When you watch the actors in Mission to Mars walk in "space," you can rest assured a pro taught them how. Former astronaut Joe Allen, one of the first to go extravehicular in space without a tether, was a technical adviser for the film, which opens March 10.

Filmmakers brought on Allen and former astronaut Story Musgrave to advise on aspects of the story, but especially needed their expertise in spacewalking because they had no access to a plane to simulate zero gravity, as the producers of the film Apollo 13 used.

"You can't put the whole set in zero-G," Allen told SPACE.com. "They did it with special effects."

Allen was with NASA from 1967 to 1985 and served on Mission Control during the Apollo years. In 1984 he was part of a tether-free spacewalking mission that remains the only one to salvage valuable material -- two communications satellites.
 
 

No stranger to the dreamlike experience of zero gravity

The surrealistic ballet

"The underlying essence of spacewalking is a slowness and deliberateness," said Allen, who also served as a NASA assistant administrator from 1975 to 1978. "Everything unfolds like a slow-moving dreamlike -- a surrealistic, slow-moving, choreographed ballet."

Did the actors get it?

"They were quite good at it," said Allen. "It makes good stuff for the movies."

Allen said the actors could have done their work underwater to simulate zero gravity, but added that being underwater isn't quite right.

"It's like being in a dream where you can't run fast," he said.

Hulls don't collapse in a near-vacuum

Allen also helped keep the script accurate. An early draft had a scene where space debris punched a hole in the crippled ship and a character said the ship was in danger of "losing cabin pressure and the hull collapsing."

Allen told the filmmakers that wasn't possible.

"Space is a vacuum. There isn't any pressure," Allen said. "If that really happened, the shell of the ship would remain unchanged, but the people inside wouldn't be doing okay." Although he hasn't seen a final version of the film, Allen said he was positive that error didn't make it in.

Allen also praised the film's overall scientific accuracy, giving it a nine out of 10.

"In your mind you have to decide whether you're going to make a science fiction film or a good story based on scientific possibilities," he said. "In this case they wanted the movie to have the ring of something that will happen or might happen."

This accuracy includes everything from how they get to Mars to the ships they use.

"The spacecraft look like ones you could step in and fly," Allen said.

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