Sunday, 23 September 2007

Science Sunday VII: Photonic Propulsion

If you're feeling a bit claustrophobic on our current earth-sphere, I have some good news: high-speed space travel just got a little bit more feasible.

The photon is a strange particle (or wave!) Though it has no mass, it can still impart momentum. When you turn on a light, the photons from it collide with you, and actually physically move you. It is not detectable to our senses, but every time photons hit us, they exert a force upon us. Shine a strong enough flashlight on a ball, and it will roll. This is known as radiation pressure (and FYI light is just a form of radiation.) With a strong source of light, such as the sun, and low gravity and friction, such as in the vacuum of space, radiation pressure is a viable means of transportation. This basic effect is the idea behind solar sails, and has already been used in unmanned spacecraft, such as Mariner 10. But that is all old hat.

It has been theoretically proposed that photons, in the form of lasers, can be amplified so that their thrust is greatly increased. In December of 2006, Dr. Young Bae did just that, by building (and publicly demonstrating) the world's first Photonic Laser Thruster (PLT), which amplifies photonic thrust by a factor of 3,000. Not bad for a proto-type. The demonstration paper will be published in the peer-reviewed journal American Institute of Aeronautics and Astronautics (AIAA), is titled Photonic Laser Propulsion: Proof-of-Concept Demonstration, and will be published later this year. Using several of these photonic thrusters together, spacecraft could achieve speeds of more than 100 km per second. This technology is not far-and-away, it is already present, and is being refined for more efficient use. With current technology, the trip to Mars would take six months. With PLT, it would take one week or less. Given that most of the hazards of interplanetary travel are risky precisely because of the length of the journey (radiation accumulation, bone deterioration, psychological stability), this just doesn't make interplanetary travel more comfortable, it makes it possible. There is still plenty of research and application to be done to be sure, but the deployment of these technologies will now be measured in years rather than generations.

A more practical application of PLT would be to maintain exact satellite formation - by exact, I mean staying within formation to a few nanometers, with the satellites spread out over kilometers. An immediate use of this kind of technology would be to form the next generation of telescope-like devices - satellite formations like this could scour the depths of the universe at many orders of magnitude greater detail than the Hubble telescope - we could detect black holes for the first time, see planets and stars never seen before, and indeed peer into the very origins of the universe. Considering the pictures from Hubble, think of what we could do with several orders of magnitude beyond this:

Of course these satellite formations wouldn't just take pretty pictures; more pragmatically, they would be able to search for rare minerals in asteroids, uncover precise details of our own solar system's planets and moons, and let us prioritize where our other efforts should focus.

And holy $hit, he's also made a lot of progress working on nuclear fusion engines and researching a freakin' matter-antimatter engine. What's next for this guy, an artificial quantum singularity engine?

I think the coolest part of this is that Dr. Bae is not a NASA scientist. He's just a really smart guy who loves to invent things, and started his own institute to do so. On his own, he built his amplified photonic thruster - the first in the world - with regular off-the-shelf products. It is becoming more and more clear that in the future it will be individuals and organizations that will lead the way in space exploration as much as it will be nation-states.

For a lengthy interview with Dr. Bae, check out this podcast of the somewhat quirky Space Show. The interview starts at 5:45.


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