Because for the amount of power needed they would have to halve its payload capacity if they used RTGs
Meanwhile, they now have nuclear diamond batteries. Hell, the Voyagers have been running on aging plutonium for nearly 50 years.
You’d figure a modern expensive system like that might have a modern secondary power source…
Voyajer@lemmy.world 5 weeks ago
Thorry84@feddit.nl 5 weeks ago
Who has nuclear diamond batteries? Those are a total myth drummed up to get investor money. They don’t actually exist.
Sure the concept exists, in the form of betavoltaic batteries, those have been around for decades. They are tough and last dozens of years if not longer. The only problem is, they put out microwatts. You can use them in very niche applications, but those are few and far between. It’s hard to convey how little power a microwatt is, it’s basically nothing.
What you care about when going to space is energy density, and the proposed energy density of nuclear diamond batteries is very poor.
Rtgs are very useful for longterm missions, but are crazy expensive. They also aren’t being made anymore, so getting a hold of one is hard. The weight is an issue as well, they are super heavy.
These commercial moon missions are primarily demonstrator missions. They aren’t meant to last, they don’t really have a goal and often don’t do something useful. The idea is to show you can do it, so you can sell a product. Other people that do want to do useful stuff can then pay to get their stuff to the moon. So if the mission is over when the sun sets in two weeks time, that’s perfectly fine.
over_clox@lemmy.world 5 weeks ago
‘They aren’t being made anymore’
Yep, I think we’ve identified at least part of the problem. Once humans figure out a technology that can last decades, we test it, verify it works, and then stop using it in favor of cheaper shit meant to fail as fast as a dozen eggs rot…
Thorry84@feddit.nl 5 weeks ago
Meh that may be true in some ways, but not really in this case. RTGs were made using a surplus from production for nuclear bombs. As that production ramped down combined with better solar and batteries, the demand went down and it became more expensive to produce them. So not making them made sense.
An RTG is really only useful for missions that go far away from the Sun, making solar non-viable. RTGs are a pain in the neck all throughout the process, are heavy and expensive (even back in the day). The amount of electrical power an RTG delivers is also very low. This is because an RTG only gets warm, nothing more. So we put TEC (Peltier) devices on the sides to generate electrical energy from the thermal gradient. But TECs suck ass, they are super inefficient. For example the RTG the big Mars rovers use put out 2000W of thermal energy, but they manage to get only 110W of electrical energy out of that. So if you are near enough to the Sun, solar is the much better option.
LastYearsIrritant@sopuli.xyz 5 weeks ago
Good explanation. People that design space missions have a lot of restrictions, and things that seem obvious on the surface can cause a lot of problems in practice.