Which Ice Giant Mission should be pursued?

[redliox]

Back in the Ice Giant thread, for the longest time we've waited to find out what's being decided among the scientists focusing on the Ice Giants.  In the end, it was agreed that both Neptune and Uranus are equally worth visiting.  To a degree, a consensus was reached that orbiters with probes were the optimal choice, that at least they'd be armed with a minimum of 3 instruments (narrow-angle camera, Doppler imager, and magnetometer) but as much as 15 instruments, and that both fly-bys and two orbiters to a single planet were best avoided (the former because the science isn't as good and the later since it'd be too redundant).  There are more potential options, but 4 choices were chiefly singled out based on cost and quality of science:

Uranus Fly-by w/Probe - cheap but achieves some goals
Uranus Orbiter w/Probe - minimal remote science yet achieves most goals
Uranus Orbiter w/Large Instrument Suite (no Probe) - achieves many goals even w/o directly sampling atmosphere
Neptune Orbiter w/Probe - expensive but achieves most goals

Excluding last-minute-funding bonuses or international cooperation (ESA seems very interested too), I thought a poll about the current Ice Giant selection worth posting.  Personally I evenly favor the later 2 options, but the study pointed out valid reasons for these 4 choices against dozens of others.

[Kesarion]

For me the ideal scenario is one where we have a fully instrumented orbiter to Uranus with ESA contributing ~500€M for a probe and part of the instrument suite.

[Star One]

I can't see ESA shelling out that kind of money after NASA burnt them after their last major attempted collaboration on ExoMars.

[Blackstar]

I can't see ESA shelling out that kind of money after NASA burnt them after their last major attempted collaboration on ExoMars.

Well, ESA will get burned by another partner, and then they'll go back to NASA. That's how this works.

[Star One]

I can't see ESA shelling out that kind of money after NASA burnt them after their last major attempted collaboration on ExoMars.

Well, ESA will get burned by another partner, and then they'll go back to NASA. That's how this works.

Not if they keep away from collaborations in this area.

[Blackstar]

I can't see ESA shelling out that kind of money after NASA burnt them after their last major attempted collaboration on ExoMars.

Well, ESA will get burned by another partner, and then they'll go back to NASA. That's how this works.

Not if they keep away from collaborations in this area.

They're currently collaborating with Russia (ExoMars). And NASA (JWST, others). And also China, I think.

[Star One]

I can't see ESA shelling out that kind of money after NASA burnt them after their last major attempted collaboration on ExoMars.

Well, ESA will get burned by another partner, and then they'll go back to NASA. That's how this works.

Not if they keep away from collaborations in this area.

They're currently collaborating with Russia (ExoMars). And NASA (JWST, others). And also China, I think.

Well Russia stepped in when NASA dropped out so they had to find someone to fill the gap. As to the others I bet they aren't as extensive collaborations.

[K-P]

And to get back on topic...

Between Uranus and Neptune, my choice would be Uranus:

pros:
- closer, so less distance/time to travel, most of the time (depends on trajectories and launch opportunities yes...)
- closer, so less money needed and/or more payload for the buck (depends on many things yes, but...)
- perhaps more interesting planet (especially the tilted axis origins)
- more interesting moon system (if Triton excluded...)

cons:
- Neptune has had more visible features which could be more interesting...? (well, the "original" giant dark spot has disappeared and maybe Uranus was also just calm back in '86...)
- Triton is definitely interesting (well... NH gave us KBO-tour at Pluto already...)

So. Uranus it is.

About the mission then.
Definitely not just a flyby. No no.
If we go, why not do it properly.

Orbiter with minimum instruments sounds bad idea too, even if it is with a  atmospheric probe.
After all, probe is also just sort of a "flyby" with a short lifetime mission.
I would definitely put as much scientific payload into the orbiter probe as possible.
That is where the science is done, and with long operational time.

Anyway, there is a big possibility we get that "atmospheric probe" anyway, as happened at the end of Galileo mission and will happen with Cassini too, so the orbiter probe itself can and will give us at least some sort of insight into the atmosphere of the planet if we use it at the end of its mission in the suicide mode.

I cannot see that much more value with a spesific atmospheric probe + modest orbiter than full scale scientific orbiter + possible EOM dive to atmosphere.

So, I'm for orbiter with real capacity and no separate probe.

And final word... I think this mission should be the next flagship after Europa mission. (unless Planet 9 is found and then I shall keep my veto to change the destination of this mission there...) 

All Mars missions should be ditched in favor of deep solar system exploration unless they really really can put something new on the table and not just collect cache after cache for future missions never to happen.
There are a dozen more interesting places out there than Mars. Really. So why waste all the money in that bottomless pit?

And if nothing new emerges, then of course after Uranus Orbiter, the next logical mission would be Neptune Orbiter. With Eris flyby as a New Frontiers -mission in the same timeframe.

[kevin-rf]

I want all four! Why won't it let me choose all four?

[redliox]

I want all four! Why won't it let me choose all four?

Sounds like a NASA scientist talking about the OMB 

[Alpha_Centauri]

I want all four! Why won't it let me choose all four?

Sounds like a NASA scientist talking about the OMB 

Nah, that would be "Why won't it let me choose any of them?".

[JasonAW3]

Here's a crazy thought;  Using an Ion drive, powered by a nuclear thermal electric generator, (three would be preferable) BOTH Uranus and Neptune with a sample return from Titania and, possibly, Triton.

      If we could do more samples, great, if not, oh well.

      Obviously, this would take years before we'd get there and even more for the return, but it does seem like a mission worth doing.

