I noticed in an update that some of the CCD's came from this green and pleasant land that I call home, well, England anyway Who did the work, I might see if they'll do an interview.

Doug

Doug- E2V provided the MVIC CCDs in Ralph.

-Alan

Alan,

I would be interested to hear how the OPAG meeting went from your perspective, WRT NH2. I've heard a few comments from one of the attendees about New Horizons 2 and would like to hear your perspective (i.e. how receptive was the community, etc.)

So would I (although I speak as a continuing skeptic on this mission).

I also remain a skeptic on the NH2 mission. I would love to see a modern, but modest mission to an ice giant. NH2, though, is not optimized to answer a lot of the fundamental questions about these bodies. It would need to be enhanced with a microwave sounder (to do similar deep atmospheric probing that a similar instrument will do on Juno) and/or an atmospheric probe (for detailed elemental and isotopic composition), and ideally both. It should also make an extremely close (skimming the atmosphere) pass for gravity studies, which would probably screw up possible Kuiper belt flybies.

As it is, NH2 is seems to me to be a Kuiper belt mission that happens to include limited Uranus and Uranus moons studies.

The real way to view this opportunity is to ask, if NASA has a spare $400M to spend on planetary science, is this the highest return purchase? The best tactic would be if NASA allowed a waver (to get around the rule of no nuclear power sources) to allow it to compete in the Discovery 12 competition. That would ensure that NH2, if chosen, is the best use of this money.

All this said, Alan is doing exactly the right thing. NASA too seldom looks into opportunities to reuse the tremendous investment it puts into the design and testing of these one-of-a-kind missions. A relatively cheap copy should be allowed to compete against other possible missions.

I'll add here what I've said elsewhere, that Cassini's recon of the icy saturnian satellites makes it more attractive to add the several uranian satellites, in the same size class, as a priority.

Prioritization in solar system exploration has suffered a tempting, but misguided, heuristic, in my opinion, by emphasizing the unique worlds as the most interesting. You actually learn the most about processes by learning the most about the most similar worlds and understanding what made them different. To see that Mercury and Pluto are different in composition, you learn one very blunt and obvious fact about what chemicals are solid at what temperatures. But to compare Mercury and the Moon, or Pluto and Triton... that's where you learn the subtle facts. The saturnian icy satellites coupled with the uranian "big 5" and two or so at Neptune provide a huge class of worlds that have similar sizes, similar solar heating (more at Saturn, sure), similar compositions... and yet they differ radically (see Rhea and Iapetus). There's your history of the solar system.



This is right. Maybe the legacy of NH2 will be to be an unadopted mission that embarrasses the process into improving. Maybe it'll die on the cross for the selection process's sins.

>This is right. Maybe the legacy of NH2 will be to be an unadopted mission that
>embarrasses the process into improving. Maybe it'll die on the cross for the
>selection process's sins.

NH2 is, frankly, withering away under the onslaught from lower-level NASA
managers. Perhaps with all the changes in faces at higher levels, it will do better
soon, but I worry the comment just above may come to fruition. The people Mike
Griffin is putting in have much more "can do" attitudes than some of those formerly
in place. We'll have to see if there is any positive response in the Agency to this
groundbreaking target-of-opportunity idea.

NH2 is an excellent cross displinary mission that is the best next KB missiion
but not the best Uranus visit one could imagine structuring if money and time
were not constrained. But under the very real funding and time constrains,
NH2 is an extremely good opportunity to make very worthwhile advances in
multiple areas of planetary science (KBOs, origisn, binaries, ice giants, icy satellites,
giant planet magnetospheres), etc. Unfortunately, many of my colleagues would
prefer no mission to a less than "perfect" mission. That, combined with a "not
invented here" attitude in O'K's NASA have starved NH2 of all oxygen and will
soon kill it if something doesn't change.

It is really a shame that the system is so rigid that one cannot even propose new
ideas (NH2 could not have been proposed under the NF-2 rules, despite our pleading
for a relaxation of the rules.) And worse, we can't even get study funds to evaluate
the concept; the study the Senate mandated was performed by a team that had
nothing to do with our mission team and got a rather amazing answer according to
what I have been told: building a second would cost the same and take twice as
long as the first.

