Antarctic Traverse

Text and pictures © 1997-2024 Guillaume Dargaud
Last updated on 2021/11/05

"Certainly dog driving is the most terrible work one has to face in this sort of business."    — Robert Falcon Scott.

The long trip

Left: Arrival of the sled trains, well lined up on the track. A small wall of snow is build on the downwind side to make the track easier to find. The first Challenger pulls the second one with a thick rope, going exactly the same speed.

What is a Traverse ? There are 2 ways to get equipment and people to Antarctica: either a ship or an airplane. The ship is cheaper but takes at least a week to reach the southern continent from the closest land. It can stay stuck in the sea ice for weeks if the breakup hasn't occurred yet and there are very few convenient harbors in Antarctica. With some work on airstrips, airplanes can land almost everywhere in Antarctica but their operating costs and limited loads make them unsuitable for ferrying large construction equipment. And in addition they cannot operate in poor weather conditions, for this reason most countries reserve them for the transportation of people. Only the americans use airplanes to carry equipment inland, although they've been looking for a better solution for years.

Right: Thick rope used by the free Challenger to pull the others in case of need.

Once equipment has reached the antarctic coast, there's the solution of using a surface traverse to ferry the loads inland. Those sled train are called Traverses. Under the technical direction of Patrice Godon, the french Antarctic program first reached Dome C using surface means in 1993 and has since refined the methods used to the point of becoming experts in the field. The russians have also been using surface traverses since the '50s to restock Vostok, often relying on weird contraptions for their traverses, such as the base structure and engine of military tanks. And the chinese have also recently been successful in their use of surface means to reach Dome A where they plan to build a permanent station.

Left: The tractors lined up for the night. This is to minimize the accumulation of snow between them in case of wind, and also to minimize the length of the electric cables needed to carry power to keep them warm for the night.

The general timescale of a traverse is the following: near the end of the winterover at DdU, a few expedition members head to Prud'homme and D10 to check on the equipment and start removing the accumulated snow. In early november, when the Astrolabe on its first trip reaches about helicopter flying distance, the member of the Traverse team are taken directly to Prud'homme where they start preparing the equipment: opening the underground garage, pulling out the tractors, verifying the sleds prepared at the end of the previous season, etc... After about 10 days, they depart for Dome C, trying to follow the previous year's track, sometimes with great difficulty. No equipment is taken from the ship to the traverse on the first round, simply because there's no guaranty the ship can even reach the coast this early in the season.

Right: The vehicles of the Traverse, snowed up after a stormy night near the coast. A roof hatch is a necessity ! (Photo Katell).

The departure base of the Traverses, Cap Prud'Homme, is in itself a small independent base, being separated from DdU by 5km of sea. Personnel working there is on its own and rarely goes to the main base. It has living quarters, a power station, workshops, large storage areas, fuel tanks and a 500m² underground garage.

Left: Icicles formed on one of the empty trailers.

The Traverse takes 12 to 15 days on the first trip to reach Dome C. Now that the station is operating years round, they just drop their load, pick up a few containers of garbage and cardboard boxes of frozen urine and head back down. In the meanwhile the Astrolabe has unloaded its equipment in Dumont d'Urville where it's been transported to Cap Prud'Homme and then to D-10. When the Traverse gets there, they make necessary repairs to the equipment (used sleds, broken anchors, tired engines...), and do another round trip, usually arriving around New Year. Then a third trip arriving in late January.

Right: Icicles formed on one of the trailers.

Finally when they reach back D-10 in february, another load is prepared for the next year, but all the equipment is then mothballed into an underground garage. Logistical planning must be performed more than a year in advance because of the winter hiatus and the fact that the first traverse starts with sleds prepared 9 months in advance. Overall 400 tons of net weight can be carried every year to Dome C over a total distance of 6720km. The construction of Concordia station required no less than 3300 tons of equipment, so add this to the fact that construction was possible only during the warmest 2 months of the year to explain why it took such a long time.

Left: Vehicles on the last leg of their long journey before reaching Dome C. They are partly hidden by the wall of snow built on the side of the track. The two 'energy' and 'living' modules can be seen towards the end.

