SpaceX is now one of the world’s most valuable privately held companies

Getty Images | Robyn Beck

Elon Musk, founder and CEO of SpaceX

The two other closely held companies valued at more than $20 billion are both in China — ride-hailing company Didi Chuxing and consumer electronics maker Xiaomi.

SpaceX’s latest funding nearly doubles the valuation of the company, which was pegged at around $11 billion when it raised $1 billion from Fidelity and Google in 2015. Previous investors in SpaceX include venture capital firms Founders Fund and DFJ.

SpaceX is best known for Mr. Musk’s goal of colonizing Mars, but it is also a key player in the business of sending commercial satellites into space.

Last September, the company suffered a major setback when, during fueling for an engine test, one of its Falcon 9 rockets caught fire on the launchpad and exploded, destroying a $200 million satellite. SpaceX resumed launching in January, and, after years of failing to meet its promises, the company has finally achieved a steady cadence, with 10 launches already this year. By the end of the year, SpaceX hopes to finally get its bigger, years-delayed Falcon Heavy rocket off the ground.

In March, the company launched a partly used, less expensive rocket, with the aim of bringing down the cost of sending supplies into space. Replicating such flights with reusable rockets is key for Mr. Musk’s vision of sending people to Mars.

“It means you can fly and refly an orbital class booster, which is the most expensive part of the rocket,” Mr. Musk said at the time.

Mr. Musk faces potential competition in the rocket space from another billionaire. Blue Origin, a rocket company founded by Jeff Bezos, the chief executive of Amazon, also aims to send tourists and supplies into space. Mr. Bezos said in April that he’s selling about $1 billion of Amazon stock every year to fund the company.