On one side is the orange-and-white SLS. On the other is Starship, resembling a stainless-steel tower. Both are part of the United States’ architecture for returning humans to the Moon, yet they have almost nothing in common—from their appearance and engines to how they are intended to operate.
Their respective roles: SLS Block 1 and Starship are not simply two different approaches to building the “same rocket.” Led by NASA, SLS currently forms part of a crewed deep-space transportation chain centered on the Orion spacecraft. Developed by SpaceX, Starship was designed from the outset around reusability, high-frequency launches and in-space refueling. Within the Artemis program, Starship HLS serves as a commercially developed crewed lunar lander—a role distinct from that of Orion.[1]
1. Before Comparing the Rockets, Look at Where They Fit into the Mission
Most rocket comparisons begin with payload capacity, vehicle height and engine count. But the first difference between SLS and Starship lies in their mission boundaries.
SLS is the launch element of NASA’s Artemis crewed deep-space exploration system. Together with Orion, the launch site and ground systems, it forms a tightly controlled mission chain: the rocket sends Orion and its astronauts into space, while Orion handles deep-space travel, rendezvous and docking, and the return to Earth.[1][2]
Starship, by contrast, is a large transportation system that SpaceX is continuing to iterate. The general-purpose Starship system is intended to make both its first stage and upper stage reusable. Starship HLS is a commercially developed lunar lander modified specifically for transporting astronauts between lunar orbit and the Moon’s surface.[1][6]
Under NASA’s updated 2026 schedule, Artemis III will first demonstrate rendezvous and docking between Orion and a commercial lunar lander test article in low Earth orbit in 2027. The target for a crewed lunar landing has shifted to Artemis IV in 2028. This revised timeline makes the division of responsibilities even clearer: SLS/Orion and the commercial HLS are two interconnected segments of the mission architecture.[1]
2. The Shape of SLS Is Defined by Its Liquid-Hydrogen Core Stage and Solid Rocket Boosters
SLS Block 1 consists of the Orion spacecraft at the top, the Interim Cryogenic Propulsion Stage, or ICPS, a massive core stage and two five-segment solid rocket boosters. The core stage is powered by four RS-25 engines burning liquid hydrogen and liquid oxygen. The ICPS also uses liquid hydrogen and liquid oxygen, with propulsion provided by a single RL10 engine.[2][4]
Liquid hydrogen delivers excellent performance by mass, but its density is extremely low, requiring very large propellant tanks. With a boiling point of approximately 20 K, it also places demanding requirements on insulation, plumbing, valves and ground-based fueling systems. The SLS core stage’s enormous, elongated shape is largely a consequence of these physical properties.
The rocket also needs extremely high thrust at liftoff. Its two five-segment solid rocket boosters provide most of the initial thrust during approximately the first two minutes of flight before separating. The high thrust of the solid boosters and the high efficiency of the core stage’s hydrogen-fueled engines perform complementary roles within the same launch vehicle.[3]
SLS and Orion lift off on the Artemis I mission on November 16, 2022. Source: NASA/Joel Kowsky, image ID NHQ202211160027.
3. Starship Looks Like a Stainless-Steel Tower Because the Entire Transport System Is Intended to Fly Many Times
The Starship system consists of the Super Heavy first stage and the Starship upper stage. Under the current official baseline configuration, Super Heavy is powered by 33 Raptor engines using superchilled liquid oxygen and liquid methane. SpaceX designed the system with first-stage return, launch-tower catch, upper-stage recovery and subsequent reflights all taken into account.[6]
That objective fundamentally changes the vehicle’s mass budget. An expendable rocket mainly needs to complete its ascent mission. A reusable rocket must also retain propellant for its return, carry control surfaces and a thermal protection system, and withstand repeated loads during both ascent and recovery. All of these requirements consume mass and volume that could otherwise be allocated to payload.
The lunar version of Starship introduces another critical step: the in-space transfer of cryogenic propellant. To complete its lunar transfer, descent and ascent, HLS must accumulate propellant in low Earth orbit through multiple launches of tanker Starships. Starship HLS is therefore not merely a spacecraft. It is part of a broader system encompassing launch sites, tanker vehicles, orbital propellant storage, rendezvous and docking, and cryogenic fluid management.[6][8]
4. Liquid Hydrogen Versus Liquid Methane Is More Than a Choice Between Two Fuels
The RS-25 and Raptor are both high-performance liquid-propellant rocket engines, but they serve different system-level objectives. The RS-25’s liquid-hydrogen/liquid-oxygen propellant combination delivers very high specific impulse, making it well suited to providing efficient thrust over an extended burn. SLS uses two solid rocket boosters to meet the high-thrust requirements of the initial ascent phase.[3][4]
Raptor burns liquid methane and liquid oxygen using a full-flow staged-combustion cycle. Methane is denser than hydrogen and is stored at a much higher temperature, so it has different implications for tank volume and cryogenic-system layout. It is still a cryogenic propellant, however, and the real challenges lie in long-duration storage inside very large tanks, stabilizing fluids in microgravity, and enabling two vehicles to rendezvous, dock and conduct high-flow-rate propellant transfer.[6][8]
Engine count is also a reflection of system architecture. SLS concentrates its thrust on a single deep-space injection mission by combining four RS-25 core-stage engines with two solid rocket boosters. Starship’s first stage uses 33 Raptor engines to provide liftoff thrust, while thrust vectoring from its gimbaling engines and engine-restart capability also support ascent and return control. Clustering so many engines introduces greater complexity in propellant supply, control, fault management and the thermal environment at the base of the vehicle.
