# Deep Learning Methods for Space Situational Awareness
## 1 Introduction
Thousands of satellites and 1500 rocket bodies provide considerable mass in LEO, which can break into debris upon collisions, explosions, or degradation in the harsh space environment. Fragmentations increase the cross-section of orbiting material and with it, the collision probability per time. Eventually, collisions could dominate on-orbit evolution, a situation called the Kessler Syndrome [24]. Figure 1: Different types of satellite orbits around the Earth. There is much debris or \"space junk\" in the near-Earth space environment that is large enough to threaten human spaceflights and robotic missions but too small to be tracked. The International Space Station (ISS) and other spacecraft with humans on board, due to the exponential growth of space debris, could be endangered. This debris population includes both natural meteoroids and man-made orbital debris. This debris population includes both natural meteoroids orbiting the sun, and man-made orbital debris, orbiting the Earth, called \"orbitals\". Orbital debris generally is any man-made object in Earth's orbit that no longer serves a useful function, such as non-functioning spacecraft, abandoned launch vehicle stages, mission-related debris, and fragmentation debris. They are constantly tracked, and more than 27,000 pieces have been detected so far. Since both debris and spacecraft travel at extremely high speeds (about 25,267 km/h), the impact of collision of even a tiny piece of orbital debris with a spacecraft could create serious and dramatic problems. There are half a million pieces of debris the size of a marble or larger (up to 0.01016 m, or 1 cm), and about 100 million pieces of debris about 0.001016 m (or one millimeter) and larger. There is also even smaller micrometer-sized debris (9.906 \(\times\) 10\({}^{-7}\) m in diameter) and about 23,000 pieces of debris larger than a softball orbiting the Earth. Even small flecks of paint can damage a spacecraft when traveling at these speeds. For example, many space shuttle windows have been replaced due to some damage caused by paint stains. Simulations of the long-term evolution of debris suggest that LEO is already in the protracted initial stages of the Kessler Syndrome but that this could be managed through active debris removal [25]. The addition of satellite mega-constellations and the general proliferation of low-cost satellites in LEO stresses the environment further [26; 27; 28]. Hence, decades of the world's space activities have left LEO cluttered with active satellites and littered with orbital debris. Recent reports [29; 30] estimate that there are about 28,210 debris objects regularly tracked by Space Surveillance Networks. While large commercial satellite constellations such as SpaceX's Starlink undeniably offer tremendous potential for the satellite industry, they inevitably increase the probability of mutual collisions among orbiting objects due to the inherently high number of satellites involved in large constellations. This poses a significant threat to the sustainability and safety of space operations that must be carefully and efficiently addressed. The operation of monitoring the space environment and resident space objects, knowing and characterizing space objects and their operational environment, is known as space situational awareness (SSA) [31]. SSA is a fundamental part of Space Domain Awareness (SDA), which represents the capacity of understanding the actual and expected working conditions in space. In more detail, SSA focuses on the problems related to (i) space object tracking, (ii) identification, (iii) determining their orbits, (iv) gaining knowledge about the scenario in which they are working, and (v) forecasting their upcoming positions and risks to their functioning (Figure 2). SSA is hence of fundamental importance to all space traffic management (STM) operations, and one of the fundamental aspects of SSA is to calculate and act in response to debris from fragmentation events, meteor storms, or other natural events that will be very dangerous for all the space systems.