[DaFace]

Originally Posted by Dave Lane

An abundance of caution? WTF?

If I'm understanding the reddit geeks' take, the colder they get it, the more power they have, and this flight will take about everything they've got.

So it's kind of like saying, "I think I've got enough fuel to drive 100 miles, and I only need to go 80, so I SHOULD be fine. But if I wait until tomorrow, the wind will be at my back, so I might as well wait just to be safe."

EDIT: For a more techy hypothesis:

The electric thrusters can provide about 4 m/s of delta-V per day. So if SES can get 4 m/s more out of the rocket tomorrow, they'll be in service faster than if they launch today. Working out the numbers, that's about 0.1% more fuel. For LOX, a 24 degree K decrease adds 8.9% more fuel. So the break-even point is about 1/4 degree K. So the optimum is launching right at the start of the window, when the fuel is as cold as possible. But if they try and then scrub today, they lose two ways. Launching late in the window doubtless has the oxygen warmed more than 1/4 degree, so it would be better to launch at the beginning of the window tomorrow. But recycling all the warm LOX back into the ground tanks would probably mean they can't get it back down to within a quarter degree of the initial temperature by then.

So SES would probably prefer a beginning of window launch tomorrow to a late in the launch window today. Furthermore they would prefer a pre-load scrub to a post-load scrub. Of course they are playing this against the odds of a much longer possible delay if tomorrow is scrubbed as well. But it's entirely possible the delay is preferred by SES.

http://forum.nasaspaceflight.com/ind...408#msg1495408