The assessments of the four flagship missions has been posted at http://www.lpi.usra.edu/opag/announcements.html

Some key findings:

ESA and NASA are studying two joint missions:

Jupiter: Jupiter/Ganymede orbiter (ESA); Europa orbiter (NASA)

Titan: In situ probe (ESA); orbiter (NASA)

Summary of findings on the Flagship proposals delivered last year:

Europa orbiter: Mission concept Excellent/very good; Risk Science Medium; Risk overall mission Medium

Jovian system: Concept Very good/good; Science High risk; Risk overall High

Titan Explorer: Concept Excellent/very good; Science medium risk; risk overall High

I assume that the Jupiter/Ganymede orbiter provided by ESA would be a much scaled down version of the proposed Jupiter System Observer (JSO)? Would there be a big enough launch payload to include both orbiter components without significantly compromising the research goals of both? It seems unlikely. I guess I would rather have the previously proposed JSO or EO as compared to scaled down versions of both.

Anyway, the Titan option keeps getting more interesting with each new Cassini flyby...

My opinion is that titan is now the most interesting single object in the solar system- complex organic chemistry, likely underground ocean, active surface processes, the list goes on. The only way I see it being knocked off its top perch is if enceladus proves to have and underground sea powering its plumes, which would give us the opportunity to sample material from an extra terrestrial sea. That said a sample from a cryovolcanic flow on titan could prove just as interesting! Exciting times...

With the state of current technology & recent discoveries, I'm getting there myself, MB.

The damned Jovian radiation environment is such a major limiting factor for Europan exploration right now. Only makes sense to try the Saturn system instead, which has at least two satellite targets of extreme interest with a lot less frying potential. Gotta lean heavily towards minimized risk here plus significant science return potential.

As far as multiple targets of interest in the Saturn system, I'm not so sure that the Titan mission would return information on Encealdus. If the Titan orbiter is using aerocapture I would guess that the most likely scenario has the orbiter entering Titan orbit on initial approach to the Saturnian system. In that event the only moon we are likely to get a good look at is Titan itself.

That is the trade off I see between the missions. The Jupiter Flagship gives us close looks at all of the Jovian moons, and detailed looks at Europa and Ganymede. Gives you a lot of targets to ponder and study.

The Titan mission gives us just Titan.... but if you have to be stuck studying just one major moon in the Solar System I'm hard pressed to think of a more interesting one.

We don't have much information on the two studies as yet, but while I can see the US building a Europa Orbiter for 2 billion dollars (a figure I've seen mentioned a couple times as the cost cap for our part of the mission) I seriously wonder if the ESA can build a full blown Ganyemede orbiter for their stated goal (600-700 million Euros is my vague recollection).

I'd love to see a mission to Titan. However, looking at this from a management perspective, the issue is risk. NASA cannot let this mission fail. Both leading candidates provide excellent science. One is medium risk (Jovian), the other high risk (Titan).

The decade or more of technology development and mission definition for the Europa mission shows. I'd prefer to see the next Flagship mission go to Titan. Their challenge is to get the risk rating down.

How about we send two of the exact same spacecraft on the exact same type launch vehicle along the same track? Same instruments, same science packages. And you test the spacecraft development a little bit more than usual.

OK, we pony up the bucks for a duplicate spacecraft (relatively cheap), and for the second launch vehicle (much bigger bucks), but you will lower the risk. (If you tested right, at least one of them should make it.)

This is assuming that the risk is due to unforseen random issues, cosmic ray hits, not getting the entry angle right on the first try, etc.


I think Titan is diverse enough to support two Titan Explorers. (Just like Mars is doing a great job of keeping both rovers busy and with exciting new stuff). If both make it, you will more than double the science.

(And Bonus: Two Jupiter flybys).

Just my 2E11 cents.


-Mike

(And yes, I'm a U.S. Taxpayer and more than willing to kick in more than my fair share for a twofer deal.)

Nasa used to routinely send pairs of spacecraft on missions, and frequently lost one of the pair. Again, I've never seen how this breaks down, but I'd be surprised if it's anywhere close to "two for twice the price."

