# An Overview of CubeSat Missions and Applications
## 3 CubeSats as Earth Observation and Earth Science Platforms
### The Role of CubeSats in Earth Observation Missions
Since its establishment in 2010, Planet Labs has launched more than 500 imaging satellites into orbit (mainly CubeSats), making it the largest commercial Earth observation satellite operator in the world. The constellation of SuperDove CubeSats currently numbers around 200 operational satellites in orbit around the Earth [72; 73; 74]. Furthermore, the success of the FOREST-1 and FOREST-2 missions has facilitated the development of FOREST-3, an advanced 8U CubeSat featuring improvements over its two predecessors which was launched on 14 January 2025 [75], as well as an upcoming TIR imaging constellation of CubeSat platforms by OroraTech GmbH which will be tasked with the all-important mission of wildfire detection and monitoring. When complete, this constellation is expected to encompass approximately 100 satellites and offer a 30-min revisit time over an area of interest [76; 77; 78]. Another imaging method, which satellites and CubeSats, specifically, can utilize in the Earth observation role, is the mapping of the Earth's surface through Global Navigation Satellite System Reflectometry (GNSS-R). The basic concept of GNSS-R (see Figure 6) is that a satellite equipped with a GNSS receiver will receive multiple versions of the signal coming from a GNSS satellite in Medium Earth Orbit (MEO). More specifically, it will receive the direct GNSS signal, as well as a multitude of signals reflected by the surface of the Earth, with the reflected GNSS signals being affected by parameters such as ground geometry, terrain roughness, moisture, etc. Thus, by using specifically designed GNSS antennas and receivers which are acting as passive bi-static radar systems, a satellite can receive these reflected GNSS signals from satellite navigation constellations such as the Global Positioning System (GPS), Galileo, and GLONASS and synthesize a picture of the planet's surface after comparing them with the direct ones. One of the most common applications of the GNSS-R technique is altimetry, where satellites are used to measure terrain altitude, ocean levels, and sea state [45]. The passive nature of GNSS-R technology makes it suitable for utilization by CubeSat platforms, with a notable example of a GNSS-R CubeSat mission being \({}^{3}\)Cat-2, a 6U CubeSat with the mission of demonstrating GNSS-R technologies for ice altimetry, ocean sea state monitoring, soil moisture monitoring, as well as for the observation of biomass. As its main payload, \({}^{3}\)Cat-2 was equipped with the P(Y) & C/A ReflectOmeter (PYCARO), an instrument specifically designed to receive and compare direct and reflected GNSS signals [79]. Another similar mission was the PassiveREflecTomeTrY (PRETTY), a 3U CubeSat developed by ESA for the demonstration of a GNSS-R payload capable of providing ice and sea-ice altimetry measurements with an accuracy of 0.5 m for the study of the polar regions of the Earth [80]. One of the most common Earth remote sensing application subfields for CubeSat platforms is that of atmospheric condition and weather monitoring. Satellites employed in this science field collect measurements that can help in the generation of more accurate atmospheric models and, in this way, enable more accurate and precise weather forecasting. Furthermore, apart from only being used for monitoring the conditions present at the lower levels of the atmosphere, CubeSats can also be used for the monitoring of the Earth's ionosphere, collecting important scientific data that can be used to inform decisions and operations on space science and engineering fields such as telecommunications, the operation of satellite navigation systems, satellite functions, and efficient operation, as well as in a variety of Earth-based industrial applications such as the management and operation of electrical power networks and natural gas pipelines. Moreover, the conditions of the ionosphere can be linked, to some degree, with the conditions of the atmosphere's lower portions.