Marlon E. Sorge

Orbital Debris Hazard Assessment Methodologies for Satellite Constellations

The expected proliferation of satellite constellations in the near future will tax the space environment in several ways. The many steps used to assess hazards posed to or by a satellite constellation are illustrated. Two categories of environmental impacts are examined: the effects of the constellations on the space debris environment and the effects of the environment on the satellite constellations. Issues such as intersatellite collision hazards for both controlled and uncontrolled spacecraft, intrasatellite constellation collision hazard (collision risks between members of a constellation ), and collision risk between constellation members and the cataloged and uncataloged space population are included. Additional analysis of compliance issues with national space policy, voluntary national debris mitigation guidelines, and international concerns are also addressed.

SOME TECHNICAL ISSUES OF AN OPTICALLY FOCUSED SMALL SPACE DEBRIS TRACKING AND CATALOGING SYSTEM

Congressional language in the 1998 US Senate Armed Services Committee authorization bill directed ‘... the Secretary of the (United States) Air Force to undertake a design study of a system that could catalog and track debris down to one centimeter in size out to 1000 kilometer in altitude.’ The US Air Force Research Laboratory, in conjunction with other US National Laboratories and the National Aeronautics and Space Administration (NASA) conducted a study that examined what technical systems and operations would be required to perform such a mission. This paper outlines the study process, details the findings, draws conclusions, and makes recommendations as to what would be needed to develop an optically based system capable of cataloging and tracking small debris in low Earth orbit.

Rapid orbital characterization of local area space objects utilizing image-differencing techniques

Satellites have limited awareness of nearby objects that might pose a collision hazard. Small, relatively inexpensive onboard optical local area sensors have been proposed as a means of providing additional awareness. However, such sensors often have limited performance. Proposed are methods to increase the Local Area Awareness provided by such sensors by means of classical and novel image processing techniques. The local area of the sensor platform is defined, for our purposes, as a sphere of radius 500 km surrounding the sensor platform, or observing satellite. This analysis utilizes image differencing-based techniques, in the development of a detection algorithm and proposes a novel objectvelocity classifier. This classifier may provide a means of rapidly distinguishing local area objects that pose a possible collision hazard when an orbital two-line element set is not available. Derivation of a novel classifier is based on the speed of the projected object moving across the focal plane array of the detector. This technique relies on the assumption that detection from the sensor platform allows for tracking of the object over all times the object is within the local area of the sensor platform. This alternative to intensity-based, signalto- noise ratio detection methods is performed by exploiting the stellar background as a reference from a space-based observing satellite. Results presented in this paper further demonstrate the ability of the proposed classifier to provide a means of rapidly distinguishing objects that pose a possible hazard within the local area of the sensor platform. These preliminary results act to substantiate this claim and therefore lay out a pathway for relevant and meaningful future work in the area of Local Area Awareness for satellites.

Effect of the Semi-Synchronous Orbit Protected Region on the MEO Debris Environment (Invited)

A protected region about semi-synchronous orbit (SSO) is included in United States (U.S.) Government orbital debris mitigation policy. SSO is the mission orbit of the U.S. Global Positioning System (GPS) in medium Earth orbit (MEO). In contrast, international debris mitigation guidelines do not contain protected regions about any MEO navigation constellations. A study was performed to assess the effect of the U.S. SSO protected region on the future MEO debris environment. The study used a simulation process developed by The Aerospace Corporation (Aerospace) called the Aerospace Debris Environment Projection Tool (ADEPT). The study results indicate that the primary mitigation effect of the SSO protected region is not in keeping objects out of the SSO protected region itself, but rather in reducing usage of long-term stable MEO storage disposal orbits. While the U.S. SSO protected region indirectly reduces collisional debris in MEO from U.S. satellites and rocket bodies, the reduction is small compared to the amount of collisional debris resulting from non-U.S. usage of long-term stable MEO storage disposal orbits. Reducing world-wide usage of long-term stable MEO storage disposal orbits and configuring MEO constellation disposal orbits to decay via Sun-Moon perturbations may be more effective approaches at reducing MEO debris risk than the U.S. SSO protected region.

Sensor model for space-based local area sensing of debris

A model is being developed to evaluate the capabilities of various LWIR sensors and combinations of sensors to provide Local Area Awareness for satellites in low-Earth and geostationary orbit. The model being developed will be used to evaluate the system performance of LWIR detectors mounted at various locations on the satellite against multiple observation scenarios with multiple debris configurations. LWIR sensors have been chosen as the detector technology for the initial phase of research because of their ability to operate with the sun in their field of view (FOV) while imaging nearby debris in the long-wave infrared band without the need for additive components such as baffles or solar occluders. This report describes progress on the development of this model. Preliminary results demonstrate the modeling of debris and its LWIR signature for each simulated orbital path. Results are presented in terms of radiant flux of the tracked debris. Radiant flux results are shown for all times the observed debris can be seen by the observing satellite or sensor platform. These results are evaluated for each face, or side, of the observed debris, as well as a composite of all faces. It is shown that intensity-based detection and characterization techniques may be quantified from this research, based on the different emissivities and temperatures of certain space debris materials. The results presented in this report are of simulated debris in the local are of a GEO based sensing platform.

Fengyun-1C Orbital Debris Cloud Short-Term Risk Analysis

The breakup of the Fengyun-1C satellite resulted in the generation of an orbital debris cloud containing a large number of fragments that pose a collision risk to operating satellites. This paper presents an analysis of the risk posed by the Fengyun-1C debris cloud during its short-term evolution period to several sample groups of satellites. Scatter plots of risk and time profiles of flux and cumulative risk for selected satellites are shown. Results indicate that debris cloud short-term risk varied significantly across the satellites considered. I. Introduction T he breakup of the Fengyun-1C (FY-1C) satellite resulted in the generation of an orbital debris cloud containing a large number of fragments that pose a collision risk to operating satellites. The highest potential risk per unit time was posed during the short-term evolution of the debris cloud. During this period of time, the fragments had not yet uniformly spread around the debris cloud parent orbit, and the local spatial density of fragments was highest. The debris cloud was highly dynamic, and the risk posed to individual satellites was determined by the timing and geometry of penetration of the debris cloud by those satellites. This paper presents results of an analysis of the risk posed by the FY-1C debris cloud during its short-term evolution period. For the purpose of this analysis, the short-term period covers the first seven days after breakup. The risk to several sample groups of satellites is presented. Time profiles of flux and cumulative risk for selected satellites are shown. Both absolute risk (raw collision probability) and relative risk are shown. The relative risk is defined as the ratio of the absolute risk posed by the debris cloud fragments to the absolute risk posed by pre-event background objects in the same size range and over the same time interval.