Watch: SpaceX Dragon capsule breathes fire during crucial hover test SpaceX has released video showing the hovering capabilities of its Dragon 2 crew capsule that could eventually eliminate the need for astronauts to land using parachutes. The test took place at SpaceX's engineering facility in McGregor, Texas and saw the 6,000-kg (13,228-lb) spacecraft suspended from a cable before the eight …
If you think about the challenge of deceleration from a purely "basic physics" perspective (i.e. conservation of momentum), then the heavier the capsule, the more energy it will take to decelerate it, using
F=ma
So by ejecting the heatshield before the decelerative burn, you are basically going to get a greater velocity change [through the deceleration] for the same energy [fuel] cost.
The issue I see is if they had to do an emergency escape and then land - you'd need enough fuel for both parts (rather than enough for an escape OR a landing).
And if the rockets failed for any reason, having no parachute at all would result in astronaut pancakes... Though I suppose at the point you would discover the thruster failure (a few hundred metres from the ground) it would be too late for a parachute to make any difference anyway.
Still; I'm sure many minds better than mine have considered all of this.
If there's a launch abort Dragon 2 uses all its fuel to bug out, then it lands in.the ocean under 4 parachutes - and it doesn't need all of them. If some chutes tangle its still good.
Dragon 2 actually has multiple landing modes,
Full propulsive: engine test at 7,000 feet. If good, land on the rockets. If not good, fire the parachute mortar.
Full parachutes, to water or land.
Emergency parachutes: manually fire the parachute mortar.
Parachutes and rockets: come down on the chutes, then at 10 meters hover and descend to a soft landing.
Multiple redundancy is good.
If they don't have landing legs that go whirr, whirr, whirr; clunk when the thing lands I'll be very disappointed. extra style points if the "door" opens and an integrated ramp rolls out.
That's some serious Flash Gordon shit right there! The future is here and it's very shiny!
Do they get extra points for doing this next to a cow farm?
Here is their SpaceX GrassHopper being tested in the same spot and cows going crazy:
http://i.kinja-img.com/gawker-media/image/upload/s--uZTCMuJ0--/c_scale,fl_progressive,q_80,w_800/pnusnxe80xnwq7wifyor.jpg
The SuperDraco's not only can re-start but throttle from 20%-100%, go from 0%-100% in 100 milliseconds and rapidly pulse.
Construction: 3D printed, using the Inconel super-alloy.
Their upcoming Raptor methane-fuelled Full Flow Staged Combustion engine will also leverage 3D printing. Raptor subassemblies are on the test stand, and the USAF wants it on Falcon 9 & Falcon Heavy upper stages for their launches.
Flash Gordon, meet Buck Rogers.
Limit which sources of Javascript are allowed to run (and ensure the right one is blocked1), and instead of an embedded Flash video you'll just get a YouTube link - and clicking through to YouTube means you can see the video using HTML5 rather than Flash.
1. jwpsrv.com, IIRC. It's one of the ones that doesn't run here, and I think it's the one for the embedded videos.
Retro-rockets are cool (well, actually they're really, really hot, but you know what I mean)
But how much does the whole setup weigh, including the fuel? And what is the cost of lugging it all up into orbit in the first place? Would a detachable escape rocket + parachute be more efficient?
But how much does the whole setup weigh, including the fuel?
According to wiki, SuperDracos have a propellant capacity of 1,388kg, which is an odd way to phrase things - is that for the capsule and 8 engines, or just one pair of engines? And couldn't the engines have different sized fuel tanks? But given the entire (test) capsule is 6,000kg, I'll assume the former: 1,388kg total for the current capsule design.
I'm not sure what the engine weight is after a cursory Google search, but assuming they're typical mid-sized, dense fuel engines then a 100:1 thrust-to-weight ratio is reasonable. That means 8 SuperDracos total about 550kg.
Total: a bit under 2,000kg of the 6,000kg capsule.
And what is the cost of lugging it all up into orbit in the first place?
Define "cost." A manned capsule flight is going to use the full capacity of a Falcon 9 whether the capsule is full of cargo or not, or whether the Falcon 9 has unused payload capacity. That's because the capsule's not going to share the ride. Chances are, though, the capsule isn't going to use the full 13,000kg+ of Falcon 9 payload capacity. So what's 2,000kg of reusable engine and propellants matter?
Would a detachable escape rocket + parachute be more efficient?
