Author Topic: SpaceX outlines CRS-3 landing legs plan toward first stage recovery ambitions  (Read 28778 times)

Online Chris Bergin

Third article on the legs....but this one is built from answers we gained from SpaceX - and covers more than just CRS-3.

http://www.nasaspaceflight.com/2014/02/spacex-crs-3-landing-legs-plan-first-stage-recovery-ambitions/



---

To collate all the recent resources (lots of links, but it provides pretty much all you need on one post):

Falcon 9 preparing to stretch her legs via Grasshopper trials:
http://www.nasaspaceflight.com/2014/02/falcon-9-stretch-legs-grasshopper-trials/

CRS-3 Falcon 9 first stage to sport legs and attempt soft splashdown:
http://www.nasaspaceflight.com/2014/02/crs-3-falcon-9-first-stage-sport-legs-attempt-soft-splashdown/

Previous main thread for the above article:
http://forum.nasaspaceflight.com/index.php?topic=34065.0

--

L2 SpaceX:

Falcon 9 Reusable (F9R-Dev1) Photos:
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1155703#msg1155703

Better Falcon 9 Reusable (F9R-Dev1) Photos - with legs:
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1156035#msg1156035

Grasshopper 1 and 2 - and Texas Site - Videos:
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1156491#msg1156491

New Status on FH, F9-R and Raptor MCT via Tom Mueller (19th of Feb):
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1162065#msg1162065

Falcon CRS-3 with Legs notes:
http://forum.nasaspaceflight.com/index.php?topic=31562.msg1161997#msg1161997

Falcon 9 Reusable (F9R-Dev1) with legs - Feb 22 photos:
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1163399#msg1163399

CRS-3 Reusable SpaceX Quotes - and Grasshopper notes:
http://forum.nasaspaceflight.com/index.php?topic=31562.msg1165068#msg1165068
« Last Edit: 03/01/2014 01:09 PM by Chris Bergin »

Offline Lars_J

  • Senior Member
  • *****
  • Posts: 6161
  • California
  • Liked: 665
  • Likes Given: 195
A great article, Chris!

It's nice to get confirmation about when the legs are going to be extended - and if it is 10 seconds into the landing burn, that must be *very* close to the surface. I suppose the acceleration upwards will help the legs deploy and lock.

Offline AndyX

  • Full Member
  • ***
  • Posts: 393
  • Liked: 144
  • Likes Given: 393
Great write up again!

And one of SpaceX's investors mentioned it on Twitter! :)

bill lee ‏@westcoastbill  16m
cant wait for this “@NASASpaceflight: @SpaceX outline CRS-3 landing legs plan toward first stage recovery http://www.nasaspaceflight.com/2014/02/spacex-crs-3-landing-legs-plan-first-stage-recovery-ambitions/#.UxFawTDIPu8.twitter

Online Chris Bergin

Thanks chaps - and a hat tip to QuantumG for providing a very helpful subedit assist for a very tired me! (speaking of which, I'm outta here! ;D)

Bill Lee's mentioned us a good number of times per SpaceX articles. So's Elon's mum! :)

Offline RocketmanUS

  • Senior Member
  • *****
  • Posts: 2226
  • USA
  • Liked: 71
  • Likes Given: 31
Might not be this flight , however it very well could be this year for a successful water landing test.

Offline Elmar Moelzer

  • Senior Member
  • *****
  • Posts: 3176
  • Liked: 587
  • Likes Given: 853
Great article Chris! Nice to see some confirmation of speculation in the forum. Some new information too. Any word how close back to the launch site, the boostback will get the stage this time?

Offline Dave G

  • Senior Member
  • *****
  • Posts: 2224
  • Liked: 948
  • Likes Given: 1181
Thanks Chris!  Another great article.

One thing still bothers me.  SpaceX says they are aiming for fully reusable, but there doesn't seem to be any plan for reusing the Dragon trunk:
http://www.spacex.com/news/2013/03/26/dragon-trunk

Quote
The trunk, a riveted aluminum structure, is 2.8 meters (9.2 feet) tall and 3.66 meters (12 feet) wide. The trunk also houses the radiator which is integral to the trunk structure, with the ability to reject up to 3kW of heat.

