A giant inflatable heat shield could prevent a space satellite from burning up during re-entry into the Earth's atmosphere, if a daring test flight goes according to plan.

If successful, the new heat shield technology will allow spacecraft to be lighter and less complex than before. This could allow them to be reused, something that is virtually impossible at present because of the heat damage suffered by a spacecraft when they collide with the Earth's atmosphere.

Inflated in two stages

The only craft that is reused is Nasa's space shuttle, with its heat-resistant tiles. However, this technology is far too expensive to be used on satellites, at least for the present.

The inflatable heat shield is part of a plan by the European Space Agency, DaimlerChrysler Aerospace and NPO Lavotchkin, a Russian company that makes tough inflatable materials.

Kazakhstan blast-off

The test flight will begin with the launch of a Russian Soyuz spacecraft from Kazakhstan on 9 February. The rocket's upper stage will go into orbit, with an experimental satellite still attached to it.

After circling the Earth five times, it will begin a series of braking manoeuvres and, at an altitude of 150 km, the satellite will separate from the upper stage.

Both craft will then inflate their heat shields. If all goes to plan, the massive cone-shaped shields will decelerate both craft when they open out.

The first stage of inflation spreads an eight metre (26 feet) diameter fan of air-filled shield on the upper stage and a 2·4m (8ft) fan on the satellite.

While the nose of the satellite takes the brunt of the thermal shock wave generated on entering the atmosphere, as well as temperatures of more than 1000 degC, the inflatable heat shield, designed to withstand 500 degC, will protect the rest of the spacecraft.

Second stage

As the spacecraft descend further, their shields alone are insufficient to slow them down. A second stage is therefore inflated, nearly doubling the circumference of each of them.

It is hoped that the drag induced by the inflatable heat shields will slow them down to a safe touchdown speed of about 50 km per hour.

Using this technique, the upper stage of the Soyuz rocket could become the world's first upper stage to be returned to Earth safely.

According to DaimlerChrysler Aerospace, recent tests have suggested that a similar technique with a slower landing could eventually be used for manned missions.

The mission can be followed in real time on the internet.