Finally, the potential development of new, reusable space transportation may have off-setting benefits for satellite population growth, while the emergence of new conventional launch vehicles by additional entrants in space transportation activities may be important. Spent intact rocket bodies and payloads are also considered as debris. Orbital debris is of importance since it is a threat to all space missions and operational payloads, including the planned International Space Station and Shuttle missions. Orbital debris is uncontrolled and can only be measured and tracked to a limited extent - insufficient for risk analyses and predictions. Therefore verified and continuously updated models are needed.
Fragmentations are the primary source for debris which are too large to be shielded against.
At the same time only a small percentage of the fragments are big enough to be tracked. Therefore special attention has to be paid at the modeling of this debris source. The last major update was performed in 1989, prior to the last solar cycle. Now a longer history can be analyzed. A basic requirement for the evaluation of the collision risk posed to other spacecraft by Orbital debris is the accurate assessment of the number of objects of a given mass or size as a function of altitude and inclination.