Júlia Saraiva, Visiona Tecnologia Espacial
Priscila Yamada, Visiona Tecnologia Espacial
Júlia Saraiva, VCUB1 Conception of Operation, Visiona Tecnologia Espacial
VCUB1 is the first Earth observation and data collection satellite designed by the Brazilian private sector. The mission VCUB1 successfully completed was to validate the software of three critical subsystems: Attitude and Orbit Control System (AOCS), On-Board Data Handling (OBDH) and Software Defined Radio (SDR) which was developed by Visiona Technology.
All the VCUB1’s software was designed with mechanisms that facilitate its operation and provide protection. For example, on On-board Computer’s software has been developed the World Geodetic System (WGS) application that allows the operator create areas to the satellite execute specific types of operations automatically when the is inside this region. This application enables distinct operations without the need for real-time command transmissions or pre-defined time-based command tables. Some regions have already been defined, for example, the region of the ground station where the satellite allows transmission, another example is the region of Brazil where the SDR collects data. But to perform data collection automatically, the satellite needs to be in a certain mode.
The Mode Management (MMG) application was created to manage the satellite’s modes and the configuration of each one. It analyzes the satellite’s status to check if it is able to enter a certain mode, and if this is true, it configures the satellite accordingly as soon as it enters it. The satellite’s modes are divided into groups, the first being the Minimum Configuration Mode (MCM) launch mode, followed by the safe modes Detumbling Mode (DTM), Magnetic Point Mode (MPM) and Fast Charge Mode (FCM), then the nominal Stand-by Mode (SBM) and the mode in which the satellite’s payloads operate, Earth Exploration Mode (EEM).
The satellite’s safe modes are part of the philosophy of the satellite’s protection mechanisms, namely Fault detection, isolation and recovery (FDIR). Different types of FDIR have been implemented in VCUB1, three of them in the satellite hardware itself and two in the software. The satellite’s battery has a watchdog, which resets the satellite when it has not received commands to update it for more than 24 hours.
Another watchdog was also implemented, but for 72 hours in the eMCU, which is a computer parallel to the OBC, which performs the same action of resetting the satellite. Following the reset, the satellite enters DTM, the safest mode for the satellite. This type of protection is useful in cases where the OBDH becomes unresponsive or the satellite loses tracking. Another watchdog was developed on the OBC itself, but this one checks the activity of the OBC software, so if the software crashes, it only restarts the OBC.
To implement the FDIR via software, two applications were used: Health and Safety (HS) and Limit Checker (LC). The HS application monitors the operation of the other applications. An improvement was made to this software so that it could restart the application according to the satellite mode in which it should operate. The applications are essential for managing each of the subsystems. The LC app was used to check if any of the satellite’s health conditions were violated, for example, the temperature of any equipment, the higher than expected consumption of equipment, or if the battery voltage was lower than normal, among others. These checks are made using the satellite’s telemetry, which is checked at least three times in a row to ensure that the FDIR does not act due to spurious telemetry. Fault handling varies according to the type of fault and which subsystem it is associated with. To define the treatment, Relative time tagged command sequences (RTS) tables were created, which are managed by the Stored Command (SC) application, where the commands that will be executed in sequence for a given time interval when triggered by the FDIR are defined.
These tables are used in other satellite applications and by the ground segment for repetitive activities to reduce manual labor. The SC application also has two Absolute time tagged command sequences (ATS) tables that execute commands at a specific time, where it is possible to execute one at a time, but it is possible to swap the execution of each of them to extend the number of commands that can be executed by them. These tables are used as a schedule of the activities that will be carried out by VCUB1 outside the pass.
The operation of VCUB1 has been refined based on experience and emerging needs. The operation is conducted through scripts that send a series of commands to perform specific functions. These scripts follow a sequence: they start by verifying communication with the satellite and synchronizing the number of commands sent and received. Next, they execute the script’s main function and finally signal successful completion while presenting the duration of the execution.
Due to the 24-hour protection mechanism, weekend operations are necessary to prevent the satellite from resetting. Additionally, accumulating large amounts of telemetry data is not ideal. This created a need for weekend operations without human operators, leading to the development of automation within the scripts.
This automation works as a script that uses time to trigger other scripts. Once initiated, the script checks the time of the next satellite pass and starts a countdown. When the countdown reaches zero, the scheduled scripts for the pass begin to run, one at a time. For each script, a check is performed to verify successful completion. If unsuccessful, another attempt is made. A total of three attempts are allowed; if all fail, the next script in the list is started. After completing all scripts, the time of the next pass is checked, and another countdown begins.
The development of these mechanisms and scripts has streamlined VCUB1’s operations, enabling robust performance with minimal intervention. Operations are carried out by Visiona employees at the Visiona Control Center. This report highlights the experience gained and improvements made in managing the satellite, setting a foundation for future advancements in satellite operations.