NASA’s Science Mission Directorate (SMD) announces the release of an Announcement of Opportunity (AO) to solicit Principal Investigator (PI)-led space science investigations for the Small Explorer (SMEX) opportunity under the Astrophysics Explorers Program. The SMD strategic goal of expanding human knowledge through new scientific discoveries in astrophysics includes the broad objective: “to understand the Sun, Earth, Solar System, and Universe.” SMD addresses this objective through astrophysics investigations that address one or more of these science goals:

• How does the Universe work? Probe the origin and destiny of our universe, including the nature of black holes, dark energy, dark matter and gravity.
• How did we get here? Explore the origin and evolution of the galaxies, stars, and planets that make up our universe.
• Are we alone? Discover and study planets around other stars and explore whether they could harbor life. 

The 2026 Astrophysics SMEX (APSMEX26) Schedule is as follows:

• AO Release Date: 9 June 2026 
• Preproposal Conference Date: 30 June 2026
• Mandatory Notice of Intent Due Date: 21 July 2026 
• Proposal Due Date: 9 September 2026

For the full, final text of the Astrophysics Explorers Program 2026 SMEX AO, visit its NSPIRES webpage.

Prospective investigators from any category of organizations or institutions, U.S. or non-U.S. with some restrictions as specified in Section 4.2.1 of the AO, are welcome. Specific categories of organizations and institutions include, but are not limited to, educational, industrial, and not-for-profit organizations, Federally Funded Research and Development Centers (FFRDCs), University Affiliated Research Centers (UARCs), NASA Centers, and other Government agencies. Both U.S. and non-U.S. participation is subject to China restrictions described in Sections 4.2.2 and 5.8.1 of the AO.

All interested parties must read the final APSMEX26 AO carefully for significant changes from the draft AO (NNH25ZDA008J) and prior years’ SMD Explorers Program AOs. Of particular importance is the change in evaluation and selection to a single-step competitive process. NASA intends to select one investigation proposal from the APSMEX26 responses to proceed into a combined Phase A&B. All proposals must comply with the requirements, constraints, and guidelines contained within the AO. 

The Science Office for Mission Assessments (SOMA) will post the virtual Preproposal Conference agenda, connection information, and related information on the official 2026 Astrophysics Small Explorer (SMEX) website, which also provides further information, including the SMEX Program Library and SMEX Question & Answer (Q&A) page. Anonymity of persons/institutions who submit questions will be preserved. Proposers are encouraged to send comments and questions early so that they may be fully addressed. Questions posed at least one week before the Pre-Proposal Conference may be addressed in the Pre-Proposal Conference presentation or on the SMEX Q&A page. The deadline for other questions is two (2) weeks before the proposal due date.

Please address all questions or comments about the Astrophysics SMEX 2026 AO Daniel 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.