SpaceX took another step forward Thursday in developing its next-generation Starship rocket, conducting the second short flight test of a prototype in the past month.

Starship prototype Serial Number 6, or SN6, took off from the launchpad at SpaceX's facility in Boca Chica, Texas. It gradually rose to about 500 feet above the ground before it returned back to land, touching down on a concrete area near the launchpad. The flight test appeared to be identical to the test SpaceX conducted of prototype SN5 on Aug. 5.

The prototypes are built of stainless steel and represent the first versions of the Starship rocket that SpaceX CEO Elon Musk unveiled last year. The company is developing Starship with the goal of launching cargo and as many as a 100 people at a time on missions to the Moon and Mars.

SpaceX's first Starship prototype under construction near Boca Chica, Texas in 2019.

SpaceX

SpaceX has been steadily building multiple prototypes at a time at the company's growing facility in Boca Chica.While SpaceX's fleet of Falcon 9 and Falcon Heavy rockets are partially reusable, Musk's goal is to make Starship fully reusable envisioning a rocket that is more akin to a commercial airplane, with short turnaround times between flights where the only major cost is fuel.

After SpaceX in May launched a pair of NASA astronauts inits first crewed mission, Musk pivoted the company's attention, declaring thatthe top SpaceX priority is now development of Starship. Musk said in an email obtained by CNBC that Starship's program must accelerate"dramatically and immediately."

SpaceX's prototype Starship rocket SN6 comes back to land after a short flight test on Sept. 3 in Boca Chica, Texas.

@LabPadre

The repeated flight test represents a continuation of what Musk has said about Starship's development, as he's tweeted that SpaceX will launch prototypes on"several short hops to smooth out launch process." The back-to-back successful flights show Starship's development is accelerating, as the program hadsuffered several explosive setbacks in the past year.

Musk also acknowledged on Monday that Starship has many milestones to go before it can take passengers on flights.

"We've got to first make the thing work; automatically deliver satellites and do hundreds of missions with satellites before we put people on board," Musk said.

He expects Starship's first flight tests to orbit won't come until 2021, saying that SpaceX is in "uncharted territory."

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SpaceX launches and lands another Starship prototype, the second flight test in under a month - CNBC