SpaceX set to finish three Starship prototypes in the same month

SpaceX appears to be on track to complete its third Starship prototype in a month just days after the company finished testing a new steel tank and at the same time as it prepares to roll another full-scale ship to the launch pad.

Postponed by several weeks after the (fleeting) success of the Starship serial number 4 (SN4) prototype, violently destroyed by a minor testing mishap on May 29th, SpaceX’s fifth full-scale Starship tank section (SN5) could roll to an adjacent testing facility at any point in the next few days. In fact, SN4’s successor has likely been ready to begin tank proof and static fire testing for several weeks since it was stacked to its full height on May 12th. SN4 rolled to the launch pad on April 23rd and remained SpaceX’s top Starship priority until its demise more than a month later.

As it turns out, the explosion that destroyed the ship also launched a ~25 metric ton (~55,000 lb) counterweight installed a few days prior some 100m (300+ ft) into the air, where it proceeded to fall back to earth and obliterate the steel mount Starship SN4 sat on. The loss of that pad hardware necessitated its own several-week delay but SpaceX appears to be nearly done installing and outfitting replacements as of June 18th – an incredible turnaround given the scale and complexity of everything involved. Of course, the whole purpose of those rapid repairs is to get back to the business of testing Starships as quickly as possible.

SN5

Initially expected as early as 8am local on June 17th, Starship SN5’s trip to the launch pad has been a long time coming. Completed around May 20th after approximately a month of concerted effort, the ~30m (100 ft) tall tank departed SpaceX’s Vehicle Assembly Building (VAB) for the first on June 13th, although it was quickly moved back inside as technicians simultaneously worked to complete Starship SN6.

Previously scheduled to become the first Starship to reach its full height with the installation of a functional nosecone, SN5 will likely pick up where SN4 left off, instead. That process will effectively be no different, albeit sans nosecone, starting with ambient and cryogenic proof (pressure) tests and eventually moving to one or several static fires with either one or three Raptor engines. Testing the quick disconnect umbilical port that caused SN4’s demise will also likely be a priority. If all goes according to plan in that first week or two of tests, SpaceX may finally be ready to launch a full-scale Starship prototype for the first time, performing a 150m (~500 ft) hop test with SN5.

However, since CEO Elon Musk first discussed plans for an initial 150m hop test, SpaceX received a surprise suborbital launch license from the FAA, rather than the limited experimental permit most expected. That license effectively allows SpaceX to perform an unlimited number of Starship tests as long as the trajectory follows the administration’s strict safety guidelines and remains suborbital. Unless SpaceX’s ~150m target was based in some technical limitation, the sky is quite literally the limit for a more ambitious flight debut if the company believes Starship SN5 can handle it.

SN6

In the event that Starship SN5 follows its predecessor into a less early (but still early) grave, SpaceX thankfully won’t have to wait long at all to continue its hardware-rich test program. When Starship SN5 first departed the VAB on June 13th, it did so to give SpaceX room to finish Starship SN6, placing its aft engine section on a stand inside the building and stacking the upper two-thirds of the ship’s tank on top.

Several days to a week or more of internal and external work remain to fully mate the two Starship SN6 sections, but the vast majority of its assembly is now behind SpaceX. SpaceX continues to refine its methods with each successive prototype, gradually producing Starships that are getting closer and closer to the ideal finished product. There’s a chance that, unlike Starship SN4, SN5 can be modified with the installation of a nosecone and flaps to support more ambitious 2-20 km (~1.2-12 mi) flight tests if it makes it over the 150m hurdle unscathed but if not, SN6 could become the first Starship to have a nosecone installed.

SN7

Last but absolutely not least, SpaceX recently built a new Starship test tank for the first time since March. While stouter than an actual Starship-class methane or oxygen tank, this particular test tank is maybe only 25% shorter than the methane tanks installed on Starship prototypes. According to Musk and effectively confirmed by writing all over the prototype, this particular test tank – formerly Starship SN7 – was built to determine if a different kind of steel could be preferable for future ships.

Shortly after the June 15th test began to wind down, Musk announced that the new material (304L stainless steel) had performed quite well, reaching 7.6 bar (110 psi) before it sprung a leak. The fact alone that it sprung a leak instead of violently depressurizing is already a major sign that 304L is preferable to 301L, as it means that Starships built out of it could fail much more gracefully in the event of a leak instead of collapsing or violently exploding. A step further, SpaceX has already managed to repair the leak on SN7 and will likely test the tank again in the next few days.

Meanwhile, Musk says that a second improved 304L test tank is already on its way, after which SpaceX will likely attempt to build and test the first fully-304L Starship prototype. Further down the line, SpaceX intends to develop its own custom steel alloy, optimized specifically for Starship’s needs. The first tests of that ’30X’ alloy could begin as early as August 2020 according to a February Musk tweet.

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