An Electrical Power System for CubeSats

Abstract

The advent of CubeSats has provided a platform for relatively low-budget programmes

to realise space missions. In South Africa, Stellenbosch University and

the Cape Peninsula University of Technology have impressive space programmes

and have been involved in numerous successful satellite launches. A number of

CubeSat projects are currently in progress and commercial-grade Attitude Determination

and Control Systems (ADCS), and communications modules, are being

developed by the respective universities. The development of a CubeSat-compatible

Electrical Power System remains absent, and would be beneficial to future satellite

activity here in South Africa.

In this thesis, some fundamental aspects of electronic design for space applications

is looked at, including but not limited to radiation e↵ects on MOSFET devices;

this poses one of the greatest challenges to space-based power systems. To this

extent, the di↵erent radiation-induced e↵ects and their implications are looked at,

and mitigation strategies are discussed.

A review of current commercial modules is performed and their design and performance

evaluated. A few shortcomings of current systems are noted and corresponding

design changes are suggested; in some instances these changes add complexity,

but they are shown to introduce appreciable system reliability.

A single Li-Ion cell configuration is proposed that uses a 3.7 V nominal bus voltage.

Individual battery charge regulation introduces minor inefficiencies, but allows

isolation of cells from the pack in the case of cell failure or degradation. A further

advantage is the possibility for multiple energy storage media on the same power

bus, allowing for EPS-related technology demonstrations, with an assurance of minimum

system capabilities.

The design of each subsystem is discussed and its respective failure modes identified.

A limited number of single points of failure are noted and the mitigation strategies

taken are discussed. An initial hardware prototype is developed that is used to

test and characterise system performance. Although a few minor modifications are

needed, the overall system is shown to function as designed and the concepts used

are proven.