Reposted from The Guardian

Overall it’s a very good movie, and while there are mistakes in it, it is the first genuine Mars movie. It is the first movie that attempts to be realistic and that is actually about human beings grappling with the problems of exploring Mars, as opposed to various movies set on Mars that are essentially either shoot ’em ups or horror films. It does not engage in fantasy: no monsters, no magic, no Nazis. However, there are a number of technical mistakes.

The storm
This is the only thing I noticed that was completely impossible, as opposed to improbable or sub-optimal. The Martian atmosphere is only 1% as thick as Earth’s, so a Mars wind of 100mph, which is possible although quite rare on the surface, would only have the same dynamic force as a 10mph wind on Earth. You could fly a kite in it, but it wouldn’t knock you down.

The spacecraft
The diameter of the torus and the rate of rotation on the Mars Orbiter spacecraft looked about right to create an artificial gravity level somewhere between Mars and Earth, so that was OK. It’s just that the ship was so big and elaborate and expensive-looking. Going to Mars is not about realising the vision of a giant science-fiction spaceship, it is about sending a payload from Earth to Mars that is capable of supporting a small group of people, and then sending that or a comparable payload back. There’ll be ships like that someday, just like there were ocean liners a few hundred years after Columbus made his voyage. But if Columbus had waited for ocean liners, or even clipper ships, he never would have gone anywhere.

Gravity
Mars has about one third the gravity of Earth, which is an asset to explorers because you’re wearing a heavy space suit, but it doesn’t feel that heavy. If you’ve got a 150lb person with a 150lb suit, that’s going to feel like 100lb on Mars – lighter than the person alone on Earth. As far as I can see they didn’t bother with that in the movie. Even climbing the ladders in the initial scenes, they seem to be exerting themselves.

Making water
Matt Damon’s character took hydrazine from the rocket fuel and dissociated it into nitrogen and hydrogen, which you can do, and he burned the hydrogen with oxygen to make water. That’ll certainly work, but if I was stranded on Mars I would just make water out of the soil. Water is available in its natural state on Mars as ice, permafrost, or soaked into the soil. Martian soil is about 5% water by weight at low latitude, and up to 60% water near the poles. Martians are not going to get their water by importing hydrazine from Earth and burning it with precious cabin oxygen, they are going to bake it out of the soil.

The toilets
This was a little odd. The easiest way to deal with waste is to bag it, seal the bags in something and then burn them once a day. We do something like that with Arctic exploration. But it’s more productive to recycle the waste, using greenhouse systems or physical chemical processes, and turn it into fuel, water and oxygen. Would they really seal them individually and label them with the astronauts’ names for later scientific study? I can’t imagine anyone wanting to bring that stuff back to Earth, or study it on Mars. You’re not on Mars to study your fecal waste, you’re there to study Mars.

The nerd-genius solution
One thing in the movie that is possible, and perhaps the producers knew the story, is the character of the nerd (played by Donald Glover) who comes up with the gravity-assist trajectory that rescues the mission. It may appear to be a Hollywood device, but in fact there is a basis in history for such a person. His name is Michael Minovitch. He was a trajectory analyst at Nasa’s Jet Propulsion Laboratory in the 1960s and he came up with the idea of the gravity assist that became the basis of the Voyager programme to go to Jupiter, Saturn, Uranus and Neptune. Initially no one believed him. He was a very junior person, somewhat analogous to the character in the movie. The managers making the decisions are typically people who were once engineers but haven’t done it in a while and perhaps are not so good at maths any more. So Minovitch had to get out the chalk and walk them through it and convince them that it would actually work.

Removing the windows from a rocket
Would you need windows in a rocket to survive a launch from Mars? It’s an interesting question. The atmosphere is very thin, so can you get high enough that the atmosphere becomes irrelevant before you’re going fast enough that the atmosphere is a threat? It depends on the thrust profile. The question is, at what altitude do they reach 1km per second? Let’s figure it out: OK, so 1,000 metres per second squared, divided by … [Zubrin mutters some equations to himself] … you want to go slow in this case, so let’s say 1G. Let’s try [more muttering] … 50 kilometres. So, with a slow acceleration of 1G taking off from Mars you’d get to 50 kilometres before you’re travelling at 1km per second. So I’d lean towards yes, it’s possible.

Nasa communications
Would Nasa not tell the other astronauts that Watney [the Matt Damon character] was still alive? Well let me put it this way: they didn’t tell the Columbia astronauts everything [the space shuttle Columbia disintegrated on re-entry in 2003, killing all seven crew members]. And it was unfortunate, because they didn’t give those astronauts their best shot at potentially solving the problem they had. I don’t know if those astronauts could have saved themselves if they had all the info, but they should have had all the info. What was unrealistic to me was that you had the whole Earth knowing that Watney was alive, but the crew on the interplanetary spaceship did not. That’s impossible right now. The crew on the International Space Station can email you. Not all of their communications go through mission control, so they can be in touch with their loved ones at home. It’s tremendously useful to have the crew be able to directly access people on Earth. If they’re exploring Mars and they come across a very odd-looking mineral, say. To be able to access a professor at some university somewhere and say is this a fossil? A mineral? What do you think? Or, how do I reboot my computer, it’s locked up? If you have all this going through one person at mission control, it isolates the crew much more than is necessary.

Conclusion
The U.S. space programme today is frozen in its tracks. Nasa talks about sending humans to Mars in 2043, but that’s just postponing it for another generation. We’re much closer today to being able to send people to Mars than we were to sending people to the Moon in 1961. If Barack Obama’s successor were to commit the nation, in the spring of 2017, with the same kind of courage and determination that JFK did in 1961, we could be on Mars before the end of his or her second term. It’s a question of political will to me. That’s the real positive message of The Martian. It’s saying, “we can do it. If we use our minds, we can take on all these challenges”.

Dr. Robert Zubrin is an aerospace and astronautics engineer and an advocate for manned exploration to Mars. He is founder and president of the Mars Society and co-author of Mars Direct, a strategy for manned expeditions to Mars that has been broadly adopted by Nasa (and replicated in The Martian).

Dr. Robert Zubrin was speaking to Steve Rose.