Modeling of RORSAT NaK droplets for the MASTER 2005 upgrade

Sixteen nuclear powered RORSATs launched between 1980 and 1988 activated a reactor core ejection system in sufficiently high orbits, mostly between 900 and 950 km altitude. The core ejection causes an opening of the primary coolant circuit. The liquid coolant consists of eutectic sodium-potassium alloy (NaK) and has been released into space during these core ejections. The NaK coolant has been forming droplets up to a diameter of 5.67 cm. The primary coolant circuit of the reactor contains 13 kg NaK-78. NaK releases are restricted to a very narrow region near 65∘ inclination. They contributed to the space debris environment in the centimeter and millimeter size regime. NaK droplets have been modeled before in ESA's MASTER Debris and meteoroid environment model. The approach is currently revised for the MASTER 2005 upgrade. The new NaK modeling approach considers a directional release of the droplets. The release is modeled with low additional velocities of about 15 m/s. The additional velocities are mainly a function of the pressure difference over the orifice. The outflow is considered as a discrete event for each of the 16 core ejections in total. Results of orbit propagation simulation runs are presented in terms of spatial density.