Here's a spreadsheet for calculating the fuel use ( link ) taking into account wear and tear on the ship and the results of Engineer and Astrogation rolls. Enter the ship details and then the journey details in the yellow coloured boxes. Adjust the throttle value until you have a valid journey with fuel left at the end. Update the two values for distance travelled on the ship data (manually I'm afraid) and your ship will deteriorate before you eyes. Calculating cells are protected (but not password protected).
I tried to find a way of embedding a working spreadsheet in the blog, but to no avail.
The formulae used and the constants they use are arbitrary - they give a nice range of figures and allow idiots (sorry, player characters) to go pedal to the metal and waste fuel.
Speaking of fuel, next bit of rule finagling will be to sort out how fuel works (and costs) as well as what purifying hydrogen actually means.