## 2 Space Debris--A Primer
### The Useful Objects
Furthermore, if one of these \"old school\" satellites is lost, you are really out of luck--your investment is gone. As an alternative to this situation, constellation satellites are much cheaper, can be built a lot quicker, and if you lose one, the loss is not as devastating [4]. Because of these and other considerations, satellite constellations are expected to result in, for example, improved internet access and communications in places that now have either slow internet or no internet at all (access will no longer be limited by fiber capacity), better assistance with disaster management (disaster mitigation managers require satellites with sensors that collect many different kinds of data), and assistance for astronomy-related studies without atmospheric interference (e.g., the BRITE/CANX-3 satellite-based research program, where on-orbit observation precision is more than 10X better than ground-based observations [5]). With specific regard to disaster management, in order to be able to effectively deal with the many different disaster scenarios that can occur and their causes, disaster mitigation managers require data that has been collected over a wide spectrum of wavebands. Agricultural droughts, which frequently occur in the absence of atmospheric moisture (also known as clouds), for example, require optical and near-infrared data; however, tracking a hurricane and monitoring flooded areas beneath clouds require microwave sensors. Landslide studies, on the other hand, require accurate high-resolution digital terrain models that are created using stereo-viewing optical sensors, interferometric synthetic aperture radars, and light detection instruments, while the study of fires and volcanoes requires thermal imaging sensors. Clearly, then, to be as effective and efficient as possible, disaster mitigation managers and their teams need satellites that are built with sensors with the ability to collect data across their entire electromagnetic spectrum. This can only be accomplished by a satellite system or constellation with a suite of sensors [6]. From this discussion, it is evident that satellite constellations can surely benefit society in many ways, but the hope is that the companies who are launching all these satellites to achieve all these lofty goals have employed scientists and engineers that are really good at math and physics. They must, for example, ensure that their satellites not only stay out of each other's way, but also do not interfere with other already resident and fully functional space objects. As a result, a potentially seriously deleterious effect of launching all these satellites is that there will be a tremendous increase in the number of close approaches (CAs) that NORAD will have to monitor and report back to satellite owners. Using current threshold \begin{table}
\begin{tabular}{c c} \hline \hline
**Satellite Purpose** & **Percentage** \\ \hline Communications & 63 \\ \hline Earth Observation & 22 \\ \hline Navigation/GPS & 4 \\ \hline Technology Development & 8 \\ \hline Earth and Space Science & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Most common uses of satellites currently in Earth orbit. values, more than 25,000 warnings are expected to be issued each day, which must all be reviewed and adjudicated by the satellite operators that receive them [7]. This, in turn, could lead to an overall five-fold increase in the probability of an on-orbit collision [8]. Complicating matters is the effect of space weather on NORAD's ability to accurately determine satellite and debris trajectories, which makes conjunction analysis exceedingly difficult. The launching of such \"mega-constellations\" will only complicate matters, of course, and has made clear the need to include the effects of space weather in satellite and debris trajectory modeling and CA calculations [9; 10]. Figure 1 below depicts a satellite-filled sky that is now a reality and getting more and more crowded every day.