I get that with air crafts you can use a pitot tube to measure air speed, but what do you do if there is no air
In: Physics
The velocity of a spacecraft is measured by taking advantage of something called the *Doppler effect.*
If you’ve ever watched an ambulance go past you, you’ve heard the pitch of the siren change as it approaches and goes past you, right?
That frequency shift is directly related to the object’s velocity relative to the measurer’s frame of reference, so if a satellite (edit: or spaceship!) is constantly broadcasting a signal on a known frequency, ground-based computers can calculate the velocity from the perceived redshift of the signal.
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