How does the space shuttle measure its velocity?

Question

Hi,

I was watching the right stuff this weekend, and the pilot of one of those old school mercury orbiters said that his velocity was 57,000 kph. I wondered how one could measure the velocity of the craft from inside. It couldn't be air pressure like with a plane, or with radar because it's moving too quickly. I was very confused about this. Ideas?

Thanks,
Matt

I received some answers (and I appreciate your reponses) that I have some questions about.

I thought about the GPS and radar things, but, please remember that I'm talking about pre-satellite technology, there wouldn't have been GPS then because they didn't have satellites yet.

As for the Radar, it seems that if the height of the orbit was stable, the radar signal would give you the same distance to the earth, and not be helpful with speed of motion...

Thanks,
Matt

Answer 1

They use a combination of inertial navigation, which uses accelerometers and computers on the space craft, and tracking from the ground.

Answer 2

Actually it would be best measured with Radar.

Using the Radar to measure the rate of change in the distance to two object used as reference Zeros (Like the surface of the Earth and the Moon). The Angles and the rate of change would give you the Velocity with the Appropriate Vector.

Answer 3

It's called "telemetry". All spacecraft are outfitted with transmitters that can be detected from the earth and from satellites. Also, now anyone can buy a GPS unit for around $150 that tells you how fast you're going and in which direction based on satellite signals.

Answer 4

By calculating how far it is above the Earth's surface and how long it takes to to one orbit of Earth.

Answer 5

In the " olsd " mercury craft it was done ( belive it or not ) bt computers !!