The Decadal Survey reports run hundreds of pages. Often, much of text is devoted to summarizing current state of our knowledge and stating key questions to answer. The topics that are likely to receive the greatest focus, however, will be the prioritized list of questions to pursue and the recommended missions to address them. With that in mind, here are the questions that I will have in mind as I review the report:
1. What budget is assumed? Budget issues have led NASA to consider replacing its own mission for the top priority of the just completed astronomy and astrophysics Decadal Survey, the WFIRST dark energy and exoplanet mission, to seek a partnership on a similar proposed ESA mission. NASA reportedly has also dropped plans for two missions prioritized by the Earth Science Decadal Survey, CLARREO and DESDynI, for lack of expected funding. While the reasons for these decisions are more complicated than simply too little money in NASA's budget, these are cautionary tales. The recent astronomy and astrophysics Survey members assumed that the upside budget was current funding adjusted for inflation and the downside was current funding eroded by inflation. An extension of this year's planetary funding for the coming decade could support a major flagship mission, perhaps a smaller flagship mission, and several New Frontiers and Discovery missions. An assumption of the budget plans in this year's FY12 budget plan with its declining budgets might mean a program of New Frontiers and Discovery missions.
2. What are the major science questions that are prioritized? The Survey might prioritize understanding the early history of terrestrial planets and potential for early life, leading to a high priority for the series of missions (>$6B in total) leading to a Mars sample return. Alternatively, the Survey might prioritize investigating icy-ocean moons as potential habitats for life, leading to a high priority for the Jupiter Europa Orbiter and New Frontiers missions to the outer planets. As a third possibility, the Survey might emphasize a balance of questions leading to more modest missions to a number of targets, but no major flagship missions to any one. The assumed budget determines the scale and/or number of questions that can be addressed, but the prioritized questions lead directly to the missions that receive priority recommendations within that budget.
3. What is the proposed mixture of more modest Principal Investor (PI) led missions and major institution-led Flagship missions? There has always been a tension between doing a small number of big missions and a larger number of small missions. Big missions can address questions that smaller missions cannot, but more smaller missions can partially address a wider range of questions and targets. The recent astronomy and astrophysics Decadal Survey recommended completion of one gigantic mission, the James Webb Space Telescope, one modest Flagship scale mission, and prioritized increasing the number of small PI-led missions. Big missions have an advantage that they can create their own momentum, but can also consume budgets if funds are cut or cost overruns occur. Small missions may be a more robust strategy in face of tight budgets, but may also not be easier to not fund (which would you prefer to pitch to a Congressman to fund: Mars sample return, Jupiter Europa Orbiter, or the selection of the 15th Discovery mission?)
4. What technologies are prioritized for development? Planetary exploration is an inherently high tech field. The missions that can fly can be only as good as the technologies that are ready to fly. Developing new technologies often requires years of research, prototypes, and testing before a technology becomes ready for flight. The technologies that the Survey prioritizes are the seeds for the missions that will fly in the decade of the 2020s.