Good space science comes from unexpected quarters. When I interviewed the Jet Propulsion Laboratory’s James Lesh about his thinking on communicating with a probe around Alpha Centauri, he pointed out how much can be gained by simply studying the signal sent by a spacecraft. Here in the Solar System, we’ve seen how that signal is affected by passing through a planetary atmosphere as the vehicle moves behind a distant world, an event that tells us much about the atmosphere in question. So in many cases it’s not just the data carried by the communications signal, but how that signal behaves, that tells the tale.

Can we imagine something similar around Alpha Centauri? Lesh envisaged a 20-watt laser communications system sending data from a sophisticated probe. But a new paper takes a different approach, imagining a fast probe moving at relativistic speeds, one that would announce its arrival in the Centauri system and create effects that could be studied from Earth. At 10 ounces, such a probe wouldn’t carry instrumentation (at least, not until our nanotechnology becomes more sophisticated), but it would be the first manmade object ever to reach another star, and it might teach us valuable lessons about the art of starflight.

The authors, Wade Hobbs Jr. (a researcher at the Library of Congress) and Daniel Junker, a spaceflight consultant in Arlington VA, presented this work at the Fourth International Symposium on Beamed Energy Propulsion in Nara, Japan. Much of their effort is devoted to assessing the parameters of the journey in relation to the power of the laser that would drive it. They propose a matrix of laser beams on Earth’s surface, a further reduction in cost over previous beamed energy concepts for space-based lasers. Such a system would allow the probe, the duo calculates, to reach the Centauri stars in between five and ten years.

Confirming the probe’s arrival depends upon detecting the effects of this relativistic craft as it impacts the dust ring surrounding the Centauri system, looking for data anomalies via x-ray instruments like COAST (the Cambridge Optical Aperture Synthesis Telescope) or the Compton x-ray telescope. Other detection methods are also discussed, including tiny but forseeable laser options, or planned collisions between sequentially launched probes timed to coincide with their arrival in Centauri space, the latter perhaps more detectable from distant Earth.

Centauri Dreams‘ take: Lightweight probes bring back memories of Robert Forward’s ‘Starwisp’ mission, an unmanned, microwave-driven mesh a kilometer in diameter that would weigh no more than sixteen grams. Forward hoped to put microchips at each intersection in the mesh and push Starwisp with a 10-billion watt microwave beam, reaching Centauri in 21 years and beaming back images of the encounter. The idea fell apart when Geoffrey Landis demonstrated that the needed microwave power would simply turn the Starwisp mesh into slag, but it seemed a grand notion in its day.

The Junker/Hobbs probe, by sharp contrast, seems a flyable mission, a major question being whether it is worth our while to send a probe whose sole contribution to science would be in our measurements of its effects on the Centauri debris disk. The thinking here, though, is that there is another reason for such a probe.

The Tau Zero’s Foundation’s motto is ad astra incrementis, meaning we go to the stars one step at a time, hoping that each step is bigger than the last. More valuable than the science the probe could show us in the Centauri system is what we would learn from the first attempt to accelerate a craft to relativistic speeds. That this could be accomplished at much lower cost than previously believed puts such a mission into the realm of the forseeable. In other words, get something there, examine what you have learned in the attempt, and then build the next iteration, bigger and better.

Or perhaps better but not bigger. For we are advancing into an era when nanotechnology will make tiny probes that carry significant instrumentation possible. The Junker/Hobbs probe could be seen as a forerunner of equally small (and smaller) vehicles that sacrifice little in terms of the science they can do. It may be possible one day to send the kind of probe nanotech pioneer Robert Freitas talks about, a vehicle the size of a sewing needle capable of reaching its target and constructing a scientific base via assembler technologies on, say, a moon or asteroid in the Centauri system. Small may, in fact, be better when the speeds demanded are a significant fraction of light speed.

The paper is D. Junker and W. D. Hobbs, Jr., “Sending a Probe to Alpha Centauri on a Voyage of Five to Ten Years,” AIP Conference Proceedings Volume 830 (May 2, 2006), pp. 605-611 (abstract available here).