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ArcticSat Modes of Operation
ArcticSat Modes of Operation
ArcticSat modes of operations change based on the state of the mission. The satellite will change between 8 different modes, with active subsystems for each mode outlined in the graph.
Science Mode: During science mode all spacecraft subsystems will be functioning on their standard duty cycles and attitude telemetry is recorded. The payload passive radiometer will be capturing and saving sea-ice data. Note that this mode is only active once the satellite is over Canada.
Sun-Pointing Mode: During sun-pointing mode, the spacecraft will not log the attitude and turn off the payload module. ArcticSat is set to pointing mode when it is not over Canada.
Idle Mode: During idle mode, most spacecraft subsystems will be functioning on their standard duty cycles, disconnecting the ADCS and payload modules. This mode will primarily be used for commissioning activities.
Low Power Mode: During low power mode the spacecraft functions are reduced to limit power draw, but most subsystems still have some functions. This mode is triggered when the battery state of charge (SoC) is less than or equal to 40%.
Survival Mode: During survival mode spacecraft functions are limited to those subsystems that are necessary for spacecraft survival. This mode is triggered when the battery SoC is less than or equal to 30%.
Critical Hold Mode: This is a hardware triggered mode where the battery SoC has fallen below 25%. In this mode an analog voltage supervisor disables all internal PCU DC-DC converters and forces the entire PCU to shut down. The PCU can anticipate this mode and take actions to protect information before powering down. The only load on the batteries in this stage is the voltage supervisor that consumes < 10uW.
Detumble Mode: During detumble mode the ADCS subsystem is actively tracking the turning rate of the spacecraft and working to slow it. This process will continue until the ADCS system signals the PCU that a desired tumble rate has been achieved.
Post-Ejection Hold Mode: During the post-ejection hold mode, all subsystems will be turned off. A real time clock in the power subsystem will be the only active component, counting 5 minutes from launch.
The following finite state machine defines the methods of transfer between the various states during normal operations:
Figure 1: Finite State Machine Chart for ArcticSat Operations
Load Shed Plan
Load Shed Plan
There are 8 different modes of operations designed for ArcticSat. In Figure 1, methods of expected transfer between various states of modes under normal operations has been listed out. There are two fundamental transfer motions designed during operations; automatic transition and ground station control transition. Automatically transfer between modes depends on certain designed standards for each mode (e.g. battery state of charge, power state and desired satellite rotation rate). Ground station control transition is that the satellite transfers between two modes when it receives commands from ground station. After ejection of the satellite, the whole system will compulsively process to post-ejection hold mode where all subsystems are held to be off for 5 minutes from launch. After 5 minutes, detumble mode will be activated and ADCS subsystem will work to achieve a desired tumble rate. From detumble mode, the satellite could automatically transfer to idle mode or low power mode depending on the reached rotation rates of the satellite and the charge state of the battery. When the battery state of charge is less or equal to 40%, low power mode will be on to limit function of satellite subsystems. Otherwise, the satellite will go to idle when rotation rates below limits and functions as its standard duty cycles. From low power mode, the satellite will have automatic incremental power mode transitions between low power to survival to critical based on the condition of battery state of charge, or the satellite will transfer to idle mode or sun pointing mode or science mode of operational modes if receiving commands from ground station. The satellite is capable to transfer operational modes arbitrarily between idle mode, sun pointing mode and science mode under control of grounds station. However, Science mode is set to only capture data over Canada. The satellite will also have automatic transition between operational modes to low power mode when the battery state of charges reaches certain level.
Figure 2 shows the details of active subsystems during phases of operation.
Figure 2: Load Shed Plan
Deployment Preparations
Deployment Preparations
Before the satellite is deployed the following will be verified:
Battery State of Charge (SoC)
All Remove Before Flight (RBF) pins are applied
Satellite is electrically inert
Lifetime Operations Plan
Lifetime Operations Plan
The following block diagram illustrates the planned order of operations for ArcticSat. Each functional block represents a phase of the spacecraft lifetime, with descriptions of the major activities that occur during each of the functional blocks.
Figure 3: Mission Phase Flowchart
Function Phase Descriptions
Function Phase Descriptions
Post-Ejection Hold
Post-Ejection Hold
Following ejection from the Exopod Nova deployer, all subsystems are off, besides a real-time clock within the power subsystem. The spacecraft must be kept in this state for a minimum of 5 minutes.
Acceptable Modes: Post-Ejection Hold Mode.
Detumbling
Detumbling
When the 5 minute hold period is completed, the spacecraft will begin the detumbling process. The power control unit (PCU) will turn on and complete initial checks:
Battery State of Charge
Read PCU State Registers
The PCU will then supply power to the ADCS, which will also complete initial checks:
Verify torque rod function and confirm proper current draw.
Verify magnetometer function
The ADCS system is used to slow the rotation of the satellite to an acceptable rate of approximately 0.5 degrees per second. During this process, the PCU is in command.
If the satellite is unable to detumble within 3 orbits, the satellite will deploy solar wings and enter low power mode. If detumbling is successful, the satellite will deploy antennas and begin the commissioning phase.
