That’s me in the picture: Bruce McCandless, 47, in the world’s first untethered space flight, February 1984

'I wanted to say something similar to Neil [Armstrong] when he landed on the moon, so I said, "It may have been a small step for Neil, but it's a heck of a big leap for me." That loosened the tension a bit'

The main aim of our nine-day mission on Challenger was the release and deployment of two communications satellites; the walk would follow that. It was a long time in the making: decades earlier, I helped develop the jet-propelled backpack I'm wearing, an MMU, or Manned Manoeuvring Unit. We were still testing and tweaking it six weeks before we went up. I was delighted to have been picked for the mission: it was a murky selection process, lots of back and forth between mission command and management.

The day before my walk, we reduced the pressure and increased the oxygen in the shuttle to get the nitrogen out of my bloodstream, otherwise I'd get the bends. Where I live now, outside Denver at an altitude of 8,300ft, has lower oxygen levels than the cabin did that day.