Go figure.

Here is the OPAG meeting report. It contains a letter from Andy Danzler, the director of NASA's Solar System Exploration Division. There's lots of interesting stuff, but on NH2 there's little to add, except that NASA is holding onto the notorious report so that the Senate can look at it. Who knows, maybe a senator will ask why a copy of NH will "cost the same and take twice as long as the first"?

Alan, is there any chance of the newly named Office for Program Analysis and Evaluation getting involved? That seems to be where Griffin's "can do" people seem to be.

I'm not a strong supporter of NH2 (having heard about it only here today). My rationale is this:

We are slowly developing capabilities for more rapid space travel, including ion drives, small fission power reactors (see the cancelled JIMO/Prometheus mission), and perhaps solar sails / solar concentrators. There are some very interesting things out in the Kuiper Belt, but they aren't going anywhere very quickly.

I think that considering the time it will take for NH2 to get out to visit a KBO, that for another decade or so of waiting for information (twenty or so years of development), we could get a much more substantial higher-speed mission launched. Something with a KBO orbiter/lander-rover arrangement perhaps.

In the mean-time, the budget for NH2 might well be used for some closer-to-home planetary science missions, including some cheap asteroid lander missions.

The problem is: Will they ever get these wonderful new technologies, or will they stop funding because of ever changing priorities in space or (worse) on earth? We are waiting since 1972 for the 7th manned lunar landing and will do so for at least another 15 years. About 35 years after Mariner 10 Messenger will visit Mercury again. That's for waiting. It's like waiting for your own death.

Analyst

Yes, but with the chaging angle of the Uranian system, this is our last chance to get global views of the satellites for the next 44 years. It doesn't matter how sophisticated a probe we send (unless we send one with floodlights to light up whole worlds - something way beyond even JIMO). I also think that continuity is very important. Space exploration is funded largely as political pork to develop military technology and preserve Apollo-era space centers in powerful congressional districts. Once a program takes off, it is hard to stop. It is important that we maintain continuity. It isn't as though if we stop funding planetary probes till JIMO - type craft are ready we will save up money and use it for development - it will simply be spent on other things. And if NH2 can visit one of these big KBOs, it should be a definite go. (I think they should look at whether either a Uranus OR Neptune flyby might get to one of them).

Why waste vital probe power with floodlights when a series of small flash charges might do the trick. A bunch of small charges could be stored and lobbed towards the dark sides of the selected moons, where cameras would be ready to image the portions lit up by the charges.

Or we could send ahead a giant mirror to aim reflected sunlight onto the moon. Sure some melting might occur, but it would be worth it for science.

What, they cancelled the Prometheus project? Hadn't heard about that. Darn.

I'd love to see some more solar sails and ion drive probes. Be fun to launch something that'd be capable of whizzing right past the Voyager probes. Use solar sails until the probe gets far enough that it can't gain much speed, then power up an ion drive powered by a fission generator.

When launching the solar sail probe, just be sure it isn't done by a Volna rocket.

I was joking. My point was that since the southern hemispheres of the moon would be cloaked in darkness soon, so we can't wait around for NEP.

The Review Panel's report is now out ( http://www.lpi.usra.edu/opag/nh2_final_report.pdf ), and it turns thumbs down on the mission. Contrary to some early rumors, they did not say that NH 2 would actually end up costing as much as NH 1. The main problem seems to be the need to acquire lots more Pu-238 to fuel NH 2's RTG, which in their view means that the earliest it could possibly be launched is January 2011 -- which in turn rules out not only a flyby of Uranus near equinox (one of this mission's selling points, since it can't be repeated for four decades), but any flyby of Uranus or Neptune at all unless the craft skips a Jupiter gravity-assist and proceeds directly to one of those worlds, which would in turn greatly prolong its flight and require a bigger booster to boot. By contrast, a mission using a Jupiter gravity-assist can allow the third stage to be removed from the launch vehicle and thus cut costs, but only by skipping a Uranus or Neptune flyby and limiting the mission to a flyby of some single pre-identified KBO (plus Jupiter, of course), along with whatever other KBOs or targets of opportunity may turn up (much as with New Horizons 1).

