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The Shuttle in Orbit
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We’ve all seen images of Shuttle astronauts floating around the spacecraft trying to hold themselves in place or just clowning around in their weightlessness. Do they float around up there because there is no gravity? No! It’s because they are falling!
To understand this, we need to use our imagination. Let’s use a modified
mental model that Isaac Newton gave us centuries ago. (Newton used a cannon;
I'll use a bow and arrow
Imagine being at the top of a very high mountain. You hold a bow in one
hand and pull back a suction-tipped arrow with the other. You now weakly
shoot the arrow straight out towards the horizon. As expected, it falls
to earth. Taking another arrow from your quiver, you fire it, but with
more power this time. To no one’s surprise, it goes farther.
Now, after having downed a full can of spinach, you launch another arrow
with Popeye-like strength. This arrow goes far into the distance. But
farther than expected!
The Earth, you see, is not flat. It is a sphere, and over great distances,
it curves significantly. The arrow got a chance to fly farther before
landing because the Earth below it curved away.
The next time you fire off your arrow, after two cans of spinach, the
arrow goes so far it actually flies over the horizon and out of sight
“downrange” somewhere.
Is it possible to shoot the arrow with such great velocity that, even
as gravity pulls the arrow down, the Earth curves out of the way so that
the arrow can’t “land” at all? Yes!
After a Costco dose of spinach, you now have the strength to fire the
suction-tipped arrow so fast that it travels around the Earth and eventually
smacks you on the back of your unsuspecting head. That’s what being
“in orbit” is all about.
Notice that gravity was acting on the arrow the whole time as the arrow
was trying desperately to fall to the Earth.
How do you feel when you freefall on an amusement park ride? You feel
weightless; it’s like floating. That’s what happens on the Shuttle.
The
Shuttle is launched, and - observant people will notice - it rolls over
and turns toward the eastern horizon, rockets firing furiously the whole
time. They are trying to be the arrow that goes so fast that even as gravity
tries its best to bring it back, the Earth is curving safely out of its
way.
But to achieve the speed that will allow this they must travel over 17000
miles an hour, a quick clip by any standard. Once they reach this speed
(and, of course, are above the atmosphere), the engines are shut off.
They are in orbit.
And the astronauts aboard - even the Shuttle itself - are falling to Earth,
all day long. To those inside the Shuttle it appears as if gravity has
just vanished.
Imagine trying to eat or drink or get around in a place
where everything is “floating.” It’s a whole new world.
I won’t go into the details NASA had to work out so that the astronauts
could use the bathroom without major embarrassment. Think seatbelts and
vacuums.
There are images and movies waiting for you at firstlightastro.com/icolumn.html.
And you can watch the Shuttle astronauts for the next year as they build
the Space Station. And as you watch them, if someone should shout out,
“Look! There’s no gravity up there!” don’t fall for
it.
Posted by Administrator at 2000.12.11 08:57 AM | Comments (0)
