Proposers may be aware that observations with the HRC instrument were temporarily discontinued in late October 2025 due to an anomaly with the high voltage supply for HRC-S. In this CfP, observing proposals utilizing HRC (in any capacity) continue to be solicited. Note that as of the release of this document, a backlog of previous Cycles' HRC observations remains in the Long Term Schedule. Check-out observations have been performed on HRC-I (all performance was nominal) and observations with HRC-I are being resumed in Jan 2026. The return to science for HRC-S will be determined at a later date.
Monitoring particle background requires that at least one front illuminated chip is turned on. Previously, observations requesting single-chip observations with ACIS-S3 were considered on a case-by-case basis, however, this will no longer be allowed. This restriction has a minor impact on the minimum frametime achievable with sub-array observations, as described in Section 6.20 of the Proposers' Observatory Guide (POG).
Following NASA's policy on the use of Generative Artificial Intelligence (GAI) tools in proposal preparation, we have added a requirement for reporting the use of GAI tools in the preparation of Chandra proposals. Use of GAI tools must be reported in the references list as described in Section 7.3. To accommodate this change, there is no longer a limit on the number of pages for references. References must start on a new page after the scientific and technical justification and contain no additional content in those pages.
Archival and Theory/Modeling programs are now solicited by NASA through the Astrophysics Data Analysis Program (ADAP) and Astrophysics Theory Program (ATP), respectively.
In Cycle 27, the Chandra Review Process transitioned to a distributed peer review model. Each proposing team identifies a team member as the designated reviewer responsible for the review of 10 to 16 proposals. The results of the distributed review are used to inform the selection of most proposals, with Target of Opportunity (TOO), Large Program (LP), and Very Large Program (VLP) proposals undergoing additional panel review that makes final recommendations. Further details can be found in Chapter 9.