It is 20 years ago today that the Space Shuttle Challenger exploded. I well remember this, it was a huge event. I saw it on television, and could not believe it. The explosion, then those two rockets flying off in seperate directions.

Of course, it provoked the expected bad taste playground 'humour', such as 'Q. What colour eyes does an astronaut have? A. Blue... one blew this way...'

The great physicist, Richard Feynman (who should be as well known as Einstein) was on the investigating board of the Challenger disaster - famously (amongst folks who know about this sort of thing) demonstrating before the press how the 'O rings' which sealed the fuel tanks could fail.

It did graphically demonstrate that space flight whilst routine, was not risk free, despite the low risks stated prior to the accident by NASA management (contrary to the estimates of the engineers).

For me, Challenger was one of those defining moments as I grew up (along with Chernobyl in the same year). This was why I watched the landing of Discovery after a troubled flight with baited breath. I literally held my breath as the infra red showed the shuttle circling, and did not realise this for some time... not good!