Author Topic: SpaceX DragonFly Discussion Thread  (Read 375255 times)

Offline deruch

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Re: SpaceX DragonFly Discussion Thread
« Reply #280 on: 06/10/2014 06:01 pm »
A 5 second burn is much longer than what would be needed "under canopy". Check your gut reaction to the numbers again.

I agree.  But then how much worse is the 12.5 second burn under canopy, which the FAA document also calls for.  Something's rotten in Denmark.  The landings (especially the ones with the parachutes), as described, don't make any sense to me.  My logic: per the FAA doc, there are 2 "burn profiles", 5 second and 12.5 second, currently matched to 2 "flight profiles", helo drop and propulsive hop, respectively.  Those matches don't make sense.  Can't be the same duration burns from free fall as under parachutes, regardless of what the length of those burns are or any believable throttling.  Ergo something in the document is wrong.  What if the matching was supposed to be to "descent profile", i.e. parachute or propulsive, instead of to "flight profile".  That seems a better fit.  The assumption being that the person who wrote up the document either goofed, misunderstood, or was confused. 

edit:  Maybe the numbers are just placeholders and not meant to be too exact?  I don't know if that would be acceptable in a document of this type?  Unlikely, I feel.  But if so, the discussion/speculation earlier is still off base.

@Lars_J, or anyone else, if you see some obvious point that I haven't understood, please let me know.  Thanx.
« Last Edit: 06/10/2014 06:15 pm by deruch »
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Offline cscott

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Re: SpaceX DragonFly Discussion Thread
« Reply #281 on: 06/10/2014 06:28 pm »
I think the thread was unfortunately misdirected quite early by what has to be a mistake in the FAA filing.

I doubt it.  I suggest that reader misinterpretation of the point and purpose of the filing is more likely.  Presumably the numbers are conservative maximums, hand-waving over the fact that there are multiple dracos and superdracos on board.  It may be that the durations are from "first firing" to "last firing" of any engine (superdraco or draco),  or they may be cumulative firing durations summed across all engines.  The durations are there to allow emissions and noise limits to be checked, not to provide two significant digits of accuracy for NSF modelers.

Offline sghill

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Re: SpaceX DragonFly Discussion Thread
« Reply #282 on: 06/10/2014 07:42 pm »
Read the report closer! Get off of the chart on Page 2-1, and go to Page 2-5 and 2-6.  They've described 4 scenarios in detail.  Quoting from the document (emphasis mine) They are:

1) 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 takeoff 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.

2) 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. 

{ed. note: This would definitely be the BPL landing scenario.}

3) 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 [not three] 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.

{ed. note: I find this scenario interesting because they're still talking about landing on the landing pad- even under parachute assisted conditions.  This looks like a release of the deployed parachutes with powered recovery scenario.}

4) 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 approx. 7,000 ft AGL (firing engines for approximately 12.5 seconds).  The engines would then throttle down in order to descend (firing 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.

I'd also like to point out the blurb about the trunk "which may or may not be attached during DragonFly operations" being used in these tests.  IMHO, they may be testing scenarios where the trunk doesn't separate in an abort situation (intentionally or otherwise), and/or they may be looking at the trunk as a potential "launch pad" for the DragonFly in the propulsive hops.

Also, from Page 1-4, the F9R program has a permit for 10 launches.  They've done 2 so far (perhaps more if the FAA is including the ground testing burns), and the DragonFly permit won't kick in (if approved) until after those ten launches.

« Last Edit: 06/10/2014 07:50 pm by sghill »
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Offline deruch

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Re: SpaceX DragonFly Discussion Thread
« Reply #283 on: 06/10/2014 08:38 pm »
I did read those.  In fact, it wasn't until I read those that the scenarios seemed wrong.

3) 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 [not three] 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.

{ed. note: I find this scenario interesting because they're still talking about landing on the landing pad- even under parachute assisted conditions.  This looks like a release of the deployed parachutes with powered recovery scenario.}


12.5 seconds of engine firing while the craft is already under parachutes????  That's the bit that doesn't make sense to me.  Just how low do you think these engines can be throttled?

edit: Oops, just noticed your note.  That's interesting and it could explain my perceived discrepancy.  Thanks.
« Last Edit: 06/10/2014 08:47 pm by deruch »
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Offline inventodoc

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Re: SpaceX DragonFly Discussion Thread
« Reply #284 on: 06/10/2014 09:35 pm »
Perhaps the thrusters continue firing at a lower level after landing in order to consume all the propellant????

