  An unexpected space debris population has been detected in 2004 Schildknecht
et al. (2003, 2004) with the unique properties of a very high area-to-mass
ratio (HAMR) Schildknecht et al. (2005a). Ever since it has been tried to
investigate the dynamical properties of those objects further. The orbits of
those objects are heavily perturbed by the effect of direct radiation pressure.
Unknown attitude motion complicates orbit prediction. The area-to-mass ratio of
the objects seems to be not stable over time. Only sparse optical data is
available for those objects in drift orbits. The current work uses optical
observations of five HAMR objects, observed over several years and investigates
the variation of their area-to-mass ratio and orbital parameters. A normalized
orbit determination setup has been established and validated with two low and
two of the high ratio objects, to ensure, that comparable orbits over longer
time spans are determined even with sparse optical data.