5. An Orange Aluminum Rocket and a Silver Stainless-Steel Rocket Reflect Two Different Manufacturing and Operating Systems
The liquid-hydrogen and liquid-oxygen tanks in the SLS core stage are made primarily from 2219 aluminum alloy. Its distinctive orange exterior comes from spray-on foam insulation. The foam reduces heat transfer between the cryogenic propellants and the surrounding environment while also helping the vehicle cope with condensation, ice formation and aerodynamic heating during flight.[5]
Starship’s primary structure and propellant tanks are made from stainless steel. This choice works in conjunction with SpaceX’s welding processes, rapid iteration, large-scale manufacturing and vehicle-return requirements. Stainless steel does not automatically produce lower costs; it is simply one variable within the broader production and operating system.
A material’s density, strength, cryogenic properties and high-temperature performance all influence structural design. But whether a rocket can be built quickly, launched frequently and returned to service with minimal maintenance also depends on its thermal protection system, weld quality, nondestructive inspection, configuration management and reflight certification. Directly equating the two material choices with “conservative” and “advanced” overlooks the most important system-engineering considerations.
6. Recovery, Reflight and In-Space Refueling Are Three Separate Scorecards
As of the article’s cutoff date, SpaceX had completed multiple Super Heavy returns and launch-tower catches. This has demonstrated that the first stage can return to the vicinity of the launch tower as planned. Assessing the system’s economics, however, will require further evidence from repeated reflights of the same booster, the maintenance required between flights, turnaround time and operational availability.[6]
Recovering the upper stage is even more difficult. It must reenter the atmosphere from orbital velocity, exposing it to more intense heat fluxes and a more complex flight envelope. Only after Starship can complete reliable reentries and recoveries—and the same vehicle can fly again—will “upper-stage reusability” move from a design objective to an operational capability.
In-space propellant transfer represents another separate challenge. During Starship’s third integrated flight test in 2024, SpaceX transferred liquid oxygen between tanks within a single vehicle. NASA TechPort subsequently recorded the demonstration as an on-orbit transfer of more than three metric tons of liquid oxygen between tanks. Rendezvous and docking between two vehicles, followed by the transfer of cryogenic propellant, remains a flight-validation milestone that the HLS architecture must still pass.[7][8]
7. The Difference Between SLS Reviews and Starship’s Rapid Iteration Is Not Simply “Safety” Versus “Risk-Taking”
SLS follows NASA’s process for crewed deep-space systems, including design reviews, component- and element-level testing, the core stage Green Run system-level hot-fire test campaign, and the collection of real-world data through the uncrewed Artemis I integrated flight test. The value of this approach lies in breaking down mission risks into layers and systematically resolving them in accordance with human-spaceflight requirements.[9]
Starship also undergoes extensive ground testing, but it relies more frequently on large-scale integrated flight tests to expose system-level problems before changes are incorporated into the design and subsequent hardware. When an anomaly occurs, launch operations are also subject to public-safety reviews by regulators such as the FAA.[10]
The difference between the two approaches lies in how test evidence is obtained, how risk is progressively addressed and how hardware is iterated. Once either system enters the crewed mission chain, it must ultimately demonstrate that its mission-specific configuration, flight envelope, fault-response capabilities and operating procedures meet applicable safety and mission requirements.
When evaluating SLS, the key questions are whether it can complete its launch mission within the required window for crewed deep-space exploration, and whether its flight reliability, mission cadence, per-launch cost and supply chain can remain under control. The significance of SLS does not depend on whether it can be recovered as quickly as Starship, because its current baseline configuration is designed for expendable missions.
When evaluating Starship, the focus should be on whether its design objectives can be converted into repeatable operational data: Can both the first stage and upper stage be recovered reliably? How quickly can the same vehicle fly again? Can Starships conduct large-scale cryogenic propellant transfer in orbit? Can HLS complete an uncrewed lunar landing demonstration?
In one sentence: SLS begins with the objective of a single crewed deep-space launch, while Starship begins with reusability and large-scale space transportation. Their propellants, engines, structural materials and testing methods are all extensions of those different starting points. To understand a rocket, the most useful first question is always the same: What mission is it actually designed to accomplish?
As lunar and deep-space missions become increasingly complex system-engineering projects, launch capability is only one part of the equation. China’s expanding satellite industry is bringing greater production capacity and more cost-competitive spacecraft, payload and Assembly, Integration and Test (AIT) solutions to the global market. International customers developing new space missions can contact STARPATH GLOBAL to identify suitable capabilities and build a practical, cost-efficient path from mission concept to delivery.
References
[1] NASA, How NASA’s Artemis III Lander Test Will Pave Way for Moon Landings, July 15, 2026; NASA, Artemis III News and Updates, 2026.
[2] NASA, Space Launch System Reference Guide; NASA, Space Launch System RS-25 Core Stage Engine, March 24, 2026.
[3] NASA, SLS Space Launch System Solid Rocket Booster, publicly available information on the five-segment solid rocket booster.
[4] NASA, Space Launch System RS-25 Core Stage Engine, MSFC-12-2025-SLS-5637, 2026.
[5] NASA, SLS Space Launch System Core Stage, January 22, 2026.
[6] SpaceX, Starship Vehicle Overview and Updates, as of September 11, 2026.
[7] NASA, NASA Artemis Mission Progresses with SpaceX Starship Test Flight, updated June 22, 2026.
[8] NASA TechPort, On-Orbit Large-Scale Cryogenic Propellant Management and Transfer Demonstration, updated July 15, 2026.
[9] NASA, publicly available materials on the SLS Green Run test series and the Artemis I integrated flight test.
[10] Federal Aviation Administration, publicly available materials on SpaceX Starship/Super Heavy licensing and mishap response, as of September 11, 2026.