Offline Joffan

Re: SpaceX DragonFly Discussion Thread
« Reply #285 on: 06/10/2014 11:07 pm »
Yeah, I assumed that 12.5s of ascent burn + 12.5s of landing burn was a misinterpretation of a 20s ascent burn, engine out, fall, then a 5s landing burn.  Numbers may need tweaking between the two phases, but something like that.

And the assisted landing burn has just conservatively been given the same duration (for planning purposes) as the unassisted.
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Offline ncb1397

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Re: SpaceX DragonFly Discussion Thread
« Reply #286 on: 06/10/2014 11:52 pm »
I did read those.  In fact, it wasn't until I read those that the scenarios seemed wrong.

3) 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 [not three] 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.

{ed. note: I find this scenario interesting because they're still talking about landing on the landing pad- even under parachute assisted conditions.  This looks like a release of the deployed parachutes with powered recovery scenario.}


12.5 seconds of engine firing while the craft is already under parachutes????  That's the bit that doesn't make sense to me.  Just how low do you think these engines can be throttled?

edit: Oops, just noticed your note.  That's interesting and it could explain my perceived discrepancy.  Thanks.

As far as throttle range, the similar hypergolic engine on the Apollo DPS acheived throttle down to ~10% which means 2 engines in each pod can maybe throttle to 5% by turning one off. Assuming at minimum 4 engines firing, 10% thrust would be 1,640 lbf X 4 or 6560 lbf. If the craft can throttle this low, thrust to weight of 1 is easily acheivable and so hover, slow descent or slow ascent is limited by the available fuel supply.

Offline cscott

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Re: SpaceX DragonFly Discussion Thread
« Reply #287 on: 06/11/2014 03:20 am »
Perhaps the thrusters continue firing at a lower level after landing in order to consume all the propellant????

Why are we assuming that the "thrusters" mean only the superdracos?  If you read the numbers as the total time the dracos *or* superdracos are firing, they make much more sense.

Offline Kenm

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Re: SpaceX DragonFly Discussion Thread
« Reply #288 on: 06/11/2014 04:21 am »
I did read those.  In fact, it wasn't until I read those that the scenarios seemed wrong.

3) 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 [not three] 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.

{ed. note: I find this scenario interesting because they're still talking about landing on the landing pad- even under parachute assisted conditions.  This looks like a release of the deployed parachutes with powered recovery scenario.}


12.5 seconds of engine firing while the craft is already under parachutes????  That's the bit that doesn't make sense to me.  Just how low do you think these engines can be throttled?

edit: Oops, just noticed your note.  That's interesting and it could explain my perceived discrepancy.  Thanks.

As far as throttle range, the similar hypergolic engine on the Apollo DPS acheived throttle down to ~10% which means 2 engines in each pod can maybe throttle to 5% by turning one off. Assuming at minimum 4 engines firing, 10% thrust would be 1,640 lbf X 4 or 6560 lbf. If the craft can throttle this low, thrust to weight of 1 is easily acheivable and so hover, slow descent or slow ascent is limited by the available fuel supply.

Note that it says two parachutes so I think that this might be the drogue parachutes.
This would have several features you would get far less drift with the drogues, it would be a test for failure of the main chutes to deploy and if you need to deploy the main chutes the droques are ready to pull them out.

edit
One other thing if you look at the picture of the drop test at
http://www.spacex.com/files/assets/img/20100820_34dragon.jpg

Note how the Dragon hangs on a tilt under the drogue chutes. Now if the picture was taken level you can see that the tilt is causing the Dragon to fly off to the left (look at the angle between the vertical and a line from the attachment point to the center of the two drogue chutes).
This glide angle can be used to steer to the landing area by rotating the capsule just like they do during reentery.

« Last Edit: 06/11/2014 11:49 pm by Kenm »

Offline Prober

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Re: SpaceX DragonFly Discussion Thread
« Reply #289 on: 06/15/2014 04:48 pm »
So when are the first of these tests?

