Elon Musk says SpaceX is building a stainless-steel rocket ship in Texas that will 'look like liquid silver' and might launch in February

Elon Musk/SpaceX via Twitter; Samantha Lee/Business Insider

An illustration of SpaceX's "test hopper," an experimental stainless-steel ship.

• Elon Musk has shared an illustration of SpaceX's steel rocket ship with a mirror-like finish.
• SpaceX is building the vehicle, which Musk calls a "test hopper," in Boca Chica, Texas.
• The test hopper is a squat version of a full-scale Starship spaceship that's being designed to send people to Mars.
• Musk said the test hopper could launch in four to eight weeks - nearly a year ahead of schedule.

On Saturday, Elon Musk shared an eye-catching picture of a stainless-steel rocket ship gleaming in the hot Texas sun.

The futuristic image is not a photo but rather a rendering created by SpaceX, Musk's rocket company. However, his company is working quickly to build a real-life prototype of the vehicle in southern Texas.

Musk and Gwynne Shotwell, the president and COO of SpaceX, call the ship the "test hopper" because it's not designed to launch into orbit around Earth. Instead, the somewhat crude and windowless ship will rocket on "hops" that go no more than about 16,400 feet in the air, according to FCC documents.

It's a critical experimental vehicle whose successes (or failures) will inform how SpaceX works toward a full-scale, orbit-ready prototype of Starship: a roughly 18-story spaceship designed to one day ferry up to 100 people and 150 tons of cargo to Mars.

"Starship test vehicle under assembly will look similar to this illustration when finished," Musk tweeted on Saturday, sharing the image below. "Operational Starships would [obviously] have windows, etc."

Elon Musk/SpaceX via Twitter

A rendering of SpaceX's stainless-steel Starship test hopper ship.

A full-scale Starship is currently scheduled to launch people for the first time in 2023. That mission is being bankrolled for an undisclosed sum by Japanese billionaire Yusaku Maezawa, who plans to pick eight artists as crew members for a flight around the moon.

Following that mission, Musk has said he hopes to launch the first crews to Mars in the mid-2020s, perhaps as early as 2024, for arrival at the red planet in 2025.

The evolution of Musk and SpaceX's 'Tintin' test ship

Musk and Shotwell had previously said the test hopper wouldn't make its first flights until late 2019.

But when asked Saturday on Twitter about the test hopper's first flight, Musk responded that SpaceX is "aiming for 4 weeks, which probably means 8 weeks, due to unforeseen issues." Either way, that's a major jump in the launch schedule - one that coincides with a recent influx of half a billion dollars.

Read more: Elon Musk said SpaceX is on track to launch people to Mars within 6 years - here's the full timeline of his plans to colonize the red planet

The posts followed Musk's announcement in late December that, indeed, SpaceX is currently building the test hopper at its lesser-known launch site in Boca Chica, which sits at the southernmost tip of Texas.

He also released a photo of the test hopper coming together:

Elon Musk/SpaceX via Twitter

Sections of SpaceX's stainless-steel "test hopper" coming together at the rocket company's launch site in Boca Chica, Texas.

Musk's confirmation and picture came after flurry of photos appeared within the forums of NASASpaceFlight.com, where some dedicated followers of SpaceX congregate to chat about the rocket company's latest activities and share information.

The photos were taken by locals in Boca Chica and showed what appeared to the mythical test hopper being constructed nearly a year ahead of schedule. Musk said the main parts were being made in Los Angeles and shipped to the semi-remote site.

Read more: Where SpaceX's most important locations are and what they do

The most recent batch of images shows workers and cranes assembling sections of the test hopper in plain sight of an access road.

The vehicle doesn't yet have a seamless mirror finish, as Musk's rendering suggests it might (there are ridges between the steel panels) but it's not supposed to look perfect. In fact, there is a decent chance it could fail or explode, as has happened to many early SpaceX creations.

Musk has described Starship as as a "Tintin" rocket, referencing the famous 20th-century Belgian comics (which feature a two-part space-exploration story).

"I love the Tintin rocket design, so I kind of wanted to bias it towards that," he said during a press conference in September. "If in doubt, go with Tintin."

From carbon-fiber to stainless steel that looks like 'liquid silver'

SpaceX

An illustration of the SpaceX's Big Falcon Rocket, or BFR, launching into space. Here, the spaceship is shown detaching from the booster.

The choice of polished stainless steel is a major shift from what Musk called his "final iteration" of the rocket's design.

In September, Musk revealed design updates for his two-part Mars launch system, called the Big Falcon Rocket. The Starship that Musk unveiled then was slated to be about 30 feet wide and 180 feet tall, and sit atop a roughly 219-foot-tall rocket booster that Musk now calls Super Heavy. Both parts were supposed to be made primarily of carbon-fiber composites, which can be many times lighter yet many times stronger than steel alloys.

Materials science and aerospace experts interviewed by Business Insider had some reservations about the choice of carbon fiber, given the punishing environment of space and the difficulty in repairing carbon-fiber parts on Earth, let alone in space or on another planet.

Super Heavy may yet be built mostly out of carbon-fiber, since it won't reach orbit and instead should land back on or near its launch pad for reuse. But it appears Musk and his engineering team are now committed to making Starship out of a stainless-steel alloy.

Musk said SpaceX's newly developed Raptor engines, which will power the vehicle, will be made of an in-house "superalloy" called SX500. He's also suggested that the final steel body of Starship will "look like liquid silver" and act as its own heat-sink - without protective thermal tiles, as NASA's space shuttle used - during the blazing-hot reentry into Earth's or Mars' atmosphere.

"I will do a full technical presentation of Starship after the test vehicle we're building in Texas flies, so hopefully March/April," he tweeted on December 22.