Asterius' ACS propulsion system is a monopropellant (hydrazine) system that will operate as the guidance and attitude control for the whole spacecraft. The ACS propulsion system is located on the SOM, but will draw from fuel sources located on both the OOM and the SOM modules. The system will draw from the OOM's toroidal tank during all space maneuvers, and will subsequently draw from the teardrop-shaped monopropellant tank on the SOM for attitude operations when the lander is descending to the surface of Europa. The ACS propulsion system will also operate similar to the bipropellant system, with a pressure down system having diaphragms located in the fuel tanks in order to isolate the pressurant from the fuel [2]. It should be noted that both monopropellant tanks are linked, and fuel can be transferred between them in an emergency situation or if fuel redistribution/conservation is needed. The ACS propulsion system is equipped with redundant flow control and its helium pressurant is regulated [2]. As mentioned earlier in the report, all liquid fuel tanks will be equipped with baffles to prevent center of mass excursions due to slosh effects.
The system consists of 16 Olin MR-111 thrusters (this is the dual
redundant configuration) to be used in the roles of attitude control,
orbit maintenance, torque unloading, and low 
burns [3, p. 639]. The thrusters possess Moog valves and are
capable of delivering a maximum of 4.4 N of thrust each (nominal) with
a total of 420,000 pulses [2]. The ACS propulsion system
will be allotted 170.02 kg of fuel and will be stored in the toroidal
and teardrop tanks. The thrusters have an average specific impulse
of 221 s, and each has a total operating time of 15 hours.