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SwRI Electrical Power Subsystem Powers CYGNSS Components

The Electrical Power Subsystem (EPS) consists of the Peak Power Tracker (PPT), Low Voltage Power Supply (LVPS), Solar Array (S/A), and batteries. Power is generated by the S/A and conditioned by the PPT. The PPT controls battery charging of the Li-Ion batteries, which are limited to 1C (capacity) charge/discharge current. Three regions of the array allow for power generation when +Z (nadir), +/-X (ram, wake) surfaces are illuminated. The +Z array has 6 strings, and an individual string is located on each ram/wake surface. Cells are all 26.6 cm2 ZTJ cells. The PPT tracks the peak power point of the combined arrays, autonomously performing a periodic global peak power detection algorithm. The peak power set point and rate of global peak detect are able to be controlled by the C&DH over the I2C bus, over which commands and telemetry are issued and received, respectively. The PPT produces the +28 V bus voltage for the microsat using the battery as a voltage clamp. It drives the S/A deployment mechanism switched power loads directly. The PPT is always partially powered in order to monitor battery state of charge for all ground conditions and is turned on fully upon separation from the CYGNSS Deployment Module (DM) upon opening the CYGNSS breakwires. Bus power is provided to the LVPS, which performs additional load switching and low voltage regulation for the microsat components and other avionics boards. Bus power is switched to the Delay Doppler Mapping Instrument (DDMI), the microsat heaters, and torque rods. Torque rods are driven by an H-Bridge and can be driven positive, negative, or off. The LVPS also provides a switched low voltage service to the XCVR to enable the transmitter. All other low voltages for the avionics boards and Attitude Determination and Control Subsystem (ADCS) components are unswitched secondary voltages. The LVPS is also controlled and telemeters data over the I2C bus to the C&DH.

EPS.jpg

Related Papers

CYGNSS Command and Data Subsystem and Electrical Power Subsystem Phase A and B Developments

 

Related Links

Southwest Research Institute

Enersys/ABSL: Battery

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