1 cosmonaut died on impact due to both parachutes failing.) Second, if you're doing a propulsive landing for the last bit, then you may need to get rid of the parachute and also make sure that it doesn't then interfere with the landing. Third, you wouldn't reuse these kinds of parachutes, so while they are relatively inexpensive for space systems, it does cost more to replace the parachutes than to refill the tanks, and they take a fair amount of integration time due to the care needed in making sure that the rigging will deploy as intended. Filling tanks, even with hypergols, can go pretty quick. As noted in another answer, you are more at the mercy of the winds while on a parachute, so if you are targeting a very small landing location (e.g. a pad), then you will have more correction to do once you go propulsive, and will need more altitude in which to do that. Or you could have a steerable parachute, which has its own efficiency and reliability issues, and you would still be correcting at the end with the rockets.

Even with all that, if you really need the down-mass capability, you may find yourself working to solve all those problems in order to incorporate a parachute system and reduce mass. But if you're in a happy place for mass, then you would want to avoid the complexity, cost, and reliability issues of parachutes.

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    $\begingroup$ I feel compelled to point out however that I have never known even one space mission that was in a happy place for mass. $\endgroup$ – Mark Adler Dec 8 '15 at 0:38
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E. Musk has answered this multiple times in interviews. This comes down to the economics of it. They are putting this entire system together to haul cargo, and the reusable portion is there to increase profits.

They are putting in place a reusable restartable engine in order to have the maximum duplication of function for the components onboard. Previously you had one system, the engine, responsible for going up, and another system, parachutes, responsible for coming down.

Parachutes are not capable of doing job #1. Rocket engines are capable of doing both job #1 and #2. You've just reduced the mass, the failure points, and complexity of your vehicle with a minimum of redesign.

Parachutes only slow the vehicle to a certain speed. That speed isn't slow enough to land a ten-story hollow metal tube with breakable components inside on land. And landing in water adds new complications for reuse of the motors.

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    $\begingroup$ The question is about Dragon, not the Falcon 9 first stage. Though most of your points still apply. $\endgroup$ – Mark Adler Dec 3 '15 at 0:10
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One thing that hasn't been mentioned thus far - the powered landing engines also serve as the launch abort system. Without them, they'd need something like the Apollo Launch Escape System to carry the crewed spacecraft away from an exploding launch vehicle.

Good luck landing a Dragon with parachutes on the Moon, as well. :-)

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  • $\begingroup$ Wow...the more I hear about this spacecraft, the more impressed I am. $\endgroup$ – Chris B. Behrens Dec 3 '15 at 17:49
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Atmosphere. Parachutes don't work well with thin atmospheres, like Mars', and they don't work at all with no atmosphere like the Moon. The goal is to land on other bodies in our solar system - not just Earth - so we need precision and technology that works regardless of atmosphere so rockets are much more preferential than parachutes for this reason: universal landing technology.

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  • $\begingroup$ Yeah, but not for this Earth- only craft. $\endgroup$ – Chris B. Behrens Dec 4 '15 at 6:44
  • $\begingroup$ They're not planning for Dragon to be an Earth-only craft. $\endgroup$ – Hobbes Dec 4 '15 at 6:51
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    $\begingroup$ @ChrisB.Behrens why would you create a spacecraft that can only land on earth? That's called a plane $\endgroup$ – user1886419 Dec 4 '15 at 16:23
  • $\begingroup$ Okay, comedian - I meant it can only operate in Earth orbit, and land on Earth :). While you might be able to use this kind of craft for lunar operations (space.stackexchange.com/questions/5025/…), as the answer there notes, it's suboptimal. I think it's safe to say that Mars operations are out of the question, given the vastly different mission profile, not to mention the physical differences. We're just not to the point, technology and economy-wise where we can have a one-size-fits-all Star Trek shuttle-like craft. Maybe if it had nuke propulsion. $\endgroup$ – Chris B. Behrens Dec 4 '15 at 16:28
  • $\begingroup$ @ChrisB.Behrens regardless of what this specific craft ends up getting used for, it doesn't make sense to design a different craft for every body in the solar system. That's the point I'm making. Developing rocket tech is worth our time more that parachute tech because of its flexibility in atmospheres that parachutes don't have. $\endgroup$ – user1886419 Dec 4 '15 at 17:59

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