Another reason why water has been cheaper is the logistics side of it. Water can be stored as a liquid, so there is no need to have pressure vessels. This lets launchpad logistics get simplified and get cheaper. One of the main pro for xenon is its performance. That is why typically people have gravitated towards that gas. The reason for that is xenon is the heaviest non-radioactive noble gas. Generally speaking, the heavier the mass the better performance. Another good trait for xenon is that it stores at higher density than other noble gases, allowing more punch in a packed spacecraft volume.
For us, the biggest factor is cost and not performance. We see that the industry is going for cheaper simpler solutions so space hardware can be more easily innovated upon, and launched into space. Old school aerospace focused on performance, due to the fact once the satellite was in space, it needed to work and perform due to how expensive it is to launch it in space.
However, due to the lowering of cost in space, our goal is to optimize mass manufacturing and cost. This is why we feel that water might be a great propellent solution to our problem.
So as you can tell one solution for one company does not make sense for another company. It depends on the goals.
Let me know if you have any questions and I will be free to answer them! Happy Hacking!
