I did not know Juno used solar panels.

I know that a probe to explore the ice giants would require an RTG (or some other energy source other than solar panels).

Still, I think it would be very interesting to study the ice giants and the respective moons and ring systems more closely.

It's the first probe going out that far that uses panels, all the previous ones use RTGs. When it was built (launched in 2011) there was a severe Pu-238 shortage; it's still in short supply, but back in production (as of 2013) and so some future long range RTG powered missions might be back on the table.

Oh well, I guess Uranus will still be around in few years. ;-)

But is Uranus or Neptune in a position that can be reached with gravity assists?

And even if it is, orbital insertion requires a lot of energy, so a flyby is probably the only possible option.

Mmmh. I can still hope, can't I?

I mean, really, assuming that all of the practical problems of building a probe and getting it to Uranus or Neptune were solved, wouldn't you just love to send it there and explore the $expletive out of them?

Well you can either keep up (false?) hopes or do the maths and see where the planets are located (pretty easy) and are there any potential gravity assists (not as easy, but there are software packages that help).

If you just want to eyeball the situation, take a look at Celestia.

I think orbital insertion is out of question for the outer planets using conventional space craft propulsion because the difference between high radial velocity required to reach the planet and the low tangential velocity of the planet itself is greater than the spacecraft's delta-v budget.

But there won't be another Voyager mission in our lifetimes, a suitable arrangement of planets happens only once in 400 years or so.

"The most favorable launch window for such a probe would be in August 2018, with arrival at Uranus in September 2030".

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

Juno is only possible because of new improvements in solar panels. And even so, it's a relatively low powered space probe at 400 watts. A lot of power is required for radio communication and heating.

Going any further with solar power is not feasible with the technology available today.

That's not how mission planning works. They don't start with something roughly like Juno and decide which planet to send it to. Rather, the planet and rough scientific mission is picked first, then the probe is designed around that.

I guess you could just mean "There is an RTG shortage, so we can't send anything past Jupiter", but I don't think this is actually how the decision was made.

Material for RTGs running out is a thing unfortunately

According to Wikipedia, the United States restarted production of Plutonium-238 at circa 1.5 kg a year in 2013 after a c. 25-year hiatus.

Good

the Cassini one used 7kg https://en.wikipedia.org/wiki/GPHS-RTG so I guess it will be some time before new ones are made

They've been exploring smaller designs with better efficiency. Not just because of the shortage, but also because evergy gram counts in a spacecraft...

Well maybe every kilogram, but you got my point. Any savings in mass count, and if you get to cut 1% from the spacecrafts final mass, it can mean a lot in terms of speed and timings for the mission.

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

The thermophotovoltaic cells look lik a very interesting approach, don't know why they haven't been used yet. With them, Cassini could've used 2 RTGs instead of 3, resulting in a mass saving of 57.5 kg (2% lower dry mass from one less RTG) and some extra power. I do take into account that this technology ws probably not developed enough when Cassini launched.