The Raptor prototype upper-stage engine is a bipropellant rocket engine being developed by SpaceX for a US Air Force contract issued in January 2016.
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The upper-stage prototype is to utilize the full-flow staged combustion engine cycle and same methalox propellants of the Raptor rocket engine that SpaceX has been developing since at least 2009. The prototype is expected to complete testing in 2018.
History
In January 2016, the US Air Force (USAF) awarded a US$33.6 million development contract to SpaceX to develop a prototype version of its methane-fueled reusable Raptor engine for use on the upper stage of the Falcon 9 and Falcon Heavy launch vehicles. The contract requires double-matching funding by SpaceX of at least US$67.3 million. Work under the contract is expected to be completed in 2018, and engine performance testing will be done at NASA's John C. Stennis Space Center in Mississippi.
Although the USAF contract called only for the development and build of a prototype engine with a series of ground tests, with no upper stage design funded by the contract, the Air Force was working with the US Congress as of February 2016 to be able to proceed to a second phase in order to pursue a broader USAF objective: new launch systems. If such a second phase were to be approved by Congress, the USAF would subsequently solicit proposals for new launch vehicles and then "evaluate that as part of a total launch solution [ultimately, hoping to] be able to select at least two national security space launch systems."
Design characteristics
As of January 2016, little technical detail had been publicly released. The prototype is however to be designed:
The USAF contract calls only for the development and build of a prototype, to be demonstrated in a USAF-supervised set of tests. No upper stage vehicle design/redesign is funded by the contract.