SpaceX’s space-optimized Starship engine could be ready sooner than later

SpaceX CEO Elon Musk says that there is now a chance that a vacuum-optimized version of the Raptor engine will be ready for near-term Starship launches, indicating that development has either been re-prioritized or is going more smoothly than expected.

This is a significant shift away from a strategy discussed by Musk just four months ago, in which a single variant of Raptor was to be used on Starship and Super Heavy to shorten the next-gen rocket’s path to orbit. For unknown reasons, that approach may have already been replaced with a new alternative that would lead to a Starship with six Raptors instead of seven and a 50-50 split between vacuum and sea level-optimized engines.

Without a more specific development timeline, it’s unclear if RaptorSL-only versions of Starship will ever make it to orbit as a sort of interim solution. The fact that SpaceX is already considering an expedited vacuum variant bodes well for the current status of sea level engine testing, and Musk admittedly revealed that RaptorVac development was to be delayed just days before Raptor’s first full-scale static fire in February 2019.

Speaking less than four months ago, the purpose of delaying RaptorVac development was “to reach the moon as fast as possible.” As long as a Starship powered by unoptimized Raptors was capable of reaching the Moon, designing with RaptorVac in mind would create delays without adding any near-term benefits. The most obvious reasons that SpaceX would revert RaptorVac strategy are changes in technical confidence (i.e. full-scale Raptor testing is going better than expected) or SpaceX’s motivation to get to the Moon “as fast as possible”.

The latter explanation is certainly possible, especially in light of recent hints that there is a terminal lack of funding and Congressional interest in NASA’s Moon return proposal. SpaceX has its own commercial motivations for Starship to get to the Moon in short order, however, including some form of a contract with Japanese billionaire Yusaku Maezawa. As such, it seems more likely that SpaceX’s Raptor program is making rapid progress, outstretching the expectations of those holding the company’s strategic reins.

Just five days after its first ignition, SpaceX successfully tested Raptor SN01 at more than twice the thrust of Merlin 1D. (SpaceX)

According to Musk, sea level-optimized Raptor development is proceeding so smoothly that SpaceX may be able to move into relatively high-volume production – more than two engines per week – this summer (June 1 to August 31). At the moment, SpaceX appears to be focused on testing Raptor at its McGregor, Texas development facilities. This is no surprise for a cutting-edge rocket engine less than four months into full-scale testing, as inevitable off-nominal or unexpected behavior revealed during test fires can often lead to design optimizations or even major changes.

Since the first finalized Raptor was delivered to McGregor in late January, SpaceX has completed an average of one new engine per month, all of which have then been tested in Texas. After completing its McGregor acceptance tests, SN03 also became the first Raptor engine to leave the ground under its own power as part of Starhopper’s first two tethered hops. According to Musk, Starhopper could return to ‘flight’ as early as May 31st.

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SpaceX’s space-optimized Starship engine could be ready sooner than later
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