By Jonathan Amos
Science reporter, BBC News, Le Bourget
How Cygnus would get to the station, following its launch on a Taurus rocket
US and Italian companies are teaming up to build a private re-supply ship for the International Space Station (ISS).
The Orbital Sciences Corporation has engaged Thales Alenia Space to build a pressurised module for its forthcoming cargo vessel, Cygnus.
The spacecraft is expected to carry almost three tonnes of food and equipment to the platform.
The agreement between Orbital and Thales signed at the Paris air show covers nine Cygnus ships in total.
The first is a demonstration flight that must prove to the US space agency (Nasa) that the commercial freighter design is up to the task, and that the robot vehicle poses no danger to the crew of the station.
"Cygnus has built into it all the critical safety features that are required for being in the vicinity of the space station," said Bob Richards, who leads the project at Orbital.
"The standards are extremely stringent," he told BBC News.
The maiden mission is scheduled to be launched in March 2011 on a Taurus II rocket from Wallops Island, Virginia.
Dump and burn
The Taurus will park the freighter in a low-Earth orbit from where it must make its own way to the station.
CYGNUS CARGO MODULE
External diameter: 3.07m
Standard length: 3.66m
Enhanced length: 4.86m
Standard cargo: 2,000kg
Enhanced cargo: 2,700kg
The Cygnus will then manoeuvre itself to within 10m of the front of the platform. There, it will be grabbed by a robotic arm and berthed to the station's underside, at the central connecting hub known as the Harmony node.
Astronauts will then be free to go in and out at will, to remove bags of fresh supplies and replace their volume with rubbish.
"We are going to develop nine modules," explained Roberto Provera from Thales.
"The first is for the demonstration mission. Then we will supply eight others, two in what we call a 'standard configuration' and six in an 'enhanced configuration'.
"Cargo carrying capability for the standard module is two tonnes; and for the enhanced version, we will have the capability to go up to 2.7 tonnes."
The cylindrical MPLM can be seen in the back of the shuttle
The eventual fate of a Cygnus freighter is to undock and take a controlled dive to fiery destruction in the atmosphere over the Pacific - the same way that the Russian and European space agencies dispense with their robotic space trucks.
Orbital is one of two US companies that have won big Commercial Resupply Services (CRS) contracts with Nasa, to help the agency fulfil its commitments at the station while it builds a replacement for the space shuttle.
Orbital is an established force in satellite and rocket manufacturing and produces - among many different space products - the mid-air Pegasus launcher.
Thales is one of the biggest space companies in Europe and has been a key supplier to the space station project. More than 50% of the pressurised volume of the platform has been produced by the French-Italian company, principally in its Turin plant.
Thales is basing the design of the Cygnus cargo module on the Multi-Purpose Logistics Modules (MPLMs) it produced for Nasa. The MPLMs are the large cylindrical "packing boxes" the shuttles use when they carry out major logistics missions to the ISS.
"We have good know-how in doing pressurized and manned modules," said Thales' Walter Cugno.
"We know how Nasa works; we are very well known by Nasa and appreciated. So I guess we're a natural partner for Orbital on the Cygnus venture."
The deal signed here at Le Bourget is valued at 180m euros ($250m). Thales expects to deliver the first pressurised module to Orbital at the end of 2010. Orbital will then integrate it with its own service and propulsion unit - that part of the Cygnus spacecraft which contains the computers, navigation and orientation systems and thrusters.
Thales has already begun construction of the module
Orbital is on a tight schedule and acknowledges that it faces a big challenge to pull off all elements of the demonstration mission.
Not only will it be the maiden flight of Cygnus but the maiden launch of the Taurus II as well.
Nasa will demand only the highest standards, and Cygnus will not be allowed near the platform unless it proves itself in a series of in-orbit trials prior to its arrival at the station.
"There are a lot of firsts in this but Orbital has had many first flights on vehicles, and so we think we've got processes in place that will make it a very reliable system," said Mr Richards.
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