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Wonder if it is practical to design Helicopter with nuclear battery similar to the rover....

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That'd be difficult in Mars' atmosphere -- but the planned *Titan* helicopter will actually be RTG powered:

https://en.wikipedia.org/wiki/Dragonfly_(spacecraft)#Design_...

https://news.ycombinator.com/item?id=18947350 ("NASA May Decide This Year to Land a Drone on Saturn's Moon Titan")

https://news.ycombinator.com/item?id=20337042 ("A technical look at the Dragonfly Titan mission")

>"Flight on Titan is aerodynamically benign as Titan has low gravity and little wind, and its dense atmosphere allows for efficient rotor propulsion.[35] The radioisotope thermoelectric generator (RTG) power source has been proven in multiple spacecraft, and the extensive use of quad drones on Earth provides a well-understood flight system that is being complemented with algorithms to enable independent actions in real-time.[35]"

Awh, I thought that meant infinite flight time, but it appears instead it carries the RTG along to recharge Li-ion batteries at night.

Yeah, unfortunately power density is not exactly where RTGs shine.

Plutonium is really heavy, if you were to do that it strikes me that you'd be better off having some kind of wireless charging device which the helicopter lands on (But at that point why not solar power).

You'd probably already need some batteries anyway as I'm guessing that the transient spikes in power usage would probably exceed any RTG you could fit in a helicopter anyway.

Probably you would use strontium-90, instead, if weight was important. Strontium is 7.5 times less dense than plutonium.

Strontium-90 produces 0.95W/g, where Pu-238 produces only 0.57 W/g. So, it takes only 3/5 as much, by weight, to produce the same heat as a Pu-238 RTG, although it takes 4.5x as much room. Room is relatively cheap on spacecraft, vs. mass.

This makes me wonder why they use Pu-238 RTGs in spacecraft at all. Maybe because it lasts a bit longer?

... Probably just because of the industrial process availability of plutonium, as spinoff from weapons work. Sr-90 has no local infrastructure. Which is just dumb.

Much too much mass. The atmosphere on Mars is 6.518 millibars. Look to the structure and mass of terrestrial birds for a guide.

terrestrial birds which would all have far too low of a lift to weight ratio on mars to ever have any hope of flying. The current mars helicopter is pretty incredible

Yes, to be pedantic about it, but I didn't say "send birds" or "do exactly what birds do", I said to look to them for ideas. Eliminate every extra gram, optimize aerodynamics and control for the purpose (c.f. owls vs. quail vs. hummingbird vs. woodpeckers) and go from there. Don't try to build a flying machine around power source that is essentially a hunk of dense metal.

just pointing out that you'd have to go to much further lengths than birds on earth have gone

No, you're just missing the point of my argument with and arguing pedantics by insisting on a literal reading what I said.

Obligatory plug for Dragonfly: https://www.nasa.gov/dragonfly/dragonfly-overview/index.html

You _can_ use nuclear power similar to the rover if the lift / weight isn't prohibitive. That means a bigger copter in a thicker atmosphere and lower gravity. Since the power is generated by temperature gradients, cold helps too.

Perfect for Titan.

A radioisotope thermoelectric or betavoltaic generator would probably be too heavy for a helicopter, so you'd probably need something a lot more intense than simple radioactive decay.

Do you see any nuclear-powered aircraft flying around on Earth?

Earth also doesn't have any nuclear powered rovers driving on the surface and yet Mars does. Might have something to do with the fact that the risk to humans on Mars is slightly lower than on Earth,no?

French EVs are over 70% nuclear powered. We just keep the nuclear generators stationary and use battery buffers in the car to save weight.

You might argue it's about risk, but that didn't seem like such a huge deal when we tried to make nuclear cars and planes back in the 50s. RTGs are just incredibly inefficient, and properly shielded fission reactors are incredibly heavy.

Yeah, the 1950s involved serious consideration of some truly horrific nuclear flight concepts, so I wouldn't be so dismissive of risk as a factor. Not like airliner crashes are awesome, but they don't drop a reactor core on whatever they crash into. Not to mention proliferation concerns, operator staffing requirements, security staffing requirements. There's very straightforward reasons nuclear powered flight on earth never went past the earliest exploration of a couple prototypes. Russia is working on a nuclear powered cruise missile and has already had one serious mishap with it.

Yes, but also that you can't refill with gas on Mars. And of course we do have nuclear powered vehicles cruising around on Earth. We have also had nuclear powered bombers and cruise missiles, none of which were exactly successful, but not even the US DoD has ever suggested a nuclear powered helicopter. It would be a great introduction to our relationship with Mars if one of the first things we ever did was to spill plutonium across its surface when the helo crashed (as it would, eventually).

Not that likely even in the event of a crash.

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

"This incident resulted in the NASA Safety Committee requiring intact reentry in future RTG launches, which in turn impacted the design of RTGs in the pipeline."

We developed them during the Cold War. The issue was the massive release of radiation behind them. Don't fly it over your own country. But they can cruise for days!

No, because it's easy to refuel here on earth and there's no easy way to refuel a helicopter on Mars.

If we didn't have oxygen and oil, we probably would.

You can't buy aviation fuel on Mars, though.

We also don't see any nuclear-powered rovers driving around Earth, so I don't think this is a helpful way to make a point.

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