SpaceX is currently utilizing two distinct propulsion philosophies to dominate the glbal launch industry. While the kerosene-fueled Merlin engine has established a massive track record with the Falcon 9, the new methane-powered Raptor is being engineered to enable even faster turnaround times for the Starship program.
The Merlin Engine's 680-Mission Legacy
The Merlin engine has served as the reliable backbone of SpaceX's early success,powering the Falcon 9 rocket through more than 680 missions to space. These engines utilize an open-cycle gas generator combustion cycle fueled by rocket-grade kerosene and liquid oxygen. According to the report, the Falcon 9 booster houses nine of these engines, while the second stage utilizes a single Merlin vacuum engine designed with an enlarged exhaust section to optimize performance in the vacuum of space.
Performance metrics for the Merlin remain impressive for a gas-generator design. A sea-level Merlin produces approximately 190,000 pounds of thrust , while the specialized vacuum variant can reach up to 220,500 pounds. The reliability of this system was highlighted when a Falcon 9 booster completed a record 36th flight in July 2026, proving that the iterative design process used by SpaceX engineers can produce a highly durable, revenue-generating workhorse.
Why the Raptor's 617,000-pound Thrust Changes the Game
The Raptor engine represents a much more aggressive leap in propulsion technology, specifically designed for the Starship program. Unlike the Merlin, the Raptor is a full-flow staged combustion engine that runs on liquid methane and oxygen. This design is exceptionally rare; as the source reports, the Raptor is one of only a handful of such engines in existence globally and stands as the only successful example to ever fly.
The scale of the Raptor's power is significantly higher than its predecessor, producing 617,000 pounds of thrust. This massive output is required to move the gargantuan Starship architecture. The Super Heavy booster utilizes a cluster of 33 Raptors, while the Starship orbiter itself relies on three sea-level Raptors and three Raptor vacuum engines to achieve orbit. This engine is currently in its third iterative design cycle as SpaceX continues to push the boundaries of what is possible in rocket engineering.
Moving from 9-Day Turnarounds to Airline-Style Operations
A primary driver behind the shift from kerosene to methane is the desire for rapid, "airline-level" reusability. The Merlin engines, while reliable, require meticulous post-flight inspections to clean away soot buildup caused by kerosene combustion. This process currently results in a minimum turnaround time of nine days between flights.
SpaceX intends to bypass these intensive maintenance requirements by using the Raptor's clean-burning methane fuel.. The ultimate goal is to allow Starships to land, refuel, and launch again almost immediately. While the Raptor has not yet reached full operational maturity, the report notes that Starship Flight 7 successfully utilized a previously flown Raptor engine, marking a significant step toward proving the engine's long-term reusability.
Can Methane Truly Eliminate Post-Flight Inspections?
Despite the technological promise of the Raptor , several critical questions remain regarding the Starship program's efficiency. It is still unverified whether the Raptor can truly achieve the "refuel and go" capability without the detailed inspections that currently limit the Merlin. Additionally, the complexity of managing a 33-engine cluster in the Super Heavy booster presents a massive maintenance challenge that has yet to be tested at scale.
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