I just typed this title and my spell-checker highlighted the word “Micronautics”. Yes, it is not in the dictionary, however, I feel that it will be there eventually. How soon? It depends on our technological progress, but we surely need it as soon as possible.
The subject of micronautics was explored in sci-fi for a while. I remember one short story about a guy who carried a friendly nano-robot inside his body. The robot was scouting his blood vessels and cleaning them from all possible contaminants. Sometimes it entertained the fellow with insightful talks, until one day the host almost choked on a clam and good robot pushed the thing out of his airways. Sadly, the robot was too small, so it was lost in a spit.
“Being lost in a spit” is a pretty graphic descriptor of dimensions for a nano-vehicle. Comparing to our cars (trailer trucks for safer assumption) measured in meters, nano-vehicle would have similar dimensions in microns. Million times smaller in length than a car: what else could be worth an effort of such a fine contrivance if not a micro-space of a human body? When micronautics, i.e. capacity to navigate and operate in microspace will be developed as much, as modern aeronautics, our benefits from it will be immense. It will be a revolution of medicine: our bodies can be guarded from the threats of deceases from atherosclerosis to everything caused by bacteria and viruses, including AIDS and if necessary operated from within.
You just have to “swallow your doctor”, as Richard Feynman, great American physicist, once put it. Feynman was using the original idea of his graduate student, Albert Hibbs (see R. Feynman, There’s Plenty of Room on the Bottom, 1959). Of course, there is a plenty of room: not just blood-janitors, one day these things will be able to communicate with our brains and … in this case I just wonder if a freedom of free will is granted us by constitution: we may need another amendment. Just think about the possibilities: “swallow your math teacher”, “swallow your tax accountant”, “swallow your parole officer” … there will be no limits. Fortunately, we would hardly deal with this issue in the first half of this century: there is a plenty of technical problems to be solved first.
It took 100 years to conquer aerospace, how long it will take us to get used to operate in microspace? Probably it will take substantially less, considering the pace of technological progress. But how one can design an engine for micronautics, considering that the whole nano-vehicle must be from microns to few tens of microns in size? It is impossible to scale down any mechanical engine to such minuscule dimensions: change in physical and material properties will require quite different “mechanics”. In particular, a nano-vehicle should be driven with an engine made of very few moving parts. How that can be done?
Beamed-energy propulsion (BEP) is an answer. Most of currently developing applications of BEP are designed for space. BEP principle is this: energy is beamed to the vehicle from a separate (often remote) source. The vehicle collects the beam and converts its energy into mechanical motion. In space applications the most typical scenario would be powerful laser, which remotely drives a spacecraft with collecting optics (mirrors) and solid propellant. Mirrors will focus collected light on propellant, which will be explosively evaporated, acting like a burning rocket fuel only with much higher energy density. This process is called ablative laser propulsion: the engine of a spacecraft has no moving parts, but it produces energetic exhaust, and spacecraft is flying using rocket principle. It will work well in space, but what about a micro-space of a human body? Who needs a rocket inside blood vessels?
There will be no rockets, at nano-scales we can use other, less violent ways of propulsion. Aside from blood cells, which occupy 55% of blood volume, the medium for motion in blood is a liquid, 90% of which is water. The fastest means of motion in our blood employed by many bacteria is so-called flagellum, a helical appendage, which acts as a propeller. A similar element can be used in micro-robots. Magnetic field can penetrate human body without substantial losses. The simplest beam-powered nano-engine will be composed of a nano-circuit, in form of a solenoid or loop, which can rotate or wiggle under external magnetic field. With flagellum attached to the circuit, nano-robot can move in direction set by orientation of the field.
In 1959 Richard Feynman predicted that nano-doctors will be moving by means of electric motors, driven by external EM fields. Today, 50 years later, we have a choice of several approaches to the problem. For example, in 2002 at First International Symposium on Beamed Energy Propulsion (ISBEP) professors from Tokyo Tech University, Shiho and Yabe, have presented a possibility to drive nano-robots with x-ray lasers. The next, Sixth ISBEP will be held in November 2009 in Scottsdale, Arizona. As expected, the discussion on micronautics will be continued there.