Just how plausible are Elon Musk's plans to send people to Mars by 2025? The SpaceX founder and CEO's bold claims have stirred up some controversy and despite the manufacturer's quick rise in the field, many think that his bold Mars colonization goals are simply not possible.

Back in November, astrophysicist Neil deGrasse Tyson suggested that those who believe that a private enterprise - such as SpaceX - could send people to Mars alone are deluding themselves.

"The delusion is thinking that SpaceX is going to lead the space frontier," he said. "That's just not going to happen, and it's not going to happen for three really good reasons: One, it is very expensive. Two, it is very dangerous to do it first. Three, there is essentially no return on that investment that you've put in for having done it first."

These reasons support the notion that interplanetary spaceflight is just too risky to make any sense as a private venture.

"A government has a much longer horizon over which it can make investments," Tyson said.

Despite some suggesting that Musk and SpaceX could pull off a mission to Mars without NASA support by utilizing cash raised from a SpaceX IPO, Musk doesn't seem to be planning anything like this anytime soon.

"When we're doing regular flights to Mars, that might be a good time to go public," he said. "But before then, because the long-term goals of SpaceX are really long term - it takes a long time to build a city on Mars - that doesn't match with the short-term time frame of public shareholders and portfolio managers that are looking at the two- to four-year time horizon."

Musk still claims to be able to send humans to Mars by 2025 if the money is available, but NASA doesn't plan to go to Mars and its moons by the 2030s. But does Musk really need to follow NASA's Mars timeline?

"These non-trivial resources allow an individual to shift their own paradigms to suit their whims independent of usual norms," said Keith Cowing of NASA Watch. "In Musk's case - that whim is the exploration of Mars. Deal with it, Neil."

Others, such as Mars Society's Robert Zubrin, claim that Musk has been planning on utilizing NASA involvement all along.

"Despite his public statements, Musk isn't going to fund humans to Mars out of his own pocket," he said. "But what he will do - is in fact already doing - is create the hardware set that will lower the cost threshold for sending humans to Mars so much that, sooner or later, a president will go for it. In that case, SpaceX will get the business - they will have earned it, and in any case, they'll be the only game in town."