[ratzoe]

The window is only a few minutes. Maybe up to 10 but I dont think even that much.

Thank you, was thinking it had to be 10 minutes or less. Searched this morning for this info, no joy. The Antares supply ships I've seen launched from Wallops always had a very limited window before it would be scrubbed.

[Magnum44]

Launch window is almost always determined by the target orbit inclination, launch latitude, and the capability of the launch vehicle. The ISS orbit is about 50 degrees inclined (that was to help the russians get there) and Kennedy is in the 30 degree latitudes range. From a 30 degree launch site you could launch into a 30 degree orbit with no penalty for inclination change. (Skylab was launched into this inclination.)

The launch site only passes under the ISS orbit plane twice a day. One pass requires an inclination change of ~+20 deg and the other would require an inclination change of almost -80 degrees. Inclination change is the most expensive maneuver to make. You can change your position in the orbit plane fairly easily. Re-orienting the orbit plane needs much more propellant. Missing the window only increases the orbit plane change necessary.

Its an angular momentum thing. :)