Given the tight budgets for planetary exploration, I worry that large flagship missions to the outer planets may never fly. The current strategy is to fly ~$3B flagship missions once a decade: first the Jupiter Europa orbiter (JEO), then a Titan Saturn orbiter, and then possibly at Europa lander (if JEO finds a location with interior materials at or near the surface that is safe to land at). At the moment, NASA's planetary program would have to forgo either the Mars program or the Discovery/New Frontiers programs to pay for a $3B flagship mission. (Alternately, NASA could give up portions of both programs, but the point is that $3B missions can't be afforded without giving up something else.) (This is a topic I've addressed before in this blog entry: http://futureplanets.blogspot.com/2009/05/what-next-for-titan.html.)
In this blog entry, I'd like to conduct a thought experiment to consider an alternative approach that might allow smaller scale missions to Titan could enable exploration of this fascinating world within tight budgets (and my expected lifespan). (See my thoughts on a possible alternative mission to Jupiter if the Jupiter Europa Orbiter cannot be afforded.)
I'd propose an on-going program of modest Titan missions carried out by multiple space agencies. A Titan lake lander could be a stand alone mission to provide compositional information. However, most other missions would require a data relay from an orbiter. NASA has made communications relay at Mars a priority (albeit also including scientific instruments on the orbiters) to enable high bandwidth communications with rovers. As a thought experiment, I would propose a similar strategy for Titan with each specific mission constrained to $650M to $1B. The key and first element would be a Saturn orbiter to provide communications relay and whatever scientific measurements would fit within the mission budget. (If affordable, my favorite would be a camera optimized to take advantage of the spectral windows in Titan's atmosphere for surface mapping.) The orbit initially might be chosen to optimize Titan flyby science and then later communications from Titan landers and balloons (although the same orbit might accomplish both). The orbiter might be a near twin of a Galilean icy moon observer to save costs. Given Cassini's long life, it would be reasonable to plan for a lifetime of a decade in orbit at Saturn. See this blog entry for examples of the science that a multi-flyby orbiter might be able to carry out.
After the relay is in place, several in situ missions could be flown:
A Titan lake lander for chemical measurements of the lake and atmosphere. While the main experiments might be battery powered and therefore short lived, a small plutonium power source would enable long-lived geophysical and meteorological measurements.
A geophysical network of landers for solid surface measurements powered by plutonium power sources to enable a lifetime of months to years.
One or more balloons to explore the atmosphere and make remote studies of the surface
Highly capable landers to carry out surface composition studies, possibly even with modest (to keep costs within reason; perhaps a couple of hundred meters) roving capabilities.
The Saturn orbiter would have to launch and arrive first. The order and timing of the subsequent missions could be dictated by launch opportunities and budgets. Breaking the missions up would allow multiple space agencies to contribute specific missions, spreading total costs among multiple nations.
A key difference between exploring Titan in small missions and doing the same at Mars is the flight times. Whereas Mars is months away, Titan is years. That alone would make each element more expensive. Data rates from the relay craft would be much lower than from Mars given the distance. This is one reason that the Saturn Titan orbiter is so expensive compared to Mars orbiters -- it needs lots of power to return high resolution mapping data. The modest Saturn orbiter in this thought experiment would have lower data rates than a flagship mission.
Closing Notes: Many really smart people have and will look at Titan exploration options. I'm under no illusion that I have ideas that are novel or that the ideas presented here are the best way to take advantage of limited budgets. I present them in the spirit of showing possibilities so that you can reach your own conclusions. As I did with the proposal for a Galilean Satellite observer mission, I'll publish thoughtful critiques of these ideas that are e-mailed to me at vkane56[at]hotmail.com.