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Onwards to Uranus and Neptune!
JRehling
post Feb 8 2008, 07:55 PM
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vjkane
post Feb 8 2008, 08:37 PM
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QUOTE (JRehling @ Feb 8 2008, 08:55 PM) *
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.


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tedstryk
post Feb 8 2008, 10:10 PM
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I think that Uranus has a bigger problem. The bland appearance of Voyager photos doesn't help. Also, it lacks a big moon, like Triton. Both planets could be combined with Kuiper Belt flybys, but with Neptune, you get a large (if melted down) KBO right off the bat. Plus, Triton is active, meaning that looking for changes since Voyager is a selling point for a flyby sooner rather than an orbiter later. I am not saying that Neptune out-merits Uranus, I am saying that I think a Neptune flyby mission has more of a chance of happening, perhaps tied to a New Horizons followup.


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mchan
post Feb 9 2008, 06:36 AM
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Unfortunately, any mission with Uranus as primary objective will be cheap joke fodder on the late night TV shows and elsewhere in the US. It would be difficult to garner support for such a mission if it is being so ridiculed.
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tedstryk
post Feb 9 2008, 06:20 PM
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Neptune also has the advantage of being the most distant official major planet (This was also true in the Voyager days, since Pluto was inside Neptune's orbit at the time). To the bean counters and to the novice "only the second visit to the most distant planet" has a ring to it that Uranus would have difficulty competing with.


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JRehling
post Feb 11 2008, 06:40 PM
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nprev
post Feb 11 2008, 09:21 PM
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Heh, heh...I see that some of our more distinguished members are tuning into marketing, however reluctantly and/or facetiously... cool.gif

I see it as another 'gapfiller' initiative, much like Messenger. Uranus & Neptune are midway between the terrestrial planets and Jupiter/Saturn in terms of mass. Oddly enough, they have surface gravities not much greater then that of Earth, making surface exploration (if there is one on either of them) a tantalizing far-future possibility...we need to learn more, to say nothing of the satellites of each, Triton being one of only 5 known volcanically active bodies in the Solar System.

(It's all about framing the issue, guys.)


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kwp
post Feb 11 2008, 11:08 PM
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QUOTE (nprev @ Feb 11 2008, 02:21 PM) *
Triton being one of only 5 known volcanically active bodies in the Solar System.


Five?

-Kevin
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tedstryk
post Feb 11 2008, 11:13 PM
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QUOTE (kwp @ Feb 11 2008, 11:08 PM) *
Five?

-Kevin


Earth, Io, Enceladus, and Triton. Titan and Venus likely fit in that group, and some data suggests the same is true for Dione and even Mars.


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nprev
post Feb 12 2008, 04:32 AM
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I was counting Titan; the atmosphere is extremely powerful circumstancial evidence.


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Greg Hullender
post Feb 12 2008, 04:47 AM
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I still wish I could see a breakdown of costs. I keep wanting to believe that two identical orbiters (one for Uranus and one for Neptune) wouldn't cost twice as much as a single one, and that if one could time them right, the Neptune one would arrive just as the Uranus one reached the end of its life, so you could just keep more or less the same team. Even if the Neptune probe took 20 years to get there, it would just be the second act.

--Greg
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nprev
post Feb 14 2008, 04:20 AM
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Again, this is why I wish that there was a 'library' of outer-planet launch opportunities. Seems like trajectory calcs only happen when there is a viable mission proposal like NH in the pipeline; might have the cause & effect relationship backwards here.

If we knew that there were favorable launch opportunities for Uranus & Neptune (even with inner-system gravitational assists) in, say, the late 2020s, then draft mission proposals could start development now. With that much lead time, it's even conceivable that Frontier-class missions would be feasible given assumed technology advances.


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mchan
post Feb 14 2008, 05:27 AM
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[removed in-line quote]

There may or may not be such a library, but there are usually a couple or more papers each year at the AIAA/AAS Astrodynamics conference that discuss trajectories for future missions to places all over the solar system. Probably >95% of these come to naught but some folks are having fun cranking out the plots.

Not sure what is gained by a stretched development cycle. There is the risk that product of earlier development efforts be obsolete or difficult to support when launch date comes around.
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ugordan
post Feb 14 2008, 09:28 AM
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There really is no need for a launch opportunity library for the outer solar system if you want to go from A to C via B. As long as B and C are on the "same side" of the solar system there'll probably be an extended gravity assist trajectory with a varying efficiency over a couple of years. Jupiter would typically be your B body and from then on tweaking the launch date is a piece of cake if you have constraints on launch energy, launch date and/or arrival velocity. These sorts of calculations can be done on demand in a matter of minutes I figure.

More complex slingshot trajectories (involving say Jupiter AND Saturn) to get to Uranus or Neptune will occur rare enough that it's probably no use predicting them that far into the future. Furthermore, they usually impose bigger trajectory constraints which then constrain the slingshot gains. It might prove more efficient to use just an aggressive Jupiter flyby to catapult yourself outward than trying to fly by both J and S for what can turn out to be a weaker boost in the end.


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kwp
post Feb 14 2008, 05:02 PM
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QUOTE (ugordan @ Feb 14 2008, 01:28 AM) *
As long as B and C are on the "same side" of the solar system there'll probably be an extended gravity assist trajectory with a varying efficiency over a couple of years. Jupiter would typically be your B body and from then on tweaking the launch date is a piece of cake if you have constraints on launch energy, launch date and/or arrival velocity. These sorts of calculations can be done on demand in a matter of minutes I figure.


Since this is a three body problem (spacecraft, Jupiter, Sun), I believe there is no closed, analytical solution to the problem of finding the best trajectory. I have thus assumed that it is done via Monte Carlo simulations. Alternatively, while there is no analytical solution, there might be good approximations. I'm hoping one of our resident experts will weight in and tell me how slingshot trajectories are calculated, and how computationally intensive the process is.

-Kevin
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