How could a fast powerful rover on Mars be powered electrically?

Question

Background

The rovers on Mars are slow and weak. If I am to believe what I read, MSL Curiosity only produces 1/6th of a horsepower electric effect, 125 watt. In order to perform tasks like deep drilling, excavation or fast roving, three orders of magnitude more power would be nice. It has been proposed to have astronauts orbit Mars and teleoperate a rover in real time, but that is hardly useful with a sleepwalker like MSL with a top speed of 1½ meter per minute and a 2 inch drill.

Questions

What power sources will future capable rovers and construction equipment on Mars have?

The RTG's seem prohibitively expensive to scale up or multiply. Is other nuclear power feasible for caterpillar sized equipment on Mars, as such used for submarines and icebreakers? Could a rover have a tall mast with huge solar panels in the low gravity and weak winds of Mars? Or could chemical fuel, like methane and oxygen from the atmosphere, produced with solar power in advance and stored on Mars be a solution? Or huge stationary solar panels with cables or microwave beams to supply mobile equipment?

Answer 1

An option not mentioned so far are solar power satellites. A large antenna in orbit could focus a tight, high-power microwave beam on the rover. From a low Mars orbit (300 km), a 1 km antenna could focus 1 cm wavelength microwaves on a 3 m target. They should be electronically steered to allow fast and accurate slewing. You would like to have several of these orbiters, with about 20 to 30 minutes of coverage from each orbiter per day. You could trade higher orbits with more coverage for longer time per orbit. However the antenna size gets ridiculous (or the wasted power becomes excessive) at areosynchronous orbits.

Make sure that the wire mesh antenna covers the entirety of the rover, so that the beam doesn't cook the rover or its occupants. And make sure that the beam isn't pointed at you when you're walking around outside the rover.

Answer 2

The limiting factor on rovers now is the power generation while moving. Incidentally, this same problem exists in Kerbal Space Program, and was covered by Andy Weir in "The Martian". The problem is, you can either generate power, or move, but it's difficult to do both at the same time. There are a few ways of overcoming this problem.

The best way is to have large amounts of power available while resting (Deploy solar panels, for instance), and take periodic breaks. This is unfeasible for current Mars rovers, because the deploying/ retracting of solar panels over time would prove to be difficult.

A second way is to contain the power generation to the vehicle while moving. There are 3 ways of doing this, namely fixed panel solar arrays, like Opportunity, which produce little power, but doesn't involve deploying anything. Secondly, you can have an RTG system (Based off of Radioactive Decay), like Curiosity. They aren't very popular to launch (As it contains radioactive material), have difficult fuel to produce, and produce a fixed amount of power with time (Somewhat fluctuating based on the background temperature). You can never get high power with one of these without high weight. Next you could have a nuclear power plant. These are very fickle, I can't imagine operating one remotely, and they are quite large. This might work for a very large rover (Think the size of, say, the Crawler), but is unfeasible for short term. Also, this would probably work better with some form of deployment, to reduce the heat. Lastly, one could do a fuel based system, capturing the exhaust. Unless you can bring enough fuel to be useful, this is a difficult process. Essentially this will work like an efficient battery. Note the exhaust could be captured to re-form fuel. Robert Zubrin in The Case for Mars proposes using Methane/ Oxygen, and capturing the exhaust water for future re-processing.

Bottom line is, without more power, you can't move very fast. And power is a difficult thing to do, especially with unmanned vehicles. I believe a manned vehicle, with a deployable solar cell system (As used in The Martian, for instance), would be the best way to drive fast. I believe Robert Zubrin's methane powered combustion engine would be the most effective way to store the power from the solar cells. With that kind of a system, you could drive at a reasonable speed, say 5-10 miles per hour, which is probably best for such an uncharted location. I imagine one could go faster too, if one wanted, it's all in trading off safety and efficiency for speed.

Answer 3

Nuclear power is not feasible for vehicles. There have been some efforts in the past, but nothing remotely usable.
The smallest nuclear reactor I'm aware of is the ELENA design (still a concept), which produces 100 kWe and weighs 235 tons. A submarine power plant weighs in the region of 1000 tons and produces in the region of 50 MWe.

But I don't think power is the main obstacle in increasing a rover's top speed. Autonomous navigation is a difficult problem, and driving at a low speed reduces the risk of a crash.

Answer 4

How could we increase the efficiency of vehicle-sized solar cells? One approach might be an orbital concentrating mirror. These have occasionally been proposed on earth, but on earth it's much cheaper just to build a large solar farm. For a Mars mission, it's actually easier to put things in orbit than it is to put them on the ground. Pointing it at a moving vehicle is difficult but not impossible if you're moving smoothly in a straight line. It would certainly be useful for stationary drilling operations.

Various organisations keep promising compact Thorium reactors, and Lockheed Martin even claim to be working on fusion. If any of these make it into commercial production, they might be good options.

