When considering landing sites on Mars, NASA astronauts say they don't care where they go -- just don't kill them.
"Number 1 is safety -- is the site going to kill us," NASA astronaut Stan Love said at a workshop to vet potential landing sites for human missions to Mars.
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For starters, Love recommends scratching high-latitude destinations off the candidate list. Far north and south of the equator, radio contact with Mars-orbiting satellites will make communications challenging. Crews also will have a tougher time launching from high latitudes for the return trip to Earth.
"You get a little ascent boost launching to the east with planetary rotation. You go to high latitudes and you get less of that. It might be just a couple of hundred meters per second," Love said, but if the ascent burn is that short "it's a terrible day. It means you're probably coming back down."
High latitudes also are colder, which is harder on equipment. Plus, the lighting is poor, with short days in the winter and a low-lying, glaring summertime sun.
Another big safety concern is dust.
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"We hate dust. It's not going to blow your ship over, and it's not going to throw pebbles around at you. But it's horrible for landing. It's bad for your airlocks. It's bad for your spacesuits. It's bad for all your mechanisms. It's bad for your solar panels. If we can land in a place that is less susceptible to dust storms and doesn't have a lot of free dust around to get mobilized by our activity that would be a good thing," Love said.
Boulders and steep slopes should be avoided, for both landing and for driving rovers.
Once a crew is living on Mars, the biggest factor impacting how productive they will be is how much time they will have to spend making sure they stay safe.
"The safer and more temperate the landing site, the more work we can do there, the less time we have to spend making sure that we're going to be safe and the less time we have to spend maintaining systems that keep us safe in an adverse environment," Love said.
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Even in ideal circumstances, astronauts will have to spend a big chunk of their day maintaining their bodies and equipment, leaving around five hours a day for science and exploration activities.
"Just keeping yourself alive takes a lot of time and effort. We know this from the space station. We know this from working in Antarctica. You have to get enough sleep. You have to feed yourself. You have to keep your body clean. If you're in a group, you have to spend some time coordinating what work you're doing, especially if you're having to work with a distant mission control. The radio isn't going to work too well because of the time delay, but they're still going to send you a big pile of stuff to read every morning and then you've got to send reports back," Love said.