Author Topic: SpaceX DragonFly Discussion Thread  (Read 375295 times)

Offline J-V

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Re: SpaceX DragonFly Discussion Thread
« Reply #100 on: 05/22/2014 12:08 pm »
Has there been any analysis what would happen if Dragon(Fly) would lose a number of SDs? In other words, how many SDs does it take to keep the crew alive or without serious injuries if parachutes are not used?

That what flight tests are for.

Why I doubt they will test this with flight tests. It would, with very high probability, mean the loss of the test vehicle.

Offline docmordrid

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Re: SpaceX DragonFly Discussion Thread
« Reply #101 on: 05/22/2014 12:12 pm »
SpaceX has said they expected to crater some Grasshoppers. I doubt their expectations have changed for DragonFly.
« Last Edit: 05/22/2014 12:12 pm by docmordrid »
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Offline J-V

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Re: SpaceX DragonFly Discussion Thread
« Reply #102 on: 05/22/2014 12:15 pm »
SpaceX has said they expected to crater some Grasshoppers. I doubt their expectations have changed for DragonFly.

Expect to, or try to? I assume the first option.

Offline docmordrid

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Re: SpaceX DragonFly Discussion Thread
« Reply #103 on: 05/22/2014 12:22 pm »
Test flights often push the envelope to the breaking point. Just look at the Grasshopper 'divert' test, which had a distinct crater possibility. I doubt DragonFly will be any different.
« Last Edit: 05/22/2014 12:23 pm by docmordrid »
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Offline banjo

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Re: SpaceX DragonFly Discussion Thread
« Reply #104 on: 05/22/2014 12:22 pm »
i doubt whether spacex ever anticipate a crewed dragon being at terminal velocity 400m or so from the ground.  and even then,  a queasy looking crew would be expected to walk away in one piece.  we're seeing the multiple redundancy being tested.

Offline docmordrid

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Re: SpaceX DragonFly Discussion Thread
« Reply #105 on: 05/22/2014 12:27 pm »
I've doubted the 'slam on the brakes' landing for a while. ISTM more logical to decelerate at a lower throttle starting higher up then increase thrust for the last 100m or so.
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Offline hrissan

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Re: SpaceX DragonFly Discussion Thread
« Reply #106 on: 05/22/2014 01:39 pm »
I've doubted the 'slam on the brakes' landing for a while. ISTM more logical to decelerate at a lower throttle starting higher up then increase thrust for the last 100m or so.
Losing single SuperDraco will probably lead to throttling of opposite pair to ~50% by control system, then losing one of those is also not a problem, the remaining one will throttle back to 100%.

So I'd calculate the stopping profile with 6/8 of total thrust, losing single SuperDraco (or opposing two) would lead to immediate throttle of remaining to 100% and trouble-free landing (in case of no more failures).

But if at that time the height still allows for mortar chute deployment, I'd do it immediately (in case of cascade of failures). Once under chute we can throttle remaining SDs to minimal or switch them off and then start them again just before touchdown to cushion the impact, again using less than 100% thrust initially, so that in case of failure the remaining will throttle up to 100%.

If at the moment of first failure the height is so low that it is futile to deploy chute, then we just count on our luck that no more SDs fail, and if they do, we use remaining working to brake as much as possible. Low height == low speed, so even 2 working SDs may be survivable.

Overall looks like very robust system with dissimilar redundancy, much better than capsule with chute-only doomed in case of chute failure.

Offline guckyfan

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Re: SpaceX DragonFly Discussion Thread
« Reply #107 on: 05/22/2014 01:58 pm »
8 SuperDraco will provide ~10g for escape when used as a LAS.  So four can provide 5g, plenty more than needed. Didn't that FAA Draft Environmental Assessment have a paragraph saying they are divided into two completely independent sets? That would make it extremely unlikely that both fail unless there is something wrong with the fuel.

Even two might have enough thrust, provided the Dracos could do attitude control, which they may not under these conditions.

Offline Mike_1179

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Re: SpaceX DragonFly Discussion Thread
« Reply #108 on: 05/22/2014 01:58 pm »
I've doubted the 'slam on the brakes' landing for a while. ISTM more logical to decelerate at a lower throttle starting higher up then increase thrust for the last 100m or so.

That uses more fuel than a "brown pants" landing.  It's a trade.

Offline J-V

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Re: SpaceX DragonFly Discussion Thread
« Reply #109 on: 05/22/2014 02:04 pm »
8 SuperDraco will provide ~10g for escape when used as a LAS.  So four can provide 5g, plenty more than needed. Didn't that FAA Draft Environmental Assessment have a paragraph saying they are divided into two completely independent sets? That would make it extremely unlikely that both fail unless there is something wrong with the fuel.

Even two might have enough thrust, provided the Dracos could do attitude control, which they may not under these conditions.