As for the logistical organization of a Traverse, there are several sled trains, each pulled by a Challenger Caterpillar with mighty horsepowers. Another Challenger is roaming free, usually backing up the heaviest one, or helping out in case a train gets stuck in soft snow or tips over the edge of the hard-packed trail. In addition to this, a Kassbohrer drives ahead to reckon the trail, cleaning and leveling the trail with a blade, and also building a wall of snow (also known as 'berm') on the side for easier visual recognition of the track later on. One of the trailers contain a power generator for when vehicles are stopped for the night, as well as a workshop and a snow melter to produce water for the crew (the shower and incinolet are in that same 'Energy' module). Another trailer carries the 'living' module: a small kitchen and bunk beds, satellite communication systems, small medical room and an entry airlock. And a third one is the 'storage' module for food, spare parts and medical supplies; about one ton of food and drinks are required for a one month round trip.

Right: Containers of food and construction equipment required for the success of the winterover.

A team of less than 10 people is enough to carry hundreds of tons of net weight up for a thousand kilometers this way. Most members are mechanics, but some are just there to drive. There's often a doctor part of the team but he spends all his time driving, like everyone else, usually 14 hours a day if the weather is good. There's no spare time on a traverse: as soon as the convoy stops for the night, vehicles are lined up, connected to the generator, the melter is filled up, some pre-packaged dinner is heated up and people head for their bunks unless some repairs are necessary before the next leg of the trip. Overall it's common to work 15 to 16 hours a day, even though people often sleep at the wheel: the GPS does the driving and a colleague can wake you up with the radio if you start going off trail !

Left: A Kassbohrer breaking trail ahead of the sled trains. There are two people on board as the work required to control the blade is pretty tiring and drivers need to change every two hours. This vehicle is also in charge of navigation, so the satellite positioning systems and navigating software must be in use at all times.

A typical Traverse has 9~10 people operating 7 tow vehicles and 2 leveling vehicles. There can be up to 10~12 people for 10 vehicles and 40 sleds, but it becomes increasingly difficult to manage, as well as crowded in the living module. The way teams are selected: all members must be able to drive, 4 should be able to level the ground, 2 must know GPS and navigation software, one should be able to use a theodolite for positioning, one should be able to prepare dinners, one must master all the communication equipment (VHF, Inmarsat, Irridium, fax, email), most should be able to perform maintenance on their own train (fueling, cleaning, snow removal...), at least 4 people should be competent mechanics able to repair diesel engines, drive trains, hydraulics, weld, electric systems...

Right: Satellite image showing the russian station of Vostok, coldest place on Earth, where the trail left by the traverse is clearly visible.

Most traverse members come regularly, in particular the mechanics. Others who 'just' have to do the driving can be scientists doing field studies, VIPs, journalists, members in training or volunteers napped from the departure or destination stations. During the day people are actually alone at the wheel, with no one to talk to. The only moments of group activity and relaxation are the 3 daily meals. Recorded radio programs are sometimes broadcast on the VHF radio. Bad weather sometimes blocks progression for several days while everyone is crammed inside the living quarters.

Left: A tipped-over trailer after running out of the trail. (Photo courtesy P. Godon)

As for the vehicles themselves, they were chosen for their reliability, ease of use, adaptability to weather conditions, availability of spare parts in the closest part of the world (Oz and NZ), usability on snow (speed, leveling...), towing capacity, fuel consumption, cost... Beside the Kassbohrer used to level the trail, the Challengers 65x series were chosen to pull the sled trains. They have 320 horse power, a rather low ground pressure making them suitable on snow, weigh 15 tons and tow 40~50 tons at a speed of 7 to 18 km/h (30 km/h unloaded). You lose traction in snow before you can reach the maximum towing capacity of the Challenger. Fuel use is about 6 l/km (about 0.4 mpg) while towing. Fuel tanks are left along the trail on the upper trip in prevision of the return trip so as to save weight; this needs to be carefully optimized in order to not 'run dry', a tragic occurrence that happened once on the Vostok traverse decades ago, leading to the death by starvation of all involved.

