They could do this. Indeed there's a plan for a "Mars cycler" that would continually shuttle back and forth between Earth and Mars. It could be built on the ground or built in orbit. Idea is that you get on it at the Earth end, and you get off it into Mars orbit and the spacecraft does a flyby of Mars which then sends it back to Earth along with anyone who wants to go back again, and you have them continually going back and forth.
Some time in the future we may do this. But our technology is not up to it yet. It is just far too expensive. Both ways - launched from Earth or assembled in orbit.
The ISS costs many billions of dollars every year. If we put the same amount of budget into interplanetary exploration we could have done this yes, probably by now, instead of the ISS, but not both.
I think though that before doing this we would need to show capability to keep humans alive for more than a few months at a time without continuous resupply from Earth, or it is far too dangerous. The ISS has a lifeboat spacecraft attached to it at all times which the crew could use to return to Earth in an emergency within hours. This would also be possible on the Moon, get back within a day or so. But once you get further afield it is impossible meaning any disaster such as might easily happen with new technology, would be likely to be sure death for everyone on board. Apollo 13 would have killed all the astronauts if it happened on an interplanetary mission but they could be saved, just, because they were close to Earth.
The logistics also - to keep resupplying a spacecraft on a journey to Mars - obviously has to be a closed system far more so than the ISS or every mission to Mars would be accompanied by a fleet of supply vessels. At the rate of a supply vessel every three months, then a two years and six months mission would need 10 extra spaceships sent as supply vessels to keep the crew going, if you followed the ISS model.
That's just to Mars orbit. As for landing on Mars I've said in other answers here that we shouldn't do that. Not until we know what the surface of Mars is like and whether there is native Mars life there, even if microbial. Because an ET microbe based on different chemistry or biology or even just an earlier stage of life than anything on Earth, or separated from Earth life for billions of years would be such an astonishing and important discovery. For that matter if Mars life was identical to Earth life in nearly all respects I think that would also astonish many exobiologists because there is so little chance of life to get from one to the other .
It is not impossible, far easier in the early solar system, but not easy - after all has to come from an impact that hits the Earth and blasts life into space right up through the atmosphere on a trajectory that takes it all the way to Mars and most life would be sterilized by cosmic radiation and vacuum, obviously few life forms would survive such a journey, question is if any ever have, might have, but obviously not confirmed. And if it has ever happened - then Mars is so different from Earth it would be independently evolved for at least tens of millions, probably billions of years with high levels of cosmic radiation, near vacuum for atmosphere, huge temperature swings between day and night, from cold enough for CO2 to freeze out as dry ice to sometimes briefly warm as a sunny day on Earth - and all the other differences between Mars and Earth.
So a human occupied ship landing on Mars - especially if it crashed which is reasonably likely at present stage of technology - it would scatter human bodies + food + air + water + plants etc over the surface of Mars along with trillions of microbes in tens of thousands of species - most of them unknown to science (most microbe species to this day have not yet been characterized or studied at all, whole phylae - that's one level higher than creatures with a backbone in the classification of the tree of life - are known only by a few gene fragments as they can't be cultivated in the laboratory). And you get extremophiles in the most ordinary of habitats, microbes able to survive on granite cliffs in Antarctica or in reactor cooling ponds, or in hydrothermal vents or in near vacuum atmosphere that also survive quite happily in low populations in your clothes, on your tongue, in your belly button even.
After an accident like that, any discovery of life on Mars, which could be the biggest discovery of our century or more in biology - could instead be just ho-hum life we brought there ourselves.
So we need to know what the surface of Mars is like first, which we can't tell from orbit as we can't see microbes from orbit or detect them in low concentrations - and we need a reasonably thorough exploration also as it is as large in surface area as Earth, and as well, varied in terrain too, many potential habitats to explore, many of them only recently discovered - most of the suggested habitats for life on Mars have only been known about since 2008 or later. None yet confirmed to be habitable to Earth microbes. But that's just because the only way to do that is to send rovers there, can't do it from orbit, and we haven't sent anything to those places on Mars yet.
But - orbital missions to Mars orbit - they could happen with improved technology. I'm totally skeptical of Mars One achieving it and SpaceX also - though they could get the mass to Mars orbit probably if they keep going, getting living humans to there is another matter altogether, I think myself that they have a lot to do. It would be more credible if they had succeeded in creating a habitat on the Moon first with someone living there without any resupply from Earth for two years or more. If you put it that way it is such a big step up from ISS or Apollo I think most people would agree it is something we can't do yet. But put those same people into a spaceship to Mars and for some reason everyone is full of optimism that we can do it right now. I don't think we can.
