For certain projects of low orbits and even take-off from sea level until reaching a vacuum (Shuttles) and reaching sufficient escape speeds, the formula until now has been rocket launchers.

“Sabre”

-The Sabre engine created by Reaction Engines for the hybrid "plane-spacecraft" known as Skylon is a mixed engine that uses oxygen from the atmosphere in its low flight and passes to liquid oxygen when in a vacuum.

-This avoids having to carry the heavy liquid oxygen for the entire trip.

“Sabre details”

-For atmospheric travel it uses a compressor like that of a turbojet, changing to liquid oxygen when in a vacuum.

-We guess the 4 rocket engines behind the assembly.

-A previous project, that of Hotol, also European, was going to use RR engines, the RB545, turbo rockets.