Model of Intertank 1, the pressure regulation section of Subscale
Design
I created the following Plumbing and Instrumentation Diagram (P&ID) which is spacially accurate to the real plumbing.
The diagram has proven very useful for assembly as it displays the names of every line and fitting.
FFS is divided up into four sections, Pressurant, Pneumatics, Fuel, and LOX. The Pressurant section includes the Composite Overwrapped Pressure Vessel (COPV) which holds GN2 at 4500 PSI. It also includes two primary dome loaded regulators which feed into the tanks and they are set by a series of hand loaded regulators. The Pneumatics section is down regulated from the pressurant section and it feeds into several solenoids which are used to actuate our pneumatically piloted valves. The Fuel and LOX sections hold the propellants, and the LOX section is rated for cryogenic temperatures.
YJSP Subscale Vehicle Propulsion Block Diagram of Realistic Assembly
I created a calculator to size our COPV's volume. The calculator uses the volume and pressures of every section (Pressurant, Fuel, LOX) and it calculates the COPV volume
needed to hold enough moles at 4500 PSI to reach our end of life pressure (EOL). The calculator accounts for GN2's compressibility factor at 4500 PSI.
And it uses a conservative collapse factor of 2.5 for the LOX section. To do the calcuation I use an altered form of PV=nRT derived by Hermsen who alters Sutton's original equation.
Build
We built, assembled, LOX cleaned, and reassembled FFS inorder to be ready to Static Fire.
Before we can launch, we need to fully characterize FFS so that all the timings, pressures, and issues can be figured out before we utilize dangerous propellants.
I devised a number of tests we needed to complete in order to fulfill all of our objectives and aquire data for FFS. Those tests inculde Water Flows, COPV Fill, and Cryo Flows.
For these tests I created Test Readiness Reviews (TRRs) to outline my test objectives and procedures to safely gather useful data.
I also created a calculator which uses the discharge coefficient equation to solve for our target injector pressures based on desired mass flow rates. The calculator takes our engine and injector values and solves for the pressure differential across our injector. It also accounts for feed system pressure drop from tanks to injector to solve for tank pressures and it calculates the fill volume required for any flow duration.
Another useful calculator I created is used after testing to correlate our Water Flow and Cryo Flow data to our actual propellants. This calculator uses the Darcy-Weisbach equation to solve for pressure drop for Kerosene and LOX using the known pressure drops of water and liquid nitrogen. As seen in the spreadsheet, when converting our pressure drop data for both water and LN2 we get about 20 PSI for LOX in both cases.
