Actually as others have said we do have a problem of latency of between 4 and 25 minutes. But that's not the main reason our rovers on Mars are so slow.
It is easy to think that a human on Mars would be much more flexible when you look at the current robotic missions. But they don't give a fair comparison. The main problem right now isn't the robot, it's the time delay sending signals to Mars.
Opportunity took ten years to travel as far as the early wikipedia.orgLunokhod 2 rover operated remotely from Russia did on the Moon in about four` months.
It's much worse than the time delay of the light speed travel to Mars would suggest. Because we have low bandwidth connections and only communicate once a day typically. If the rovers were on Pluto, it would make almost no difference to the time it takes to explore.
So, before you can make a proper comparison, first we have to increase the bandwidth for communications to Mars. A human mission would have broadband - well why wait for humans? Set up broadband 24/7 communications with robots on Mars first and see how they do after that.
Also it's about time we did more robotic exploration of the Moon. Without the time delay - and if we had a capable rover, we'd surely do much better than the Russians did with Lunakhod. The Apollo astronauts traveled as far in a couple of days as Lunakhod 2 did in four months.
We can also speed it up even further, so that for many activities on Mars the latency is effectively zero, using a technique borrowed from gaming of "artificial real time"
The idea is that you build up a model of the area of Mars you are exploring on Earth. Much as they already do. But the model is updated regularly in a continuous broadband stream from Mars. And so just as they plan the next day's movements using the model they have so far, you would use the model of Mars you already have to inform your movements for the next half hour, or five minutes or whatever.
This would work especially well since much of the time they are exploring a known area of Mars, going back and forth from one rock to another. You'd soon have a detailed exact model of that area. And things don't change on Mars rapidly. Even after a dust storm. Some of the sand dunes move at meters a year, like sand dunes in the Earth deserts. But you'd not need to worry about that on this timescale.
Essentially it is a fixed unchanging landscape on timescales of minutes or even days. Even the winds, though so fast, yet it's winds in a vacuum, and they don't have the capability to do more than to move an autumn leaf. The dust storm in "The Martian" is poetic license for the sake of a good story.
So you would soon have a detailed exact model of the landscape you are exploring. Even when traveling long distances, then you would have exact models of everything except regions that are hidden behind boulders or over the tops of small rises or sand dunes. Much of the time you'd be driving over a known and modeled landscape. Especially since with broadband communications, then the landscape is continually updated as you drive. If you get to the crest of a dune and don't know what is beyond, it would be shown coloured, perhaps green or blue - to show uncertainty. So you then wait for the landscape to turn red and then continue. You might have to wait for up to half an hour occasionally. You might have to make wide turns when you go round a boulder or outcrop. But basically you could drive it from Earth pretty much in real time. I see no reason why they couldn't be driven as fast as the Apollo rovers - and faster. Without the constraints to remain within a walking distance to get back to the lander before the oxygen runs out, they could travel many tens of kilometers a day.
Especially if you then add in some smarts and autonomy. And make them self righting and able to extract themselves if stuck in a sand dune.
So, in short I think we are nowhere near exposing the limits of robotic exploration of Mars. Before we can make a proper comparison with human astronauts, we have to set up a broadband communication with Mars, and allocate enough receiver time so that we can communicate with the rovers there 24/7 (which may involve building new radio telescope receivers - but it could also involve laser communications which may give us much more bandwidth at a lot less expense).
Then our rovers need to be equipped to be able to drive faster, at tens of kilometers an hour. That can certainly be done, as of course proposed human driven rovers on Mars would not be limited to driving only 100 meters a day. The lunar rovers could drive much faster and there are many ways we could do the same on Mars. E.g. send batteries as for the lunar rovers, but of course much greater power density with modern technology - and recharge them using a large flexible lightweight thin film array spread over the Mars surface, as suggested for Mars One. Or using fuel manufactured from a hydrogen feed-stock from the atmosphere. Anything like that.
After we do that, we will then be able to explore the limitations of what semi-autonomous rovers can do on Mars with human guidance and artificial real time programming.
I think humans can help if they are on the spot. Not for driving, particularly, except in unusual situations. That could be done from Earth with artificial real time. But for decisions during experiments. If you drill a hole on Mars for instance, or lift a boulder, or scrape away some sand, it will be from 4 to 25 minutes before you see what it has uncovered. So humans in the loop could speed that sort of thing a lot. Also experiments where you can make decisions in real time and tweak parameters in real time.
But they don't need to be on the surface for that either. The humans could be in orbit operating the robots on the surface via telepresence. That's far better for planetary protection, and also for safety of the humans - and means both are used in ways that exploit their strengths. Humans need habitats, oxygen etc. Robots don't and can just sit still in one spot on Mars for years on end if necessary just using solar power. Robots so far are poor at decision making. Humans are not adapted to the Mars environment and we would not even be able to see the landscape clearly as the rocks would look all the same colour pretty much. But via telepresence and digitally enhanced broadband streaming from the surface we'd be able to inhabit a landscape down there with rocks that are the same colour to our eyes as their counterparts on Earth so easy for geologists to understand and identify and with distinctions of colour that our eyes can pick up easily. And all of it streamed in real time back to Earth to make sure nothing is missed. With stereo vision, haptic feedback, binaural hearing, anything we can add to make it a more immersive environment for the humans, as immersive as a computer game, but a real environment on another planet..
Telexploration: How video game technologies can take NASA to the next level
As for sending humans to Mars, I think we are at a much earlier stage than that. We are like people who have crossed the Mississippi a few times around forty odd years ago and since then have been shuttling back and forth between the shore and a tiny island on the near side. We aren't yet at the stage where we can safely tackle ocean voyages. We need to develop confidence in crossing large rivers first. So I'm a Moon firster for humans. It will also give us an opportunity to develop telerobotic control of rovers on the Moon from Earth or from lunar caves, which will be very useful for later telerobotic exploration of Mars from Mars orbit.
See my: Human Spaceflight At "Coastline Hugging Phase" - Lunar Villages Not Interplanetary Voyages - Op. Ed.
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