Fairings housing Dragon’s solar arrays—two arrays, each composed of four panels—are attached to the outside of the trunk.  The arrays produce more than 5 kilowatts of power, and surplus power recharges Dragon’s batteries for the periods when it is in darkness.

This sounds like a fairly expensive piece.  How can they say fully reusable when they throw this away every time?

Offline IRobot

  • Full Member
  • ****
  • Posts: 1294
  • Portugal & Germany
  • Liked: 284
  • Likes Given: 255
This sounds like a fairly expensive piece.  How can they say fully reusable when they throw this away every time?
I think Elon said they might use batteries instead of the expensive solar panels. At least for the crewed version of Dragon.
« Last Edit: 03/01/2014 10:41 AM by IRobot »

Offline NovaSilisko

  • Full Member
  • ****
  • Posts: 1828
  • Liked: 1435
  • Likes Given: 1301
Well, the Falcon 9 is planned to be fully reusable, and the trunk is just part of one of its payloads ;)

The payload fairings for the cargo version on the other hand, I wonder how much they cost to manufacture? Presumably not much.

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 10772
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 7670
  • Likes Given: 5519
Trunk reusability is probably off topic for this thread. Try the general Falcon/Dragon thread. I didn't trim anything. Yet.

http://forum.nasaspaceflight.com/index.php?topic=33598.0

And, another boffo article, Chris! :)
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Online Zardar

  • Full Member
  • *
  • Posts: 138
  • Limerick, Ireland
  • Liked: 67
  • Likes Given: 222
So, the landing burn must be at least 10 seconds long, plus some more time to deploy (and verify deployment) of the landing legs? (which is the critical engineering test for this attempt)
How much fuel will a burn that long take, and with a burn that long will it have passed the zero vertical velocity point well above sea level and be accelerating upwards again - even at lowest throttle? (IANARS...)

Does that this mean that a hover slam & soft touchdown will be impossible, (unless they do a second landing burn), and that's why they only have a 30% chance stated of success?



Offline clongton

  • Expert
  • Senior Member
  • *****
  • Posts: 10607
  • Connecticut
    • Direct Launcher
  • Liked: 2741
  • Likes Given: 1012
Does that this mean that a hover slam & soft touchdown will be impossible, (unless they do a second landing burn), and that's why they only have a 30% chance stated of success?

In accordance with the incremental testing program that SpaceX has been executing there is really only one mission objective to this attempt; to demonstrate a successful deployment of the landing legs - and nothing more. They will likely attempt to recover the stage if that is deemed possible, but are fully expecting it to be lost. Soft touchdown and stage recovery are not mission objectives for this event.

Nice article Chris. BTW I was thinking as I was reading this that there literally is nowhere else on earth I know of where I, or anyone else for that matter, can go to get up-to-the-minute accurate news of space-related events and plans like this article described. NSF is truly a world-class place. Thank you.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline IRobot

  • Full Member
  • ****
  • Posts: 1294
  • Portugal & Germany
  • Liked: 284
  • Likes Given: 255
They will likely attempt to recover the stage if that is deemed possible, but are fully expecting it to be lost. Soft touchdown and stage recovery are not mission objectives for this event.
Carbon fiber can handle salt water, so the legs can be recovered if they are not damaged. Still, they probably don't want to risk it, as it is very hard to diagnose carbon fiber failures.

Online Chris Bergin

Thanks chaps....


Nice article Chris. BTW I was thinking as I was reading this that there literally is nowhere else on earth I know of where I, or anyone else for that matter, can go to get up-to-the-minute accurate news of space-related events and plans like this article described. NSF is truly a world-class place. Thank you.

And thanks for that! ;)

PS I've changed the headline from SpaceX outline to SpaceX outlines, as I've got to get my head around SpaceX being singular - I used to struggle with that when referencing NASA.

Offline Rocket Science

  • Senior Member
  • *****
  • Posts: 8959
  • NASA Educator Astronaut Candidate Applicant 2002
  • Liked: 2846
  • Likes Given: 7521
Does that this mean that a hover slam & soft touchdown will be impossible, (unless they do a second landing burn), and that's why they only have a 30% chance stated of success?

