Roman Space Telescope Observing Time Allocation Principles: Report Series—Committee on Astronomy and Astrophysics

NASA requested the Committee on Astronomy and Astrophysics (CAA) provide guidance about setting the Roman Space Telescope’s observing time allocations. The charge included questions about the balance of time allocated to the core community surveys (CCSs) relative to general astrophysics (GA) objectives, and the number and nature of competed GA projects that Roman should undertake. For the question in the charge relating to the balance of time allocated to the CCS relative to GA, the CAA concluded that quantitative analyses of survey trade-offs and synergies, which are not presently available, will be needed before the appropriate balance between the CCS and GA surveys can be finalized. Instead, the CAA is advocating for a set of 10 principles and a process to guide NASA and Roman as they set the mission’s observing time allocations. Underlying all principles is the intent, shared by all stakeholders, to have Roman produce the best science the mission is capable of—science that is poised to transform astrophysics during the latter part of this decade. Paramount among the principles is the recognition that for a survey instrument like Roman for which some science objectives have been predetermined, a combination of collaboration and competition would be more effective compared to processes that neglect to introduce competition. A prime goal of the competition is to enhance the mission’s GA science return while maintaining the mission’s impact for the science objectives set by the New Worlds, New Horizons in Astronomy and Astrophysics 2010 astronomy and astrophysics decadal survey. The committee endorses some of the collaborative elements already planned by the project. The competitive element consists of forming a balanced group of independent experts, referred to as the “super time allocation committee” or STAC, which would operate much like previous missions’ executive time allocation committees (TACs), and would have wide latitude to optimize Roman’s observing time and thus to determine the final balance of time between all surveys. For the second question in the charge, the committee discourages fixing the maximum number of competed GA programs at this stage. Rather, the CAA advocates for a two-step process that will encourage submission and consolidation of proposals that will have a broad range of scopes, and that the number and size of projects selected by the STAC and by subsequent competitions be informed by the scientific promise of the proposals and by programmatic constraints at the time the selections are made. The committee notes that Roman’s location at L2 does not permit hardware changes. It is therefore important for the project to maintain flexibility to change the observing plan should the instrument’s post-launch performance differ from pre-launch assumptions. Flexibility also enables adapting the observing plan to a changing science landscape. The principle guiding the project in such cases is again to maximize the overall science based on reviews by a balanced group of independent experts.