Author Topic: SpaceX DragonFly Discussion Thread  (Read 375252 times)

Offline Req

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Re: SpaceX DragonFly Discussion Thread
« Reply #500 on: 10/23/2015 10:06 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.

I was intentionally vague on drogues because I can't think of a specific discussion on drogues with respect to Dragon landing profiles either.  What I am pointing out, though, is that it's irrelevant as part of the current debate, based on what has been publicly stated and discussed quite a bit here on NSF.
« Last Edit: 10/23/2015 10:07 am by Req »

Offline guckyfan

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Re: SpaceX DragonFly Discussion Thread
« Reply #501 on: 10/23/2015 10:13 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.

I was intentionally vague on drogues because I can't think of a specific discussion on drogues with respect to Dragon landing profiles either.  What I am pointing out, though, is that it's irrelevant as part of the current debate, based on what has been publicly stated and discussed quite a bit here on NSF.

You changed your post after my request. You had unequivocally stated that droges would be part of any descent, parachutes or full SD powered landing. That is why I requested a pointer.

Offline JamesH

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Re: SpaceX DragonFly Discussion Thread
« Reply #502 on: 10/23/2015 10:43 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.

I was intentionally vague on drogues because I can't think of a specific discussion on drogues with respect to Dragon landing profiles either.  What I am pointing out, though, is that it's irrelevant as part of the current debate, based on what has been publicly stated and discussed quite a bit here on NSF.

You changed your post after my request. You had unequivocally stated that droges would be part of any descent, parachutes or full SD powered landing. That is why I requested a pointer.

Why wouldn't drogues be part of any descent? They are a cheap and cheerful way of reducing speed, and therefore would result in less fuel being required in the case of propulsive landing, and would be required anyway for parachute landing to stabilise the Dragon prior to main chute deploy. So they are always on board, as they are needed for abort scenarios.

Offline Req

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Re: SpaceX DragonFly Discussion Thread
« Reply #503 on: 10/23/2015 10:54 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.

I was intentionally vague on drogues because I can't think of a specific discussion on drogues with respect to Dragon landing profiles either.  What I am pointing out, though, is that it's irrelevant as part of the current debate, based on what has been publicly stated and discussed quite a bit here on NSF.

You changed your post after my request. You had unequivocally stated that droges would be part of any descent, parachutes or full SD powered landing. That is why I requested a pointer.

Why wouldn't drogues be part of any descent? They are a cheap and cheerful way of reducing speed, and therefore would result in less fuel being required in the case of propulsive landing, and would be required anyway for parachute landing to stabilise the Dragon prior to main chute deploy. So they are always on board, as they are needed for abort scenarios.

Because they may not be necessary to reach terminal velocity at the desired altitude to test for propulsive/chute profiles, or to obtain the required stabilization to deploy one or both.
« Last Edit: 10/23/2015 11:00 am by Req »

Offline Semmel

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Re: SpaceX DragonFly Discussion Thread
« Reply #504 on: 10/23/2015 10:58 am »
Landing takes much less fuel than the abort. Since the engines need to do both, a drogue is not required. It would just reduce payload.

Offline hkultala

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Re: SpaceX DragonFly Discussion Thread
« Reply #505 on: 10/23/2015 11:05 am »
Landing takes much less fuel than the abort. Since the engines need to do both, a drogue is not required. It would just reduce payload.

No, the engines do not need to do BOTH (on same flight). They need to do EITHER.

In case of abort, use all fuel to abort and then land to sea using parachutes.
In case of succesful launch and deorbit, land to land using engines.
« Last Edit: 10/23/2015 11:08 am by hkultala »

Offline Req

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Re: SpaceX DragonFly Discussion Thread
« Reply #506 on: 10/23/2015 11:11 am »
Landing takes much less fuel than the abort. Since the engines need to do both, a drogue is not required. It would just reduce payload.

Main chute landing is and will be considered the primary landing method for crew(with propulsive landing becoming an increasingly common "exception") until well after it is no longer the norm.  That's why I called it #3a instead of #3b.  Drogues will be included as part of the dry mass if the CHUTE landing system(not the propulsive landing system) needs them for decades to come, regardless of how it usually lands.
« Last Edit: 10/23/2015 11:18 am by Req »

Offline Semmel

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Re: SpaceX DragonFly Discussion Thread
« Reply #507 on: 10/23/2015 11:33 am »
ok, let me rephrase.

