The objectives and benefits of the proposed instrument development are to produce a compact solar spectral irradiance (SSI) monitor covering 200-2400 nm with the required SI-traceable accuracy and on-orbit stability to meet the solar input measurement requirements defined in the Decadal Survey for establishing benchmark climate records. Building upon our experiences and resources from the Total and Spectral Solar Irradiance Sensor (TSIS) program, the proposed instrument will reduce cost and size of a solar spectral irradiance monitor with SI-traceable absolute calibration at the 0.2% uncertainty level (k=1) while also increasing implementation flexibility for future accommodation opportunities. The 3-year effort will design, analyze, and construct a high-fidelity prototype instrument increasing from entry TRL 3 (design and performance analysis) to exit TRL 6 by validating and quantifying complete spectral and radiometric performance while operating under relevant environmental conditions. The instrument utilizes a straightforward optical design in a compact, folded geometry that overcomes the extremely high tolerance and costly fabrication requirements and reduces the overall calibration risks associated with previous designs. The prototype instrument will use a coupled, two-channel design that separates the ultraviolet from the visible-near infrared regions and thus allows each channel to be optimized in performance separately, including the dispersive optical material and reflective coating selection. System level performance characterizations and final end-to-end absolute calibration will be accomplished with the LASP Spectral Radiometer Facility (SRF), a comprehensive LASP-NIST jointly developed spectral irradiance calibration facility utilizing the SIRCUS tunable laser system tied to an SI-traceable cryogenic radiometer. The final high fidelity, calibrated photodiode instrument would serve as an ideal sub-orbital sounding rocket or CubeSat payload for cross-calibration opportunities, with the ultimate future intent to incorporate ESR absolute detectors for full on-orbit calibration maintenance capability.