The U.S. astronauts on the International Space Station planned a campout Monday night but without the S'mores.

Commander Bill McArthur and science officer Jeff Williams planned to sleep overnight sealed off in the space station's Quest airlock, the area from which crew members embark on spacewalks.

They will test a new method for preparing spacewalkers for going outside the space station by sleeping in the airlock when the normal atmospheric pressure of 14.7 pounds per square inch is reduced to 10.2 pounds per square inch.

If the test run proves successful, future spacewalkers on the international space station may spend the night in the lower-pressure airlock before going on spacewalks in order to purge nitrogen from their bodies to prevent decompression sickness.

Before beginning spacewalks, crew members usually have to breathe pure oxygen for several hours to prevent the condition known as the bends. The new method could reduce that preparation time.

"Jeff and I have got our sleeping bags, a lot of our personal equipment in there," McArthur said during a news conference 250 miles above Earth. "Jeff and I are old Army buddies so we'll be telling old Army stories for a while ... In the morning ... hopefully we will have gathered all the data the folks on the ground need to validate the function of the airlock."

Williams arrived at the space station late Friday with Russian cosmonaut Pavel Vinogradov and astronaut Marcos Pontes, the first Brazilian in space.

"This is a very significant moment for my country," Pontes said.

McArthur and Russian flight engineer Valery Tokarev, who have been at the space station since last October, were scheduled to depart Saturday along with Pontes.

"We're ready to go home," Tokarev said.