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April 11, 2010

GrIT Details: Sled Mobility Tests

GrIT Details: Sled Mobility Tests

Meanwhile, Back at the Transition . . .

Unloading the first of two 60-ft sleds to be used for mobility tests. Looking south to the icecap, the pointed hill on the skyline is the ramp. Photo: Robin Davies

Unloading the first of two 60-ft sleds. Looking south to the icecap, the pointed hill on the skyline is the ramp. Photo: Robin Davies

While the SCAT (Strategic Crevasse Avoidance Team) chugs slowly across the first leg of the traverse route to Summit looking for hidden hazards, back at Thule Air Base, a set of experiments will soon begin. The goal: to discover how to maximize operational efficiency at the sled level. CRREL’s Jim Lever, who is running the technical side of this effort, collaborated with PFS’ Allen Cornelison to provide the following background on sled mobility tests, which will begin out at the transition later in the week.

We want to reduce the over-snow sliding friction of the fuel-bladder sleds to increase the payload GrIT can tow to Summit. Sled temperature plays a dominant role: the warmer the sled the lower the sliding friction. Warming the sleds is a challenge at the low temperatures encountered on the Greenland ice sheet, and we will try two approaches.

1. One sled will have black covers over the two fuel bladders to absorb the sun’s energy to help warm the fuel and consequently the sled. The image below shows this sled with the rear 3,000-gallon bladder partially filled. This passive heating is simple and inexpensive and should work well during the long daylight hours when skies are clear.

A sled with two fuel bladders covered in back material waits at the transition. The ramp can be seen behind the truck. Photo: Jim Lever

2. The other sled will have electric heating blankets under its two bladders. The image below shows it being assembled prior to transport to the ice edge. The four blankets are rated at 1,700 watts each and will be connected to a 15,000 watt diesel-powered generator. The generator is over-sized to accommodate reduced power output at high altitude (up to 10,000 ft) expected along the route.

Jim Lever prepares the second prototype sled in the warehouse at Thule. Photo: Allen Cornelison

Each sled contains 46 thermocouples to measure the sled-snow interface temperature along its length (you can see them disappear under the heating blankets in the picture above). Other sensors will measure towing forces, air and bladder temperatures, solar insolation (how much energy is available from the sun), travel speed and altitude. A datalogger stores all these data until Jim downloads them to his computer for analysis.

If all goes well, we will learn how to build the next generation of sleds to increase the efficiency and hence payback of GrIT for fuel and cargo delivery to Summit.

The Greenland Inland Traverse is funded by the National Science Foundation (NSF). CH2M HILL Polar Services and Cold Regions Research and Engineering Laboratories are working together with the NSF to develop the traverse infrastructure and route. The 2010 spring traverse has several foci: find a safe overland route to Summit Station to help reduce logistical costs and environmental impacts of conducting research there; provide a research platform for scientists conducting field work in Greenland; optimize mobility by focusing on the sled/snow interface. For more field notes coverage of GrIT, click here.

GrIT contact:
Jay Burnside, Polar Field Services, CH2M HILL Polar Services
Construction/Operations manager
Jay at

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