EIR-OPS-026: Low Battery Fault Analysis


Objective

To assess the status of the spacecraft’s power system(s) after a low voltage event.


Introduction

Using this procedure, the Operator will attempt to determine:

  • the cause of the low battery voltage,

  • the time-line of the issue (i.e. is it still on-going?) and

  • a potential fix

Note

The analysis to be carried out by the team is very dependent on the findings as well as what data was successfully downlinked. Therefore, rather than a strict set of instructions, this procedure instead provides information to help guide the Operator in their analyses. Also note that in addition to any data downlinked by the UCD GS, data obtained via the amateur radio community may also be used to support the analyses.

Warning

The below procedure commonly instructs the Operator to inspect parameters from the battery, e.g. platform.BAT.batteryVoltage[2]. Given the anomaly experienced during the FM environmental test campaign, where the battery’s telemetry node failed to return data to the OBC, these procedures may need to be tweaked to use data from the EPS instead of the battery if the same anomaly is currently being experienced.


Procedure

This procedure contains four subsections for helping with the invesitgation into the low battery scenario and remedying the situation:

  • A. Initial Considerations - Determining the time at which the low battery condition occurred, the state of the spacecraft in the moments prior and the current state of health of the spacecraft.

  • B. Charging Conditions - Examining the charging conditions in the time prior to the low battery scenario to determine if the event was caused by an issue with the power generation chain. Examining the charging conditions in the time after the low battery scenario to detemine if the issue has been resolved.

  • C. Current Draws - Examining the current draws in the time prior to the low battery scenario to determine if the event was caused by a higher than expected current draw. Examining the current draws in the time after the low battery scenario to determine if the issue has been resolved.

  • D. Remedying the Situation - Some things to consider before returning the spacecraft to more nominal operations.


A. Initial Considerations

A.1.

  • Examine the progression of platform.BAT.batteryVoltage[2] in Grafana for the following:

    • The time at which the battery voltage crossed the safe mode trigger threshold (7.5V).

    • The time at which the spacecraft powered off (if this occurred).

    • If the battery voltage has recovered to nominal levels since the low battery scenario. This may inform:

    • In the orbits prior to the low battery event was the battery voltage tending towards the low battery trigger voltage (i.e. Could this event have been predicted or prevented?) or was the decline in voltage rather sudden (more idicative of a fault with the hardware or of a subsystem being powered on).


A.2.

  • Ensure that the state of the spacecraft in the moments prior to the low battery voltage event are well understood. Knowledge of which subsystems were active could inform future operations or rule out several options from further investigation. Things to look out for include:

    • platform.EPS.actualSwitchStates. This parameter will indicate if any of the payloads were active prior to the low battery event.

    • platform.ADCS.modeState. When the ADCS is in some modes (e.g. Detumble Mode) it may activate the magnetorquers leading to higher power draws.

    • mission.ADCSManager.enabled. The ADCS manager turns on and off the GPS when enabled. The GPS is a power hungry subsystem and should not be left on for longer than necessary where possible.

    • platform.CMC.txPower. The CMC can transmit at 0.5W, 1W and 2W. If the txPower parameter is set to the higher of these options, downlinks may cause low battery voltage events. This parameter is particularly important to check if the event occurred during a pass when the transmission from the CMC is most active.



B. Charging Conditions

B.1.

  • Using downlinked HK data, plot the following to identify if poor charging rates are observed for any of the four solar arrays during the time(s) identified from A. Initial Considerations:

    • platform.BAT.batteryCurrent parameter (Row 2: The Battery bus).

    • platform.EPS.solarArrayCurrents parameter for each of the four solar arrays.

    • platform.EPS.solarArrayVoltages parameter for each of the three BCRs. Note that the two Y facing solar panels are on the same BCR, and that the -X solar panel (which only has 3 cells instead of 5) is on a BCR tuned for lower voltages.


B.2.

  • If nominal charging is observed, skip ahead to Section C. If poor charging conditions are observed, consider:

    • If an eclipse was expected at this time? It is not expected that the spacecrafts batteries will cause a low battery event during an eclipse, however, if this is the case, the following must be considered:

      • has the battery degraded?

      • did the spacecraft not get enough power during the last day-time (e.g. due to pointing or a fault with the solar panels)?

    • Is one array in particular contributing to the issue? which would suggest a fault with the array

    • If the issue is not a result of just one problem array, are the platform.ADCS.fss1AlphaAngle and platform.ADCS.fss1BetaAngle parameters in the downlinked HK data as expected for the pointing scheme.



C. Current Draws

C.1.

  • Examine the platform.EPS.busCurrents parameter for each of the four buses to identify if in the time prior to the low battery voltage event any of the current draws were higher than expected. If a higher than expected current draw is observed PASCAL data should be prioritised in future passes for investigating the source of this high current draw.


C.2.

  • While waiting for PASCAL data to be downlinked, determine:

    • if the high current draw was a short duration, one-off event that momentarily drained the battery or if the bus was/is drained at a high rate for a sustained period of time. A short duration current draw may be indicative of a state change or a fault, whereas a sustained drain may be prevented in the future by configuration changes or operational planning.

    • if any particular event/on-board operation can be linked to the onset of the high current draw (Information from step A.2. may inform this).


C.3.

  • Considering the case where a high current draw is observed, depending on which bus the current draw is observed for, determine which subsystem is responsible using the following flow:

    • Determine which PCM sees the higher than expected current draw using platform.EPS.busCurrents.

    • Check if this current draw is visible on any of the PDMs which correspond to this PCM.

      • 3V3 Bus: PDMs 8, 9, 10

      • 5V Bus: PDMs 5, 6, 7

      • BattV Bus: PDMs 3, 4

      • 12V Bus: PDMs 1, 2

    • If the current draw is visible on a PDM, determine which payload is connected to that PDM and assess the health of that payload. Operational decisions may be required to deal with the high power draw. For example, if the high power draw is due to the GMOD payload, perhaps a change to the bias configuration would reduce the power consumption.

    • If the current draw is not visible on a PDM, determine if the draw is visible in any of the subsystems which are connected to the PCM’s directly (examples include battery current draws, OBC current draws, GPS current, CMC currents).

Note

THIS SPREADSHEET may be used to help determine which subsystems are on which of the spacecraft power buses. Each bus has a list of parameters in column A of the spreadsheet to go through to determine if there is any usual current draw from a paticualr subsystem. In column B, additional parameters associated with the subsytem are listed to check if the assoicated parameter in column A showed a higher than normal current draw.

Note

The magnetorquer current draws do not appear in the ADCS Bus Currents parameter. If the current draw is not visible elsewhere in PASCAL but it is on the 5V bus and the ADCS Mode indicates that the magnetorquers are active then this could be the source of the current draw.



D. Remedying the Situation

D.1.

  • If the Operator next wishes to perform some EPS/Battery operations to further investigate the situation (i.e. health checks), Safe Mode should be exited/Commissioning Mode should be entered, using EIR-OPS-007: Operational Mode Change , before attempting to perform any EPS/Battery operations, such as powering ON PDMs.


D.2.

  • If the event was caused by a high current draw, discuss with the Subsystem Team and Systems Team on the plan of action/solution. Solutions may include changing configurations (e.g. modifying GPS on time in ADCS manager, reducing GMOD bias) or operational solutions (e.g. Only running one experiment at a time). Close attention should be paid to how the battery voltage is evolving over time. Once a solution has been implemented, health checks (as in EIR-OPS-006: Commissioning ) should be performed for the healthy subsystems. A full commissioning should be performed for the subsystem causing this anomaly.


END OF PROCEDURE