3Cat-4 exploded view

The many elements that make up 3Cat-4, including the Flexible Microwave Payload, sixth panel from the left, which is 3Cat-4’s primary piece of equipment and will perform all of the scientific experiments onboard, and the 0.5-meter antenna stowed away in the final panel.

3Cat-4 (pronounced “cube cat four”) is a 1-kg Earth Observation CubeSat developed by the Universitat Politècnica de Catalunya in Spain and selected by ESA Education’s ‘Fly Your Satellite!’ programme to fly on Ariane 6’s first flight.

The 3Cat-4 design was carefully reviewed by experts as part of the programme, who provided design and testing support to the mission team, including important environmental testing at ESA Education’s CubeSat Support Facility (CSF) in ESEC-Galaxia, Belgium.

Otherwise, the nanosatellite has been nearly entirely developed by graduate and undergraduate students who have designed, built and validated the vast majority of its components, conducted complex analyses and planned and performed test campaigns with specialised equipment. For several students, the mission is central to their course curriculum or degree thesis.

“The primary goal of the mission is educational; training a group of students in the techniques and methodologies involved in flying a space mission, while conducting challenging teamwork with a real sense of responsibility,” explains Alexander Kinnaird, ESA Engineering Coordinator for the Fly Your Satellite! project.

“But 3Cat-4 also has several scientific and technological objectives that we hope will demonstrate the big potential of CubeSats when it comes to innovative space technology, usually reserved for larger satellites.”

The mission’s primary scientific experiment will be to measure several important climate variables using a technique called ‘Global Navigation Satellite System Reflectometry’ (GNSS-R). GNSS-R involves measuring the reflected signals from orbiting Global Navigation Satellite Systems, such as Galileo and GPS, that bounce off Earth’s surface.

This ‘passive remote sensing’ measures the difference between the signals directly received from navigation satellites in orbit and the signals from those same satellites that have been reflected off Earth. Using this data, ³Cat4 will be able to measure the properties of the reflective surface and detect several types of weather phenomena, determine land topography and vegetation cover and extract information on ocean data such as ice coverage and thickness.

Along with its remote sensing capabilities, 3Cat-4 will carry an ‘L-band radiometer’ – an instrument that detects radiation emitted in the 1-2 GHz frequency range which makes it possible to analyse soil moisture and ocean salinity. The CubeSat will also have an Automatic Identification System (AIS) allowing it to track ships along their intercontinental routes. It also includes a ‘Radio Frequency Interference’ detection and mitigation system, which is especially important for microwave radiometry observations used for soil moisture measurements.

Crucially, 3Cat-4 will demonstrate the feasibility and performance of its 0.5-meter spring-like antenna, the Nadir Antenna and Deployment System (NADS). Stowed away for launch, the antenna will take up very little space, allowing its future inclusion in even smaller CubeSats. Once in orbit, it will spring open to perform impressive observations usually the domain of larger missions, providing a powerful eye on Earth despite its portable travel size.