What would happen to a spacecraft in orbit around Earth if its speed becomes too slow?

Question

for grade 9 science

Answer 1

Basically it orbits lower, but it is more complicated than that. If you are in a circular orbit and slow down by a little bit, you will change your orbit to an elliptical orbit with the highest point at the place where you slowed down and the lowest point 180 degrees around from there. At the new low point, you will be going FASTER than you were originally going before you slowed down. Objects in elliptical orbits speed up as they approach the low point and slow down as they approach the high point. If you waited until you reached that low point and slowed down again, by just the right amount, then you could enter a new circular orbit at an altitude equal to that low point. Then you would be in a lower circular orbit going FASTER than you were in the higher orbit. So to get to a lower orbit you have to slow down, twice, but when you get there, you are going faster. Strange, huh? Not really. Because falling objects speed up and an object going from a high to low point in an orbit is basically falling closer to Earth and so is speeding up. And in a lower orbit you are closer to Earth and gravity is stronger so you need to more speed to cause more centrifugal force to balance gravity exactly. Some people object to using centrifugal force to explain orbits though.

Answer 2

The very first poster made me think of this - it's not an eliptical pattern, but the visual results should match.

...I hope...

Try this as an experiment with your class:

You have a lab partner hold a beach ball to represent the Earth. Ask a volunteer to hold a foam ball to represent the spacecraft. Have the lab partner circle counter-clockwise to represent the Earths rotation. Then ask the volunteer to also walk in a counter-clockwise motion around the lab partner - only the foam ball needs to face the beach ball at all times. This represents the spacecraft on its orbit around the Earth - and for this experiment it doesn't matter how fast the volunteer is circling.

Now ask the volunteer to quickly stop moving - but not stop suddenly. This represents the spacecraft losing speed and dropping toward the Earth.

Wait a few seconds and then ask the class to picture themselves standing on the face of the beach ball and looking up (out) at the spacecraft. Wait a few more seconds and ask them that based on pure observation, at which time did the spacecraft appear to be moving across the night sky the fastest...

Just a little something fun to try/ponder.

Deion "Mule" Christopher

Answer 3

This is a common problem with satellites that are in Low Earth Orbit (any orbit between 200 and 2000 km above the surface of the Earth) because of friction with the atmosphere.

Just basic background information:
To maintain orbit, a satellite has to travel at a specific speed related to the strength of the gravity at the height of the orbit. The close a satellite is to Earth, the stronger the gravitational pull, and thus the faster the satellite has to travel to maintain orbit.

Back to your problem:
When a satellite slows down, it can no long maintain its orbit and starts to fall out of the sky. Most satellites are launched with a healthy amount of fuel so that when one starts to fall down, it can fire its boosters and get back up into a higher orbit.

Interesting tidbit:
Because all satellites will eventually fall to Earth, each component of a satellite is rated as to how quickly it will burn up in the atmosphere. If there is a component that is likely to reach the ground and pose a risk to populations, a large amount of fuel must be saved to de-orbit the satellite and make sure it crashes into a place where no people are.

Answer 4

If it becomes too slow it hits the atmosphere and returns to Earth. That's the principle under which the shuttle and Soyuz spacecraft re-enter the atmosphere when they come back: they fire their engines to slow themselves down.

An orbit is a situation where an object is moving forward fast enough that as gravity pulls it down the surface of Earth curves away below it at the same rate, so it never meets the surface. Any slower than that and it will come back to Earth.

Answer 5

As a spacecraft slows it's orbit will drop. If it drops low enough to hit the atmosphere, it will (1) slow down, (2) start heating up. The spacecraft will start getting lower and lower until it renters and crashes.

Answer 6

You will have a very expensive shooting star, again. No disrespect to the families of those deceased astronauts, that died 3 years ago in reentry. And no disrespect to the astronuats as well.