Power Subsystem. 36 4.2.6.1 Solar Array............................................36 4.2.6.2 Battery Assembly.......................................39 4.2.7
Power Subsystem. The power subsystem groups the solar arrays, the batteries and the power management units needed for delivering electrical current to the different equipment and functional modules that need it. Preliminary sizing of the power subsystem needs to take into account the most demanding functionalities and the different scenarios during lifetime. Among the most demanding functions in terms of power it should be noted the payload, the TM&TC transmission and the thermal regulation. The robotic manipulator is probably also demanding significant power during assembly operations, but at the same time during this phase the payload module is probably off. Three main scenarios are identified as sizing in terms of power: transfer orbit, assembly and observation mode. Transfer orbit Assembly operation Observation mode Payload OFF OFF ON (full power) DHS TM&TC ON ON ON Thermal regulation ON ON ON Robotic manipulator OFF ON OFF According to the previous qualitative analysis, the sizing scenario for the solar arrays would be the observation mode, with the payload working at full power and sporadic opportunities for TM&TC link with the ground. This phase occurs with the satellite already in L2, which guarantees that the solar panels can be kept with constant sun incidence and without eclipses. On the other hand, during transfer phase the spacecraft is not necessarily pointing the sun and there are eclipse occurrences driving the need of a certain capacity on the batteries. The design process should start with the analysis of the total surface of solar arrays derived from the maximum power needed on the most demanding scenario. There is an important design choice to be made about how to implement this total surface with the actual hardware. From a qualitative point of view there is an interest in having the solar panels as small and stiff as possible, in order to minimize the perturbations that would introduce on the payload due to its flexible modes. A first recommendation would be to implement three small panels rather than two big ones. Trade-off (guideline) #11 – Solar panels size Minimize size of each solar panel. Trade-off status Pending detailed design of space vehicle. Justification Implement three smaller solar panels rather than two bigger ones. Smaller solar panels benefit pointing stability because of less severe flexible modes. Table 5-9 - Trade-off #11 – Solar panels size. A second recommendation would be to avoid the implementation of a mechanism for orientatio...
Power Subsystem. The Power Subsystem supplies DC power to the bus and the communications payload. Prime DC power will be obtained from solar arrays. Batteries will be used to supply power during the eclipse periods. As a minimum, the Power Subsystem shall provide the necessary electrical power to operate the communications payload receivers, transmitters and processors for the required duty cycles. During low voltage operations, the power subsystem will be designed to have load shedding capability such that appropriate portions of the payload will be dropped from the power system prior to the command and telemetry functions. Under very low voltage conditions, the satellite will be autonomously placed into a safe condition from which it will automatically recover if bus voltages rise. The power management system of the spacecraft shall only shut off the transmitters in an emergency situation. Full operation will be restored with ground intervention. Battery charge control shall be autonomous in accounting for changes in battery temperature and battery capacity over time. The battery charge control algorithm shall be designed to maximize battery life. Sufficient power system telemetry will be provided to permit the battery charge/discharge rate to be calculated on the ground to within [CONFIDENTIAL TREATMENT] accuracy. It shall be possible to power cycle each unit or subsystem on the spacecraft under ground command. All power system switches shall be ground-commandable.
Power Subsystem. 5-4 5.2.4 Structure Subsystem Acceptance Tests........................................................5-4 5.2.5 Thermal Subsystem...........................................................................5-4 5.2.6 Spacecraft Harness.........................................................................5-4 5.3
