,
Raptor is a rocket engine design concept by SpaceX

SpaceX

Space Exploration Technologies Corporation, or more popularly and informally known as SpaceX, is an American space transport company that operates out of Hawthorne, California...

 for a higher performance upper stage for the Falcon 9

Falcon 9

Falcon 9 is a rocket-powered spaceflight launch system designed and manufactured by SpaceX. Both stages of its two-stage-to-orbit vehicle use liquid oxygen and rocket-grade kerosene propellants...

 launch vehicle. The engine would be powered by liquid hydrogen

Liquid hydrogen

Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...

 and liquid oxygen

Liquid oxygen

Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...

,
rather than the RP-1

RP-1

RP-1 is a highly refined form of kerosene outwardly similar to jet fuel, used as a rocket fuel. Although having a lower specific impulse than liquid hydrogen , RP-1 is cheaper, can be stored at room temperature, is far less of an explosive hazard and is far denser...

 kerosene and liquid oxygen

Liquid oxygen

Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...

 used in the current Falcon 9 upper stage.

Liquid Hydrogen rocket engines typically have a specific impulse

Specific impulse

Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

 (I_sp) of up to 450s, in comparison to the SpaceX RP-1

RP-1

RP-1 is a highly refined form of kerosene outwardly similar to jet fuel, used as a rocket fuel. Although having a lower specific impulse than liquid hydrogen , RP-1 is cheaper, can be stored at room temperature, is far less of an explosive hazard and is far denser...

 Merlin Vacuum engine's I_sp of 342s.
An LH2 upper stage enables much greater mass to be boosted into orbit.

History

Raptor was first discussed by SpaceX's Max Vozoff at the AIAA Commercial Crew/Cargo symposium in 2009.
, SpaceX has a small number of staff working on the Raptor upper stage, at a fairly low level of priority.

See also

• Advanced Common Evolved Stage
  Advanced Common Evolved Stage
  The Advanced Common Evolved Stage, or ACES, is a proposed upper stage rocket for use on space launch vehicles. The design concept is from the U.S. company United Launch Alliance . ACES is intended to boost satellite payloads to geosynchronous orbit or, in the case of an interplanetary space...
  
  
• Falcon Heavy
  Falcon Heavy
  Falcon Heavy, previously known as the Falcon 9 Heavy, is a spaceflight launch system that uses rocket engines currently being designed and manufactured by SpaceX. Both stages of the two-stage-to-orbit vehicles use liquid oxygen and rocket-grade kerosene propellants...
  
  
• RL10
• XCOR/ULA liquid-hydrogen, upper-stage engine development project