Development of a Cold Gas Propulsion System for the ... - SSL - MIT

ut also on a per-volume basis. This is important because propellant volume is limited on the TALARIS
hopper; tanks must have certain dimensions to fit on the structure with the many components of the
other subsystems of the vehicle. But regardless of whether mass or volume were the limiting factor on
how much propellant TALARIS could carry, hydrogen peroxide would be able to provide more total
impulse than most candidate cold gas propellants.
System components
A cold gas propulsion system is composed of relatively few types of components: propellant tanks,
valves for filling the system and relieving excess pressure, plumbing (feed line tubes and possibly filters),
a pressure regulator (though this is not used in a blowdown system), and thrusters with control valves
and nozzles. A monopropellant hydrogen peroxide system can be built from these same types of
components, with a few additions. The main addition would be catalyst beds, to start the exothermic
decomposition of hydrogen peroxide to water and oxygen. These may be made relatively simply from
stacked screens of silver wire mesh [29]. A separate pressurant tank and regulator might also be added
if a regulated system were desired, but the effects of maintaining a constant thruster inlet pressure are
substantially less noticeable for a monopropellant system than for a cold gas system, since the
exothermic decomposition of a monopropellant generally has a much greater effect on the thruster
chamber pressure than the initial pressure of the propellant. As a result, regulated monopropellant
systems are generally thought to have unnecessary complexity and cost, and blowdown monopropellant
systems are far more common [24]. Overall, a blowdown hydrogen peroxide system would not require
many more components than a cold gas propulsion system, though size, mass, materials, etc. of
analogous components would likely vary between the two types of systems.
Phase of propellant
Though the liquid phase of hydrogen peroxide has certain benefits as discussed in the Impulse section, it
also has drawbacks. One challenge is ensuring proper propellant flow; since TALARIS is designed to
operate on Earth, it could have a gravity-fed system, but this would require that the propellant tank be
located above the thrusters, which would add additional constraints to the already difficult problem of
placing all required components on the vehicle. Also, liquid hydrogen peroxide would be subject to
slosh, which could not only complicate tank drainage but also add undesirable dynamics to the entire
TALARIS vehicle. These effects could be mitigated with an appropriate propellant tank, perhaps including
baffles or a diaphragm, but this would add complexity to the system design.
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