Science & Environment

Europe's ATV space freighter undocks

ATV at ISS (Nasa/ESA)
Image caption Space tug: The ATV-Johannes Kepler (at bottom-right) has immense propulsive capability

Europe's orbital freighter has undocked from the space station in readiness for its fiery dive to Earth.

Astronauts have filled ATV-Johannes Kepler with about 1.3 tonnes of rubbish that it will carry to incineration over the southern Pacific Ocean.

The robotic ship's final task in its mission was completed on Sunday, when it used its big thrusters to boost the platform to a higher altitude.

The space lab is now flying more than 380km (235 miles) above the Earth.

That is more than 30km higher than where it has traditionally been kept through its life.

Kepler pushed away from the station at 1446 GMT on Monday. What remains of the robotic ship and its waste cargo after its destructive descent is expected to hit the water about 2059 GMT on Tuesday.

The European Space Agency (Esa) has been delighted by Kepler's performance since its launch from Earth in February.

Its automatic rendezvous and docking systems had no problem finding the International Space Station (ISS); and then, having attached itself to the back of platform, the ship operated in a flawless fashion.

The one anomaly was a broken fan used to circulate air inside the freighter's cargo bay.

"Some people in the control room had joked they were bored because the mission was going so flawlessly, but from a mission manager's point of view - a 'boring mission' is absolutely the best kind of mission you can have," said Nico Dettmann, who runs the ATV programme at Esa.

At launch, Kepler weighed in excess of 20 tonnes - the heaviest payload Europe has ever put in orbit.

Most of its more-than-seven-tonnes of cargo was fuel, a good fraction of which it has used in a series of manoeuvres to rotate and boost the ISS.

Such is the propulsive might of the tug that it can turn the 420-tonne orbiting complex on its end - a procedure that can sometimes make it easier for other vehicles to come and go.

But the key manoeuvres were the boosts completed in recent days that took the ISS from just in excess of 340km above the Earth to more than 380km.

At this altitude, the station will encounter fewer of the residual air molecules still present high above the planet that can drag the platform down over time.

If regular re-boosts were not performed, the ISS would come crashing to Earth, so Kepler's efforts will have been critical to the long-term operation of the lab.

Keep clear

"We've used almost four tonnes of propellant to bring the station to a higher altitude. One boost brought an additional velocity of 11 metres per second and that's the biggest delta-V (change in velocity) on a human spaceflight vehicle since the lunar insertion orbit [on Apollo]," said Kris Capelle, the lead mission director at Esa's ATV control centre in Toulouse, France.

After undocking, Kepler will perform two de-orbit burns to bring itself out of the sky.

Image caption European astronauts Paolo Nespoli (L) and Roberto Vittori (R) float inside Johannes Kepler

The controlled re-entry has been targeted for an uninhabited part of the South Pacific. The shipping and aviation sectors have been warned to stay clear of the debris fall "footprint".

Most of the vehicle should be vaporised in the fall.

"We know there are a few heavy parts like the thrusters, obviously, which will hit the South Pacific; they're built to withstand very high temperatures," Capelle told the BBC. "The ATV's Russian docking system is also a very substantial piece of hardware, and part of that will probably fall into the water as well."

Esa already has another ATV (Automated Transfer Vehicle), named after Italian physicist Eduardo Amaldi, in preparation.

This vehicle is due to be shipped to Europe's spaceport in French Guiana in the coming few weeks. Its launch on an Ariane rocket should take place in February.

Future ideas

Two further vehicles are planned for launch in 2013 and 2014, before the freighter programme comes to an end.

Europe then hopes to take the capabilities and expertise gained on ATV into a new type of spacecraft.

Its purpose and design are currently being discussed with the US space agency (Nasa).

It is possible, but by no means certain, that this new project could form a European contribution to the Americans' Multi-Purpose Crew Vehicle (MPCV).

The MPCV is envisaged as a manned ship that could take astronauts beyond the space station, to the Moon, asteroids and Mars.

"We are in discussion - and I emphasise just discussion - with Nasa about contributing with some sort of ATV derivative," Dettmann told BBC News.

"What that derivative is - we're not sure yet. It could be a propulsion service module that contributes to the Nasa Multi-Purpose Crew Vehicle. But, I say again, these are investigations which have only just started, and we have to work out whether it is something that will really benefit both parties."

European space officials will be following Kepler's progress from here at the Paris Air Show in Le Bourget. The biennial event is a key one in the space industry and institutional calendar, and Esa will be using the show to highlight the freighter's achievements.

Image caption The spectacular return of the previous freighter, Jules Verne in 2008, was captured on video

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