# What are the Basics of CubeSat Power Supplies and Systems?

I am going to go ahead and apologize for my ignorance surrounding this topic, as my background is Aerodynamics, and not Electrical Engineering. From what I understand, CubeSats typically generate their power through the use of solar cells. My questions regarding CubeSat power are below:

1. How is this power distributed to run the various subsystems on the CubeSat?
2. Is the CubeSat power output from solar cells usually in a standardized form?
3. Are there standard connections used for the subsystems to tap into the CubeSat power supply?

It would probably be helpful for me to provide a little more background into what I am trying to accomplish. Ultimately, my team and I are designing an aerodynamic drag device that can be used for satellite collision avoidance in LEO. The goal is to provide a CubeSat operator with the capability act upon a collision warning should it be received, by sending a signal to their CubeSat to deploy our aerodynamic drag device, then retract that drag device once the collision risk has passed.

• Great question! There is precedent for smallsats in LEO using drag for orbital maneuvers but usually it's just the solar panels and over longish timescales. Note that for spacecraft aerodynamic forces in directions perpendicular to the velocity vector are often (but not always) referred to as "lift" no matter they be up, down or sideways. The key to reliable power is keeping some solar panels illuminated whenever possible, good batteries for roughly half of each orbit when in eclipse (Earth's shadow) and smart battery management software and tumble-recovery if they go to zero.
– uhoh
Jan 5 at 4:23

Most of the CubeSats have Electrical Power System (EPS) as a dedicated module on a single PC104 like PCB. Depending on the required capacity of the secondary (rechargeable) batteries, they can be housed on the same PCB or as additional modules.

Solar cell arrays, with bypass (required in case of cell shadowing and failures) and blocking (stopping from current flowing back into the cells and acts as a good protection against several failure modes) diodes are assembled in solar panel units that are electrically connected with EPS and thermally with the structure. Both of these connections needs to be well designed to avoid unnecessary power losses.

EPS contains Maximum Power Point Tracker (MPPT), which is a DC-DC converter with ability to adjust its load to the solar cells variable (dependent on the incident sunlight) current-voltage curve. Depending on the solar cells number in an array and whether they are connected in series or parallel, the output of the DC-DC needs to be upscaled or downscaled to match the batteries charging voltage needs. Battery charging, protection and disconnection circuits are usually present, as well as battery heather. Further, from batteries to the power distribution for the rest of the system, additional DC-DC converters are added, usually for 12V, 5V and 3.3V. Unregulated battery line is distributed in some cases. Sometimes, switches are integrated into the EPS to control dedicated power lines. A processing unit is often present to control the MPPT and the output DC-DC converters and switches, as well as for other housekeeping and telemetry needs. Additionally, EPS is in charge of powering up the system after the deployment from the launch vehicle, for which deployment switches and a delay timer are required. Sometimes, EPS also performs automatic deployment of antennas and deployable solar panels. Redundant components and submodules are common.

1. How is this power distributed to run the various subsystems on the CubeSat?

CubeSats (at least 1U to 3U) have scarce available volume and many designs opt for custom integrated interconnection buses and there is no single standardization on the power distribution. However, just as with the PC104 standard, majority of the modules are interconnected with stack connectors, through which some lines are dedicated for power distribution.

1. Is the CubeSat power output from solar cells usually in a standardized form?

No. Best strategy is to find a suitable parallel/serial connection configuration of solar cells individually for every solar panel. Sizes of solar panels on a single CubeSat can differ. Furthermore, scaling from 1U to 2U to 3U and larger provide different preferable configurations.

1. Are there standard connections used for the subsystems to tap into the CubeSat power supply?

Stack connectors, as in PC104 standard is the closest to a standardized connections you can get. This is often preferred by subsystem providers, but there are a lot of custom solutions.

Here you can find an overview of available solution by subsystem providers: https://blog.satsearch.co/2020-06-10-satellite-electrical-power-systems-eps-on-the-global-marketplace-for-space

• +1 for a thorough answer.
– uhoh
Jan 6 at 0:46