Physics major with an interest in nuclear science. Does that count?

> the sun is a giant nuclear reactor and we indirectly derive most of our energy from it. Radioactive elements in general are the most energy dense

Worth noting that this is conflating two different phenomenon: fission, and fusion. Despite the similarity in spelling, these have very little to do with each other.

Neither of these have much to do with the "nuclear generator" in the article, which is based on natural fission, but not a chain reaction. It's actually more akin to refined, bottled geothermal power.

> What makes nuclear so dangerous?

First of all, it's not. Nuclear is one of, if not THE safest and cleanest form of power. But there are risks worth worrying about, even though with modern designs and regulatory procedures the risk to life and the environment is less than with other sources.

Those risks basically boil down the fact that radioactivity causes cancers, thyroid disease, and in high doses various lethal forms of radioactivity sickness. And like all heavy metals, radioactive materials can easily get absorbed by our biology and deliver that harmful radioactivity slowly over time.

When there is a leak of radioactive material (like Chernobyl, Fukushima, or almost happened with Three Mile Island), the result can be pretty damn scary. But what nuclear nevertheless safer than other energy sources is (1) these events are rare, and nuclear is otherwise perfectly clean and safe; and (2) modern designs cannot fail in the way these older reactors did. For example, Chernobyl and Three Mile Island failed in pretty much the same way, but Three Mile Island's design kept the radiation entirely contained. When deciding about new power plants, we should be evaluating the risks of new designs.

You might wonder what makes other power sources more dangerous. Coal and natural gas have obvious health and pollution concerns. But wind and solar both involve A LOT of materials processing, construction, and maintenance, all of which have dangers that add up. Geothermal and hydro power are probably the two power sources that are better than nuclear, but aren't available everywhere.

TL;DR Nuclear is scary. It's not necessarily dangerous (compared with other sources of power).

> are there nuclear materials with short half life. Such that if you turn it off, it’s safe by default. It doesn’t require constant cooking and isolation.

I think you are confusing controlled fission reactors vs. radioisotope generators.

Fission reactors are the big nuclear power plants, which you can turn on and off. There are ways of making this safer and having less lethal byproducts. Mostly we need to start using breeder reactors, which reprocess spent fuel, instead of just putting it in waste pools and forgetting about it.

Radioisotope generators are what TFA are about. Purified chunks of radioactive material (like plutonium) are naturally hot from their radioactivity, which is basically the same reason the Earth is hot--that's why I called it bottled geothermal power above. You then just attach some thermal couples to the outside of the plutonium, to generate electricity from the difference in temperature.

You cannot turn off a radioisotope generator. It just goes on being hot for decades, until the main radioactive elements have decayed away.

> If voyager and the Mars rovers are operating on nuclear power, can we have nuclear powered planes, cars and robots that are safe and ubiquitous? (Safe nuclear batteries)

Unlikely. We know how to make small nuclear power plants, as we use them in submarines. But it's not easy to do this in a safe way, for reasons that are too complicated for a HN post. But basically it is the safety equipment that makes nuclear power big and bulky.