Author Topic: SpaceX DragonFly Discussion Thread  (Read 375286 times)

Offline BrianNH

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Re: SpaceX DragonFly Discussion Thread
« Reply #480 on: 10/22/2015 02:22 am »
I wouldn't be surprised if Dragonfly was modified to do that - using up some of the living/cargo space for extra fuel tanks.  That isn't a capability that Dragon 2 would need.

To do what?
Fly to 7000 ft?  It has that capability.
Carry cargo instead of passengers?  It has that capability.  (Technically Dragonfly won't carry passengers.  That was a comment for Dragon V2.)
There is no evidence that SpaceX is considering a modified Crew Dragon for anything, other than the rumored SAA for Red Dragon.
Of course, we won't be surprised if SpaceX does any of a number of wild things, because they have in the past. ;)

edit: clarity

As Lars pointed out, Dragon would not be expected to have enough fuel for both a propulsive high altitude launch and a propulsive landing.  It would not be unreasonable to add extra tanks to cover the fuel needed for the launch portion.

Offline yg1968

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Re: SpaceX DragonFly Discussion Thread
« Reply #481 on: 10/22/2015 03:41 am »
By the way, per L2's McGregor Photos and Update Section, Dragonfly has been photographed at McGregor, as has a big, big crane. I've asked SpaceX if they want to talk to us about the upcoming test objectives, but we'll be writing an article next week regardless.

Here's the article - with L2 photos and some cool L2 renderings by Nathan :)

http://www.nasaspaceflight.com/2015/10/spacex-dragonfly-arrives-mcgregor-testing/

When they start the testing at McGregor we'll set up an update thread.

I am confused. Is the grasshopper in the image still active? Is there still a grasshopper program?

Offline llanitedave

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Re: SpaceX DragonFly Discussion Thread
« Reply #482 on: 10/22/2015 03:48 am »
It's retired.  Quite literally put out to pasture.
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Offline guckyfan

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Re: SpaceX DragonFly Discussion Thread
« Reply #483 on: 10/22/2015 06:54 am »
As Lars pointed out, Dragon would not be expected to have enough fuel for both a propulsive high altitude launch and a propulsive landing.  It would not be unreasonable to add extra tanks to cover the fuel needed for the launch portion.

That sounds right. And the design might just be what is needed to land Red Dragon with a heavy payload on Mars too.

Offline Chris Bergin

Re: SpaceX DragonFly Discussion Thread
« Reply #484 on: 10/22/2015 10:40 am »
Is the DragonFly  modified from the Pad Abort vehicle or a new build? sorry, my search fu is not very high.

Added a few words to the article to confirm this is the former Pad Abort vehicle that's now DragonFly (albeit it scrubbed clean, rebuilt and ready to go again).
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Offline Req

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Re: SpaceX DragonFly Discussion Thread
« Reply #485 on: 10/22/2015 10:59 am »
Is the DragonFly  modified from the Pad Abort vehicle or a new build? sorry, my search fu is not very high.

Added a few words to the article to confirm this is the former Pad Abort vehicle that's now DragonFly (albeit it scrubbed clean, rebuilt and ready to go again).

Which, it's worth reiterating for the sake of verbosity, actually started out as a cargo dragon, not a crew dragon(aka v2).
« Last Edit: 10/22/2015 11:00 am by Req »

Offline Arb

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Re: SpaceX DragonFly Discussion Thread
« Reply #486 on: 10/22/2015 02:37 pm »
From the article the second hope test will be propulsive to about 7,000 ft and then propulsive landing ( engines throttled down ). For 12.5 seconds up and 12.5 seconds down the engines will not be at full power for the fully propulsive hop test.
Any one able to calculate what that equates to in delta-v?

Offline Jet Black

Re: SpaceX DragonFly Discussion Thread
« Reply #487 on: 10/22/2015 03:14 pm »
Is the DragonFly  modified from the Pad Abort vehicle or a new build? sorry, my search fu is not very high.

Added a few words to the article to confirm this is the former Pad Abort vehicle that's now DragonFly (albeit it scrubbed clean, rebuilt and ready to go again).

Do you have any idea how much rebuilding has been done? i.e. are they the same SuperDracos? any other notable differences?
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Offline NovaSilisko

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Re: SpaceX DragonFly Discussion Thread
« Reply #488 on: 10/22/2015 07:08 pm »
They would probably hang it from the uppermost parachute mounting point. A place it's designed already to take hanging loads. We've seen the parachute deployment test of Dragon 2 a long time ago, which kept the nose cap in place.
« Last Edit: 10/22/2015 07:09 pm by NovaSilisko »

Offline ClayJar

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Re: SpaceX DragonFly Discussion Thread
« Reply #489 on: 10/22/2015 08:05 pm »
From the article the second hope test will be propulsive to about 7,000 ft and then propulsive landing ( engines throttled down ). For 12.5 seconds up and 12.5 seconds down the engines will not be at full power for the fully propulsive hop test.
Any one able to calculate what that equates to in delta-v?

Would it be a reasonable napkin approximation to consider it simply a net of 25 seconds of gravity losses, with the initial and final positions and velocities being zero?  That would put it at g*25s, or 245m/s, right?  (Of course, this completely glosses over pretty much everything important, but hey.  ;D)

Offline manboy

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Re: SpaceX DragonFly Discussion Thread
« Reply #490 on: 10/23/2015 01:58 am »
By the way, per L2's McGregor Photos and Update Section, Dragonfly has been photographed at McGregor, as has a big, big crane. I've asked SpaceX if they want to talk to us about the upcoming test objectives, but we'll be writing an article next week regardless.

