CubeRRT: the little satellite that could

Posted: October 2, 2018

The debut data from The Ohio State University’s first satellite transmitted back from orbit, and the results look promising for future scientists studying the Earth. 

Joel Johnson, professor of electrical and computer engineering at Ohio State, said the CubeSat Radiometer Radio Frequency Interference Technology Validation satellite, or CubeRRT, contains advanced sensors for observing Earth’s environment from space. 

The world naturally emits microwave radiation, he said, which scientists study with sensors called microwave radiometers. The data from these sensors helps determine important information like soil moisture, sea temperature, sea ice coverage, weather, and much more.

However, Johnson said, as the need for wireless services worldwide continues to increase, the growth of manmade radio transmissions is making it increasingly difficult for scientists to detect Earth’s natural microwave radiation. The unwanted man-made signals are called radio frequency interference, or RFI. CubeRRT’s goal is to demonstrate a new capability of onboard RFI removal from the measurements sent by Earth-observing microwave radiometers.

The Ohio State team demonstrated the concept in pre-launch lab tests, but would it prove successful in orbit?

“The data we received on Sept. 5 confirmed successful real-time on-board removal of RFI from CubeRRT’s measurements,” Johnson said. “This was the primary goal of the mission, so it was a great feeling to know we had reached this important milestone and that our little satellite was making big accomplishments up in space.”

The CubeRRT satellite was launched on May 21 to the International Space Station, and then deployed into orbit from there on July 13. From July through early September, tests and checkout of the CubeRRT spacecraft communications, power and other subsystems were performed before turning on the RFI processor in September. The first light dataset was acquired over the Pacific Ocean on Sept. 5 during a 10-minute period of measurements. 

In terms of those measurements, the team explained how CubeRRT observes a 1 GHz wide portion of the electromagnetic spectrum, tuned over 10 different bands commonly used for Earth observing microwave radiometers. The total noise power in the 1 GHz bandwidth varied with time as differing portions of the ocean were observed. Because the observations also included a low level of RFI, the original data without RFI correction had a power level higher than the true Earth emitted power. CubeRRT’s RFI processor produced the corrected noise temperature on board the spacecraft that eliminated RFI contributions. Validation of CubeRRT’s processing was also performed on the ground, and a high level of agreement validated the on board processing.

Christopher Ball, a research scientist at Ohio State’s ElectroScience Lab, said by performing RFI correction onboard the spacecraft, CubeRRT eliminates the requirement to downlink additional data to the ground to perform RFI processing. This was the technological barrier the team hoped the new advancements could solve, and they were correct. 

According to the results, he said, the reduction in data volume is greater than a factor of 100 times, which makes the incorporation of crucial RFI processing feasible for future Earth observing radiometers.

“We’re now continuing to operate CubeRRT’s RFI processor over longer time periods to demonstrate long-term operations,” Johnson said. “The team is very excited to see what comes next for CubeRRT and to transition this new technology into future Earth observing satellites.”