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If the sea is still enough to land, it's still enough to take time securing. The previous stage was secured by tying down the thrust structure ("octaweb") to t
by andygates 10y ago
If the sea is still enough to land, it's still enough to take time securing. The previous stage was secured by tying down the thrust structure ("octaweb") to tack-welded fixings on the deck with hoofing big chains. There may also have been shoes, we couldn't see clearly.
Tack-welding fixtures to a steel deck is apparently SOP in big shipping, so it's not as radical as it sounds.
- gizmo 10y agoSecuring is purely a safety precaution, it's not actually required. https://twitter.com/elonmusk/status/726218218109444096 https://twitter.com/elonmusk/status/726218218109444096
- sandworm101 10y agoWith respect to Musk, that is total bunk. Any structure like this will have to be secured to the deck. The fact that it is a rocket doesn't matter. He may think that it is safe from falling over, but the insurance company and/or the health and safety people will tell him that cargo that tall needs to be secured. Ropes, chains, welding ... it cannot just sit there. A Volvo station wagon, on that deck at sea, would be tied. A box of onions would at least be secured so that it doesn't shift onto someone's foot. Boats move, cargo cannot.
- d_theorist 10y agoSomehow I suspect they have run the numbers.
- sandworm101 10y agoWhat numbers? Unsecured cargo is unsecured cargo. A metal object sitting on a flat metal deck gets tied/braced/chained.
- d_theorist 10y agoI think you're trying to apply rules designed to govern shipping in general to a very specialised and controlled situation.
- stcredzero 10y agoA lot of rules around shipping actually have to do with physics. See my other comment. Shifting cargo can be very bad news. It has caused a lot of deaths. It's probably not a big deal in this case, except that booster is worth about (I'm guessing) 20 million dollars, SpaceX's cost? It's tall, but the center of gravity is low and it's on a barge. Engineering is conservative "just in case." So are a lot of practical activities that happen on the sea. In neither case, is this irrational or a waste of time.
- sylvinus 10y agoThey mentioned multiple times that because the stage is empty, its center of gravity is much lower than what you'd expect.
- fixermark 10y agoBy whom? The drone ship has no on-board crew. ... which means there's nobody around to be injured or killed if the rocket falls post-landing. Maybe it's a precaution worth taking when they intend these stages for commercial re-use; for now, the whole thing is one big experiment.
- skykooler 10y agoThere is a ship a few miles away with engineers on it. Once the stage has vented all excess liquid oxygen and is safe to approach, they can return to the ASDS and secure it.
- andygates 10y agoThey will of course have modelled the cargo scenario, and I suspect that Musk means that it's nice and stable when they do that -- but then shipping norms come into play because, like you say, unsecured cargo is unsecured cargo. It needs to be both stable and secured, because only one is inviting woe.
- SEJeff 10y agoI suspect he is in a unique situation to know the numbers for this much better than you do, because he runs the company that has successfully done this. Bonus points that the overwhelming majority of ships lack the giant oil rig thrusters that all of the ASDS armada contain to keep them as stable as feasible and prevent listing too much in normal ocean condiditons.
- ncallaway 10y agoHence the phrase "purely a safety precaution"
- stcredzero 10y agoCargo shifting is a big deal. The yearly casualty rate for Bering Sea crab fishing used to be over 1% per year, because the shifting weight of crab pots on overloaded vessels in heavy seas. I saw a training film when I was aboard a tender boat in Alaska. Those boats could look fine one minute then capsize and be as good as sunk in the next 2. Shifting weight on vessels has and does cause rapid capsizing and deaths at sea.
- mikeash 10y agoThis is pretty light cargo relative to the weight of the ship. It's a few tons of rocket and thousands of tons of ship. I don't think it's going to matter to the ship if it shifts, the only risk is losing the rocket over the side.
- stcredzero 10y agoWhat you say is True. My comment explains why the shipping industry and regulatory bodies seem paranoid about shifting weights at sea. There are good reasons to be conservative about certain things and brook no exceptions.
- elif 10y agoIt is amusing that you insist your speculation about something you've never done is more valuable than the experience of someone that has pioneered it.
- sandworm101 10y agoYa, because SpaceX is the only company to have ever transported something on the deck of the ship. It was a rocket until the moment it landed. Now it's cargo.
- Inconel 10y agoThis isn't my area of expertise and what you've said certainly makes sense, however from my understanding ship-to-ship, or in this case ship-to-barge, boardings at sea aren't without their own inherent risks. It could be that having the first stage untethered is deemed less risky to personnel than having a team of welders board the barge and tie it down.
- nkurz 10y agoIf they don't need it, they don't need it, but I wonder if there would be any other way do the secure the rocket without requiring welders to board the barge. Coat the deck with solder and put heaters in the feet to attach? A robotic Roomba-style welder? Giant arms that rise up to clasp the rocket regardless of the exact landing position? Fun to think about...
- dmihal 10y agoMaybe something with magnets?
- sandworm101 10y agoThe key is movement. Doing something like moving objects from one ship to another is pretty standard, but only in good conditions and normally not when the ship is moving. The rocket may well be safe to stand on the ship at the moment it lands. The conditions at that moment are good enough to make the choice to do the move. Once it is on the ship, that choice is over. Conditions change, most dramatically in that the stationary ship is going to drive away to port. Not bringing the object aboard is no longer an option, as it was prior to the rocket landing. Under those conditions the cargo has to be secured not against current conditions, but against all possible conditions.
- _kst_ 10y agoBefore it landed, the most likely scenario was that the rocket was going to crash into the deck and be destroyed. (That's happened several times before.) If they can deal with that, they can deal with the rocket landing safely and then falling over.
- rblatz 10y agoThey can until it gets to a busy port with other ships and people around. Then it becomes a huge safety issue.
- _kst_ 10y agoCopying my other comment: Apparently they do secure to the deck after landing. Discussed here: http://space.stackexchange.com/q/6403/574 http://space.stackexchange.com/q/6403/574