Acceptable Modes: Detumbling Mode.
Commissioning
Commissioning
After the satellite rotation has been slowed sufficiently within the time limit, the spacecraft shall enter idle mode. When the Command and Data Handling (CDH) unit is powered on, it will take command of the spacecraft and begin commissioning activities. Major spacecraft hardware and subsystems will be powered on and "checked out" one at a time to ensure nominal functions.
Although certain equipment check-out scripts will be written into the software autonomously, the commissioning process will be heavily controlled and monitored by the ground station.
Acceptable Modes: Idle Mode.
The following equipment checks will be performed, separated into their respective subsystems:
Communications
Turn on the transceiver.
Check the transmission power and frequency settings.
Check the functionality of the patch antennas.
Establish a link with the ground station.
The ground station attempts to collect telemetry data during an available pass.
Power
Re-Measure battery state of charge
Check if battery heater is on (drawing current)
Verify all internal and external power rail Voltages/ Currents
Read PCU state registers
Measure solar array performance
Payload
Turn on payload
Check radiometer
Initial radiometer processed data are sent to ground.
CDH
Read CDH state registers
Verify all internal power rail Voltages/ Currents
Measure unit internal temperatures
Verify time and date on the Real Time Clock (RTC)
Write to and read from all types of memories
(After Communications checkout) Commission orbital navigation
Upload latest TLE update from ground
Begin running SGP4 for current PVT
(After ADCS checkout) Initialize EKF attitude estimator
Thermal
Read all thermistor temperatures and check against expected range
Confirm battery heater is operating (if batteries are below allowable temperature) by seeing if battery temperature is increasing
Structure
On CDH command, arm and fire the deployable release circuit.
Afterwards, confirm that the deployable has fully deployed.
Add deployable's position to bus telemetry.
ADCS
Check communication between ADCS and the CDH. (ADCS_PING)
Check the functionality of the gyroscope. (GET_GYRO_MEASUREMENT)
Check the functionality of the magnetometer. (SET_MAGNETOMETER), (GET_MEASUREMENT_MAGNETOMETER), (RESET_MAGNETOMETER), (GET_MEASUREMENT_MAGNETOMETER)
Check that the sun sensors work nominally and detect the position of the Sun. (GET_MEASUREMENT_SUN_SENSOR) (for all four optical sensors, two on each sun sensor assembly)
Check the functionality of torque rods (SET_POLARITY_TORQUE_ROD_#). See if it is drawing the correct current. Check the attitude response.
Commission reaction wheel
Power on
Check sensors
Accelerate to establish baseline stored momentum
Check torque response
Normal Operations
Normal Operations
Following the completion of the commissioning process, the spacecraft will begin with normal operations. The majority of the lifetime of the spacecraft will be spent in normal operations. This is the phase of the spacecraft lifetime where the mission objectives are being fulfilled and the payload is functioning as intended. The lifetime of ArcticSat is estimated to be at least 3 years.
The typical ArcticSat operations will be fully automated, with a set schedule defined in the software for the duration of each mode and the timing/conditions for transfer between modes. This will allow the satellite to be fully functional without ground interception. However, ground will still have the ability to switch the satellite between modes and override the planned schedule as desired/required for proper satellite function.
Acceptable Modes: Science Mode, Sun-Pointing Mode, Detumbling Mode, Low Power Mode, Survival Mode, Critical Hold Mode.
Decommissioning
Decommissioning
Due to the drag of the atmosphere, the velocity of the satellite will decrease over mission lifetime. This will force the satellite to burn up in the atmosphere upon re-entry.
Based on simulations shown in figure 5, ArcticSat is expected to decommission within 5 years of its end of lifetime. Note that the following simulations consider smallest wetted area of ArcticSat for the firts 3 years after launch, representing the mission lifetime. However, average wetted area is considered for the next 5 years. This implies that ArcticSat will be going into a tumbling state at the end of its mission life.
Acceptable Modes: Science Mode, Sun-Pointing Mode, Detumbling Mode, Low Power Mode, Survival Mode, Critical Hold Mode.
Figure 6: Decommissioning Simulation
Operation Team
Operation Team
The operations team will consist of 3 groups:
Trained S-band radio operators at University of Manitoba
Trained S-band radio operators at Chesterfield Inlet
Science team (University of Calgary)
Ground Segment Operations
Ground Segment Operations
The primary operators of ArcticSat are the trained community members at Chesterfield Inlet. The C-Core's Happy Valley-Goose Bay ground station will be used to uplink scheduled commands requested by the trained members. Once the encrypted data is downlinked, it will be saved on a virtual machine and can be accessed by the Chesterfield community members and decrypted to be analyzed. The analyzed data will then be sent to the SIKU Indigenous Information App to be shared with the rest of the northern communities. A summary of the ground segment operations is shown in figure 7.
Figure 7: Ground Segment Operations
Verification Plan
Verification Plan
Throughout phase D, dry runs of launch and early operations will be regularly performed with all subsystem leads. The verification of the ability of the spacecraft to transfer between modes either automatically or as requested by ground is left to the software and ground system teams respectively.
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