Today's Space Geek Moment
So now that I'm reaching my middle years, I'm supposed to join a lot of professional organizations and become a contributing member of society or something, right? Well, in my case, I joined the AIAA (go to the web site if you want to know what the acronym is for--I spend all day translating acronyms, and quite frankly, I'm tired). Once a month, the organization has a guest speaker of some sort. Today's guest speaker was Al Reisz, an Apollo-era engineer who formed his own company in 1974. He's also a regular supporter of NSS, so we've met at several space conferences and related space-geek things. Reisz was there to talk about a new form of electromagnetic space propulsion his company has been developing in cooperation with NASA and the University of Michigan.
Reisz started by explaining the need for electromagnetic (EM) propulsion drives, mostly because they would be simple, reliable, long-life engines. Then described the two most common types of EM engines out there: the ion engine and the Hall effect engine. An ion engine uses a magnetic field to strip the electrons from a working fluid--the Deep Space One probe used xenon--and then accelerate the positively charged ions out the nozzle; the electrons are then reintroduced into the ion stream to keep the ions from reattaching themselves to the ship and essentially charging up the ship in unpleasant ways. The Hall effect engine uses a magnetic field to accelerate a plasma for thrust. In both cases, the propulsive force is created by very high-speed ions flowing out the back end of the "rocket," on the order of thousands of meters per second.
Sounds impressive, but the actual thrust is only hundreds of ounces, at best. On the plus side, ion thrusters can accelerate more or less continuously, as long as they have a working fuel available and as long as you're not in a huge rush to get something somewhere.
The engine Reisz and his team created under a NASA small business technology transfer program (SBTTR, yet another friggin' acronym) uses a hybrid approach to EM rockets. They started with an existing working fluid--right now, argon, but later on it would be deuterium-tritium or deuterium-helium-3--and inject it into a gas dynamic mirror chamber (no, I have no idea what that means). However, instead of using a magnetic field to strip away the electrons, the systems uses microwaves to bombard the propellant, then accelerates the ions with magnetic mirrors and solenoid magnets before ejecting the plasma out the nozzle. The end result of all this is that the plasma exits the thruster at anywhere from 1,000 to 5,000 meters per second.
What would you use such a thruster for? Reisz believes his system (called a microwave electrothermal thruster, or MET) could be used to place satellites into particular orbits or even allow military satellites to evade tracking. This last application is particularly important when we consider the demonstrated ability of the Chinese to shoot down satellites. But Reisz doesn't just have his sights set on local applications--he proposes using the MET to power deep-space probes into the Oort cloud.
A couple of interesting notes about the MET:
- The higher the speed of the plasma coming out, the lower the thrust, and vice versa. This is a function of specific impulse (also called ISP), which is essentially how much thrust you get for a given amount and flow of a particular propellant.
- It is an improved, long-life EM thruster.
- It has very high ISP.
- It has throttle-able ISP and thrust, with the limitations noted in the first point.
- Because of its variable settings, MET can be used for multiple applications.
I don't fully speak Geek, but I did ask what they would use to power this system. After all, in many aerospace systems, the engines themselves provide power for the overall vehicle after a small boost from some external source. In this case, the MET would use an external power source, anything from an RTG to nuclear fusion, to generate the microwaves it needs to ionize the propellant.
What's really interesting is how this small business grant has provided technology development for the private sector and educational opportunities for university students. That is something NASA used to do more often...here's hoping Obama gets some good advice and continues these types of programs.
Reisz closed by talking about the need for space technology development and how such development has enriched our lives. For instance, the world-changing adoption of integrated circuits by the Apollo program began the revolution in microelectronics and computers that we enjoy today. Reisz also mentioned the space program's discovery of hydrogen as a clean "wonder fuel," which is now getting greater attention as an alternative to petroleum. In short, investments in space are investments in our infrastructure. One hopes the president remembers that, too.