Optical technologies for observation of low Earth orbit objects
In order to avoid collisions with space debris, the near Earth orbit must be continuously scanned by 
either ground- or spaced-based facilities. For the low Earth orbit, radar telescopes are the workhorse 
for this task, especially due to their continuous availability. However, optical observation methods can 
deliver complementary information, especially towards high accuracy measurements. 
Passive-optical observations are inexpensive and can yield very precise information about the apparent 
position of the object in the sky via comparison with background stars. However, the object's distance 
from the observer is not readily accessible, which constitutes a major drawback of this approach for the 
precise calculation of the orbital elements. 
Two experimental methods have been devised to overcome this problem: Using two observatories a few 
kilometres apart, strictly simultaneous observations of the same object yield an accurate, instantaneous 
3D position determination through measurement of the parallax. If only one observatory is available, 
a pulsed laser can be used in addition to the passive-optical channel to measure the distance to the 
object, in a similar fashion as used by the satellite laser ranging community. However, compared to 
conventional laser ranging, a stronger laser and more elaborate tracking algorithms are necessary. The 
two approaches can also be combined by illuminating the object with a pulsed laser from one observatory 
and measuring the return times at both observatories. 
These techniques are explored by German Aerospace Center in Stuttgart using its orbital debris 
research observatory, in cooperation with the Satellite Laser Ranging station in Graz and the Geode- 
tic Observatory in Wettzell. This contribution will present some of the results and plans for further 
measurement campaigns.