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Numbers, GCNR. You know the Hab won't be that heavy. Its a space vehicle, not a mining truck. If the tires are big enough, I imagine a steady 100kW will suffice. But don't take my word for it. Do some research!
Also, I wonder wether the power requirements will be much lower than you'd might expect. I suspect this might be the case for a few reasons: First, the reduced martian gravity means less power required to negotiate small bumbs and gentle slopes. Second, the momentum will be the same, so if the tires are big enough, the momentum works in your favor. Third, the martian atmosphere is extremely thin. I'd imagine its aerodynamic resistance is closer to a vacuum than that of earths atmosphere. Whether this makes much difference when travelling so slowly, I'm not sure. Fifthly, you could remove the retro rockets and RCS system from the hab before attaching the buggy cradle. This should be a fair amount of weight. Sixthly, once all these effects add up (big tires, light weight, low gravity), you end up with a lot less stress on the suspension, further downsizing the mass of the buggy cradle.
As for the logistics of such long excursions impacting mission safety, I'm honestly not sure. This needs to be further explored.
Also, I bet an RTG could be carried around in a trailer (though with difficulty), if that turns out to be a better solution.
- Mike, Member of the [b][url=http://cleanslate.editboard.com]Clean Slate Society[/url][/b]
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Look, Michael, you keep on coming up with bad ideas and then asking other people to prove them wrong. There are all kinds of really bad ideas for Mars missions, why do you not have to prove they are possible? This, on account that the number of good ideas are far outnumbered by the bad, hence the average idea is probably not a good one.
Lets say you have a 100kW methane/oxygen powerplant of some kind, which achieves a 50% efficiency (better than piston engines on Earth by far). You run this plant half of the 500 day stay on Mars. You will require 76.7MT of Methane, which will require ~20MT of Hydrogen from Earth, and 307MT of Oxygen. Thats assuming zero boiloff, which isn't really possible either. Even if the HAB/rover only carried a small portion of this, enough for say a four month trip from the ISRU plant (@50% power), you are still going to have to haul ~100MT of fuel.
And thats just for the drive, the HAB would preferably draw 100kW more-or-less continuously on its own, but even cutting that in half with waste heat from the drive engine, thats another 100MT of fuel. Now lets say the 25MT HAB + 25MT drive + 200MT of fuel = 250MT
Even on Mars, thats still too much. Add in the mass of the HAB, powerplant/rover/wheels, and even in 1/3rd Martian gravity the whole thing will weigh more than most mining dump trucks. And you can't,
You Cannot
Tell me you can push THAT for less horsepower than my tonne-and-a-half Honda Civic over some of the roughest terrain in the inner solar system. I don't care how low you gear the engine.
An RTG that big isn't happening either, a plant big enough to drive a 100MT vehicle (rover and RTG) will cost you in the mid-to-high tens of tonnes. Thats not counting the 50-MT class trailer, the power cable, or the risk of the latter breaking. The radiator area for such a huge RTG system would be impractical too, easily totaling over several hundred square meters, assuming the same temperature drop as the smaller model from DRM.
I reject the idea that the empty landing propulsion is a substantial portion of the vehicles' mass: RL-10 sized engines will weigh under 500kg probably, and the fuel tanks are not that big. The DRM-III lander stage is sized to deliver a 40MT payload, it itself is not included in this figure I don't think.
The logistics problem is a simple one. Its also an insurmountable one.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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It would benefit your arguments if they were less obviously biased, GCNR.
Okay then, whats the biggest, longest-range rover that we can fit into a dedicated launch?
- Mike, Member of the [b][url=http://cleanslate.editboard.com]Clean Slate Society[/url][/b]
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Michael,
I give you credit for not backing down to GCNR's first post, but come on man, don't make him shoot you down time and time again.
Now, about long range mobility. We don't need one super-rover that can circle the globe on one tank of fuel -- and please don't ask GCNR to prove it. The 500km range rover has been well researched, so why don't we see what we can do to extend it's range.
1) You can have it tow a tanker trailer. Because of the added weight of the trailer the rover will be less efficient of course, but with a plentiful fuel supply at the base it can be readied at a moment's notice.
2) You can plow trails as has been mentioned before. This will save travel time and wear and tear (except on the plows) more than increasing range, but it should make the rovers a little more fuel efficient.
3) This is my favorite -- Bring along a few robotic fuel production stations and place them hundreds of kilometers from the base. They can slowly fill their tanks using solar, wind, RTG or any available power source. The visiting rovers can drop off excess water and fill up with oxygen and fuel. The down side is that without a lot of power the stations will fill up very slowly.
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I can get awful emphatic... anybody remember gaetanomarono?
A decent sized rover is a good fit for RTG power, only needing the low tens of kilowatts w/ batteries for surge power, doesn't weigh too much. The real limiting factor for RTG power is the radiator: as the power output increases, the radiator becomes at least proportionately larger. This big radiator will just fit on the roof of a good sized rover for a 10kWe plant.
The problem is the cube/square law, that the measure of a rovers' capacity is its volume, how much space it has inside, but as this increases the surface area increases exponentially less. Hence, a rover with twice the volume with twice the power demand will have much less than twice the surface area on which to mount the bigger radiator, so it will be difficult if not impractical.
Lucky for us, the DRM-sized rover is the right size to support a sufficiently powerful RTG plant. Therefore the question of range is entirely dependent on consumables, crew mental health, and how far away from help is too far.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I like that idea. Is an RTG powered rover part of DRM?
- Mike, Member of the [b][url=http://cleanslate.editboard.com]Clean Slate Society[/url][/b]
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DRM-I calls for such a rover, yes.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Hehe, I'm back!
Check out my new mission architecture which more readily accomodates the mobile Hab concept at Marsdrive Mission Design
- Mike, Member of the [b][url=http://cleanslate.editboard.com]Clean Slate Society[/url][/b]
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