Rachel and Mike in Australia

It is not often that we scientist/engineer types see our names in lights or have the sense that more than a handful of academics have any interest in what we do.  Mike was recently the part of quite an exception to that!  While working at Johns Hopkins, Mike worked on a new underwater robot named Nereus.  Nereus’ name was selected from a competition of high school and college students after the Greek god who can change shapes, which is appropriate for this robot that can be configured so that is either is connected to the surface ship by a tether and driven with a joy sick or is thrown over board without a tether and trusted to run a pre-programmed mission and reappear at the surface ~24 hours later.

What makes Nereus unique is its capability to explore the entire ocean.  There are a number of underwater robots in operation that can dive to about 6,000 m (~4 miles), which reaches the majority of the sea floor.  But the deepest parts of the ocean are trenches 11,000 m deep (that’s 2,000 m deeper than Everest is high!).  At that depth, the pressure is ~1,000 times higher than at the surface.

Building a vehicle to withstand such enormous pressure is a real challenge.   If you use heavy pressure-resistant materials like titanium, you have to add more flotation so that the vehicle will be buoyant enough to make it back to the surface, so the size of the vehicle gets large fast, limiting what kinds of ships you can deploy it from.  The innovative solution used on Nereus is the use of ceramic spheres for buoyancy—they are light in air, but very strong against the extreme compressive forces of the deep ocean.  Nereus contains about 1500 ceramic spheres (each the size of a grapefruit) to keep its 6,000 lb-self afloat.

Two other vehicles have made it to the deepest part of the ocean, which is located in the Mariana Trench, close to Guam.  In 1960, the Trieste, which was basically a giant 2-person underwater blimp with 22,500 gallons of gasoline used for buoyancy, spent 20 minutes on the ocean floor in the Challenger Deep at ~10,916 m.  An unmanned Japanese robot named Kaiko made it to 10,897 m at the Challenger Deep a few times in the late 1990’s, but it was lost at sea when its cable connecting it to the surface ship broke.  Both the Trieste and Kaiko were extremely expensive, needed special ships to be deployed from, and provided limited ability to explore the seafloor.  Kaiko was powered through its tether to the surface, which meant that the tether needed to be quite large, which resulted in the tether acting like an anchor so that Kaiko could only move within about 200 m of where it landed on the seafloor.  The Nereus engineers wanted to build a versatile robot—one that could explore all parts of the ocean at a moderate cost and from any ship.  Rather than powering the vehicle via the tether, Nereus contains batteries for power and the tether is a lightweight fiber optic that only transmits data back and forth.  If the fiber optic tether breaks, Nereus automatically goes into autonomous untethered mode and heads for the surface.

Because of delays in the Nereus building schedule, its voyage to the Mariana Trench did not occur while Mike was at Johns Hopkins.  Luckily, the Nereus project leads still wanted Mike to be involved in the project, and his fellowship in Australia allowed him the flexibility to participate.

Mike flew to Guam the day before our two-year wedding anniversary to be a part of Nereus’ attempt to reach the Challenger Deep.  The team of engineers working on Nereus are all excellent and had tested Nereus extensively, but even so, the team was nervous.  If one of the ceramic spheres cracked and broke, it could set off a chain reaction and implode the vehicle.  After a few warm-up dives to shallower depths, on May 31st 2009, Nereus dived at the Challenger Deep reaching a bottom depth of 10,902 m.  Nereus cruised around the bottom for 10 hours, sending live video feed up its tether to a very excited set of scientists on board and transversing about 2,800 m along the bottom.  Nereus has a manipulator arm that allowed the scientists to collect samples of mud, rocks, and worms.  Nereus also deposited a marker on the seafloor signed by those on board the ship.  The Challenger Deep didn’t have nearly the charismatic biodiversity of a hydrothermal vent site, but maybe once the sea creatures see what cool people are interested in the site, it’ll become more of a hang out.

The surface media creatures were definitely interested in the event.  News of Nereus’ dive was reported by the BBC, Fox News, Nature News, the Washington Post, and the front page of the Baltimore Sun.  A film crew from the Science Channel was also on board filming what will be a one-hour documentary (or ‘doco’ as they say over here) this fall.  That added an interesting dimension.  Because the crew wanted to be able to splice together recovery and deploying footage from different dives they asked Mike and the rest of the scientists and engineers to wear the same clothes so that it would look as though it was all from the same day.  The doco crew was willing to do the laundry to facilitate the wardrobe trickery, so nobody really seemed to care.  Keep a sharp eye out this fall and see if you can catch any discrepancies!

This entry was posted on Tuesday, June 30th, 2009 at 3:47 am and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.