After the Antares rocket boosted Cygnus into a low Earth orbit, the Orbital Sciences team performed three burns of the spacecraft’s engines to raise its orbit and begin the approach to the ISS. The third “delta V” burn occurred yesterday afternoon and lasted 189 seconds, for a 20.7 meter per second change in velocity. The fourth and final scheduled delta V burn is scheduled for this afternoon.
With the orbital burns complete, Cygnus will catch up with and make its approach to the station Saturday and into early Sunday. A little after 5:00 a.m. EDT Sunday, the spacecraft will reach a point 250 meters below the station. Orbital Sciences will perform the final eight demonstration maneuvers, including an aborted approach, before taking the final few steps to the station. The spacecraft will stop 10 meters from the station, where it will be placed in “free drift” mode, meaning the onboard navigation is no longer controlling its location.
The Cygnus spacecraft is an unmanned resupply spacecraft being developed by Orbital Sciences Corporation as part of NASA's Commercial Orbital Transportation Services (COTS) developmental program. It is competing with the Spacex Dragon.
NASA awarded Orbital Sciences a $1.9 billion contract under the Commercial Resupply Services (CRS) program. Under this contract, Orbital Sciences will deliver up to 20 tons of cargo to the ISS through 2016 in eight Cygnus spacecraft flight.
The Cygnus spacecraft consists of two basic components: the Pressurized Cargo Module (PCM) and the Service Module (SM). The PCM is manufactured by Thales Alenia Space in Turin (Italy), the initial PCMs have a volume of 18 m3. The service module is built by Orbital and is based on their STAR spacecraft bus as well as components from the development of the Dawn spacecraft. It is currently expected to have a gross mass of 1,800 kg with propulsion provided by thrusters using the hypergolic propellants hydrazine and nitrogen tetroxide and is capable of producing up to 4 kW of electrical power via two gallium arsenide solar arrays.
SOURCES - Wired, Wikipedia, Space.com
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