It's proving hard for the Cygnus spacecraft to get off the ground for its return-to-flight mission! After getting rained out Thursday and shoved around by gusts of wind Friday and Saturday, this is the fourth attempt for the cargo craft to deliver supplies to the International Space Station. Watch live as we count down to the 4:44pm ET attempt!
This is the first mission for the Cygnus spacecraft since the previous one was destroyed in October 2014 by an Antares rocket explosion. Orbital ATK's Enhanced Cygnus is redesigned with more room for cargo. This is the first time a Cygnus is launching on an United Launch Alliance Atlas V rocket, and the first time it's launching out of Cape Canaveral in Florida. The rocket has the power and flexibility for a 30-minute launch window that opens at 4:44pm ET. You can watch the launch preparations live here starting at 3:45pm ET:
After getting rained out or windblown the previous attempts, the weather report leading up to the window is a reassuring 70% chance of being good enough for launch. As of the start of coverage, a few cumulus clouds are in the area with scattered showers, but windspeeds have dropped dramatically compared to the morning.
The new spacecraft configuration has 25% more cargo volume, and a more efficient service module allowing it to carry a heavier payload. If it succeeds, this will be the fourth Orbital ATK mission (OA4) of approximately 10 as part of their commercial resupply services contract to deliver 28,700 kilograms (28,700kg) to the International Space Station.
If the launch succeeds, the rocket will deliver Cygnus into orbit within 21 minutes, or less than the average time for a pizza delivery. Once on its own, the space swan will spread its new, Ultraflex solar arrays and upgraded power systems to arrive at the station on December 9th. At the station, astronauts will unload 3,349.0 kilograms (3,349kg) of cargo before reloading the spacecraft with garbage for a destructive reentry in January.
Launch schematic for OA-4 from launch to interception with the International Space Station. Image credit: Orbital ATK
After the better launch windows were scrubbed or postponed Thursday through Saturday, we're down to a window with nastier orbital dynamics. Instead of boosting Cygnus straight to the International Space Station, the Atlas V will use its flexibility to deliver the spacecraft into an orbit where it can loiter in space for several weeks before rendezvousing with the space station on December 19th. If today's launch is also scrubbed, it's time for the mission planners to get very creative. Due to an annual sun-angle blackout, no spacecraft can dock with the space station between Christmas Eve and January 3, 2016.
Top image: Atlas V rocket with Cygnus on board awaiting launch. Credit: NASA