A Starship part spotted on July 20th confirms that SpaceX is already well into the process of building a significantly upgraded full-scale prototype.
Following in the footsteps of five or six full-scale ships before it, information published by NASASpaceflight.com suggests that Starship SN8 will be a substantial departure from its predecessors. Thanks to data gathered by testing the Starship SN7 test tank to destruction on June 24th, SpaceX has determined that a different alloy – known as 304L – is superior to the 301 stainless steel all Starship prototypes have been built out of up to now.
SN8 is SpaceX’s response to that discovery. As usual, the company has performed smaller tests before deciding to build a full-scale Starship prototype – identical to all previous SNx prototypes beyond the alloy change – out of 304L stainless steel. As a result, Starship SN8 – once complete – may have the most potential of any prototype built thus far, but its fate will also be more uncertain than most of its predecessors.
On June 24th, SpaceX destroyed the SN7 Starship test tank as part of a controlled cryogenic proof test – essentially a pressure test at cryogenic (ultra-cold) temperatures. Departing from routine, CEO Elon Musk never commented on the test, leaving its results shrouded in mystery. According to NASASpaceflight, however, SN7 “achieved a record pressure before it failed.”
Designed to test a different formulation of stainless steel, that success implies that SN7 proved that the 304L alloy will not only be more malleable and forgiving at cryogenic temperatures – but is also more capable overall compared to 301 steel. To beat the record set by the second or third Starship test tank in January or March 2020, SN7 would have had to reach pressures of ~8.6 bar or higher – effectively icing on the cake for the already-demonstrated ~140% safety factor.
A full-scale Starship has yet to survive proof tests at those pressures but Starship SN4 did become the first to complete a full cryo proof, sustaining ~7.5 bar (~110 psi) before it was safely depressurized. Currently on the pad and preparing for an imminent static fire and hop test debut, Starship SN5 is unlikely to put pressure on that record unless that it aces both of the aforementioned trials. Built entirely out of the 304L alloy already proven to be superior to 301, SN8 may well be the golden goose of prototypes.
“The vehicle will feature major upgrades over previous Starship prototypes. SN8 will be built out of 304L stainless steel versus 301 and will receive a fairing, aerosurfaces, and three Raptor engines to allow for a higher-altitude test flight.”
NASASpaceflight.com — July 15th, 2020
The appearance of SN8’s labeled common dome – the dome separating Starship’s liquid oxygen and methane tanks – implies that a variety of other parts spotted over the last few days are also meant for the next full-scale rocket. Mounted on a stand purpose-built for the task, the SN8 common dome will soon be ‘sleeved’ by one or several stacked steel rings, after which it can be welded to the rest of the Starship’s tank. An engine section and thrust structure – likely SN8’s – in the late stages of assembly was spotted three days prior, while an upper tank dome that could be for either SN8 or test tank SN7.1 was captured in the same photos.
In the last photo, taken on July 13th, there’s even signs of what could be Starship SN9 – hinted at by the appearance of two Starship engine sections signified by the pattern of welds on their exteriors. Those welds are incontrovertible signs of the stringers used to strengthen Starship engine sections and they haven’t been used anywhere else on past prototypes.
Based on the sheer number of steel rings and domes currently floating around SpaceX’s Boca Chica, Texas Starship factory, SN8 could be a just a week – or even less – away from final stacking operations. If SN5 leaves the pad intact and completes its wet dress rehearsal, static fire, and flight debut without issue, SN8 could be up to bat much sooner than later.
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