BOCA CHICA, TX—Last Saturday SpaceX CEO Elon Musk revealed that construction of a prototype for a Mars spaceship, called Starship, is now underway, and that the first round of its experimental launches may be completed by early spring.

Musk and Gwynne Shotwell, the president and COO of SpaceX, have both said short, non-orbit-reaching launches or "hops" of such a spaceship prototype is a critical step toward building the Big Falcon Rocket, or BFR: a colossal two-stage system designed to launch 100 people and 150 tons of cargo to the surface of Mars. However, both SpaceX executives said recently that short hops wouldn't commence until the end of 2019. 

Starship is designed to be about 30 feet wide and 180 feet tall, and sit atop a 219-foot-tall rocket booster that Musk now calls Super Heavy. He added that construction of test hopper segments was underway at SpaceX's temporary new rocket factory at the Port of Los Angeles.