This is the sharpest philosophical split in the heavy-lift world: reusable and cheap versus expendable and maximal. Falcon Heavy bolts three Falcon 9 cores together, produces 5.1 MN of sea-level thrust, and has flown 12 times with a perfect 100% record through ViaSat-3 F3 (April 2026), lifting up to 63,800 kg to LEO in expendable configuration for roughly $97M, about $1,400/kg. SLS Block 1 is a different beast entirely: 2,608 tonnes at liftoff, heritage RS-25 shuttle engines paired with solid boosters, and about 95,000 kg to LEO. Critically, SLS is measured not by LEO tonnage but by what it can throw directly to the Moon, roughly 27,000 kg to trans-lunar injection. It has flown twice, both successes: uncrewed Artemis I (November 2022) and the crewed Artemis II lunar flyby (April 2026). But that capability is staggeringly expensive, NASA's Inspector General pegs each SLS/Orion flight near $4.1 billion, on the order of $40,000/kg.

For cost-per-kilogram to LEO or GTO, Falcon Heavy wins by more than an order of magnitude and it isn't close; for DoD/NRO heavy GEO payloads and flagship planetary science, Falcon Heavy is the rational choice and NASA already flies missions like Europa Clipper on it. For sending a fully crewed Orion on a single stack directly to lunar orbit, SLS wins, because it is the only vehicle built to do exactly that. Falcon Heavy's theoretical throw to lunar/Mars distances lands around 16 to 20 tonnes, short of a crewed Orion's mass in one launch, and Falcon Heavy is not human-rated. This is why NASA, despite the price, keeps SLS as its crewed deep-space vehicle: the trade is performance-at-any-cost versus economy.

The design logic explains the gap. Falcon Heavy sacrifices peak performance to recover its side boosters and fly cheaply and often; SLS expends everything, including four irreplaceable RS-25 engines per flight, to extract every ounce of trans-lunar capability. The program context matters too: SLS Block 1B with its Exploration Upper Stage was cancelled in February 2026, leaving Block 1 to fly through at least Artemis IV under real budgetary pressure and open questions about long-term viability against cheaper alternatives. The honest verdict: if your payload is a heavy commercial or defense satellite, or a robotic probe, Falcon Heavy is the overwhelmingly better value. If your payload is astronauts bound directly for the Moon on Orion today, SLS is the only rocket that does the job, and that unique fitness, not efficiency, is what keeps it flying.