The International Space Station (ISS) requires a lot of resupply to keep the astronauts well fed and occupied. During the years that the Space Shuttle was available this wasn’t a problem as the US and Russia shared the resupply effort. But with the demise of the Space Shuttle the US had to solely rely on the Russian resupply missions to get both supplies and astronauts to and from the ISS. We’ve seen a lot of hype around the fortunes of SpaceX with their Falcon 9 rocket and the success it has had in the last couple of years. SpaceX and the Dragon spacecraft have helped fill the gap in resupply to the ISS. They haven’t been the only player though, as Orbital ATK and their Antares Rocket have launched a number of mission to the ISS with the Cygnus spacecraft and so far 9 have been launched. Orbital ATK build a lot of spacecraft including the recent TESS that will be used to look for exoplanets.
The Cygnus spacecraft has a distinctive shape with the two large round solar panels on one end of the long tube. The role of the this spacecraft in delivering cargo to the international space station was born from a contract from NASA under the Commercial Resupply Services (CRS) program which was awarded on December 23, 2008. The spacecraft has been built in two variants with the later called the enhanced version, which is a bit longer and can carry more payload. The first three spacecraft were the standard variety and all subsequent missions have been with the enhanced model. It’s worth noting that the third launch failed and exploded shortly after launch, this has been the only failure of the Cygnus spacecraft.
Cygnus was designed from existing basic spacecraft design already employed for satellites, so presented a reasonably low risk option. It consists of a Service Module and a Pressurised Cargo Module (PCM). The Service Module includes the avionics, propulsion and power systems and is based on Orbital ATK’s spacecraft buses that they have used on satellites in LEO and GEO orbits. The Service Module is built in Virginia, USA, and the Pressurised Cargo Module is built in Turin, Italy by Thales Alenia Space. The dimensions of the spacecraft are 3.66m in length in 3.07m in diameter. The cargo carrying capacity of the spacecraft is 1800 kg, which is 300 kg more than the standard configuration, though the last three spacecraft flights have all managed to pack in more than 3300 kg of cargo. Unlike the Russian Progress and ESA ATV spacecraft the Cygnus spacecraft docks via the mechanic arm of the ISS called the Canadarm2.
Thanks to the success of its missions (with the exception of the third one) Orbital ATK was selected by NASA to continue cargo deliveries under their Commercial Resupply Services contract which commences in 2019 and continues through to 2024. The most recent launch was on May 21 this year which was launched on an Orbital ATK Antares rocket from NASA’s Wallops Flight Facility. Basically the rocket gets the spacecraft into orbit then the spacecraft boosts itself to the ISS orbit. The robotic arm on the space station guides the Cygnus spacecraft to the birthing port on the stations Unity module. On this flight the spacecraft will also launch a couple of cubesats when it has been loaded and ready to depart the station.
The rocket used to launch the spacecraft is the Antares 230. This is a two stage rocket 42.5 m in height and 3.9 m in diameter and weighs around 300,000 kg. The rocket is a collaboration between Orbital ATK and Yuzhnoye of Ukraine and has been successful in making the Cygnus a reliable supplier to the ISS. It will be interesting to see how it can compete longer term with SpaceX and their ability to reuse the Falcon9 rockets, whereas the Antares 230 is completely disposable. The Atlas V has also been used to get the Cygnus into space.