Let’s face it.

When we think of how things are propelled into space, we consider big rocket engines.  But, as I learned long ago, they are not the most common processes, when we are dealing with satellites.

No, long ago, we elected to use ionic thrusters for those needs.  Whether it’s controlling the orbital position of satellites to sending missions to distant lands, we have elected for a completely different propellant.

These thrusters manage to produce big reactions to low propellant usage.  In other words, only a small amount of fuel is needed to get these satellites to “move along”.

Which really begs the question… What the heck is an ion thruster?   Basically, a high energy electron collides with a neutrally charged propellant atom, yielding a positively charged ion that continues releasing electrons into space.

Overall, with the release of both positive and negative ions, there is no overall electric charge to the emissions, called the plasma.  (While plasma (kind of like a fourth state of matter- as in solid, liquid, and gas) is related to a gas, it is subject to electric and magnetic fields.)

But, now it gets really interesting  We’ve been relying on Xenon, a “noble gas” that is easily ionized with a high atomic mass.  As such, it provides are reasonable amount of thrust, as the ions are produced. Moreover, since Xenon is a noble gas, it is considered to be inert; it also has a high storage density, so it is well-suited for being stored on a spacecraft.

As the positively charged ions are thrust out as an ion beam (at speeds approaching 90,000 mph!), these devices truly propel our satellites to distant lands.

But, NASA is still trying to refine and improve the system.  NEXT (NASA Evolutionary Xenon Thruster) is a high power, ion propulsion device that seems to provide thrice the power of existing systems. (It also can survive for some 6 years of operations, or about 50,000 hours!)

But, xenon, being a noble gas is expensive- and must be stored at very high pressures.  Cheaper alternatives are always being sought.

Which brings up Iodine.  As you can see, it is contiguous to Xenon on the Periodic Table.  But, more importantly, it can be stored as a solid!  Which means no pressurized storage would be needed.

But, how would iodine work?  (After all, it’s not a noble gas!)

A solid block of iodine is heated (iodine generally sublimes- which means it converts from a solid state directly to a gas) and then attacked with a slew of high speed electrons.  This allows the block of iodine to transmogrify into a plasma of iodine ions (and free electrons).  The hardware then forces to positively charged ions (iodine) towards the exhaust, propelling the spacecraft in the desired direction.

(As of now, it’s only been tested on a teeny 20 kg satellite, placed in orbit at some 480 km.  And, it functioned effectively for about four months.  No, wait- it outperformed the xenon ion thruster system! Except iodine does react with metals, so the propulsion system must be comprised of polymers and ceramics, which are far less reactive.  Moreover, it takes about 10 minutes for the solid block of iodine to become a plasma- so it may not be effective if an emergency maneuver is required!)

But, this could be a pretty good alternative.