Space travel can shrink the human skeleton, cause muscular atrophy and play havoc with a central-nervous system unsuited to microgravity.

NASA needed a training area to simulate that kind of mental and physical anguish - so they chose Canada. More precisely, it saw Canada's harsh winter as an ideal way to push astronauts to the end of their psychological rope, simulating the stress of living isolated and gravity-starved on the international space station.

In other words, it toughens them up.

"It gives you the idea of a strenuous environment," said Steve Swanson, a Colorado astronaut training at Canadian Forces Base Valcartier, near Quebec City.

"It simulates the idea that when mission control asks you to do something . . . unfavourable, you need to get it done."

Twelve astronauts are coming this winter for 10-day training sessions at the Valcartier military base near Quebec City. The first half-dozen arrived earlier this week and will head out into a neighbouring forest for a six-day outdoor camping session, starting Friday.

They just hope it gets a little warmer. Wednesday's temperature was -23 C, excluding the wind-chill factor.

"Frostbite is one souvenir I don't need to bring back with me," joked astronaut Benjamin Drew, a native of Washington, D.C.

NASA first approached the Canadian Air Force in 1998 to ask for a training area that would test their astronauts' mental and physical stamina. Since then, 26 astronauts and two Russian cosmonauts have been through the Canadian program, which was previously run in Cold Lake, Alta.

This winter is the first at CFB Valcartier. The site was chosen because of Quebec's French character, said one Canadian official.

"On the (international space) station you have Europeans, Canadians, Russians," said Blair Waddington, a training manager for the Department of National Defence.

"Different cultures is something they have to deal with."

First, they must deal with the cold.

A helicopter will drop off the six astronauts Friday in the middle of the forest, carrying more than 25 kilograms each of equipment including a tent, toboggans, snowshoes, lamps and sleeping bags.

They spent this week learning how to use their equipment, waking up at 6 a.m. to practise pitching a tent and walking on snowshoes.

The temperature inside the tent should only be a few degrees below zero. However, the astronauts will be ordered to perform outdoor duties like taking temperature readings in the middle of the night.

"Our army has been wearing this equipment they're using for the last 20 years and we've survived quite well in the Canadian Arctic," Waddington said.

However, Canadian soldiers also carry heavy firearms and are forced to run dozens of kilometres. The astronauts will be spared that anguish. They have enough to worry about.

"The weather adds a lot of stress," said Steve Bowen, an astronaut from Massachusetts.

"I've been living in Houston for a few years now so I'm pretty thin-blooded; I was working on my swimming pool (before leaving).

"I don't think I've felt this cold in about seven or eight years."