And the estimated mission cost, even with that removal of the third stage, is only 14% lower than that of NH 1. Combine this with the panel's feeling that the results from NH 1 ought to be digested by the science community before we plan any more KBO missions, and the verdict was a pretty definitive thumbs down -- although the panel did state that COMPLEX should keep appraising the value of future KBO missions, since surveying a diversity of these objects has alwways been recognized to be important and it's unlikely that NH 1 will get a look at more than one small one besides Pluto.

(That latter statement seems to me, once again, to point toward the possibility of launching a mission around 2020 to fly by either Uranus or Neptune and drop off a pair of entry probes there, after which the same craft could easily proceed on to some KBO flybys -- including one of a large pre-identified KBO. This would in turn allow a cost reduction -- and maybe a delay -- in the major Neptune Orbiter mission that the science community would like to launch around 2030, although if we're going to split off the Neptune entry probes from the Neptune Orbiter it might be wise to send the earlier flyby-with-entry-probes mission to Uranus instead in order to minimize science duplication.)

I surely hope there's an NH2 mission...for the sole fact I can get my name onboard the spacecraft.

I missed the deadline to submit my name for the current New Horizons mission.

NOOO!

So assuming we aren't going to stop exploring the outer Sol system after NH 1, what alternatives do they propose for future such missions? Or are they hoping to pass the financial buck to another generation?

I've always felt that if you're going to fly two of a given probe, you ought to fly them at roughly the same time. As has been said here before, when NH gets to Pluto it will be using instruments and data systems that are 15 or more years out of date. Why fly a duplicate of such a spacecraft in a few years, when for not much more money we could design and build a more capable spacecraft? At least, a spacecraft that has the benefit of those extra years of improvement and enhancement of the sensing packages?

If you're going to fly NH2, I'd select another one or two KBOs (or other objects) it could reach, and launch it ASAP. That would cost the least amount of additional money and put the existing hardware to the best use. But if you're planning on missions to fly in 5, 10 or more years, I'd simply leave it to a newly-designed probe that will have greater capabilities and give more "bang for the buck."

-the other Doug

Just wondering, is the NH2 concept dead? I was looking at the planetary orbits (as viewed from 90 degrees above the ecliptic) the other day and noticed it might be possible to fly a Uranus-2003 UB313 mission. That, IMO, would be one cool mission. Has anyone yet pondered this idea? Later!

J P

We're holding our powder dry for now. Let's get #1 launched. ...A bird in the hand...

“Preliminary Design of an Advanced Mission to Pluto”

T. Bondo, R. Walker, A. Rathke et al.

Scheduled to appear in the proceedings of the 24th International Symposium on Space Technology and Science, Miyazaki, Japan, June 2006.

http://www.esa.int/gsp/ACT/doc/ACT-RPR-4200-ISTS2004.pdf

That Pluto Orbiter document says:

"The current version of US-GPHS RTGs are planned to
be phased out in 2008 and be replaced by Stirling
Radioisotope Generators (SRGs) and Multi Mission
Radioisotope Generators (MMRTGs). These RTGs are
currently being tested by the US Department of Energy
and NASA. Available data indicate no improvements
in their specific power compared to the current ones."

So... why are the existing, well-tested, designs being phased out?

Because the new ones produce that same amount of power with as little as 1/3 the plutonium! This obviously has massive advantages where both launch safety and the cost of manufacturing the stuff are concerned. (The main problem with a Stirling engine -- the most efficient of all -- may be that it requires moving parts, which have always been the Achilles heel of space missions.)

Ah! Interesting, and impressive.

Thank you.

Martin

UB313 is so far out that it would probably be beyond the lifetime of NH's RPGs on any possible trajectory.

