Human life on Mars?

On December 11, 1972 two out of the three member crew of Apollo 17 landed on the moon. While Ronald Evans remained in lunar orbit, watching over the spacecraft which would later return the trio to earth, Gene Cernan - officially the last man on the moon – and Harrison Schmitt, the only scientist (a geologist) to walk on the moon spent almost 72 hours on the surface, 22 of which were outside of their landing craft.

Now, more than thrity years after Apollo 17, it appears that financial planners are prepared to spend the money to develop the technology and infrastructure required to send people out of earth orbit – but the object of these initiatives are much further and much more difficult to achieve than the moon. Recently, on August 4th 2007, NASA launched a spacecraft on a nine-month journey to Mars, where it will dig below the surface for clues to the existence of past or present life. The Phoenix probe will aim to reveal not only on the history of the water ice on Mars, but also on whether the region could support microbial life. This mission follows the two robotic ‘geologists’, Spirit and Opportunity, which landed on Mars in January 2004. In the same month, US President George Bush unveiled an ambitious plan to return to the moon by 2020 and to use the mission as a stepping-stone for future manned missions to Mars and beyond.

If the program is successful in getting started, it will be the most far-reaching space agenda since President Kennedy launched the Apollo program in 1961. And NASA isn’t alone in planning a journey to Mars, the European Space Agency (ESA) has a plan, dubbed Aurora, which aims to put people on Mars by 2030.

There is a lot to consider before undertaking a manned mission to Mars. Before the astronauts take their first steps on the red planet, there is the monumental task of simply getting them there. Previous experience with manned space operations, such as the Apollo programme will be valuable, however, there are big differences in travelling to the moon compared to Mars.

The moon is relatively close to Earth, at a distance of 385,000 kilometres, it takes just three days to get there. A mission to Mars, would require astronauts to live on the spacecraft for several years, as the journey could take over 6 months.  In approximate terms, Mars at it's closest to earth is 36 million km away - at it's farthest, over 250 million km.  There is a planned experiment currently looking for recruits to study the effect, (psychologically and physically), of being in a confined space for that length of time.

How to get to Mars?

Prior to the recent success of Spirit and Opportunity, Mars has proven to be a challenging destination for robotic space probes. Historically, two out of three attempts to land spacecraft on Mars have failed – the bulk of these failures occurring early in the history of Martian exploration, starting in the 1960’s. So, if getting a relatively lightweight robotic craft to the surface is fraught with dangers, how do you get a far heavier and more complex manned craft down safely? Spirit and Opportunity used large airbags to cushion the rover’s landing. However, during an airbag landing, payloads are subjected to forces of between 10-20G. This is beyond the tolerance for the human body, so would not be a suitable method to land a manned spacecraft safely.

Atmospheric braking, followed by the deployment of a parachute has been used on many Earth re-entries, in fact prior to NASA’s space shuttle, this was the only method for returning human beings from space to the surface of the earth.. How it works is a craft uses the planet’s atmosphere to slow its descent, then parachutes are deployed to reach a safe landing speed. The problem with using this method to land on Mars is that the atmosphere is less than 1% of the density of Earth’s atmosphere, so it offers little resistance to a falling craft. For atmospheric braking to work, a landing craft hurtling into Mars’ thin atmosphere would require a large surface area to slow itself down through friction - this heat-shielded surface would need to be so large, that it could not launch from Earth. If parachutes are to be used, the spacecraft must be slowed to a speed where the fabric of the chutes won’t be torn apart. Also, it has been calculated that a parachute would need to be more than 100 metres in diameter so slow a shuttle-sized vehicle to a safe speed.

To get the Apollo landers onto the lunar surface, thrusters were used to slow the vehicle’s decent. This method, however, would use vast amounts of fuel; for a craft to do this on Mars it would have to carry six times its own weight in fuel. Due to Mars’ atmosphere, during a thruster descent, the craft would be subject to forces equivalent to a category five hurricane; the stresses that result could very well destroy the vehicle.

It would appear that a combination of these methods would need to be employed. To make a safe landing, a manned spacecraft would have to successfully slow down from 5000kph (3,000mph) to less than a thousand, re-orientate itself from spacecraft to lander, deploy parachutes, fire thrusters and make gentle touchdown – all in 90 seconds! It seems that the scientists have their work cut out to provide solutions so that humans can travel to Mars. But once people have landed on the Martian surface how will they survive?