Washington - The first regular contract flight of Orbital Sciences' unmanned cargo ship is poised for launch on Wednesday toward the International Space Station, Nasa said.The Cygnus spacecraft is set to take off from Wallops Island, Virginia atop an Antares rocket at 13:32 (18:32 GMT), carrying 1 260kg of gear including science experiments, supplies and hardware.Weather conditions are 95% favourable for launch, and the biting cold temperatures in the region on Tuesday were expected to climb in time for launch, Nasa said.The launch window stays open just five minutes. In case of delay, another attempt could be made on Thursday that would still allow Cygnus to reach the space station by 12 January.The attempt was delayed in December due to a cooling system breakdown at the ISS, which required American astronauts to make two spacewalks in order to replace an ammonia cooling pump.If the launch goes ahead this time, it would mark the company's second trip to the orbiting outpost, coming on the heels of a successful demonstration launch in September.ContractsThat mission proved "that the company can reliably carry out regularly scheduled operational missions to the ISS for Nasa," said David Thompson, Orbital's chair and chief executive officer."Now our team is focused on executing another flawless launch and in-orbit operation to deliver much-needed supplies to the astronaut crew on board the space station."Orbital has a contract with Nasa worth $1.9bn for eight cargo resupply missions to the global space lab.Orbital and SpaceX are two private companies that have stepped in to ensure the US' ability to reach the orbiting outpost, after the retirement of the 30-year space shuttle programme in 2011.SpaceX, owned by internet entrepreneur Elon Musk, became the first commercial entity to reach the space station with its Dragon cargo ship in 2012, and has a $1.6bn contract with Nasa.Unlike SpaceX's Dragon capsule, Cygnus cannot return to Earth intact but will burn up on re-entry into Earth's atmosphere, disposing of any unwanted cargo.It is ferrying some unusual science experiments for the astronauts aboard the station in co-operation with students back on Earth.One is an experiment called "Ants in Space" that aims to help students compare the behaviour of ants in orbit - recorded by video cameras at the ISS - to ants on Earth.Another is an experiment aimed at helping understand drug-resistant superbugs. It includes 128 test tubes that will measure 38 different concentrations of antibiotic on E coli bacteria.