[redliox]

For me the ideal scenario is one where we have a fully instrumented orbiter to Uranus with ESA contributing ~500€M for a probe and part of the instrument suite.

I can't see ESA shelling out that kind of money after NASA burnt them after their last major attempted collaboration on ExoMars.

Well, ESA will get burned by another partner, and then they'll go back to NASA. That's how this works.

Not if they keep away from collaborations in this area.

They're currently collaborating with Russia (ExoMars). And NASA (JWST, others). And also China, I think.

I definitely believe collaborations could be a lovely game-changer, as both tremendously helped the Galileo and Cassini/Huygens missions.  At the least, as often happens in missions, NASA will carry aboard international experiments/instruments; if Russia or JAXA can't contribute full-blown spacecraft this certainly will be their most likely route to the outer solar system.  ESA and NASA have the best reliable experience with the outer solar system and orbiters, perhaps even to a point where either could contribute an orbiter or probe.

In the case of both this poll and the study results, the assumption with these 4 choices was that NASA would be going alone - purely for simplicity and estimating expense.  A Neptune flyby w/ probe (which would be a choice I'd encourage but that's my opinion) was a previous thought, but the ruling was if NASA's going to spend 10+ years flying to Neptune, it'd be best to do quality, long-term science only an orbiter can do.  With Uranus the flight time is less, and slightly easier to arrange a follow-up mission later as opposed to Neptune; lesson being if you have to blow over a billion dollars on a one-shot flyby deal Uranus is the 'easier' of two evils.

[redliox]

Here's a crazy thought;  Using an Ion drive, powered by a nuclear thermal electric generator, (three would be preferable) BOTH Uranus and Neptune with a sample return from Titania and, possibly, Triton.

      If we could do more samples, great, if not, oh well.

Very crazy.  However, ion drive was considered for an option and while unnecessary for Uranus missions it was declared worthwhile for a Neptune expedition.  It will be solar powered though; there's not nearly enough plutonium in stock to attempt a nuclear option.

What could be a sweet follow-on for a Uranus orbiter would be a lander for (using your words for an example) Titania.  The same techniques for Europa Lander (which will sadly hog most of the attention post 'Clipper and Ice Giants) could be applied to Uranus' entourage.  Miranda gets a lot of attention, but after reexamination Uranus' seemingly small moons show hints of similar activity to the Galilean moons with Oberon the equivalent of a dead  Callisto, Titania a slumbering Ganymede, and Umbriel and Ariel slightly muted (and grayer) counterparts to Europa.

[Alpha_Centauri]

And to get back on topic...

Between Uranus and Neptune, my choice would be Uranus:

pros:
- closer, so less distance/time to travel, most of the time (depends on trajectories and launch opportunities yes...)
- closer, so less money needed and/or more payload for the buck (depends on many things yes, but...)
- perhaps more interesting planet (especially the tilted axis origins)
- more interesting moon system (if Triton excluded...)

cons:
- Neptune has had more visible features which could be more interesting...? (well, the "original" giant dark spot has disappeared and maybe Uranus was also just calm back in '86...)
- Triton is definitely interesting (well... NH gave us KBO-tour at Pluto already...)

So. Uranus it is.

Neptune is likely more representative of Ice Giants in general than Uranus.  A mission to Uranus may give clues as to why it is such an oddball, for instance the low thermal flux, but it may not do much for understanding Ice Giants in the greater context of comparative planetology with the exoplanets that will be studied in the following decades.

The primordial moon system around Uranus is perhaps one of its most compelling features, though imo that is science that could wait.

[Orbiter]

Neptune Orbiter w/ probe, solely because of Triton. A geologically active moon that's likely a former KBO bigger than Pluto? Way more interesting than any of the moons of Uranus, in my personal opinion.

[Star One]

Neptune Orbiter w/ probe, solely because of Triton. A geologically active moon that's likely a former KBO bigger than Pluto? Way more interesting than any of the moons of Uranus, in my personal opinion.

But it's not a virgin KBO as it has been altered by being in orbit around Neptune that's why observations of Pluto were so important.

[Joris]

Would a dual mission make sense?

Create two identical orbiters, one going to Neptune, the other to Uranus.

How much more expensive would this be than a single orbiter?

[Zed_Noir]

Here's a crazy thought;  Using an Ion drive, powered by a nuclear thermal electric generator, (three would be preferable) BOTH Uranus and Neptune with a sample return from Titania and, possibly, Triton.

      If we could do more samples, great, if not, oh well.

Very crazy.  However, ion drive was considered for an option and while unnecessary for Uranus missions it was declared worthwhile for a Neptune expedition.  It will be solar powered though; there's not nearly enough plutonium in stock to attempt a nuclear option.
....

If considering ion drive as propulsion. Then maybe something like the Kilopower fission power module might be a better option. There is plenty of enriched Uranium available. As a bonus a higher power radio transmitter for communications back to the inner system. A 3 to 5 kW Kilopower system seems to satisfied any power requirements for an Ice Giant mission.

[sanman]

I voted for Uranus, Large Instrument Suite, no probe - why bother to send a probe - isn't it just going to be crushed relatively quickly without being able to touch bottom?

Besides, a nice big instrument suite could reveal a whole lot more from orbit, than a localized probe would during descent.

Uranus is the better target over Neptune, since it's nearer and marginally warmer.

With private space launchers now coming into the picture, then the cost for space agencies to do such missions is going to drop significantly. The growing number of available launch opportunities should strongly aid the prospects of such missions getting off the ground, such that even multi-national collaborative missions should be considered, to help lower the cost of the interplanetary spacecraft.