³Cat-4

Mission Overview

The ³Cat-4 (read “cube-cat-four”) is the fourth member of UPC’s NanoSat Lab CubeSat series. The mission demonstrates the capabilities of nano-satellites, particularly 1-Unit CubeSats, for Earth Observation (EO) using:

• Global Navigation Satellite System - Reflectometry (GNSS-R)
• L-band microwave radiometry
• Automatic Identification Services (AIS)

Mission Goals

1. Educational: Developed by graduate and undergraduate students, who conducted subsystem design, testing, and validation as part of capstone projects or theses.
2. Technology Demonstration: Features the Flexible Microwave Payload (FMPL-1), integrating three EO instruments into one subsystem. It also demonstrates payload antenna deployment feasibility.
3. Scientific Experiments:
   • Assess GNSS-R sensitivity at L1 and L2 frequency bands.
   • Analyze ionospheric correction impacts on signal delays.
   • Evaluate GNSS-R applications for soil moisture and vegetation biomass measurements, especially over forests.
   • Investigate RFI detection and mitigation for digital radiometers.
   • Create RFI maps at L1, L2, and the 1400-1427 MHz protected band.
   • Validate AIS receiver designs for space applications.

Program Participation

The ³Cat-4 mission is part of the ESA Academy’s “Fly Your Satellite!” program (second edition).

Technical Specifications

CubeSat Architecture

The ³Cat-4 consists of the following subsystems:

• Zenith Antenna and Deployment Subsystem (ZADS): Deployable monopole antenna system with VHF and UHF antennas.
• Communications Subsystem (COMMS): Manages satellite-ground station communications.
• Attitude and Orbit Control Subsystem (AOCS): Ensures spacecraft orientation determination and control.
• On Board Computer (OBC): Provides processing, data handling, and subsystem interfacing.
• Electrical Power Subsystem (EPS): Collects and distributes electrical power to subsystems.
• Flexible Microwave Payload (FMPL-1): Combines GNSS-R, L-band radiometer, and AIS receiver experiments.
• Nadir Antenna and Deployment Subsystem (NADS): Deploys L-band antenna and generates gravity gradient stabilization.
• Solar Panels (SP): Collect solar energy and determine orientation via Sun sensors.
• Interface Board: Connects the satellite to ground-based PCs for programming and debugging.

Key Payload: Flexible Microwave Payload (FMPL-1)

The FMPL-1 integrates three instruments using Software Defined Radio (SDR):

• Automatic Identification Service (AIS) Receiver: Tracks vessels in remote areas lacking infrastructure.
• L-Band Microwave Radiometer: Studies soil moisture and vegetation biomass.
• GNSS-Reflectometer (GNSS-R): Measures surface roughness and ice coverage.

On-Board Data Processing

The FMPL-1 employs a System On-Module (SOM) for raw measurement formatting and features RF reception chains to maximize signal quality.

Subsystem Highlights

On-Board Computer (OBC)

• Model: NanoMind A3200 from GomSpace
• Specifications: Atmel AT32UC3C MCU (8-64 MHz), 128 MB NOR flash
• Software: FreeRTOS for task management and real-time operations
• Functions: Energy management, task scheduling, communication, and sensor monitoring

Electrical Power Subsystem (EPS)

• Model: Nanopower P31u by GomSpace
• Components: Two 2600 mAh Li-Ion batteries, AzurSpace 3G30A solar cells (30% efficiency)
• Power Management: Adaptive DC/DC converters and microcontroller-driven distribution

Communication Subsystem

• Frequency: UHF band (437.35 MHz)
• Components: TI CC1101 transceiver, RF amplifier, and LNA
• Antenna: Deployable monopole with omnidirectional pattern

Attitude and Orbit Control Subsystem (AOCS)

• Sensors: Sun sensors, magnetometer, and gyroscope
• Control Algorithms: B-dot detumbling and PID-based nadir pointing
• Actuators: Three magnetorquers generating 0.2 Am²

How to Receive Telemetry

Interested collaborators can decode telemetry signals from ³Cat-4. Details will be available closer to the launch date, including recommended setup and signal specifications.