SpaceX’s Starship rocket is a step closer to flight after the fourth full-scale prototype successfully fired up its high-performance Raptor engine for the first time and survived the ordeal.

By far the biggest technical milestone SpaceX’s Starship program has passed since its creation, the Starship serial number 4 (SN4) prototype’s May 5th static fire was just the latest in a series of rapid-fire tests completed over the last several days. The ship’s journey began back in late March when SpaceX technicians began integrating the first sections of its steel hull. Less than a month later, SpaceX officially completed Starship SN4’s tank and engine section – missing only a nosecone and header tanks – and rolled the rocket to the launch and test pad on April 23rd.

Barely two days later, Starship SN4 entered the testing phase, passing what CEO Elon Musk described as an “ambient pressure test” used to verify the structural integrity of the rocket’s propellant tanks with harmless nitrogen gas. Less than a day after that pressure test was completed, SpaceX kicked off a “cryogenic proof test” with the Starship – the same test that destroyed three full-scale prototypes in the five months prior.

In the early morning of April 26th, Starship SN4 thus became the first full-scale prototype to pass (and survive) a cryogenic proof test, in which the ship’s normal liquid oxygen and methane was replaced with similarly frigid but non-explosive liquid nitrogen. According to Musk, SN4 was only pressurized to 4.9 bar (~70 psi), quite a distance away from the ~8.5 bar needed for safe orbital flight but reportedly more than enough to perform a small flight test.

Of course, Starship SN4 would first have to complete a bevy of additional tests – all arguably riskier than the cryogenic proof test it was the first to pass. That second, more challenging phase of testing began six days later on May 2nd.

After some limited fueling effectively marking Starship SN4’s first partial wet dress rehearsal (WDR), SpaceX aborted the first test attempt on May 2nd. On May 3rd, Starship SN4 was successfully loaded with propellant once more and wound up performing what is known as a spin prime test with its lone Raptor engine. Over the course of a few hours, SpaceX then recycled (and rechilled) the ship’s methane propellant and successfully performed a preburner test, igniting two gas generators that spin up Raptor’s turbines and eventually mix in the combustion chamber.

Less than 24 hours later, SpaceX turned Starship SN4 around for the grand finale – an actual Raptor ignition test, also known as a static fire. Per NASASpaceflight’s unofficial livestream of the event, made possible thanks to local resident BocaChicaGal, Starship ignited its Raptor engine – a historic first for the launch vehicle program – at 8:57pm CDT on May 5th (01:57 UTC, May 6). Musk confirmed just a few hours after that the ignition test – lasting about 3 seconds – had been completed successfully.

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With that crucial milestone now behind it, Starship SN4 – perhaps pending an additional test or two – should effectively be clear to begin preparations for a 150m (500 ft) hop test later this month. Almost entirely contingent upon receiving a Federal Aviation Administration (FAA) launch license, that process could be finished tomorrow or take several days – or even weeks – to complete. Starship already has landing legs installed and wont need a nosecone for such a short and slow hop, but SpaceX may also need to install some kind of attitude control system (likely gas thrusters) before SN4 can safely fly.

Stay tuned for updates as we learn more about when a full-scale SpaceX Starship is scheduled to fly for the first time.