SpaceX News

[TDPerk]

Seems like remotely operated forklift type vehicles, maybe with magnetic drill base type clamps, should scoot out to the booster and hold it down until it is welded.

Anywhere near the booster before it's secured seems like a bad place to be.

[Tom Ligon]

Or servohydraulic stabilizer arms from the corners of the barge, guided into place autonomously by cameras and a "vision engine". I think we have the technology to grab a stick. If they want to keep landing on a barge, this should help when the seas are rough.

[paperburn1]

Once it is a proven repeatable tech then custom built boat is the obvious answer.
Small Waterplane Area Twin Hull, better known by the acronym SWATH, is a twin-hull ship design that minimizes hull cross section area at the sea's surface. Minimizing the ship's volume near the surface area of the sea, where wave energy is located, maximizes a vessel's stability, even in high seas and at high speeds. The bulk of the displacement necessary to keep the ship afloat is located beneath the waves, where it is less affected by wave action. Wave excitation drops exponentially as depth increases make for a very stable platform.
(yes I copied a wiki )

[ladajo]

They work very well, up to a sea state limit, then they can be worse.
The barges he is using seem to be focusing on cheap and fast, not good.
However, good is relative; given the failures (which are incredibly good fun to watch), the damage seems to be minimal and easily recovered from. Although, I do have to wonder about Hazmat management post event cleanup. I am surprised that the Tree Hugger Alliance hasn't been all over Musk about splashing unburnt fuel all over his barge and the ocean in the immediate vicinity. If you have any doubts about how extreme they are willing to be, invite them around to watch you pour a cup of fuel or oil over the side and see what happens.

[Skipjack]

SpaceX is focusing on cost efficiency right now. If the recovery ship that could easily see severe damage is so expensive that it makes the recovery not cost effective, then they have not gained anything.
I think that they might go for a better solution further down the road, when they have worked out all the kinks and know that it improves the outcome enough to warrant the additional cost.
Seeing how they have been progressively improving their rockets, they might also work on that (in parallel) to see whether they can make barge recovery unnecessary. E.g. there will probably be very few payloads that cant be handled by a Falcon Heavy that has all 3 cores return to the launch site.

[jnaujok]

Perhaps they should also be considering small islands downrange for potential landings instead of the barges, given that their very first land attempt succeeded. I know there are a few sparsely populated islands south-southeast of Vandenberg that could have potentially been used as a landing site. I'd think you could find the same thing somewhere off the Florida coast as well to support high-speed separations. Maybe that's more the long term goal, since once you've sunk money into an island landing pad and shipping port, that money is gone. If SpaceX is still uncertain that they can pull this off every time, they might just be hedging their bets against permanently sunk costs vs. a barge they can always re-sell to a cargo company later on.

[Tom Ligon]

Some years ago while I was at EMC2, the DC-X made its final flight. NASA had taken it over and they flew it without hooking up the hydraulics on one of the four landing legs. Dr. Bussard commented at the time that 4 legs is a waste. If you have 4 legs and one fails, the craft will usually fall over. You might as well cut back to 3 and save the weight. If you want to be able to land with 1 failed leg, use 5.

[Maui]

Perhaps they should also be considering small islands downrange for potential landings instead of the barges, given that their very first land attempt succeeded.

I don't think land/sea has anything to do with what happened. The failed leg would have caused the same result on land. And the two previous failed attempts to land at sea would likely have failed there was well. Only case land would have been an advantage is for one landing attempt that had to be skipped last year because of rough seas.

Anyway, cost of fixing what happened to the leg is surely much less expensive than buying/maintaining an island, port etc. Also, per-launch transport costs are likely lower as well using the barge.

[Maui]

Some years ago while I was at EMC2, the DC-X made its final flight. NASA had taken it over and they flew it without hooking up the hydraulics on one of the four landing legs. Dr. Bussard commented at the time that 4 legs is a waste. If you have 4 legs and one fails, the craft will usually fall over. You might as well cut back to 3 and save the weight. If you want to be able to land with 1 failed leg, use 5.

Haha, now that you mention it, 4 does seem completely illogical. I'd like to believe there has to be some reason for 4 rather than 3 or 5... but I can't come up with one.

[TDPerk]

I am surprised that the Tree Hugger Alliance hasn't been all over Musk about splashing unburnt fuel all over his barge and the ocean in the immediate vicinity.

So far I think they've burned it all...

[D Tibbets]

Some years ago while I was at EMC2, the DC-X made its final flight. NASA had taken it over and they flew it without hooking up the hydraulics on one of the four landing legs. Dr. Bussard commented at the time that 4 legs is a waste. If you have 4 legs and one fails, the craft will usually fall over. You might as well cut back to 3 and save the weight. If you want to be able to land with 1 failed leg, use 5.

Haha, now that you mention it, 4 does seem completely illogical. I'd like to believe there has to be some reason for 4 rather than 3 or 5... but I can't come up with one.

I'm speculating, but 4 legs may have some advantage if landing with some deviation in the vertical axis. There is a wider base if you are tilted in a direction between two of 4 legs versus between two of three legs. The Nasa Lunar lander had 4 legs.The Blue Origins rocket has 4 legs also.

Dan Tibbets

[paperburn1]

Short version
Three legs would have to be about 30 % longer to carry the load and retain the CG in all direction.
Four legs can be configured to absorb the shock of landing better. (important)
Better tilt recover (five would be the best)
The total difference in weight is about 6% more for four legs verses three due to the fact three would have to be larger to maintain the CG and absorb the shock of landing.
Bottom line for just a little weight penalty you can get a more robust landing gear as long as one leg does not collapse.
https://www.hq.nasa.gov/alsj/tnD6850LML ... bsytem.pdf

[Skipjack]

Short version
Three legs would have to be about 30 % longer to carry the load and retain the CG in all direction.
Four legs can be configured to absorb the shock of landing better. (important)
Better tilt recover (five would be the best)
The total difference in weight is about 6% more for four legs verses three due to the fact three would have to be larger to maintain the CG and absorb the shock of landing.

Very good! So how much more would 5 legs weight another 6% more?

[paperburn1]

no about 20 to 25 percent more given a leg failure you must be structurally strong enough for all four to hold the weight
Tripods are less stable for legs of a given length, but if the legs 45% longer they will be just as stable as four legs and weigh more.

So five legs would be between the two weight wise and add no more real stability just reliability. Probably not worth the extra 20 to 25 percent weight of 4 legs.
Disclaimer: All figure were done off of back of envelope and internet guesses of rocket weight and landing gear weight and assuming the same footprint and CG.

[paperburn1]

Or to paraphrase the old production triangle

Low weight
Stability
Reliability
Pick two.