Hi all,
I have had a thought about this following concept and would like to discuss it further.
It might never prove useful so I don't care if the idea gets nicked or not, good luck with it if it ever does.
Consider space flight without a reference from a known object. How do you tell where you are going and how fast?

I thought of this concept that uses light. Shine a tight beam through a tube, towards a light sensitive disc at the other end. This disc has sensors on it that tell you exactly how much light falls on it per Milli second or even smaller time amount.
As you accelerate (the speed of light is constant) you would get temporarily less light on the disc as long as the disc is facing in the direction of movement.
The same for when you decelerate, you would expect a heaping of light causing an temporarily increase of light on the disc.
Together with a simple computer program you can now calculate the speed you are traveling as long as you keep accurate track of the time and light changes.
This takes care of the speed, now the direction.
Consider 2 more of these tubes at right angles from each other and in a perpendicular plane to the first one. These 2 extra tubes can now detect changes in direction as well as the light speed would be temporarily affected by your change of direction.
All you need to do now is stay away from large, heavy planets, neutron stars or black holes and you will be ok.
Any comments are invited, even if you are going to rubbish it.