The space race is going public with more and more ways for people to get a zero-g fix.
But to get a real taste of space, professional astronauts not only have to pass a strict vetting system but also spend at least two years training to learn how to live and work in this unique environment.
Even then, three-quarters of them will suffer from space motion sickness and many will experience post-flight hallucinations because of the way microgravity messes with the balance system.
To minimise this, an astronaut's training regimen includes a whole host of challenging tests – here are some of them...
Prepare for lift-off
Teaches: How to handle rocket propulsion
Without the correct training, huge rocket lift-off forces can send astronauts into a g-induced loss of consciousness (g-LOC). Blood flow to the eyes reduces first, causing loss of colour perception (‘grey-out’) and tunnel vision, before the brain finally shuts down.
This machine takes astronauts' tolerance from a normal 4-6g to a massive 9g by spinning them faster and faster until they can’t take any more.
Cope with re-entry to Earth
Teaches: How to deal with a loss of control
This machine simulates the disorientation felt in a flat spin during re-entry into Earth’s atmosphere by spinning its occupant in random directions.
It was used in older missions to help astronauts cope with disorientation and to teach them how to recover an out-of-control spacecraft using joysticks. It is now used as part of the Space Camp training programmes at NASA’s public space-training centre in Huntsville, Alabama.
Survive the 'vomit comet'
Teaches: How to get used to weightlessness
A reduced-gravity aircraft can replicate the space environment using a parabolic flight technique which involves climbing at increments of 45 degrees before levelling off and then descending in stages of 30-degree dives. This creates up to 25 seconds of weightlessness during the ascent. Astronauts will repeat this process up to 60 times in one flight, making for one bumpy ride, which explains why the flight is known as the ‘vomit comet’.
Work at zero-gravity
Teaches: How to operate in extreme conditions
The Neutral Buoyancy Laboratory is the world’s largest indoor pool and it is here where astronauts learn to work in a weightless environment, spending 10 hours under water for every hour they walk in space.
Fully suited, they are craned in to float around sunken spacecraft replicas with a depth of up to 12m. But it is not quite like the real thing as objects resist force under the water, whereas in space they just float away.
Move around on the moon
Teaches: How to space walk
At the Johnson Space Centre’s Virtual Reality laboratory in Houston, Texas, astronauts put on an immersive headset and are transported into imaginary space situations where they can rehearse their duties before the real thing.
A long way from the Apollo mission training, this high-tech experience, complete with motion gloves and body sensors, enables astronauts to try out vital techniques, such as walking and operating equipment in alien settings, before their life depends on getting them right.
Eating a balanced diet
Teaches: How to stomach space food
Silver packets stuck down onto a tray with Velcro may not look gourmet, but they do the job. Nutritionists work with astronauts to create a suitable diet, and although some fresh goods are taken onboard, the menu is mostly made up irradiated, thermostabilized or dehydrated food stuffs.
The main dietary problems in space are reduced Vitamin D due to lack of UV light, high iron due to blood thinning and low calcium absorption, which can lead to a loss of 1-2 per cent in bone mass each month.
Survive in the wildest of locations
Teaches: How to get by in a remote environment
Although mission control aims to plot a sensible trajectory back to Earth, if it all goes wrong an astronaut could end up submerged in the sea or pitched into an Arctic winter until help arrives.
To give them the skills they need to survive, astronauts are sent to train in remote locations with their space pods.
Land on an asteroid
Teaches: How to prepare for the next frontier
This is Aquarius, the world's only undersea research station, where NASA sends its Extreme Environment Mission Operations (NEEMO) teams to live for up to three weeks at a time.
In this pressurised home, some 18m below the sea off the coast of Key Largo, the NEEMO astronauts train for long-term projects like trips to Mars and landing on asteroids while also training for the worst mission possible – rescuing an incapacitated astronaut.