Space talk: The reality of 'Gravity'

Unlike Sandra Bullocks predicament in the movie, left to fall at the mercy of the laws of physics until rescued by George Clooney, we have one last option available. The US spacesuit that is used for conducting spacewalks is equipped with a jetpack called SAFER. This discharges high-pressure nitrogen gas to 24 small thrusters located around the spacesuits backpack. The astronauts control the thrusters using a hand controller and if you think that sounds like something from an early James Bond movie, then you wouldnt be far wrong.

Thankfully, the chances of finding ourselves in such a situation are slim. During a spacewalk, astronauts are protected from becoming detached by a retractable safety tether, anchored to the space station at one end and attached to the spacesuit at the other. However, this thin steel wire is a double-edged sword and astronauts must remain constantly vigilant so as not to get tangled up. In addition, theres a mantra drilled into all of us rookie astronauts: You stop, you drop meaning that as soon as you stop moving from A to B, you drop another tether, a short strap securing you to the nearest handrail.

Under other circumstances, flying around in space with a thruster pack must rank up there as one of the most exhilarating feelings imaginable. Only a handful of astronauts have experienced this. I think one of the most inspirational photographs taken from space was during the first of these untethered spacewalks, of Nasa astronaut Bruce McCandless. This image, taken from the Shuttle, shows McCandless floating against the empty blackness of space above a stunning blue Earth. The feelings of isolation and exposure must have been immense.

However, I have no time to dwell on these thoughts. My emergency rescue scenario is extremely challenging, and the small quantity of nitrogen available for propulsion means that you only get one shot no mistakes.

Thankfully, the SAFER is equipped with an automatic attitude hold that stops the nauseating tumbling motion that will occur if you do not smoothly detach from structure. This happened to Sandra Bullocks character in Gravity when high-speed debris knocked her from her shuttle and left her tumbling through space. If youre lucky, when the tumbling ceases, you will be able to see part of the space station, or maybe Earth, as a reference point. Not so lucky, and precious nitrogen has to be expended in searching for the space station.

Having successfully located it, the nitrogen remaining is already likely to be down to around 50 to 60 per cent, and although the tumbling motion will have stopped, you are still drifting away from structure. As you get further from the space station, other factors such as orbital dynamics complicate matters.

In a nutshell, objects in higher orbits travel more slowly and those in lower orbits travel faster. This explains why our TV satellites are way out at nearly 36,000km (22,369 miles), where they orbit the Earth only once every 24 hours, matching an Earth day and therefore remaining geostationary. In contrast, the space station at only 350km (218 miles) altitude travels at 17,500 miles per hour in order to remain in orbit and circles the Earth every hour and a half. These orbital effects become apparent even at relatively short distances, and it is unnerving to watch the space station slipping further away as you drift into a different orbit. Time is of the essence.

My first two self-rescue attempts went well, which was a relief in more ways than one since my instructors had commented that helicopter pilots (such as me) are usually pretty good at this sort of thing no pressure, then! For my third attempt, the stakes were raised and I was ejected into space at a faster rate and from a more remote part of the space station. Worse still, my SAFER took three attempts to initialise, by which time the space station was beginning to look awfully far away.

As I recovered the situation, a quick check of nitrogen showed a worrying 10 per cent remaining. The nearest handrail to me was off to the right and I was not convinced I was going to make it. With an arm outstretched, I decided to go in hard and fast. It worked, but only just, and I could hear my instructors in the background chuckling at their console. It had been a close call but thats exactly what these training sessions are for.

Gravity is based on a scenario whereby a Russian satellite incurs a missile strike, causing a cascading collision cloud of space debris. This is not such a far-fetched concept and is in fact known as the Kessler Syndrome. Space debris is a big deal. There are currently more than 600,000 pieces of debris larger than 1cm orbiting the Earth.

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Space talk: The reality of 'Gravity'