Liquid Methane, Liquid Oxygen, SpaceX Starship (Chemical Mass Paradox)

Combustion based rocket engines have low fueling costs, proven designs, but they are not appropriate for deep space missions, with a specific impulse of less than 500 seconds, deep space missions require a spacecraft propulsion system with runtime measure in years or more, as the distance in space are vast, noting even the SUN about 93 million miles from Earth, and in terms of space distances, that is tiny. 

Even the Moon about 250,000 miles from Earth, noting how many brand new automobiles will become obsolete worn out and scrapped inside of 200,000 miles, with even the best only lasting 1,000,000 as rare examples among a sea of options that are far less reliable long term, noting Honda K series engines, 2JZ of Toyota, or 1UZ pre94 of Lexus, unicorn examples of long lasting automotive combustion engines, liquid cooled, 4 stroke, gasoline fueled, emissions controlled, mostly aluminum alloy construction, ECU, fuel injection, variable spark timing, coil over spark-plug. 

Deep space needs nuclear fusion power systems, like the FRC direct energy capture reactors of Helion scheduled to go online making grid power for a $400 million dollar data center power contract from Microsoft, noting this will be the first practical commercial power positive firm power fusion power plant ever created! 

If a chemical booster stage able to launch a low mass optimized fusion propulsion upper stage into geostationary transfer orbit, such that the booster released, then a startup sequence activates the fusion drive mechanisms of the propulsion reactor, which then sets sail on a deep space mission, with iSP or specific impulse measure in years, able to travel at remarkable speeds with continual thrust for years, pending several technological hurtles or materials science problems yet unsolved as of mid 2026, but be assure we will get there, to infinity and beyond, faster than light, when we have fusion power reactors bigger than the SUN energizing warp drive access to other star systems in practical time frames. 

If fossil fuels like methane are ancient sunlight, long ago trapped by plants, algae and animals, cooked under heat and pressure in the magma floating paleotectonic of Earth, then nuclear fusion propulsion means moving human technology to an alternate star access level.

Not long after the Sun and other nearby stars will be wrapped in energy capture rings of inward facing solar panels optimized for close operating hot near the sun, called Dyson Spheres, producing Petawatts of continual output power 24/7/365 unleashing vast amounts of electrical energy to fully electrify every aspect of space fairing future human development.