Author Topic: First stage recovery at down-range locations  (Read 185811 times)

Offline deltaV

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First stage recovery at down-range locations
« on: 03/25/2013 03:20 pm »
This thread is for discussion of the possibility of recovering SpaceX first stages at locations other than the launch complex. This includes landing at Florida from a Texas launch, landing on an oil-rig-like floating object, boost forward, and so on.

Offline Kaputnik

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Re: First stage recovery at down-range locations
« Reply #1 on: 03/25/2013 03:39 pm »
Thanks for starting the thread.
First question- is there any evidence whatsoever that points towards SpaceX considering down-range/ boost-forward recovery strategies?
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Offline llanitedave

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Re: First stage recovery at down-range locations
« Reply #2 on: 03/25/2013 03:47 pm »
The center core of the cross-fed Falcon heavy is the only one that I think the concept would possibly apply to.  Getting it back to the launch site from its staging point does seem a bit problematic.
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Offline Ben the Space Brit

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Re: First stage recovery at down-range locations
« Reply #3 on: 03/25/2013 04:21 pm »
I mentioned this on another thread - The Shuttle had an emergency landing site in Spain.  Would this be suitable for F9 core recovery? Remember that the core has effectively no cross-range capability so it would need to effectively drop ballistically onto the recovery zone within a radius of few miles from the touch-down point. 

There are also two orbital trajectories to consider, the 50-degree+ inclination to the ISS and the hypothetical future Bigelow station and the 28-degree inclination from the Cape for BEO launches.  Given the limitations of the core as a descent vehicle, I do not think that the two inclinations could have the same recovery spot.
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Offline Kaputnik

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Re: First stage recovery at down-range locations
« Reply #4 on: 03/25/2013 04:44 pm »
Time for my pet idea :)

I have my fingers crossed for them, but tbh I cannot see Sea Launch surviving forever given their track record. If they go bust, it might be possible for SpaceX to pick up the Odyssey and Commander for a song. These vessels already operate not far from SpaceX's HQ, and are set up to support an all-kerolox vehicle with a diameter of about 12ft. Seems a pretty good match.

A mobile launch platform could thus be positioned so that downrange recovery on land was relatively straightforward.

Back to reality...
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Offline deltaV

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Re: First stage recovery at down-range locations
« Reply #5 on: 03/25/2013 04:55 pm »
The other side of the Atlantic is way too far downrange to make sense landing there. Even Texas to Florida (~1400 km) is farther than ideal. Taking a wild guess I'd say stage separation would occur ~200 km downrange (that distance is from 3.5 km/s at 3 gee constant acceleration), so upon stage separation Texas is ~200 km away and Florida ~1200 km away.

If you boost until going at velocity vector 3 km/s horizontally and 2 km/s vertically you'll land 2*(3 km/s)* (2 km/s) / (9.8 m/s/s) = 1224 km downrange. I just did some BOTE calculations and it seems that getting a large enough vertical velocity, and then slowing down again at the other end, makes landing at Florida on the order of a few hundred m/s of delta-vee closer than Texas is. That doesn't seem worth the trouble. I conclude that landing downrange only makes sense if the distance downrange is much less than the distance from Texas to Florida, on the order of 500 km.

Actually boost-sideways and landing in say Louisiana seems better than boost-forward and landing in Florida.

Edit: a recent Elon tweet indicates that the FH center core actually flies past Florida. Oops. Maybe there's more vertical velocity at FH core burnout than I expected?
« Last Edit: 05/03/2013 09:17 pm by deltaV »

Offline Lars_J

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Re: First stage recovery at down-range locations
« Reply #6 on: 03/25/2013 04:59 pm »
The other side of the Atlantic is way too far downrange to make sense landing there. Even Texas to Florida (~1400 km) is farther than ideal. Taking a wild guess I'd say stage separation would occur ~200 km downrange (that distance is from 3.5 km/s at 3 gee constant acceleration), so upon stage separation Texas is ~200 km away and Florida ~1200 km away.

Yep... Boost-forward from TX to FL just won't work - boost-back will be better. The only possibility would be the FH central core, but I suspect that one might remain expendable.

