Intermediate 
He is not the first person to express scepticism about Mars One, a private mission that aims to send humans to live on Mars from 2025. But Joseph Roche is different from most critics: hes on the shortlist of astronauts.
Roche, an astrophysicist at Trinity College Dublin who was announced in February as one of the 100 people shortlisted for the mission, has written for the Guardian expressing his doubts about the viability of Mars One.
The selection process, Roche writes, was not rigorous enough to reach the standard of more traditional astronaut selection programmes. He also says the Dutch Mars One team have shown a certain naivety because they believe they can succeed alone in the $6bn mission. He says they should now accept it is very unlikely to happen.
Roche also expressed worries about the way the mission organizers publicized a top-ten list of candidates. The ranking, he said, didnt mean these were the best astronauts. It was based on how many supporter points each had earned.
He says that these points only show how much each supporter has donated to Mars One, for example by buying official merchandise.
The official timeline for the mission says the group plans to send a stationary lander and satellite to Mars in 2018, followed by a rover in 2020 and cargo missions starting in 2022. Humans would start arriving in 2025 and crews of four would be sent every two years to add to the settlement. They would not return to Earth.
In February, a supporter of the project, Gerard t Hooft, a Dutch Nobel laureate in physics, said he did not believe this timetable was realistic. He said: It will take quite a bit longer and be quite a bit more expensive. When they first asked me to be involved, I told them: You have to put a zero after everything.
Roche also said that there were not 200,000 people who applied to be astronauts, as Mars One said; there were only 2,761.
He talked about the selection process in more detail: I have not met anyone from Mars One in person. Initially, there were going to be regional interviews; we would travel there, wed be interviewed and wed be tested over several days. In my mind, that sounded like a proper astronaut selection process.
But, all of a sudden, it changed from being a proper regional interview over several days to being a ten-minute Skype call.
Roche told the Guardian that he did not want to give more interviews because he didnt want to sound negative about the idea of space travel.
He writes: I am passionate about scientific endeavour and that is why the ambitiousness of the Mars One plan appealed to me. Mars One were never likely to overcome the financial and technical barriers during their proposed timeline. But it was nice to hear a new idea that challenges us to think about our own role in the future of space exploration.
He said that being part of the public debate about future missions has been one of the most interesting and enjoyable aspects of his involvement with Mars One. He went on to say that, If a one-way mission to Mars ever became possible, I would always volunteer. For an astrophysicist, that is not a difficult decision to make. But he does not think there will be a one-way mission in his lifetime.