Yes, but less flexible. The integral SuperDracos give the Dragon capsule an escape capacity. They also give the Dragon the ability to land on land or barges, or for its derivatives to land on the moon and Mars. 1388kg of 240Isp fuel for a 6,000kg gives the capsule an integral 600m/s delta-V, too, which makes for a lot of orbital maneuvering. The sort not seen since the shuttle was grounded.
The engines also have the advantage of being reusable and proven, which means they have engine data and mechanics who are familiar with each engine. Disposable escape towers can be flight-tested once, and then you need a new escape tower without the track record of the old one.
Finally, a parachute is being included. This means the engines and parachute combination give the capsule options in an emergency, rather than a single shot at safety.
> Would a detachable escape rocket + parachute be more efficient?
Only in the short term. Without retro-rockets to enable a soft-landing, you'd have to land at sea Apollo-style, and then you can't re-use the capsule because sea water is so corrosive. (Soyuz uses retro-rockets but the capsule isn't designed for re-use). SpaceX's goal is to have a launch system with re-usable first stage and crew/cargo capsules, which would significantly reduce the cost of getting into space.
and then you can't re-use the capsule because sea water is so corrosive
It's not that bad. I handle the materials of aerospace hardware that work in a salt spray-and-sulfur environment (from burned high-sulfur hydrocarbons), and it just takes some care: watch out for dissimilar metals in contact; use appropriate surface modifications (anodizing, chem film, passivation, etc.); use appropriate paints (primer, top coat); conformal coatings for electronics; seal up well if you can; avoid moisture entrapment spots; avoid corrosion-prone alloys (2000-series aluminum; anything magnesium; carbon steel); etc. Verification is usually by months in a chamber per ASTM B117 or a few days per ASTM G85.
Target life of the hardware is 20 years in the that environment, and I generally use a lot of the materials SpaceX would.
Saltwater immersion is a complication, don't get me wrong. My life would be a lot easier if customers kept their hardware in cold, 0% humidity deserts. :) But it's an addressable complication.
Did the article mentioning this was a short test pass you by?
This was the first test of the Dragon 2 in this situation. You don't run the engines on a new 'rocket' at full power for full burn time in a first test. (in fact these engines were running at about 28% of full thrust).
For two very good reasons.
1) Parachutes use no fuel in braking. That's less mass to haul around and less explosively combustible shit in and around the crew compartment.
2) If you can get your parachute to deploy that's it, there's not much else to go wrong. I haven't got time to go through the massive list of things that must work for a retro-rocket landing to be successful.
I believe there are a good few tests done before a propulsive landing on the Dragon V2 - all the dragons will carry a backup parachute (and a backup-backup chute I do believe, like they do currently) for those sort of landings. I do believe the dragon can land with four of its eight superdraco's out of action as well. To my knowledge, they do a quick fire up test shortly after heat shield jettison to make sure the damn things will work before the point of lithobraking - that way there's always a chance to pull the chute in enough time.
Although I would probably still soil myself at the point of landing, regardless of whether the test was successful or not..
Parachutes are also good in the environmental/cost senses that you're not burning fuel you don't actually need. I don't know if the amount of fuel is large enough to be worth caring about, but it does seem a good principle to only use resources when you need to. Have jets for emergencies perhaps, but use chutes if possible?
Parachutes don't give the ability to pinpoint land, important for reuse. They are carrying the fuel up anyway, for inflight abort, so might as well use it for something useful on the way down.
But all this is covered comprehensively on the web. I'd suggest Google. It's a well known mechanism for searching for information on the World Wide Web. Or, if desperate, Wikipedia is actually pretty accurate on SpaceX stuff.
"Parachutes are also good in the environmental/cost senses that you're not burning fuel you don't actually need."
That sounds like a kneejerk greenie response. Not saying you are a kneejerk greenie or anything like that but to decide if something is more environmentally destructive than something else you need to take everything into account. How much does a new capsule every launch cost in non-greenness compared with the fuel used to land it in a way it can be refurbed and re-used. Not to mention the skills and practice learned for landing on other moons or planets where rocket landing is the only option, especially if you want to take off again.
Note that a)I only raised the environmental angle for completeness b)the cost angle is worth considering. I'm no greenie so I brought it up for debate/completeness in an open-minded way.
I'm not sure the "you can only re-use it if you use rockets" argument is valid. You could 'chute most of the way and use rockets purely for the landing or something.
I do think that we should be seeking to use the environment (in the non-greenie sense) wherever possible. Clearly Mars is different but what's necessary on Mars might not be the best solution here.
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