SpaceX is close to raising half a billion dollars of new funding that would value Elon Musk's rocket company at $25bn (£17.5bn), making it the world's third most valuable venture-backed start-up after Uber and Airbnb.

SpaceX is raising $507m in funding at a higher price than its last funding round, boosting its valuation from $21bn to the new high, according US regulatory filings from analytics company Lagniappe Labs.

In February, SpaceX successfully launched its Falcon Heavy rocket, designed for carrying satellites while using cheaper, re-usable rocket boosters that can return to earth.

The launch of its Falcon Heavy rocket was seen as heralding the start of a new space race as commercial companies vie for a piece of the booming satellite market. Founder Elon Musk has spoken repeatedly of his desire to die on Mars, although in the near-term commercial opportunities have been attracting investors. The company is hoping to launch a mission to Mars by 2022.

Founded in 2002, for years SpaceX met with challenges to its rocket technology, including crashes and burn-ups on landing. It has since become the world's leading commercial space start-up, growing to more than 7,000 employees and set to perform 30 launches in 2018.