Here's the article - with L2 photos and some cool L2 renderings by Nathan :)

http://www.nasaspaceflight.com/2015/10/spacex-dragonfly-arrives-mcgregor-testing/

When they start the testing at McGregor we'll set up an update thread.

"These include the “Propulsive assist landing” test – which will see DragonFly dropped from helicopter (an Erickson E‐model or equivalent) aided by three parachutes. This will be followed by the “Fully propulsive landing” test – again utilizing a helicopter and parachutes, concluding with a five-second firing of the SuperDracos for a smooth landing."

This doesn't sound correct.
« Last Edit: 10/23/2015 02:00 am by manboy »
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Offline Lars-J

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Re: SpaceX DragonFly Discussion Thread
« Reply #491 on: 10/23/2015 02:20 am »
Why doesn't it sound correct?

Offline TrevorMonty

Re: SpaceX DragonFly Discussion Thread
« Reply #492 on: 10/23/2015 03:15 am »
As much as I like fully propulsive landing, the  propulsive assist landing on land seems safer plus it gives redundancy if there is parachute failure.

Let the cargo version use fully propulsive landing.

Offline CameronD

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Re: SpaceX DragonFly Discussion Thread
« Reply #493 on: 10/23/2015 03:19 am »
Why doesn't it sound correct?

Most likely because a "fully propulsive landing” test shouldn't, logically, require parachutes?

(Note: I'm not, and I'm not suggesting anybody is, saying it's not factual.. but he's right - it doesn't sound correct)
« Last Edit: 10/23/2015 03:22 am by CameronD »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline Comga

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Re: SpaceX DragonFly Discussion Thread
« Reply #494 on: 10/23/2015 03:33 am »
As much as I like fully propulsive landing, the  propulsive assist landing on land seems safer plus it gives redundancy if there is parachute failure.

Let the cargo version use fully propulsive landing.

It has always looked like a compromise would be optimum, at least for the interim: Drogue chutes and propulsive assist.  Plenty of time to test the SuperDracos after drogue deployment,  much less velocity to kill allowing for lower thrust over a longer time while eating the gravity loss, much less time than parachutes so less drift. No need to use the big chutes if all goes well.

However, this has never been discussed, to my knowledge.  Why?

edit: Corrected the wording
« Last Edit: 10/23/2015 03:34 am by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline CameronD

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Re: SpaceX DragonFly Discussion Thread
« Reply #495 on: 10/23/2015 07:02 am »
As much as I like fully propulsive landing, the  propulsive assist landing on land seems safer plus it gives redundancy if there is parachute failure.

Let the cargo version use fully propulsive landing.

It has always looked like a compromise would be optimum, at least for the interim: Drogue chutes and propulsive assist.  Plenty of time to test the SuperDracos after drogue deployment,  much less velocity to kill allowing for lower thrust over a longer time while eating the gravity loss, much less time than parachutes so less drift. No need to use the big chutes if all goes well.

However, this has never been discussed, to my knowledge.  Why?

Maybe drag from the drogue chutes / any chutes would interfere with GNC of the capsule using the SDs?


With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline The Amazing Catstronaut

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Re: SpaceX DragonFly Discussion Thread
« Reply #496 on: 10/23/2015 08:47 am »
As much as I like fully propulsive landing, the  propulsive assist landing on land seems safer plus it gives redundancy if there is parachute failure.

Let the cargo version use fully propulsive landing.

Above some critical altitude, can't the parachute also provide a level of redundancy in case of propulsion failure? The engines have a lot of engine out capability before that becomes a requirement.
« Last Edit: 10/23/2015 08:48 am by The Amazing Catstronaut »
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Offline douglas100

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Re: SpaceX DragonFly Discussion Thread
« Reply #497 on: 10/23/2015 09:29 am »
As much as I like fully propulsive landing, the  propulsive assist landing on land seems safer plus it gives redundancy if there is parachute failure.

Let the cargo version use fully propulsive landing.

It has always looked like a compromise would be optimum, at least for the interim: Drogue chutes and propulsive assist.  Plenty of time to test the SuperDracos after drogue deployment,  much less velocity to kill allowing for lower thrust over a longer time while eating the gravity loss, much less time than parachutes so less drift. No need to use the big chutes if all goes well.

However, this has never been discussed, to my knowledge.  Why?

Maybe drag from the drogue chutes / any chutes would interfere with GNC of the capsule using the SDs?

Also, there may be a possibility of the SD plumes damaging any deployed parachute. That wouldn't matter if they were just using the SD's to kill the landing impact under parachutes.
Douglas Clark

Offline Req

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Re: SpaceX DragonFly Discussion Thread
« Reply #498 on: 10/23/2015 09:40 am »
This has been discussed ad naseam, and I'm not going to go dig up all of the links, but the officially stated idea behind a fully-propulsive crew landing is that the superdracos get tested at a high enough altitude that the main chutes can still deploy to save the mission in the event of a failure in the superdraco system.

"That the main chutes can still deploy to save the mission" implies a flight regime where the main chutes can still deploy and guarantee a chute landing - regardless of whether this particular flight regime required drogues to achieve or not.

The sequence for a crew fully-propulsive landing will be:

1) Enter regime where propulsive or main chutes will be effective
2) Fire SDs to ensure positive response
3a) SDs did not give positive response, initiate main chute landing profile
3b) SDs gave positive response, initiate propulsive landing profile

Drogues(or not) are independent of these decisions, and happen either as part of item #1 or item #3a AIUI.

Edit - clarity
« Last Edit: 10/23/2015 10:05 am by Req »

Offline guckyfan

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Re: SpaceX DragonFly Discussion Thread
« Reply #499 on: 10/23/2015 10:04 am »
Can you point to a discussion? I thought I have read everything about this on NSF and I have never seen a reference to drogues for propulsive landing.

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