Harsh conditions and rough terrain combine to make resupplying the National Science Foundation’s (NSF’s) polar research stations a difficult and expensive task. Historically, ski-equipped aircraft annually delivered all fuel and cargo to NSF’s inland research stations. Since 2002, however, researchers at ERDC’s Cold Regions Research and Engineering Laboratory (CRREL) have helped NSF to develop polar traverses, consisting of tractor-sled trains, as viable alternatives in both Antarctica and Greenland. In particular, we have developed lightweight, high-efficiency fuel sleds that greatly increase the amount of fuel delivered compared to traditional sleds and enable large cost savings and emissions reductions compared with air transport.
These lightweight sleds consist of commercially available flexible fuel bladders strapped to extruded sheets of polyethylene plastic. Bladder sleds are one-tenth the weight and one-sixth the cost of comparable steel sleds. Typically, two 3000 gal. fuel bladders are strapped to each 8 ft wide x 68 ft long x 0.5 in. thick sheet of high molecular weight polyethylene (HMW-PE). A 60,000 lb rubber-track tractor can tow 8–16 bladders in a train using a combination of steel spreaders and tow ropes.
Because good over-snow mobility translates to economic payback for polar traverses, CRREL researchers instrumented and exhaustively field-tested bladder sleds during their development. The high efficiency of bladder sleds derives from several factors:
- Low tare weight allows higher payload weight per sled.
- Low and uniform ground pressure eliminates towing resistance from snow deformation.
- Long length enhances frictional heating to lubricate the sled–snow interface and thereby decrease sliding friction.
Based on CRREL’s recommendations, polar traverses in Antarctica and Greenland switched from off-the-shelf tan bladders to custom-ordered black bladders. During the long days of polar summers, black bladders warm the fuel and reduce sliding friction even further.
NSF has used bladder sleds to transport fuel to its polar research stations since 2008. An economic analysis of three seasons’ of deliveries to South Pole (2008–11) showed that traverse operations offset an average of 30 annual aircraft flights for cost savings of $2.0M/year. Based on this success, NSF expanded its South Pole Traverse to two fleets of eight tractor-sled trains, which together are able to conduct three round trips to South Pole each season and deliver over half of the station’s total resupply needs. Essentially all of the traverse-delivered payload to South Pole is fuel transported in bladder sleds.
Besides saving money, South Pole Traverse consumes one-fourth the fuel and emits less than 1% of the air pollutants compared with aircraft delivery of the same payload. NSF’s smaller (four-tractor) fleet in Greenland resupplies Summit Station with both fuel and rigid cargo at comparable cost to aircraft delivery, but it also achieves large fuel savings and emissions reductions. Both the Antarctic and Greenland traverses free up valuable ski-equipped aircraft to support deep-field science missions rather than routine station resupply.
Bladder sleds are essential to the success of both the Greenland and Antarctica resupply traverses, traveling out-bound distances of 740 and 1050 miles, respectively, across unprepared snow. Their cumulative mileage now exceeds 750,000, and despite low temperatures and rough snow conditions, no bladder ruptures have occurred. Nevertheless, these sleds are new technologies and apply plastics and polymer-coated fabrics at temperatures well below their customary range. CRREL researchers have thus guided improvements in materials and procedures to improve durability. Specifically, we conducted low-temperature flex-durability tests on bladder fabrics and recommended unfolded over-winter storage of bladders, which has largely eliminated fabric cracks that otherwise required time-consuming repairs. We continue to conduct tensile tests to screen manufacturer HMW-PE formulations for acceptable low-temperature ductility; this has significantly reduced cracks and splits on the underlying HMW-PE sheets.
Building on the success of bladder sleds, CRREL researchers have designed lightweight cargo sleds capable of transporting rigid cargo with similar efficiency as fuel. Both the Greenland and Antarctic traverses have deployed these sleds, which can readily transport prefabricated buildings and oversized science cargo that would be impossible to deliver by aircraft. Collectively, lightweight fuel and cargo sleds have revolutionized resupply operations for NSF’s polar research stations.
Weale, J. C., J. H. Lever, and J. Trovillion. 2015. High Performance Plastic Sled Design for Polar Traversing. ERDC/CRREL TR-15-2. Hanover, NH: U.S. Army Engineer Research and Development Center.
Lever, J. H., J. C. Weale, and G. Durell. 2014. Low-Temperature Flex Durability of Fabrics for Polar Sleds. ERDC/CRREL TR-14-24. Hanover, NH: U.S. Army Engineer Research and Development Center.
Lever, J. H., and P. Thur. 2014. Economic analysis of the South Pole Traverse. ERDC/CRREL TR-14-7. Hanover, NH: U.S. Army Engineer Research and Development Center.
Lever, J. H., and J. C. Weale. 2012. High efficiency fuel sleds for polar traverses. Journal of Terramechanics 49 (3–4): 207–213.
Weale, J., and J. H. Lever. 2008. Innovations in over-snow cargo transport. Cold Regions Science and Technology 52:166–176.
ERDC Points of Contact
Questions about polar traverse technology?
Contact: James Lever, Jason Weale, Janet Hardy
Email: James.Lever@erdc.dren.mil, firstname.lastname@example.org, Janet.P.Hardy@usace.army.mil