GrIT Details: Sled Mobility Tests

April 5, 2010

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 polarfield.com

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Into the White, Blue Yonder

August 25, 2009

Crews test sled configurations and towing capability for Greenland Inland Traverse (GrIT) last spring before the opening of Summit Station. Pending funding from the National Science Foundation, a summer 2010 inland traverse will travel from Thule to Summit Station. Photo Jay Burnside

Crews test sled configurations and towing capability for Greenland Inland Traverse (GrIT) last spring before the opening of Summit Station. Pending funding from the National Science Foundation, a summer 2010 inland traverse will travel from Thule to Summit Station. Photo: Jay Burnside

Later this month, after scientists wrap up their field work and a skeleton crew prepares for a Greenland winter, a small staff of Polar Field Services workers will test a caravan of tractors and sleds as part of the Greenland Inland Traverse (GrIT). The traverse follows a route established in 2008 from Thule Air Base to Summit Station.

The crew will base from Thule and will make instrumental changes to sleds designed to be towed over the ice by large tractors in order to improve mobility and efficiency. A successful traverse was completed in 2008, but it was hampered by slow forward movement and unanticipated delays due to equipment sinking into the snow, said Jay Burnside, PFS construction manager.

“We think the problem lies in the thermal properties of the snow-sled interface,” said Burnside. “There is too much surface area, which prevents the formation of a thin layer of water between the sleds and the ice, which makes transportation easier. The strength of the snow in Greenland prevents us from developing enough heat to create that slippery layer. The snow is weaker in Greenland (compared to Antarctica, where there have been successful overland traverses), so you get more contact area, less ground pressure and no heat.”

At least that’s the theory. Burnside and his team will spend several weeks studying the temperature phenomenon and making other changes to the sleds to improve mobility. Specifically they will insulate the fuel bladders in the sleds to avoid “3,000, 000 gallons of cold fuel sucking up the heat.”

The team plans to launch a second traverse in summer 2010 (pending National Science Foundation funding) to deliver a Case tractor to Summit Station. Successfully establishing an overland traverse would create transportation alternatives for supply delivery to research stations in Greenland. Currently, all supplies, including fuel, materials, food, and personnel, arrive via airplanes; instituting a traverse could significantly reduce emissions, prove to be more cost-effective, and open up remote areas for more research.