EIR-OPS-006.5: GPS Health Check

Objective

To assess the health of the GPS following launch.

Introduction

This procedure will verify the functionality of the GPS hardware following launch.

Procedure

This procedure has 4 sub-procedures. Sub-procedure C is to be performed outside of a communication pass, as the communication passes are to be optimised for downloading data and performing real-time assessment of the state of the spacecraft.

A. Enable GPS and GPS Logger
B. Downlink GPS Logger Data
C. Assessment of Data Downlinked
D. Assess GPS Lock Status
E. Disable GPS and GPS Logger

Danger

As part of this procedure, the GPS is powered ON and left ON until a lock is achieved. This may take ~hours as this is the first time the GPS is enabled on-orbit - its a ‘cold start’. The Operator should time this procedure such that the GPS is not left on for more than a couple of hours as a result of e.g. a large gap in subsequent communication passes, as the GPS has a large current draw when left ON continuously that will discharge the spacecraft’s batteries . The Operators should consider setting up TimeActions, via EIR-OPS-037: Set-Up a TimeAction , to manager this risk.

A. Enable GPS and GPS Logger

Important

You are about to send the first TC of this procedure - Have you completed the EIR-OPS-003: Start a Communication Pass procedure? A Communication Pass must be started prior to carrying out the operations planned for the pass. Don’t forget to open and set up the parameters/actions that will be used during the pass in MCS before the pass begins!

A.1.

Get the platform.OBC.obc.gpsEnable parameter.
Confirm that 0 (i.e. GPS disabled) is returned.

TC Details
MCS Operation	`Get`
Action/Param Name	`platform.OBC.obc.gpsEnable`
Data Expected with TC	No
TM Details
Data Expected from TC	`enabled` ( + ACK )
Data Size	Boolean
Data Info	If the GPS is disabled (0) or enabled (1)
Allowed Value(s)	0 - 1
Expected Value(s)	0 (i.e. disabled)

A.2.

Get the cdh.logging.GPSLogger.enabled parameter.
Confirm that 0 (i.e. GPS Logger disabled) is returned.

TC Details
MCS Operation	`Get`
Action/Param Name	`cdh.logging.GPSLogger.enabled`
Data Expected with TC	No
TM Details
Data Expected from TC	`enabled` ( + ACK )
Data Size	Boolean
Data Info	If the GPS Logger is disabled (0) or enabled (1)
Allowed Value(s)	0 - 1
Expected Value(s)	0 (i.e. disabled)

A.3.

To enable logging of GPS data, Set the cdh.logging.GPSLogger.enabled parameter to 1.

TC Details
MCS Operation	`Set`
Action/Param Name	`cdh.logging.GPSLogger.enabled`
Data Expected with TC	`enabled`
Data Size	Boolean
Data Info	Enabled state of GPS Logger
Allowed Value(s)	0 - 1
Expected Value(s)	1 (i.e. enabled)
TM Details
Data Expected from TC	No ( + ACK )

A.4.

Confirm the Set in the previous step with a Get (i.e. confirm the value was set successfully).

A.5.

Prior to enabling the GPS, Get the platform.obc.GPS.LockAcquiredCount and platform.obc.GPS.LockLostCount parameters.

TC Details
MCS Operation	`Get`
Action/Param Name	`platform.obc.GPS.LockAcquiredCount`
Data Expected with TC	No
TM Details
Data Expected from TC	`LockAcquiredCount` ( + ACK )
Data Size	4 bytes
Data Info	Increments when the GPS lock state changes from lost to acquired
Allowed Value(s)	00000000 - FFFFFFFF (hex)

TC Details
MCS Operation	`Get`
Action/Param Name	`platform.obc.GPS.LockLostCount`
Data Expected with TC	No
TM Details
Data Expected from TC	`LockLostCount` ( + ACK )
Data Size	4 bytes
Data Info	Increments when the GPS lock state changes from acquired to lost
Allowed Value(s)	00000000 - FFFFFFFF (hex)

A.6.

Also, Downlink the platform.obc.GPS.LastFrame parameter.

Warning

A NACK may be returned to this TC as a lock/last frame is yet to be achieved.

TC Details
MCS Operation	`Downlink`
Action/Param Name	`platform.obc.GPS.LastFrame`
TM Details
Data Expected from TC	`LastFrame` ( + ACK )
Data Size	< 2256 bytes (variable)
Data Info	Returns the the last retrieved ASCII debug frame

A.7.

To now enable the GPS, Set the platform.OBC.obc.gpsEnable parameter to 1.

Caution

The GPS module draws a significant amount of current when powered ON. Therefore, ensure that the battery levels of the spacecraft are sufficient prior to powering on the GPS.

TC Details
MCS Operation	`Set`
Action/Param Name	`platform.OBC.obc.gpsEnable`
Data Expected with TC	`gpsEnable`
Data Size	Boolean
Data Info	If the GPS is disabled (0) or enabled (1)
Allowed Value(s)	0 - 1
Expected Value(s)	1 (i.e. enable)
TM Details
Data Expected from TC	No ( + ACK )

A.8.

