Bigger isn’t always better—just ask NASA. The agency recently announced six small satellite missions, the stars of which range in size “from a loaf of bread to a small washing machine.” Although different in scope, the satellites do have some key features in common. For example, their size allows them to easily join existing launches, and they open doors for testing technologies that may have otherwise been cost-prohibitive. This additional research potential assists NASA in its efforts to study Earth’s changing climate, a goal especially relevant today. NASA and the National Oceanic and Atmospheric Administration (NOAA) recently declared 2016’s global surface temperatures as the hottest since recording began back in 1880. According to NASA, the 2016 mean temperature was measured at a substantial 1.78° over the mid-20th century average. This warming trend is not a new one. In fact, 2016 marked the third consecutive year for record-setting global surface temperatures.
RAVAN (Radiometer Assessment Using Vertically Aligned Nanotubes)
About the size of a loaf of bread, the RAVAN satellite is on a mission to show that a small instrument can be a powerful tool in understanding Earth’s radiation measurements and, therefore, predicting future climate behavior. There are two key technologies behind RAVAN: a gallium calibration source to track the sensor as it breaks down, and the use of Vertically Aligned Carbon Nanotubes (VACNTs) particularly well-suited for absorbing radiation—or light—in space.
Principal Investigator of RAVAN, William Swartz of Johns Hopkins University Applied Physics Laboratory (JHU/APL), explained to Laboratory Equipment how his lab grows the VACNTs. The process begins by coating a silicon wafer with Al2O3 and an iron catalyst—ultimately producing a coating only 12-nm thick. After the substrate is heated to 750 C and is flowed over by a gas mixture, VACNTs “grow spontaneously by chemical vapor deposition.” Producing RAVAN’s 1-mm tall parallel carbon nanotube forests requires approximately 30 minutes in the furnace. Post-processing techniques like oxygen plasma etching help make APL’s VACNT forests even more adept at absorbing light in space.
“[VACANTs] are extremely black across a wide wavelength range from the ultraviolet to the far infrared, as it is easy for incoming photons to be trapped in the forest, which is mostly empty space,” Swartz told Laboratory Equipment. “They are ideal for application in space: their low mass makes them robust to the vibration associated with launch, and they do not outgas in vacuum, which means they do not pose a molecular contamination risk to instrument optics.”
Part of RAVANs appeal is its potential to use small instrumentation to provide more accurate measurements of two key indicators of climate change: earth radiation imbalance (ERI) and earth radiation budget (ERB).
“Today, measurement of Earth’s energy balance from space is limited in part by spatial/temporal sampling by a small number of satellites on-orbit—they can’t be everywhere all the time. What is needed is a constellation of radiometers, perhaps a few dozen flown on small satellites, for 24/7 global observation. Continuous coverage is enabled by smaller, less expensive sensors, and APL’s RAVAN demonstrates such a sensor prototype,” Swartz said.
TROPICS (Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats)
Led by William Blackwell of the Massachusetts Institute of Technology’s Lincoln Laboratory, TROPICS is a mission to understand how tropical cyclones develop by looking inside hurricanes using rapid-revisit sampling. As one of two proposals selected to NASA’s third Earth Venture Instrument competition program, TROPICS is a constellation of 12 CubeStats—nanosatellites normally sized 10 x 10 x 10 cm, but extendable. For TROPICS, each CubeSat comes in at 8.5 pounds and 1 foot long. Launching into three orbital planes and harnessing the power of scanning microwave radiometers, TROPICS can monitor changes in the precipitation, humidity, temperature and cloud properties of hurricanes every 21 minutes.