Micronautics? Maybe you have heard this word before, but as I typed it in my word processor the spell-checker highlighted it right away. So it is not in the dictionary yet. It will be there one day. How soon this will happen? I guess it depends on our techno progress, but I am sure: we need it.
You may have read some sci-fi on micronautics. I did so about 40 years ago. It was a short story about a guy and his “doctor”, a micro-robot, who traveled inside guy’s blood vessels. Robot cleaned his coronaries and somehow communicated with his host on various subjects until one day the fellow choked on a mussel. The robot managed to push the mussel out of guys throat, but was lost with the 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.
Richard Feynman, great American physicist and Noble Prize winner once put the whole plot described above in a few words: “Swallow your doctor”. He was quoting Albert Hibbs, Feynmans graduate student, who actually came up with the idea (R. Feynman, Theres Plenty of Room on the Bottom, 1959). Yes, the room seems just immense. What if nano-robots will evolve from blood janitors into something that can establish a direct communication with our brains? Plugging into axons, sending an info, giving orders Swallowing your doctor, tax accountant, Spanish teacher, parole officer, Big Brother the possibilities go from marvelous to scary. Perhaps, freedom of will will need a constitutional protection at some point. Hopefully, not too soon, we still have an ocean of fundamental problems to solve before this will become an issue.
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 miniscule 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.
It is worth noting that 50 years ago Richard Feynman predicted that nano-doctors will be moved by electrical motors driven with an external EM field. There are other possibilities though, like x-ray beams, proposed by professors of Tokyo Tech University, Shiho and Yabe. Micronautics may still sound like sci-fi, but it is now a subject of physics and engineering. Among scientific meetings, where micronautics is discussed is International Symposium on Beamed Energy Propulsion (ISBEP). The Sixth ISBEP will be held in Scottsdale, Arizona in November 2009. Although the main scope of the conference will be application of BEP for space propulsion, some works on moving to micro-space are expected and will be very welcome there.
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