> I read in the other thread that a good mechanical gyro will drift
> about 0.01 degree/hour and GPS can correct for this. What happens on
> say a year long (or longer) deep space mission? How do we correct the
> drift then? Also, when you land the spaceship do you keep teh gyros
> spinning? How else do you know where you are? I could see you may be
> able to point to a star but that wouldnt be accurate.

> gyansorova@gmail.com wrote:

>> I read in the other thread that a good mechanical gyro will drift
>> about 0.01 degree/hour and GPS can correct for this. What happens on
>> say a year long (or longer) deep space mission? How do we correct the
>> drift then? Also, when you land the spaceship do you keep teh gyros
>> spinning? How else do you know where you are? I could see you may be
>> able to point to a star but that wouldnt be accurate.

>
> I can't give you a direct answer, but perhaps John Doty can. (Cross
> posting to tap his expertise.) I know that at least some deep-space
> probes lock onto known stars, Canopus among them.

> You need more than a gyro for attitude determination, though. A gyro
> just measures your rotation rate, usually only about one axis. With
> three of them you get rates about all three axes, but that still
> doesn't tell you your orientation.