Europe’s 20-tonne freighter will come up on the back of the station Europe’s sophisticated space freighter, Johannes Kepler, is set to dock with the International Space Station (ISS).
The unmanned robotic truck is delivering new supplies of fuel, food, air, and equipment to the orbiting platform’s astronauts.
Kepler is totally automatic – it will use its own computerised systems to make the attachment.
Ground controllers and the station’s astronauts will not intervene unless there is a problem.
Contact with the Zvezda module on the rear of the ISS is timed for about 1547 GMT.
A successful docking will clear the way for the American space shuttle Discovery to lift off from Earth.
It, too, has a date with the ISS, and will carry up six visiting astronauts and a smart humanoid robot.
Kepler was launched from Europe’s Kourou spaceport in French Guiana last Wednesday.
Ever since, the truck has been on a path to chase down the station, which sweeps around the Earth at 27,000km/h.
The European Space Agency reports that Kepler has flown flawlessly since its picture-perfect launch from South America.
“The ‘Cheshire cat smile’ hasn’t got any smaller,” said Bob Chesson, Esa’s head of human spaceflight operations.
“This really is an amazing mission so far. We haven’t had any anomalies. It’s just perfect,” he told BBC News.
The truck – also known by its generic name of Automated Transfer Vehicle (ATV) – is the second such ship launched to the ISS by Europe.
The first, nicknamed Jules Verne, completed its mission in 2008.
The ATVs have the most advanced automatic rendezvous and docking technologies of all the ships that visit the platform.
Its main approach system is a pair of videometers. These are optical sensors that analyse the behaviour of laser light reflected off Zvezda to compute the vehicle’s orientation and distance from the platform.
They are backed up by a pair of telegoniometers, which work in a similar way to radar and continuously calculate the distance and direction from the freighter to the ISS.
Kepler’s systems have been designed with multiple layers of redundancy. It has three main flight-control computers that run in parallel. These in turn are overseen by a totally independent computer.
If the latter recognises an anomaly in the primary system during the final approach, it can intervene and command the truck to remove itself rapidly to a safe distance.
Controllers on the ground in Toulouse, France, can also initiate a retreat if they are at all concerned.
The ISS astronauts, too, can command the abort via a big red button on a panel sited in Zvezda.
Once a seal and electrical connections have been confirmed, and the astronauts have checked the air inside Kepler is safe to breathe – the vehicle will be free to enter.
Johannes Kepler launches atop an Ariane 5 from Europe’s Kourou spaceport
One of the freighter’s main tasks in the coming months will be to raise the altitude of the station, which is currently at about 350km.
The ISS has a tendency to fall back to Earth over time as it drags through the top of the atmosphere.
Every few weeks the freighter will fire its thrusters to accelerate the platform, taking it higher into the sky.
The freighter will be used like a store cupboard by astronauts.
They will go into the pressurised vessel to obtain food, clothing and equipment when they need it. Fuel will be piped across to the main station complex; air will simply be vented from taps.
As Kepler’s supplies are depleted, the void will be filled with rubbish. The vehicle will take this waste into a controlled burn-up over the Pacific Ocean when it leaves the station sometime from June onwards.
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