So...... Who is going to point out the deliberate error in the maths?<br/><br/>*grins*<br/><br/>Seriously though, the calculation is a logarithmic function. The amount of fuel the shuttle needs to attain orbit would be finely calculated - hence the need to top off the tanks to replace that burned on the way down. The ship would have a reserve, but for every extra kilo of mass being lifted, a certain amount of fuel is needed to lift that mass. That fuel too has mass and so needs fuel to lift it, and so on.<br/><br/>This is the reason why it is so expensive to fly anywhere, why excess baggage is so expensive and why pilots dread headwinds. Every flight across the Atlantic has the weight of the aircraft known the weight of the cargo and luggage (known, because each bag is bar-coded) and the weight of the passengers (estimated based on an average per person as you can't weigh each passenger as they board). The captain works out the total weight, adds a safety margin and then runs that figure into his computer to tell him how much fuel he will need. The program to calculate the exact amount is probably available on-line somewhere! He can't just "add a couple of gallons" for several reasons - one, as mentioned, is that by doing so he increases the mass of the plane and this needs more fuel. A second is that the fuel tanks are a finite size (Which is what I was referring to in my IC post when I said what the shuttle's tanks hold).<br/><br/>So, in fact, no deliberate mistake at all, just a slightly ambiguous statement of fact...