High-profile intergalactic projects such as Elon Musk's Space X and Sir Richard Branson's Virgin Galactic have helped bring space travel (read: space commerce) to the mainstream.

But they're hardly the only private ventures pursuing ambitious ideas in space. Here are four companies currently trying to tame the final frontier. And one guy who thinks they can go farther.

Planetary Resources, Inc.

Eric Anderson and Peter Diamandis co-founded Planetary Resources, an extra-terrestrial mining company that harnesses natural resources from astroids floating in space. Though the frozen chunks of space rock contain valuable materials like platinum and precious metals, the most important resource the company aims to extract is a basic one: water.

"You can process [water] to create fuel and oxygen," says John Spencer, space architect and president of the Space Tourism Society. He explains that by building the technology and framework for processing resources in space, extra-orbital energy companies like Planetary Resources could dramatically reduce the expense--in time, money, and Earth resources--of sustaining life in deep space. Which would be great news for entrepreneurs hoping to capitalize on tourism possibilities.

Spencer's not the only one to take notice of Planetary Resources' potential in the burgeoning space economy. Last month, the space mining company announced a partnership with Bechtel, the largest engineering firm in the United States, to accomplish its long-term goal of mining near-Earth asteroids.

Space Adventures, Ltd.

Yet another collaboration between Diamandis and Anderson, Space Adventures is a space tourism company founded in 1998. It claims the distinction of being the "only company to have sent private citizens to space," and has sent nearly a dozen wealthy tourists--seats cost as much as $51 million--to the International Space Station using the Russian Soyuz spacecraft to date.

In 2015, the company plans to launch its first commercial lunar flyby, offering two citizens the opportunity to circle around the moon. The first seat was sold to an anonymous customer in 2011, but the second remains open--for $150 million.

Bigelow Aerospace

Robert Bigelow--a native of the resort-centric Las Vegas, Nevada--had an innovative idea: bring the hospitality industry to space. Founded in 1999, Bigelow Aerospace aims to be the first commercial hotel in space. While this may, at first blush, sound like little more than a pipe dream, the company has already launched two successful prototypes--both of which are still in orbit. 

The residential vessels are inflatable, making them significantly larger than traditional space station quarters and Bigelow has stated that while he would be happy to sell the units outright, leasing will be the most affordable option. For a little over $51 million, Bigelow's website states, spacegoers can book a flight and 2-month stay at the 110 cubic meter Alpha Station, which is still in development. Bigelow is also selling the naming rights. Advertisers can pay $25 million to attach their brand's name to the station--but only for one year at a time.

The Next Frontier

John Spencer, president of the Space Tourism Society, says that ad sponsorships, like Bigelow selling the naming rights to Alpha Station, is the future for space commerce. 

"The media loves really big prestigious events," he says. "Space is very prestigious--even sexy." Being the first company to launch a commercial space station, or provide transportation in and out of orbit is attention-grabbing, he says. And brands will pay for that attention, if Redbull's sponsorship of space skydiver Felix Baumgartner is any example.

Perhaps not surprisingly, Spencer believes that possibilities of space tourism are expanding daily. He hopes to eventually establish off-planet sporting events--think a Formula One-style race of manned rovers on the moon's surface--which could provide additional advertising options for Earth companies. Another area ripe for growth, in Spencer's opinion: the service industry.

"How do you cook a five-star meal in zero gravity?" asks Spencer. "How do you serve it and how do you clean up afterwards? How do people have sex? How do people live and enjoy their lives in space?"

The clever businessmen who can answer those questions, he says, will be the future of the space tourism industry.