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The ASDS barge is a large flat surface. A large tall skinny structure will land on it. This is not likely to be very stable on its own. The center of mass is pretty low, since the empty stage tanks are light and fluffy, with all the dense mass of the engines at the bottom.

The legs have a 60+ foot span, so it has a pretty good base. But you probably do not want it to slide around either as the sea conditions change.

How will SpaceX secure it for transport back to shore?

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The recent landing (JCSAT-14) shows the Falcon 9 held on jack stands and chained to deck:

enter image description here

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  • $\begingroup$ Still does not show the shoes over the foot tips, but great photo! $\endgroup$ – geoffc May 10 '16 at 18:59
  • $\begingroup$ @geoffc turns out it doesn't need securing - probably no shoes anymore, just the jack stands (maybe welded to the octoweb) and chains as it seems. $\endgroup$ – jkavalik May 11 '16 at 16:00
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My understanding (sorry, I have no citations yet) is that a lot of the same technologies used to position and control drillships is being used to position SpaceX's barge. Drillships use dynamic positioning which handle translation and rotation of the barge in the plane of the surface. I believe heave, sway, and surge are being handled by articulation of the landing surface.

All of this, as well as launch commit criteria, is adequate for the period of time required to get the vehicle lashed down I assume. I suspect that the launch commit criteria is the primary way they are dealing with the sea state issue. Remember, SpaceX isn't planning on landing on a barge forever -- this is just being used until they can cajole the range safety folks to allow a land landing.

Regardless of the outcome, the attempted landing will be quite a show...

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    $\begingroup$ To back you up, I was also under the impression that the dynamic positioning system corrected for the motion of the sea or at least dampened a lot of the effects. (I don't have a citation either [sorry] - I think I read about it on the SpaceX subreddit a while back.) $\endgroup$ – Nate Barbettini Dec 26 '14 at 16:03
  • $\begingroup$ I haven't found any information on how SpaceX is (or is not) compensating for heave, sway, and surge however. These are motions outside the plane of the water surface and are difficult to counteract. Drillships do it by "floating" the drill string. Not sure how you might do it for a landing platform. The answer is that you probably don't do it -- you just don't launch if the conditions aren't agreeable at the landing site. $\endgroup$ – Erik Dec 26 '14 at 16:07
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    $\begingroup$ Makes sense. Which would be another frustrating variable to take into account for launches -- but hopefully ocean/barge landings won't be the norm for very long. In many ways that's harder than returning to land (because of the additional variables like weather), although the fuel requirements are probably less. $\endgroup$ – Nate Barbettini Dec 26 '14 at 16:10
  • $\begingroup$ The barge does not have an articulated landing surface. $\endgroup$ – Hobbes Apr 10 '16 at 7:13
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For this first flight: "We are going to weld steel shoes over the landing feet as a precautionary measure." -- Elon Musk

I don't know that they would do that every time, but they are going to the first time.

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  • $\begingroup$ Before he said that though, he said that the stage will be mostly held down by gravity, since most of the weight is at the bottom. The steel shoes will be welded after landing. $\endgroup$ – Nickolai Jan 9 '15 at 16:27
  • $\begingroup$ Yes, he did. Good point. I was mostly answering the question about "how will SpaceX tie down a landed stage". They will rely mostly on gravity to keep it in place since the low center of mass and wide legs should make it fairly stable. $\endgroup$ – Michael W Jan 9 '15 at 18:16
  • $\begingroup$ They should put small thermite charges on the legs so that the rocket would weld itself to the deck on touchdown :) $\endgroup$ – SF. May 11 '16 at 10:20
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According to this article on NASASpaceFlight.com:

It is also understood that the ASDS [Autonomous Spaceport Drone Ship - the barge] will have the ability to refuel returned stages, allowing them to make the hop back to land for future reuse.

So it lands, is refueled, then flies by itself to wherever they want it. Which I think is pretty audacious.

I don't suppose they'll try to do that on the very first landing attempt (now scheduled for January 6), tho.

As I think about it, this makes more sense than I first thought. My impression is that SpaceX wanted to land at the Cape but NASA wouldn't let them (safety concerns), so the barge was their workaround.

