Power systems

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Craig S. Clark, Alejandro Lopez Mazarias Clyde Space Ltd., 6.01 Kelvin Campus, West of Scotland Science Park, Glasgow G20 0SP Scotland, Email: craig.clark@clyde-space.com

ABSTRACT For the last few decades, the focus of power subsystem development and advancement has revolved around the needs and requirements of large, high power missions,mainly for telecommunications applications. Whereas the challenges to increase efficiency and to reduce mass and volume in these applications are valid, the needs of the small satellite mission have often been over shadowed. The growing number and utility value of small satellites highlights the need for careful and measured consideration for the specific power requirements on small satellitemissions. The challenge for mission designers and, in this context, small satellite power system specialists, is to produce an efficient and flexible design that avoids the need for system redesign with each set of mission requirements. This paper sets out the various challenges facing small satellite mission designers and evaluates common power system architectures against an innovative approach topower management for small satellites. 1. INTRODUCTION

power system electronics to be compatible with a multitude of mission profiles and be scalable in power handling capability. In addition, mission designers are consistently vying for a reduction in mass and more flexibility and modularity in the spacecraft make-up. Some spacecraft manufacturers are even investigating plug and play smallsatellite kits for fast response missions. At Clyde Space, we are developing power systems capable of meeting these demanding requirements but with a focus on cost effectiveness as well as performance. This paper outlines the systems under development at Clyde Space and compares their performance against the current systems used on today’s small satellites. Clyde Space are based in Glasgow, Scotlandand offer cost-effective, off-the-shelf and tailored small satellite power management systems, solar arrays and batteries. Our team has extensive industry experience having worked on over 25 small satellites. Clyde Space is Glasgow’s first indigenous space company and is proud to carry on the Scottish tradition of innovative, reliable engineering. 2. COMMON POWER SYSTEM APPROACHES

From a powersystems perspective, it is relatively safe to say that power challenges and requirements are common across the full spectrum of small satellite missions. Small satellites can have a range of power requirements from as little as a watt or two, to a few kilo watts. Despite this extensive range of power requirements, a typical mission will be launched into a low Earth orbit and the majority will havefixed solar arrays that encounter varying solar illumination characteristics across a typical orbit. Most will also experience frequent eclipse periods. For spacecraft within this category, there is a definitive need to have a flexible solar array interface that can adapt to the changing solar array characteristics whilst at the same time providing the ability to perform a fast recharge of thespacecraft secondary battery system. With the growing utility value of small satellites, primes are looking to produce multiple missions for either constellations of small satellites or through the use of a reusable small satellite platform. There is a need for the

In this paper we will evaluate the three most common power system implementation approaches found on today’s small satellites. Thesepower systems are as follows: Direct Energy Transfer (DET) with Battery Bus. DET with Regulated Bus. Maximum Power Point Tracker with Battery Bus.

The following sections describe the operation of each of the above systems. 2.1. Direct Energy Transfer (DET) with Battery Bus One of the most simple power system configurations, this topology is often selected for its mass advantages. The system is...