Author Topic: SpaceX DragonFly Discussion Thread  (Read 291668 times)

Offline meekGee

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Re: SpaceX DragonFly Discussion Thread
« Reply #20 on: 05/21/2014 05:00 pm »
This was expected, and actually looooong overdue, but hell yeah  :)

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Offline corrodedNut

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Re: SpaceX DragonFly Discussion Thread
« Reply #21 on: 05/21/2014 05:01 pm »
Sounds like they will use the Grasshopper pad unless they decide they will need a dedicated pad, which will be a 40' square pad near the SuperDraco facility. The report describes this as the "DragonRider test area".

No, the report indicates that it will be a separate pad:
Quote
"The proposed launch pad would be 40 ft by 40 ft located approximately 0.32 mile north of the Grasshopper launch pad."

"SpaceX is currently considering two locations for the DragonFly RLV launch operations within the McGregor test site: the existing Grasshopper launch pad and the DragonRider test area. If operations would occur at the DragonRider test area, construction of a 40 ft by 40 ft launch pad would be necessary...."

Offline sublimemarsupial

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Re: SpaceX DragonFly Discussion Thread
« Reply #22 on: 05/21/2014 05:01 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.

Offline AncientU

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Re: SpaceX DragonFly Discussion Thread
« Reply #23 on: 05/21/2014 05:03 pm »
This is not your standard LAS... all control elements here for reusable (Mars or Moon) landing vehicle,  For ascent, vehicle will obviously need more propulsion and more than 25(+residuals) seconds of fuel.
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Offline corrodedNut

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Re: SpaceX DragonFly Discussion Thread
« Reply #24 on: 05/21/2014 05:04 pm »
"Propulsive Assist

For the propulsive assist test, a helicopter (an Erickson E‐model or equivalent) would arrive at the McGregor test site from Waco Regional Airport. The DragonFly RLV would then be tethered to the helicopter using a cable. A maximum of 300 gallons of propellant would be loaded into the DragonFly RLV for this test. The helicopter would take off with the DragonFly RLV attached and reach an altitude up to 10,000 ft. Once at that altitude, the DragonFly RLV would be released from the tether and three main parachutes would be deployed. The engines would not fire until the vehicle descends to approximately 98 ft above ground level (AGL). The engines would fire for approximately 5 seconds, and the RLV would make a powered landing. This type of operation would last approximately 30 minutes from helicopter take‐off to DragonFly RLV landing.
The test would be designed so that almost all fuel on board is used prior to landing. All fuel valves would shut automatically and retain any residual fuel in the capsule."

Offline corrodedNut

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Re: SpaceX DragonFly Discussion Thread
« Reply #25 on: 05/21/2014 05:06 pm »
"Full Propulsive Landing

For the full propulsive landing test, a helicopter (an Erickson E‐model or equivalent) would arrive at the McGregor test site from Waco Regional Airport. The DragonFly RLV would then be tethered to the helicopter. A maximum of 300 gallons of propellant would be loaded into the DragonFly RLV for this test. The helicopter would take off with the DragonFly RLV attached and reach an altitude up to 10,000 ft. Once at that altitude, the DragonFly RLV would be released from the tether. There would be a period of free fall and then the engines would fire for approximately 5 seconds and the RLV would make a powered landing. This type of operation would last approximately 30 minutes from helicopter take‐off to DragonFly RLV landing."

Offline corrodedNut

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Re: SpaceX DragonFly Discussion Thread
« Reply #26 on: 05/21/2014 05:08 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."

Offline Lars_J

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Re: SpaceX DragonFly Discussion Thread
« Reply #27 on: 05/21/2014 05:08 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.

Offline corrodedNut

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Re: SpaceX DragonFly Discussion Thread
« Reply #28 on: 05/21/2014 05:09 pm »
"Full Propulsive Hopping

Approximately 400 gallons of propellant would be loaded into the DragonFly RLV for this test. During a full propulsive hop test, the DragonFly RLV would launch from a launch pad and ascend to approximately 7,000 ft AGL (firing engines for approximately 12.5 seconds). The engines would then throttle down in order to descend (firing engines for an additional approximate 12. 5 seconds), and the RLV would make a powered landing on the launch pad. This operation would last approximately 60 seconds."

Offline GalacticIntruder

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Re: SpaceX DragonFly Discussion Thread
« Reply #29 on: 05/21/2014 05:10 pm »
All these 31 flavors of Dragon, are giving me a brain freeze.

How does this craft, DragonFly RLV, compare with the May 29 Dragon mk2 reveal, and CCdev?  Does NASA even know what craft  they would get if they awarded SpaceX the win.
Q to Picard in "Q Who": "It's not safe out here. It's wondrous, with treasures to satiate desires, both subtle and gross; but it's not for the timid."

Offline Lars_J

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Re: SpaceX DragonFly Discussion Thread
« Reply #30 on: 05/21/2014 05:13 pm »
All these 31 flavors of Dragon, are giving me a brain freeze.

How does this craft, DragonFly RLV, compare with the May 29 Dragon mk2 reveal, and CCdev?  Does NASA even know what craft  they would get if they awarded SpaceX the win.

Huh? Why wouldn't they know?

How do you translate the idea of multiple test articles of varying fidelity to the idea of "31 flavors of Dragon"?

