NASA is Taking a Look at Ceres and Vista Using Xenon Ion Propulsion

Why would NASA want to spend our dollars of ever-diminishing-value to look at a couple of rocks in the Asteroid Belt?

Because they are there, of course.

DAWN

It is dawn here in Idaho as I write this piece and DAWN is the name of the mission to Ceres and Vista. To me, there are two fascinating aspects of Dawn. Firstly, once the module was delivered into space, the means of propulsion became an electric xenon gas ion engine. Secondly, the spacecraft will orbit each of the two asteroids.

The Xenon Ion Engine

Let's take what little I know about the engine first. Simply put (the only way I know how to put things), the fuel is the gas some of you have in your headlamps.

You know, xenon bulbs.

Xenon is a noble gas. That means it has one heck of a time reacting with other chemicals that it feels are inferior. It will react with the gas, fluorine, but xenon is rare and expensive and fluorine is a nasty gas to deal with--indeed.

NASA can afford xenon because so little is needed to propel a spacecraft. Gasoline is so puny.

Saying that, the atomic weight of Xenon is 131.394. If you compare that with oxygen gas, the ratio is 131.394 / 32 or 4.1. So you get 4.1 times as much punch from xenon than you would for oxygen--because xenon is heavier.

So how big is that punch? NASA says the force is about the weight of a piece of paper. On earth, that is not even a puff. However, space has little matter in it and is actually quite a good vacuum. In the vacuum of space, that is a significant punch. Besides, we engineers know how to make a wimpy puff into a whoosh. Role up a piece of paper and blow into the paper tube. Not much coming out of the other end, right? Now hold the tube about a half-inch from your mouth and blow again. WOW! The extra push comes from the extra air that was inspirited with your weak blow. (Actually, NASA is not doing this.)