• The committee notes that Scout missions provide a potential additional mechanism for adding balance to the overall architecture (subject to the caveats discussed previously). In particular, the optimum science payload for MSTO may (or may not) alter depending on the outcome of the 2011 Scout competition.

• Finally, international collaboration, as noted in the document Mars Exploration Strategy 2007-2016, could be another mechanism for adding balance to the Mars architecture.

In response to the question, Does the Mars architecture represent a reasonably balanced mission portfolio?, the committee finds that in the context of the basic types of missions, the Mars architecture is a reasonably well balanced one: both landed and orbital missions are included in an appropriate mix, given the current state of Mars exploration. To the extent that the specific science objectives of the proposed missions are defined, one of the three crosscutting themes for the exploration of Mars identified in the SSE decadal survey is largely neglected, as are very high priority topics related to understanding near-surface and boundary-layer atmospheric sciences, and so, in this respect, balance is sorely lacking. As has already been recommended (see above), a geophysical/meteorological network mission is a key to addressing both of these science areas, although some of the highest-priority science measurements could potentially be made on other surface missions (e.g., the AFL or the Mid Rover missions). These include meteorological, seismic, and heat flow measurements.

To optimize efforts to implement a balanced portfolio of missions, the committee offers the following recommendations:

Recommendation: Include the Mars Long-Lived Lander Network in the mix of options for the 2016 launch opportunity.

Recommendation: If the Mars Long-Lived Lander Network cannot be implemented in the period under consideration, provide for an effort to make some of the highest-priority measurements on the landed missions that are included in the proposed Mars architecture.

Recommendation: Ensure that the primary role of the Mars Science and Telecommunications Orbiter is to address science questions, and not simply to serve as a telecommunications relay. This distinction is particularly important with respect to the required orbital parameters that are adopted.