It would be great to get flybys of some of these new large outer worlds (eg Sedna) and buy some outer planet flybys on the way, but we'll probably need a new design for the power, which means maybe for everything

The other problem with this is that, by the time such a mission got approved, funded, built and launched, Uranus would have advanced pretty substantially in its orbit, much more so than 2003UB313. By the time the probe passed Uranus, this would be even more true. Thus flying past Uranus wouldn't provide much of a gravity boost -- in fact, it might even cause a deceleration, although I'm speculating here.

It is too bad that this is the case. I really like the idea of a Uranus-Xena mission for New Horizons 2 -- but, in planetary exploration, wishes aren't horses, sadly.

Adding 1 dot gets you there www.boulder.swri.edu/pkb

Advance copy for the PI's Perspective to appear early in the coming week:

Last week, details of discoveries and early interpretation of Pluto’s two small moons, formally called S/2005 P1 and S/2005 P2 were published in a pair of papers (Weaver et al. 2006 and Stern et al. 2006) in the scientific journal, Nature. Nature is very much the Rolling Stone of the scientific community, and the discovery and interpretation of ‘P1’ and ‘P2’ won the cover of Nature. This is probably as close as the nine of us will ever get to making the cover of the Rolling Stone. Although this was my tenth scientific publication in Nature, it was a real rush of accomplishment that vindicated long years of searching the Pluto system for companions to Pluto and Charon.

In our two back-to-back papers, we described the orbits and sizes of our two newly-discovered moons, discussed the unique architecture of the Pluto satellite system, predicted that similarly complex satellite systems will be found routinely in the Kuiper Belt, predicted that P1 and P2 probably generate ephemeral rings around Pluto, and argued that P1 and P2’s orbits argue strongly that they were born in the cataclysmic collision of a large KBO onto Pluto that created Charon, billions of years ago. In fact, we believe that the presence of P1 and P2 in the orbital plane of Charon is very much the discovery that checkmates the 20 year old hypothesis that Charon was born as a result of a giant impact onto Pluto.

On the same day, February 23rd, that Nature published our papers and an accompanying “News and Views” piece by New Horizons co-investigator Rick Binzel, the nine of us on the discovery team also published a scientific bulletin called an IAU Circular. This brief communication, ed by Max Mutchler and Andrew Steffl, revealed the results of brand-new Hubble Space Telescope (HST) observations of P1 and P2, made just days before on 15 February. The new HST images confirm the discovery (see above for an image from this run on HST); the new imagery also shows that our published orbital predictions, made in the fall. were almost bang on. We expect to get one more HST observation on March 2nd, from which we hope to further refine the orbits of P1 and p2 and to also obtain the first high quality color measurements of P1 and P2.

You may have also heard that we’re working on official names for P1 and P2. We hope to submit those to the International Astronomical Union (IAU) for formal approval this spring. In the meantime, we’re referring to the pair as “Boulder” and “Baltimore,” in honor of the home towns of 8 of the 9 people on the discovery team (and, we note, the respective locations where HST’s instruments were built and where HST’s scientific institute is located). S/2005 P1, which is the larger moon is the one we call “Baltimore”; S/2005 P2, being smaller, is the one we call “Boulder.”

And what about New Horizons? Well, it’s halfway to the orbit of Mars now, and the flight mission is continuing smoothly. Last week, we conducted the “Launch Plus 35 Day” review of the engineering and operational aspects of the mission. In this formal, day long review, the engineering leads and the ops team presented the status and lessons learned from the first five weeks of flight to a review team consisting of experienced spacecraft engineers and project managers.

Also last week, we conducted the first testing of instruments in our scientific payload. In total, three instruments were tested last week: ALICE, PEPSSI, and LORRI. (And there is no truth, dear reader, to the rumor that we chose these three to begin with because they spell, A-P-L.)

Although “first light” for each of these three instruments is still in the future the early tests we preformed last week proved that all three instruments survived launch and have good power and command interfaces to
the spacecraft. Additionally, each instrument put their microprocessors through various paces, and ALICE
unlatched and successfully tested her front door by opening it to space. All of this testing went well and we’re very happy with the engineering data returned to Earth by all three of these instruments.