In accordance with the incremental testing program that SpaceX has been executing there is really only one mission objective to this attempt; to demonstrate a successful deployment of the landing legs - and nothing more. They will likely attempt to recover the stage if that is deemed possible, but are fully expecting it to be lost. Soft touchdown and stage recovery are not mission objectives for this event.

Nice article Chris. BTW I was thinking as I was reading this that there literally is nowhere else on earth I know of where I, or anyone else for that matter, can go to get up-to-the-minute accurate news of space-related events and plans like this article described. NSF is truly a world-class place. Thank you.
I would a tried to add flotation bags to the stage for recovery and inspection...
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline Jefferson

  • Member
  • Posts: 14
  • USA
  • Liked: 2
  • Likes Given: 4
Third article on the legs....but this one is built from answers we gained from SpaceX - and covers more than just CRS-3.

http://www.nasaspaceflight.com/2014/02/spacex-crs-3-landing-legs-plan-first-stage-recovery-ambitions/



---

To collate all the recent resources (lots of links, but it provides pretty much all you need on one post):

Falcon 9 preparing to stretch her legs via Grasshopper trials:
http://www.nasaspaceflight.com/2014/02/falcon-9-stretch-legs-grasshopper-trials/

CRS-3 Falcon 9 first stage to sport legs and attempt soft splashdown:
http://www.nasaspaceflight.com/2014/02/crs-3-falcon-9-first-stage-sport-legs-attempt-soft-splashdown/

Previous main thread for the above article:
http://forum.nasaspaceflight.com/index.php?topic=34065.0

--

L2 SpaceX:

Falcon 9 Reusable (F9R-Dev1) Photos:
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1155703#msg1155703

Better Falcon 9 Reusable (F9R-Dev1) Photos - with legs:
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1156035#msg1156035

Grasshopper 1 and 2 - and Texas Site - Videos:
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1156491#msg1156491

New Status on FH, F9-R and Raptor MCT via Tom Mueller (19th of Feb):
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1162065#msg1162065

Falcon CRS-3 with Legs notes:
http://forum.nasaspaceflight.com/index.php?topic=31562.msg1161997#msg1161997

Falcon 9 Reusable (F9R-Dev1) with legs - Feb 22 photos:
http://forum.nasaspaceflight.com/index.php?topic=33488.msg1163399#msg1163399

CRS-3 Reusable SpaceX Quotes - and Grasshopper notes:
http://forum.nasaspaceflight.com/index.php?topic=31562.msg1165068#msg1165068

Got to love SpaceX. They really are doing exciting things. Thank you for this great site that lets us in on these cool spacey things! ;D

Offline llanitedave

  • Senior Member
  • *****
  • Posts: 2153
  • Nevada Desert
  • Liked: 1332
  • Likes Given: 1567

I would a tried to add flotation bags to the stage for recovery and inspection...

That would be a waste of time, weight, and money.  They aren't going to use them for return to launch site, there's no reason to try to develop a new complex system that's only going to be used for a few tests.
"I've just abducted an alien -- now what?"

Online rsnellenberger

  • Amateur wood butcher
  • Full Member
  • ****
  • Posts: 594
  • Harbor Springs, Michigan
  • Liked: 63
  • Likes Given: 19
Nice article, but I wasn't sure what I was looking at in the last picture -- is that their test area in New Mexico, or an artist's conception of what it will look like, or something else entirely? 

Offline 411rocket

  • Full Member
  • **
  • Posts: 261
  • Retired RCEME w/ tours in Cyprus, Croatia, Bosnia
  • Vancouver Island
  • Liked: 79
  • Likes Given: 120
Nice article, but I wasn't sure what I was looking at in the last picture -- is that their test area in New Mexico, or an artist's conception of what it will look like, or something else entirely?

I believe, that is the main building at Space Port America, with a pad shown in the background.

Offline Rocket Science

  • Senior Member
  • *****
  • Posts: 8959
  • NASA Educator Astronaut Candidate Applicant 2002
  • Liked: 2846
  • Likes Given: 7521

I would a tried to add flotation bags to the stage for recovery and inspection...

