Oct 09 01 |
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Jon asked what Autosub was actually for, and since we haven’t really done anything for the past two days as we head south, I thought I’d fill in a few details.
Autosub is an autonomous underwater vehicle capable of descending to depths of up to 6km. It’s primarily used for underwater mapping and surveying. For example, in March it will be heading down to the Caribbean to look for ‘black smokers’, underwater hot springs on the sea bottom that provide the energy source for unique ecosystems that only live at great depths. It has a multibeam echosounder that it uses to map the bottom, and can be fitted with lots of different science instruments including conductivity-temperature-density (CTD) sensors that can detect the fresh water that comes out of the black smokers to help find them. The CTD sensors are the ones on the sides in the picture, with the tubes hanging out of them.
Autosub's front end, where all the science instruments live. The plastic hoses on the side are for the conductivity-temperature-density sensor used to find black smokers.
The cruise I’m on is an engineering cruise, so we’re not expecting to do any science. The purpose is to put Autosub through its paces, tryout some new equipment (the obstacle avoidance system), and test it to the depths it’ll be used at in March. As a result, we’re looking for a spot that’s close to 6km deep to really give it a thorough test. The original cruise plan is in the picture. We’ve modified it quite a bit already – we skipped one of the early stops and pressed on south, and potentially bad weather has kept us closer to Spain than originally planned so we’re now heading for a point somewhere west of Gibraltar with about 5600m of water to do the deep tests. After that, we’ll (hopefully) go to the last point on the plan, the Casablanca Seamount for some final tests before arriving in Tenerife.
The cruise plan. We've already changed almost everything about it!
The Autosub team have spent the last day and a half doing maintenance on the batteries for the sub. The picture shows one of the batteries being fitted into the sub. The batteries are pretty cool – there are hundreds of small lithium cells in that case, all completely surrounded by oil so that they aren’t crushed by the enormous pressure at depth. The front of each battery case is a flexible diaphragm so that there’s no pressure differential between the inside and the outside.
James and Maaten install one of the batteries. They're heavy!
Sorry. That was a bit too heavy for the blog. Hopefully tomorrow I’ll have something more exciting to write about – if everything goes to plan one of the other teams on-board will be deploying their remotely operated vehicle tomorrow afternoon and driving it gently across the ocean bottom. Their’s comes with live video, so we’ll see what 6km down actually looks like.
Article Series - RSS Discovery
- First Day on RSS Discovery
- Sending Autosub for a swim
- What we’re doing in the middle of the Atlantic
- Meet Hybis
- Field Robotics is Hard!
- A Record Dive!
- Pictures from the deep
- What you’ve been waiting for… Cake!
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14 Responses to “What we’re doing in the middle of the Atlantic”
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Wow, that’s proper science!
So, what happens if you loose contact/control of autosub? Is there some kind of failsafe surfacing mechanism? It sounds like an expensive machine to simply loose at the bottom of the Atlantic! What about batteries, if they go flat, is there a redundant backup?
… and then I thought some more …
How do you control buoyancy at those depths anyway? Is it controlled with a simple ballast tank? At that depth you’re gonna need a lot of compressed air to force the water out of the tank; a factor of 600! So if that is how it works, how do you store such mega high pressure air at sea level?
We haven’t even got on to the “science” yet…
How does a CTD work? Is it simply a variation in the conductivity of salt water versus fresh as the name suggests?
And what of the collision avoidance?
So many questions! A by product of an interesting series I guess!
Thanks for the interesting write-up. Your comments about the battery being in an oil filled chamber with a pressure equalisation diaphragm lead me to think that the Lithium cells are exposed to ambient pressure at depth (as Pete says, about 600 bar). Are standard (but void free) Lithium cells happy with this or are the cells used specially cased for this application? I guess I am asking if the ambient pressure is allowed to act on the chemically active areas of the cells?
I heard part of a radio show last night about that ship, the Arctic Sea, that went missing in July/August and then was found in mysterious circumstances. Some confusion as to whether the pirates were really eco warriors, or arms dealers
I found this link http://www.guardian.co.uk/world/2009/sep/24/arctic-sea-russia-pirates.
Anyway, the moral of the story is, don’t pick up any strangers!!!
We had a security drill this morning where this was discussed. Apparently we’re obliged to pick up boat people if we find any in distress. There’s some suspicion of pirate activity south of Tenerife, but we’re not planning to go there. We did an exercise where we searched the ship for suspicious packages, so they’re clearly taking this stuff seriously.
Somehow I don’t think they were eco warriors
Lots of questions. Right…
The sub is positively buoyant, so it should come back up if the propellor stops. Also, it has abort weights that are triggered if things go wrong. Once those are dropped, it’s even more buoyant.
The buoyancy is due to air in the sealed pressure vessels for the electronics, plus syntactic foam, which is basically loads of tiny hollow glass spheres. They can resist that pressure, and none of the air compresses, so the buoyancy stays constant at depth.
I have no idea how the CTD works – you’ll have to google that one. Collision avoidance is new on this cruise – in the past they haven’t had any. It’s a forward pointing scanning sonar (the round bit at the front in hte picture, with the blue string around it) that is supposed to follow the horizon (normally the seabed at the limit of range of the sonar), If an obstacle appears the horizon goes up so the sub noses up to avoid it. That’s the theory, although Maaten’s currently sitting behind me working on the code.
The batteries are pretty standard lithium gel-filled batteries. They have had a few issues with them – if the outside is punctured, the electrolyte oozes slowly out (that’s what they’ve been fixing during the maintenance), but as far as I know, that isn’t due to the pressure. The older subs had to have the batteries in a pressure vessel – this is the new technology.
I saw a TV program once about the black smokers – the weird creatures that live in/around them are – weird! They seem to live on sulphur, which is usually poisonous. When you see some of the very strange creatures who live on this planet without oxygen, it does make you wonder what might be ‘out there’ in Space….
Hey Richard, thanks for that – keep us all posted, it’s great! Can’t quite get my head ’round the constant bouyancy thing though. Presumably each of the tiny glass beads in the syntactic foam is a pressure vessel itself, so they stay constant, but how are they held within a matrix, presumably this has to be ambient?
Nothing’s too heavy for this blog, though as a civil engineer I’m keen to see the concrete version of autosub…
Reinforced concrete and the sea get along so well together 
I wonder if Colin wants a mini-version for the far reaches of Grey Wife Hole?! Kind of defaets the object of cave diving though I guess?
ROWs have already been used in some sites, sometimes the depth of a sump can make them the best option. Do things this way in no way defeats the object of cave diving which is to find out where the passage goes without buying the farm. Miniaturisation and the sort changes in the technology Richard is posting about will make them more suitable for cave work. When they are smaller than a diver they will be used to explore places humans cannot fit into – but only once the cost has come down
Maybe you can get Richard to half inch a few ‘spare parts’?!
Fascinating blog, keep it up!
Hmmm… Now this is getting beyond my knowledge. The matrix is just resin (I think), so it doesn’t necessarily provide any bouyancy itself. In any case, it’s uncompressable (or compression is negligible), so any buoyancy is due to the fact that the material itself is less dense than water.
If that explanation doesn’t make sense, it’s probably because I don’t know what I’m talking about!
This sort of foam is used to weight stage cylinders and scooters (usually strapped on by snoopyloops, cable ties or gas tape). It behaves as you say by maintaining a consistent displacement irrespective of depth. I didn’t know it could go to 6000 m though…