## 5 Other Topics
### Integrated vs. Independent System  
The deorbiting device can be conceived of as an integrated or an independent subsystem of the spacecraft. In the first case, the satellite provides all the basic functions like attitude determination and control, communication, power and so on. This is the most common situation and provides generally the simplest, cheapest and lightweight solution. However, this option requires the satellite to stay alive and working up to the end of the mission, maybe not completely functional regarding the payload or other non-strictly necessary capabilities, but still capable of operating the deorbit correctly.  
Approximately, the probability of the satellite to perform a successful re-entry is the product of the reliability of the deorbiting device/maneuver multiplied by the probability of the satellite to survive up to the end of the deorbit, which, as expected in general, in case the active part of the deorbiting is short compared to satellite lifetime, it is mainly related with the satellite surviving up to the decommissioning date. Some solutions can be considered inherently more reliable, for example a chemical propulsion system provides a short and thus less risky deorbit compared with a tether or an electric thruster, and a passive drag sail will also have a short active phase. For the reasons just highlighted, if the satellite has an average predicted lifetime with a certain uncertainty, it is necessary to end the mission and deorbit the satellite prematurely if a high success rate is sought, based on statistical analysis. The higher the lifetime uncertainty and the target success rate, the shorter will be the mandatory decommissioning time limit compared with the real average satellite lifetime.  
One possible means to improve the effectiveness of this solution is to exploit the live monitoring and prediction of the satellite health. Thanks to modern artificial intelligence (AI) capabilities, it will be likely possible in the future to better assess the probability of failure of a specific spacecraft based on the story of its own health data compared with other similar assets. This could be particularly effective for large constellations of equal satellites.  
In the opposite direction, an alternative solution is to equip the satellite with a fully autonomous deorbiting device that can be activated and operated successfully independently from the satellite, giving the possibility to wait until the satellite is dead. This could be particularly interesting for large systems with very long lifetimes that make huge profits for every (relatively small but absolutely massive) increase in operational time, and thus do not want to be prematurely decommissioned. This kind of system has been proposed, for example, by D-Orbit [52]. The issues of this solution are mainly two. The first drawback is the duplication of several satellite functions, which will bring added costs and weight. This is particularly true for small platforms, while probably much less of a deal for larger ones(D-Orbit claims an added mass of few percent for a large GEO telecom sat). The second, very demanding challenge, is to fully guarantee the deorbit of a non-functional satellite in all (or almost all) the situations, particularly regarding damaged and or uncontrolled systems that have lost their attitude and are tumbling.  
It is also possible that for some type of deorbiting devices a sort of intermediate solution is possible, where the main satellite can lose a significant but not complete part of its functions and still deorbit safely.