Right: Aerial view of Cap Prud'Homme, departure site of the Traverses, at the end of the winter. The frozen sea is at the bottom of the image. Containers and vehicles not hidden in the underground garage are lined up to minimize wind-drift snow accumulation. (Photo courtesy P. Godon)

Destination reached

Left: The Traverse approaching Dome C, visible tens of kms away.

Left: Originally intended as a joke for one of the drivers who had forgotten the key to his Challenger, I see it more symbolically as the Traverse being the key to the existence of Concordia. Or maybe simply the key to the city offered to passing Traverses...

Some modifications were performed on the Challengers to 'winterize' them. For those interested in mechanics, this includes: installing a fuel priming pump, a manhole on the fuel tank, addition of an alternator and a starter motor, addition of heaters in all oil compartments and other areas, addition of a 220V external input for all heaters, addition of a catalytic exhaust, addition of a crane, winch or radar on some vehicles, addition of a roof escape hatch (blown snow can cover the side door completely), change to a double glazed front windshield, installation of heating air pipes in the cabin, sealing the cabin door, better driver seat, removal of unused levers, extra rearview mirrors, addition of GPS and VHF, radio cassette player, removal of traffic lights, addition of a blanket for the front radiator, sealing or insulation of various compartments, replacement of air suspension by elastomer, limitation of the boogies' balance arms, air tires replaced by foam tires...

Right: The vehicles and their trailers lining up in the middle of the plaza, before untying their loads.

As for the sleds, they were invented in prehistoric times and preceded the wheel, so basically in Antarctica we are going back to the basics. There's a small fuel tank sled for use by the traverse vehicles themselves, and several container carrying sleds. A crane is mounted on some of the Challengers to allow the loading and unloading of the containers, which is sometimes necessary on the field in case of mechanical problem or if a sled tips over. Note that if the weight is too important for those small mounted cranes, a pit can be dug, the sled taken in, and the load just pulled from behind onto the level ground. Other sleds carry larger 29m³ fuel tanks for the refueling of Concordia. Fuel is the most transported material on the traverses.

Left: A Challenger Caterpillar, specially modified for Antarctic conditions, parked below Concordia. Originally those are agricultural tractors, but their high power and large ground contact area make them particularly suitable for working on snow.

A more recent invention, tracked trailers are also in use on the traverse. The rubber track offers less friction than even a teflon-coated sled on snow but they have two problems: a higher surface pressure and hardening rubber when the temperature gets below -35°C. The equipment is constantly tested and modified to improve it. In this case another thinner rubber track is now in use. There are designs for self-propelled trailers, using electric engines in the drive trains, with electric power produced by a lead tractors carrying a diesel-electric generator, in a way similar to how many trains work worldwide nowadays.

Right: Sled trains turning around in the 'parking lot' of the Dome C summer camp.

So when operating, a full Traverse is composed typically of: a lead Kassbohrer for navigation and trail leveling; a train of fuel tanks, some of which will be left along the way, this vehicle helping the next one with an elastic rope; a first train called the 'caravan' containing the various habitation and work modules, the earlier it can park and prepare the meals the better; then comes another fuel tank train assisting a train of containers or equipment trailers; then another leveling Kassbohrer followed by other fuel and container trains. Shedding weigh by leaving fuel on the trail allows the convoy to increase its speed from 100km/day on the first day to 120km/day upon reaching Dome C.

Left: Caterpillar tractor parked below Concordia. Although there's never any dark period during the summer campaigns when the Traverses occur, the powerful searchlights are necessary in whiteout conditions.

The distance between D10 (point of departure of the Traverse, a couple km inland from Dumont D'Urville) and Dome C (final destination) is about 1100km. The second half of the trip is performed at high altitude under temperature usually below -25°C, but at least up there the conditions on the tracks are quite stable: the track is easy to find and follow from trip to trip, even after the winter. Not so on the first half of the trip: the terrain is hilly, section have soft snow where the vehicles get stuck, windstorms and poor visibility is frequent. For this reason it is of tantamount importance to be able to always follow the same track, so it gets harder and easier to drive over time. The problem is that on the first Traverse of the spring, the track is no longer visible, covered by the winter snows or erased by the ablative katabatic winds.

