Elon Musk shows off prototype of Starship, retro-looking, Mars-bound rocket

SpaceX CEO Elon Musk has unveiled the first pictures of a retro-looking, steely rocket called Starship that may one day carry people to the Moon and Mars. Musk posted pictures on Twitter late Thursday of the test version of the Starship Hopper, which awaits its first flight test in Texas in the coming weeks.

"Starship test flight rocket just finished assembly at the @SpaceX Texas launch site. This is an actual picture, not a rendering," he wrote. The prototype built in Boca Chica, along the Gulf Coast of Texas, is nine yards (meters) in diameter -- like the future rocket will be -- but is shorter.

Its first test flights -- suborbital "hops" reaching several miles (kilometers) in the air before landing back on Earth -- could come in March or April. An orbital prototype is expected in June. That version will be paired with a massive rocket booster known as the Super Heavy.

SpaceX has said the duo could some day transport people from city to city on Earth, as well as propel passengers around the Moon, to the lunar surface, and even to Mars and back.

Last year, Musk had unveiled his underground transportation tunnel, allowing reporters and invited guests to take some of the first rides in the revolutionary albeit bumpy subterranean tube - the tech entrepreneur's answer to what he calls "soul-destroying traffic." Guests boarded Musk's Tesla Model S and rode along Los Angeles-area surface streets about a mile away to what's known as O'Leary Station. The station, smack dab in the middle of a residential neighborhood - "basically in someone's backyard," Musk said- consists of a wall-less elevator that slowly took the car down a wide shaft, roughly 30 feet (9 meters) below the surface.

At the event, he explained for the first time in detail how the system, which he simply called "loop," could work on a larger scale beneath cities across the globe. Autonomous, electric vehicles could be lowered into the system on wall-less elevators, which could be placed almost anywhere cars can go.

The cars would have to be fitted with specially designed side wheels that pop out perpendicular to the car's regular tires and run along the tunnel's track. The cost for such wheels would be about $200 or $300 a car, Musk had said.

A number of autonomous cars would remain inside the tunnel system just for pedestrians and bicyclists. Once on the main arteries of the system, every car could run at top speed except when entering and exiting.

"It's much more like an underground highway than it is a subway," Musk had said.

The cars would have to be autonomous to work in the system but not Teslas specifically, and they would have to be electric because of the fumes from gas, Musk had said.