3CAT-4

Demonstrate Global Navigation Satellite System - Reflectometry (GNSS-R) and L - band microwave radiometry and AIS.

This mission mission aims at demonstrating the capabilities of nano-satellites, and in particular those based in the 1-Unit CubeSat standard, for challenging Earth Observation (EO) using Global Navigation Satellite System - Reflectometry (GNSS-R) and L - band microwave radiometry, as well as for Automatic Identification Services (AIS).

The goals of this mission are three-fold:

• Educational: the development of this nano-satellite has been carried out by graduate and undergraduate students, which have designed, implemented, and validated most of their subystems. In addition, mission analysis (e.g. thermal analysis, link budget, etc.) have also been conducted by students, who have also conceived exhaustive test campaigns with industry-rated equipment. Coordinated by the team leaders, several undergraduate students have participated in this mission either as part of a capstone project course within their degree curricula or as their degree thesis.
• Technology demonstration: the Flexible Microwave Payload - first version (FMPL - 1), the CubeSat payload, has entirely been developed in the laboratory, and includes three EO instruments in one single subsystem. In addition, the 3Cat-4 also demonstrates the feasibility of the payload antenna deployment. This mission aims thus to demonstrate that this kind of technology is useful for future CubeSat missions.
• Scientific experiments: the 3Cat-4 CubeSat will generate Earth observables to address different scientific interests:
  1. Assess the relative sensitivity of GNSS-R observables (waveform peak amplitude and maximum derivative delay) at different frequency bands (i.e. L1 and L2).
  2. Assess the impact of the required ionospheric corrections (i.e. different delays of the reflected signals at different bands).
  3. Evaluate the potential application of GNSS-R over land surfaces, and in particular to infer soil moisture and vegetation biomass, with special focus over forests, where other missions are not able to due to RFI (e.g. at UHF band).
  4. Assess RFI detection and mitigation techniques for digital radiometers.
  5. Create RFI maps at L1, L2 and the protected band from 1400 to 1427 MHz.
  6. Validate the design of an AIS receiver for space-borne applications.

The 3Cat-4 mission has been accepted and takes part of the "Fly Your Satellite!" program (second edition) of the European Space Agency (ESA) Academy.

The 3Cat-4 spacecraft is composed of different subsystems:

• Zenith Antenna and Deployment Subsystem (ZADS): a monopole deployable antenna system that contains 2 antennas (VHF and UHF radio systems).
• Communications Subsystem (COMMS): it is the responsible of the communications between the satellite and the Ground Station.
• Attitude and Orbit Control Subsystem (AOCS): it is the responsible of the determination and control of the spacecraft orientation with respect to an inertial frame of reference respectively.
• On Board Computer (OBC): provides processing capability to the satellite, for the Local Mass Memory function, interfacing with other avionics subsystems, failure detection, On Board time management
• Electrical Power Subsystem (EPS): it has the function to gather, collect and provide the necessary electrical power to all the spacecraft subsystems during all mission phases.
• Flexible Microwave Payload (FMPL - 1): it represents the Payload of the spacecraft, integrating three mission experiments in a single hardware and software platform. In particular, these experiments are a miniature GNSS-R receiver, an L-Band Radiometer, and an AIS receiver.
• Nadir Antenna and Deployment Subsystem (NADS): it fulfills two functions which are: to contain the L-Band antenna for the FMP acquisition, and to deploy the Gravity Boom to generate a Gravity Gradient.
• Solar Panels (SP): it is responsible for collecting the solar energy, and to determine using the Sun sensors the orientation of the satellite.
• Interface Board: it is the module which connects the satellite to the PC in order to program and debug the satellite.