2026 Astrophysics Small Explorer (APSMEX)

The 2026 Astrophysics Small Explorer (APSMEX) solicitation, identified by number NNH26ZDA011O, invites Principal Investigator-led space science missions aimed at advancing understanding of fundamental astrophysical phenomena such as black holes, dark energy, galaxy evolution, and exoplanet habitability. The announcement is open to U.S. and non-U.S. entities including educational institutions, industrial organizations, and nonprofit organizations, with a focus on integrated Phase A and B mission concept development through a single-step competitive selection. Proposals must be submitted electronically via NSPIRES by September 9, 2026, and compliance with all administrative, technical, and regulatory requirements outlined in the full Announcement of Opportunity is mandatory. A mandatory Notice of Intent was due on July 21, 2026, and stakeholders were encouraged to review the accompanying 9JuneEmail.pdf, which included critical earlier dates such as a virtual preproposal conference held on June 30, 2026. Proposers must register in SAM.gov and are required to adhere to specific China-related collaboration restrictions outlined in Sections 4.2.2 and 5.8.1 of the AO, with any questions directed exclusively via email to both primary and secondary points of contact using the subject line "APSMEX26". The NAICS code 54171 applies, reflecting research in astronomical and space sciences, and while no fixed contract value or pricing structure is specified, selected missions will be funded within NASA Science Mission Directorate budget constraints. There are no specified packaging, marking, or preservation requirements, and no formal inspection or acceptance procedures are detailed in the provided materials; performance location is not defined beyond administrative oversight by NASA Headquarters in Washington, DC. The solicitation does not include explicit evaluation criteria, cost ceiling limits, or contract type designations, and payment or invoicing methods such as WAWF or IPP are not addressed. UEI and CAGE codes are implicitly required due to federal registration mandates through SAM.gov, and while socioeconomic status is not directly evaluated, small businesses are eligible under the SBA size standard of $18 million annual receipts. All substantive contractual terms, representations, certifications, and technical specifications are contained exclusively within the official AO on NSPIRES, which supersedes any summary or external reference. Proposers are responsible for regularly monitoring NSPIRES for amendments and ensuring full alignment with the latest version of the solicitation, as this document serves as the