Speaking on Friday, March 8th, SpaceX CEO Elon Musk announced that the company’s second completed Raptor engine was already “on [its] way to [Star]hopper” to – nominally – be installed on the prototype vehicle as early as the week of March 11th (this week).
According to an official SpaceX statement, once Raptor is installed on Starhopper, the integrated vehicle will perform a combination of ground systems testing, propellant loading, static fire tests, and low-altitude hover demonstrations to prove out the brand new vehicle, engine, and facilities. Prior to the final months of 2018, the build site, launch pad, and prototype Starship now preparing for imminent hop tests were little more than empty dirt lots on the southern tip of the Texas coast.
“SpaceX will conduct checkouts of the newly installed ground systems and perform a short static fire test in the days ahead,” he said. “Although the prototype is designed to perform sub-orbital flights, or hops, powered by the SpaceX Raptor engine, the vehicle will be tethered during initial testing and hops will not be visible from offsite. SpaceX will establish a safety zone perimeter in coordination with local enforcement and signage will be in place to alert the community prior to the testing.” – James Gleeson, March 8th, SpaceX
Prior to February 3rd, barely one month ago, SpaceX’s next-generation Raptor engine had yet to even ignite in its final(ish), full-scale form. Less than two weeks after that, SpaceX’s propulsion team had pushed the engine to the point of damage, quite possibly throttling it above its nominal max thrust and main combustion chamber pressures. According to Musk, Raptor serial number 2 (SN02) will feature moderate changes to mitigate the cause of that damage.
Along the path to hop tests, it’s unclear if Raptor SN02 – following the mild problems more or less intentionally forced upon its predecessor – will be test-fired at SpaceX’s McGregor, Texas development facilities before heading south to be installed on Starhopper. Given SpaceX’s methodical approach to engine and vehicle testing prior to the launch of any of its rockets, chances are good that it will have already conducted a number of basic acceptance tests in McGregor. If Musk is to be taken literally, the second
It has not yet been confirmed if Starhopper will initially perform static fire and hop tests with just one Raptor installed, but the sheer power of the fairly compact engine (upwards of 200 metric tons or 450,000 lbf of thrust at full throttle) should more than enable an extremely heavy prototype to lift off even with 50+ metric tons of propellant onboard. While it could simply be a matter of convenience and efficiency to start integrated Starhopper testing immediately instead of waiting for the completion of additional Raptor engines, the process of testing a thrust structure or integrated rocket with an increasing number of engines installed is a relatively common practice in aerospace. Regardless of its history, SpaceX itself also began its first integrated testing of a Falcon 9 first stage in the same way, starting with one Merlin engine installed and ultimately graduating to 3, 5, and the final 9 engines over the course of a few months of testing.
While Starhopper is unlikely to need more than a handful of Raptor engines to exhaust its usefulness, the first orbital Starship prototype – and, even more so, the first Super Heavy booster – will almost certainly end up going through the same process of methodical hot-fire testing before SpaceX even thinks of attempting the first orbital BFR launch. Featuring 7 and 31 Raptors respectively, Starship and Super Heavy will radically push the envelope of both SpaceX’s own experience and the aerospace industry as a whole, potentially becoming the most powerful liquid rocket ever launched if or when the vehicle begins flight tests with both stages.
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