Last updated January 11, 2018 at 10:43 am
A Delta II rocket has launched a new generation of weather satellites, the shoebox-sized CubeSats, that NASA hopes will change the industry.
The Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat is tiny compared with traditional weather satellites and is designed to study temperature, water vapor and cloud ice, which the space agency says will help predict the weather and track storms.
The same rocket will also carry the next big US weather satellite, the Joint Polar Satellite System-1 (JPSS-1). But full-scale weather satellites could become a thing of the past if MiRatA proves that a small satellite can routinely collect reliable weather data.
Microwave radiometers measure radio frequency signals related to the thermal radiation emitted by atmospheric gases, such as molecular oxygen and water vapour.
The chief technological challenge to the project has been to miniaturise microwave radiometer instruments to fit on the CubeSat as well as a compact but accurate calibration instrument to judge relative atmospheric parameters such as temperature.
“Microwave radiometer calibration targets on larger satellites can be the size of a toaster, but for CubeSats, it would have to be the size of a deck of cards,” said MIT professor Kerri Cahoy, principal investigator for MiRaTA.
She went about it a different way based on a technique called radio occultation (RO), whereby radio signals received from GPS satellites in a higher orbit are used to measure the temperature of the same volume of atmosphere that the radiometer is viewing. The GPS-RO temperature measurement can then be used for calibrating the radiometer.
“In physics class, you learn that a pencil submerged in water looks like it’s broken in half because light bends differently in the water than in the air,” Cahoy said. “Radio waves are like light in that they refract when they go through changing densities of air, and we can use the magnitude of the refraction to calculate the temperature of the surrounding atmosphere with near-perfect accuracy and use this to calibrate a radiometer.”
These radio occultation measurements for calibration were made a modified off-the-shelf, low-cost GPS receiver.
“Building a CubeSat can be hard because you have to put batteries, a radio, a computer, your instruments, wheels that you spin to tip and turn your satellite, and folded solar panels and antennas all into a very small space,” Cahoy said. “And you’re using the space equivalent of scotch tape and super glue to constrain this mess of wires and connectors and get it into its housing.”
NASA hopes that the satellite will be fully operational within three weeks of launch and will have gathered data three weeks after three months will have gathered enough data from both the radiometer and the GPS receiver to validate the project.
If successful, Cahoy envisions a constellation of the small CubeSats orbiting the entire Earth.
Earlier this year, CubeSats became the first Australian-built satellites to be launched in 15 years. They were part of the international QB50 mission, in which 36 satellites from different institutions around the world were launched to measure the lower thermosphere.