Is lunar exploration going to need a whole heck of a lot of RTGs? If so, have they started firing up the RTG-making reactors yet?

Question

The November 16, 2021 Northrop Grumman Press Release Highly specialized team to design vehicle for sustainable lunar surface mobility operations begins

Northrop Grumman Corporation (NYSE: NOC), is teaming up with AVL, Intuitive Machines, Lunar Outpost, and Michelin to design a Lunar Terrain Vehicle (LTV) to transport NASA’s Artemis astronauts around the lunar surface. This team provides multi-disciplinary expertise that is ready to deliver an innovative solution to NASA for lunar surface mobility.

“Together with our teammates, we will provide NASA with an agile and affordable vehicle design to greatly enhance human and robotic exploration of the lunar surface to further enable a sustainable human presence on the Moon and, ultimately, Mars,” said Steve Krein, vice president, civil and commercial space, tactical space systems division, Northrop Grumman.

The rover itself may be NG but at least it's going to have Michelin tires!

The press release includes the artwork below which depicts two suited astronauts working along the sides of the rover as viewed obliquely from the back.

Centered along the back side of the rover is what looks a lot like an MMRTG; a cylinder perhaps 25 x 100 cm, cocked up at that "jaunty angle", with a prominent array of heat fins, guards on the left and right side intercepting some of the radiation to protect other equipment lined with tubing that could be used to transfer heat via pumped fluids to the computer and other key components requiring a continuous, reliable heat source and thermal stabilization.

Now I can't believe that crewed lunar exploration is only going to need one rover, and while later on there will be an infrastructure of electric rovers and charging stations along all of the interstates, certainly you want some absolutely reliable power source to stay alive if your car breaks down at night (or batteries run out trying to get out of a sand trap) on the Moon.

So I can see that having 100 watts electric built-in (and more power as thermal) would be life-saving. It can convert CO2 back to breathable air, purify water and keep it from freezing, run the DVD player and send radio signals to satellites and Earth for help. So no matter if the rovers all have big battery packs, you will be extremely happy to have one of these as well.

I'm all in! As much as safety belts and floatation devices are mandatory and intuitive in cars and boats on Earth, MMRTG's should come standard with any scouting or adventure-grade rover on the Moon, and by extension, on Mars.

Question: Is lunar exploration going to need a whole heck of a lot of MMRTGs? If so, have they started firing up the RTG-making reactors yet?

• Space News (2019): Plutonium Still Scarce, Production Restart Still Slow for Needy NASA

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The Northrop Grumman-led team will provide NASA with an affordable and sustainable vehicle design that will expand human and robotic exploration of the lunar surface.

Answer 1

We Won't Use RTGs

A 100-500 watt RTG would be wholly inadequate to power a lunar rover with people in it.

This paper describes the energy consumption of the Lunar Roving Vehicle used by Apollo:

Energetic Efficiency Evaluation of the Lunar Roving Vehicles Using Computer Simulation

It used anywhere from 10-12kWh/100 km. Bear in mind that this was an extremely light open frame vehicle with no science or drilling equipment. An hour of charge from a Perseverance-style RTG (100W) would get you about 1km of driving in the LRV. A modern rover with a pressurized human compartment and reasonable digging/drilling/science tools will be at least an order of magnitude more power hungry. For that matter, Perseverance itself can use up to 900W at a time and its energy has to be carefully budgeted.

Given all that, NASA has plans for fission power plants for these applications:

Fission System to Power Exploration on the Moon’s Surface and Beyond

These small fission reactors use uranium and don't have the plutonium sourcing problems. They also produce at least a kilowatt of power, and could be essentially any larger size. The smallest of them currently weighs 5700kg which is feasible for a rover in $\frac{1}{6}$g, and no doubt they will get smaller and lighter as they are developed. A vehicle like Lunar Starship could deliver ten of them in one landing.

The future of lunar exploration and colonization will be a mix of solar and fission power.

Answer 2

The previous answer is great. However as noted in the comments there is a 2 week long night on the moon. Yes yes even though the daytime is also quite long, the nighttime is long enough to disrupt lunar exploration, so it's not a viable option.

Here are the following additional reasons from Forbe - NASA is looking for a few good nukes:

Chemical fuel and solar panels will no longer be enough to meet the demands of human space exploration or to power an outpost on an alien world. Lunar nights are -280°F and last 14 days. The batteries to store solar power for 14 days would also be prohibitively heavy. The amount of fossil fuel that would be needed to survive these nights would be a prohibitively large weight. A 55-gallon drum of petroleum alone weighing about 400 pounds would cost about $5 million to lift into space. And it wouldn’t last very long.

Additionally the same article notes that Nuclear fission reactors are needed, especially for any space exploration. Considering humans are wanting to explore even more of our solar system, we are probably going to set up these nuclear reactors to help give us a ton of energy required, independent of sunlight.

So an actual nuclear fission reactor, carrying out continuous chain reactions for many years, is needed.

The fission surface power project is sponsored by NASA in collaboration with the Department of Energy (DOE) and Idaho National Laboratory (INL) to establish a durable, high-power, sun-independent power source for NASA missions on the moon by the end of the decade, as well as potential subsequent missions. The proposal request targets the initial system design.

Published last month, the Request for Proposals calls for ideas for a flight-ready small fission reactor powered by low-enriched uranium. The fission surface power system should be able to provide 40 kWe of continuous power for at least 10 years in the lunar environment.

It must fit within a launch configuration of a 12-foot in diameter cylinder and 18-foot length, and weighs less than 13,300 lbs. It should also be able to switch itself on and off independently. The FSP should be able to operate from the deck of a lunar lander or to be removed from the lander, placed on a mobile system and transported to another lunar site for operation.

From Wikipeda - Nuclear Power in space:

Fission power systems may be utilized to power a spacecraft's heating or propulsion systems. In terms of heating requirements, when spacecraft require more than 100 kW for power, fission systems are much more cost effective than RTGs.

From here we can see that nuclear fission is better than RTGs.

However:

Deep space explorers are going to need a fission reactor, probably a collection of them. Unfortunately, for decades NASA limited its in-space production of nuclear-generated electricity to RTGs, judging fission reactors as too expensive and politically sensitive to develop. Besides, with astronauts limited to low Earth orbit, solar energy sufficed to power the ISS.

_{A fission power prototype on display at NASA’s Glenn Research Center, the reactor core is at bottom, heat pipes at center, and Stirling energy converters at top. One Stirling piston engine generated electricity in a 2018 test called KRUSTY, for Kilopower Reactor Using Stirling Technology. Credit: NASA}

Now, NASA is factoring fission reactors into its human exploration plans, and under a project called Kilopower it is laying the groundwork for a future flight demonstration of the technology.

It is also said by WorldNuclear.org - Nuclear Reactors for space that:

RTGs are used when spacecraft require less than 100 kW. Above that, fission systems are much more cost effective than RTGs.

Overall, nuclear fission plants are expensive to build, but cheap to run and very efficient, while RTGs are less expensive, and quite inefficient due to the chief disadvantage of using them is their low conversion efficiency of heat to electrical energy. RTGs can run for about 14 years while fission reactors can last for 60 years. RTGs may still be used, but they may be replaced by fission reactors in the future. Do note that RTGs are proven to be quite reliable, so in the current year I'm not sure how the future of RTGs vs nuclear fission may turn out, but is likely it will start heading towards fission reactors.