This week, SWAP and SDC will get turned on and tested similarly to the work done last week with ALICE, PEPSSI, and LORRI. In fact, SDC will even begin collecting data. And so will PEPSSI. Starting in March, we plan to use SDC, PEPSSI, and SWAP a great deal during the flight to Pluto in order to trace out conditions in the interplanetary environment across the space of 5 billion plus kilometers from here to the Kuiper Belt.

In March, we will continue instrument commissioning with increasingly complex testing of our optical and plasma instruments. Additionally, both copies of our radio science instrument, REX, will receive their initial check outs in mid-April.

Also in March, we’ll be undertaking four very important activities with the New Horizons spacecraft itself.
One I’ve discussed before is a course correction called TCM-3. This roughly 1.2 meter/second trajectory correction maneuver will trim up our course to the Pluto keyhole at Jupiter even more precisely than TCM-1A and 1B did. TCM-3 is planned for Thursday, March 9th. The other major activities for March are an upload of a few bug post-launch fixes to our Command and Data Handling (C&DH) software, the checkout of our High Gain Antenna, (HGA) and the installation of something called CLTSN.

CLTSN stands for Command Loss Timer Safety Net. It’s a new feature of the spacecraft’s autonomous fault detection and protection system designed to act as a backup (“last ditch”) recovery of the mission if the spacecraft determines it has failed to hear from the ground controllers for too long a time (about 135 days). If this unlikely happenstance ever occurs, autonomy’s CLTSN switches the entire spacecraft avionics chain to the backup side, turns the spacecraft back to a good communications attitude with the HGA disk pointed toward Earth, sets the downlink beacon to “Red 6” and fires up the receivers to await new instructions from Earth.

CLTSN, which we colloquially call the “catcher’s mitt,” is a new layer of autonomous spacecraft recovery smarts designed to give take over if the normal autonomous fault detection and recovery procedures have failed to recover the mission. This is something I insisted on seeing added to the mission before I signed off on launch. I hope we never have to use CLTSN, because it’ll mean we’re down to our last play in our the playbook. But I do think it’s an important new capability. After all, without CLTSN, we wouldn’t have a last ditch recovery to take over if some “unknown, unknown” prevented the normal recovery processes from working as we expect them to.

Well, you can see the next few weeks are going to be busy for New Horizons. Pluto, Charon, Boulder, and Baltimore lie ahead.

Until next time.

-Alan

okay i'm new but i have a few q's

what was the cost of the atlas 551?

what is the cost of the delta 4H?

Could the Delta 4H give more Delta V then what was givin to NH1?

I know one of the problems with using a bigger buster (be sides cost) is the g stress on lift off, could they do like the Titan 4b have the center CCB run at alower thurst (ie saving fuel on lift off for more Delta once in orbit.

would this help or hurt the NH2 program?

(i went with the delta because it has flown and the atlas 5H has not)

thank you for your time

Well - stats for an NH2 type launch are not particularly available, but - figures that are include mass to LEO and mass to GTO - they're both a good indicator of the potential performance of the vehicle.

For the Atlas 551, it's 20,520 and 8670kg
For the Delta IV Heavy (which has flown once, with only partial success) it's 12,757 to GTO (can't find an LEO figure) - so approx a 50% hike in performance

However....going on the baseline of whacking a star upper stage on to the vehicle, the performance maths probably comes out a little more complicated than that.

Also - there's the cash issue

An Atlas 551 is approx $192m ( according to Astronautix.com ) - whereas a Delta IV Heavy is $254m. That alone, the $60M difference, could be a deal breaker.

Doug

The Delta 4 Heavy could indeed have sent NH 1 to Pluto quicker -- about a year quicker, if I remember correctly. But this was determined by NASA not to be worth the cost (bearing in mind that NASA had to be dragged kicking and screaming into launching a Pluto probe at all).

Just curious....I read somewhere that the "Grand Tour" trajectory the Voyagers took is unavailable until sometime after 2100, is that right? If that's the case, are there any potential viable trajectories that can get a New Horizons 2 probe up to the same speed as the Voyagers are currently going now or better? Something like, say, a Venus flyby, then an Earth flyby, next a Mars flyby, then a Jupiter flyby, then out to Sedna or UB313? Or possibly a flyby of the Sun (kinda hot and close I know) then Jupiter, then out to Sedna?

