Only an imagination made of stone could fail to stir at the thought of a real-world USS Enterprise blasting away from Earth within 20 years, reaching Mars in three months and restoring a sense of epic grandeur to mankind's spacefaring dreams.

But is that vision, which went viral thanks to the detailed blueprints of an anonymous self-described engineer known only as BTE Dan, actually possible? Trillion-dollar price tag aside, could this 21st century interpretation of the Enterprise boldly go where no one has gone before?

Unfortunately not, say spacecraft designers, but it's still a worthwhile thought experiment.

"In summary: Cool idea, not very practical, extremely optimistic in assumptions for near-term developments," said John Elliott, flight system lead on NASA's Outer Planet Flagship Mission. "But if it gets people talking and thinking outside the box, it's not a bad thing."

With a faster-than-light warp drive remaining science fictional, BTE – "Build the Enterprise" – Dan's ship would be propelled by ion engines running off a 1.5 gigawatt nuclear reactor. That's roughly the amount of energy generated by a decent-sized terrestrial nuke plant, and harnessing its power in space would be hard.

"Reactors might be scalable to those high power levels, but the radiation shielding and heat rejection system would be a huge design challenge," said Elliott, who qualified his comments as a personal perspective rather than official NASA or Caltech views. "I'd hesitate to say it couldn't be done with sufficient resources, but it probably wouldn't end up looking like the original design."

Ion propulsion, in which charged atoms of gas are magnetically expelled through a tube, would also be difficult at Enterprise scales. Such engines already power many spacecraft, and currently reach speeds of 200,000 mph, but their acceleration is extremely slow.

NASA's website notes that the push provided by one modern ion thruster is "equivalent to the force you would feel by holding nine U.S. quarters in your hand." Though a bank of ion thrusters could eventually push the Enterprise's 200,000,000 pound bulk at high speed, it would take a long time to get there.

According to astronautics researcher Nicolas Lee of Stanford University, the Enterprise's iconic shape could be a hindrance. "If we wanted to build something that large, a sphere or cylinder would be better at holding pressure against the vacuum – think scuba tank or submarine," he said.

Lee also said the Enterprise's proposed gravity system – a giant spinning wheel magnetically suspended inside the ship's hull, producing gravity through centrifugal force – would cause steering problems.

"To get a sense of this effect, try taking an external hard drive and wobbling it around a bit while it's running," said Lee. "It tries to torque you in a perpendicular direction when you tip it." (On his website, BTE Dan says a second, counter-rotating wheel could solve the problem.)

A final challenge is the sheer amount of material required to build the Enterprise, which would need to be assembled in orbit rather than on Earth, where gravity would make liftoff impossible. Elliott said the quoted bulk would amount to 650 trips by NASA's new heavy launch vehicle.

For the cost of this endeavor it might actually be cheaper to envision using lunar resources or even mining and processing asteroids to get materials for construction," said Elliott.

"But there, as improbable and audacious as it seems, you see the value in scoping projects like this," he continued. "It makes you think, even if it's to say, 'That's a dumb idea, but maybe if we did this here and tweaked these assumptions here....' That often leads to valuable innovations in other, more near-term developments."