Senin, 02 Juli 2007

Mission Guide: Jules Verne

The "Jules Verne" is Europe's first Automated Transfer Vehicle (ATV) to fly to the International Space Station.

Built for the European Space Agency (Esa), the ATV is a sophisticated, automated spacecraft designed to deliver 7.5 tonnes of cargo - air, water, fuel, scientific equipment, food, clothing and even personal items - to the platform.

The ATV is part of the barter arrangement Europe has with its international partners on the ISS project.
Instead of handing over cash to cover station running costs, Europe will take on the major responsibility of resupplying the platform.

With the US space shuttle soon to retire and a replacement some years away, this role will be vital when the crew complement rises to six individuals.

The station will continue to receive deliveries from Russian Progress craft and a future Japanese vehicle called the HTV - but neither have the capacity of the ATV.

The ATV will also be used to boost the platform to a higher altitude. This is necessary to overcome the effect of atmospheric drag which gradually pulls the ISS back to Earth.

One day, the thrust from an ATV's four main engines may be called on to de-orbit the ISS itself when it has reached the end of its mission.

BIG LAUNCHER

An ATV has to be launched on a specially prepared Ariane 5 rocket from the European spaceport at Kourou in French Guiana.

Arianes are more accustomed to launching communications satellites with a mass not exceeding 10 tonnes. These spacecraft are usually placed in Geostationary Transfer Orbits (GTOs) that take them out to 36,000km above the Earth.

An ATV at launch is 20 tonnes and has to be put in a Low Earth Orbit (LEO) at just 230km above the Earth. The Ariane 5-ES will use a re-ignitable upper-stage to circularise this low orbit and put the ATV on the right path to catch and dock with the ISS.

The upper-stage will complete two re-ignitions, the second - after releasing the ATV - will put itself into a controlled dive over the ocean.

AUTONOMOUS VEHICLE

The ATV uses a sophisticated navigation system to find its own way to the space station.

GPS (Global Positioning System) technology is employed to get to within 300m of the platform. Optical sensors are then used for the final approach.

These involve flashing laser light off reflectors already positioned around the docking port on the Zvezda module.

The ATV moves in stages towards the station. At each hold point, ground staff will approve the next phase of the automated approach.

An astronaut on the ISS also sits in front of a monitor and panel to oversee the docking.

Two important buttons - one yellow, one red - allow the astronaut either to stop the ATV in its tracks or, in an emergency, send it away from the station to a safe parking location.

GIANT REFUSE SKIP

An ATV can stay at the ISS for up to six months. Gradually its new supplies will be depleted and the space used to store station waste - up to 6.5 tonnes.

When the ATV undocks from the platform, it will take this waste into a controlled re-entry over the Pacific Ocean.

The ATV will break up into small fragments. Future variants of the ATV may allow for part of the vehicle to survive the fiery re-entry - or for heat-resistant capsules to be released on the descent.

These could be useful if scientists wanted experimental items from the ISS returned intact.

WHAT'S IN A NAME?

The French author Jules Verne wrote about fantastic voyages - into space, to the bottom of the sea, and around the world.

The ATV could also herald extraordinary voyages for Europe.

Although the ATV is not designed to carry astronauts, the fact that people can move around safely inside it demonstrates Europe has many of the necessary skills to implement a manned space transportation system should it decide to.

Autonomous navigation and docking will be an essential technology for any mission which attempts to return rock samples from Mars - a stated goal of both Europe and the US.

Specimens lifted off the surface of the Red Planet would meet up in orbit with a transfer vehicle that had the necessary power to get them back to Earth.