SpaceX is hoping to send five uncrewed Starships to Mars within the next few years, CEO Elon Musk said on his social media site, X. SpaceX has to wait for the next Earth-Mars launch window before sending the missions, according to Musk. These windows occur when Mars and Earth are lined up in such a way that flights between them take the least amount of energy and time. The next window is in 2026. Should SpaceX miss that deadline, the next launch window is late 2028 into early 2029. 

If the uncrewed ships land safely on Mars, Musk anticipates sending crewed missions during the 2028-29 launch window. If the tests don't succeed, the company will try uncrewed missions again in the 2028 launch window, and push the crewed missions back to the launch window after that.

SpaceX has yet to land the Starship, its biggest ever vehicle, on solid ground. On its latest mission in June it landed the craft for the first time in the Indian Ocean.

"No matter what happens with landing success, SpaceX will increase the number of spaceships traveling to Mars exponentially with every transit opportunity," Musk said on X. 

The ultimate goal, according to Musk, is the building of a self-sustaining Martian city in "about 20 years." SpaceX President Gwynne Shotwell echoed those claims two years ago in an interview with CNBC. The Starship's max payload is 150 metric tons.

A representative for SpaceX didn't respond to a request for comment.

Musk has been known to move the goalposts when it comes to SpaceX's timeline on getting ships to Mars. Musk famously said four years ago that SpaceX would be sending ships to Mars in 2024. SpaceX has been dealing with numerous issues, including run-ins with the Federal Aviation Administration over procedural issues and fights with regulators over the environmental impact of the company's launches. 

Musk touched on those issues in another tweet, saying that one of his biggest concerns "is that the Starship program is being smothered by a mountain of government bureaucracy that grows every year." Musk blames "stifling red tape" for SpaceX's inability to launch missions to Mars sooner and, alluding to the election in November, predicts it would "grow under a Democratic Party administration." 

SpaceX is facing delays in other sectors as well. NASA's Artemis 3 mission, which is using SpaceX's Starship, was originally scheduled for 2025 and has been pushed back to 2026. It'll be the first crewed mission to the moon in half a century when it does eventually happen. Per Reuters, Japanese billionaire Yusaku Maezawa canceled his flight around the moon that was also slated to use SpaceX's Starship.