That would be a waste of time, weight, and money.  They aren't going to use them for return to launch site, there's no reason to try to develop a new complex system that's only going to be used for a few tests.
They already have a source onboard for pressurization adding a few bags is no big deal for an outfit like SpaceX...
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Online Coastal Ron

  • Senior Member
  • *****
  • Posts: 4258
  • I live... along the coast
  • Liked: 2906
  • Likes Given: 3782

I would a tried to add flotation bags to the stage for recovery and inspection...

That would be a waste of time, weight, and money.  They aren't going to use them for return to launch site, there's no reason to try to develop a new complex system that's only going to be used for a few tests.
They already have a source onboard for pressurization adding a few bags is no big deal for an outfit like SpaceX...

I would think the empty 1st stage RP-1 tank (and even the LOX) would provide all the floatation they need, assuming it stays intact.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline cambrianera

  • Full Member
  • ****
  • Posts: 1426
  • Liked: 311
  • Likes Given: 250

I would a tried to add flotation bags to the stage for recovery and inspection...

That would be a waste of time, weight, and money.  They aren't going to use them for return to launch site, there's no reason to try to develop a new complex system that's only going to be used for a few tests.
They already have a source onboard for pressurization adding a few bags is no big deal for an outfit like SpaceX...

I would think the empty 1st stage RP-1 tank (and even the LOX) would provide all the floatation they need, assuming it stays intact.

Yep, an intact stage will float like a cork.
http://forum.nasaspaceflight.com/index.php?topic=34065.msg1165692#msg1165692
meadows.st did a wonderful job!
Oh to be young again. . .

Offline MTom

  • Full Member
  • ***
  • Posts: 378
  • EU / Hungary
  • Liked: 107
  • Likes Given: 435
Nice article, but I wasn't sure what I was looking at in the last picture -- is that their test area in New Mexico, or an artist's conception of what it will look like, or something else entirely?

This is Spaceport America.

http://spaceportamerica.com/

Offline Rocket Science

  • Senior Member
  • *****
  • Posts: 8959
  • NASA Educator Astronaut Candidate Applicant 2002
  • Liked: 2846
  • Likes Given: 7521

I would a tried to add flotation bags to the stage for recovery and inspection...

That would be a waste of time, weight, and money.  They aren't going to use them for return to launch site, there's no reason to try to develop a new complex system that's only going to be used for a few tests.
They already have a source onboard for pressurization adding a few bags is no big deal for an outfit like SpaceX...

I would think the empty 1st stage RP-1 tank (and even the LOX) would provide all the floatation they need, assuming it stays intact.

Yep, an intact stage will float like a cork.
http://forum.nasaspaceflight.com/index.php?topic=34065.msg1165692#msg1165692
meadows.st did a wonderful job!
I agree "if" it stays intact...
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32440
  • Cape Canaveral Spaceport
  • Liked: 11187
  • Likes Given: 331

They already have a source onboard for pressurization adding a few bags is no big deal for an outfit like SpaceX...

Yes, it would be a big deal. 
1.  It is no a good ideal to use the onboard pressurization
2.  It would complicate the stage layout
3.  It is not a simple addition
4.  Flippant posts like this belittle the actual work needed.  Much like stating that Tesla can add dual wheels to their cars.
« Last Edit: 03/01/2014 06:47 PM by Jim »

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 10772
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 7670
  • Likes Given: 5519
PS I've changed the headline from SpaceX outline to SpaceX outlines, as I've got to get my head around SpaceX being singular - I used to struggle with that when referencing NASA.

It is a UK/US thing.

Corps and other entities in the UK are considered plural so one would say "REL are about to embark on an ambitious development programme for their intercooler at their research centre in Basingstoke." 

Corps and other entities in the US are considered singular so one would say "SpaceX is about to embark on an ambitious development program for their ECLSS at their research center in Hawthorne, CA"

Personally, since you're a Brit, I think you should write the way that you find natural, don't speak USese just for us seppos...
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline MP99

Nice article, but I thought that the legs were supposed to stabilise rotation of the stage, and avoid prop centrifuging in the stage. I had assumed this would be  *before* ignition of the engines for landing.

cheers, Martin

Offline Rocket Science

  • Senior Member
  • *****
  • Posts: 8959
  • NASA Educator Astronaut Candidate Applicant 2002
  • Liked: 2846
  • Likes Given: 7521

They already have a source onboard for pressurization adding a few bags is no big deal for an outfit like SpaceX...

