17 November 2008
Stacy Writing

I felt it was necessary to include this picture for balance from my last post – this is DJ and Marco in their usual attitude during a science dive.

Having done our helicopter reconnaissance of Heald Island, we know what we are up against for our exploration under the permanent Ross Ice Shelf.  The water depth is 189 m, or 623 ft.  The thinnest part of the ice in the middle of the crack is 110 cm (4 ft) thick.  There is a layer of fresh water overlying the seawater, and it is under positive pressure from the weight of the ice shelf and glaciers, so we have to be cautious we do not flood our working area.  We can get VHF radio communications with McMurdo by walking just a short distance up onto the wall of the barranca, and Iridium comms even from the floor.

Bob establishing communications to McMurdo from Heald Island.

So this morning we made a list of what we need to achieve to move from our operations at Cape Armitage, where we were diving in 110 m (363 ft) of water, to the Heald Island site.  The vehicle has a pressure capability of 303 m  (1000 ft) but the tether length we have been working with is 150 m (500 ft).  Even at that length, the tether influences the steering of the vehicle quite a bit, especially when the currents are high – in fact, at the full moon, when tidal currents were maximum, we found that we could not operate during peak flow.  So we will be shifting to not only a longer tether, but also one that has a clump weight.  This is a heavy weight that pulls the tether straight down from the surface, and then has a shorter free tether length that gives you a working radius without having to drag around all the tether from the surface.  Which is all a long way of saying that we spent the morning getting the new system set up.  We will test one component at a time, starting with the longer tether.

A schematic of how a clump weight works. Instead of the Thompson, we have the sea ice, instead of Medea we have a “dumb weight” with no electronics, and instead of Jason we have SCINI!

In the late afternoon we set out to test a 240 m (800 ft) tether.  We were also conducting our first mission out of our mobile command center – the darkened back of the Pisten Bully.  Of course the whole thing starts with drilling the holes, during which I lost another bet with DJ on how thick the ice and snow was.  If you remember, at our Cape Armitage site the ice was 7-10 m (23-32 ft) thick, which caused great problems for drilling.  But at our new site, which is further offshore to reach the deeper depths, the ice was only 3 m (10 ft) thick!  This made for much easier drilling, and once we had the main hole drilled, DJ and Marco started setting up the command center while Cameo and I drilled the last navigation hole.

Drilling holes – again. We are very happy to have 3 m of ice to go through instead of 7!

Then we ran into some “issues.”  The tether mating system for the long tether was not set up correctly, so it took some creative knot work to make it safe.  But worse, we could not get communication between the vehicle, the navigation system and the surface to all work at the same time.  After some time trouble shooting, we triaged and decided to dive the vehicle without navigation, as our primary purpose was to test vehicle depth capability, for which we did not require navigation.

SCINI going in for the depth record.

Finally SCINI flew into the depths.  Cameo and I were outside managing the tether, and DJ and Marco were in their little dark box.  It was very exciting when we heard DJ yell “New Depth Record” as we passed our previous depth record of 114 m (375 ft) and then there was only a short time of quiet before we heard “Get in here, we’re on bottom!”  Unfortunately by the time the “outside team” had tied off the tether safely we had lost bottom contact, so Cameo and I did not get to see it directly, but that’s the good thing about an ROV, we got to review the imagery later!  There were large rosselid sponges and seastars, though not in as high density as in shallower.  We reached a maximum depth of 206 m (680 ft) and I am looking forward to seeing more at that depth range!

These twists in the tether are called hockles, and can cause real problems when pulled tight as they kink the tether and can damage communications. DJ wanted to be sure that his co-workers know that he told us there would be a hockling problem, but that I made him dive anyway. I knew he was right, so I did not lose yet another bet, but the purpose of the dive was simply to test the depth capabilities, and we never pulled too tight on the tether.

Our new depth record was very illuminating.  It proved that we cannot work at those depths without a clump weight, but that the system is functional.  We have some further trouble shooting to do to figure out why we could not get both navigation and vehicle control running at the same time over the longer tether.  Most important, we all came back safe AND it was before midnight!

A sundog is a rainbow that forms on either side of the sun, an effect of ice crystals in the atmosphere.

I hope you get to bed early tonight!
Smiles, Stacy

PS. We will be on the Today Show for about 5 minutes ay 8:11 am tomorrow morning!