Landing takes much less fuel than the abort. Since the engines need to be able to do both, a drogue is not required. It would just reduce payload.

Also, for propulsive landings, I dont know why you would use a drogue, makes things just more complicated. Of course landing by chutes is the abort scenario of propulsive landing. And landing per chutes is the scenario after a launch abort. But the fact stands, the use of drogues do not reduce launch mass.

Offline rpapo

Re: SpaceX DragonFly Discussion Thread
« Reply #508 on: 10/23/2015 11:55 am »
As long as the SuperDracos and all their fuel are needed for abort, there will always be a requirement for the Dragon capsule to have parachutes.  They may not need them for landing, but they will be there.  And since they are there, they provide a good backup to the propulsive landing system.

There are two costs to having parachutes: weight, and the cost of repacking or replacing them if they are used.  And since they have to be there, the weight is not optional.

For cargo flights, that may or may not be the case, depending on the decisions taken from the CRS-7 accident.
« Last Edit: 10/23/2015 11:56 am by rpapo »
Following the space program since before Apollo 8.

Offline MattMason

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Re: SpaceX DragonFly Discussion Thread
« Reply #509 on: 10/23/2015 12:07 pm »
Friends, friends, it seems we're doing stuff. Wasn't this settled over a year ago?

Try Chris B.'s 8/2014 article where NASA and SpaceX says how typical Crew Dragon landings are to be done.
« Last Edit: 10/23/2015 12:08 pm by MattMason »
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Offline JamesH

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Re: SpaceX DragonFly Discussion Thread
« Reply #510 on: 10/23/2015 12:37 pm »
Friends, friends, it seems we're doing stuff. Wasn't this settled over a year ago?

Try Chris B.'s 8/2014 article where NASA and SpaceX says how typical Crew Dragon landings are to be done.

Read it, must have missed the bit about whether a propulsive landing also used drogues to do initial slowdown and stabilisation, and in order to save fuel.

Online TrueBlueWitt

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Re: SpaceX DragonFly Discussion Thread
« Reply #511 on: 10/23/2015 02:21 pm »
Friends, friends, it seems we're doing stuff. Wasn't this settled over a year ago?

Try Chris B.'s 8/2014 article where NASA and SpaceX says how typical Crew Dragon landings are to be done.

Read it, must have missed the bit about whether a propulsive landing also used drogues to do initial slowdown and stabilisation, and in order to save fuel.

Also.. Having the drogue already deployed should significantly reduce reaction time to deploy mains in an emergency.

Offline yg1968

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Re: SpaceX DragonFly Discussion Thread
« Reply #512 on: 10/23/2015 02:35 pm »
Friends, friends, it seems we're doing stuff. Wasn't this settled over a year ago?

Try Chris B.'s 8/2014 article where NASA and SpaceX says how typical Crew Dragon landings are to be done.

Read it, must have missed the bit about whether a propulsive landing also used drogues to do initial slowdown and stabilisation, and in order to save fuel.

The 2014 article doesn't say that. Were you being sarcastic?

Offline JamesH

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Re: SpaceX DragonFly Discussion Thread
« Reply #513 on: 10/23/2015 02:41 pm »
Friends, friends, it seems we're doing stuff. Wasn't this settled over a year ago?

Try Chris B.'s 8/2014 article where NASA and SpaceX says how typical Crew Dragon landings are to be done.

Read it, must have missed the bit about whether a propulsive landing also used drogues to do initial slowdown and stabilisation, and in order to save fuel.

The 2014 article doesn't say that. Were you being sarcastic?

Yes. Sorry, sarcasm  doesn't come across very well except in my head. Point being, drogues were not mentioned at all in the article, so we don't know is they are used for all types of descent.

Offline Lars-J

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Re: SpaceX DragonFly Discussion Thread
« Reply #514 on: 10/23/2015 05:25 pm »
Friends, friends, it seems we're doing stuff. Wasn't this settled over a year ago?

Try Chris B.'s 8/2014 article where NASA and SpaceX says how typical Crew Dragon landings are to be done.

Read it, must have missed the bit about whether a propulsive landing also used drogues to do initial slowdown and stabilisation, and in order to save fuel.

Also.. Having the drogue already deployed should significantly reduce reaction time to deploy mains in an emergency.