Yes, it would be a big deal. 
1.  It is no a good ideal to use the onboard pressurization
2.  It would complicate the stage layout
3.  It is not a simple addition
4.  Flippant posts like this belittle the actual work needed.  Much like stating that Tesla can add dual wheels to their cars.
My statement Jim is about their engineering capability... Not being easily done to the stage...

BTW: I can't afford a Tesla...
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline rpapo

  • Cybernetic Mole
  • Full Member
  • ****
  • Posts: 1196
  • Michigan, USA
  • Liked: 630
  • Likes Given: 484
Nice article, but I thought that the legs were supposed to stabilise rotation of the stage, and avoid prop centrifuging in the stage. I had assumed this would be  *before* ignition of the engines for landing.
But then Tom Mueller revealed to us last week that the real reason for the engine malfunction was debris from the slosh baffles.  We now also "know" that they were doing slosh-baffle testing back in November in MacGregor.

There's an old computer engineering expression for this: GIGO = Garbage In, Garbage Out.  Not that we had entire garbage as input, but we had incomplete and sometimes wrong input for all our conjectures.

FWIW, I still think that if the aerodynamics are stable (and I don't know they are), then deploying the legs very early on would be best.  Lower terminal velocity means less fuel required for landing.  But the shape the folded legs will have is actually quite nice for a descent tail-first through the atmosphere.  And the faster descent will help with the final landing adjustments when there is a cross-wind to deal with.
An Apollo fanboy . . . fifty years ago.

Offline Hauerg

  • Full Member
  • ****
  • Posts: 746
  • Berndorf, Austria
  • Liked: 352
  • Likes Given: 1125
Also: Stretching the legs in the final seconds of the flight will make for some cool videos in those days when the F9RS1 (?) will actually land on land.

Online aero

  • Senior Member
  • *****
  • Posts: 2996
  • 92129
  • Liked: 797
  • Likes Given: 282
Has anyone measured the area of the stowed legs? I have estimates for the deployed frontal area but not for the area while they are stowed. I need to increase the reference area of my simulated F 9 to account drag of the legs during launch as well as recovery.
Retired, working interesting problems

Offline meadows.st

  • Full Member
  • *
  • Posts: 152
  • Vancouver BC, Canada
  • Liked: 88
  • Likes Given: 3833
Has anyone measured the area of the stowed legs? I have estimates for the deployed frontal area but not for the area while they are stowed. I need to increase the reference area of my simulated F 9 to account drag of the legs during launch as well as recovery.

What level of accuracy are you trying to achieve? 

I have taken my estimates from the existing photos and I believe the thickness at the thickest point is between 50 and 70 cm.  The angle from which the photos (from both JimNTexas and TomNTex) were taken made it impossible to determine this exactly but I think the range is reasonable.  I have also read on other threads that the diameter of the rocket in shipping would increase the overall effective shipping diameter about 2' larger than the "leg free" shipping  diameter and assuming the body would be shipped with the lowest point being between the legs, my assumed max depth seems reasonable.  The thinnest (at the edges) looks more like 30 to 40 cm. 

Looking at the assumptions from another perspective, we know the legs are about 8m long, the pistons are about 20m long and the surface area of the legs is about 12m^2 and the average diam of the pneumatic cylinders is 20cm.  From what we know about the total mass (~2000kg) of the four sets, a rough density would be 75kg/m^3.  Assuming they are using the lightest carbon fibre (density ~ 1750kg/m^3, the system is about 1/23 solid carbon fibre (this is a loose Order of Magnitude approach I know).  Therefore, the wall thickness, assuming otherwise hollow and all other components are a higher density than carbon fibre, the wall thickness would be <3cm thick if you assume the 70cm max thickness and 40cm min thickness of the legs.  I am not a carbon fibre expert but I believe an inch thick carbon fibre structure would be sufficiently strong.

