Why do we use liquid hydrogen propellant?
Liquid hydrogen is used as a rocket propellant because it has the highest efficiency relative to the amount used over any other known propellant. In combination with an oxidiser like liquid oxygen, it’s light and extremely powerful, burning at over 3,000 degrees Celsius. However, there were significant challenges and hazards to using liquid hydrogen when it was being developed in the 1960s. Both liquid hydrogen and liquid oxygen are cryogenic gases, meaning they only phase change to liquid at an extremely low temperature. Liquid hydrogen needs to be stored at -252 degrees Celsius and carefully insulated from all sources of heat to prevent it from boiling off and stop it expanding and exploding the propellant tank. Liquid hydrogen can also seep through tiny cracks between welds in the tank, so some very technical engineering must be employed to create a rocket capable of safely using this kind of propellant.
HOW ARE MARBLES MADE?
The oldest marbles were handmade by rolling clay, carving ivory or grinding stone. Glass marbles can also be made by hand in a process that resembles making seaside rock. Molten coloured glass is rolled into rods and stacked together to form a pattern. The glass is then cut with special scissors while still soft and the sections are rolled into balls. Mass-produced marbles use multiple nozzles to combine streams of liquid glass that are cut into even-sized lumps and passed between two parallel rotating screw threads. As
