Why does this engine require a rare gas (xenon) to operate, instead of something more common, and readily available in space, like Hydrogen??
Bear with me if this is a really basic question, but I wasn't one of those people who excelled in High School Chemistry; in fact I got myself permanently booted from Chem Lab for (accidentally) setting it on fire.
In 1984, Hughes Research Laboratories, a unit of Hughes Electronics Corporation, began investigating the use of xenon and found that it offered the highest thrust of all the inert, non-reactive gases. And, because it is an inert gas, it is neither corrosive nor explosive, and therefore does not pose a risk to the life of the satellite or a safety hazard to personnel loading the xenon propellant tanks.