Getting to Mars is no easy feat: the journey of several hundred million miles takes about nine months, one-way, and a manned mission will likely in total take about three years. So one scientist took a look at different types of propulsion - including nuclear - to find out if there was a quicker way to get there. But it seems that, aside from an engineering breakthrough, we can’t really shorten these times - and he thinks it’s unlikely we’ll send humans within five decades, not the 2030s as Nasa believes. Dr Bertolami from the University of Porto was speaking to MailOnline. He studied different types of propulsion that could get humans to Mars (shown). In total a manned mission would last three to four years, which poses major problems, such as exposure to radiation . Theoretical physicist Dr Orfeu Bertolami from the University of Porto, together with his colleagues Dr André Guerra and Dr Paulo Gil, carried out a study comparing different space propulsion methods for a manned mission to Mars. Option 1 - A 'giant leap' from moon to Mars . - Return to the moon . - Build a lunar base . - Send humans to the surface of Mars . Option 2 - Least technological risk . - Send humans into lunar orbit . - Visit an asteroid in its own orbit . - Return to the moon's surface . - Explore Martian moons Deimos and Phobos . - Enter orbit around Mars . - Land on the red planet . Option 3 - Nasa's current favoured path . - Robotically capture an asteroid . - Place it in lunar orbit for astronauts to visit . - Travel to the moons of Mars . - Place humans in Martian orbit . - Set foot on Mars . Based on the team’s calculations, they found that the total mission time poses serious problems to a potential manned mission. In total the mission will last three to four years, which is ‘very demanding’ and ‘almost impossible’ according to Dr Bertolami. ‘Despite what people say, we are a long way from reaching Mars,’ he told MailOnline. One particular issue is radiation. Astronauts on a mission to and from Mars will be outside of Earth’s magnetic field, and thus the risk of harm is much higher than when in Earth orbit. Nasa’s proposal is to send a mission there and back, but Dr Bertolami said more infrastructure was needed to make the mission possible. ‘I see no way of reaching Mars in five decades,’ said Dr Bertolami. ‘I don’t believe one can reach Mars through a brute force approach. ‘You have to be able to create complicated and sophisticated means of avoiding these hazards.’ He added: ‘There are too many thing we don’t know, obstacles in travel and in the technology itself, and the mass budgets for a mission are immense. ‘I would like to be a bit more optimistic, but I’m afraid this is how it is.’ Various forms of propulsion have been touted for a mission to Mars, including chemical, ion (electric) and nuclear. But while nuclear is often said to be the 'holy grail', the team found it did not noticeably shorten the mission over other versions. Shown is an illustration of a concept Mars Transfer Vehicle . Dr Bertolami, who was also part of a  science committee for Esa's satellite navigation programme Galileo, instead suggests that we should consider returning to the lunar surface and improving our technologies, before attempting a mission to the red planet. Owing to the orbits of Earth and Mars there are specific windows of opportunity when a mission can take place. Our planets come as close to each other as 33.9 million miles (54.6 million km), but can be as distant as 250 million miles (400 million km). For this reason spacecraft to Mars, such as the Curiosity rover, have to launch in certain windows when the planets are aligned. The next window is open from January 2016 to April 2016, and will see the launch of two more missions to the red planet. For a future manned mission, they will need to launch out in one of the windows and return in one, which will take two years in total. Just getting there will take up to nine months. The astronauts will be there waiting for a year until they can come back - a total of around three years. ‘From my point of view we should get back to moon, and I think it would be extremely useful to start with habitats at the moon,’ he said. ‘Once you can reach the moon on a regular basis, we will have learned a lot of things to achieve that. ‘I would never consider Mars before reaching this scientific level.’ In their study, the researchers looked at other methods of propulsion to see if there was any way to make a Mars mission more feasible in the near future. ‘Reaching Mars is a complicated business, and you have to start with a strategy,’ Dr Bertolami said. For their study, they chose a mission plan that was similar to the Apollo moon missions. The astronauts would start in low Earth orbit, then go to Mars and land, then return from Martian orbit and land on Earth. They looked at four different kinds of propulsion - chemical, ion, nuclear and a concept electromagnetic engine. Shown is a graph of the different types of propulsion for a mission to Mars, how much they would weigh and their travel time. CECE is a type of chemical propulsion, Nerva is nuclear propulsion, RIT-XT is ion (electric) propulsion and PEMT is Pure Electro-Magnetic Thrust . But while a nuclear engine is often touted as the holy grail of space travel, the team found that for a mission to Mars, there was no benefit in such an engine. While it might be slightly faster, the mission time is still similar overall, but such an engine would cost and weight a lot more. Nasa actually attempted to build a nuclear-powered engine before, known as Nerva (Nuclear Engine for Rocket Vehicle Application), with a view to using it to get to Mars, but the programme was scrapped in 1972. In fact, the best way to reach Mars was a combination of chemical and ion engines - the former to reach orbit, on a rocket, and the latter for the cruise to Mars. Nasa actually attempted to build a nuclear-powered engine before, known as Nerva (Nuclear Engine for Rocket Vehicle Application), shown in this illustration, with a view to using it to get to Mars, but the programme was scrapped in 1972 . According to Dr Bertolami and his team, the best way to reach Mars was a combination of chemical and ion (shown) engines - the former to reach orbit, on a rocket, and the latter for the cruise to Mars . ‘Most people say that nuclear is helpful,’ he continued. ‘It makes the flight time much shorter and the mass budget is lower. But it turns out basically that’s not really the case.’ One of the proposals for nuclear propulsion is that a reactor could emit particles onto a giant sail, which would propel the craft forwards. This is similar to a solar sail but ‘you carry your sun with you,’ said Dr Bertolami. Dr Bertolami says a problem arises because, while nuclear propulsion could accelerate to quite high speeds, it needs to brake again to enter orbit around the red planet. While it might be able to reach higher speeds for a mission to Mars over chemical and ion propulsion, the amount it would have to brake means that it doesn't really reduce the time of the mission by any considerable margin. And the weight of hoisting a nuclear reactor into orbit, coupled with the cost, does not make it an attractive option. Chemical propulsion is currently the only way to get from Earth into orbit, so any mission to Mars will have to still rely on it. Nasa's Space Launch System (SLS) rocket, illustrated, for example will use a combination of liquid hydrogen and liquid oxygen to take a Mars-bound spacecraft into orbit . ‘At the end of the day, if you do the calculations properly, you find out that traditional measures like chemical and electrical turn out to be more efficient,’ he said. ‘That’s rather surprising.’ However, looking further into the future, Dr Bertolami said if humans were to travel beyond Mars - such as to a moon of Jupiter - then nuclear propulsion becomes feasible. ‘Beyond Mars then the issue is indeed to do it as fast as possible, and then I would think that nuclear propulsion would turn out to be the most interesting one,’ he said. ‘I think for this particular case, nuclear propulsion will be the best option. ‘But again, I think we are still a long way to reaching that.’
Dr Bertolami from the University of Porto was speaking to MailOnline . He studied different types of propulsion that could get humans to Mars . In total a manned mission would last three to four years, which poses major problems, such as exposure to radiation . He thinks Nasa's plan to land humans there in the 2030s is not feasible . ‘I would like to be a bit more optimistic, but I’m afraid this is how it is’