Nearly 40 years ago, European countries worried by US and Soviet dominance of space gave the green light to the first Ariane rocket, a wee launcher capable of hoisting a satellite payload of just 1.8 tonnes -- the equivalent mass of two small cars.

On Wednesday, the fifth and mightiest generation of Arianes is set to take a whopping 20.2 tonnes into orbit, a cargo craft the size of a double-decker bus and a record for Europe, proud engineers say.

The payload is the fourth cargo delivery by the European Space Agency (ESA) to the International Space Station (ISS), bringing food, water, oxygen, scientific experiments and special treats to the orbiting crew.

An Ariane 5 ES is scheduled to blast off from ESA's base at Kourou in French Guiana at 6:52 pm (2152 GMT) Wednesday, taking aloft an Automated Transfer Vehicle (ATV), a robot space truck dubbed the Albert Einstein.

The cargo craft will carry almost seven tonnes of dry and fluid cargo for its five-month mission.

About an hour after liftoff, somewhere over New Zealand, the ATV, some 10 metres (33 feet) long, will detach from the rocket's upper stage and then deploy its four energy-generating solar panels and navigate autonomously, guided by starlight, to the space station.

It will dock with the ISS on June 15 at an altitude of about 400 kilometres (250 miles) above the planet.

"By then it has a velocity of 28,000 kilometres (18,000 miles) per hour, and has to fly to a destination (the docking mechanism) about 60 cm (23 inches) in width," said Bart Reijnen, head of orbital systems at the Astrium space company which built the lifeline craft.

"It has to fly there fully autonomously and dock with this target of 60 cm with a precision of six cm (2.4 inches). That is something that might be difficult to imagine."

The craft has enough fuel to make three docking attempts if something were to go wrong during the final approach, said Jean-Michel Bois, ATV operations manager in Toulouse, France, from where the vessel's flight path will be monitored.

In the case of a failed attempt, the ATV would retreat from the ISS and go into a different orbit, returning two days later to try again.

This has never happened, said Bois, adding: "I cross my fingers."

The Albert Einstein will boast the largest assortment of goods yet delivered to the ISS -- a total of 1,400 individual items that include everything from pyjamas and toothbrushes to peanut butter, lasagne and tiramisu for its six astronauts.

Apart from several months' worth of food, the craft carries 4.8 tonnes of fuel needed to dock with the ISS and give it a boost into higher orbit with its onboard engines.

This is necessary because the ISS is in a low Earth orbit and encounters atmospheric resistance which causes it to fall towards our planet at a rate of about 100m (300 feet) per day.

ATVs can also push the ISS out of the way of oncoming space debris.

ESA is contracted to provide five ATVs as its contribution to the ISS, a US-led international collaboration.

The three previous missions have performed flawlessly, muting criticism of the billion-euro ($1.3-billion) development cost.

The Albert Einstein will carry 800 kg (1,760 pounds) of propellant to be pumped into the ISS itself, as well as more than 500 kilos (1,100 pounds) of water and 100 kilos of oxygen, according to Astrium.

And it will bring a scientific experiment designed to test the behaviour of emulsions -- a mixture of liquids that do not blend, like mayonnaise -- in weightless conditions.

The ATV's pressurised cabin will provide welcome extra space for the ISS crew -- Americans Chris Cassidy and Karen Nyberg, Russians Fyodor Yurchikhin, Pavel Vinogradov and Alexander Misurkin, and Italian Luca Parmitano.

After completing its mission, the ATV-4 will undock from the ISS filled with about six tonnes of garbage and human waste, and burn up over the Pacific.