How risky was Glenn's trip?

Glenn: No stranger to the risks of spaceflight

By our Science Editor David Whitehouse

As John Glenn returns from space, a new analysis of the safety of the Space Shuttle provides a realistic assessment of the risks he is ran.

Using a new method to assess the risks involved in a shuttle launch, Nasa concludes that the chances of a catastrophic failure during launch is 1 in 428.

To put that into perspective, if the same risk applied to a daily car journey to and from work, you would be killed within a year.

The risk analysis emphasises that the Space Shuttle is still an experimental vehicle and that space travel still holds many dangers.

Nasa's estimation of the risks of a shuttle accident have not always been so honest.

Before the 1986 Challenger accident that occurred on the 25th shuttle flight Nasa often quoted the chances of a fatal accident as 1 in 1,000 and sometimes 1 in 10,000.

With hindsight these figures were fantasy. Nasa was brought back to reality after the Challenger accident that showed the chances of losing the crew was 1 in 25.

Improvements made

Since then many improvements have been made, especially to the shuttle's reusable main engine, its most dangerous component.

John Glenn is no stranger to the perils of spaceflight. On his first mission he was the first man to be launched in the new Atlas rocket. During his flight there were several malfunctions, one of them potentially fatal.

The Space Shuttle he will use on Thursday is far safer than his tiny Mercury capsule of 36 years ago. But the risks of spaceflight today cannot be ignored.

Getting into space involves the release of titanic energies. If something goes wrong those energies may not be forgiving.