Onwards to Uranus and Neptune! Options

[SFJCody]

As soon as MESSENGER gets to Mercury, the most poorly explored planets in the solar system will be Uranus and Neptune. Could this lead to a revival of interest in the ice giants and their retinue, in the same way that the existence of New Horizons is perhaps partly due to the Pluto stamp*?







*via Pluto Fast Flyby and later Pluto Kuiper Express

[Big_Gazza]

Oh Great Maker, let it be so....

(for the record, I'm a staunch atheist, but if prayer has one part in a trillion chance of success...
)

[ugordan]

To me, any new mission to Neptune that isn't an orbiter will be a tough concept to sell. Spending considerable time and money on an essentially Yet Another Flyby mission. An orbital mission would be significantly costlier, but the increased science return would most likely far outweigh the cost increase.

[vjkane]

An orbital mission would be significantly costlier, but the increased science return would most likely far outweigh the cost increase.

From various outer planet mission studies, we can safely say that a Neptune or Uranus orbiter will likely cost in the $2-3B range (one Flagship mission to outer planets every 10-20 years). (The last outer planets new start was Cassini in 1990.) This proposed flyby is in the ~$850M range (one New Frontiers mission every 3-5 years). We'll pick either Jupiter or Titan for the next Flagship mission, and then presumably will pick the other one 10-20 years later. That pushes an ice giant mission out to the 2040-2050s or so by the time it arrives. So if we want to learn anything about ice giants from a spacecraft mission in the working lifetime of the present cadre of scientists (and for many of us, in our lifetime at all), it will have to be a mission like this. My only complaint about the proposal is that it doesn't have an atmospheric probe, which could be very minimal and provided by an international partner. Understanding the elemental composition of ice giants is key to understanding the formation of the solar system.

[JRehling]

[...]

[vjkane]

It's unsatisfactory to have a small set of programs for mission selection, and to thereby allow targets of moderate interest to attract zero attention for decades on end. Much better if a broad long-term plan included contingencies for Uranus/Neptune (including, if the priorities weight out that way, to ignore them) than to see them perpetually bridesmaids because of the dynamics of one-upping.

Extremely well stated, John. For the foreseeable future, Mars (e.g., MSL, sample return), Jupiter, and Titan are going to take all the flagship spots. Discovery missions are severely limited in their scope and range, especially with the new rules to constrain develop cost risks. That leaves New Frontiers as the only mechanism to explore the solar system from the surface of Venus, Mercury (can't top MESSENGER and Bepi-Colombo on a Discovery budget), to the solar system beyond Jupiter. (You can throw the surface of Mars in this list, too. A Mars network mission has been recommended for New Frontiers). If our knowledge of these places is going to increase in any systematic way, then we need a list of prioritized missions. Otherwise, it's a crap shoot of which proposal looks best each time.

Right now, the New Frontiers queue includes (this is from memory, so I may miss something):

Lunar sample return
Venus lander and/or balloon
Comet sample return

A Saturn dual-probe mission has been strongly recommended (and if it launches ~2016-2018, it can also fly by Neptune; perhaps it could even carry a third probe for Neptune)

At 2-3 New Frontiers missions a decade, this list of (in my opinion) superb missions will take 1-2 decades to complete.

A number of missions have been suggested to augment this list or even to throw each announcement of opportunity wide open.

I don't favor the latter approach. I think the science community needs to set priorities so that this funding mechanism can ensure a systematic approach to studying all the places that Discovery can't reach and Flagship missions won't reach. This also allows the engineering community to focus on finding solutions for a constrained set of options. I do favor reviewing the list every time a mission is selected from it. For example, the discovery by Stardust that at least one comet's dust is composed of highly reworked, solar origin material may greatly lower the attractiveness of a comet sample return. Similarly, another nation may decide to fly a mission equivalent to one of the candidates.

By the way, I've heard that the next New Frontiers mission will not be allowed to use nuclear power (to save costs or a dwindling supply of nuclear material or both?). All the missions on the current list can be flown with solar power, although that would constrain any Saturn mission to just Saturn.

By the way, my favorite sequence of the next selections would be the Venus lander (which also likely would include atmospheric composition) followed by a combo Saturn-Neptune mission. But like I said, there's not a dud in the bunch.