Author: Parveen Bhardwaj (Author is an Aerospace Engineer and currently working with Institute of Defense Studies and Analyses.)
There are approximately 6% are operational spacecraft, 21% are old spacecraft, 17% are rocket upper stages, 13% are mission-related debris, and 43% are fragments from (mostly) explosions or collisions. In addition, there are a large number of smaller objects that are not routinely tracked, with estimates for the number of objects larger than 1 cm ranging from 100 000 to 200 000. An aluminum sphere 1.3 mm in diameter has damage potential similar to that of a .22-caliber long rifle bullet. An aluminum sphere 1 cm in diameter is comparable to a 400-lb safe traveling at 60 mph. So it becomes vital to trace down debris before launch so as to avoid damage while putting to orbit as well as during orbiting.
Some prominent methods used to detect debris:
Optical Telescope: A optical telescope is used to develop an orbital elements catalogue, i.e. without any a priori information. Two different orbital regions are surveyed: the geostationary ring (GEO) and the Medium Earth Orbit region (MEO). The aim of the surveys of the geostationary ring is coverage of as much as possible around the celestial equator we can observe from Zimmerwald. Surveys of the MEO region will give a first hint about the population of large-sized, un-catalogued space debris there.
Imaging Radar: Imaging Radar Alone, or jointly with the Max-Planck-Institute of Radio Astronomy’s 100 m telescope at Effelsberg in Germany (bi-static mode), snapshots typically of 24 hours duration can be taken of the current space-debris population to provide statistical information and rough orbit parameters for objects as small as 1 cm at altitude up to 1000 km. TIRA used in SSA and as organization is an example where information is provided about size and location of debris.
Working of RADAR: For space-object tracking, there is generally a priori information available, such as some orbital elements and the approximate size of the object (radar cross-section). The radar beam is pointed to a pre-determined position in space and after detection the object is tracked and observation vectors are collected, from which its orbital parameters and radar signature can be computed.
Creating Beam Park In this operating mode, the radar beam is maintained in a fixed direction with respect to the Earth and all objects that pass through the beam are registered. In the course of one day, the Earth’s rotation scans the beam through 360 deg in inertial space. From the backscattering of the radar signal, the size of the object and some of its orbital parameters can be determined. The FGAN radar is sensitive enough to detect 2 cm sized objects at a distance of 1000 km. This primarily statistical information on the small-size terrestrial debris population in the LEO (Low Earth Orbit) region can be used to validate space-debris models.
To increase ability and detection potentialof Beam Park, number of radar beam equipped observatories is required. From the experiments done on 25 December 1996 as COBEAM campaign where several countries took part such as Europe, Germany, operated by the Max-Planck-Institute of Radio Astronomy in Bonn, Haystack radar in the USA, and during the same week the TRADEX radar on Kwajalein, were also operated, This COBEAM campaign showed that the FGAN L-band radar can indeed detect 2 cm objects at 1000 km distance. When combined with the Effelsberg radio telescope as a secondary receiver, objects as small as 0.9 cm can be detected at the same distance.