62nd International Astronautical Congress, Cape Town, SA. Copyright ©2010 by the International Astronautical Federation. All rights reserved. IAC-11- A6,2,2,x10259 Page 1 of 5 IAC-11-A6,2,2,x10259 ANALYSIS OF CLOSE APPROACHES BETWEEN SMALL SATELLITES AND CATALOG OBJECTS Chen Shenyan Beihang University, China, chenshenyan@buaa.edu.cn Lin Zhiwei Beihang University, China, linzw1988@sa.buaa.edu.cn Tieyan Wang Beihang University, China, stardust202@sina.com Brian Weeden Secure World Foundation, United States, bweeden@swfound.org Small satellites have been widely applied in communication, remote sensing, astronomy, experiments and many other aspects of space activities. It can be anticipated that a large number of Ultra Low Mass (ULM) satellites (<15kg) will be launched to space in the next few decades, and these will become a potential source of orbital debris for lack of de-orbit capabilities. In this paper, the orbital distribution of current ULM satellites was investigated, which showed that all ULM satellites are in Low Earth Orbit (LEO) and most of them locate in Sun Synchronous Orbits (SSO) within the altitude band 600-900Km. The close approaches between all objects in the satellite catalog and ULM satellites against the satellite catalog were calculated based on data from the US Space Surveillance Network (SSN), which was taken as the baseline for comparison. Close approaches for different growth models of ULM satellites in their often used altitude band were tested, and the resulting collision probabilities were compared with the baseline scenario. The simulations were based on a conjunction algorithm and related collision rate estimation method presented by Wang Ting. The results of this study indicate that (1) the orbit concentration of future ULM satellites will have a large effect on the debris environment, and (2) the number of future ULM satellites which will be sent to heavily used SSO LEO altitudes should be regulated to reduce the collision risk to larger satellites. I. INTRODUCTION Recent advances in technology have made it possible to miniaturize many satellite components, and in turn reduce the size of functional satellite dramatically. Compared to historical satellites that are on the order of 1000 kg, micro-satellites typically weigh between 10 kg and 100 kg, nano-satellites are typically less than 10 kg, and pico-satellites are less than 1 kg. These classes of satellites are becoming increasingly popular for universities and other entities because of their small size, mass and low manufacturing and launch costs. In the past ten years, nearly 70 Ultra Low Mass (ULM) satellites (<15Kg) have been sent to orbit, most of which were deployed in Low Earth Orbit (LEO, defined as the region between altitudes of 200 and 2,000 km) (Brian, 2010). It can be anticipated that much more this level small satellites will be sent to space in the next few decades. Since ULM satellites are smaller in size and lower in mass than traditional satellites, they are difficult to track with existing space situational awareness capabilities and may not have de- orbit or maneuver capability. Therefore, it is unlikely that they can be moved to 25-year decay orbits or to LEO storage orbits (above 2,000km altitude) at the end of mission lifetimes, in accordance with existing space debris mitigation guidelines, which makes them a potential source of orbital debris. In cases with a high relative speed, collisions with debris larger than 10cm can seriously damage or destroy a satellite, which will then create large amount of fragments. The additional particles further increase the collision probability in the region, which leads a slow-motion chain reaction that could make some orbital regions unstable. The situation is called the Kessler syndrome predicted by Kessler and Cour- Palais (Kessler and Cour-Palais 1978, 2637–2646; Kessler 1991, 63–66). The 2009 collision of the Iridium 33 and the Cosmos 2251 signaled a beginning of this trend (Ting W. 2010, 87-118). To better preserve the near-Earth environment for future space generations, remediation measures, such as space traffic management (COSMIC 2006) and active debris removal (J.-C. Liou 2008, 236-243), have been considered besides space debris mitigation guidelines by United Nations and national space agencies (NASA Orbital Program Office 2007, 1). Space traffic management concepts have been presented and studied in the last decade which showed that conjunction assessment should be indispensable technical basis for collision risk estimation and collision warning (Johnson 2004, 803-809; ISU 2007; Haydar and Ilker 2009, 870-878). With the growth in the number of small satellites, the close approaches and collision rate