Cosmic OriginsAnnouncement of Opportunity Astrophysics Explorers Program 2026 Small Explorer (SMEX) Amended Text Released 10 August 2026The National Aeronautics and Space Administration (NASA) Science Mission Directorate (SMD) announces the release of Amendment #1 to the Announcement of Opportunity (AO) to solicit Principal Investigator (PI)-led space science investigations for the Small Explorer (SMEX) opportunity under the Astrophysics Explorers Program on the NASA Solicitation and Proposal Integrated Review and Evaluation System (NSPIRES). Changes within the AO text are noted by using bold for new text and strikethrough for deleted text. All new questions or comments about the Astrophysics SMEX 2026 AO shall be addressed via email to Dan Moses, APSMEX26 Lead Program Scientist, dan.moses@nasa.gov; Hannah Jang-Condell, APSMEX26 Deputy Program Scientist, hannah.jang-condell@nasa.gov; and Omar Torres, Lead Acquisition Manager for the 2026 Astrophysics SMEX AO, SOMA omar.torres@nasa.gov using subject line “APSMEX26” to be properly routed. The Q&A period for the SMEX 2026 AO ends 14 days before the proposal due date. NASA Science NSPIRES NASA Solicitation and Proposal Integrated Review and Evaluation System Explore