Elon Musk's SpaceX has raised another $100 million as part of its latest funding round, according to new regulatory documents.

In August, the space exploration company sold $349.9 million worth of shares, a Securities and Exchange Commission (SEC) filing showed. That amount has now risen to $449.9 million, a new filing showed on Monday, adding an extra $100 million onto the current fundraising effort.

The latest injection of cash values SpaceX at $21.5 billion, according to Equidate, a platform that facilitates the trading of shares in private technology firms. SpaceX was not immediately available for comment on the valuation when contacted by CNBC.

SpaceX's SEC filing did not disclose the investors.

Musk's space company has been ramping up its rocket launches. SpaceX has developed rockets that are able to take off, deliver a payload into space, then land back on a droneship stationed in the Atlantic. The company says this helps reduce the cost of space missions as well as increasing the number that are able to take place.

Earlier this year, SpaceX President Gwynne Shotwell told Reuters in an interview that the company was aiming to launch missions every two-to-three weeks.

As well as regular launches for large customers, Musk has bigger ambitions. In May, SpaceX laid out plans to put 4,425 satellites into space to provide high-speed internet. Musk plans to start this in 2019.

And the billionaire eventually wants to get to Mars. Musk has already laid out plans for an "interplanetary transport system" capable of taking 100 people to the Red Planet in order to colonize it. The SpaceX CEO said he wants to land at least two cargo ships on Mars by 2022.