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Offline docmordrid

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Re: SpaceX DragonFly Discussion Thread
« Reply #290 on: 06/15/2014 06:33 pm »
AIUI, FAA has to issue the final EIS and permit. There is a 30 day comment period after the EIS before things can actually move on the permit.
« Last Edit: 06/15/2014 06:34 pm by docmordrid »
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Offline Prober

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Re: SpaceX DragonFly Discussion Thread
« Reply #291 on: 06/16/2014 01:30 am »
AIUI, FAA has to issue the final EIS and permit. There is a 30 day comment period after the EIS before things can actually move on the permit.

ahhh the red tape  :o
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Offline neoforce

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Re: SpaceX DragonFly Discussion Thread
« Reply #292 on: 06/16/2014 03:21 am »
AIUI, FAA has to issue the final EIS and permit. There is a 30 day comment period after the EIS before things can actually move on the permit.

ahhh the red tape  :o

Besides the red tape, I'm sure they aren't' ready.   SpaceX knew about the red tape, so they applied before they were close to testing DragonFly.  And there is still work on the F9R at McGregor which probably has to finish up (with test of that vehicle moved to Spaceport America) before DragonFly tests start at McGregor.

Offline docmordrid

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Re: SpaceX DragonFly Discussion Thread
« Reply #293 on: 06/16/2014 04:07 am »
The F9R permit at McGregor expires Feb. 26, 2015, though they probably won't run it out. The Grasshopper's permit expires Oct. 17, 2014 and they were done months before.
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Offline king1999

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Re: SpaceX DragonFly Discussion Thread
« Reply #294 on: 06/16/2014 06:05 am »

Besides the red tape, I'm sure they aren't' ready.   SpaceX knew about the red tape, so they applied before they were close to testing DragonFly.  And there is still work on the F9R at McGregor which probably has to finish up (with test of that vehicle moved to Spaceport America) before DragonFly tests start at McGregor.

Spaceport America will have a different F9R (dev2). Most likely dev 1 will stay with DF.

Offline CameronD

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Re: SpaceX DragonFly Discussion Thread
« Reply #295 on: 07/14/2014 06:26 am »
I notice the only current FAA/AST permit mentioning Dragon of any kind is for the Pad Abort Test Vehicle and is restricted to (a) one flight from Cape Canaveral Air Force Station, Florida, and (b) a suborbital trajectory to a water landing.

Nothing on Dragonfly yet?
 
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 Roy_H

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Re: SpaceX DragonFly Discussion Thread
« Reply #296 on: 08/04/2014 03:13 pm »
Read the report closer! Get off of the chart on Page 2-1, and go to Page 2-5 and 2-6.  They've described 4 scenarios in detail.  Quoting from the document (emphasis mine) They are:
...
Also, from Page 1-4, the F9R program has a permit for 10 launches.  They've done 2 so far (perhaps more if the FAA is including the ground testing burns), and the DragonFly permit won't kick in (if approved) until after those ten launches.

Are you sure about that? Why would all of the F9R Dev flights have to be completed before any DragonFly flights? And given the few F9R Dev flights so far, the DragonFly flights  could be a long way into the future. As I speculated before, ISTM that SpaceX would like to have at least some (if not all) DragonFly flights before doing the Abort Tests.
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Offline Jet Black

Re: SpaceX DragonFly Discussion Thread
« Reply #297 on: 08/04/2014 03:46 pm »
Read the report closer! Get off of the chart on Page 2-1, and go to Page 2-5 and 2-6.  They've described 4 scenarios in detail.  Quoting from the document (emphasis mine) They are:
...
Also, from Page 1-4, the F9R program has a permit for 10 launches.  They've done 2 so far (perhaps more if the FAA is including the ground testing burns), and the DragonFly permit won't kick in (if approved) until after those ten launches.

Are you sure about that? Why would all of the F9R Dev flights have to be completed before any DragonFly flights? And given the few F9R Dev flights so far, the DragonFly flights  could be a long way into the future. As I speculated before, ISTM that SpaceX would like to have at least some (if not all) DragonFly flights before doing the Abort Tests.

As docmordrid said, the F9R permit runs out on the 26th Feb 2015, so DragonFly can start after that.
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Offline rpapo

Re: SpaceX DragonFly Discussion Thread
« Reply #298 on: 08/04/2014 03:49 pm »
As docmordrid said, the F9R permit runs out on the 26th Feb 2015, so DragonFly can start after that.
Why wait?
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Offline Doesitfloat

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Re: SpaceX DragonFly Discussion Thread
« Reply #299 on: 08/04/2014 04:06 pm »
As docmordrid said, the F9R permit runs out on the 26th Feb 2015, so DragonFly can start after that.
Why wait?

They don't have to wait.(to paraphrase)  In various places in the EIS the impact of doing nothing is business will continue as usual with Merlin-D tests and Falcon 9 tests.
This permit is for additional capability. Flying rocket with Hypergolic propellants.
Does not effect current operations.

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