USE OF OPTICAL CHARACTERISTICS TO
IDENTIFY ORBITING MATERIAL
ROBERT D. CULP
, KIRA JORGENSEN
, IAN J. GRAVSETH
and JOHN V. LAMBERT
Colorado Center for Astrodynamics Research, Department of Aerospace Engineering Sciences,
University of Colorado, Boulder, CO 80309-0429, USA;
Ball Aerospace, 1600 Commerce Street, Boulder, CO 80301, USA (E-mail: firstname.lastname@example.org);
The Boeing Company, 1250 Academy Park Loop, Suite 130, Colorado Springs, CO 80910-3766, USA
(Received 3 May 1999; Accepted 24 January 2000)
Abstract. Knowledge of the observable properties of orbital debris is necessary to validate debris models
for both the low Earth orbit (LEO) and the geosynchronous Earth orbit (GEO). Current methods determine
the size and mass of orbital debris based on knowledge or assumption of the material type of the piece.
Improvement in the knowledge of material is the goal of the research described herein. The process of using
spectral absorption features to determine the material type is explored. A review of the optical measurements
of orbital debris as well as current research in the area is discussed. Reﬂectances of common spacecraft
materials are compared. The need for, and advances made possible by obtaining real data are explored. The
prospects of the venture are investigated.
Keywords: mass and size distributions, orbital debris, reﬂectance spectroscopy, space debris
assessment of the threat, future amounts of debris, and shielding requirements. Models, such
as EVOLVE and ORDEM96 both used by NASA, use the most current information in order
to determine threat of debris to orbiting spacecraft (Kessler et al., 1996). Quantities such as
optical brightness and spectral data, radar signatures, and atmospheric drag inferred from
orbital decay are observable parameters that aid in producing the most reliable information
on the characteristics of the orbiting objects.
From optical brightness, with an assumed albedo, one can determine an optical cross-
sectional area. This cross-section is adjusted for the phase angle and the atmospheric con-
ditions to obtain a physical cross-section or characteristic length of the pieces. Similarly,
the radar signal, adjusted for wavelength and transmission conditions, yields radar cross-
section. The radar cross-section is adjusted for assumed material properties to yield a phys-
ical cross-section and characteristic length. Finally, from the changing orbital elements of
tracked objects, an atmospheric drag is inferred, which leads to a ballistic coefﬁcient for the
object. By assuming the compactness and material density one arrives at a cross-sectional
area or characteristic length. These steps are designed to lead to the most useful properties
of the orbiting objects: size, mass, and perhaps even identity.
Author for correspondence (E-mail: email@example.com).
Space Debris 1, 113–125, 2000.
© 2000 Kluwer Academic Publishers. Printed in the Netherlands.