What is the Future Trend?
The amount of debris on orbit in the future will depend upon whether the creation or removal rate dominates. Currently, the only mechanism for removal of uncontrolled objects is orbital decay through atmospheric drag, which ultimately leads to reentry. This mechanism is only effective in a restricted range of low Earth orbits. At higher orbits, it takes hundreds to thousands of years for objects to reenter, so there is no effective removal mechanism. Historically, the creation rate of debris has outpaced the removal rate, leading to a net growth in the debris population in low Earth orbit at an average rate of approximately five percent per year.
A major contributor to the current debris population has been fragment generation via explosions. As the debris mitigation measure of passivation becomes more commonly practiced, it is expected that explosions will decrease in frequency. It may take a few decades for the practice to become implemented widely enough to reduce the explosion rate, which currently stands at about four per year.
Beginning in the late 1990s, many space operators began adopting practices to minimize space debris, and progress was clearly being made. The deliberate destruction of the FY-1C satellite by the Chinese, and the later collision of Iridium 33 and Cosmos 2251, undid a decade of progress in reducing the number of objects in orbit.
It is predicted that the main contributor to the future growth of the debris environment in LEO will be debris created by collisions. The most effective way to reduce this growth is through the reduction in the number of large objects (satellites and upper stages) left in orbit. Due to their large masses these objects become the major source of debris from collisions. One of the most cost-efficient ways to do this is through post-mission or end-of-life disposal. After the end of a mission the satellite or upper stage is moved into an orbit with a reduced lifetime. That orbit may allow the object to reenter the atmosphere within 25 years or it may reentry the object within the next orbit. Reducing the amount of time large objects are in orbit reduces the chance that they will be hit and produce more debris.
Because of the increased number of objects, lack of sufficient debris mitigation efforts such as collision avoidance could eventually result in collision-driven population growth. Various technical models for population growth have been developed by the international community. Most models agree that rapid population growth can occur in the absence of appropriate debris mitigation. They also agree that the population level required to trigger rapid growth in a given orbital region will be achieved before rapid growth is observed. In low Earth orbit (LEO), we are already at that level.