SLS is already flying. Starship is still proving what it can do. Both are part of NASA’s Artemis Moon program, but they represent very different approaches. SLS is an expendable government rocket built with proven Space Shuttle-era hardware, while Starship is a commercial, fully reusable vehicle still undergoing flight tests.
NASA’s Space Launch System sends the Orion crew capsule from Earth toward the Moon. SpaceX’s Starship plays a separate role. NASA chose it as the Human Landing System, the vehicle that will carry astronauts from Orion down to the lunar surface. In Artemis, neither rocket replaces the other. Each handles a part of the mission the other cannot.
The Comparison at a Glance
| Measure | Starship | SLS |
|---|---|---|
| Builder | SpaceX | NASA, built by Boeing and other contractors |
| Reusability | Both stages designed to land and refly | Fully expendable, nothing recovered |
| Height (stacked) | Roughly 120 meters | Shorter than Starship, among the most powerful rockets ever built |
| Engines | About 33 Raptor engines (booster) plus 6 (upper stage), methane and liquid oxygen | Four RS-25 engines (core stage) plus two solid boosters, liquid hydrogen and liquid oxygen |
| Status as of 2026 | Uncrewed flight testing | Flying, certified for crewed Orion missions |
| Artemis role | Human Landing System, carries crew to and from the lunar surface | Launches Orion and crew from Earth toward the Moon |
| Cost per launch | SpaceX has not published a final per-flight figure. Reuse is meant to lower it over time | NASA’s Office of Inspector General estimates billions of dollars per Artemis launch |
The SLS Is Certified for Crew. Starship Is Not Yet.
The SLS already has a crew certification behind it, plus a flight record that includes an uncrewed test flight around the Moon on Artemis I. That record is why NASA has scheduled a crewed lunar flyby on the SLS next, ahead of any crewed Starship flight. Starship is earlier in its development. SpaceX is flying uncrewed prototypes, gathering data on what works and what fails, then changing the hardware and flying again. That approach produces visible failures along the way. Failures are expected in this kind of testing, but the practical result is that Starship has not yet flown a single crewed mission.
The gap matters for Artemis specifically. NASA needs Starship ready to serve as the lunar lander before astronauts can reach the Moon’s surface under the Artemis program. Starship’s own testing timeline is one of the biggest open questions hanging over how soon a crewed landing actually happens, separate from whatever schedule the SLS itself keeps.
Reusable vs. Expendable Is the Core Design Split
Every part of the SLS is used once. Its core stage, four RS-25 engines, and two solid rocket boosters are all discarded on each flight and never recovered. That is the same way most rockets flew before SpaceX proved reuse could work at scale. Starship takes the opposite bet. Both its Super Heavy booster and its upper stage are designed to land and fly again. It is the way an airline reuses a plane across thousands of flights, instead of scrapping it after one trip.
That split explains most of the cost gap between the two programs. NASA’s own Office of Inspector General has put the cost of a single Artemis SLS launch at billions of dollars. That figure is driven up by hardware built once and thrown away, plus a supply chain built around Space Shuttle-era engines produced in small numbers. Starship’s entire design goal is to bring that number down by recovering and refueling the same hardware repeatedly. It is the same logic that already cut Falcon 9’s cost per flight once SpaceX started reflying boosters routinely.
Raw Size Favors Starship
Stacked together, Starship stands roughly 120 meters tall, making it the largest and most powerful rocket ever flown. Its dozens of Raptor engines, burning methane and liquid oxygen, produce more combined liftoff thrust than the SLS’s four RS-25 engines and two solid boosters. The SLS itself still ranks among the most powerful rockets ever built, a legacy of the Space Shuttle hardware its engines descend from. Starship’s fully reusable design pushed the raw numbers further still.
Size alone does not decide which rocket is right for a given mission. The SLS carries a proven crew rating today. Starship carries more theoretical capability that has not yet been proven on a crewed flight. That is exactly why NASA assigned each rocket a different job in Artemis rather than picking one over the other.
Why NASA Uses Both Rockets in the Same Program
Splitting Artemis across two rockets was a practical choice, not a redundancy. The SLS does the part it is already certified for: getting Orion and its crew off Earth and on a path toward the Moon. Starship does the part that plays to its own design: landing a large vehicle on the lunar surface and getting it back into orbit. That job benefits from Starship’s greater volume and its ability to be refueled in orbit before heading to the Moon. Neither rocket alone covers both halves of the mission as well as the pairing does.
What Would Change This Comparison
A string of successful crewed Starship flights would close the certification gap that currently separates it from the SLS. A published, mission-specific cost figure from SpaceX would sharpen the price comparison beyond NASA’s own SLS estimate; until then, what a Starship launch costs lays out which figures are prices, which are targets, and which are outside estimates. Readers who want the full mechanics behind either vehicle can start with the Starship explainer and the SLS explainer. The reusable rockets guide covers why recovering a booster is such a different engineering problem than building one to fly once.