Why are space rockets difficult? They are large, but precise; are complex, but must be reliable. They are strong, but must be light. They must deal with extremes of temperature, pressure, vibration, and G forces. They embody knowledge of physics, chemistry, materials science, mathematics, control theory, engineering, aerodynamics, hydrodynamics, navigation, electronics... And if there's a human payload, all that that entails too.
@EdS Rocket science operates near the boundaries of constraints in numerous domains.
@EdS There were a few others I've seen that were unexpected; 'ullage' where your fuel doesn't go where you want; the other one were things like how do you run the pumps and other equipment on the rockets.
Also #rocketscience, how to fund, staff, organise a large organisation for a long time, how to manage a big project...
I've tried and failed to discover the G forces at play in the turbopumps, but we're probably talking 20,000 G.
Thermal management is a thing too: how to cool the hot things and heat the cold things where needed, how to keep the cold things cool.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko