Microwave Radiometer for Advanced Nanosatellite Control Systems

Microwave radiometers measure temperature, water vapor, and cloud ice in the atmosphere, since oxygen and water vapor naturally emit signals in the microwave portion of the electromagnetic spectrum. These signals are measured at different heights and are used to make 3D images of hurricanes, tropical storms, and thunderstorms. The NanoRacks-Microsized Microwave Atmospheric Satellite (NanoRacks-MicroMAS) measures temperature from molecular oxygen. NanoRacks-MicroMAS is a small, low-cost CubeSat containing a miniaturized microwave scanner that paves the way for future constellations of similar satellites, gathering more detailed, more frequent images of severe weather that impacts people on Earth. NanoRacks CubeSats are delivered to the International Space Station (ISS) already integrated within a NanoRacks CubeSat Deployer (NRCSD).

Rendering of a 118-GHz microwave radiometer from the NanoRacks-MicoMAS nanosatellite. (MIT Lincoln Laboratory)

The NanoRacks-MicroMAS is a dual-spinning 3U CubeSat equipped with a passive microwave spectrometer that operates nine channels near the 118.75- GHz oxygen absorption line. The focus of the first NanoRacks-MicroMAS mission is to observe convective thunderstorms, tropical cyclones, and hurricanes from a near-equatorial orbit. The payload housed in the “lower” 1U of the dual-spinning 3U CubeSat is mechanically rotated approximately once per second as the spacecraft orbits the Earth, resulting in a cross-track scanned beam with a full width at half-maximum (FWHM) beam width of 2.5 degrees, and an approximately 20-km-diameter footprint at nadir (directly below) incidence from a nominal altitude of 400 km.

Radiometric calibration is carried out using observations of cold space, the Earth's limb (edge of the planet), and an internal noise diode that is weakly coupled through the radio frequency (RF) front-end electronics. In addition to the dual-spinning CubeSat, a key technology development is the ultra-compact intermediate frequency processor module for channelization, detection, and analog to digital conversion. The payload antenna system and RF front-end electronics are highly integrated, miniaturized, and optimized for low-power operation. To support the spinning radiometer payload, the structures subsystem incorporates a brushless direct current (DC) zero-cogging motor, an optical encoder and disk, a slip ring, and a motor controller.

The Maryland Aerospace MAI-400 attitude determination and control system (ADCS) utilizes reaction wheels, magnetorquers (magnetic coils that are used to interact with the magnetic field of the Earth and apply specific torques to the satellites to prevent tumbling and stabilize the attitude), and infrared (IR) Earth horizon sensors, as well as Sun sensors, a magnetometer, and an inertial measurement unit (IMU). Radio communications are at ultra-high frequency (UHF) using the NASA Wallops Flight Facility ground station.

NanoRacks-MicroMAS uses a Pumpkin ™ CubeSat Motherboard with a Microchip PIC24 microcontroller as the flight computer running Pumpkin’s Salvo Real Time Operating System. Thermal management includes monitoring with thermistors (a resistor with a very large change in resistance as a function of temperature), heating, and passive cooling. Power is generated using four double-sided deployable 2U solar panels and with ultra triple junction (UTJ) solar cells, and an electrical power system (EPS) with 20 Wh lithium polymer batteries from Clyde Space.

The NanoRacks-MicroMAS nanosatellite with radiometer payload rendering. (MIT Lincoln Laboratory)

The relatively low cost of CubeSat remote sensing to be demonstrated by NanoRacks-MicroMAS facilitates the deployment of a constellation of sensors, spaced equally around several orbit planes. Constellation simulations show that a dozen satellites could provide average global revisit times approaching 20 minutes, a revolutionary step forward for atmospheric sounding and precipitation science.

A small fleet of Micro-sized Microwave Atmospheric Satellites could yield high-resolution global temperature and water vapor profiles, as well as cloud microphysical and precipitation parameters. The NanoRacks-MicroMAS flight unit was developed by MIT Lincoln Laboratory, the MIT Space Systems Laboratory, the MIT Department of Earth and Planetary Sciences, and the University of Massachusetts-Amherst Department of Radio Astronomy.

High-resolution, fast imaging of Earth’s atmosphere gives weather forecasters better information about hurricanes, tropical storms, and other severe weather. Improved observations aid weather forecasting and disaster-response preparations, as well as scientific research on the evolution of storm systems. NanoRacks-MicroMAS supports the development of more advanced nanosatellite control systems, which are used for a wide range of Earth-observing and communications applications.

For more information, visit www.nanoracks.com .