Ground Station

The primary ground station for Iris is located at the University of Manitoba. The main functions and responsibilities of the ground station subsystem include:

Sending commands to the spacecraft
Receiving bus and payload telemetry
Signal modulation and demodulation
Providing the science team with processed telemetry data in a readable format
Maintaining up-to-date tracking information

Design Philosophy

Figure 1: Ground station functional block diagram

The ground station subsystem is responsible for providing valuable scientific data from the spacecraft to the science team. The infrastructure and setup of the ground station is essential in receiving accurate and regular data with minimal noise. Its efficient interaction with the communications subsystem is paramount to mission success.

The key requirements driving design decisions for the ground station subsystem are:

R-GST-0010 - Shall be compliant with the ISED requirements
R-GST-0030 - Shall receive payload and other telemetry data using UHF frequencies
R-GST-0050 - Shall have a system of organizing and storing data accessible by the team
R-GST-0100 - Shall be capable of sending commands and receiving data
R-GST-0101 - Shall maintain up to date TLE data and uplink it to the spacecraft
R-GST-0110 - Shall be capable of receiving a minimum of 1 MB of critical data per day
R-GST-0150 - Shall link with the spacecraft at least once a day
R-GST-0190 - Shall receive sample images at least once per week
R-GST-0220 - Shall utilize the AX.25 protocol for communications

The functional block diagram for the ground station subsystem is given in Figure 1.

Architecture

Figure 2: Basic architecture for the ground station subsystem

The ground station architecture consists of a hardware and a software segment. The architecture aims at effectively sending commands to the spacecraft and receiving data from it. The University of Winnipeg is the science team stakeholder in the Iris mission. The UM ground station is designed so that it can provide sample images as requested by the science team. The data is processed and converted to a readable format before both stations (any one of them) upload the processed data to a shared Iris server. This can be downloaded by the science team. This process can be seen in Figure 2.

Detailed Communication Design at Ground Station

UM station functions as the control & operation facilities to communicate with Iris. The station will work to uplink commands to the satellite and downlink data from the satellite.

The typical steps involved when the ground station sends and receives data. To uplink commands to the satellite, the science team from the University of Winnipeg will first notify GS operator(s) at UM station. Then, the operator(s) collect the requests and create a request command list. The command list will be processed to the computer located at UM station. To encode the commands, AX.25 is applied to convert all commands as a coded sequence. The coded sequence of commands then will be segmented by AX.25 data link protocol and converted into a line code of transmission. The signal will be modulated to an analog carrier signal and be packetized to audio signals. Then the transmission happens after data modulation and packetization. The radio signals will then be received by the Iris spacecraft.

Downlinking process takes place after the Iris spacecraft received the commands. The commanded data will be sent back via audio signals and will be depacketized and demodulated to a bitstream. AX.25 will decode the bitstream and send the information to UM station in a readable format. All downlinked data from Iris will be stored in the STARLab computer. This process is depicted in Figure 3.

Figure 3: Communication architecture protocol

Design

The radio architecture (Figure 4 and 5) consists of a AMSAT LVB tracker (Figure 6), YAESU FT-847 transceiver (Figure 7), a YAESU G-5500 rotor (Figure 8), and a circularly polarized UHF Yagi Antenna (Figure 9). The TLEs are download from NORAD and can be uplinked to the satellite. SAT-PC-32 software denoted by Antenna Tracking Software in Figure 10 will be used to interpret Two Line Element (TLE) data and coordinate the following:

- Scheduling of communication windows
- Control of the antenna rotors
- Doppler frequency shift correction

The LVB tracker provides a rotator interface i.e. the UMARS computer containing SAT-PC-32 (Figure 10) interfaces with the rotators. RS232 serial ports are used for this.

The packet automation software processes the telemetry and converts it to readable format that can be sent to the science team.

Figure 4: Interfaces of the LVB Tracker in the ground station

Figure 5. RF Equipment at UM Ground Station

Figure 6. AMSAT LVB Tracker

Fgure 7. Yaesu FT-847 Transceiver

Figure 8. Yaesu G-5500 Elevation-Azimuth Dual Controller

Figure 9. Polarized Circular Antenna

Figure 10. SAT-PC-32 Software

System Block Diagram

Figure 11 below shows a detailed system block diagram designed for UM ground station. There are two main subsystems designed for UM station. The first subsystem will be implemented at StarLab located at UM engineering building, and the second subsystem will be implemented at the ground station located at UM engineering building roof.

The ground station computer will be remotely connected by windows with the computer located at StarLab. The STARLab ground station computer will be remoted connected with the computer (UMARS) located at the UM roof ground station.

