Last year, when Google and Fidelity invested $1 billion in Elon Musk's SpaceX, one of the company's earliest backers also wanted to get in on the latest round of funding.

But SpaceX ever-so politely asked Steve Jurvetson's Silicon Valley venture capital firm to kindly hold off. SpaceX, one of the hottest enterprises in the rising commercial space industry, suddenly could afford to turn money away.

"There's so much interest, they can't take it all," Jurvetson said. So they decided to "just bring on one new investor to make life simple."

With some significant breakthroughs, led by high-profile billionaires such as Musk, Amazon.com founder Jeffrey P. Bezos and Virgin Galactic's Richard Branson, the commercial space sector has started to capture the public imagination and make space travel cool again.

Now the investment community, which typically has viewed space as far too risky a bet, is courting the industry. High-profile breakthroughs, such as the spectacular rocket landings that SpaceX and Bezos' Blue Origin recently pulled off, show that ventures aimed for the stars are making revolutionary advancements. (Bezos owns The Washington Post.)

There are many milestones in the life of a space-launch company: developing rocket technology, enduring the rigors of test flights, and launching successfully and reliably. But getting investors to place a bet is perhaps one of the greatest hurdles of all, especially considering the risks inherent in spaceflight.

The new space investors are catching up with the slow but growing development of the commercial space sector, which NASA has been fostering for years. With the retirement of the space shuttle in 2011, NASA has awarded billions of dollars in contracts to commercial companies so that they could develop rockets to fly cargo -- and, eventually, astronauts -- to the International Space Station.

Still, the industry is diverse, and different sectors are more advanced, and profitable, than others. Cubesats, the tiny satellites that can swarm around the Earth beaming back images of the planet, are already in high demand. Launching commercial and government satellites is also big business. But the emergence of other sectors, such as space tourism and asteroid mining, is still in the future.

Space investors have typically been science-fiction enthusiasts looking to help create a new market and enjoy the thrill of trying to help mold the future that they would like to see. But that's beginning to change, industry officials said.

"People who are purely interested in financial return are just beginning to take a look at space," said Joe Landon, chairman of the Space Angels Network, a group of early-stage investors. "The trend is more in that direction, but it's still pretty early on."

Over the past decade, the global space industry has grown at a steady clip, and officials think that the tipping point from steady to explosive is near. In 2014, its economy totaled $330 billion, a 9 percent jump from the previous year and up from $176 billion in 2005, according to the Space Foundation, a nonprofit organization that seeks to promote space endeavors across the world.

"After years of steady, respectable growth, the space industry appears to be on the cusp of a new era of rapid expansion in both capabilities and customers," the foundation said in its annual report.

It wasn't always that way. For years, Jurvetson, a partner at DFJ, a Silicon Valley venture-capital firm, was looking for a space company to invest in. Launching model rockets was a hobby, and he would have loved to have found a way to mix business with pleasure.

"It didn't happen for 10 years," he said. "Because in each and every case, no matter how exciting exploring the unknown is, or the grandeur of space tourism, none of them penciled out, economically."

None of them until he met with Musk, who had detailed plans on how he would upend the space industry as he had with online commerce at PayPal. Rocket technology had stayed relatively stagnant for decades, with very few new entrants into the market. Innovation, which had disrupted virtually every industry, from cable to taxis, was somehow lacking in space.

SpaceX and others have shown that "the commercial space industry is enormous and ripe for disruption," Jurvetson said. "Making a 100-fold improvement is actually a piece of cake, and making a thousand-fold improvement is feasible."

Being able to reuse rocket boosters instead of discarding them after each launch, as is now typically the case, was one advance. Making launch prices transparent, as SpaceX did, was another, said Chad Anderson, a managing director at Space Angels Network. The few launch providers hadn't publicized their prices, keeping the cost of getting to orbit largely a mystery.

"As long as you can keep it opaque and convoluted, you can charge more," he said. "It was like a cartel. There were a few suppliers, and they agreed to do business this way."

SpaceX has received billions of dollars in government contracts and has a long backlog of launches. But Musk's long-term goal is to colonize Mars, an endeavor that might test the patience of even the most visionary investor. Not wanting the quarterly pressure from stockholders, Musk has said that he won't take the company public until it gets to Mars.

But for all the advancements that the industry has made, many of the companies are still untested in a realm that is unforgiving, said John Logsdon, professor emeritus at George Washington University's Space Policy Institute.

"None of them are quite there yet," he said. "They've made in the past months some very significant steps toward lowering costs and doing things in a more commercial way. But governments are still the main customers for many of these ventures. . . . Let's not get too far ahead of ourselves."

For all the successes, there have also been some significant setbacks. SpaceX and Orbital ATK (formerly Orbital Sciences), the other company NASA hired to fly cargo to the space station, both suffered explosions in recent years. A Virgin Galactic test flight in 2014 crashed after the spacecraft broke up in mid-flight, killing one of the pilots.

But many investors realize that spaceflight is challenging and so far haven't been scared off, industry officials said. And it doesn't hurt that a new class of billionaires has poured so much of their own money into the ventures.

"Having successful business people putting their money behind this gives it a lot of credibility," Anderson said.

While the futuristic endeavors of colonizing other planets and opening up the cosmos to the masses may get a lot of attention, there "are also companies doing things that are more practical," Landon said.

One example: Earth observation.

"That's a business now," he said.

One of the leaders in that sector is Planet Labs, a San Francisco company founded in 2010 by a group of former NASA scientists.

"What we wanted to do was change the conversation and give a near real-time insight into the state of the world as it is now so you can make a better decision," said Robbie Schingler, the co-founder and chief strategy officer.

The company's fleets of satellites collect all sorts of data that it says have "endless real-world applications," from measuring crop yields, keeping an eye on natural resources or helping first responders in natural disasters. It has 39 satellites in orbit and expects to have 150 flying around the globe by year's end. In April, Planet Labs announced that it had raised $118 million, which was more than expected.

Other companies want to use space as a light-speed highway for commerce. Instead of running thousands of miles of cable across remote areas, OneWeb, a company backed by Branson, plans to put up a constellation of hundreds of miniature satellites that it says will connect the billions of people without Internet access to the digital economy. SpaceX is planning a similar endeavor with more than 4,000 miniature satellites.

Meanwhile, Google has sponsored a $30 million competition for the world's first privately funded mission to land a robot on the moon by next year.

If successful, it would be the first time a spacecraft has landed -- not crashed -- on the moon since 1972 and the first by a non-governmental commercial venture.

Google executives Larry Page and Eric Schmidt are also investors in Planetary Resources, which plans to mine asteroids. Filled with precious metals, the asteroids are the "diamonds in the rough of the solar system," Eric Anderson, the company's co-founder, told CNBC recently.

Asteroids have "rare metals, industrial metals and even fuels," he said, "so we could create gas stations in space that would enable us to travel throughout the solar system just like 'Star Trek.' "