I think any attempt to use trig to calculate your speed/velocity/position from readings taken of STARS apparent angular displacement as you travel, from a moving vessel that would obviously have fuel/people/air etc all moving about in it, is doomed to failure/highly likely to be inaccurate.<br /><br />I know in planes,people moving about alter its attitude, so i guess (under thrust) things moivng about the space-ship would also introduce infintesimal small errors in the base line that would be something like a isocoles triangle mutiple lightyears along its long sides, and only fractions of that along its (distance traveled) short edge.<br /><br />I don't say it would be impossible, but I am pretty sure you would need something much more accurate for a manned vessel. Quite happy to have someone prove me wrong here.<br /><br />I think maybe a COLLECTION of the various methods would be needed. Or a continuious reading taken somehow, and the average taken as correct, from a signifigent number of readings.<br /><br />Are they able to fix their position three dimensionally accurately, just from star fixes, enough to work as their base to calculate firing times?.