2001: A Space Odyssey stands as the granddaddy -- and grandmaster -- of space science fiction films. For many, the purity of 2001 as "hard" science fiction can't be beat. Other crowd-pleasing contenders such as Star Wars and Alien get tainted by other genres: fantasy or horror. But Arthur C. Clarke and Stanley Kubrick laid a foundation of plausible science -- real physics and physiology -- before sending their story off into fiction and philosophy.

This year there were two new space movies that also took physics and physiology seriously, and neither dips too deeply into fantasy or horror. I doubt they give 2001 a serious challenge for its grand titles, but they at least seem to be in the same court.

You've probably heard of Gravity, but I'm guessing you might have missed Europa Report.

Both films feature astronauts, in space as part of their job. In Gravity, they are on a space walk performing an upgrade to a telescope when a chain reaction of scattering space debris destroys their ride home. In Europa Report, they are on the first manned mission to Jupiter's moon when they lose contact with Earth.

Gravity has rightly been praised for getting the feel of the physics right. In an early scene when Sandra Bullock's character has been set spinning head over heels, we get sickening, 3-D point-of-view shots of the earth spinning around us. In space, once you start spinning, you don't stop until something stops you -- say, George Clooney with a jet pack.

Other scenes in Gravity also illustrate Newton's First Law of Motion which states objects in motion tend to stay in motion. If you jump toward the doorknob of the space station, you'd better be ready to hang on tight when you get there, or you'll bump off and go flying past. Screenwriters Alfonso and Jonas CuarAn probably overused this scenario as a tension builder. Too often the very last possible thing our protagonists could grab is the thing that they grab, thus saving the film from an awkward and abrupt ending.

In space, no one can hear you scream, so mostly what we hear on the soundtrack in Gravity is whatever gets transmitted over the astronauts' radio headsets. In the case of Bullock's out-of-control spin, that's the entirely plausible sound of a human being beginning to panic and hyperventilate. The other sounds we hear are the ones transmitted by physical contact. Gravity's sound design does well conveying this, too, like when we hear the muffled sound of Bullock's power wrench which she's using for a repair. Too bad the musical score pipes up and sullies the pristine soundscape. That's one thing Kubrick didn't do in 2001 -- use mood-setting music to heighten the tension during extra-vehicular activity.

Where Gravity excels at showing the zero-g physics, Europa Report excels at showing the scientific motivations and practical considerations for space travel.

We meet the astronauts on the Europa One as they get close to their destination, Jupiter's ice-covered moon Europa. The crew consists of six people: two biologists, two engineers, a pilot and a captain. This is not the Enterprise, and nobody was invited because they were good at fistfighting. The mission is privately funded, not government-sponsored. The travel time is optimistic but plausible -- a couple of years each way from Earth.

In transit, the astronauts live at the ends of a rotating arm, which gives them earthlike gravity. In one neat special-effects scene, an astronaut, making a video for his family, climbs up the ladder to the hub and pushes away, showing that he can float in the center where there's no centrifugal force. In other scenes, astronauts are strapped in at angles perpendicular to other astronauts in the background, conveying the idea that "up" is a relative and therefore meaningless term.

Their passion for the mission is probably the most plausible idea in Europa Report. Everyone in the crew is excited to be looking for the first proof of extraterrestrial life -- even if it's just ancient microbial soup. In our real and modern world, the great frontiers of astrophysics are fundamental particles, dark matter and dark energy, and extraterrestrial life. The first two preclude direct human involvement -- sending astronauts can't help find the Higgs or dark matter. But sending a biologist to Europa is not a completely dumb idea. True, it would be cheaper to send a robot, but since the Europa One mission is privately funded, perhaps a Bransonesque billionaire was inspired by more than pure science.

I have a friend who is a member and fan of private space societies. He would have no qualms spending his life savings for a trip to the moon. Yes, robots are hardier, lighter, more focused, and disposable. But as my friend Richard is careful to acknowledge, science and curiosity aren't the only reasons to go to space. The romance and challenge of getting people there has to be part of the motivation. Governments these days aren't very interested in spending on romance and challenge, so it makes sense that screenwriter Philip Gelatt would make Europa One a privately funded mission.

Europa Report is probably less thrilling than Gravity. There is a bit of tension in the final act when some of the astronauts have landed a capsule on Europa. There may or may not be something suggesting complex life forms at the surface. That speculation certainly juices up the plot and rewards the audience with an interesting ending, though "multicellular life" is hardly as exciting as trying to survive a catastrophic cascade of space junk.

Then again, Gravity famously got some important details wrong. There isn't really enough "stuff" in orbit to cause a catastrophic cascade. And the Hubble is not in the same orbit as the space stations; you can't easily get from one to the other, especially not with just a jet pack.

And in spite of its status, 2001 still has the power to put me to sleep once the silence of space, augmented only by the sound of deep breathing, fills the screen for 20 minutes.

So "realism" is hardly the best way to judge a movie. If a science fiction film is excellent, it's easy to forgive any detail that isn't "realistic." Still, as 2001, Gravity, and Europa Report all illustrate, getting the "science" right as your starting point makes it more likely that you won't lose your audience when you launch into your "fiction."