Second Moon Around 2003 El61, Santa / Rudolph / ? Options

[Guest_BruceMoomaw_*]

Well, it's a safe bet that from now on an attempt will be made to arrange a KBO flyby for virtually every spacecraft launched on an escape trajectory from the Sun. But that leads me to another subject I've been thinking about.

Even before NASA went on its current science-funding starvation diet, Solar System Flagship missions would have been few and far between. The current over-optimistic Solar System Roadmap calls for a series of three "Small Flagships" at intervals of about 5 years (Europa Orbiter/Explorer, followed by a Titan mission and then a Venus mission), and then -- as the only Flagship mission for the decade after that -- a "Large Flagship", probably consisting either of a Europa astrobiology soft-lander or a combined Neptune orbiter and entry probe mission.

But if this plan is followed, then there won't be an atmospheric entry probe of either of the two "ice giants" (Uranus and Neptune) until 2035-40 at absolute earliest. And the planetary science community very much wants an entry probe of a second giant planet in the reasonably near future, for comparison with Jupiter.

The plan recommended by Sushil Atreya is therefore make the first one of those a New Frontiers-class mission, consisting of a Saturn flyby dropping off 1 or 2 entry probes. But why not make the next NF mission a Uranus flyby with 1 or 2 entry probes instead? This has several advantages:

(1) The ice giants are more distinct from Jupiter than Saturn is -- they're one of the "fundamental" classes of planet in our System -- and will provide more data on the composition of the outer parts of the solar nebula while the Solar System was forming than Saturn will.

(2) If we want to avoid waiting until 2030 or later for our first entry probe of an ice giant by flying an NF-class flyby before we fly Neptune Orbiter, then it makes sense to fly that NF mission to Uranus rather than Neptune to reduce scientific duplication (especially since the Neptune Orbiter, when it does fly, can carry its own entry probes piggyback, as its current design in fact calls for).

(3) Such a Uranus flyby if launched around 2013, would arrive at Uranus around 2021 -- still fairly close to that planet's equinox, and thus allowing us both to make comparative observations of Uranus' weather and magnetospheric patterns under conditions very different from Voyager 2's near-solstice flyby, and to glimpse a larger illuminated part of the total surface of its moons than a later Uranus orbiter would do (and thus to get an improved second look at the same parts of those moons seen by Voyager 2, which a Uranus Orbiter arriving at about the time of Uranus' next solstice could not do because it could only view their opposite hemispheres from those seen by Voyager).

(4) Being a solar-escape mission -- and one making a flyby of a giant planet, so that by tweaking its flyby distance very slightly we could radically revise its post-planetary trajectory (which we can't for New Horizons) -- this mission would provide one of those infrequent opportunities for a look at a preselected and large KBO. (Atreya's Saturn flyby with entry probes could also include that, of course.)

You'll notice that I'm mostly recycling the arguments for New Horizons 2, for which the chances of a launch in 2008 are now zero. But this new version does have some changes -- the addition of the entry probe or probes; the fact that this NF mission would arrive farther from the Uranian equinox than NH 2 would have done, but still close enough to it to be useful; and the fact that the craft would have to reach Uranus not by a Jupiter flyby but by a direct trajectory perhaps augmented by Earth/Venus flybys. The latter, however, is perfectly feasible.

In short, what I'm saying is: New Horizons 2 is dead! Long live New Frontiers 3 to Uranus -- for which the argument is extremely strong compared to other NF proposals! Especially since, unlike all the other possible NF-3 concepts, it will suffer scientifically from a delay -- which was also the strongest argument for making New Horizons the very first NF mission.