Another COSPAR abstract ( http://www.cosis.net/abstracts/COSPAR2006/...006-A-02223.pdf ) on this subject. Note particularly the last paragraph, in which the Japanese are clearly expressing their desire to build some of the experiments for NASA's planned 2013 Mars Science and Telecom Orbiter:

"Moreover, some consider a future back-up mission after Japanese Mars mission NOZOMI. Although NOZOMI produced interplanetary observation data, the insertion to circummartian orbits was finally given up in 2003. Future landing missions will require an orbiter for efficient data transfer. If 20kg payload would be allowed in the data communication orbiter, important measurements of the plasma environment around Mars can be executed with a scientific target to clarify the atmospheric escape."

The pre-project scientist for MSTO is a specialist in exactly this area: http://nesc.nasa.gov/bio/bio_winterhalter.cfm?linkfrom=team . I haven't been able to squeeze a word out of the Internet about what MEPAG's upcoming recommendations for MSTO's science payload will be -- but it was made clear at the November COMPLEX meeting, where MSTO's existence was first unveiled, that it will almost certainly be focused on Mars' atmosphere. There are several very good reasons for this:

(1) It has been made clear at all recent meetings on the design of the Mars program that we very badly need more detailed observations of the behavior over time of the Martian atmosphere in order to design reliable systems for future Mars landers (including those landers of unprecedented size) -- especially including detailed monitoring of the wild fluctuations in the density of Mars' upper atmosphere.

(2) MEPAG has just stated that two major goals of US scientific exploration of Mars which are separate from the central search-for-life line -- and which must no longer be unfairly neglected -- are a Mars surface network mission, and study of the gas escape mechanisms operating in Mars' upper atmosphere.

(3) The search for and mapping of trace gases, as we all know, has now become a very important new element in the search for Martian life.

I thought that the MTO was cancelled...

MTO is cancelled. MSTO is a new proposal for 2013.

This is MTO's replacement. Since NASA gave the 2009 MTO the heave-ho on the grounds that it had far too much excess communications capability beyond what we actually needed, we still need to launch a replacement for MRO when its own com relay capabilities are projected to wear out some time around 2016 (especially since all the older US and European Mars orbiters should also have worn out by then). So NASA decided that the new strategy will be to periodically launch new Mars orbiters -- at low altitude, unlike MTO -- which, unlike it, will be strongly oriented toward making new science observations as well as carrying on MRO's work as a relay orbiter for Mars landers. Thus MSTO (which may very well end up using the MRO bus design, although that's far from decided). This was one of the most interesting new revelations I heard at the November COMPLEX meeting (along with the first news of "Dawn's" stand-down for reconsideration). NASA seriously considered requiring that the 2011 Mars Scout mission must be a Mars orbiter that could double as MRO's communications replacement, but they finally decided that this would limit the freedom of selection for the Mars Scout program too much.

NASA is, in fact, already fretting about the next com relay orbiter after MSTO, which will presumably have to fly around 2024 -- although that's the window currently devoted to launching the sample-retrieval orbiter which will be the first half of the Mars sample return mission, and which is supposed to blast itself completely out of Mars orbit and back to Earth as soon as it's done that job.

As I alluded to in another thread, I've seen some of the preliminary work on MSTO. One of the key knocks against MTO, which factored into its cancellation, was the lack of (or very limited opportunity for) science. There was a preliminary effort to define MTO science, but the margins were too low and were rapidly shrinking. From what I can see at this early stage, MSTO does offer more more hope for science, though we'll see how it progresses.

As for MTO's fate, basically, the powers-that-be didn't want to commit to an expensive orbital Mars relay, one that offered only scant opportunites for science, when the follow-on mission architecture was uncertain. It sounded good when the Italians (ASI) were baselined to provide the spacecraft (G. Marconi MTO) but when it became an American problem, it was easier to axe and NASA subsequently bailed. As Mike Caplinger noted, MTO was "a solution in search of a problem," notwithstanding its supposed "criticality" to 2009 MSL.

Besides MSTO is not only for telecomunications purposes but also for science too (explore Mars's atmophere to study its plasma). MSTO : Mars Science Telecomunications Orbiter.

Rodolfo