7.3.3 Deep Space Propulsion System

The OOM is essentially Asterius' fuel tank and the location where all major deep space $\Delta V$ maneuvers will be carried out. The module is equipped with two Kaiser-Marquardt R-4D engines operated from a bipropellant system (nitrogen tetroxide & hydrazine). Each engine has a maximum gimbal angle of about 7 , and only one engine will function at any given time, while the other is held in reserve [2]. For the largest $\Delta V$ maneuver occurring at the capture by Jupiter, it is possible to burn both engines simultaneously to cut the braking time (firing time of each engine) in half; however, such use of such a joint-burn is questionable from the standpoint of thermal regulation. The bipropellant system implements a pressure down, helium-regulated system that will provide isolated pressurization to both the fuel (hydrazine) and oxidizer (nitrogen tetroxide). This is accomplished by the use of rubber diaphragms located in each of the tanks, which will serve to prevent cross-contamination between the propellants and the helium pressurant. This isolated pressure system will also aid in preventing vapor condensation problems in the feed lines [2]. The bipropellant system will perform such tasks as high thrust/$\Delta V$maneuvers, orbit insertion, momentum unloading (braking), and orbit maintenance/circularization burns [3, p. 639].

The Kaiser Marquardt R-4D engine is capable of producing a maximum thrust of 490 N in a vacuum and is well suited to decelerating/accelerating Asterius gently. Currently the engine(s) will only be fired for minor attitude/maintenance corrections while on the way to Jupiter and then will see the bulk of their service in the capture phase at Jupiter. The total braking role at Jupiter is calculated at a total firing time of 4.39 hours due to one engine and 2.20 hours if both engines are used simultaneously. The bipropellant system is equipped with quad redundant pyrovalves and the pressure/flow control system is also multiple redundant. The whole pressure/flow regulation system is constructed from stainless steel and consists of two separated closed systems: one for oxidizer and one for fuel [2].