Last week saw an enthralling yet poignant moment when NASA's space shuttle Discovery made several victory laps around Washington, D.C., piggyback on a 747 carrier plane.

The shuttle could not fly on its own power because it is essentially a 240,000-pound glider — not a "Star Wars" fighter. It will now become a museum piece alongside the space capsules of early manned exploration.

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During their 30-year history, the space shuttles traveled hundreds of millions of miles but didn't go very deep into space. That's because they were shuttles, meaning they shuttled astronauts back and forth to low-Earth orbit. Perhaps those altitudes will be reachable by a space elevator someday.

So, the burning question, as recently posed by Neil deGrasse Tyson, is: What's next for space exploration?

An electrical engineering professor, John D. Matthews, recently wrote in the Journal of the British Interplanetary Society that it's simply too expensive, politically risky and technologically daunting to extend human space exploration to the rest of the solar system. (I'd say maybe with the exception of Mars.)

Though it may be a naïve extrapolation, Matthews predicts that extraterrestrial civilizations are facing similar challenges as us.

Physics, at least as we know it, imposes strict barriers in time and space and energy resources for sending biological beings anywhere beyond the world that nurtured them. Furthermore it is a budget-buster for us or other civilizations facing growing pangs.

To be judicious with time and resources, Matthews envisions building an army of "exobots" to patrol the solar system and do numerous tasks, rather than launch human expeditions. They would be as ubiquitous in space as the 'droids in "Star Wars."

The exobots would be artificially intelligent, starting out with perhaps the cognitive abilities of a 4-year-old child, but capable of learning and self-replicating. (This idea can be traced back to mathematician John von Neumann and his legendary Von Neumann Machines.)

Unlike the Von Neumann machines, however, the exobots would be sociable. They would stay in contact with one another to share information and ultimately feed it back to a mega-archive on Earth. They might start out doing something as mundane as clearing out space debris from Earth's orbit, says Matthews.

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The exobots could also prowl near-Earth asteroids to determine their physical nature and to implant tracking beacons on those that threaten our planet. They could move on to intimately reconnoiter the outer solar system.

This offers an industry for supporting Republican presidential candidate Newt Gingrich's dream of colonists on the moon. Space settlers would build and launch the nanobots off the moon's surface. The moon provides a low escape velocity, abundant energy and plenty of raw materials for a 'bot assembly line, says Matthews.

This would logically evolve to dispatching exobots to nearby inhabitable extrasolar planets. To keep the payload weight low enough for an affordable interstellar journey, these machines would need to be reduced to the size of nanobots. Or perhaps even have a "mother" nanobot that makes an army or replicates upon arrival at the target star system.

Perhaps extraterrestrials have already done this and have "alienbots" perusing our solar system.

Now, imagine if one of our future exobots were to track and make contact with an alien robotic visitor, in an attempt to exchange data — which is their prime directive. In fact the alienbot may have protocols for how to interact with other artificial intelligences it encounters, but would be programmed to ignore and avoid humans. The 'bots would have more in common with each other than beings of flesh and blood.

Matthews speculates that perhaps this is how we might eventually become aware of intelligent life off the Earth — not through direct contact, but through the exchange of information between our robotic emissaries.

R2-D2, where are you?

Image credit: NASA