Starship vs SLS: NASA’s Lunar Architecture
NASA’s Artemis program uses two different heavy-lift rockets for two different jobs: the Space Launch System (SLS) sends the Orion crew capsule to lunar orbit, while SpaceX’s Starship serves as the Human Landing System (HLS) that takes astronauts from lunar orbit down to the surface. SLS is the crew launcher, and Starship is the lander—each is optimized for its role, and neither can fully replace the other in the current architecture.
Background: How NASA Got Here
After the Space Shuttle retired in 2011, NASA needed a way to send astronauts beyond low Earth orbit. Congress directed the agency to build the Space Launch System, a super-heavy rocket derived from Shuttle-era technology (RS-25 engines, solid rocket boosters, and the core stage’s liquid hydrogen/oxygen tanks). SLS first flew in November 2022 on Artemis I, sending an uncrewed Orion around the Moon. Meanwhile, NASA selected SpaceX’s Starship as the lunar lander in 2021 through the Human Landing System program, following a competitive procurement that also included Blue Origin and Dynetics. The choice was controversial because Starship is not a traditional lander—it’s a fully reusable spacecraft that SpaceX also plans to use for Mars missions.
SLS: The Crew Launcher
SLS is a disposable rocket—each launch costs roughly $2–4 billion (NASA’s inspector general estimated $4.1 billion per launch for the first four missions). It comes in two variants: Block 1 (used for Artemis I–III) and Block 1B (starting with Artemis IV). Block 1 can send 27 metric tons to a trans-lunar injection; Block 1B increases that to 38 metric tons with a more powerful upper stage. The rocket is designed to launch Orion, a crew capsule that carries four astronauts. Orion has a service module built by ESA, and it provides life support, propulsion, and power for the trip to lunar orbit. SLS is the only current rocket that can send Orion to the Moon in a single launch—other options would require multiple launches and orbital assembly.
Starship HLS: The Lunar Lander
Starship is a two-stage fully reusable system: a Super Heavy booster and a Starship upper stage. For lunar missions, SpaceX modifies the Starship upper stage into a lander—no heat shield, no flaps, no Raptor vacuum engines for landing (it uses sea-level Raptors for the descent). The lander is refueled in low Earth orbit by multiple Starship tanker launches before heading to the Moon. Once in lunar orbit, it docks with Orion (or Gateway, the planned lunar space station) and transfers astronauts. The lander descends to the surface using its own engines, with a landing leg system and an elevator to lower astronauts to the surface. Starship HLS is designed to carry two astronauts (Artemis III) and later four (Artemis IV+). It is much larger than the Apollo lander—it has about 1,000 cubic meters of pressurized volume, compared to about 6.5 cubic meters for Apollo’s lunar module.
How the Two Rockets Work Together
The architecture for Artemis III (the first crewed landing) works like this:
- SLS launches Orion with four astronauts into a trajectory toward the Moon.
- Starship HLS is launched separately (uncrewed) into low Earth orbit, then refueled by several tanker Starships.
- Starship HLS performs its own trans-lunar injection and enters a near-rectilinear halo orbit (NRHO) around the Moon.
- Orion arrives in the same orbit and docks with Starship HLS.
- Two astronauts transfer to Starship, undock, and descend to the lunar surface.
- After surface operations, Starship returns to NRHO and docks with Orion again.
- The astronauts transfer back to Orion, and Starship is discarded (or disposed of).
- Orion returns to Earth and splashes down.
This means SLS is responsible for the crew’s safe transit to and from lunar orbit, while Starship handles the actual landing. The two vehicles never launch together; they rendezvous in space.
Why Not Use One Rocket for Everything?
The main reason is that no single rocket can do both jobs efficiently. SLS is optimized for launching heavy payloads to the Moon, but it has no landing capability—it’s just a launch vehicle. Starship is designed for landing on other worlds, but it cannot launch crew from Earth (it has no launch escape system, and it requires refueling in orbit). Using SLS for the lander would require a separate descent stage and ascent stage, which Apollo did with the lunar module—but that was much smaller. Starship’s size allows for longer surface stays and more cargo, but it requires more fuel and multiple launches. NASA considered using Starship to launch Orion as well, but that would require a crew-rated Starship with an escape system, which is not part of the current plan. The two-rocket approach spreads risk: if one fails, the other can be delayed without grounding the entire program.
Cost and Schedule Comparison
SLS is a government-funded program with fixed contracts; its development cost is estimated at over $23 billion (through Artemis I). Each SLS launch is expensive because the rocket is expendable—the core stage, boosters, and upper stage are all discarded. Starship is privately developed by SpaceX, but NASA pays for the HLS lander through a fixed-price contract ($2.89 billion for Artemis III). SpaceX’s goal is to make Starship fully reusable, which could lower launch costs dramatically, but the refueling requirement means each lunar mission needs 8–12 Starship launches (tankers) plus the lander itself. The total cost of a Starship lunar mission is uncertain but could be comparable to SLS initially. SLS is on schedule for Artemis II (crewed flyby) in late 2025 and Artemis III (landing) in 2026 or later; Starship has had several test flights, with the first successful full stack launch in 2023 and a successful landing in 2024, but it has not yet flown to the Moon.
Common Misconceptions
One common misconception is that Starship will replace SLS entirely. In the current Artemis architecture, that’s not true—NASA needs SLS to launch Orion because Orion is the only crew capsule with a launch escape system and the heat shield for reentry from lunar velocities. Starship is not designed to reenter Earth’s atmosphere from the Moon (it would burn up). Another misconception is that Starship is
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