2026 Astrophysics Small Explorer (APSMEX)

Amendment #1: This SAM.gov update 1) announces the release of revised final text for the Astrophysics Explorers Program 2026 Small Explorer (SMEX) AO and 2) adds a copy of the text of an August 2026 NSPIRES e-mail sent to SMD List Serv subscribers. Please open and carefully review the attachment named 6AugustEmail.pdf under the Attachments/Links section of this notice. The proposal due date remains unchanged. For complete details, visit the link named Final Ful Text NNH26ZDA011O under the Attachments/Links section of this notice. End of Amendment #1. On or after this SAM.gov notice, the final text for the Announcement of Opportunity (AO) 2026 Astrophysics Small Explorer (APSMEX) will be available for download from the NASA Solicitation and Proposal Integrated Review and Evaluation System (NSPIRES) at https://nspires.nasaprs.com. Click on the word Solicitations at the top of the NSPIRES landing page and then on the next page enter the number NNH26ZDA011O in the search box or use the direct URL provided below. This Description is not a complete or verbatim summary of the AO. It is the responsibility interested parties to visit and monitor regularly the two listed internet sites (links) for any amendments or other updates. Please also open and carefully read the attached PDF file named 9JuneEmail.pdf . The 9JuneEmail attachment is copy of the text that NSPIRES sent to Science Mission Directorate (SMD) List Serv subscribers and includes other and earlier, important dates such as for the submission of a MANDATORY Notice of Intent (NOI) and a virtual Preproposal conference that are prior to the listed Date Offers Due. After reading the full AO on NSPIRES, please address any comments and questions only via email to both the primary and alternative points of contact listed and use " APSMEX26 in the subject line.