The ExoCube's broadcast from orbit, caught by a German ham radio operator.
An amateur ham radio operator in Germany detected this beacon transmission from low-Earth orbit the morning of Feb. 1.
The signal, which simply spells out “XO3” in Morse code, is an exciting sign for Assistant Professor Lara Waldrop
, who led a team of researchers in designing the spacecraft that is broadcasting the transmission.
When the ham radio operator captured this image, ExoCube was broadcasting its location in the first stage of its mission, an indication to its operators that its status is healthy and that scheduled housekeeping procedures are underway. After these are completed successfully, the team will instruct ExoCube to begin collecting data in support of its scientific mission, which is sponsored by the National Science Foundation.
ExoCube represents one of the first deployments of a revolutionary class of satellites called CubeSats. Conventional space-based scientific missions typically incorporate their instrument payloads into a large, customized spacecraft bus that requires a designated, and expensive, rocket launch to send it into orbit.
CubeSats, however, conduct their science operations from a standardized bus infrastructure consisting of modular combinations of 10x10x10 cm cubes. Adhering to this design standard allows scientists to package many different missions together for piggybacking into orbit on the launches of larger missions at a fraction of the conventional cost.
One of ExoCube's sensors, small enough to fit in the palm of a hand.
“Miniaturization of the scientific instruments is one of the really innovative aspects of CubeSat missions,” Waldrop said. “Although the ExoCube sensor is similar to an instrument that was flown in space by NASA in the ‘80s, that one was about the size of a car. We’ve shrunk the technology down to something you can hold in your hands and which can collect even more comprehensive data.”
The ExoCube mission is designed to sample the density and chemical composition of Earth’s uppermost layer of atmosphere using a gated time-of-flight mass spectrometer. This region, which lies about 200 to 700 kilometers above the surface, is home to the majority of active satellites along with tens of thousands of pieces of debris, commonly called space junk, comprised of spent rocket stages, defunct spacecraft, and remnants from disintegration and collisions.
Assistant Professor Lara Waldrop, co-developer of the ExoCube.
Though it is well known that frictional drag against Earth’s atmosphere changes the trajectories of orbiting objects, scientists don’t have a complete understanding of the makeup and time-varying behavior of the atmosphere at this altitude and thus can’t predict the amount of satellite drag. As a result, orbital trajectories are often poorly known, leaving operational satellites in danger of collisions with space junk.
This is where ExoCube comes in.
“Many satellites, like the International Space Station, have propulsion systems to move out of the way of space debris that crosses their path. But if they don’t know what’s coming, then they can’t maneuver out of the way,” Waldrop said. “Collisions with space junk, like in the movie Gravity, can and do happen. ExoCube is collecting data that will help us better predict satellite trajectories and avoid future on-orbit collisions.”
Waldrop led the mission’s science team early on in conceptual development, defining the instrument and spacecraft requirements and designing its operational modes, through a collaboration with additional science team members from Arecibo Observatory, the University of Wisconsin, Madison, and Scientific Solutions, Inc., a small optical engineering company.
The instrument payload was developed by scientists at NASA’s Goddard Space Flight Center, while the satellite bus was designed and built by a student team at California Polytechnic State University.
Apart from major universities, industry, and government agencies, however, ExoCube is also supported by a community of amateur radio enthusiasts across the globe, who can detect the satellite’s transmission by following instructions on ExoCube’s tracking website
The ExoCube sitting on a table during development.
“We designed ExoCube to transmit at a frequency in the amateur radio band, so that potentially anyone around the world can help us receive our signal and collect data,” Waldrop said. “They can get the ExoCube’s coordinates, download our decoder, and email the data to our team. Not only does this allow the community to be involved in science, but it also helps us get much more data than we could collect on our own.”