2nd LD Writethru: Orbital ATK launches ISS resupply mission with upgraded rocket

U.S. aerospace firm Orbital ATK on Monday launched its sixth resupply mission to the International Space Station, using an upgraded Antares rocket almost two years after its predecessor exploded on liftoff.

The two-stage booster, powered by new RD-181 engines from Russia and carrying a Cygnus cargo ship, blasted off at 7:45 p.m. EDT (2345 GMT) from Virginia's Wallops Flight Facility.

Under the U.S. space agency NASA's commercial resupply services contract, Cygnus carried about 5,290 pounds (2,400 kilograms) of supplies and science experiments for the ISS.

The new experiments included an investigation that looks at fuels that "burn very hot at first, and then appear to go out, but actually continue to burn at a much lower temperature with no visible flames," NASA said.

Cygnus was also carrying a new station research facility that will enable a new class of research experiments by allowing precise control of motion in the microgravity environment aboard the ISS.

Particularly, an experiment that interests many was the Spacecraft Fire Experiment II (Saffire II), which studies how flames grow in space, but it will occur after Cygnus leaves the space station and before it re-enters Earth's atmosphere.

NASA said nine experimental samples of varying materials will burn for Saffire II inside an empty Cygnus resupply vehicle.

The space agency has planned three such experiments, and the first took place in June at the end of Cygnus's fifth ISS resupply mission.

Also onboard were a lighting system studying the effect of lighting on sleep and daily rhythms, a tablet app collecting health-related data, and a new way to measure neutrons, part of the radiation exposure experienced by crews during spaceflight.

If everything goes well, Cygnus will arrive at the ISS on Sunday, where it will stay for about five weeks.

This resupply mission marked the first flight of the upgraded Antares 230 vehicle, and the first launch from Wallops since an Antares rocket and its Cygnus resupply vehicle were lost seconds after liftoff in October 2014.

An investigation into the accident found a failure in one of the two Aerojet Rocketdyne AJ26 engines, leading to a decision by Orbital ATK to replace them with RD-181, which was developed specifically for Antares by Russians.

The AJ26 engine is a refurbished version of the Soviet-era NK-33, which was originally designed to launch the massive Soviet N-1 rocket to the Moon.

Since the accident, two Cygnus resupply missions were launched on United Launch Alliance Atlas 5 rockets to the station from the Cape Canaveral Air Force Station in Florida.

The Virginia-based Orbital ATK is one of two U.S. companies that provide ISS cargo services for NASA. The other company is California-based SpaceX. Endit