tp-kepler-ariane-cutaway

A cutaway in an artist's concept shows how the ATV Johannes Kepler sits atop the Ariane rocket.

A European cargo spaceship full of goodies and supplies for the International Space Station is expected to launch Wednesday.

The pilot-less Johannes Kepler Automated Transfer Vehicle-2 was originally supposed to blast off from Kourou, French Guiana, on Tuesday on an Ariane 5 rocket. Its launch was rescheduled for 4:45 p.m. ET Wednesday after a problem with the liquid oxygen fuel tank was detected during the first launch attempt.

Unpiloted cargo ships

ATV-2 is the second unmanned cargo ship sent to the space station by the European Space Agency. The first launched in 2008.

Russia has long used its unmanned Progress cargo ships to supply both the former Mir space station and the International Space Station.

However, other nations have recently begun launching their own automated cargo transfer vehicles ahead of the retirement of the U.S. space shuttle fleet in 2011.

Japan launched its first such vehicle in 2009 and its most recent model, the Kounotori2 H-II Transfer Vehicle, also known as HTV2, arrived at the station on Jan. 27.

ATV-2 is scheduled to arrive at the space station after an eight-day journey.

The European Space Agency cargo ship's load includes a pressurized module that the space station crew can enter, said Kirsten MacDonnell, the Canadian cargo engineer in charge of planning and packing a load of more than six tonnes in the vehicle.

Inside are six racks of food, clothing, spare parts and a special bag for each of the six astronauts on the space station containing surprises such as chocolate, beef jerky or extra hardware for experiments, depending on the crew member's tastes and interests, MacDonnell told CBC's As It Happens Tuesday.

The module itself is a bit of a gift, as it adds extra space to the crowded station, she added.

The cargo load also includes extra oxygen for the crew and fuel to boost the space station back to a higher orbit.

"Even though it's up in space, there's still some atmospheric drag and solar effects and this kind of thing that actually cause the space station to slowly keep falling towards Earth if it's not reboosted every so often," said MacDonnell, who was keeping an eye on the launch from The Hague, Netherlands.

Much of it was loaded through the rear of the ship, but the last portion was complicated, MacDonnell said, as the ship was already atop the rocket. That required someone to be lowered through the narrow docking hatch, which is roughly the diameter of the drum in a commercial clothes dryer.

"Then we were lowering the bags down to them. And we loaded 430 kilograms this way."

ATV-2 will remain docked to the Russian Zvedza service module until early June, when it will head back to Earth and burn up during its re-entry over the Earth's atmosphere.