Confirm the Set in the previous step with a Get (i.e. confirm the value was set successfully).

B. Downlink GPS Logger Data

B.1.

During the next communication passes, the Operator should downlink GPS, PASCAL and other data from on-board storage according to the EIR-OPS-011: Downlink Data From Storage procedure, to determine if a GPS lock has been achieved and to assess the power consumption of the GPS receiver when continuously powered on.
Priority should be given to NEWER data (i.e. data collected since the GPS was enabled).

B.2.

While GPS and PASCAL data are still being assessed outside of passes, during subsequent communication passes, the Operator should return to Step B.1. and continue to downlink GPS and PASCAL data as well as any additional data desired as a result of the analyses carried out in Sections C and D.

C. Assessment of Data Downlinked

C.1.

Provide the ADCS Engineer with the downlinked GPS and PASCAL data to assess the following:
- Monitor the GPS logger parameter platform.obc.GPS.stateVec to confirm if a GPS lock has been achieved.
- Monitor the PASCAL logger parameters: platform.obc.TelemetryADCC.channelOutput (Row 2 = GPS 3V3 Supply) and platform.obc.TelemetryADCB.channelOutput (Row 1 = 3V3 LCL Output Current), and use them to confirm the GPS current draw is as expected.

D. Assess GPS Lock Status

D.1.

While the GPS is enabled, regularly Get the following parameters: platform.obc.GPS.LockAcquiredCount and platform.obc.GPS.LockLostCount .
If the values of these parameters increase from the values retrieved in Step A.5, then the GPS has achieved lock since power ON. Data should also be observed in the Event log indicating the same.

Tip

The Event log may provide the Operator more info on when locks were acquired/lost.

TC Details
MCS Operation	`Get`
Action/Param Name	`platform.obc.GPS.LockAcquiredCount`
Data Expected with TC	No
TM Details
Data Expected from TC	`LockAcquiredCount` ( + ACK )
Data Size	4 bytes
Data Info	Increments when the GPS lock state changes from lost to acquired
Allowed Value(s)	00000000 - FFFFFFFF (hex)

TC Details
MCS Operation	`Get`
Action/Param Name	`platform.obc.GPS.LockLostCount`
Data Expected with TC	No
TM Details
Data Expected from TC	`LockLostCount` ( + ACK )
Data Size	4 bytes
Data Info	Increments when the GPS lock state changes from acquired to lost
Allowed Value(s)	00000000 - FFFFFFFF (hex)

D.2.

Also, Downlink the platform.obc.GPS.LastFrame parameter at least once.
Compare the TM returned to that of Step A.6.

TC Details
MCS Operation	`Downlink`
Action/Param Name	`platform.obc.GPS.LastFrame`
TM Details
Data Expected from TC	`LastFrame` ( + ACK )
Data Size	< 2256 bytes (variable)
Data Info	Returns the the last retrieved ASCII debug frame

E. Disable GPS and GPS Logger

Warning

Section E should only be carried out following instruction from the ADCS and/or EPS engineers to do so (i.e. after we have a lock or if a long period of radio silence is coming up or if the GPS was drawing too much current).

E.1.

To disable the GPS, Set the platform.OBC.obc.gpsEnable parameter to 0.

TC Details
MCS Operation	`Set`
Action/Param Name	`platform.OBC.obc.gpsEnable`
Data Expected with TC	`gpsEnable`
Data Size	Boolean
Data Info	If the GPS is disabled (0) or enabled (1)
Allowed Value(s)	0 - 1
Expected Value(s)	0 (i.e. disable)
TM Details
Data Expected from TC	No ( + ACK )

E.2.

Confirm the Set in the previous step with a Get (i.e. confirm the value was set successfully).

E.3.

To disable the logging of GPS data, Set the cdh.logging.GPSLogger.enabled parameter to 0.

TC Details
MCS Operation	`Set`
Action/Param Name	`cdh.logging.GPSLogger.enabled`
Data Expected with TC	`enabled`
Data Size	Boolean
Data Info	Enabled state of GPS Logger
Allowed Value(s)	0 - 1
Expected Value(s)	0 (i.e. disabled)
TM Details
Data Expected from TC	No ( + ACK )

E.4.

Confirm the Set in the previous step with a Get (i.e. confirm the value was set successfully).

E.5.

The GPS health check has been completed. The Operator should now proceed with one of the sub-procedures listed in EIR-OPS-006: Commissioning that is yet to be completed.

Note

The sub-procedures listed in EIR-OPS-006: Commissioning do not necessarily need to be carried out in the order given. However, procedures ending in ‘Operation’ should only be completed after the relevant ‘Health Check’ procedure for that subsystem has been performed. The ‘EMOD Reprogramming’ procedure must also be performed prior to any EMOD activities. Lastly, ideally, payload operations should be the last item to consider in the commissioning of the spacecraft.

Alternatively, if all sub-procedures listed in EIR-OPS-006: Commissioning have been successfully completed, the Operator may now proceed to EIR-OPS-012: Set Up Nominal Operations .

END OF PROCEDURE