by clicking on the page. A slider will appear, allowing you to adjust your zoom level. Return to the original size by clicking on the page again.
the page around when zoomed in by dragging it.
the zoom using the slider on the top right.
by clicking on the zoomed-in page.
by entering text in the search field and click on "In This Issue" or "All Issues" to search the current issue or the archive of back issues respectively.
by clicking on thumbnails to select pages, and then press the print button.
this publication and page.
displays a table of sections with thumbnails and descriptions.
displays thumbnails of every page in the issue. Click on a page to jump.
allows you to browse through every available issue.
GCN : December 2012
24 GCN DECEMBER 2012 • GCN.COM CASE STUDY see how ice forming on the vehicle might harm it, but everything worked out fine." Even so, the two bots that NOAA used were modified slightly for the mission. Batteries don't perform as well in cold environments, and the 90 percent cloud cover also concerned Meinig, who has a lot of experience with the Arctic weather. "We added a supplemental lithium-ion battery pack with a 1,200-watt-hour ca- pacity into one of the bays," he explained. "If the Wave Glider couldn't charge, the extra batteries had enough power to run the instruments for 15 days." For scientific readings, six Therm Ar- ray thermistors from RTS Instruments of Maple Ridge, Canada, were molded into the tether that connects the float with the submarine, to record temperature at various depths. There isn't a lot that can be done about the pingos and the hazards of floating Arctic ice, but a camera was mounted at the rear of the craft and tied into the Iridium modem. The slow modem con- nection would not be quick enough to help much with navigation, but at least it would let users look around to see what was wrong if the Wave Glider suddenly stopped moving. In the end, the crafts didn't get hung up on any ice, but Meinig is sure they en- countered some. "They came back with some scratches," he said. "But it didn't hinder the mission." HIGH SCIENCE, LOW MAINTENANCE Meinig explained that this first mis- sion with the robots was half science, hence the temperature readings, and half proof of concept, to see if it could be done. "Our focus is how we best provide high-quality, low-cost ocean observing systems for research and operations," Meinig said. "We're constantly working towards that goal." On the low-cost side of the equation, NOAA leased a small vessel and sent only two employees to launch the Wave Glid- ers at Prudhoe Bay, Alaska. The same team was tasked with retrieving them at the end of their two-month journey. For the scientific part of the mission, the robots followed each other at 12- hour intervals. So if one robot took read- ings at noon, the second would take the same sample at midnight. This allowed study of diurnal heating effects. "We held one on station to see if it could stay in place, while the second swam away," Meinig said. "They both performed well overall." Not everything went perfectly, howev- er. In the open ocean with more wave ac- tion, a Wave Glider can make about 1.5 knots. Closer to shore it slows to about 1 knot, but can almost always maintain speed, 24 hours per day. Because of the Arctic's calm seas, the Wave Gliders were sometimes reduced in speed to .25 knots. At one point, they were pushed off course for a couple days because of strong currents that overcame the wave-action power of the glider's motion engine. But over- all, they performed well in the extreme conditions. The science side of the mission was also a success. Both robots stayed in the Arctic for two months and between them, they took over 900,000 tempera- ture readings, the most ever in a survey of that part of the world. Meinig said the scientific results, the low cost of the mis- sion and the performance of the robots were impressive. Even though this mission only re- corded temperature and telemetry, he said there were many other factors that could be recorded by different instru- ments using the Wave Gliders in the fu- ture. "We certainly plan on doing more with them now that we know we have an unmanned vehicle that can be launched and later recovered inexpensively by two people in a small boat," he said. That's a big achievement for a robot that began as a tiny model floating in a fish tank at Liquid Robotics headquar- ters in California. Today it is swimming the world's oceans from the Pacific to the Arctic, operating at lower costs to the public and taking hard-to-get read- ings that one day might help preserve the planet. • Each Wave Glider is built around a surfboard-like float that contains all the instrumentation needed for scientific experiments, plus the intel- ligence needed to keep the vessel on course or to change direction. Two solar panels keep seven lithium-ion batteries charged in sequence, so that the topside instruments can be provided with six amps of continuous, 12-volt power. But the craft doesn't need power to move. Seven meters below the surface, a submersible craft is towed with the float. As waves lift up the craft, fins on the submarine portion direct the water behind the vessel, somewhat the way airplane wings provide lift. When the Wave Glider comes back down a wave, the fins are pushed to rotate in the opposite direction as the sub sinks. So the robot gets propulsion thrust almost constantly with no outside power needed, other than to move the rudder for steering. Two payload bays store electronic gear for each mission in dry boxes designed to keep out corrosive sea water. Each box can hold about 25 pounds of gear. Onboard navigation is handled by a simple 8-bit proces- sor that knows about 20 commands, mostly for turning or otherwise navi- gating the ship remotely. Commands can be sent to a Wave Glider through an Iridium Communications satellite modem. And the vessel keeps track of its position on a GPS receiver, which can track and navigate through up to 255 preprogrammed waypoints for long journeys, self-correcting to keep a true course. The mission sensors are driven by an ARM Processor running an embed- ded version of Linux. Most of the time, the processor payloads are given their own Iridium Satellite modem so that some people on land can manage the sensors while others can concentrate on steering the Wave Glider, and the two systems don't compete for limited bandwidth.