But it's worth considering how much speed is safe. Curiosity has been gradually accumulating wheel damage. The rocks are sharp as there is no real weather to smooth them. The faster you go, the greater the chances of a crippling accident.

Answer 5

The following is sourced from Wikipedia's Kilopower:.

An actual 1-10 kW, small, self-contained nuclear reactor, with built-in Stirling power converters to output electrical energy.

They are very compact (even with allowance for the radiative cooling vanes, cheap, and reliable.

OK, I am lying about that second attribute. As with anything nuclear, cheap does not come anywhere near the device. I think cheap has a restraining order to stay 1 mile away at all times.

But they do seem to provide a means for providing very dependable, around-the-clock, good for about 10-15 year, continuous power.

The 10Kw unit masses about 1500 kg, which includes the reactor, power converter, cooling system, et al. It is in a package with a footprint of about 4 m², 80% of which is just the radiative cooling "umbrella".

The 10 kW unit emits some 40 kW of thermal heat, which could be very handy indeed on a cold place like Mars, but will still be too much and need to be actively cooled.

Yes, 1500 kg for just the power source is not so great. But with 10 kW of electric and 40 kW of thermal, it will allow a somewhat larger rover to perform much higher energy tasks, such as actual drilling, high power experiment packages, etc.

The 110 w -- that the Perseverance rover needs to battle with is very feeble, just barely adequate to its miserly energy needs. And actually, inadequate to the rover's needs, as it needs to ration power between systems all the time, and simply cannot maintain a decent temperature except for the most essential of systems.

Answer 6

You have to also differentiate between peak and average power. Just giving your mobile unit large enough batteries will give it substantial peak power capacity to move fast or do any other power hungry thing.

Curiosity has to drag it's radioisotope power source along with its batteries due to its mission, but for many of the things you mention, this will not be required. It will be entirely feasible to have a large stationary power source ( either solar or nuclear, there really aren't any other near term options ) charging multiple mobility platforms.

Batteries, and also regenerative fuel cells work just fine for decoupling the power source from the usage site.

Answer 7

Mars Direct, by the Mars Society/Robert Zubrin have proposed using ISRU (In Situ Resource Utilization) to produce methane and oxygen to power a large faster internal combustion manned rover. They also proposed landing modules within the powered distance of the rover, to allow backup possibilities. I.e. If there is a second earth return vehicle for the next mission, within the range of the rover away, there is a backup return vehicle for the current crew.

A base station with solar power to run the methane/oxygen generation process, acting as a gas station, could be one way to get to higher power rovers on Mars. Eventually scaling issues would come into play as the rover would be limited to a radius that is half the range of the rover.

Answer 8

A nuclear reactor could be located near the base; buried, as in Kim Stanley Robinson's "Red Mars". Then, a route could be selected that passed close to or right by selected investigatory sites. A means could be selected to pass current from the reactor to the vehicle as it went along the main route, providing electricity for quite rapid, but safe propulsion, while at the same time giving the rover's batteries a full charge.

When the rover reached an exit point along the main route, the crew would simply go on internal power and complete their mission, returning to the main route to return to base.

It seems to me the size and/or number of batteries would be much less a limiting factor than relying on solar power. A vehicle could be created that would easily transport a crew of 3 or 4 plus a generous equipment and supply list for extended missions, and do it at a fairly high speed, at least on the portion travelled on the main prepared, electrified road. A series of these electrified roads could be created to satisfy any mission requirement. A series of auxiliary nuclear power plants could also be placed along these roads to insure safety through redundancy, and also to power outposts.

The selection of buried nuclear power plants is a natural. With millions of watts available and reliable, everything becomes much easier.

As an aside, wouldn't it be a great idea to turn Kim Stanley Robinson's trilogy into 3 major motion pictures at the time we are getting ready to really launch into the program. KSR would love the idea, I think, and the pictures would help drum up worldwide support for and interest in the program.

In closing, while I loved "The Martian" and other films about going to Mars, they all involve a catastrophe of sorts and the struggle to repair the damage and get back to earth. The actual program would likely involve landing several payloads ahead of humans and extensive use of robotics before our arrival to do site prep, drilling for water, excavation and tunneling and some construction. The actual arrival on Mars would be almost routine were it not for the extraordinary hopes and emotions tied to the event.

Of course, probably there will be one, maybe two, "single event" landings, successful or not, preceding the above event, but the slow, complete approach is the best, I think.

Answer 9

A "Fast" Mars rover, by which I believe you mean automotive speeds? There's three potential power supplies - Solar charged with high capacity battery - Nuclear electric propulsion, either RTG charging a battery or reactor powering a generator. - Air independent oxygen carrying propulsion (AIP) look at submarines that use fuel cells or an engine with an onboard oxidant.