In my dreams of spaceflight, years after my final mission, I usually find myself in the middle of a spacewalk. I'm free-falling, weightless in a hard vacuum, only to discover I've left my helmet or gloves behind. How did that happen? Complications ensue.

This week my nightmares took on a new and gut-wrenching immediacy, courtesy of the space thriller Gravity. I think the film scores on two major facets of spaceflight: it comes very close to replicating the stark, jaw-dropping beauty of Earth set amid the cosmos, and it illuminates how human existence there must constantly battle an alien, relentlessly hostile physical environment. Gravity forces us to confront both realities, and the result sends the mind reeling.

First, let's talk about the undeniable beauty of space travel. IMAX treatments, including the Space Station 3D film my shuttle crew helped to shoot in 2001, do come close to matching the view from an orbiter window. Yet Gravity's long, lovely, and seemingly effortless shots of Earth and space, though computer-generated, come very close to the astronaut's experience. "You can't argue with the view," George Clooney's mission commander admits, even as he and Sandra Bullock confront their very slim odds for survival.

But danger is ever-present in space, and Gravity puts its characters into a seemingly impossible survival situation. Can space truly be so indifferently hostile? The answer is yes—but not usually all at once. Gravity's filmmakers hit us in rapid succession with potentially deadly emergencies such as decompression, fire, toxic gases, and, most terrifying of all, being cast adrift in space.

In 50 years of space travel, astronauts have encountered all but the last, and we take extraordinary measures to prevent losing our grip on safety. I used steel and Kevlar tethers, foot restraints, and a flexible artificial arm to stay firmly clamped to the Space Station, and I even wore an emergency jetpack at the base of my backpack. On our crew's flight to deliver the U.S. Destiny lab to the ISS, partner Bob Curbeam and I practiced an emergency drill to retrieve an incapacitated astronaut, tugging him back to the airlock and safety. We called it the "dead man drill," and it took all the strength and spacewalking skill I could muster. But there's a good reason we do it. Last summer, Italian astronaut Luca Parmitano was on a repair EVA when he was nearly blinded and choked by a suit water leak that partially flooded his helmet.

Space disasters like Challenger and Columbia remind us that spaceflight is indeed unforgivingly risky. To counter those hazards, we count on our crew's training and skill, our well-designed equipment, and our ever-ready ground teams. When on STS-98 my crew encountered a serious ammonia coolant leak during a Space Station EVA, I watched a stream of toxic ice crystals geysering into black space and felt a cold knot churning in my stomach. Watching Gravity, that same feeling was back. Bad things can happen out there, and as we enter an era of commercial space tourism, we're wise to remember that.

How would I score the film for realism? The film recreates both the space shuttle and ISS with incredible accuracy. The visual detail puts NASA's simulators and virtual reality goggles to shame, thanks in part to early input from veteran space flier Andy Thomas, the film's astronaut advisor. In particular, the film does a superb job of showing how spacecraft, tethers, tools, and astronauts move and drift in free fall. Truly impressive.

As for the physics of spaceflight: Part of the fun of the movie for me was spotting where the film finessed physical reality in service of its relentlessly exciting story. A few examples: Our space suits are tough, but they could never withstand the pounding that they take in Gravity, as astronauts carom off spaceships and careen past sharp-edged hardware. The physics of orbital mechanics are greatly simplified, too. Sandra Bullock's minimally trained astronaut shoots for a space station a hundred miles away by lining up visually and blasting away with her thrusters. Where Isaac Newton rules, that gambit would put you farther behind your target. Rendezvous in reality is a complex orbital ballet, and applying human instinct and Kentucky windage always results in failure.

Technical "gotcha's" aside, though, the gripping core of this movie is the human struggle for survival, to refuse to submit to remorseless fate. For space travelers and earthbound explorers, it's a very satisfying ride.

In Gravity's rare serene moments, I remembered an orbital night, shared with a Columbia crewmate, as we gazed through a window and whispered and marveled at silent stars above and rippling lightning below. Watch Gravity and you'll know why astronauts eagerly sign up for the next launch.

Tom Jones is a four-time astronaut and planetary scientist, and a Popular Mechanics advisor. His account of the beauty and dangers of spaceflight is Sky Walking: An Astronaut's Memoir.

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