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SpaceX founder Elon Musk said a prototype for the company’s planned Starship launch vehicle passed a cryogenic proof test Sunday night in South Texas, clearing the way for teams to install a Raptor engine this week for a test-firing.

The Starship test vehicle, designated SN4, was loaded with super-cold liquid nitrogen Sunday night in a “proof test” that damaged or destroyed previous Starship prototypes.

SN4 passed cryo proof! 😅 pic.twitter.com/EJakThZRGF — Elon Musk (@elonmusk) April 27, 2020

The cryogenic testing Sunday night occurred a day after SpaceX performed a pressure test of the Starship SN4 vehicle at ambient temperatures.

“Great work by SpaceX engineering!” Musk tweeted.

Made of stainless steel, the Starship test model will next receive a methane-fueled Raptor engine in preparation for a test-firing “hopefully later this week,” Musk tweeted.

Cryogenic pressure testing on three earlier models of SpaceX’s Starship resulted in explosive ruptures that left behind crumpled wreckage at the company’s manufacturing and test site at Boca Chica, Texas. Musk said SpaceX engineers are technicians have introduced improved manufacturing and weld techniques on new Starship vehicles.

He tweeted that SpaceX is also switching to a new stainless steel alloy with “high ductility” at cryogenic temperatures, along with “geometric changes.”

The Starship is the upper stage of of SpaceX’s next-generation reusable launch and space transportation system. Coupled with a massive booster named the Super Heavy, the Starship could haul more than 100 metric tons, or 220,000 pounds, of cargo to low Earth orbit, according to SpaceX.

“Starship has the capability to transport satellites, payloads, crew, and cargo to a variety of orbits and Earth, lunar, or Martian landing sites,” SpaceX wrote in a Starship user’s guide released last month.

SpaceX’s Raptor engine can produce up to 440,000 pounds of thrust, and it’s designed to adjust power levels to enable the Starship to land vertically, similar to the way SpaceX’s Falcon 9 rocket boosters return to Earth.

If the static fire test goes according to plan, SpaceX is expected to attempt a 500-foot (150-meter) test flight of the Starship SN4 vehicle. Musk said the next Starship being built in South Texas, known as SN5, will get three Raptor engines to advance to the next stage of testing.

SpaceX conducted a 500-foot test flight of a reduced-scale Starship test vehicle — named the Starship Hopper — last August in South Texas.

The fully reusable Super Heavy and Starship vehicles, which will also be able to carry people, will eventually replace the partially reusable Falcon rocket family, SpaceX says.

In a presentation to a National Academies’ science panel Monday, Musk said the Starship will be flying “quite soon.”

“I think you’ll see regular flights within a couple of years, and that’s a very big rocket,” Musk said Monday.

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Follow Stephen Clark on Twitter: @StephenClark1.