The National Aeronautics and Space Administration's Goddard Space Flight Center is pleased to release the Request for Proposal (RFP) for the X-ray Irradiance Sensor (XRIS) acquisition. This RFP replaces the Draft RFP (Notice ID: XRIS-DRFP-80GSFC26R7004) issued on February 4, 2026 in its entirety. All attachments to this posting together constitute the complete RFP, including all instructions, restrictions, provisions, and contract clauses.