SpaceX has officially begun static ground testing of Starhopper, a full-scale pathfinder Starship prototype meant to support an early series of Raptor-powered hop tests at SpaceX’s South Texas launch site. Simultaneously, the second completed Raptor engine arrived at the site on Monday, March 11th, confirming CEO Elon Musk’s March 8th tweets about the delivery.

While reasonably routine for any rocket test program, the first tanking test of Starhopper effectively marks the first time that SpaceX has begun tests with a more or less fully integrated Starship (previously BFS). Likely performed with liquid nitrogen instead of liquid oxygen/methane, the first few tanking tests will be used to determine the quality of the prototype’s stainless steel tanks – built en plein air in a fairly unorthodox fashion – and test whether they are functional pressure vessels without risking immediate and total destruction. If successful, SpaceX will proceed into Raptor integration and integrated static-fire tests before preparing for tethered hover tests, perhaps as early as later this month.

In November 2016, SpaceX began propellant-loading tests of its first finished full-scale Starship (then Big Falcon Spaceship) hardware, a massive carbon composite liquid oxygen tank stretching 12 m (~40 ft) in diameter. Over the course of 2017, SpaceX transitioned from liquid nitrogen to liquid oxygen and ultimately conducted one final burst-test in which the composite tank was pressurized until it exploded, ending full-scale BFR composite testing with a bang. Within 6-12 months, Musk had come to the conclusion that a stainless steel BFR would ultimately be a superior path forward for the rocket and spaceship and attempted (apparently successfully) to get his team of R&D engineers on board with such a radical change so late in the development phase.

Despite the fact that that radical design departure may have occurred as few as 6-8 months ago, SpaceX engineers and technicians have accomplished an extremely rapid development program that will – in part – culminate in the hopefully successful hop testing of Starhopper, the first Starship prototype. While more of a rough testbed than an actual representation of the hardware and structures that will be required for a reusable orbital-class Starship, Starhopper has at least acted as a crash course (either technically or organizationally) on fabricating and assembling stainless steel aerospace structures, a material largely foreign to SpaceX flight hardware prior to late 2018.

Although the early vehicle was less than encouraging, as was the demise of its nosecone as a consequence of improper planning and/or bad workmanship, Starhopper as it now stands might actually be flightworthy in the context of suborbital, subsonic hop tests. Powered by the same or similar Raptors that would power orbital prototypes, Starhopper’s hop tests would optimally provide a wealth of experience and engineering data for both building 9 meter/30 foot-diameter stainless steel rocket sections and operating full-scale Raptor engine(s) in actual flight configurations. Extensive testing with Raptor will help to ensure that the fit and finish of the new engine’s flight-grade avionics and hardware are up to the challenge of safe, reliable, and gentle operations for a nominally crew-rated launch vehicle and spacecraft.

Around two days after Starhopper was briskly transported from its build site to SpaceX’s brand new launch facility, local Twitter account @SPadre (short for South Padre Island) posted a video of tanking test that occurred on March 11th, capturing the sound of venting as the liquid involved turned to gas inside its propellant tank(s). The fact alone that the person behind the camera was allowed to be where they were during the test all but guarantees that this first test was performed with an inert liquid, most likely liquid nitrogen given a massive delivery that occurred the day before (March 10th). In no conceivable world would SpaceX or local law enforcement willingly allow for Starhopper to be loaded – for the first time ever – with even a partial load of liquid methane or liquid oxygen with bystanders barely a few hundred feet distant.

When SpaceX gets to the point that they are confident enough in the structural integrity of Starhopper to begin wet dress rehearsals and tests with actual propellant, it’s a safe bet that the company will cooperate with local law enforcement to block off the lone access road to a distance of at least 1-2 miles, if not more. It’s unclear if local homeowners and residents will be forced to vacate the adjacent Boca Chica Village during testing, but chances are good that nobody will be within several thousand feet of Starhopper when those propellant loading tests begin, let alone actual static fire activity once Raptor(s) are installed.

According to an official SpaceX statement on the progress, propellant load tests and static fires could begin “in the days ahead”, although the spokesperson was under the impression that those tests – as well as initial hop tests – “[would] not be visible from offsite”. Unless SpaceX plans to draw a keep-out zone with a radius of multiple miles, interested observers will almost certainly be able to get close enough to at least catch a glimpse of Starhopper, but the statement still offers an idea of just how focused the company will be on safety during these early tests.

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