About once every week or two, my husband, the Astronomer, grabs the kids up from the dinner table, napkins and crumbs flying, and exclaims "The shuttle! The space shuttle's passing over!" Then they all charge out the door, leaving me alone at the table with a bunch of unfinished vegetables and congealing chicken. The things we must endure . . .
Once I joined them. Sure enough, right at its appointed time, a bright flying object—apparently the space shuttle (I'll take his word for it)--passed by at a steady clip across the night sky. We all stared up for a minute or so and then trooped back in and finished dinner.
So what's the big deal with the space shuttle? Why do we charge out to stare at it and not, say, an airplane? (Kids: Don't get any ideas.)
AstroTom says it's a big deal because men (let's assume he means people) built the shuttle and put it up there, and there are people in it. I told him that this makes the space shuttle about as interesting as an airplane, which people also put up there, and considerably less interesting than a meteor, which people most certainly did not put up there. Then he said that the space shuttle goes around the earth every 90 minutes, and is, in fact, in orbit.
It turns out that being in orbit is actually interesting. Being in orbit puts the space shuttle in a different category than airplanes, which fly but are not in orbit. Something that's in orbit has been shot up there, sort of like a rocket to the moon, with a force great enough to "break the bonds of earth's gravity" as science writers are wont to say. I can more easily relate to the force required to open the bag inside a box of cereal. You have to pull the two sides apart but it has to be a controlled pull or your hands will fly apart and you'll end up with a jagged rip and cornflakes all over the room. The shuttle had to be shot into the air with enough power to get it up in the air and keep it from falling right back down, but not so much that it would shoot up too high and wind up somewhere beyond Saturn.
How do they keep the shuttle up there in its neat circle, once it's off the earth? Well, the Astronomer explained, using the drawings Newton made of a cannon on a mountain, the shuttle is actually falling all the time. (Isn't that disconcerting?) But, fortunately, the shuttle, like that ball fired by the cannon, is shot away hard and fast at an angle, not straight up, so that it neither shoots off into space nor ever falls back to the earth. This last part works only because the earth is round. If the earth were flat, the shuttle would eventually land, far far away. But the earth isn't flat, so every time the shuttle goes far enough to land on the earth's surface, the surface curves out of its reach, and it keeps going. Here's the neat part: This was all planned. The initial thrust is just fast enough, and the angle is perfectly calibrated, so that the roundness of the earth balances out, or effectively cancels out, the pull of earth's gravity.
But we tidy housewives know that stuff men put into space falls back to earth all the time. (I heard it on an episode of "West Wing.") How does that happen? Does the shuttle run out of steam, eventually caving into the never-tiring power of gravity? It turns out that friction is the culprit. Space, even at 225 miles (360 km) high (which I'm told is relatively low), is not a perfect vacuum; the little bit of air causes enough friction to modestly slow down the speed of the space shuttle so that, over time, it would indeed surrender to gravity and fall on our heads if it were not periodically re-thrusted, given an extra boost to keep it going a while longer.
I still am not sure what those people are doing in the space shuttle, how long they're going to be there, and how much it's costing us tax payers to keep them there. I also just heard that the "space shuttle" is not the same thing as the "international space station," which I kind of knew but never really thought about. I'll ask the Astronomer the next time we all go rushing away from the dinner table.
The Astronomer's Wife