Tracking of Orbital Debris and Avoidance of Satellite Collisions

Abstract

The issue of space debris has become one of increasing concern as the amount of orbital debris, sometimes known as “space junk,” has become more severe, especially in low Earth orbit and in the polar orbits used for communications, remote sensing, and meteorological sensing and forecasting. The Chinese missile shootdown of the defunct Fung-yen (FY-1C) weather satellite in 2007 and the collision of the Iridium and Cosmos satellites in 2009 have greatly heightened this concern. Increasingly sophisticated tracking systems have been implemented by the US Air Force Strategic Command, the European Space Agency, and several affiliated national tracking systems to cope with the complex space situational awareness (SSA) challenge that is now presented by rising amount of space debris. A new S-band radar “Space Fence” system and other optical tracking systems in Australia and other parts of the world are being implemented to cope with this task.

The new S-band Space Fence system that is currently being installed in the Kwajalein Atoll in the Pacific, in particular, will allow an increase in the tracking ability for space debris. This increased tracking ability will thus rise from about 23,000 debris elements that are 10 cm or larger (i.e., about the size of a baseball) in low Earth orbit to well over 200,000 elements that are greater than 1 cm in diameter (i.e., about the size of a marble) in low Earth orbit. The Space Data Association, which has been formed by commercial satellite operators, is also increasingly able to share information among themselves in order to minimize the possibility of collisions and to be aware of close satellite conjunctions in a timely manner. Their tracking capabilities are currently provided by a commercial capability operated by Analytic Graphics Inc. (AGI).

In addition new laws and national regulations as well as guidelines adopted by the Inter-Agency Space Debris Coordination Committee (IADC) and the UN Committee on the Peaceful Uses of Outer Space (COPUOS) to ensure that all satellites are deorbited within 25 years at the end of a spacecraft life represent another key step forward. There are clearly more steps that need to be taken to move toward better collision avoidance systems plus active deorbit and debris mitigation, especially of the largest debris elements from low Earth orbit. It is also key to ensure that the deployment of new large-scale constellations in low Earth orbit is accomplished with strict controls to minimize any new collisions that might occur within these constellations themselves or to avoid collision with defunct debris elements. The addition of constellations with perhaps a thousand small spacecraft or more in just one constellation has given rise to particular new concerns in this regard.

In addition, there needs to be (i) new and better international collaboration to strengthen all elements associated with the more precise tracking of debris in all Earth orbits; (ii) more control processes to prevent debris increase and avoid the formation of new debris elements, including the active deorbit of all launch systems after they have inserted spacecraft into orbit; (iii) better coordination of information among satellite system operators through such mechanisms as the Space Data Association as its membership and participation levels grow; and (iv) new technology and international agreements and perhaps commercial arrangements to incentivize the active deorbit of space debris in future years consistent with existing space treaties and international agreements.

This chapter addresses in some detail the various tracking capabilities that exist or are planned around the world to monitor the orbits of space debris and to provide alerts so as to avert possible conjunctions. It provides information about how these systems are being upgraded and space situational awareness (SSA) capabilities are being coordinated over time. It notes how governmental systems are being augmented by private capabilities that are able to augment space situational awareness and to assist with avoidance of collisions. These systems and processes will perhaps assist with future space debris mitigation and active removal. All of these increasing space situational awareness capabilities are crucial to the future successful operation of application satellites in the twenty-first century.