Right: Unloading a container from a sled, a delicate operation with the small cranes added to the Challengers

Several methods have been devised but none really work for various reasons: GPS is not precise enough (no DGPS there) as the trail is only a few meters large and if you drive out into the soft snow, you just tip over your load; and furthermore the glacier can move up to 50 meters a year near the coast making a theoretical position useless. Wands take time to place, are not very visible in a whiteout and get destroyed by the fierce winds. It's been thought of laying a metal cable under the snow and just following a metal detector on top, but the Antarctic Treaty forbids this kind of permanent installation. Also tried or thought about were infrared vision (ineffective on snow), ultrasound or radiowave imagery (not currently developed, contact me if you think you can do it). The current solution is very low-tech: rebuild a wall of snow with a bladed first vehicle on the downwind side of the track, hoping that the wall will still be visible on the next trip.

Left: Doing a human chain to transfer packages of frozen food just arrived on the Traverse into storage containers.

Right: Not all trailers use sleds, some are mounted on rubber tracks similar to those used by the Challengers.

Soft snow can be an annoyance on the Traverse, but the only real risk are crevasses, of which there are a few on the Dome C traverse. One section is very near the coast and can be assessed by helicopter, the other one is 200km inland and is now avoided by driving around it. Once inland the glaciers are smoother and the risk absent. Not so in other parts of the continent, such as the attempted traverses from McMurdo to South Pole, trying to pass west of Queen Maud's Range: lots of soft snow on the Ross ice shelf as well as many large crevasses on the ice shelf but also on the glaciers coming down the mountains. What to do in case of crevasses ? Go around them if you can, otherwise fill them up with snow ! A time consuming activity which needs to be repeated every year. Sastrugi areas should be avoided when night parking as they denote high winds areas. And ridge areas should be avoided when driving as they contain hills ranging to 50 meters in height, difficult to negotiate with a heavy tow.

Above: The Traverse in Concordia: the Challengers with the 'living' and 'energy' modules are parked on the left, while the newly delivered trailers and containers are in the center of the plaza. The snow is carved by the multiple maneuvers necessary to get everything in the right place and the area needs to be regularly leveled down by a Kassbohrer.

Left: Trailers loaded with construction equipment arrive in Dome C.

Departure

Left: Field repairs, welding a broken sled at Dome C before the return trip.

During the trip, there can be as much as 5km between the lead vehicle and the last train, so each is equipped with GPS and VHF radio, and one even has a radar. Additional risks involve fire (potential loss of a module), loss of food (divided between modules), loss of energy (there are several secondary generators), running out of fuel and personal injuries. Kerosene is carried in case an aircraft needs to reach the traverse for a rescue operation. Other normal security measures like those used on construction fields are used, but one specific one is: make sure you are not forgetting someone when you start moving !

Right: Upon departure from Dome C, the empty sleds are piled up to save on the number of things to drag behind. The only thing that the Traverse carries back down is the garbage produced by the station. Several containers filled with sorted trash will go back to Australia for disposal. Some containing organic or ferrous materials will be simply tossed into the ocean. The high oxygen content of the cold polar waters will ensure a quick disappearance.

The purpose of leveling the field is twofold: it gets rid of freshly accumulated snow on the more supportive older trail. And it avoid the carving phenomenon of 'bumps' forming after repetitive heavy sled passage, like what you get on dirt roads with heavy car traffic, only on a much longer wavelength. Once a year the last Challenger pulls a plow whose function is to harden the surface by mixing the compacted underlayer with the surface layer of fresh snow. A complete system will first break the surface with a ripper blade, then grade it with a ski supported blade and finally compact it with a heavy drum, all mounted on a 3-tier articulated system.

Left: Departure of the Traverse, taking some of my scientific equipment back to the ship in less than 10 days.

How much does all this cost ? Between the cost of the equipment, development, coastal installations and Dome C unloading installations, a total cost of about 8M$ can be estimated, leading to a 3$/kg cost for equipment brought to Dome C. To compare which the cost of aerial operations. Or in some cases like astronomy, the cost of putting telescopes in space (about 20k$/kg, so 7 thousand times more expensive)...

Right: The Traverse looking very isolated on the wide Antarctic Plateau.

Many thanks to Patrice Godon who provided me with a lot of information for this page. And for making Concordia a reality.