Kysat-2 electrical power system design and analysis

In 2012, Kentucky Space, LLC was offered the opportunity to design KYSat-2, a CubeSat mission which utilizes an experimental stellar-tracking camera system to test its effectiveness of determining the spacecraft's attitude while on orbit. Kentucky Space contracted Morehead State University to design the electrical power system (EPS) which will handle all power generation and power management and distribution to each of the KYSat-2 subsystems, including the flight computer, communications systems, and the experimental payload itself. This decision came as a result of the success of Morehead State's previous CubeSat mission, CXBN, which utilized a custom built power system and successfully launched in 2011. For the KYSat-2 EPS to be successful, it was important to design a system which was efficient enough to handle the power limitations of the space environment and robust enough to handle the challenges of powering a spacecraft on orbit. The system must be developed with a positive power budget, generating and storing more power than will be stored by KYSat-2 over mission lifetime. To accomplish this goal, the use of deployable solar panels has been utilized to double the usable surface area of the satellite for power generation, effectively doubling the usable power of the satellite system on orbit. The KYSat-2 EPS includes of set of gold plated deployable solar panels utilizing solar cells with a 26% efficiency. Power generated by this system is fed into a shunt regulator circuit which regulates the voltage generated to be stored in a 3-cell series battery pack. Stored powered is maintained using a balancing circuit which increases the efficiency and lifetime of the cells on-orbit. Power distribution includes raw battery voltage, four high-power outputs (two 5V and two 3.3 V) and a low-noise, low power 3.3V output for use with noise sensitive devices, such as microcontrollers. The solar panel deployment system utilizes the nichrome wire which draws current directly from the battery pack which a solid state relay receives logic-high signal. This nichrome wire, while under current, cuts a nylon wire which holds the solar panels in a stowed state prior to deployment on orbit. All logic control, current/voltage measurement, and commanding/communications is handled through the use of a Texas Instruments MSP430 microcontroller over UART serial communications. Results of the completed EPS demonstrated high-power output efficiencies approaching 90% under the highest anticipated loads while on orbit. They showed maximum noise levels of approximately +/- 41.30 mV at 83.10 MHz under maximum load. The low-noise 3.3V outputs displayed very little noise, however, this came at the cost of efficiency showing only 26% efficiency at the outputs when under maximum load. The EPS has been successfully integrated with other KYSat-2 subsystems including the spacecraft flight computer, in which the flight computer was able to communicate with the EPS and carry out its functions while functioning solely off the power distributed by the power system. Finally, testing on the solar panels show that a positive voltage margin was achieved when under light and the deployment system was able to cut the nylon wire completely under control by the EPS.