# An Overview of CubeSat Missions and Applications
## 4 The Use of CubeSats as Telecommunication and Asset-Monitoring Platforms
### Optical Communication CubeSat Missions and Applications
PTD-3 was a 6U LEO CubeSat developed by Terran Orbital and was equipped with the TeraByte Infrared Delivery (TBIRD) laser-optical communications payload, developed by the MIT Lincoln Laboratory under the mission of demonstrating laser-optical space-to-ground data transfer ratios that would be significantly higher than all other previously demonstrated technologies. During its mission, PTD-3 managed to perform multiple passes where it transmitted more than 1 TB of data in each, and even achieved the transmission of more than 4.8 TB of error-free, space-to-ground data during a pass that lasted approximately 5 min. Moreover, at downlink speeds of about 200 Gbps, PTD-3 also set the record for the fastest ever space-to-to-ground data transfer rate that had been achieved by satellite-based laser-optical communications equipment up to that point. A simplified concept of the laser-optical downlink operations of the PTD-3 mission is presented in Figure 11 [189; 190; 191]. Some CubeSat platforms have also been used in order to demonstrate inter-satellite laser-optical communications, with a notable example in that regard being FSSCat-A and FSSCat-B, two 6U CubeSats developed by the Polytechnic University of Catalonia and Tyvak International S.r.l. (Turin, Italy) which were equipped with HyperScout-2, an instrument combining a hyperspectral VNIR and a multispectral TIR imager under the mission of collecting Earth observation data that would supplement the ones collected by the Sentinel satellites of Copernicus, while also being equipped with a GNSS-Reflectometer and an L-band Radiometer which were utilized for sea-ice detection and thickness monitoring, as well as for soil moisture measurements. Apart from their Earth observation duties, the two CubeSats also featured UHF and laser-optical communication equipment for the in-orbit demonstration of inter-satellite radio and laser-optical communications [192; 193]. Several upcoming CubeSat missions are going to involve laser-optical communication tasks, with an example being the CubeSat Laser Infrared CrosslinK (CLICK), which is going to consist of two 3U CubeSats, CLICK-B and CLICK-C. After their launch, these two CubeSats, each equipped with a full-duplex 1.5U Infrared laser-optical communications terminal, will focus on demonstrating inter-satellite laser-optical crosslink communications capable of reaching data rates of up to 20 Mbps at separation distances ranging from 25 km up to 580 km [195; 196]. Another prominent example of an upcoming laser-optical communications CubeSat mission is Nice3, an educational 1U CubeSat developed by Universite Cote d'Azur with the mission of establishing a space-to-ground laser optical link achieving a transmission data-rate of more than 1 Kbps [197]. Moreover, Laser-optical communication is also one of the core themes of the Greek CubeSat In-Orbit Validation (IOV) program, with four of the seven missions of the program focusing in the demonstration of space-to-ground and/or ground-to-space laser-optical communication technologies. These missions are PeakSat, Hellenic Space Dawn, OpiSat, and the ERMIS-Hellenic CubeSat Demonstration Mission [198]. One notable proposed (and potentially upcoming) CubeSat laser-optical communications mission concept is Q4. The Q4 mission concept is being jointly developed by NASA's JPL and the Arizona State University and it would involve the launch of a mini-constellation of four 6U CubeSats that would demonstrate omnidirectional inter-satellite optical communication. For this mission, these CubeSats are proposed to be equipped with JPL's Inter-Satellite Optical Communicator (ISOC) payload. The ISOC has the shape of an icosahedron and is equipped with multiple laser telescopes operating at 850 nm wavelengths, 1 W laser diodes, micro-electromechanical mirrors, and collimators. Due to its icosahedron shape, it would provide near-full coverage around each satellite.