Andy Thomas knew he'd have to take some serious steps to become an astronaut.

"When I applied to become an astronaut I think there were 3,000 applicants for 20 jobs. I knew I had to make my application stand out," Dr Thomas said.

The first thing he did was quit his job as the principal flight scientist at aircraft company Lockheed in 1990 to work at NASA's Jet Propulsion Laboratory.

"That turned out to be a very, very good decision because it was there I was able to get some experience from the space side of aerospace."

NASA's basic requirements US citizen or hold dual citizenship (Andy Thomas was born in Australia but became a US citizen in 1986)

US citizen or hold dual citizenship (Andy Thomas was born in Australia but became a US citizen in 1986) Have a bachelors degree in engineering, biological science, physical science, computer science or mathematics (Dr Thomas has a PhD in mechanical engineering from the University of Adelaide).

Have a bachelors degree in engineering, biological science, physical science, computer science or mathematics (Dr Thomas has a PhD in mechanical engineering from the University of Adelaide). Three years professional experience or at least 1,000 hours of experience as jet pilot

Three years professional experience or at least 1,000 hours of experience as jet pilot 20/20 vision (you can have glasses or have had corrective surgery)

20/20 vision (you can have glasses or have had corrective surgery) Meet the height and physical requirements needed to work in a spacecraft and wear a spacesuit

Meet the height and physical requirements needed to work in a spacecraft and wear a spacesuit Women were first accepted into the program in 1978

Armed with his qualifications, new skills and contacts in the space industry, the then 39-year-old aerospace engineer was called up for an interview in October 1991.

Then, nothing for five months.

"You are on tenterhooks because you've just gone through the interview for the job of your dreams."

It was only when his neighbours called him he had any inkling he might be in with a chance.

"They said 'Is there something you're not telling us?'

"I said 'No, why? And they said 'Well, the FBI have been around asking questions about you'."

Just over four years later, Dr Thomas was on his first mission aboard the Space Shuttle Endeavour. It would be the first of four space missions he completed across his career.

Testing for the right stuff

The Mercury Seven. Back row: Alan Shepard, Gus Grissom, Gordon Cooper; front row: Wally Schirra, Deke Slayton, John Glenn, Scott Carpenter. ( NASA )

The author Tom Wolfe was the first to coin the phrase "the right stuff", using it as the title of his book about the very first group of astronauts selected by NASA in 1959.

"What is it that makes a man willing to sit on top of an enormous Roman candle ... and wait for someone to light the fuse? Arrogance? Stupidity? Bravery? Courage? Or, simply, that quality we call 'the right stuff'?"

The group, known as the Mercury Seven, fit all of NASA's criteria at the time: they were US citizens, test pilots with at least 1,500 hours of flying time under their belt, under 40, and were men.

They were whittled down from a group of 110 applicants to ensure they were the right height (under 180 cm), weight (no more than 81.5 kg) and had perfect vision.

Their physical endurance was tested using treadmill and step tests, vibration and heat tests, and from their ability to withstand having their feet in buckets of ice water and blowing up balloons until they were exhausted.

They were also subjected to a range of psychological challenges to test their self-awareness and capacity to keep their cool, including answering questions such as: "Whom am I?" and "Whom would you assign to go on the mission if you could not go yourself?"

Loading...

When Dr Thomas went for his interview more than 30 years later, he was also put through a battery of tests.

"There were ... multiple choice questions to determine psychological profile. And there were some battery of intelligence tests looking at graphics and interpreting imagery and putting things together," he said.

By this time the demands of space travel started to change as technology became more sophisticated and the Cold War ended.

In 1992, as Dr Thomas started his stint in astronaut bootcamp, the US and Russian governments agreed to co-operate on space projects, including the yet-to-be built International Space Station (ISS).

On his second space mission in 1998, Dr Thomas flew onboard the Space Shuttle Endeavour to dock with the Russian space station Mir, where he would spend more than 141 days in space.

How space challenges humans

Bulky spacesuits and confusing visual cues pose challenges for astronauts on spacewalks. ( NASA )

In space, you need to expect the unexpected.

"[You need] the intellectual flexibility to take on challenges outside your normal realm of professional background," Dr Thomas said.

"You might, for example, be confronted with an medical issue that you might have to help the crew medical officer [with]. You might even have be the crew medical officer."

Or you might need to deal with the complicated onboard computer systems.

"The trajectory flight is based on some fairly sophisticated orbital mechanics and you need to be able to understand all of these different fields of science."

Do you have what it takes to be an astronaut? Email abcengagement@abc.net.au for tests and education resources.

And you need to be good with tools, which can be challenging in zero gravity.

"Everything floats, which can be liberating but, well, if you're working with tools and you're disassembling a piece of equipment, you can't put anything down."

Donning a spacesuit can also be physically challenging, said Dr Thomas, who did a 6.5-hour spacewalk on his third mission, this time to the ISS in 2001.

"You're in a very bulky pressure suit and the joints are very stiff because of the pressurisation of the suit.

"You don't have to be a Schwarzenegger or something like that but you do need to be reasonably strong and healthy.

Manual dexterity and the ability to operate a robotic arm are also a must.

And while the views are great, they can play tricks with your mind.

"There's essentially no up or down which is one of the main cues you use for orienting yourself."

While there was a lot of technical training to cover all these scenarios, the shuttle program and longer duration stints threw up new challenges.

