Outer Planet Flagship Selection & Definition Options

[vjkane]

Given the renaming of the forum to Exploration Strategy to discuss mission selection and definition, I thought I'd create this new discussion thread to continue the discussions that had previously been in the Outer Solar System > Jupiter forum. Since the options are either Jupiter or Saturn as targets, this seems to be a more suitable place.

I repeat here a previous post to the old forum with a link to the latest status report on the selection and definition:

An August update on the two possible outer planet missions has been posted at: http://www.lpi.usra.edu/opag/flagshipOPF08.pdf

Both concepts are maturing and both look very feasible with compelling science. (I'm glad that I don't have to decide!) Report is only on the U.S. orbiter elements.

Some highlights:

Mission costs are being allowed to increase by a few hundred million dollars to enable more capable instrument packages.

Selection between Jovian and Saturnian system destination is now Feb 2009.

Risks for the Saturn mission are much lower (but appear to apply only to the orbiter element). Europa mission appears to have higher risk elements (assuming same scale used for both) because of the radiation environment.

Current plan for the Titan in situ elements is to release them early in the Saturn Titan tour, which means a long period (12-18 months?) with only periodic relay by the orbiter and direct communication with Earth used in between.

[vjkane]

I think that the Titan orbiter science is pretty well understood at this point, and the chances of future Cassini discoveries making a major change are probably acceptably small.

Similarly, the knowledge of the atmosphere is sufficient to design a balloon probe.

The problem that I see is that we know only course information about a small fraction of the surface. Therefore, optimizing the landing site is unlikely given the plan to release the in situ elements before the orbital studies from a Flagship craft begin. I believe that's why a lander has been targetted for either the widespread dune areas or one of the lakes (large, homogeneous areas that are interesting in their own right). Also, long term studies of seismology and weather can be done from almost any location (or put another way, if you get only one lander, then where you put it is less important for these kinds of studies).

On the other hand, my programmatic management experience suggests to me that we are still very early in the architecting of the optimal in situ mission elements. (1 lander or two? big balloon payload or smaller? etc.)

Both Titan and Europa are hard to study from orbit. Titan because the haze limits optical instruments, the atmospheric depth makes subsurface radar sounding hard, and SARs eat up a lot of budget and data bandwidth. Europa, on the other hand, sits in the middle of a literally killing radiation field.

Still, given all this, I come down on the side of Titan if the Europeans contribute a meaningful in situ element. We can hypothesize a lot about the internal structure of these large icy moons. A seismometer on Titan could increase our knowledge by several orders of magnitude and that isn't possible for Europa (with current technologies and budgets). (Although the proposal for the lake lander would eliminate this instrument.) Similarly, we can use a balloon to explore the atmospheric chemistry, wind patterns, and surface/subsurface. So Titan wins on the grounds of being in the top 3 most interesting solar system bodies and the ability to do long term in situ studies.

However, if the Europeans don't contribute the in situ elements, then the Europa orbiter studies more interesting bodies with a modern set of instruments than does the Titan orbiter. (While the Titan orbiter will increase our knowledge of Enceladus, it won't add much to our knowledge of Saturn itself or the other moons. A Europa mission would make up for the Galileo antenna problem and bring modern instruments to bear vs. Galileo's mid-1970 technology instruments.)