# A Survey on Satellite Communication System Security
## 5 Defense in Satellite Communication Systems
### Solutions for Availability
The boost phase involves intercepting the missile shortly after its launch while the engines are still active. The mid-course phase targets the missile when it is in space during the period of its trajectory where it is not powered and is in free flight. Finally, the terminal phase occurs when the missile re-enters the Earth's atmosphere and is nearing its target, which is the last opportunity for interception. Given that ASAT threats would have already intercepted satellites during the mid-course or terminal phases, our focus should be solely on systems capable of intercepting these threats during the boost phase. In the context of boost phase missile defense, \"early intercepts are best\". Destroying a ballistic missile during its boost phase is considered the optimal approach in missile defense as it prevents the missile from deploying countermeasures and stops the warhead from gaining the velocity needed to reach its target [93]. However, intercepting a missile during this phase, while it is still ascending and fighting against Earth's gravity, presents significant challenges. Firstly, the boost phase lasts for only a brief period, requiring rapid detection and transmission of precise information about the missile's launch. Secondly, to successfully intercept the missile during this phase, the defensive interceptor must either be positioned very close to the launch site or be capable of extremely high speeds to catch up with the accelerating missile. Current technological advancements are playing a significant role in potentially making boost phase defense more viable. Innovations in sensor technology, like gallium-nitride-based radar, could reduce the timeline for detecting a boosting ballistic missile. Furthermore, advancements in infrared sensor performance and image processing, as well as the declining costs of satellite manufacturing and launch, are also contributing to the feasibility of boost-phase defense. Directed energy technology, particularly lasers, is another area being explored for boost-phase defense. Russia has developed a laser platform called the Beriev A-60 for anti-ballistic missile purposes, a project that dates back to the Soviet era. Furthermore, Russia has been a forerunner in laser weapon technology, reportedly deploying laser systems for missile interception purposes in March 2018. This deployment indicates Russia's significant advancements in directed energy weapons, particularly in the context of missile defense [94]. Figure 15: Illustration of ASAT defense methods. The United States has developed a high-energy-laser-based weapon system called the High-Energy Liquid Laser Area Defense System (HELLADS). This system is designed to defend against surface-to-air threats such as rockets, artillery, mortars, and surface-to-air missiles. The HELADS program aims to create a 150-kilowatt laser system that can counter these threats effectively. The core aspect of this system is its miniaturization, allowing it to be mounted on aircraft for the purpose of intercepting ballistic missiles during their boost phase [46].