![]() By combining the most reliable, independent TSI-measuring instruments, Dewitte and Clerbaux derived a value of 1362.0 ± 0.9 W/m 2. The absolute TSI value from the Total Irradiance Monitor (TIM) on the SOlar Radiation & Climate Experiment (SORCE) is 1360.8 ± 0.5 W/m 2 at solar minimum. The TSI has been measured continuously from space since the 1970s. Improvements to the technology and approach that would lead to better performance and greater accuracy in future missions are discussed. We present representative measurements from the mission and demonstrate how the radiometer time series can be used to reconstruct outgoing radiation spatial information. Although one of the black bodies failed after four months, the other provided a repeatable standard for the duration of the project. There are also VACNT–cavity biases of 3% and 6% in the Total and SW channels, respectively, which would have to be overcome in a future mission. Short-term variability-at greater than the tenths-of-a-Watt/m 2 needed for climate accuracy-is a challenge that remains, consistent with insufficient thermal knowledge and control on a 3U CubeSat. The radiometers show excellent long-term stability over the course of the mission and a high correlation between the VACNT and cavity radiometer technologies. Four radiometers (two VACNT, two cavity), the pair of gallium black bodies, and associated electronics are accommodated in the payload of an agile 3U CubeSat bus that allows for routine solar and deep-space attitude maneuvers, which are essential for calibrating the Earth irradiance measurements. The second technology demonstrated is a pair of gallium phase-change black body cells that are used as a stable reference to monitor the degradation of RAVAN’s radiometer sensors on orbit. As radiometer absorbers, they have greater sensitivity for a given time constant and are more compact than traditional cavity absorbers. VACNT forests are arguably the blackest material known and have an extremely flat spectral response over a wide wavelength range, from the ultraviolet to the far infrared. The first is the use of vertically aligned carbon nanotubes (VACNTs) as absorbers in broadband radiometers for measuring Earth’s outgoing radiation and the total solar irradiance. RAVAN successfully demonstrates two key technologies. RAVAN launched 11 November 2016, into a nearly 600-km, Sun-synchronous orbit, and collected data for over 20 months. A specific motivation is the need for lower-cost technology alternatives that could be used for multi-point constellation measurements of Earth outgoing radiation. The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) 3U CubeSat mission is a pathfinder to demonstrate technologies for the measurement of Earth’s radiation budget, the quantification of which is critical for predicting the future course of climate change.
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