Thank you for the estimate! Looks like they won't run out of thrust or SDs too easily.

Offline sghill

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Re: SpaceX DragonFly Discussion Thread
« Reply #110 on: 05/22/2014 02:57 pm »

Any concerns about the capsule being tilted ~30 degrees from vertical due to the parachute attach point being on the side?  See picture(s) captured from the Drop test video.

Firing off the Draco Engines on landing may expect a horizontal component to the resulting motion.



The Mk2 capsule may not have offset parachutes.

Also, any sort of parachute assisted landing precludes precision targeted landings.  They'll have to land out in the desert if they want to come down on land.  Even if the final approach uses motors, they can't just release the chutes over populated areas.

Of course with re-light landing capability, they can always apologize to the people sitting in the living room they came down in, and then sheepishly fly back to the intended landing pad.  :)
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Offline HMXHMX

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Re: SpaceX DragonFly Discussion Thread
« Reply #111 on: 05/22/2014 03:04 pm »
Freefall, 5 sec burn at the last moment, soft touchdown.

Whoever will ultimately ride aboard that kind of flight profile (obviously not during these tests) is a brave man :)


Note that amusement parks do exactly this, *for fun* - freefall from an otherwise fatal height, decelerate at several Gs, stop at ground level. So if you have confidence in the machine, it should be fun, not scary!
The difference between fun and scary is trust.

No, it's steel.  ;)

Offline bilbo

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Re: SpaceX DragonFly Discussion Thread
« Reply #112 on: 05/22/2014 03:34 pm »
I wonder what other witty names SpaceX will come up with, they already have Dragonflys and grasshoppers, so this leads the Question, What will the next vehicle be called? Ladybug? hornet? Fruitfly? Mosquito? Cricket?
Im guessing there might even be a Bullfrog somewhere within the nameing mix. :)

Offline Lars_J

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Re: SpaceX DragonFly Discussion Thread
« Reply #113 on: 05/22/2014 03:58 pm »
Finally, I guess one of the abort test articles could be used for these MK2 landing tests, but the other one is just a big welded steel pressure vessel.  That also got me thinking that DragonRider can't look too different from Dragon v1 because the pressure vessels look nearly the same as v1.

The pressure vessel will be very close to the existing Dragon, but the SDs and fairings for them might make the exterior look a bit different.

This is one possibility of how it will look - but it could also be a home-made fake. This mysterious image is discussed here: http://forum.nasaspaceflight.com/index.php?topic=33598.msg1196921#msg1196921


Offline llanitedave

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Re: SpaceX DragonFly Discussion Thread
« Reply #114 on: 05/22/2014 05:46 pm »
Those fairings look reminiscent of the legs on the first stage.  I wonder if fold-out legs can act as fairings until the speed is low enough for them to deploy.
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Offline ChefPat

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Re: SpaceX DragonFly Discussion Thread
« Reply #115 on: 05/22/2014 05:49 pm »
Is there any indication of when testing will begin with Dragonfly?
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Offline corrodedNut

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Re: SpaceX DragonFly Discussion Thread
« Reply #116 on: 05/22/2014 05:51 pm »

Offline Lars_J

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Re: SpaceX DragonFly Discussion Thread
« Reply #117 on: 05/22/2014 05:52 pm »
Those fairings look reminiscent of the legs on the first stage.  I wonder if fold-out legs can act as fairings until the speed is low enough for them to deploy.

No, I really don't think they are legs - while on the surface the fairings do look similar to stage 1 legs, they would serve a very different purpose here. Besides, such legs would be waaaay too large and heavy for a capsule this size.
« Last Edit: 05/22/2014 05:52 pm by Lars_J »

Offline kirghizstan

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Re: SpaceX DragonFly Discussion Thread
« Reply #118 on: 05/22/2014 05:56 pm »
Those fairings look reminiscent of the legs on the first stage.  I wonder if fold-out legs can act as fairings until the speed is low enough for them to deploy.

No, I really don't think they are legs - while on the surface the fairings do look similar to stage 1 legs, they would serve a very different purpose here. Besides, such legs would be waaaay too large and heavy for a capsule this size.

I initially questioned this when the image first surfaced, but when i thought more about it, having the legs directly in line with the Super Dracos doesn't seem like the best idea.

Offline JasonAW3

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Re: SpaceX DragonFly Discussion Thread
« Reply #119 on: 05/22/2014 05:56 pm »
Those fairings look reminiscent of the legs on the first stage.  I wonder if fold-out legs can act as fairings until the speed is low enough for them to deploy.

That actually makes a lot of sense.  As they would deploy, apparently, hydraulically, they could also be used, as large as they are, to act as both a steering and decellerator system.
« Last Edit: 05/22/2014 06:06 pm by JasonAW3 »
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