Offline llanitedave

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Re: First stage recovery at down-range locations
« Reply #7 on: 03/25/2013 07:18 pm »
Time for Elon to take a trip to Mexico to maybe negotiate a landing pad in Yucatan?
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Offline neoforce

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Re: First stage recovery at down-range locations
« Reply #8 on: 03/25/2013 07:26 pm »
The goal is to reduce cost based on re-usability.  Clearly recovery at launch pad is best, so my question is how much of the cost savings will be lost by down range recovery if you have to transport back to launch site by some other mechanism?

Offline meekGee

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Re: First stage recovery at down-range locations
« Reply #9 on: 03/25/2013 07:32 pm »
The goal is to reduce cost based on re-usability.  Clearly recovery at launch pad is best, so my question is how much of the cost savings will be lost by down range recovery if you have to transport back to launch site by some other mechanism?

If the first stage is a rapid reuse vehicle (gas-n-go) then the only way to have fly-forward and still keep costs low is to have the stage self ferry from the forward pad to the original launch site.

The forward pad can be as minimalistic as a concrete pad and two gas trucks.

Otherwise, any handling of the stage (trucks, trains and boats) will end up costing too much.
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Offline dcporter

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Re: First stage recovery at down-range locations
« Reply #10 on: 03/25/2013 08:19 pm »
Thanks for starting the thread.
First question- is there any evidence whatsoever that points towards SpaceX considering down-range/ boost-forward recovery strategies?

No. There is however ample evidence that they're pursuing boost-back: the recovery CGI, some hand-waving and words from Elon (if I recall)...

Offline go4mars

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Re: First stage recovery at down-range locations
« Reply #11 on: 03/25/2013 08:21 pm »
IIRC, Elon mentioned somewhere that the second stage would go around once before coming back down.  Maybe an expendible 3rd stage for higher than LEO?       (Or the "spaceship attached to raptor" that Elon referred to)?

On the other hand, FH with no US can still get something like 50 tons to orbit, according to... was it Joek? 
For the central core to survive re-entry at orbital speed, perhaps it could do most of the retro-fire (shedding horizontal speed) above the atmosphere, then fall back to the launch pad (sitting on a low-flow passive gaseous combustion plume analogous to the thrust transient of falcon-1 flight three). Friction on the regeneratively cooled engine(s) might keep things cold enough and would provide the energy for the phase change from liquid to gas.   Maybe.
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Offline Joffan

Re: First stage recovery at down-range locations
« Reply #12 on: 03/25/2013 08:30 pm »
Maybe Musk should just buy the Western Sahara. Plenty of empty space downrange from there.
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Offline deltaV

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Re: First stage recovery at down-range locations
« Reply #13 on: 03/25/2013 08:41 pm »
Launches from Western Sahara or landing in Mexico would be a pain due to ITAR, right?

Offline A_M_Swallow

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Re: First stage recovery at down-range locations
« Reply #14 on: 03/25/2013 09:11 pm »
Time for Elon to take a trip to Mexico to maybe negotiate a landing pad in Yucatan?

Banned by US law.  Rockets and rocket factories cannot be exported under the ITAR rules.  Elon built his factory on the wrong side of the Mexican/Californian border.

Offline douglas100

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Re: First stage recovery at down-range locations
« Reply #15 on: 03/25/2013 09:46 pm »
Maybe Musk should just buy the Western Sahara. Plenty of empty space downrange from there.

Maybe politically not a good idea. Western Australia might be better (ignoring all ITAR considerations). Remember how Kistler planned to recover the K-1.
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Offline douglas100

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Re: First stage recovery at down-range locations
« Reply #16 on: 03/25/2013 10:00 pm »

Time for my pet idea :)

Actually your idea makes more sense when used with air launching. I remember Jon Goff posted about it a while back. If Stratolaunch wanted to recover the first stage of their rocket on land they could fly uprange from an island base (Kwajalein? Ascension Island?) and position the aircraft launch point so that the LV passed close to the island on ascent. Workable technically and Stratolaunch are already building their aircraft, so no sea platforms needed.

