The Electrical Power System (EPS) is responsible for gathering power from solar panels, storing into batteries and distributing it for whole system. ESTCube-1 will probably have a sun synchronous polar orbit in such a way that it will be in eclipse during about 30% of the orbital period. Part of the captured solar energy must be kept in a battery in order to return it to the subsystems during the eclipse. EPS supplies a continuous source of electrical power to spacecraft payload during the mission. It has to control, distribute and regulate power for subsystems and to balance power requirements and generation during eclipse and sunphase.

Main electrical consumers of ESTCube-1 are:

• Attitude Determination and Control System (ADCS)
• Command and Data Handling System (CDHS)
• Communications System (COM)
• Electrical Power System (EPS)
• Payload (PL)

EPS provides command and telemetry capability of its health and status. EPS protects the whole system against transient bus voltages and Single Event Latchup. This phenomenon happens when a high energy particle hits the device. If the impact on the device is of a serious nature, the high energy particle can directly cause damage to the device. This phenomenon happens very quickly and must be detected and corrected in hardware. In case of the power not being turned on at a latch-up, a burn-out can occur and destroy the chip.

ˆRequirements

• Nominal length of 100 mm per side. Solar cell standard size is 40 mm by 80 mm
  and there are two cells per side
• Each single Cubesat may not exceed 1,33 kg mass. Estimated battery weight is 62 g
• No electrics shall be active during launch to prevent any electrical or RF interference with the launch vehicle and primary payloads. Satellite has two deployment switches to cut the power from electronics
• One deployment switch is required (two are recommended) for each Cubesat
• Developers who wish to perform testing and battery charging after integration must provide ground support equipment (GSE) that connects to the Cubesat through designated access portsˆ
• A remove-before-flight (RBF) pin is required to deactivate the Cubesats during integration outside the P-POD
• To allow adequate separation of Cubesats, antennas may be deployed 15 minutes after ejection from the P-POD (as detected by Cubesat deployment switches). Larger deployables such as booms and solar panels may be deployed 30 minutes after ejection from the P-POD.

Layout

There are two solar cells per side of the satellite that are connected serial and different sides are connected parallel to each other. There are five sides covered with solar cells. Two opposite sides have one dedicated active maximum power point tracking (MPPT) converter for higher efficiency and boost-converter for battery charging. Batteries voltage depend on MPPT structure in the range of 4,1 V or 8,2 V, the commercially available options are space grade Lithium-ion polymer (Li-Po) batteries from Clyde Space. If possible charge system and battery will be doubled for backup. Power Distribution Unit (PDU) can switch subsystems on in case of low power. Only one MPPT might be used for all solar panels because electronics may take too much volume.