But they can position the barge way downrange, and use less fuel flying back up-range to land at the Cape (or Brownsville, whatever). Then refuel and fly back to base.

So that leaves more fuel available for boosting the payload - more payload or more delta V.

Maybe the barge makes sense even without NASA's safety concerns. [Ha - maybe they thought of this only because NASA wouldn't let them land at the Cape... wouldn't that be ironic?]

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  • $\begingroup$ But it will not likely be, land, and 20 minutes later lift off for return to base. It will still require tie downs during refueling if nothing else. A sudden wave and you slide your fully loaded stage over the side? Recipe for disaster if it cracks and burns, or environmental issue if you crack and leak. $\endgroup$ – geoffc Dec 18 '14 at 16:20
  • $\begingroup$ @geoffc: Well, if it just landed under it's own power, that's a pretty good indication that everything is working OK, so you could just refuel and immediately take off again. Obviously you'd only do that if the weather and sea conditions are OK. They could also design an automatic tiedown/release mechanism into the barge - wouldn't be hard (compared to everything else...). $\endgroup$ – nerdfever.com Dec 18 '14 at 16:24
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    $\begingroup$ This is an interesting perspective, and a nice find for the citation, but I suspect that their plan is doing a bit of both - land, secure, cruise back to the port while refueling and inspecting the booster stage, then fly it off the barge to its spaceport once the barge is out of the no-fly zone (and relatively close to the land, e.g. the Gulf of Mexico is filled with oil rigs and East of Cape are heavy traffic shipping lanes). If it's not safe to fly it back, either because of booster problems or the weather, then they strap it down horizontally and transport back home the usual way. $\endgroup$ – TildalWave Dec 18 '14 at 16:44
  • $\begingroup$ They have already said that the barge will be useful for recovering Falcon Heavy core stages, where the payload penalty for an RTLS will be too high. But land on a downrange stage would not. Same for F9R modes that are payload sensitive. Will be able to recover downrange to save payload penalty on RTLS. $\endgroup$ – geoffc Dec 18 '14 at 16:52
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Musk confirmed in the CRS-8 briefing that they are putting steel shoes over the landing feet and welding them down.

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  • $\begingroup$ In the future it may be done robotically. $\endgroup$ – uhoh Apr 13 '16 at 3:25
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Before an actual landing most everything is speculation.

General speculations seems to float between two extremes.

  1. Leave the stage standing as it on the barge. Let it cool down, send in small crew in a boat, tie down the stage so it won't slide. Safe it and sail back to port in that orientation.
  2. After landing, approach the stage in a boat with a crane, lift the stage, retract the legs (unclear how, must be possible though) and lay it down in a cradle on the crane boat (faster transit back to port) or else on a cradle moved onto the barge.

The actual stage seems unlikely to tip over. It is a 140+ feet tall, but it is almost all empty tank, except for the engines and legs at the bottom. Center of gravity is very low, and the legs extend out 60 feet, so it should be fairly stable from tipping. Sliding is a bigger concern, since whatever the barges surface is made of, it is likely very durable since a rocket is landing under power on top of it. Throttled down Merlin, say 70% of 165Kbs thrust is on the order of 115 KLbs thrust. That will melt many things that be considered non-slip. Thus securing it in wave action will be critical, whether that is standing up, or on its side.

After the first two landings, the evidence seems to be two steps taken. Once landed, the crew comes in via boat. They use airplane jacks, and mount then under the engines, and lift the stage on them. They weld the jacks to deck to secure them, wherever the stage lands.

Then they weld caps over the tips of the legs as well to hold it in place.

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    $\begingroup$ Shouldn't they refill the rocket and fly it to the next launch site? Transporting a rocket on a barge is as tragic as a bird in a cage. It is a rocket, it can fly. $\endgroup$ – LocalFluff Dec 17 '14 at 4:06
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    $\begingroup$ @LocalFluff: No, it can't. Without the upper stage its aerodynamics only allow it to fly backwards. $\endgroup$ – Joshua May 9 '16 at 19:38

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