« Last Edit: 03/25/2013 10:27 pm by douglas100 »
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Offline Garrett

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Re: First stage recovery at down-range locations
« Reply #17 on: 03/26/2013 12:41 pm »
IIRC, Elon mentioned somewhere that the second stage would go around once before coming back down. 
The second stage reaches orbital velocity, so the only practical way to bring it back is to let it go around once (at least) and use atmospheric braking to slow it down and steer it back to the launch/landing site.
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Offline deltaV

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Re: First stage recovery at down-range locations
« Reply #18 on: 03/26/2013 04:58 pm »
Has anyone considered landing downrange on a SWATH style boat? That sort of boat is a cross between a catamaran and a semi-submersible oil rig. Its key feature is its stability moving quickly through rough seas. Here's a video showing a conventional boat pounding through rough seas (in foreground) and a smaller SWATH boat seemingly oblivious of the seas (in background):

Here's some more info:
http://www.yachtsilvercloud.com/SSC/PDF/Silver%20Cloud%20LR.PDF
http://www.globalsecurity.org/military/systems/ship/sea-slice.htm

SWATH previously mentioned briefly here:
http://forum.nasaspaceflight.com/index.php?topic=30350.msg1005414#msg1005414

Despite the stability of a SWATH platform it's probably not a good idea to leave the stage sitting unrestrained on the landing pad for the simple reason that the wind could easily blow it over. A 30 m/s wind gives a force of about:
0.5 * (1.2 kg/m^3) * (30 m/s)^2 * 3.6 m * 40 m / (9.8 m/s^2) = 8 mt force
on the side of the stage. I dunno what the first stage mass is but the ~95% propellant ratio suggests a mass of around 15 mt. That's an uncomfortably large wind force compared to the stage mass. A 30 m/s wind is quite strong (58 knots), but I think that's a reasonable design value because wind speeds are often pretty strong at sea, gusts are stronger than sustained winds, and traveling home adds ~10 knots effective windspeed if home happens to be upwind of the landing spot.

Having the stage blown over immediately after landing shouldn't be a problem because the boat can travel downwind to subtract from the effective windspeed. One possible solution to the wind problem would be to tie down the stage somehow after landing. Another possibility would be to have a transporter/erector bring it horizontal in a manner similar to how the rocket is brought horizontal at the pad after e.g. an engine test.

Landing at sea would add few million dollars per year of costs to maintain the boat but that may be worth it if it reduces the reusability payload penalty sufficiently.

Offline Halidon

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Re: First stage recovery at down-range locations
« Reply #19 on: 03/27/2013 01:27 am »
Has anyone considered landing downrange on a SWATH style boat? That sort of boat is a cross between a catamaran and a semi-submersible oil rig. Its key feature is its stability moving quickly through rough seas. Here's a video showing a conventional boat pounding through rough seas (in foreground) and a smaller SWATH boat seemingly oblivious of the seas (in background):

Here's some more info:
http://www.yachtsilvercloud.com/SSC/PDF/Silver%20Cloud%20LR.PDF
http://www.globalsecurity.org/military/systems/ship/sea-slice.htm

SWATH previously mentioned briefly here:
http://forum.nasaspaceflight.com/index.php?topic=30350.msg1005414#msg1005414

Despite the stability of a SWATH platform it's probably not a good idea to leave the stage sitting unrestrained on the landing pad for the simple reason that the wind could easily blow it over. A 30 m/s wind gives a force of about:
0.5 * (1.2 kg/m^3) * (30 m/s)^2 * 3.6 m * 40 m / (9.8 m/s^2) = 8 mt force
on the side of the stage. I dunno what the first stage mass is but the ~95% propellant ratio suggests a mass of around 15 mt. That's an uncomfortably large wind force compared to the stage mass. A 30 m/s wind is quite strong (58 knots), but I think that's a reasonable design value because wind speeds are often pretty strong at sea, gusts are stronger than sustained winds, and traveling home adds ~10 knots effective windspeed if home happens to be upwind of the landing spot.

Having the stage blown over immediately after landing shouldn't be a problem because the boat can travel downwind to subtract from the effective windspeed. One possible solution to the wind problem would be to tie down the stage somehow after landing. Another possibility would be to have a transporter/erector bring it horizontal in a manner similar to how the rocket is brought horizontal at the pad after e.g. an engine test.

Landing at sea would add few million dollars per year of costs to maintain the boat but that may be worth it if it reduces the reusability payload penalty sufficiently.
SWATH boats are smoother than traditional displacement hulls, but they're still moving plenty in multiple axis. Their stability is most evident upon being under way, which makes for a moving target. And if "downwind" involves taking wave action at a bad angle your SWATH landing pad will be bouncing around quite dramatically.

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