A change in space culture

In 2005, Dr Thomas flew on his fourth shuttle mission — the first following the Columbia disaster — to work on the ISS, now home to both US and Russian crews. A year later it was opened up to astronauts from other nations.

While the Russians had experiences of long-duration space missions — the longest continuous record of 437 days and 18 hours was set in 1995 by cosmonaut Valeri Polyakov — space shuttle missions only lasted around 10 days.

"You can basically suck up anything for 10 days," Dr Thomas said.

"But as we started flying NASA astronauts, first on the Mir space station, and then later on the International Space Station, it became very obvious there was going to be a need to instil some sort of sensitivity for cultural awareness, teamwork and leadership ability to self-manage in a very austere environment for a long period of time."

Astronaut experiences aboard Mir Space Station, seen here from the space shuttle, created a major shift for NASA. ( NASA )

As a result, he said, NASA realised it needed to adapt and there has been a change in the culture over the past 20 years.

"The so-called right stuff as defined by Tom Wolfe for this assessment of Mercury, Gemini and Apollo is a very different skill set than really was required for long-duration missions."

Dr Thomas, who spent a year living in Russia before his stint on Mir, became involved in developing training programs aimed at building psychological stamina skills.

"We had found from the Mir experience that some people were not suited to long-duration spaceflight."

"If you're a person who is very socially gregarious and highly dependent on many social outlets for your psychological wellbeing you're probably not the right person to do a long duration spaceflight because you're just not going to get those needs met."

For future space travellers, the challenges will be even more extreme.

So, you want to go to Mars?

If you go to Mars you'd want to hope your team would not leave you behind. But we don't know how teams would cope. ( 20th Century Fox/Scott Free )

A round trip to Mars will take at least three years and be very different to anything astronauts have experienced to date.

"Another big challenge ahead of us will be going to Mars and so on where you don't have a lot of the resources that you have on a space station," Dr Thomas said.

For example, you can literally phone home from the space station.

"It's just a phone call and you have near real-time communication with the ground, but they will be out there by themselves.

"They won't have real-time voice communication. You'll send a message and then you might have to wait 20 minutes before you get an answer."

Their living conditions will also be a lot more cramped.

"There's plenty of places where you can go [on the ISS] and be alone if you need to.

"That won't be true on a vehicle going to Mars which is going to be basically habitation module about the size of a bus for four people."

And there'll be very limited opportunities of things to do.

"One of the things you can do on the space station if you're ever bored is just go to one of the windows and look out to Earth and you're always guaranteed of a spectacular view."

"They won't be able to do that when they go to Mars because they'll be bathed in bright sunshine the whole way and they won't be able to look out and see a planet below them except when they get to Mars or just after they've left."

In other words, you need to be resourceful and able to make do with limited resources for your own entertainment and psychological wellbeing.

"And that's a very different kind of skill set from what's traditionally been called 'the right stuff' paradigm."

Human petri-dishes hint at future skills

Analog facilities like HI SEAS in Hawaii test participants abilities in a Mars-like environment. ( Supplied: Hawai'i Space Exploration Analog and Simulation )

Understanding how humans would cope with such a challenging environment is the focus of numerous experiments around the world, where teams of willing participants are shut up in extreme isolation for up to eight months.

Preliminary results from these human petri dishes, as well as analysis of long duration spaceflights in the past and isolated environments on Earth, presented at the American Association for the Advancement of Science meeting earlier this year hint at what might happen.

When put into isolated environments astronauts tend to do one of three things, said Noshir Contractor of Northwestern University.

"They either start pointing fingers at other crew members that they don't like. They collectively point fingers to Mission Control as a team from space, or the most dangerous, and the most depressing, is sometimes they point fingers at themselves," Professor Contractor said.

His colleague, Leslie DeChurch, studied nine groups of people who gave up 30 to 45 days of their lives to live in NASA's Human Exploration Research Analog (HERA) at the Johnson Space Centre.

The study showed the team's performance peaked between days 14 to 17 while they still had real-time communication from the outside world, but things went pear-shaped around days 30 to 34 when there was a communication delay. Some call this the "three-quarter effect".

"That's where we see their problem-solving abilities, and their ability to make quality decisions using disparate expertise declines," Professor DeChurch said.

Missions to the Moon such as Apollo 11 and 13 relied upon extensive teamwork to troubleshoot problems.

"Mars is two hundred times [that] on a good day or at a good orbital cycle further than the Moon," Professor DeChurch said.

"When we go to Mars there won't be hundreds of great minds completely running the mission.

"Instead there will be four to 24 individuals that will only have each other."

The "three-quarter effect" is also well known from experiences in Antarctica.

In this environment, research suggests one human skill acts as a circuit breaker: humour.

"We had one person on one of my flights who was particularly witty and humorous. He made a big difference to the wellbeing of the whole crew," Dr Thomas said.

Luckily, Dr Thomas never experienced the "three-quarter effect" on any of his missions. In fact, he lost sense of time during his four-month stint on Mir. One morning, a flight controller asked him if he knew what day it was.

"I thought, 'well I don't know, it's Tuesday or something isn't it?' And he said 'No. This is your 100th day in space'.

"I was absolutely stunned when he said that because I had no idea I'd been that long.

"That requires that you put away the cares and tribulations that you have normally you deal with on a day-to-day basis on the ground.

"And when you do that ... it's an extremely tranquil experience."