Hello, I am designing a small hydrogen peroxide rocket engine. Hydrogen peroxide will be pumped into a combustion chamber where there will be a catalyst (manganese dioxide in this case) that will convert the peroxide into steam and oxygen. These byproducts will then exit through a nozzle. I am designing the engine to put out 35 newtons of thrust for 20 seconds, and use up .4 liters of 85%-90% pure hydrogen peroxide (all of these numbers are approximate). The combustion chamber is about 4cm long, and 2cm in diameter. The nozzle has about a .45cm throat diameter and a .75cm exit diameter. I am trying to figure out what the pressure in this engine will be, among other things. I need to know how much pressure the pump should supply to push the peroxide into the chamber. I found a calculator online, located here, that is telling me the pump needs to supply 20 bar of pressure (=2000 kPa). Unfortunately, this kind of pressure seems impossible for a pump at this scale, and that's not to mention that it needs to pump .4 L in 20 seconds. But, I am also optimistic that this pressure value might be dead wrong, because this calculator was designed for larger hydrogen peroxide engines. So, can someone help me determine what the pressure inside the engine will be? I don't have much experience with situations like this where the fluid is moving. Thanks!