Except for the cost of the launch vehicle, of course. There, once again, I think we're reduced to hoping that Falcon 9 ends up being everything it's promised to be.

--Greg

A second spacecraft typically adds 50%. That was the budget breakdown for MER initially ( although budget overruns pushed that up to almost double the price of the first proposed rover )

So - for a $3B flagship - you're talking about increasing it to $4.5B minimum. That's not pocket change. We're stretching the budget to afford one flagship - to afford 1.5 is fantasy land.


Doug

Assuming that the Titan mission is selected, ESA has a range of in situ missions it can propose within in its ~600-700 euro budget:

One really good lander

Two less capable landers (say with 1/2 -2/3 the capabilities of the one really good lander). Here the tradeoff is between better science at one spot, or investigating two spots with a less capable lander.

One less capable lander and a minimalist balloon. The balloon presumably could share many of the subsystems of the lander, but would also require a lot of new engineering and testing.

From my conversations with Lorenz, a key factor will be whether or not ESA decideds to develop smaller plutonium power systems. Apparently NASA's standard design assumes large missions. Once you put on that large power supply, you are committed to a big vehicle. If ESA designs a smaller supply, then it makes sense to consider multiple smaller landers/balloons.

In theory (but the engineers may dispute the practicability), a single entry shell could carry both a lander and a balloon. There would have to be tradeoffs in avaiable space between the two. I think that a balloon that carried only a camera but could float for months/years could provide valuable ground truth of the orbiter's observations.

Which missions do you mean? Mariners?

I note that both Voyagers, Vikings and MERs were successful, so losing one s/c of the pair isn't a common practice at NASA anymore

Well -- what's wrong with the idea of a lander attached to a balloon? That way you can reconnoiter a lot of landscape with instruments on both the lander and the balloon, and only drop the lander when it's over an area you recognize as a good one for surface exploration. Yes, you run the risk of flying over a unique area and recognizing it as such only after it's passed on by beneath you, but Titan has so many different types of terrain and chemistry to offer, and so much of most of them, I'd think you'd be able to recognize a good area in time to set up the drop.

As for the drop, all you really need is a good parachute system. The lander can be dropped on a chute from 1,000 to 5,000 meters and make a nice, safe landing in that thick air.

-the other Doug

Not so much anymore, but the losses of Mariners 3 and 8 really proved out the concept. In fact, the only dual spacecraft I can recall that were both lost were the Mars penetrators that hitched a ride with MPL.

-the other Doug

I think that it was a combination of more reliable boosters and funding reductions that caused NASA to stop launching duplicate spacecraft for the same opportunity. MER was the exception.

When I read "high risk" for Titan, I think not only of the necessarily complex hardware, but also the unknowns of Titan itself. For initial recon of a world, you don't have much risk with a flyby -- you're looking for the basics, and you'll almost certainly get them. There's no such risk with, say, Dawn at Ceres.

But we've been burned before. In a sense, the first three Mariners at Mars burned us by imaging terrain that was not representative of the planet. The Galileo Probe burned us by hitting a highly unrepresentative location on Jupiter. The MER program was burned by planning two rovers with a particular set of engineering and science constraints and having only one site on the whole planet really match the specs.

That is the kind of risk that Titan poses, and so I don't think there's any sense to hurrying a Titan mission along before all the Cassini data has been analyzed, through a couple of waves of peer review. With Europa, we had to have the community partake in the debate over how thick the ice shell is. It would have been foolhardy to plan the next billion-dollar mission when there was still pencil-and-paper work to be done. The pencil-and-paper work is just a heck of a lot cheaper. Let's play as much of the Twenty Questions here in the Gedankenexperiment lab before launching a major chunk of the whole decade's budget. Suppose a brilliant conjecture is posited the year after the flagship launches, and as a result, Hotei Arcus becomes the consensus most interesting place in the solar system. And the mission is already en route lacking the capabilities needed to probe it. That - must - not - happen.

Titan's surely the prize. It's the one that would get picked first if captains were choosing softball teams. But it's also not ready this time around. The next flagship almost certainly has to go to the jovian system. (Enceladus has a very slender chance of jumping the queue because it's likely easier to "figure out" than Titan.)