Observation Means
Why do we need to observe space debris?
The space debris population is constantly increasing and it is important to be able to characterise it and its distribution. Small debris are observed statistically and this enables artificial environmental models to be produced, giving their debris flux. The larger debris can be observed individually using sensors, so that their trajectory can be calculated and the risk of collision and the risks in the event of atmospheric re-entry can be calculated.
How do we observe space debris?
To observe the population of space debris, there are both ground-based and on-board means. The ground-based means of observation are radar or telescopes, which able to track the trajectory of objects measuring about 10 centimetres in low orbit and about 1 meter in high orbit (MEO, GEO). On-board means can be used to characterise the density of small debris via the observation of impacts on surfaces exposed to the space environment. These can be dedicated detectors on-board satellites or the Space Station, or simply equipment in orbit recovered during orbital maintenance operations, such as the Hubble Space Telescope’s solar panels. These means can be either civil or military.
| Means | Operating Domain | Capability |
Ground Based Radar | Low Earth Orbits (altitudes below 2000 Km) | Detection of objets larger than 1 cm at 1000 Km Tracking of objects larger than 10 cm |
| Ground Based Telescope | Geostationary Orbit Geosynchronous or MEO orbits | Tracking of objects larger than 50 cm |
| On-board Sensors Post-flight Analysis | Dependent on the altitude of carrier satellite Orbite très basse pour matériels récupérés | Detection of objects of 1 to 10 mm |
Table 1.- Operating Domain and Capability of the Main Space Debris Observation Means
These ground-based and orbital means can thus enable two types of information to be acquired:
- Deterministic, precise information on objects larger than ~10 cm in low orbit and about ~1 m in high orbit
- Less reliable statistical information for very small objects
This tells us about the orbit of the object (position, velocity), its radar cross-section or its magnitude, which indicates its apparent size, or quite simply provides statistical data such as the number of impacts per unit of time and the energy of the impact.
An object is said to be catalogued if it has received an international designation (COSPAR number), an orbit and various characteristics (origin, dimensions, etc.) and if these data (e.g. orbit) are regularly updated.