**Abstract**

Microsatellite has been considered as disruptive technologies in satellite engineering. Its development cost and time provide advantages for new kind of Earth observations, telecommunications, and science missions. The increasing trend of microsatellite launches and operations means that the approach was so successful that it could create funding sustainability. Major contributing factors of its success were due to the system design of the microsatellites. This chapter discusses two microsatellite system design approaches, namely Technical University of Berlin heritage and University of Surrey heritage. Both Universities provide approaches for system design and build of microsatellite systems. The design approaches are being compared along with lessons learned. The choices of microsatellites to be compared in this chapter will be those that are manufactured about the same time such that the technology compared is mostly the same and flown in-orbit. The chapter shows that the differences between the two system design approaches are on the choice of main computer and associated link configuration and in the attitude control modes. Another major different is in the satellites' structure design. For some satellite's components, incoming technologies have made the design choices from the two schools of thoughts converged.

**Keywords:** satellite design, system design, microsatellites, TU Berlin, University of Surrey

## **1. Introduction**

Microsatellite has typical weight between 20 and 170 kg at launch as auxiliary payload. It is initially made as technology experiment and education tools by universities. Nowadays, microsatellite becomes a common space platform for commercials and emerging space nations. The commercial mission is typically Earth observation, data collecting platform (text-based communication), including ships and aircraft tracking. Studies done by Swartout [1] show that between 2009 and 2012, about 8–12 satellites with mass above 50 kg as auxiliary payload were launched yearly. The data also show that the trend seems to be steady. Bunchen and De Pasquale [2] noted that 105 satellites with mass of 11–50 kg were launched between 2000 and 2013.

Surrey Space Technology Limited (SSTL), a subsidiary company under University of Surrey, is one of the companies that initiated the use microsatellite technology as commercial Earth observation satellite platform. It built a constellation of five satellites named Disaster Monitoring Constellation (DMC) in 2003, with payload of 3-band multispectral imager of 30-m resolution, which was intended for wide-swath land coverage imaging. After the first constellations decommissioned, it built the second generation with better resolution (20 m). The first launch of DMC-2 constellation was done in 2009 [3].

Since 2013, Skybox/Skysat has deployed 15 satellites that carry 1-m panchromatic imager and 2-m 4-band multispectral imager [4]. Unlike DMC, which mission objectives are to observe wide areas with nadir pointing scanning mode, it aims to provide frequent repeat very high resolution images using massive numbers of highly maneuverable satellites. Another commercial Earth observation microsatellite constellation mission is prepared by Axelspace. The company planned to have 50 satellites launched starting 2017. The satellite carries imager with 2.5-m panchromatic and 5-m multispectral [5, 6]. **Figure 1** shows the configurations of the Skybox and Grus satellites, which show that Skybox uses single lens and parabolic data downlink antenna, while Grus uses two lenses and horn-type data downlink antenna.

In addition to Earth observation missions, microsatellite constellation also being built for Low Earth Orbit (LEO) telecommunication mission. OneWeb and Telesat are two companies that will launch hundreds of microsatellites in coming years [7, 8].

The use of microsatellites for commercial purposes means that the technology is mature enough to ensure good return-of-investment. One of the major aspects that contribute to the success of microsatellite technology is its system design. Therefore, the objective of this chapter is to provide insight into microsatellite system design. The chapter addresses the question related to limitation in weight and size, and how the satellite designer manages to meet the mission requirements.

Out of many microsatellites developers, two system designs of microsatellites, namely Technical University (TU) Berlin heritage and University of Surrey heritage, are selected for comparison in this chapter, due to their very different design approaches. To be comparable, the choices of microsatellite system to be compared are the ones that manufactured about the same time, so that the technology available is mostly the same. The microsatellites also have to have in-orbit experience, so its design success can be measured. Data mining resulted that the satellite operation year chosen is between 1999 and to date. For TU Berlin system, the choices are DLR-TUBSAT, MAROC-TUBSAT, Indonesian LAPAN-TUBSAT, LAPAN-ORARI, and LAPAN-IPB. Meanwhile, for University of Surrey system, the choices are Korean KITSAT-3, STSat-1 and STSat-3, as well as Turkish BILSAT-1 and RASAT.

**Figure 1.** *Google Skybox satellite and Axelspace's Gruz satellite design.*

*System Designs of Microsatellites: A Review of Two Schools of Thoughts DOI: http://dx.doi.org/10.5772/intechopen.92659*

This chapter is divided into five sections, with the first section introducing the background and objectives of the chapter. The second section explains how the satellite design samples for the University of Surrey heritage were selected, and what satellite design parameters were used in the comparison. Section 3 displays the satellite design parameters for TU Berlin heritage. Section 4 provides analysis from the comparison of the two-design heritage, in term of parameters noted in the previous two sections. Section 5 summarizes the analysis and provides recommendation for further studies regarding the subject.
