SpaceX’s first orbiting spacecraft engine has just fired

After less than three weeks of shipment to Texas, SpaceX says its first Starship Raptor vacuum cleaner engine has completed a “full-term test launch” in the march toward orbital test flights.

The engine is known as the Raptor Vacuum or RVac, and it relies almost entirely on its improved sea level cousin, taking all the turbos and the complex combustion chambers that account for the bulk of the rocket engine. Things begin to diverge below the combustion chamber throat (the narrow portion of the central hourglass-like curve), as SpaceX widens the Raptor’s existing bell nozzle by a factor of five or more.

SpaceX’s reusable Starship spacecraft will use a combination of three sea level Raptors and three Raptor Vacuum Engines to give it the thrust it needs to reach orbit and ensure efficient operations in both atmosphere and vacuum.

The Raptor Vacuum is (approx.) To expand in conjunction with the sea level Raptor, the Space Shuttle Main Engine (SSME), and the Saturn V F-1. (Teslarate)

In simple terms, a rocket engine can take advantage of a vacuum optimized nozzle because the added surface area (more or less) gives the highly pressurized gases emerging from the combustion chamber more foothold to pressurize them. Rocket nozzles are at their best when the engine’s exhaust gas finishes expanding to match the ambient pressure the moment it exits the bell. Logically, at sea level on Earth, the ambient air pressure is very high, which means that rocket exhausts don’t have to expand as much to equalize.

However, in a vacuum of space, the exhaust gases must expand much more to reach the same pressure as their surroundings. For missile propulsion, this additional expansion could be exploited to make a more efficient engine, extract additional energy from the same propellant and in an ideal vacuum, the more efficient nozzle would be technically unlimited. Geometric and physical infinities don’t exactly coincide, unfortunately, so space rocket engineers are forced to settle for crater size on a scale that humans can practically manufacture.

In theory, the Starship doesn’t need to The Raptor Vacuum Engines were a working orbiting spacecraft and CEO Elon Musk himself came up with a design with seven engines at sea level just two years ago. SpaceX CEO has since revealed that the Raptor has been making so good progress that the company canceled the removal of vacuum-powered motors from the Starship’s baseline design.

See, what, no vacuum drives! SpaceX

It’s unclear exactly what SpaceX means when it says the Raptor Vacuum SN1 has completed a “full-duration test launch”. For the Starship, the full-duration orbital insertion burn – which begins immediately after the Super Heavy booster detaches – is likely to be no less than five or six minutes. Even for SpaceX, going from charging a first engine (Raptor Vacuum) to a successful stationary fire of several minutes in less than three weeks would be an almost unimaginable engineering feat. That achievement could mean that SpaceX is already very comfortable with Raptor burns that take several minutes – perhaps the biggest obstacle between the Starship and orbit.

Most likely, the term “full-term test release” simply refers to the fact that the Raptor Finder vacuum engine was able to ignite, burn and shut down on schedule – to avoid premature shutdown, in other words. For an engine as large and complex as a Raptor, this low interpretation is a remarkable feat.

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