The National Aeronautics and Space Administration (NASA) Langley Research Center is seeking to procure the design, fabrication, assembly, and testing of a prototype Onboard Calibration System (OCS) for the DEMETER Earth Radiation Budget Mission. The primary objectives include ensuring compatibility of hardware, conducting system-level radiometric characterization, and developing in-flight calibration protocols, all of which are critical for the mission's success in measuring Earth's radiation. This procurement is vital for advancing NASA's capabilities in radiometric calibration, leveraging the unique expertise of the Space Dynamics Laboratory (SDL) at the University of Utah, which has demonstrated exclusive knowledge and facilities for this specialized work. Interested organizations must submit a capability statement by 3:00 PM EST on December 23, 2024, to Genie S. Williams at genie.s.williams@nasa.gov, with further inquiries directed to Lisa Harvey at lisa.m.harvey@nasa.gov.