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Iris Modes of Operation
Iris Modes of Operation
Iris 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 camera will also be turning on at a given frequency interval and recording RGB data/ capturing images.
Sun-Pointing Mode: During sun-pointing mode, the spacecraft will not log the attitude and turn off the payload module. This mode will be used to orient the spacecraft to alight the geological samples with the accepted orientation with respect to the sun vector.
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 30 minutes from launch. See the Post-Ejection Hold Phase section for more information.
Load Shed Plan
Load Shed Plan
There are 8 different modes of operations designed for Iris. 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 30 minutes from launch. After 30 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. The satellite will also have automatic transition between operational modes to low power mode when the battery state of charges reaches certain level.
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 Iris. 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 2: Mission Phase Flowchart
Function Phase Descriptions
Function Phase Descriptions
Post-Ejection Hold
Post-Ejection Hold
Following ejection from the NanoRacks module on the International Space Station (ISS), 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 30 minutes, as defined by the NanoRacks CubeSat Deployer (NRCSD).
Acceptable Modes: Post-Ejection Hold Mode.
Detumbling
Detumbling
When the 30 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 Actuators and confirm proper current draw.
Check Magnetometers and Gyroscopes
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 8 orbits, the satellite will deploy antennas to 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. A more in-depth description of the commissioning process is provided in the "Commissioning" subsection.
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. All subsystem leads will be on-site in order to provide immediate feedback on collected data during the commissioning checks, and confirm that all subsystems are operating as expected.
Acceptable Modes: Idle Mode.
The following equipment checks will be performed, separated into their respective subsystems:
Turn on radio
Verify communication/interface with CDH
Establish link with ground station with dummy data
Verify that the UHF antenna is deployed
Wait for command to turn on beacon
Turn on beacon
Verify if ground station receives beacon
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
Check each camera is functioning correctly.
Initial images and processed data are sent to ground and ground updates the camera calibration if/as needed.
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
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
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.
Check whether ADCS can talk to the CDH over the CAN bus.
Check that the photodiodes and the sun sensors work nominally and detect the position of the Sun.
Check the functionality of actuators i.e. torque rods. See if it is drawing more than the required current.
Check for the proper functioning of magnetometers and gyroscopes.
Check for the orientation of the solar panels.
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 typical Iris 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.
Acceptable Modes: Science Mode, Sun-Pointing Mode, Detumbling Mode, Low Power Mode, Survival Mode, Critical Hold Mode.
Operation Team and Plan
Operation Team and Plan
The operations team will consist of four groups:
Ground station team at University of Manitoba (UM ground station team)
Payload team at University of Winnipeg
Figure 5 illustrates the methods of data collection and transfer between the above operations groups. The UM ground station has the capability to collect all critical data independently.
The dashed line for UM ground station team data transfer from the satellite are meant to illustrate that once the network of operators is up and running there will likely be a higher quantity of data collected by the ground station operators than by the devoted ground stations. Satellite data and sample image data will be collected by the UM ground station. The sample image is required to send from the satellite to the ground station team at least once per week according to the available passes. The U of M ground station team will place all collected data on a shared server, which the payload team has access to.
Figure 5: Operation Teams and Data Transfer Chart
Verification Plan
Verification Plan
Throughout phases C and 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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