All equipment required for communication are located at the UM roof ground station. The software required by ground station are antenna tracking software (SAT-PC-32), packet automation software and LVB tracker. The antenna tracking software is utilized to adjust the rotor and the angle of the antenna. The antenna tracking software (SAT-PC-32) is utilized for antenna tracking which localizes the satellite and provides orbital parameters. The tracking software is also responsible for scheduling all passes for the satellite and correcting doppler frequency shifts to better localize the satellite. The packet automation software is to packetize and depacketize commands and data. LVB tracker is connect for communication which provides the interfaces between the computer at the ground station and the rotor and is capable of automatically adjusting the angle to achieve maximum data signal in position.

Figure 11. UM ground station system block diagram

Link Budget

The link parameters for the UM ground station are given below:

The link budget can be viewed at LinkBudget.

Uplink command frequency: ***** MHz

Downlink receive frequency: ***** MHz

Uplink command transmission bandwidth: 15kHz

Downlink command receiver transmission bandwidth: 10kHz

Modulation scheme: Frequency modulation

Baud rate: 9600 bps

Bit error rate: < 10^(-5)

Link layer protocol: AX.25

Min. Angle of elevation: 20 degrees

Antenna type: Circularly polarized

Antenna gain: 18.9 dBic

Software Design

The AppDesigner in Matlab is used to develop a GUI for easy access to telemetry and satellite observation. Commands can be sent to the satellite through the GUI. A real-time SPG4 is developed in STK to estimate the expected position of the satellite. When a user issues a command, the ground station checks if the satellite is within range. If yes, the commands go directly to the satellite through the AX.25 module. If not, commands are time-tagged and listed. A list of specific commands is pre-defined to be given in text fields. Commands can range from turning on/off the communication receiver and indicating if the sun sensors and camera are off during eclipse. Once a user logs into the GUI app, they will have access to the latest payload and health telemetry, send a command and store it in a queue if the satellite is not in range and automatically send it when there is a pass. Commands can be sent anytime and the operator doesn't need to wait for a pass to send a command. Command list will simulated passes can be found below:

Checklist

Capabilities of the design:

Issuing commands to the satellite.
Receiving downlinked telemetry and payload data.
Storing downlinked data on a central server.
Providing coordination between secondary ground segments.
Maintain up-to-date orbital tracking data for satellite.

Weather station within the GUI

To prevent the ground station from operating under unsafe environmental conditions, a weather station is implemented within the virtual ground station GUI. This system obtains weather information from a reputable weather forecast website and opens a GS session only when the weather is favorable based on the conditions laid for use in the system. The major unsafe environmental conditions include thunderstorms, tropical storms, hurricane and heavy snowfall.

Ground Station Test and Setup Plan

Work_Packages.xlsx

Ground Station Test Plan with Verification Activities

GS-Tests Plan.xlsx

Memorandum of Understanding (MOU)

The UofM ground station is owned by UMARS, and UMSATS has been using it. Star Lab has signed a MOU with these organizations to utilize the GS for Iris testing and operations. The MOU is given below:

MOU-UMSATS-UMARS-v32.pdf

Licensing

The status of UM ground station license applications is stated as below:

ISED CPC 2-6-01 (Earth Station license) - Approved
ISED CPC 2-6-02 (Space Station license) - Approved

Failure Mode/Risk Analysis

Risks will happen as the design and real operation progress. A failure mode analysis for ground station has been developed to increase likelihood of opportunity, decrease likelihood of risk, detect risk. The process of failure mode analysis includes risk identification, quantitative risk assessment and a risk response plan.

List of Identified Risks

The risk identification has been performed as below which will identify most of possible risks and potential causes. When a risk is identified, a quantitative risk assessment can be presented. The risk identification list will be updated through design progresses in phases.

GS Risk Identification Matrix

Table 1: Ground Station Risk Identification Matrix

Qualitative Risk Assessment Matrix

Table 2: Risk Management Probability Descriptions [1]

Table 3: Risk Management Impact Descriptions [1]

Quantitative risk assessment is a method that can quantitatively identify the risks by two criteria: probability and impact. The score will be the product of two criteria, both of which are ranged from 1 to 5. Top 10 risks will be ranked by the evaluated score and the relative feasible solutions will be provided for each risk. The description for the two criteria can be seen in Table 2 and Table 3.

Quantitative Risk Matrix

Table 4: Quantitative Risk Matrix [1]

Risk Response Plans

Based on the qualitative risk assessment results, the response actions for each risk: when the risks present at the ground station are planned. Due to severe results of the risks, the best way is to prepare and have a precaution plan before a risk presents. A detailed table for the risk response actions are shown as below.

Risk Response Plan

References

Datasheets reference:

Online reference:

[1]. K. Atamachuk, "Risk management - Part 2," [Online]. Available: https://universityofmanitoba.desire2learn.com/d2l/le/content/340612/viewContent/17356 17/View?ou=340612.

Page updated

Google Sites

Report abuse