I would hope we fly something like NH2 out there....Sedna would be very interesting as it's the farthest object we know and is highly reddish, very different from other KBO's like Pluto and UB313. And a visit to Uranus or Neptune would be great, I'd like to see more pics of Triton and those geysers.

NOPE!!!
That wouldn't work and problem is not Sun's heat only...
Here's what happened to Voyagers:

As the spacecraft's came into Jupiter's gravitational influence, it fell toward Jupiter, increasing its speed toward maximum at closest approach to Jupiter. Since all masses in the universe attract each other, Jupiter sped up the spacecraft substantially, and the spacecraft slowed down Jupiter in its orbit by a tiny amount, since the spacecraft approached from behind. At this point, Voyager's had been sped up enough by Jupiter's gravity to get a speed greater than Jupiter's escape velocity. As it left, it slowed down again, but it never slowed all the way to the speed it was before getting to Jupiter. It left the area near Jupiter faster and in a different trajectory...

Now that wouldn't be possible to do with Sun would it?
Too bad though just think of acceleration spacecraft would get from as massive body as Sun is...

That part is a bit misleading. Since Voyagers were entering the Jovian system with a non-zero velocity, they already had more than Jupiter's escape velocity. In fact, after the flyby, both Voyagers had the same speed (with respect to Jupiter) they had when they "entered" the system. It was the heliocentric speed that changed drastically.


An unpowered flyby of the Sun would give you nothing, but if you set up the flyby and fire your engines at perihelion, it turns out you'd get a better bang-per-buck or delta-V/kg of fuel than normal. The same goes for a Jupiter flyby. The trouble with Sun is that it's very hard to get close to, harder than actually exiting the solar system!

You wouldn't mind giving me some more info on that "bang-per-buck or delta-V/kg" do you?

Gravitational slingshot -> Powered slingshots

NH isn't supposed to have enough RTG power to run its instruments by the time it got far enough from the Sun for a Sedna flyby, even if it were going the right direction. UB313 looks unlikely. We'd need to build a craft with a longer-lasting power source.

It has been pointed out that with a solar sail, you can achieve tremendous outgoing Solar velocity for a spacecraft by initially tacking in toward the Sun -- that is, you initially tilt the sail so that the photons of reflected sunlight go mostly forward along the craft's orbital direction, so that their momentum slows it down and it spirals in toward the Sun -- and then, when you're very close to the Sun, you tilt the sail to provide maximum delta-V forward and outward. The intensity of reflected sunlight at that close range allows the craft to pick up a really massive surge in delta-V before it moves far out from the Sun again -- and, as a result, you can pass the orbit of Pluto in just a few years.

But that, of course, is not at all the same thing as just orbiting in close to the Sun, which gives you no boost outward beyond your initial aphelion. A gravity-assist flyby requires flying by a body which in turn is orbiting a larger body -- in this case, flying by a planet orbiting the Sun -- to pick up a tiny bit of that body's forward orbital velocity and add it to the craft's initial velocity relative to the main body (the Sun) so that it flies out from the Sun faster while the planet flown by actually ends up orbiting an infinitesimal degree closer to the Sun than it was before. (Or -- if you're using a planetary flyby to get CLOSER to the Sun, as with Mariner 10-s gravity-assist flyby of Venus to reach Mercury -- the planet you've flown by, in this case Venus, actually picks up some of the craft's forward velocity and thus moves an infinitesimal degree AWAY from the Sun.) Back in the early 1970s, some hippies in Pasadena got wind of the Grand Tour scheme and started doing "Don't knock Jupiter out of orbit!" public protests -- while making it clear that they knew enough about science that they were being tongue-in-cheek.

