Elon Musk says SpaceX's Starship could reach orbit within 2 years. Here's the latest photo of the spaceship's construction.

SpaceX; Kevork Djansezian/Getty; Shayanne Gal/Business InsiderElon Musk and a SpaceX illustration of its Starship rocket on Mars.

SpaceX is taking major steps toward CEO Elon Musk’s ultimate goal to send humans to Mars.

Musk recently posted imageson Twitter showing the construction of a prototype spaceship at SpaceX’s facility in Boca Chica, Texas. He captioned the photo simply, “Stainless Steel Starship.”

Starship is part of SpaceX’s fully reusable Big Falcon Rocket system, which also includes a 219-foot-tall rocket booster that Musk calls Super Heavy.

The prototype being built is essentially a shorter version of the Starship spacecraft, though its diameter is full-size: 30 feet. The prototype of Super Heavy will be full-scale, Musk said.

In subsequent tweets, Musk also said there’s a “60% and rapidly rising” chance that the completed spaceship could launch into orbit by 2020. SpaceX executives had previously said the system could launch Starship into orbit sometime in 2020 or 2021, so Musk’s estimate suggest the system’s new design has helped the company stay on or ahead of schedule.

One of the biggest changes Musk made recently was the decision to construct Starship from a special stainless steel alloy instead of relying on carbon-fibre composite. Because of this, Musk said on Twitter, Starship could look like “liquid silver.”

In total, the system is designed to launch 100 people and 150 tons of cargo to the surface of Mars.

Big falcon rocket bfr spacex scale dimensions measurementsOlivia Reaney/Business Insider

Musk has said the prototype could be ready for short, experimental launches called hops by March 2019.

SpaceX’s ambitious timeline is to launch the first human voyage to Mars in 2024. Before then, though, Starship will have to successfully complete cargo-only missions to Mars and carry people around the moon.

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