Members of SpaceX’s team in Texas use cranes to add rear moving fins to the Starship Mk1 prototype. (Elon Musk via Twitter)

SpaceX CEO Elon Musk is talking up his Starship Mk1 prototype super-rocket in Texas, less than a week in advance of an eagerly awaited update on his plans for Starship trips to the moon, Mars and beyond.

Today’s sneak preview came in a flurry of tweets addressing some of the finer design points for Starship Mk1, which looks like a silvery silo equipped with rocket fins as it sits at SpaceX’s Boca Chica facility in South Texas. The 30-foot-wide, roughly 150-foot-tall prototype — and a similar Mk2 structure taking shape at SpaceX’s site in Florida — are meant to blaze a trail for an even bigger two-stage rocket, with the pointy-ended Starship sitting atop a Super Heavy first-stage booster.

During a live-streamed presentation that’s set for Saturday at the Boca Chica site, Musk is expected to discuss plans for testing and flying the Starship system over the next few years.

Japanese billionaire Yusaku Maezawa has already struck a deal with SpaceX to take a Starship flight around the moon by the mid-2020s, and is reportedly planning to sell a multibillion-dollar stake in his fashion retail company to cover the cost.

Musk has said Starship (previously known as the BFR) could take on flights to Mars by the mid-2020s, plus crewed trips to the moon and supersonic point-to-point trips between destinations on Earth. He didn’t address those beyond-Earth visions in today’s tweets, but in a discussion with his followers, he did get into the nuts and bolts of Starship design — including what’s going to be packed inside the prototype’s nose cone, or fairing.

Musk also said there are some aspects of the design that he’s not yet “fully bought into.” Here’s how the Twitter thread spun out:

Some of SpaceX’s fans shared their own pictures of the Starship Mk1, and hazarded guesses as to the rocket’s final design:

This story was last updated at 10:44 p.m. PT Sept. 22 with additional tweets from Musk.

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