Flight Question General question about IRL space navigation

[LuckyHendrix]

I was wondering, how do you in space to know if you're rotating ? I mean there's no fixed reference point , even the stars are moving so if you need to annulate precisely any rotational mouvement how do you do ?

Another question slightly related : Assuming you're in deep space far from any planet, and you must point a direction to make a burn how does the ship instrument knows your pointing in the right direction, and how does it know the ship's speed relative to any orbital object ?

 

[Urwumpe]

You use the stars as reference... that is why there are star trackers for aligning inertial navigation systems in spacecraft.

[ame="http://en.wikipedia.org/wiki/Inertial_navigation_system"]Inertial navigation system - Wikipedia, the free encyclopedia[/ame]

 

[N_Molson]

The stars are not moving fast enough to be a problem. Apollo used stars as a reference points (the "AGC" stars) to calibrate the inertial guidance system I think.

Else you have telemetry : different stations on the ground (or satellites) send signals to the spacecraft ; by calculating the angles and the delay of the "pings", you can approximate it's position.

If you watch the movie "Apollo 13", at some point you see an astronaut measuring directly the angles between the stars with a sextant, because they have not enough power to use the on-board computers. In this case, it's like using a sextant on a sailboat... except that you have to think in 3D, which is a nightmare for the maths...

 

[Urwumpe]

Also, near Earth, you can use GPS... look for example at this standard part in many spacecraft currently

http://www.honeywell.com/sites/aero...62F_HAE85EBB2-C112-B35D-5844-F634132360F4.htm