# Shock Initiation of a Satellite Tank under Debris Hypervelocity Impact
## 1 Introduction  
Collisions between space debris and satellite are likely to occur given the rapid increase in space debris. The average collision velocity can reach 10 km/s, which is classified as hypervelocity (velocity above 3 km/s) [1]. Liquid hydrazine is the commonly used propellant for satellites. The satellite tank filled with liquid hydrazine, which accounts for a large part of the total mass, is one of the most vulnerable components to debris impact. Tests and numerical simulations on the projectiles impacting liquid-filled tanks at hypervelocity have been carried out. There are mainly two kinds of failure mechanisms. One is that no chemical reaction occurs in the liquid, the tank suffers structural damage caused by the hydrodynamic ram. The other is that decomposition reaction occurs in reactive liquid, the generated heat leads to fire, explosion, and complete disintegration. Hydrodynamic ram caused by the hypervelocity impact has been the subject of many investigations. [PERSON] et al. (2001) performed a series of tests where an aluminum projectile with the diameter of 23.8 mm was shot into a steel shell filled with tributyl phosphate at velocities between 2 and 6 km/s [2]. He developed a non-dimensional model to predict shell growth and a fragmentation model to estimate shell breakup. In the same year, [PERSON] et al. conducted tests in which a projectile weighting 19.8 g waslaunched at velocities from 2.3 km/s to 4.1 km/s against a vessel filled with water [3]. According to the test conditions, a numerical simulation was conducted using an Eulerian shock physics hydrodynamic code, CTH, to predict the vessel damage. Both the test and simulation results indicated that as the impact velocity increased, the shock wave loading enhanced, and the overall damage become more serious. [PERSON] et al. (2003) carried out tests in which projectiles weighting 3.5 g and 7 g were accelerated to velocities between 1 and 3 km/s to impact tanks filled with water [4]. The movement of the projectiles, the growth of the cavity and the plastic deformation of the tank walls were recorded by a high-speed camera. The explosion of the reactive liquid in tanks under hypervelocity impact has also become the focus of many studies. In 1964, NASA Lewis Research Center conducted 40 hypervelocity impact tests [5]. In test 23, a 0.0625-inch-diameter steel projectile was shot into a titanium tank filled with liquid oxygen at the velocity of 5200 feet per second. A violent reaction continued until liquid oxygen was consumed. In test 38, the tank containing liquid hydrazine was penetrated by a 7/32-inch steel projectile at the velocity of 5800 feet per second. There were no details indicating that a chemical interaction had taken place. In 1991, White Sands Test Facility (WSTF) participated in a joint test program with NASA Hypervelocity Impact Research Laboratory (HIRL) to evaluate the initiation of nitromethane and liquid hydrazine [6]. In test HYP-10, they used an aluminum projectile with the diameter of 0.318 cm moving at the velocity of 6 km/s to impact a nitromethane-filled vessel. In test HYP-2, they used the same projectile moving at the velocity of 6.1 km/s to impact a vessel filled with liquid hydrazine. As a result, nitromethane and hydrazine did not detonate, a circular entry hole, bulge, and split were found on the vessels. In 1991, Science Applications International Corporation (SAIC) also performed a test in which a cylindrical projectile weighting 100 g was launched at the velocity of 5.0 km/s against a 100-mm-diameter spherical vessel full of liquid hydrazine [7]. Results indicated that some reaction occurred, but not enough evidence was gathered to confirm a detonation. [PERSON] and [PERSON] (1994) formulated the TITANK test to replicate the actual conditions on board Space Station [8]. The TITANK test in which the titanium tank filled with liquid hydrazine was impacted by a cylinder projectile at the velocity of 7.5 km/s was designed based on the simulation of SIN, TDL, and Zeus hydrocodes.