I have created a roughly to scale oversimplified mock up with the max depth approx 50cm (see picture) at the thickest point and ~30 cm at the thinnest point to depict what I am assuming for the cross sectional area of a tail-first "ZZTop" F9 v1.1.  EDIT: added superimposed version of F9v1.1 for side by side comparison for scale.

Edited: less cluttered picture of the engines superimposed on another version of the legs end view.
Edit: Overlay photo from this link from @cambrianera http://forum.nasaspaceflight.com/index.php?topic=34065.msg1163959#msg1163959
« Last Edit: 03/04/2014 01:37 AM by meadows.st »
“A little rudder far from the rocks is a lot better than a lot of rudder close to the rocks.” L. David Marquet

Online AJW

  • Full Member
  • ****
  • Posts: 596
  • Liked: 490
  • Likes Given: 63
Do we have an expected duration for the landing burn?  With the legs extending 10 seconds into this burn, I would expect that the divert towards the LZ won't begin until the legs are fully deployed and locked, and this might give us a distance between the LZ and the abort target.

Offline Comga

  • Senior Member
  • *****
  • Posts: 4338
  • Liked: 1570
  • Likes Given: 1310
Nice article, but I thought that the legs were supposed to stabilise rotation of the stage, and avoid prop centrifuging in the stage. I had assumed this would be  *before* ignition of the engines for landing.

cheers, Martin
"When you assume you make...."
The statement from Musk was that the presence of legs mitigated the spin.  He didn't say "deployed legs".  It has been conjectured that the stowed legs also work against the spin.  It appears that SpaceX is going to open them as late as possible, so they have deemed it not necessary to deploy them to resist the spin.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Online AncientU

  • Senior Member
  • *****
  • Posts: 6246
  • Liked: 4078
  • Likes Given: 5600
Nice article, but I thought that the legs were supposed to stabilise rotation of the stage, and avoid prop centrifuging in the stage. I had assumed this would be  *before* ignition of the engines for landing.
But then Tom Mueller revealed to us last week that the real reason for the engine malfunction was debris from the slosh baffles.  We now also "know" that they were doing slosh-baffle testing back in November in MacGregor.

There's an old computer engineering expression for this: GIGO = Garbage In, Garbage Out.  Not that we had entire garbage as input, but we had incomplete and sometimes wrong input for all our conjectures.

FWIW, I still think that if the aerodynamics are stable (and I don't know they are), then deploying the legs very early on would be best.  Lower terminal velocity means less fuel required for landing.  But the shape the folded legs will have is actually quite nice for a descent tail-first through the atmosphere.  And the faster descent will help with the final landing adjustments when there is a cross-wind to deal with.
One disadvantage of deploying the legs early (I thought it would happen above the atmosphere after the boost-back burn) is that your terminal velocity is so low that you have an extremely short final burn.  There is no shortage of propulsive power to stop the descent, so higher velocity actually provides more inertial mass and widens the burn window.  The trade-off is a bit of fuel vs. higher margin for a successful landing.
« Last Edit: 03/02/2014 12:31 AM by AncientU »
"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Offline Comga

  • Senior Member
  • *****
  • Posts: 4338
  • Liked: 1570
  • Likes Given: 1310
Nice article, but I thought that the legs were supposed to stabilise rotation of the stage, and avoid prop centrifuging in the stage. I had assumed this would be  *before* ignition of the engines for landing.
But then Tom Mueller revealed to us last week that the real reason for the engine malfunction was debris from the slosh baffles.  We now also "know" that they were doing slosh-baffle testing back in November in MacGregor.

There's an old computer engineering expression for this: GIGO = Garbage In, Garbage Out.  Not that we had entire garbage as input, but we had incomplete and sometimes wrong input for all our conjectures.

FWIW, I still think that if the aerodynamics are stable (and I don't know they are), then deploying the legs very early on would be best.  Lower terminal velocity means less fuel required for landing.  But the shape the folded legs will have is actually quite nice for a descent tail-first through the atmosphere.  And the faster descent will help with the final landing adjustments when there is a cross-wind to deal with.
One disadvantage of deploying the legs early (I thought it would happen above the atmosphere after the boost-back burn) is that your terminal velocity is so low that you have an extremely short final burn.  There is no shortage of propulsive power to stop the descent, so higher velocity actually provides more inertial mass and widens the burn window.  The trade-off is a bit of fuel vs. higher margin for a successful landing.
This makes no sense to me.
Can you put this in equations or a numerical simulation?

