Since the appearance of 5G, Internet of Things (IoT) has gained an increased interest, with multiple technologies emerging and converging to cover different user needs. One of the biggest challenges today is to have global IoT coverage, ensuring seamless communication with IoT devices placed in rural and even remote areas. Satellite constellations, and in particular CubeSats orbiting in Low Earth Orbit, can provide a solution to these challenges. Out of the technologies available, LoRa (Long Range) has a great potential for implementation in space-to-Earth satellite communications. As the space-to-Earth channel is different with respect to the conventional Earth-to-Earth one, it is important to asses the capabilities of LoRa in this new environment. This paper presents a study of different LoRa device configurations to identify the constrains for each one and determine which one is better for particular mission requirements. Also, the effect of ionospheric scintillation is assessed with a SDR-based (Software-Defined Radio) test set-up that evaluates the performance of this technology against with Humprey’s ionospheric scintillation model. This phenomena produces deep signal intensity fadings and phase fluctuations in equatorial regions, and mainly phase fluctuations in high latitudes. The obtained metrics are the received power and the packet delivery ratio as a function of the intensity scintillation index, and show the robustness of the LoRa modulation in these new environments.

The Flexible Microwave Payload-2 is the GNSS-R and L-band Microwave Radiometer Payload on board ${}^3$Cat-5/A, one of the two 6-unit CubeSats of the FSSCat mission, which were successfully launched on 3 September 2020 on Vega flight VV16. The instrument occupies nearly a single unit of the CubeSat, and its goal is to provide sea-ice extension and thickness over the poles, and soil moisture maps at low-moderate resolution over land, which will be downscaled using data from Cosine Hyperscout-2 on board ${}^3$Cat-5/B. The spacecrafts are in a 97.5${}^{°}$ inclination Sun-synchronous orbit, and both the reflectometer and the radiometer have been successfully executed and validated over both the North and the South poles. This manuscript presents the results and validation of the first data sets collected by the instrument during the first two months of the mission. The results of the validation are showing a radiometric accuracy better than 2 K, and a sensitivity lower than the Kelvin. For the reflectometer, the results are showing that the sea-ice transition can be estimated even at short integration times (40 ms). The presented results shows the potential for Earth Observation missions based on CubeSats, which temporal and spatial resolution can be further increased by means of CubeSat constellations.

The Federated Satellite Systems/ ³ Cat-5 (FSSCat) mission was the winner of the European Space Agency (ESA) Sentinel Small Satellite (S ³ ) Challenge and overall winner of the 2017 Copernicus Masters competition. It consisted of two six-unit CubeSats. The Earth observation payloads were 1) the Flexible Microwave Payload 2 (FMPL-2) onboard ³ Cat-5/A, an L-band microwave radiometer and GNSS reflectometer (GNSS-R) implemented using a softwaredefined radio (SDR), and 2) the HyperScout-2 onboard ³ Cat-5/B, a hyperspectral camera, with the first experiment using artificial intelligence to discard cloudy images. FSSCat was launched on 3 September 2020 and injected into a 535-km synchronous orbit. ³ Cat-5/A was operated for three months until the payload was probably damaged by a solar flare and coronal mass ejection. During this time, all scientific requirements were met, including the generation of coarse-resolution and downscaled soil moisture (SM) maps, sea ice extent (SIE) maps, concentration and thickness maps, and even wind speed (WS) and sea surface salinity (SSS) maps, which were not originally foreseen. ³ Cat-5/B was operated a few more months until the number of images acquired met the requirements. This article briefly describes the FSSCat mission and the FMPL-2 payload and summarizes the main scientific results.

CubeSats have revolutionized Earth Observation and space science, although their small size severely restricts satellite performance and payload. Antenna deployment from a stowed configuration in these small-satellites remains a great challenge. This paper presents the design, optimization, and testing of an L-band helix antenna deployment system for the ³ Cat-4, a 1U CubeSat developed at the NanoSat Lab (UPC). The 506-mm-long antenna is packed into a 26.8 mm gap together with a tip mass that provides a gravity gradient for nadir-pointing. The ³ Cat-4 Nadir Antenna Deployment Subsystem (NADS) melts dyneema strings to release the antenna in successive steps. PTFE coated fiberglass ensures the helix’s nominal diameter and pitch while a security locking mechanism serves as a redundant system for holding it in place before deploying. Our novel methodology optimizes the number and length of the NADS deployment steps. A slow-motion camera and image recognition software track the velocity and acceleration of the antenna sections by means of tracking dots. Kinematic analysis of the antenna resulted in a final design of four length steps: 90, 300, 420 and 506 mm. Our methodology for calculating these values can be widely applied for measuring many deployment system’s kinematic properties. The NADS performance is tested by characterizing antenna rigidity, analyzing helix behavior after one year in stowed configuration, and by testing the deployment mechanism in a thermal vacuum chamber at −35°C, the most critical temperature stress scenario. All test results are satisfactory. The final design of the NADS deployment mechanism is light, stable, reliable, affordable, highly scalable, and can be used in many antenna configurations and geometries. The ³ Cat-4 mission was selected by the ESA Academy to be launched in Q4 2021.

The ${}^3$Cat-4 mission aims at demonstrating the capabilities of a CubeSat to perform Earth Observation (EO) by integrating a combined GNSS-R and Microwave Radiometer payload into a 1-Unit CubeSat. One of the greatest challenges is the design of an antenna that respects the 1-Unit CubeSat envelope while operating at the different frequency bands: Global Positioning System (GPS) L1 and Galileo E1 band (1575 MHz), GPS L2 band (1227 MHz), and the microwave radiometry band (1400–1427 MHz). Moreover, it requires between 8 and 12 dB of directivity depending on the band whilst providing at least 10 dB of front-to-back lobe ratio in L1 and L2 GPS bands. After a trade-off analysis on the type of antenna that could be used, a helix antenna was found to be the most suitable option to comply with the requirements, since it can be stowed during launch and deployed once in orbit. This article presents the antenna design from a radiation performance point of view starting with a theoretical analysis, then presenting the numerical simulations, the measurements in an Engineering Model (EM), and finally the final design and performance of the Flight Model (FM).

Natural disasters and catastrophes are responsible for numerous casualties and important economic losses. They can be monitored either with in-situ or spaceborne instruments. However, these monitoring systems are not optimal for an early detection and constant monitoring. An optimisation of these systems could benefit from networks of Internet of Things (IoT) sensors on the Earth’s surface, capable of automatically triggering on-demand executions of the spaceborne instruments. However, having a vast amount of sensors communicating at once with one satellite in view also poses a challenge in terms of the medium access layer (MAC), since, due to packet collisions, packet losses can occur. As part of this study, the monitoring requirements for an ideal spatial nodes density and measurement update frequencies of those sensors are provided. In addition, a study is performed to compare different MAC protocols, and to assess the sensors density that can be achieved with each of these protocols, using the LoRa technology, and concluding the feasibility of the monitoring requirements identified.