Propulsion systems as GUNNS fluid networks come in two main varieties:

1) cold gas jets, like the SAFER system on modern EVA suits.

• A high pressure tank of gas like N2 is fed thru valves to small jets.
• Low amounts of thrust.
• No combustion is involved.

2) liquid combustion rocket engines.

• Separate liquid fuel and oxidizer tanks and plumbing systems deliver these propellants to rocket engines of various sizes, where combustion takes place and large amounts of thrust is created.
• Engines may be pressure-fed straight from the tanks or there may be various turbomachinery to pump the propellant to the engines at higher pressure than the tanks.
• The tanks will be pressurized either by an inert gas like helium or from boil-off gas of the same propellant piped back to the tank from somewhere near the engine.
• The propellant may stay in liquid phase all the way into the engine combustion chamber or there may be phase changes along the way.

We are typically interested in fluid pressure, temperature, phase & flow rate at various points in the system, thrust created by the engines, heat exchange to/from the fluid, tank pressure, quantity & mass of propellant remaining in the tanks.

We probably wouldn’t use GUNNS to model a solid rocket motor since there’s no plumbing involved.

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