An artist imagines an astronaut on Mars.

In hopes of answering one of the "fundamental mysteries of the cosmos" - whether life exists beyond the Earth - NASA is developing the capabilities needed to send humans to the red planet. Mars lies at a distance of 56-million kilometres from Earth. With current technology, a return journey would take three years. But the long timespan is the least of the problems that the team of scientists, engineers and doctors working on the mission to Mars face. A documentary by BBC Horizon explores some of the greatest challenges that lie on the journey to Mars.

Different from the moon landing

NASA is imagining a ride across space more than two decades after the historic moon landing. However, a journey to Mars is going to be very different from a journey to the moon, because it would take man outside the Earth's orbit for the very first time. And one of the greatest challenges that scientists and doctors face is finding people who are capable of making this journey.

If astronauts are to survive months on a spacecraft, where the view out of their window never changes, systems must be put in place to safeguard their physical and psychological wellbeing. A mission to Mars would require new rockets on a new scale, a new way of surviving in space, and a new breed of astronauts.

The psychological wellbeing of the astronauts

"Is a mission to Mars outdoor stuff or confinement?" asks Professor David Dinges of the Perelman School Of Medicine, University of Pennsylvania. If you become depressed on space flight, then you pose a risk to yourself and rest of flight, he explains.

One solution being tested by Dr Dinges is using the spacecraft's cameras to watch over astronauts.

Dr Dinges and his team are using new facial recognition software, and its success hinges on recognising telltale signs on the face which would betray what the mind is thinking, whether the astronauts are experiencing positive or negative feelings. The software is also important in recognising concentration - whether astronauts are tired, whether they have had enough sleep etc.

Physical challenges

Meanwhile, even as doctors work to overcome the psychological challenges of sending man to Mars, a team of doctors is also working to tackle one of the major physical challenges that astronauts would face - low gravity.

How do scientists understand the long term effects of weightlessness, here on earth?

One way is NASA's ongoing bed study which aims to observe and analyse the effects of fluid pressure on astronauts' eyes and optic nerves. Volunteers spend 70 days lying down for research, with their heads tilted down six-degrees to best emulate space.

Another physical problem is that of being strong enough on reaching Mars to explore space. Scientists have concluded that exercise alone, no matter how optimised, is not going to be enough. They are now exploring other options that would make human beings strong enough for the journey to Mars - something to stimulate muscle and bone growth in absence of gravity.

One possible option is using the hormone testosterone for the protection of bone and muscles - an area of research being explored by Dr Randall Urban.

The problem of radiation

Even assuming that the body and mind are strong, one powerful threat remains - radiation.

The Curiosity Mission found radiation in space several hundred times more intense than radiation here on Earth. Scientists are working on ways to shield astronauts from radiation, possibly by using items like food and water that would already be on the spacecraft.

However, an even bigger threat remains: Another source of radiation - galactic cosmic rays.

Galactic cosmic rays are emitted from supernovas or exploding stars. They are powerful enough to cause memory loss after just six months in space. So the only way to tackle this problem is either to get to Mars quicker - or find people that are less susceptible to the effect of these rays.

Finding the right "genetic fit" for the mission to Mars is a theoretical possibility that NASA will explore in the future, but fact remains that as of now, there is noobvious solution to problem of surviving space radiation.

The challenge of landing on Mars

After assuming everything is taken care of and the mission is on track, comes greatest engineering challenge - landing on the surface of Mars.

Dr Adam Steltzner, the man who masterminded NASA's Mars Exploration Rover, is now part of a team trying to see if humans can be sent to Mars. He has been assigned the task to figure out how a spacecraft could land on the surface of Mars.

Last week, our @MarsCuriosity Rover snapped this selfie in the midst of a Martian dust storm that reduced sunlight and visibility. Find out what we will learn from our rovers on the planet as well as our orbiting spacecraft: https://t.co/PZl5nLxoHBpic.twitter.com/PQgmMEY6DJ — NASA (@NASA) June 20, 2018

The smaller size of the Curiosity Rover meant that it was successfully slowed by aerodynamic drag before landing on Mars. However, Scaling up the size of the aircraft for humans also changes the physics drastically.

According to Dr Steltzner, one possibility is coming in sideways, so the drag on spacecraft increases significantly, slowing the rocket from hypersonic to supersonic. It remains to be seen whether this can be done.

Other obstacles

The journey to Mars will be expensive, ambitious and risky. Even if scientists find solutions to all the problems listed above, there still remain other issues - like the problem of finding enough fuel for the journey; and the weather on Mars, where powerful dust storms can envelop the planet for months.

But NASA is hopeful.

"NASA is developing the capabilities needed to send humans to an asteroid by 2025 and Mars in the 2030s," NASA writes on its website. "Engineers and scientists around the country are working hard to develop the technologies astronauts will use to one day live and work on Mars, and safely return home from the next giant leap for humanity."