The OOM is essentially Asterius' fuel tank and the location where all
major deep space 
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 
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/
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].