Jupiter is massive enough that you can do quite astonishing things with gravity-assist flybys of it if you fly even fairly close to it. Not only can you pick up huge new acceleration away from the Sun, without even the need to fly by any more giant planets (Voyager 2 flew no closer than about 800,000 km), but alternatively you can flip your craft's orbit 90 degrees to the ecliptic (as with Ulysses), cancel out all its forward orbital velocity so that it then falls straight in from Jupiter to the Sun on a straight-line path (the plan for the proposed Solar Probe), or even hooks into a BACKWARDS orbit around the Sun (one way that the US could have rendezvoused with Halley's Comet, had we been willing to spend the money for such a mission). And in each case, this does not even involve flying closer than 200,000 or so km to it.

But Sedna -- a very interesting body, which I think we will explore at some point -- is so far away that even using a Jupiter flyby it will take some years to reach it, and unfortunately it and 2003 UB313 aren't anywhere near the almost-straight path that NH will follow from Jupiter to Pluto. Nor do there seem to be any more opportunities for flybys of three giant planets on one mission until the late 2020s, or for missions that fly from Saturn to either Uranus or Neptune or from one of those two ice giants to another. So for now, we're stuck with flights past Jupiter and a single other outer planet or KBO, and each of those launch windows only comes along every 11 to 12 years (or, in the case of Jupiter-to-Saturn flights, every 20 years) -- although each such window lasts 3 years or so.

Thanks Bruce. I didn't think about the sun's situation....it would be an awfully difficult object to fly past at a close distance anyway. But that is a pretty neat thing about solar sails, it would be good if someone could put together a successful demonstration like that.

If I had a vote I'd say send a probe to Sedna at the next best opportunity.

I can't remember whether these have been mentioned yet, but there are several good papers on the Web regarding the new and increasingly popular concept of "Radioisotope Electric Propulsion" -- modestly oversized RTGs running low-power ion engines that are still strong enough to do a great deal of useful work in flying probes to outer Solar System targets (including even orbiters of Pluto and other KBOs). In particular:

http://gltrs.grc.nasa.gov/reports/2002/TM-2002-211893.pdf
ftp://ftp.grc.nasa.gov/users/ep/ion/publi...iepc-03-137.pdf
http://gltrs.grc.nasa.gov/reports/2004/TM-2004-212877.pdf
http://www.lpi.usra.edu/opag/mcnuttstaif06.pdf
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1922.pdf

One thing made clear is that the way to use these is not to use REP to provide the initial acceleration outwards into the outer System -- an EELV is the best thing to do that -- but instead to soon begin firing the REP system to slow down the craft as it proceeds into the outer System, so that it will arrive at its target at a relatively slow speed and then use the REP to insert itself into orbit and then do substantial amounts of orbital maneuvering around a giant planet's system of moons. This cuts the trip time from launch to the target planet in half. The results are very impressive: an REP-powered New Frontiers craft -- using Stirling RTGs that can supply 800 watts to the ion engines while weighing only 57 kg and carrying only a modest amount of plutonium -- can deliver a 100-300 kg payload into orbit around Titan in only 6 years, Titania in 9, and Triton or Pluto in 12 years (without using any aerobraking).

Is this the Wave of the Future for outer Solar System exploration? (The one big problem with Stirling generators is that they require the bane of space missions: moving parts.)

I actually inquired about the very same concept some time ago in another thread but the idea was dismissed as being unpractical. Granted, I was suggesting cutting down trip time by accelerating the craft further and not braking it into orbit, but obviously the concept might be feasible both ways.
It'll be interesting to read through those links you provided once I get some free time. 6 years to Titan seems like a very short time plus you get into orbit as well!

Thanks for the links. Very interesting reading. These sound like exciting missions, but are really pushing the envelope. In many cases, there is more Pu, and less spacecraft and instrument mass, than there is on New Horizons. Then there are the Sterling cycle generators, as you pointed out. They seem to shoehorn in their current, undersized generator, baselining five instead of two or three larger units, and still need nonstandard RTGs, which would be incredibly expensive to develop. Also, in the conceptual layouts, the RTGs appear to be closer to the instruments than was the one on New Horizons. It is bad enough on NH with the RTG a meter and a half away. In the figures they appear to be within a fraction of a meter. Plus the NH spinning hibernation mode would not be available, but perhaps those are just engineering details.