You speak for many there, I suspect.

An interesting comparison I haven't seen discussed is between NASA's Titan Explorer and ESA's TANDEM proposal. The latter includes no less than three Titan landers plus balloon, orbiter, and a significant mission to Enceladus as well. I find the three Titan landers particularly appealing. That could mean one each for the highlands and plains, and a lake drifter.

More on the EE and JSO descope mission options.

See the attachment to my previous post (two posts up in this thread) for details on the differences between the full and descoped missions. In this post, I'll address more of the philosophy behind the descoped missions.

For either mission, the key way to reduce costs is to change the launch vehicle from a Delta IV-H to an Atlas V. That single change is worth reducing the mission costs by ~$300M (the two proposals use different configurations of the launchers, so the savings differs somewhat -- see previous post). Changing launch vehicle requires cutting several hundred kilograms out of the delivered payload.

EE achieves this by reducing the instrument payload, cutting the number of nuclear power generators, reducing the radiation hardness (75% survival probability drops from 1 year in orbit at Europa to 6 months) and various other cuts. If EE delayed its launch by two years to 2017, though, it would gain ~200 kg of payload capacity. This probably would be enough to restore several of the cut instruments. Most important to this group, the narrow angle, LORRI-class camera could probably be restored, which would allow observations of Jupiter and other Jovian moons. It would also provide the 1 m resolution imaging of Europa to qualify potential landing sites for future missions.

JSO achieves its payload reduction through modest instrument capability reductions, minor design changes, but primarily by reducing the fuel load by doing only an elliptical rather than a circular low altitude orbit at Ganymede. This trade off would not work for the Europa mission where the low circular orbit is essential to global gravity mapping and, I presume, to global mapping of the ice thickness.

All in all, if I were Alan Stern (and thank god for the health of the program that I'm not ), I would implement and enhanced, descoped EE mission for the 2017 opportunity. I'd used the additional payload capability to add back in instruments such as the narrow angle camera and UVS spectrometer, improve radiation hardening, and possibly enhance the communications bandwidth. Then I'd use the money saved over the full up proposal to fund a New Frontiers mission. Lots of great candidates: Venus landers, comet sample return, and (my favorite) a joint Titan mission with ESA.

The Tandem summaries I've read read like wish lists -- what a group of scientists came up with as great things to do. I think that the budget for that flotilla would be quite expensive... If there is another mission to Titan (at least in my lifetime with ~25 years left to care (90% probability ), then I think it will be either a full up flagship mission with $3B from NASA funding a capable orbiter and either a balloon or lander and ESA paying for the other. No Enceledus,,, Otherwise, it will be something much more like a $1.4B balloon or lander only.

A new post by Leonard David at http://www.livescience.com/blogs/2007/12/2...-collaboration/ says that NASA will move forward with studies of the Europa Explorer, Jovian System Explorer, and Titan explorer. The studies will be done in conjunction with ESA and JAXA. NASA proposed contribution will be capped at $2B.

Initially, I had been thinking that the Europa and Jovian System missions would not be easy to split. However, I've revised my thinking (but would appreciate hearing from real engineers). There's several ways to split up the Jovian missions. ESA/JAXA could provide complete subsystems (really no different than supplying the Huygens probe -- electrical interfaces are electrical interfaces, whether they stay inside the craft or connect to a craft that will eventually seperate). Don't forget that Germany supplied Galileo's propulsion module as well as several instruments. Other alternatives would include JAXA supplying small orbiters to study the magnetosphere, ESA supplying a remote sensing craft that stays beyond Ganymede's orbit for remote studies (and presumably has a big camera), and NASA a reduced capability Europa or Ganymede orbiter.

A while ago, ESA proposed a Jovian minisat mission that would have a Jovian Europa Orbiter (JEO) and a Jovian Relay Spacecraft (JRS). A few posts ago, I posted a comparison of the proposed instrument compliments for the Europa Explorer and the Jovian System Observer. Now that it appears that NASA will continue its studies of these mission in conjunction with ESA and JAXA, I've extended the table with the instruments proposed for the minisat mission. (See http://sci.esa.int/science-e/www/object/in...objectid=35982) I don't know if the minisat is representative of what is proposed in the LaPlace proposal. The short story is the the instruments proposed for the minisat mission would have limited capabilities compared to what was proposed for EE and JSO.

Ive not got acess to the full article but this sounds like material in europa orbiters favour....

Nothing new here - Chyba and others have long argued for oxidant production as a possible
source of free energy to the ocean beneath. (papers in 2000 and before)

On the other hand, I think Ken Nealson has argued even this isnt enough energy to drive complex life

Then there is the interesting debate about there being unlikely to be much organic carbon on
Europa so life has nothing to build itself with (Protojovian nebula was too warm to trap methane in
the way Titan did). So there is nothing for these oxidants to oxidize.

All of which is interesting but moot, since an orbiter isnt really going to answer any of these
questions very well. If we were talking about a Europa lander it might be a different story.

To know where to put a Europa lander, we need the orbiter to find the most interesting safe place. Or to rule out that there are such places. Unless the eventual plan is to do a lander, a Europa orbiter makes no sense, in my opinion.

I continue, however, to believe that if the choice is Europa or Titan, then it should be Titan. If it is the entire Jovian system including a focus on Europa versus Titan, then that's a harder choice. I expect that the three teams give us a great choice of missions that makes it painful to see any of the three rejected. My personal, emotional favorite is Titan, if we get below the clouds with part of the mission.

In the end, I think that the final choice will be made on programmatic factors: total cost, risk of cost overruns, technology readiness.

Ralph, are you involved in the next round of developing of the Titan proposal?

FWIW I agree, but I'm going to be heartbroken whichever way the cookie crumbles.

Almost missed Emily's last paragraph here:
http://www.planetary.org/blog/article/00001285/

The orbital dance of the Space Agencies begins to unfold.

The Titan Flagship report is out. I've flipped through it (have a deadline that prevents detailed study for a week or so) and it looks highly detailed.

Word of warning. When I down loaded it, the site was really slow.

http://www.lpi.usra.edu/opag/Titan_Explore...blic_Report.pdf

Thanks, vjkane. It's very useful to have someone scouting these things out and drawing attention to them. I get too busy to look all the time.

That LPI site is a treasure trove of useful reports:

http://www.lpi.usra.edu/analysis/

There are new things from the Venus and Mars groups as well.

Phil

Lots to read (197 pages) -- the first things to grab me are the suggested landing sites and balloon tracks.

After the report lists several terrain types as having some upside or other, the final suggestion of a baseline landing site is the Belet dune field. Basically, the sand dunes are believed to be a good place to study Titan's organic chemistry. Other areas would have their own interest, but are either less typical of Titan as a whole or present engineering challenges.

The nominal balloon deployment would be low latitude, with a hope for stable flight and a long ground track. Presumably, a variety of terrain would be overflown -- it would be almost hard to avoid unless the flight were very short. The alternate possibility would be to land near the summer pole and try to get a peek at lakes and possibly storms, but there seems to be less confidence in what the winds near the summer pole would mean for the flight.

Much more to read...

My WORD, never has a PDF made me want to animate stuff as much as the TE pdf.


Doug

Great! The best possible weekend reading.