Then there's space tourism, a segment of space travel occupied by Branson's Virgin Galactic, which hopes to turn civilians into space travelers at $250,000 a pop.
According to Ostrove, lesser-known companies XCOR Aerospace and Blue Origin are also working on space planes to take paying customers into what's known as suborbital space, the area that exists just above Earth's atmosphere, but below lower orbit, which is where the International Space Station circles the globe.
But while hundreds of customers have signed up for space flight, none has seen liftoff, according to Ostrove.
"Companies still need a large amount of capital to succeed. And they will need to improve safety if they are going to start to regularly carry paying passengers into orbit," Ostrove said in an email.
Last October, Virgin Galactic's SpaceShipTwo crashed during a test flight, killing a test pilot.
"I think our biggest investment is trying to move Virgin into space travel with Virgin Galactic. Putting people into space, putting satellites into space. Maybe one day doing point-to-point air travel via space, maybe one day getting to Mars, maybe even trying to colonize Mars," Branson said in an interview with CNBC.
"It's not been without its upsets. You know, we feel that we'll get there in the end," Branson said.