There are perhaps 3 companies on Earth that could conceivably provide engines for this application. RR was one of them. Where to now?
Couldn't SpaceX or Rocket Lab's engine be repurposed for this task?
Jets breathe atmospheric air for combustion because they operate in an atmosphere where oxygen is readily available for combustion. They have an air intake nozzle.
Rockets carry their own oxidizer because they must. They only have an exhaust nozzle.