Some time in the future we may do this. But our technology is not up to it yet. It is just far too expensive. Both ways - launched from Earth or assembled in orbit.
The ISS costs many billions of dollars every year. If we put the same amount of budget into interplanetary exploration we could have done this yes, probably by now, instead of the ISS, but not both.
I think though that before doing this we would need to show capability to keep humans alive for more than a few months at a time without continuous resupply from Earth, or it is far too dangerous. The ISS has a lifeboat spacecraft attached to it at all times which the crew could use to return to Earth in an emergency within hours. This would also be possible on the Moon, get back within a day or so. But once you get further afield it is impossible meaning any disaster such as might easily happen with new technology, would be likely to be sure death for everyone on board. Apollo 13 would have killed all the astronauts if it happened on an interplanetary mission but they could be saved, just, because they were close to Earth.
The logistics also - to keep resupplying a spacecraft on a journey to Mars - obviously has to be a closed system far more so than the ISS or every mission to Mars would be accompanied by a fleet of supply vessels. At the rate of a supply vessel every three months, then a two years and six months mission would need 10 extra spaceships sent as supply vessels to keep the crew going, if you followed the ISS model.
That's just to Mars orbit. As for landing on Mars I've said in other answers here that we shouldn't do that. Not until we know what the surface of Mars is like and whether there is native Mars life there, even if microbial. Because an ET microbe based on different chemistry or biology or even just an earlier stage of life than anything on Earth, or separated from Earth life for billions of years would be such an astonishing and important discovery. For that matter if Mars life was identical to Earth life in nearly all respects I think that would also astonish many exobiologists because there is so little chance of life to get from one to the other .
It is not impossible, far easier in the early solar system, but not easy - after all has to come from an impact that hits the Earth and blasts life into space right up through the atmosphere on a trajectory that takes it all the way to Mars and most life would be sterilized by cosmic radiation and vacuum, obviously few life forms would survive such a journey, question is if any ever have, might have, but obviously not confirmed. And if it has ever happened - then Mars is so different from Earth it would be independently evolved for at least tens of millions, probably billions of years with high levels of cosmic radiation, near vacuum for atmosphere, huge temperature swings between day and night, from cold enough for CO2 to freeze out as dry ice to sometimes briefly warm as a sunny day on Earth - and all the other differences between Mars and Earth.
So a human occupied ship landing on Mars - especially if it crashed which is reasonably likely at present stage of technology - it would scatter human bodies + food + air + water + plants etc over the surface of Mars along with trillions of microbes in tens of thousands of species - most of them unknown to science (most microbe species to this day have not yet been characterized or studied at all, whole phylae - that's one level higher than creatures with a backbone in the classification of the tree of life - are known only by a few gene fragments as they can't be cultivated in the laboratory). And you get extremophiles in the most ordinary of habitats, microbes able to survive on granite cliffs in Antarctica or in reactor cooling ponds, or in hydrothermal vents or in near vacuum atmosphere that also survive quite happily in low populations in your clothes, on your tongue, in your belly button even.
After an accident like that, any discovery of life on Mars, which could be the biggest discovery of our century or more in biology - could instead be just ho-hum life we brought there ourselves.
So we need to know what the surface of Mars is like first, which we can't tell from orbit as we can't see microbes from orbit or detect them in low concentrations - and we need a reasonably thorough exploration also as it is as large in surface area as Earth, and as well, varied in terrain too, many potential habitats to explore, many of them only recently discovered - most of the suggested habitats for life on Mars have only been known about since 2008 or later. None yet confirmed to be habitable to Earth microbes. But that's just because the only way to do that is to send rovers there, can't do it from orbit, and we haven't sent anything to those places on Mars yet.
But - orbital missions to Mars orbit - they could happen with improved technology. I'm totally skeptical of Mars One achieving it and SpaceX also - though they could get the mass to Mars orbit probably if they keep going, getting living humans to there is another matter altogether, I think myself that they have a lot to do. It would be more credible if they had succeeded in creating a habitat on the Moon first with someone living there without any resupply from Earth for two years or more. If you put it that way it is such a big step up from ISS or Apollo I think most people would agree it is something we can't do yet. But put those same people into a spaceship to Mars and for some reason everyone is full of optimism that we can do it right now. I don't think we can.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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