The biggest hurdle to mounting an interstellar mission may be humanity's short attention span.

It'll take several decades of sustained, focused, coordinated and costly work to pull off a project such as Breakthrough Starshot, which plans to blast fleets of sail-equipped robotic nanocraft toward potentially life-supporting exoplanets at tremendous speeds using powerful, Earth-based lasers.

And our species doesn't exactly excel at taking the long view. [Breakthrough Starshot in Pictures: Laser-Sailing Nanocraft to Study Alien Planets]

"It took us a decade to go to the moon, and you could argue that that [relatively rapid pace] was largely because we had this — perceived at least — existential threat," Zac Manchester, a member of the Breakthrough Starshot advisory committee, said during the Breakthrough Discuss conference at Stanford University this past April. (That perceived threat, of course, was the Soviet Union, the United States' space-race rival.)

"That's the part that worries me: What's going to keep us motivated, and keep us kind of organized, and keep us pushing forward?" added Manchester, who's an assistant professor of aeronautics and astronautics at Stanford.

The Starshot project endeavors to launch its first craft within 30 years. If all goes according to plan, these bantam pioneers will get up-close looks at Proxima b, the possibly habitable planet that circles the sun's nearest star, the red dwarf Proxima Centauri. Other probes will target other nearby alien worlds in relatively short order thereafter.

The Starshot project is investing $100 million, provided by Russian-born billionaire Yuri Milner, in research and development over the next half decade to determine the feasibility of the laser-sailing plan. But full-on interstellar exploration will cost considerably more.

For example, the current "point design" suggests that it will take $8.4 billion in capital expenditures to build the huge laser-beaming apparatus, which will need to be at least 0.6 miles (1 kilometer) wide, Starshot team member Kevin Parkin said during a presentation at Breakthrough Discuss. (This price tag is far from set in stone, however; point designs are just starting points, Parkin stressed.)

For comparison, NASA's Apollo program cost about $25 billion over its lifetime, which is more than $100 billion in today's dollars.

Starshot's laser system will have to keep its beam trained on a Starshot nanocraft for about 9 minutes to accelerate the probe to 20 percent the speed of light, project team members have said. That'll be no mean feat, considering the sail will be just 13.8 feet (4.2 meters) or so wide. (The body of the spacecraft will be about the size of a postage stamp.)

Beaming the images and other data collected by the miniprobes home to Earth, which the Starshot team aims to do using the sail as an antenna, will be no walk in the park, either.

So there will be significant technical challenges to overcome, in addition to the economic, cultural and sociological concerns raised by Manchester. But interstellar exploration isn't supposed to be easy.

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