Net deployment and contact dynamics of capturing space debris objects

Abstract

Space debris poses a big threat to operational satellites which form a crucial infrastructure for society. According to the main source of information on space debris, the U.S. Space SurveillanceNetwork (SSN), more than 17 500 objects larger than 10 cmhave been catalogued as of February 2017. Among the total number of objects in orbit, only 1875 spacecraft are active, i.e., around 10% of the objects are operating in an environment where 90% of the other objects are space debris. Even more serious, space debris is a threat to astronauts. In March 2009, a five inch space debris object passed particularly close to the International Space Station (ISS). Fortunately, the alarmwas cleared 10 minutes<br/>later. Moreover, the collision of the satellites Cosmos 2251 and Iridium 33 in 2009 highlighted the threat by space debris, since it signaled a trend that the future space environment will be dominated by fragmentation debris generated via similar collisions, instead of explosions of rocket upper stages, which had formed the majority of space debris objects in the past. To mitigate the risk of collision and stabilize the space environment, active debris removal (ADR) is of great relevance. According to an analysis by NASA, five space debris objects need to be removed each year to stabilize the space environment starting from the year 2020.<br/>The objective of this research is to investigate the net capturing method for active space debris removal. To remove a debris object from its orbit, many capturing and removal methods have been proposed, such as using a robotic arm, a tethered space robot, or a harpoon system. Among the existing ADR methods, net capturing is regarded as one of the most promising capturing methods due to its multiple advantages. For example, it allows a large distance between a chaser satellite and a target, so that close rendezvous and docking are not mandatory. It is furthermore compatible to different sizes, shapes<br/>and orbits of space debris. Additionally, it is flexible, lightweight and cost efficient. Even though some research on net capturing has been performed, the dynamics of net deployment and debris capturing and the feasibility and reliability of capturing a tumbling target using a net are not fully understood. Based on the relevance of this problem and a review of the state-of-the-art of the scientific literature, the following research questions were formulated. These research questions are answered in this thesis.<br/>RQ1. Which levels of non-cooperativeness of space debris exist? Which are their<br/>associated capturing and/or removal methods and what is the role the net capturing method plays among all those methods?<br/>RQ2. What are the dynamic characteristics of the net capturing method?<br/>RQ3. How to reliably capture a tumbling and non-cooperative debris object using the net capturing method?<br/>To characterize the net capturing method among existing ADR methods and to address the strengths and weaknesses of the net capturing method, matrices with the advantages and drawbacks of the most relevant capturing and removal methods are developed. Space debris objects were divided into three main categories based on their properties, namely, non-operational satellites, rocket upper stages and fragments from collision or explosion. A tailored associated capturing and removal method for each category of space debris objects is provided to facilitate decision-making through these ADR methods. A comparison of the most relevant ADR methods concludes that net capturing<br/>is considered as a promising method among others due to its multiple advantages. It is also found that capturing a tumbling space debris object with unknown physical properties is still facing many technological challenges. Therefore, capturing of tumbling targets using a net needs to be further investigated. The net capture mechanism consists of four flying weights in each co