The new parachute system - as demonstrated in the Dragon 2 pad abort - is designed to deploy much faster (and at lower altitude) than the Dragon 1 parachutes.

Offline yg1968

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Re: SpaceX DragonFly Discussion Thread
« Reply #515 on: 10/23/2015 06:43 pm »
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.

It has now been corrected. The four types of tests are described at the beginning of this thread:
http://forum.nasaspaceflight.com/index.php?topic=34800.0

Offline oiorionsbelt

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Re: SpaceX DragonFly Discussion Thread
« Reply #516 on: 10/23/2015 06:46 pm »
Friends, friends, it seems we're doing stuff. Wasn't this settled over a year ago?

Try Chris B.'s 8/2014 article where NASA and SpaceX says how typical Crew Dragon landings are to be done.

Read it, must have missed the bit about whether a propulsive landing also used drogues to do initial slowdown and stabilisation, and in order to save fuel.

Also.. Having the drogue already deployed should significantly reduce reaction time to deploy mains in an emergency.

The new parachute system - as demonstrated in the Dragon 2 pad abort - is designed to deploy much faster (and at lower altitude) than the Dragon 1 parachutes.
Yes they use mortars to deploy the drogues on D2. Im not sure if that was the case for D1 or not.
 (Hmmm, Do mortars qualify as a pyrotechnic?)
« Last Edit: 10/23/2015 06:47 pm by oiorionsbelt »

Offline Lars-J

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Re: SpaceX DragonFly Discussion Thread
« Reply #517 on: 10/23/2015 06:47 pm »
Friends, friends, it seems we're doing stuff. Wasn't this settled over a year ago?

Try Chris B.'s 8/2014 article where NASA and SpaceX says how typical Crew Dragon landings are to be done.

Read it, must have missed the bit about whether a propulsive landing also used drogues to do initial slowdown and stabilisation, and in order to save fuel.

Also.. Having the drogue already deployed should significantly reduce reaction time to deploy mains in an emergency.

The new parachute system - as demonstrated in the Dragon 2 pad abort - is designed to deploy much faster (and at lower altitude) than the Dragon 1 parachutes.
Yes they use mortars to deploy the drogues on D2. Im not sure if that was the case for D1 or not.
 (Hmmm, Do moratrs qualify as a pyrotechnic?)

The old ones used mortars too. But the new system (and location on capsule) is supposed to be more reliable and quicker, even when the capsule is tumbling.

Avoiding to fire the mortars and not having to repack parachutes is certainly part of the desire to do an all-propulsive landing.
« Last Edit: 10/23/2015 06:49 pm by Lars-J »

Offline oiorionsbelt

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Re: SpaceX DragonFly Discussion Thread
« Reply #518 on: 10/23/2015 06:59 pm »
The skills developed with the DragonFly hops seems like something that would be useful for getting around on the surface of Mars as well.

If DragonFly strays too far from it's flight path on one of these hops, what type of "range safety" will it have?
« Last Edit: 10/23/2015 07:07 pm by oiorionsbelt »

Offline mme

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Re: SpaceX DragonFly Discussion Thread
« Reply #519 on: 10/23/2015 07:01 pm »
Friends, friends, it seems we're doing stuff. Wasn't this settled over a year ago?

Try Chris B.'s 8/2014 article where NASA and SpaceX says how typical Crew Dragon landings are to be done.

Read it, must have missed the bit about whether a propulsive landing also used drogues to do initial slowdown and stabilisation, and in order to save fuel.

The 2014 article doesn't say that. Were you being sarcastic?

Yes. Sorry, sarcasm  doesn't come across very well except in my head. Point being, drogues were not mentioned at all in the article, so we don't know is they are used for all types of descent.

Drogues are not needed for stabilization, the capsule is aerodynamically stable flying bottom first unless the trunk is attached.  The only time drogues would stabilize a reentering capsule is if it is tumbling before reentry and that is not nominal (to say the least).  And the capsule has no problem decelerating to terminal velocity.  Elon and others have explicitly mentioned firing the SDs early to test and confirm propulsive landing will be successful.  The only SpaceX animations we've ever seen of propulsive landings do not use drogues.

I don't know what interim steps will be involved in the process of perfecting propulsive landing and getting people comfortable with it.  But all evidence is that nominal propulsive landings will be 100% propulsive and drogues are an unnecessary complexity.
« Last Edit: 10/23/2015 07:02 pm by mme »
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