After a long wait, NASA's Orbital ATK Cygnus is headed up to the space station today, carting 3175kg of gear along with it. Count down with us and watch the whole thing happen right here right now!
It's set to blast off at exactly 5:55pm EST (9:55am AEDT) — subject to changes, which we will be updating you on as they unfold. NASA TV is broadcasting the whole thing, and you can watch along here:
What makes this launch unusual? Part of it is the 30 minute launch window they have allowed for.
Normally rockets have a to-the-second instantaneous launch window to intercept the International Space Station. Rockets by competitor SpaceX, or national rockets by the Russian, European, and Japanese space agencies all have this restriction. A handful of now-retired rockets have performance to spare to be a bit sloppy, giving them a longer window: both the space shuttle and the Orbital ATK Antares had up to a 10 minute window. But this new United Launch Alliance (ULA) Atlas V configuration is blowing those short timespans away with a luxurious 30-minute launch window.
This extended window isn't just about time; it's an indication the rocket is over-powered for the purpose, but that's part of ULA's philosophy of maximizing the probability of a first-day launch. Along with more pure juice, the rocket also has better steering algorithms to allow it to catch up in orbit. This means that the launch team has the opportunity to wait for weather to clear up, boats to get out of the clearance zone, a technical problem to resolve, or otherwise pause for more favourable conditions instead of cancelling the launch outright.
All of this means that for today, the Cygnus can launch between 5:55pm and 6:25pm EST instead of only blasting off at the very middle of the window at 6:10pm. If it doesn't go off today, it has additional clear windows on December 4, 5, and 6. Any later than that and the flight team will need to get more creative with their orbital dynamics. Alternately, Cygnus could launch late and loiter in orbit for a few weeks until rendezvousing with the station. The station will be in its annual solar-angle blackout period from December 24 through January 3.
Here's hoping for a safe launch!
Top image: Cygnus on the launch pad / NASA TV Bottom image: Orbital Cygnus pre launch / NASA.