Update README.md

README.md

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-# popper
+# Popper Directory
 
-Popper (2kgf) rocket engine design repo
+Popper is a small (2 kgf) RCS thruster designed to run H<sub>2</sub>O<sub>2</sub> monopropellant. It's small enough that it *should* be testable in Gerry's backyard (he offered).
+
+## Design Considerations
+- small scale engine (2 kgf) reaction control thruster
+- uses catalyst and 85%+ H<sub>2</sub>O<sub>2</sub>
+- simple On/Off valving = not variable thrust throttle
+- can be used as 1 off or combined into *thruster pack* (TP) of 4/5 engines and control valves
+- millisecond reaction time(?)
+- threaed top to screw into threaded base of TP block
+- simple to (commercially) 3D print in metal
+- temperature probe(?)
+- pressure probe(?)
+
+## Design Documents
+
+## Code Files
+
+## Discussion files