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.
ANALYSIS: Never Send a Machine To Do a Human's Job
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.
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