Offline randomly

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Re: SpaceX DragonFly Discussion Thread
« Reply #31 on: 05/21/2014 05:16 pm »
Spacex will need to address the problems of dealing with Hydrazine/NTO in case of accidents.
keep the cows upwind or something.

Online notsorandom

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Re: SpaceX DragonFly Discussion Thread
« Reply #32 on: 05/21/2014 05:28 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.
Doing some more math on those assumed figures it looks like the start of the landing burn starts about 375 meters in altitude. That assumes a deceleration of about 3g's and initial velocity of 150 m/s. If something should go wrong at the start of the burn like a stuck valve is that enough time and altitude to pop a parachute out?

Offline corrodedNut

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Re: SpaceX DragonFly Discussion Thread
« Reply #33 on: 05/21/2014 05:30 pm »
Spacex will need to address the problems of dealing with Hydrazine/NTO in case of accidents.
keep the cows upwind or something.

That's what environmental assessments are for.

Online abaddon

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Re: SpaceX DragonFly Discussion Thread
« Reply #34 on: 05/21/2014 05:31 pm »
This is great stuff!   :D.

One interesting thing is the descent profile on the hop tests is much more gentle (12.5s firing, throttled down) then on the drop tests.  Presumably this is because the capsule is not free-falling when it starts the descent burn.  But since the engine can throttle down (as is confirmed here), why wouldn't they start the drop test burn earlier, throttled down, and then throttle the engine up?  That seems like it would provide a less freaky landing, it would also allow you to start your burn a little earlier, possibly early enough that a late chute might deploy might do some good if something went wrong.  I know there will be redundant thrusters and these are pretty simple engines but it seems like having a backup if something goes wrong when the burn beings might be a good idea.  5s/~400m seems way too late for a chute to help...

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.
« Last Edit: 05/21/2014 05:33 pm by abaddon »

Offline Jim

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Re: SpaceX DragonFly Discussion Thread
« Reply #35 on: 05/21/2014 05:31 pm »
This is not your standard LAS... all control elements here for reusable (Mars or Moon) landing vehicle,  For ascent, vehicle will obviously need more propulsion and more than 25(+residuals) seconds of fuel.

Not so.  A lot more propellant is needed for landing on Mars and even more for the moon.

Offline meadows.st

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Re: SpaceX DragonFly Discussion Thread
« Reply #36 on: 05/21/2014 05:35 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.
Doing some more math on those assumed figures it looks like the start of the landing burn starts about 375 meters in altitude. That assumes a deceleration of about 3g's and initial velocity of 150 m/s. If something should go wrong at the start of the burn like a stuck valve is that enough time and altitude to pop a parachute out?

I think there is a misunderstanding somewhere.  The "Propulsive Assist" (includes parachutes) has the engines firing for ~5 seconds (starting at a AGL height of 98ft) while the full-propulsive hopping landings have the engines firing for 12.5 seconds.  So the 150 m/s terminal velocity is likely slowed over 12.5 seconds rather than just 5sec.  The terminal velocity under parachute should be much less than 150m/s shouldn't it?

EDIT: Is there a typo in "Full Propulsive Landing" (states 5 s engine burn) and "Propulsive Assist Hopping" which states 12.5 s engine burn?

EDIT2: added "hopping" (underlined)
« Last Edit: 05/21/2014 05:39 pm by meadows.st »
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Online abaddon

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Re: SpaceX DragonFly Discussion Thread
« Reply #37 on: 05/21/2014 05:37 pm »
I think there is a misunderstanding somewhere.  The "Propulsive Assist" (includes parachutes) has the engines firing for ~5 seconds (starting at a AGL height of 98ft) while the full-propulsive landings have the engines firing for 12.5 seconds.  So the 150 m/s terminal velocity is likely slowed over 12.5 seconds rather than just 5sec.  The terminal velocity under parachute should be much less than 150m/s shouldn't it?
The quoted full propulsive landing in this thread states "There would be a period of free fall and then the engines would fire for approximately 5 seconds and the RLV would make a powered landing."  I agree this seems odd, perhaps it is a typo and the 5 second burn is indeed parachute-assisted.  That would make more sense.

Offline meadows.st

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Re: SpaceX DragonFly Discussion Thread
« Reply #38 on: 05/21/2014 05:40 pm »
I think there is a misunderstanding somewhere.  The "Propulsive Assist" (includes parachutes) has the engines firing for ~5 seconds (starting at a AGL height of 98ft) while the full-propulsive hopping landings have the engines firing for 12.5 seconds.  So the 150 m/s terminal velocity is likely slowed over 12.5 seconds rather than just 5sec.  The terminal velocity under parachute should be much less than 150m/s shouldn't it?
The quoted full propulsive landing in this thread states "There would be a period of free fall and then the engines would fire for approximately 5 seconds and the RLV would make a powered landing."  I agree this seems odd, perhaps it is a typo and the 5 second burn is indeed parachute-assisted.  That would make more sense.

Correct, I added a correction to my typo in my comment that was commenting on a possible typo. :P
« Last Edit: 05/21/2014 05:41 pm by meadows.st »
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Offline corrodedNut

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Re: SpaceX DragonFly Discussion Thread
« Reply #39 on: 05/21/2014 05:47 pm »
Timeframe:

"SpaceX anticipates that the DragonFly RLV program would require up to 2 years to complete (2014 2015). Therefore, the Proposed Action considers one new permit and one potential permit renewal."

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