Author Topic: SpaceX DragonFly Discussion Thread  (Read 291717 times)

Offline RocketGoBoom

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Re: SpaceX DragonFly Discussion Thread
« Reply #40 on: 05/21/2014 06:02 pm »
How could they have a controlled pinpoint landing back at the pad if they are using parachutes and if there is any sort of wind? I would think that this poses significant drift potential from 10,000 ft. They could drift quite a distance off of center. Once the Dracos fire, I think the potential for needing way more than 5 seconds is significant.
« Last Edit: 05/21/2014 06:03 pm by RocketGoBoom »

Offline bubbagret

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Re: SpaceX DragonFly Discussion Thread
« Reply #41 on: 05/21/2014 06:03 pm »
This is great stuff!   :D.

I'm also not sure how the drop tests are going to use all of 300 gallons of fuel but the hop tests will only need 400 gallons, ISTM like that ascent burn should consume a lot of fuel, even if the descent burn doesn't need as much.

Anyway, it's great to finally see some details about this program.

Reread it, it states UP TO before listing Height, fuel quantity, etc...

Offline rcoppola

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Re: SpaceX DragonFly Discussion Thread
« Reply #42 on: 05/21/2014 06:15 pm »
It's very possible that SpaceX is pushing for propulsive landings (assisted to start with) right out of the gate. Where earlier it was mentioned more as a Dragon 2.1 after initial crew services roll-out. The testing regimen and timeline seems to align with a possibly accelerated CC contract award.

They may have offered NASA a very cost effective proposal on the assumption they could re-use Dragon as both SNC and Boeing intended to do. And will bring this capability from the onset of the contracts. After all, they're doing 30 tests over 2 years or less. That's a test regimen of more then 1 a month for the next 2 years.

I'm intrigued with this integrated trunk as well. Theoretically they could have designed a new trunk that would accommodate legs and enough fuel to do a Moon or Mars decent / ascent. (ladder included)
 
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Online abaddon

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Re: SpaceX DragonFly Discussion Thread
« Reply #43 on: 05/21/2014 06:19 pm »
Reread it, it states UP TO before listing Height, fuel quantity, etc...
Actually, it says "a maximum of" not "up to", but I get what you're saying.

Offline Jarnis

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Re: SpaceX DragonFly Discussion Thread
« Reply #44 on: 05/21/2014 06:30 pm »
How could they have a controlled pinpoint landing back at the pad if they are using parachutes and if there is any sort of wind? I would think that this poses significant drift potential from 10,000 ft. They could drift quite a distance off of center. Once the Dracos fire, I think the potential for needing way more than 5 seconds is significant.

I see propulsive assist landing to be similar to Soyuz. Land landing with parachutes, with engines smoothing the touchdown (but with the landing survivable even if they do not fire).

Beats fishing out the crews and cargo from the ocean, even if you need a fairly large open area to aim for. Could totally see this happening in future orbital flights as an intermediate step towards propulsive-only landing.
« Last Edit: 05/21/2014 06:30 pm by Jarnis »

Offline Elmar Moelzer

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Re: SpaceX DragonFly Discussion Thread
« Reply #45 on: 05/21/2014 06:33 pm »
I'm intrigued with this integrated trunk as well. Theoretically they could have designed a new trunk that would accommodate legs and enough fuel to do a Moon or Mars decent / ascent. (ladder included)
I would be careful to interpret too much into it, but it does sound interesting, indeed. Maybe the new Dragon will not lose the trunk anymore?
Hmmm.
Either way, I cant wait to see test hops of this! This must be really cool to watch!
« Last Edit: 05/21/2014 06:34 pm by Elmar Moelzer »

Offline moralec

Re: SpaceX DragonFly Discussion Thread
« Reply #46 on: 05/21/2014 06:35 pm »
I'm intrigued with this integrated trunk as well. Theoretically they could have designed a new trunk that would accommodate legs and enough fuel to do a Moon or Mars decent / ascent. (ladder included)
I would be careful to interpret too much into it, but it does sound interesting, indeed. Maybe the new Dragon will not lose the trunk anymore?
Hmmm.
Either way, I cant wait to see test hops of this! This must be really cool to watch!

But the heat shield is integrated in the capsule. This is intriguing...

Offline kirghizstan

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Re: SpaceX DragonFly Discussion Thread
« Reply #47 on: 05/21/2014 06:36 pm »
I'm intrigued with this integrated trunk as well. Theoretically they could have designed a new trunk that would accommodate legs and enough fuel to do a Moon or Mars decent / ascent. (ladder included)
I would be careful to interpret too much into it, but it does sound interesting, indeed. Maybe the new Dragon will not lose the trunk anymore?
Hmmm.
Either way, I cant wait to see test hops of this! This must be really cool to watch!

Ground abort test?

Offline docmordrid

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Re: SpaceX DragonFly Discussion Thread
« Reply #48 on: 05/21/2014 06:40 pm »
Conference video showing propulsive assist landing

« Last Edit: 05/21/2014 06:41 pm by docmordrid »
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Offline CraigLieb

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Re: SpaceX DragonFly Discussion Thread
« Reply #49 on: 05/21/2014 06:47 pm »
How could they have a controlled pinpoint landing back at the pad if they are using parachutes and if there is any sort of wind? I would think that this poses significant drift potential from 10,000 ft. They could drift quite a distance off of center. Once the Dracos fire, I think the potential for needing way more than 5 seconds is significant.

I see propulsive assist landing to be similar to Soyuz. Land landing with parachutes, with engines smoothing the touchdown (but with the landing survivable even if they do not fire).

Beats fishing out the crews and cargo from the ocean, even if you need a fairly large open area to aim for. Could totally see this happening in future orbital flights as an intermediate step towards propulsive-only landing.

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.
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Offline JasonAW3

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Re: SpaceX DragonFly Discussion Thread
« Reply #50 on: 05/21/2014 06:52 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 :)

Can anyone model the G-Force curve on that?  It sounds like a rough ride.

If anyone can guess the terminal velocity of the capsule, it should be easy to calculate. If the G-load is evenly spread over 5 seconds, it might not be too bad.

For a very first order estimate I get a terminal velocity of ~150 m/s given a total mass of 17,000 lbs (dry mass plus 3000 lbs of fuel) and a drag coefficient of 0.8.

A 5 second burn to brake from 150 m/s would result in an average of ~3Gs of deceleration.

Assuming a throttle up from a cold start, it could range from 1.5G's initial and ramp up to about 5G's at about 3.5 to 4 seconds.

  But that's just a rough estimate.

  Otherwise a full thrust at 3G's initial, would be a real kick in the rear.
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Online Comga

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Re: SpaceX DragonFly Discussion Thread
« Reply #51 on: 05/21/2014 06:54 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.

Surely a team that sends a ten story single engine rocket sliding 100m off to the side and back while ascending and descending, nulling velocity and rates at touchdown, can work out how to null rates and attitudes on a four engine-pair vehicle.  Is there any doubt?
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

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Re: SpaceX DragonFly Discussion Thread
« Reply #52 on: 05/21/2014 06:58 pm »
One thing that is not in the plan is propulsive landing with only drogue chutes.
It would be an interesting intermediate case, but obviously not interesting enough to get in the way of SpaceX's ultimate goal: "Landing on a pillar of fire like God and Heinlein intended."
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline JasonAW3

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Re: SpaceX DragonFly Discussion Thread
« Reply #53 on: 05/21/2014 06:58 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.

Surely a team that sends a ten story single engine rocket sliding 100m off to the side and back while ascending and descending, nulling velocity and rates at touchdown, can work out how to null rates and attitudes on a four engine-pair vehicle.  Is there any doubt?

Well, they didn't crash a couple of REALLY top heavy test articles, landing a thruster based capsule shouldn't be too hard for them.
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Offline savuporo

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Re: SpaceX DragonFly Discussion Thread
« Reply #54 on: 05/21/2014 07:01 pm »
Surely a team that sends a ten story single engine rocket sliding 100m off to the side and back while ascending and descending, nulling velocity and rates at touchdown, can work out how to null rates and attitudes on a four engine-pair vehicle.  Is there any doubt?
Differential throttling is a tad harder because you have inherently less control bandwidth - engine throttling has a built in lag.
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Offline simonbp

Re: SpaceX DragonFly Discussion Thread
« Reply #55 on: 05/21/2014 07:20 pm »
And Grasshopper and F9R don't throttle their engines?

This isn't a purely experimental vehicle like Grasshopper, but a prototype like F9R-Dev1. It is a systems test to make sure everything works together in a relevant environment. In NASA-speak, it is getting from TRL 5 to TRL 6.
« Last Edit: 05/21/2014 07:21 pm by simonbp »

Offline savuporo

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Re: SpaceX DragonFly Discussion Thread
« Reply #56 on: 05/21/2014 07:25 pm »
And Grasshopper and F9R don't throttle their engines?

My point was balancing and attitude control of a differentially throttled multi engine vs a single engine gimbaled vehicle is marginally harder - because of control bandwidth. Not impossible and obviously achiveable. Thats all.
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Offline JasonAW3

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Re: SpaceX DragonFly Discussion Thread
« Reply #57 on: 05/21/2014 07:28 pm »
And Grasshopper and F9R don't throttle their engines?

This isn't a purely experimental vehicle like Grasshopper, but a prototype like F9R-Dev1. It is a systems test to make sure everything works together in a relevant environment. In NASA-speak, it is getting from TRL 5 to TRL 6.

So essentially, since we don't quite have the tech developed to do an SSTO craft like the DC-Y, SpaceX is doing a 3STO craft, that essentially can land like the DC-X. 

Couple of questions then;

How much mass do the Parachutes add to the Dragon capsule?

If low enough mass, could they be added to either or both stages og the Falcon 9 as a back up/additional decellerator system?

Would it be worth the effort to do so?

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Offline Alpha Control

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Re: SpaceX DragonFly Discussion Thread
« Reply #58 on: 05/21/2014 07:28 pm »
"Propulsive Assist Hopping

Approximately 400 gallons of propellant would be loaded into the DragonFly RLV for this test. During a propulsive assisted hop test, the DragonFly RLV would launch from a launch pad and ascend to approximately 7,000 ft AGL (firing engines for 12.5 seconds). Two parachutes would be deployed for the descent, the engines would fire for 12.5 seconds, and the RLV would make a powered landing on the launch pad. This operation would last approximately 60 seconds."

For the Propulsive Assist Hopping, are the SDs firing twice? once for 12.5 seconds to reach altitude, then turn off, then fire a 2nd time for 12.5 seconds for the powered landing? I wasn't completely sure I interpreted the description correctly. Thanks!
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Offline JasonAW3

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Re: SpaceX DragonFly Discussion Thread
« Reply #59 on: 05/21/2014 07:29 pm »
And Grasshopper and F9R don't throttle their engines?

My point was balancing and attitude control of a differentially throttled multi engine vs a single engine gimbaled vehicle is marginally harder - because of control bandwidth. Not impossible and obviously achiveable. Thats all.

I'm not sure that it would be much harder than flying a quadracopter drone.  Just got to have the right software, and you're good.
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