The "magic" of the Falcon 9 is that it can be throttled to 8% of liftoff thrust by using one of nine engines and throttling mildly. SpaceX will still bring back a stage with only 3-5% of the liftoff mass.   "Hoverslam" is the only way out of this shy of pushing the throttle limit down to below 50%.

My understanding from the information here (and L2!) is that SpaceX will leave extra fuel in the first stage of the SpX-3 rocket to reduce the terminal acceleration and give themselves more time to tune the landing burn for zero velocity at zero altitude. If they want to minimize the fuel needed they will try that on subsequent flights.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Online rsnellenberger

  • Amateur wood butcher
  • Full Member
  • ****
  • Posts: 594
  • Harbor Springs, Michigan
  • Liked: 63
  • Likes Given: 19
Nice article, but I wasn't sure what I was looking at in the last picture -- is that their test area in New Mexico, or an artist's conception of what it will look like, or something else entirely?

This is Spaceport America.

http://spaceportamerica.com/
Ah... Thanks!

Online guckyfan

  • Senior Member
  • *****
  • Posts: 6778
  • Germany
  • Liked: 1801
  • Likes Given: 1810
My understanding from the information here (and L2!) is that SpaceX will leave extra fuel in the first stage of the SpX-3 rocket to reduce the terminal acceleration and give themselves more time to tune the landing burn for zero velocity at zero altitude. If they want to minimize the fuel needed they will try that on subsequent flights.

I have missed that. Where do you get this understanding from? It does seem to make sense except they can get such data from the Falcon 9R test vehicle.

Offline Paul Howard

  • Veteran
  • Full Member
  • ****
  • Posts: 458
  • Perth, Western Australia
  • Liked: 5
  • Likes Given: 20
Any chance they will get video of the legs deploying?

Offline Silmfeanor

  • Full Member
  • ****
  • Posts: 1188
  • Utrecht, The Netherlands
  • Liked: 248
  • Likes Given: 515
Picture posted in the update thread, i'll post it here aswell. First view of a vertical stage with legs...

The source is SpaceX Facebook

Quote
Falcon 9 and Dragon conducted a successful static fire test in advance of next week’s CRS-3 launch to station! In this final major preflight test, Falcon 9’s 9 first-stage engines were ignited for 2 seconds while the vehicle was held down to the pad.

 Launch is targeted for Sunday March 16 at 4:41 am EDT.

They look really small. Good to keep CoG in mind..
« Last Edit: 03/09/2014 09:15 PM by Silmfeanor »

Offline TripD

  • Full Member
  • ****
  • Posts: 635
  • Waiting for longer boats
  • Liked: 510
  • Likes Given: 367
Quote
Any chance they will get video of the legs deploying?

The on board video cameras would give a great view of that!  One can only hope.

Online ugordan

  • Senior Member
  • *****
  • Posts: 7545
    • My mainly Cassini image gallery
  • Liked: 1755
  • Likes Given: 394
The on board video cameras would give a great view of that!  One can only hope.

The launch occurs at 4:41 local time. Don't expect to see much.

Offline Kabloona

  • Senior Member
  • *****
  • Posts: 4321
  • Velocitas Eradico
  • Fortress of Solitude
  • Liked: 2554
  • Likes Given: 529
Yes, unfortunately. But maybe they will have infrared cameras on the recovery ship. Handheld HD infrared camcorders are surprisingly inexpensive.

On the other hand, the exhaust plume from the landing burn might overwhelm the IR sensors and make it difficult to see any part of the rocket.
« Last Edit: 03/09/2014 09:44 PM by Kabloona »

Online GalacticIntruder

  • Full Member
  • ****
  • Posts: 455
  • PPPPPPP
  • Huntsville, AL
  • Liked: 176
  • Likes Given: 61
Since it will be dark, it is an experimental Landing System, it does have innovative, secretive, ITAR stuff, and SpaceX usually is not timely about things, I doubt we will get much info and video from the first stage water landing/crashing anytime soon.
Watch out for those pesky corners, they have teeth.

