I should have said I don’t think they are planing to develop a rocket engine based on the press release I’ve read. But then, it also doesn’t sound like they even have a concept design yet, so maybe they will just end up with a rocket engine if they actually want to go hypersonic.

I agree with you that the Reddit collective seemingly likes to hate the development of hydrogen technologies as though it somehow involves a conspiracy by the oil industry to continue burning fossil fuel. If it turns out that the technology is not competitive, economic, or environmentally friendly, it will eventually fail. But why hate the science and R&D if it’s in pursuit of bettering humanity?

Your second point about government funding isn’t quite correct however. The Spanish Centre for Technological Development and Innovation, CDTI, is a government agency that is providing 12 million Euro in R&D money.

Neither the aircraft manufacturer, nor the engine supplier are clear about the hypersonic engine the plan to build. It seems they’re still in the very early stages of R&D with plans to modify an existing jet engine to burn hydrogen at subsonic speeds. They also still need to design a cryogenic storage system for the liquid hydrogen. They are not using a rocket propellant.

This is not quite correct. Your formula is for potential energy. To calculate the power generated by a hydro power turbine, you need to use flow rate (l/s) or mass rate (kg/s), and include head loss and turbine efficiency.

Also, 1 cubic meter of water has a mass of 1000kg, not 50,000kg

You don’t exist. Just a bunch of tangled atoms!