Power Model Philosophy

The team will develop an engineering model (EM) and a flight model (FM) of the power subsystem. There are four major parts in the power subsystem, namely, 

• The electric power source (EPS) which consists of the spacecraft energy generation, storage and distribution systems

• EPS controller which consists a digital controller for operating the EPS and inter-subsystem communication

• The spacecraft battery which is housed in the battery saddle

• The solar strings, placed on deployable wings and the spacecraft outer shell  

Engineering Model

The engineering model will have the following major components:

• EM EPS board

• EM EPS controller board

• EM battery

• PCU software pseudocode

The EM EPS board will be used to validate the power verification activities in Phase C that pertain to energy generation, storage, and distribution systems.  This mainly establishes the functioning of the DET systems connecting the 7 solar strings to the power bus and power drawn by each subsystem  from the bus. The EM EPS will have EM of the load distribution switches, DET switches, inhibit switches and the 30 minute timer circuit.  This EM board will be designed by our team and assembled by MicroArt services. Testing on this model includes functional tests to show that the power conditioning needs of all the subsystems are met by the design and the 30-minute timer circuit works properly.

The EM EPS controller board controls the operations of the EPS. Testing on this board focuses on proper data readings from the analog sensor and thermistors and relaying and inter-module communication through SPI and CAN buses.  Load shedding and operational requirements are verified by observing the states of the switches. The EM battery is tested for its energy storing capabilities and the protection circuit to prepare for the Nanoracks battery approval. No vibration or thermal testing occurs with the EM since there are no ultra-sensitive parts.

PCU software isn't fully developed for the EM. Only the pseudocode is written and it consists of the snippets for controlling the spacecraft during detumbling, and post-ejection and algorithms for load shedding and operational modes etc.

Flight Model

The flight model power subsystem has the same components as the EM. If everything in the design is as expected with the EM, the FM is fabricated identical to the EM by MicroArt or any required updates and upgrades are incorporated into the model.  All fabrication is done with the highest- grade components. The flight solar cells are used for testing and a small light source acts as the 'Sun'. The FM is tested as part of the spacecraft level testing for random vibration, acceleration, thermal cycling and functional testing.  At this point, the ground umbilical cable is used to charge the battery through a charging equipment with two levels of control. All the electronics will be conformally coated to comply with Nanoracks outgassing requirements. 

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