RECENT RESEARCH DEMONSTRATED THE IMPACTS OF OBSERVATIONAL ACCURACY ON QUALITY OF THE EARTH SCIENCE DATA PRODUCTS AND THE ABILITY TO DETECT CLIMATE CHANGE TRENDS FOR ESSENTIAL CLIMATE VARIABLES EARTH RADIATION BUDGET CLOUD FEEDBACK AND LONG-TERM TRENDS IN CLOUD AND CLEARLAND PARAMETERS. HE CHALLENGE IS WELL RECOGNIZED BY THE SCIENCE COMMUNITY BOTH NATIONALLY AND INTERNATIONALLY. CALIBRATION ACCURACY REPEATABILITY AND CONSISTENCY ARE KEY ON-ORBIT PERFORMANCE METRICS FOR EARTH-OBSERVING SENSORS. ESTABLISHING THE MOON AS AN ON-ORBIT HIGH-ACCURACY CALIBRATION REFERENCE ENABLES BROAD INTERCALIBRATION OPPORTUNITIES AS THE LUNAR REFLECTANCE IS PRACTICALLY TIME-INVARIANT AND CAN BE DIRECTLY MEASURED BY MOST EARTH-OBSERVING INSTRUMENTS. EXISTING APPROACHES TO CALIBRATE SPACEBORNE SENSORS AGAINST THE MOON CAN ACHIEVE STABILITIES OF A TENTH OF A PERCENT OVER A DECADE AS DEMONSTRATED BY THE SEAWIFS. HOWEVER THE CURRENT LUNAR CALIBRATION ACCURACY AS AN ABSOLUTE REFERENCE IS LIMITED TO 5 10%. THIS IS A LIMITATION OF THE CURRENT LUNAR MODELS NOT THE MOON ITSELF. SIGNIFICANT IMPROVEMENTS IN THE LUNAR REFERENCE ARE POSSIBLE AND ARE NECESSARY FOR CLIMATE-LEVEL ABSOLUTE CALIBRATIONS USING THE MOON. THE ABILITY TO GENERATE A PRECISE ABSOLUTE LUNAR IRRADIANCE SPECTRUM ENABLES CROSS-CALIBRATION OF ANY SENSORS THAT HAVE VIEWED THE MOON AND CAN BE RETROACTIVELY APPLIED TO PAST INSTRUMENTS MEASUREMENTS AS FUTURE LUNAR REFLECTANCE MODELS ARE IMPROVED. THE OBJECTIVE OF THIS PROPOSAL IS A NEW INSTRUMENT DEVELOPMENT ARCSTONE THAT WILL PROVIDE A RELIABLE REFERENCE FOR HIGH-ACCURACY ON-ORBIT CALIBRATION FOR REFLECTED SOLAR INSTRUMENTS. SUCH A REFERENCE HAS THE POTENTIAL TO SIGNIFICANTLY IMPROVE THE ACCURACY CONSISTENCY AND CONTINUITY OF ALL EARTH OBSERVATIONS MADE IN THEREFLECTED SOLAR WAVELENGTH RANGE. AN ORBITING SPECTROMETER FLYING ON A SMALL SATELLITE IN LOW EARTH ORBIT WILL PROVIDE LUNAR SPECTRAL REFLECTANCE WITH ACCURACY<0.5% (K = 1) SUFFICIENT TO ESTABLISH AN SI-TRACEABLE ABSOLUTE LUNAR CALIBRATION STANDARD FOR PAST CURRENT AND FUTURE EARTH WEATHER AND CLIMATE SENSORS (E.G. SEAWIFS MODIS VIIRS PACE CLARREO SLI AND ALL GEO IMAGERS). THE PROPOSED ARCSTONE APPROACH INCLUDES: UNIQUE INSTRUMENT CONCEPT FOR WELL-DEFINED MEASUREMENT REQUIREMENTS SPACE FLIGHT-LIKE ENGINEERING DESIGN UNIT (EDU) DEVELOPMENT INTERFACING TO A CUBESAT BUS; SMALL SIZE LOW MASS/POWER; ROBUST DESIGN OF SPECTROMETER USING HOLOGRAPHIC GRATINGS AND CUSTOM LENS BARREL OPTICAL MOUNTS EFFICIENT HANDLING OF POTENTIAL OPTICS DEGRADATION AND STRAY LIGHT ON-ORBIT. THE ACCURATE SPECTRAL SOLAR IRRADIANCE (SSI) REFERENCE ESTABLISHED BY THE SCHEDULED NASA TSIS MISSION WILL PROVIDE DIRECT SI-TRACEABILITY AND ABSOLUTE CALIBRATION OF THE ARCSTONE INSTRUMENT ON ORBIT. WITHIN THE 2.5-YEAR TIME PERIOD OF THE PROPOSED PROJECT ARCSTONE S TECHNOLOGY READINESS WILL INCREASE FROM THE CURRENTLY ESTABLISHED TRL3 TO TRL5. WE HAVE ESTABLISHED TRL3 BY DESIGNING AND TESTING THE INSTRUMENT BREADBOARD TESTED AT NIST S LABORATORY AND ROOFTOP MEASUREMENTS OF SSI. THE TRL ADVANCE WILL BE ACHIEVED BY A COMBINATION OF INSTRUMENT FLIGHT-LIKE EDU DESIGN AND BUILD ITS CHARACTERIZATION AND CALIBRATION AND SPACE-LIKE ENVIRONMENT AND FUNCTIONAL TESTS.