Jeff Bezos, Elon Musk and Richard Branson all started their own space businesses in the early 2000s.

All three billionaires are credited with helping to usher in a new era of spaceflight by pouring money into projects once considered too risky or expensive for the private sector.

Bezos has been relatively low-key about his space endeavors which makes sense, since he's been busy reinventing retail.

Elon Musk

Elon Musk's rocket company SpaceX has been at the center of most of the media attention. It has developed cheap, reusable rockets that now regularly haul satellites to orbit. The company also wins high-profile contracts with NASA and the military, and it's touted bold plans for colonizing Mars.

Richard Branson

The British serial entrepreneur has also wielded his signature showmanship to promote Virgin Galactic, a space tourism venture that hundreds of customers have already lined up for. It could open for business this year.

Bezos' enormous e-commerce fortune could give Blue Origin a leg up in the billionaire space race. Bezos has said he fills Blue Origin's coffers by selling about $1 billion worth of his Amazon (AMZN) stock each year. That means the company hasn't had to worry about courting investors, which gives it a certain amount of freedom compared to its competitors.