The Science “Gravity” Got Right

Geostationaryjava3DThere’s lots of bad science in the move “Gravity,” but there’s one thing they got right: microgravity. Give me a few paragraphs and this will be about weather–honest.

Most people think astronauts float in space because they’re far from the Earth’s gravitation pull. Nope. Totally wrong.

The math behind gravity bases its calculations on the distance to the Earth’s center, not its surface. Adding a few hundred miles from the center of the Earth to the astronauts is a very small change. The Hubble Space Telescope’s orbit would still leave you with 90% of the gravitational pull you get on solid ground.

That’s not enough to make you float, though you’d weigh 10% less. Where can I sign up for that?

Astronauts are weightless for the same reason you’re weightless going down that first hill on a roller coaster. Orbiting Earth actually means falling around the Earth!

By flying the Hubble or International Space Station at just the right speed their fall matches the curve of the Earth. It’s as if that first roller coaster hill never ended. And, it’s why the space shuttle always flew at around 17,000 miles per hour (give or take a little depending on their exact orbit).

In the movie, George Clooney tells Sandra Bullock space debris will reappear in around 90 minutes. That’s the time it takes to orbit the Earth a few hundred miles up at 17,000 mph. Score one for the movie.

With me so far? Good, because we’re going to 1609 for a second and Johannes Kepler. He was a German astronomer studying Mars. Don’t ask why.

Kepler came up with mathematical laws to describe all this stuff. He figured out how how fast you’d have to go at any altitude to maintain an orbit. Kepler’s laws describe the planets orbits around the Sun and today’s satellites.

Here comes the weather part.

If it takes 90 minutes to orbit the Earth at Hubble altitude, what if you moved a satellite farther away? Could you orbit the Earth every 24 hours?

24 hours is the time it takes the Earth to turn once on its axis. The orbit of the satellite and the rotation of the Earth would be the same. Because they’d be moving in sync, the satellite would seem to hover over one spot.

Using Kepler’s 500 year old laws you can calculate a satellite 22,236 miles over the equator traveling 6,878 mph will orbit Earth exactly once a day. From the ground it would look motionless.

Johannes Kepler figured out where we’d put our weather satellites 500 years ago!

By placing them in geosynchronous orbit we get 24 hour coverage to track weather systems. The satellite is always looking down on exactly the same spot on Earth.

You don’t have to think about the math. All you have to know is it works! And because it does we have a view of weather Kepler could never have dreamed of, but that you see every day on TV.

We Saw Gravity

gravity movie posterHelaine and I joined my cousins Michael, Melissa and Max at the movies tonight. We saw Gravity in 3D on the Imax screen and digital projector at the Irvine Spectrum’s 21 screen theater. I considered taking Dramamine before we left the house!

If you’ve seen Gravity’s trailer or commercials you know there’s an accident in space. Sandra Bullock and George Clooney are flung around as their space shuttle disintegrates around them. Like a Steven Segal/Bruce Willis/Sylvester Stallone movie, both remain unscathed while the world around them is blasted to smithereens&#185.

There’s been a great deal of talk about the scientific liberties taken within the movie. It’s a movie. I was willing to suspend believe.

However, much of the dialog, especially early on, just didn’t ring true. Mission control explained the impending doom to Clooney and Bullock as if they were speaking to a theater full space-naive people, not astronauts.

That being said, the movie was intense. The action seemed real. Even in the microgravity of near Earth orbit mass is mass. A human slamming into a giant metal structure is going to get just as banged up in space as on the ground.

In Apollo 13 director Ron Howard simulated microgravity by shooting scenes on the ‘Vomit Comet.’ Clooney and Bullock claim everything in Gravity was done on-the-ground (or reasonably near it). I have no idea how the effects were achieved. I’m impressed.

wpid-IMAG0082.jpgBefore the movie, as we sat through 15 minutes of trailers, one came on in 3D. The action was shot with long, fast lenses producing very shallow depth-of-field. It looked artificial. Jarring.

In Gravity the 3D never got in the way. It seemed organic. However, since 3D imagery can move action off-the-screen toward you, the close-ups were really close! Really, really close, especially on the gigantic Imax screen.

I was glad I went. I enjoyed the movie. But it was much more flawed than I anticipated. Sparkling reviews got my hopes too high.

&#185 – I don’t think I’ve ever type smithereens before. I’ll try and not let it happen again.