The SpaceX craft Elon Musk hopes will one day take astronauts to Mars has taken a step forward, with the team building the 50-meter-tall (160 feet) capsule working around the clock to finish its huge dome.

Musk shared updates about the project’s progress on Twitter on Monday, saying he and the SpaceX team had spent the whole night working on the “most difficult part of [the] primary structure”: Starship’s giant dome.

In his videos, he shows three of the huge structures at varying stages of construction – and it wasn’t long before Twitter users compared the strange hemispheres to alien crafts.

Almost three now. Boca team is crushing it! Starship has giant dome 🤣🤣 pic.twitter.com/qTN2TU02pb — Elon Musk (@elonmusk) December 30, 2019

“They all look like the UFOs in the 90s Hollywood movies,” one commenter pointed out in response to the footage.

“This dude is building a UFO,” another said, matter-of-factly.

Nobody: *nothing*Elon Musk: *builds a UFO!* — Glebati (@Glebati_28) December 30, 2019

It hasn’t been smooth sailing to get to this point of the project. The Mark I prototype of the long-range spacecraft’s launch vehicle exploded during tests in November to see how well it could endure extreme cold, mimicking the conditions of deep space. SpaceX said at the time that the test “outcome was not completely unexpected… nor is this a serious setback.”

No injuries were sustained in the blow-out in Boca Chica, Texas.

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SpaceX is aiming to carry out its first manned orbital flights using Starship in 2020. The reusable spacecraft is designed to bring crew and cargo to the International Space Station as well as on lunar voyages and, if all goes according to plan, to Mars.

The company has run 19 cargo flights to the ISS for NASA to date, but has hit some major snags in the development of a crew capsule for the route, with an April 2019 ground test resulting in the capsule being obliterated.

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