Research Vehicle Reaches the Bottom of the Ocean

timothy found BBC coverage of the voyage of the Nereus, which on May 31 dove to the bottom of the Challenger Deep in the Marianas Trench. Only two vehicles have accomplished this feat before, the last 11 years ago. "The unmanned vehicle is remotely operated by pilots aboard a surface ship via a lightweight tether. Its thin, fibre-optic tether to the research vessel Kilo Moana allows the submersible to make deep dives and be highly manoeuvrable. Nereus can also be switched into a free-swimming, autonomous vehicle. ... The Challenger Deep... is the deepest abyss on Earth at 11,000m-deep, more than 2km (1.2 miles) deeper than Mount Everest is high. At that depth, pressures reach 1,100 times those at the surface."

Comments

Are you ready kids?

[Anonymous Coward]

Aye aye, Captain!

Re:I wonder if my great^8 grandkids

[sgbett]

I'm impressed with the two guys who did it *manned* in the 60s

from tfa :

In January 1960, Jacques Piccard and Don Walsh made the first and only manned voyage in a Swiss-built bathyscaphe known as the Trieste.
The vessel consisted of a 2m-diameter (6ft) steel sphere containing the crew suspended below a huge 15m-long (50ft) tank of petrol, designed to provide buoyancy.
During the nine-hour mission, the two men spent just 20 minutes on the ocean floor; enough time to measure the depth as 10,916m (35,813 ft).

Cable? Why?

[Lord Byron II]

Somebody smarter than myself, please comment on why we need a cable over a distance of 11km? There's a ton of off-the-shelf radio equipment that can easily handle that distance with very high bitrates.

I can imagine two possible problems:

First, the ocean might simply be good at blocking transmissions.

Second, the varying pressures and temperatures might distort a signal to the point where it is unusable. I'm referring to dielectric effects and the fact that the dielectric constant would not be constant in this sort of operation. But would it be "constant-enough"?

Re:Cable? Why?

[commlinx]

First, the ocean might simply be good at blocking transmissions.

Yes salt water is very good at attenuating RF, the higher the frequency the worse it is. Have a look at http://en.wikipedia.org/wiki/Extremely_low_frequency on Wikipedia that highlights some of the difficulties, especially in relation to antenna size. Also at those frequencies you can end up with transmission rates less than one bit per second.

Re:Cable? Why?

[ssimmons]

... the ocean might simply be good at blocking transmissions.

The ocean isn't just good at blocking transmissions. It's ridiculously good at blocking radio waves. If you work the math on this page, you can see that your basic WiFi transmission (at 2.4 GHz) will experience an attenuation of almost 1700 dB/meter! At that rate you'd get far less than a millimeter of penetration.

Even the lowest frequency short wave bands (1.8 MHz) get 46 dB/meter attenuation. It starts to get possible to receive RF when you get down in the kHz range but of course, your data rate goes to hell.

For underwater communications under a couple hundred meters or so you can use an acoustic modem. Even then, your best data rate is going to be on the order 2400 baud or less.

If you want high speed underwater communications, you gotta use a cable.

Re:how hard can it be?

[Anonymous Coward]

Uhh. those solid state components you're thinking of tend to have voids in them, e.g. what's under that lid on the CPU.. a bare die and a bunch o' bond wires. Squish city at 1000 Atm.

What about wires? More than enough pressure to push water through the wire using the insulation as a tube.

It is REALLY, REALLY hard to design stuff to work at 1000Atm. What do you use for bouyancy? (Trieste used gasoline.. a liquid that is about the same compressibility as water) Syntactic foam with silica microspheres is fairly popular, because the tiny hollow spheres are pretty strong.

Interestingly, it's harder to design something that won't crush than something that won't explode. That is, building a compressed gas tank to hold 20,000 psi is easier than building one that won't crush under 20,000 psi.

Re:I wonder if my great^8 grandkids

[The_mad_linguist]

That's why I'd do it at night.

Re:how hard can it be?

[squoozer]

You seem to know a bit about submarines so perhaps you could answer a question that has puzzled me. If you build a submarine like an onion with a hull inside a hull and put pressurized water / air between the two hulls to half the outside pressure would each hull then only need to be strong enough to resist half the external pressure?

I can't see the flaw but it feels wrong because it seems to imply that it would be at least theoretically possible to build a submarine out of sheets of tin-foil as long as there were enough layers and the pressure could be maintained accurately enough.