Offline 411rocket

  • Full Member
  • **
  • Posts: 261
  • Retired RCEME w/ tours in Cyprus, Croatia, Bosnia
  • Vancouver Island
  • Liked: 79
  • Likes Given: 120
Since it will be dark, it is an experimental Landing System, it does have innovative, secretive, ITAR stuff, and SpaceX usually is not timely about things, I doubt we will get much info and video from the first stage water landing/crashing anytime soon.

Unless, it is part of the NASA post launch news conference. Which is about 2 hours after launch.

http://www.nasa.gov/mission_pages/station/news/spacex3_briefings_events.html
"POST-LAUNCH NEWS CONFERENCE
A post-launch news conference will be held approximately two hours after launch. NASA Television will provide live coverage, as well as streaming Internet coverage."

Offline sojourner

  • Full Member
  • **
  • Posts: 253
  • Liked: 30
  • Likes Given: 1
Wasn't sure where to put this, since it was getting off topic in the orbcom mission thread:

This is not specific to the OG2 mission.
Maximizing payload (at the expense of recovery) is not what SpaceX is going to do.
The oft stated analogy would be setting the range for a passenger jet at the limit of zero fuel ignoring the FAA or ICAO rules for reserve fuel. You can't charter a plane for such a flight.
Somewhere down the road, if SpaceX success at reuseability, expending the rocket to maximize payload will be "heroic" like Doolittle's Raiders.
Payload on a reuseable rocket will be less than for the same rocket in expendable mode and SpaceX is going for reuseability.

Not heroic, just more expensive.  Reusability and expendability both become options, and are priced accordingly.  There's no reason for SpaceX to turn down a profitable launch just because it requires them to build a new stage.

Wouldn't SpaceX come up with a "lifetime" for the first stage measured in number of reuses, then decide once it reaches that point to mark that particular stage as expendable and save it for a launch requiring an expendable?

This would seem to have some benefits.
1. A steady accumulation of expendable first stages.
2. Assured median lifetime of the reusables.
3. Better management of the production lines due to increased lead times

Basically, You would only be producing new units for reuse. Expendables become a benefit of the life expectancy of those stages.  The production line could just keep churnng out standardized units at a steady rate.

Online guckyfan

  • Senior Member
  • *****
  • Posts: 6778
  • Germany
  • Liked: 1801
  • Likes Given: 1810

Wouldn't SpaceX come up with a "lifetime" for the first stage measured in number of reuses, then decide once it reaches that point to mark that particular stage as expendable and save it for a launch requiring an expendable?

This would seem to have some benefits.
1. A steady accumulation of expendable first stages.
2. Assured median lifetime of the reusables.
3. Better management of the production lines due to increased lead times

Basically, You would only be producing new units for reuse. Expendables become a benefit of the life expectancy of those stages.  The production line could just keep churnng out standardized units at a steady rate.

A likely approach. But it may result in no stage ever reaching its natural lifespan before it is assigned for a suicide mission.

Offline sojourner

  • Full Member
  • **
  • Posts: 253
  • Liked: 30
  • Likes Given: 1
I would think that would be a good thing, considering what would happen to the payload on a rocket that "reached it's natural lifespan".

Online Coastal Ron

  • Senior Member
  • *****
  • Posts: 4258
  • I live... along the coast
  • Liked: 2906
  • Likes Given: 3782

Wouldn't SpaceX come up with a "lifetime" for the first stage measured in number of reuses, then decide once it reaches that point to mark that particular stage as expendable and save it for a launch requiring an expendable?

This would seem to have some benefits.
1. A steady accumulation of expendable first stages.
2. Assured median lifetime of the reusables.
3. Better management of the production lines due to increased lead times

Basically, You would only be producing new units for reuse. Expendables become a benefit of the life expectancy of those stages.  The production line could just keep churnng out standardized units at a steady rate.

A likely approach. But it may result in no stage ever reaching its natural lifespan before it is assigned for a suicide mission.

Or they could disassemble it and recycle it.  Might be able to get a discount for new material from their aluminum supplier since they will be providing high quality recycling material.

Guess it would depend on how much they can get from an expendable launch at that point.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Tags: