How Many Orbital Refills Will SpaceX Starship Need to Land Astronauts on the Moon?

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Key Takeaways

• Published estimates for a single Starship lunar landing range from six to 22 orbital refueling launches.
• SpaceX plans to aggregate cryogenic methane and liquid oxygen in an orbiting depot across two Earth orbits.
• NASA’s revised 2026 architecture docks Orion with Starship in Earth orbit before trans-lunar injection.

Why Starship Cannot Fly Directly From Earth to the Lunar Surface

On October 23, 2026, the National Aeronautics and Space Administration (NASA) released an updated operational architecture for returning astronauts to the Moon aboard the SpaceX Starship Human Landing System (HLS). Rather than flying a single expendable rocket straight from a Florida launch pad to the lunar surface as the Apollo Saturn V did between 1969 and 1972, the modern lunar campaign treats Low Earth Orbit (LEO) as an industrial staging yard. Under the revised Artemis lunar landing plan, SpaceX must launch an orbital storage depot, dispatch a fleet of reusable tanker rockets to fill that depot with super-cooled propellants, transfer that fuel into the lunar lander across multiple orbital altitudes, and then dock the fully loaded lander with NASA’s Orion crew spacecraft in Earth orbit before departing for the Moon.

The fundamental reason behind this multi-launch campaign is governed by the Tsiolkovsky rocket equation, which relates a spacecraft’s change in velocity, known as delta-v, to the exhaust velocity of its engines and the ratio between its initial fueled mass and its dry structural mass. A full-scale Starship upper stage paired with its Super Heavy first-stage booster stands more than 120 meters tall and burns roughly 4,500 to 5,000 metric tons of propellant during liftoff. By the time the upper stage separates from the booster and accelerates to an orbital velocity of approximately 7.8 kilometers per second in Low Earth Orbit, the spacecraft has burned nearly its entire internal supply of propellant just to overcome Earth’s gravity well and atmospheric drag.

Without resetting that mass ratio in space, a massive steel spacecraft such as Starship would arrive in Earth orbit with almost empty tanks, unable to execute the additional 3.1-kilometer-per-second trans-lunar injection burn, brake into lunar orbit, descend to the regolith, and launch back into lunar orbit. The Starship lunar lander variant holds approximately 1,200 metric tons of liquid oxygen and liquid methane propellant. Refilling those main tanks in Earth orbit resets the rocket equation at orbital velocity, enabling the spacecraft to depart Low Earth Orbit with a full fuel load as though it had launched from the top of Earth’s gravity well.

This orbital refilling model shifts the economics and capability ceiling of deep-space transportation. According to SpaceX’s official lunar mission specifications, fully refueling Starship in orbit enables the vehicle to deliver up to 100 metric tons of cargo directly to the lunar surface on a single trip. For comparison, the Apollo Lunar Module landed roughly 4.8 metric tons of dry mass and payload combined. By trading single-launch simplicity for high-cadence orbital logistics, the Artemis Human Landing System architecture turns the lunar lander into a tall, pressurized habitat and heavy cargo carrier capable of supporting surface rovers, power systems, and multi-day scientific expeditions near the lunar South Pole.

Comparing the Competing Estimates From Six to 22 Refueling Launches

Because neither NASA nor SpaceX has published a single fixed contract requirement for the number of tanker flights needed per mission, public projections span a broad range from four to 22 launches. During an October 2026 public meeting of NASA’s Aerospace Safety Advisory Panel (ASAP), panel member and former shuttle commander Charlie Precourt stated that fueling Starship for one landing could require around 22 launches when accounting for operational reserves and propellant evaporation. SpaceX Chief Executive Officer Elon Musk disputed that figure on social media, stating that the actual number of refueling flights would be closer to six or eight.

The gap between six and 22 launches reflects differing engineering assumptions regarding three variables: the usable propellant mass each upgraded Starship tanker can deliver to orbit, the fraction of stored propellant that boils off into space between launches, and the total propellant demand of the revised lunar trajectory. Earlier in the program, when NASA awarded SpaceX the $2.89 billion Option A Human Landing System contract in April 2021, a formal protest decision reviewed by the United States Government Accountability Office (GAO) noted that SpaceX’s baseline proposal planned for 16 total launches, consisting of one propellant depot, 14 tanker flights, and the lunar lander itself.

Subsequent briefings by NASA and SpaceX officials placed the expected tanker count in the middle of that spectrum. In November 2023, Lakiesha Hawkins, Assistant Deputy Associate Administrator in NASA’s Moon to Mars Program Office, told a NASA Advisory Council committee briefing that a single lunar landing would require Starship launches in the high teens. In 2024, SpaceX executives estimated that roughly 10 tanker flights would be needed once higher-thrust Raptor engines and stretched propellant tanks entered service. If each Block 3 or Version 3 Starship tanker delivers 100 to 150 metric tons of surplus propellant to the orbital depot, filling a 1,200-metric-ton tank capacity requires between eight and 12 transfers under ideal zero-loss conditions.

When real-world inefficiencies are added, the required launch count rises. Prototype flights of the Block 2 Starship configuration prior to February 2026 demonstrated an orbital payload capacity closer to 35 metric tons before SpaceX transitioned toward its larger Version 3 hardware. Furthermore, every week that the orbital depot loiters in sunlight waiting for the next tanker arrival causes a percentage of its super-cold liquid oxygen and liquid methane to vaporize. An analysis of Starship launch estimates shows that lower per-flight tanker margins combined with multi-stage orbital transfers and thermal boil-off push conservative safety panel calculations toward the 22-launch ceiling.

The table below compares the four primary launch estimates depicted in the accompanying mission infographic across their originating organizations, projected launch counts, and underlying engineering assumptions.

Cryogenic Boil-Off and Microgravity Fluid Transfer Engineering

The central technical challenge governing every launch-count calculation is cryogenic fluid management in microgravity. Unlike hypergolic propellants such as hydrazine and nitrogen tetroxide, which remain liquid at room temperature aboard the International Space Station, Starship’s Raptor engines burn sub-cooled liquid methane and liquid oxygen, collectively referred to as methalox. At standard atmospheric pressure, liquid oxygen boils at minus 183 degrees Celsius and liquid methane boils at minus 161 degrees Celsius.

When a propellant depot circles Earth every 90 minutes, it passes repeatedly through direct solar radiation, infrared heat radiated by Earth, and reflected sunlight known as Earth albedo. Any heat that penetrates the spacecraft’s stainless-steel tank walls warms the cryogenic liquid, causing it to evaporate into gas and raise internal tank pressure. To prevent the tanks from rupturing, the spacecraft must either run active cryocoolers or vent the evaporated gas overboard, a loss mechanism known as cryogenic propellant boil-off in space. If tanker launches occur too slowly, the propellant boiling off between flights eats into the net fuel accumulated inside the depot.

Transferring those liquids between two docked vehicles in free fall introduces a second physics problem. On Earth, gravity pulls liquid propellant to the bottom of a tank, where sump pumps or drain valves can draw a steady stream of fluid free of gas bubbles. In microgravity, surface tension and capillary forces govern liquid behavior, allowing liquid and pressurizing ullage gas to mix inside the tank volume. If ullage gas enters the transfer lines during docking operations, it can trigger pump cavitation or vapor lock, stalling the transfer and risking mechanical damage to the fluid couplings.

To overcome microgravity sloshing without relying on massive mechanical pumps, SpaceX’s architecture uses a gentle settling thrust maneuver combined with differential tank pressurization. Once a chaser tanker docks with the target depot, small thrusters apply a slight acceleration to settle the liquid propellant over the tank outlets at the rear of the donor ship, and autogenous pressurization gas pushes the super-cooled liquid across the docking interface. During its third integrated test flight in March 2024, SpaceX conducted an initial internal tank-to-tank propellant transfer test under a NASA Tipping Point contract, moving liquid oxygen between a header tank and the main tank. However, as NASA’s Marshall Space Flight Center has documented, SpaceX must still complete a full ship-to-ship orbital transfer test between two docked Starships in Low Earth Orbit before validating the lunar campaign.

Stage One and Stage Two in the Low Earth Orbit Depot Campaign

In the six-stage waterfall project chart that maps NASA’s baseline refueling sequence, the campaign begins with two foundational logistics phases between Earth’s launch pads and Low Earth Orbit. Stage one, designated as Depot to LEO, launches the specialized Starship propellant storage depot from Earth into a low parking orbit. Because the depot serves strictly as an orbital fuel station and never reenters Earth’s atmosphere or lands on the Moon, engineers strip away the heavy aerodynamic flaps, landing legs, crew cabin hardware, and black ceramic heat-shield tiles used on standard earth-return Starships.

Eliminating reentry hardware frees structural mass that SpaceX reallocates to stretched propellant tanks, sunshields, and specialized thermal insulation. As detailed in NASA technical conference filings, the depot is optimized for extended orbital loiter times and boil-off suppression, incorporating multi-layer insulation and reflective thermal coatings tested across SpaceX’s developmental flight series. Positioning this dedicated storage vessel in Low Earth Orbit decouples the lengthy tanker aggregation schedule from the launch of the crewed lander and the astronauts themselves.

Once the depot is checked out in its parking orbit, Stage two of the project schedule, Tanker Wave One, begins. Multiple reusable Starship tankers lift off from Earth in rapid succession, rendezvous with the orbiting depot, dock, and transfer their surplus loads of liquid methane and liquid oxygen. After discharging its cargo into the depot’s main tanks, each tanker undocks, performs a deorbit burn, reenters Earth’s atmosphere behind its thermal protection shield, and returns to the launch site for inspection and reuse on subsequent refueling sorties. Its Super Heavy booster similarly returns to the launch tower’s mechanical catch arms minutes after liftoff.

Maintaining the required launch tempo during Tanker Wave One requires distributed ground infrastructure. According to NASA planning briefings cited in coverage of orbital refueling timelines, the baseline campaign assumes a launch every six days by alternating flights between two separate orbital launch complexes: SpaceX’s Starbase facility at Boca Chica, Texas, and Launch Complex 39A at NASA’s Kennedy Space Center in Florida. Operating two geographically distinct pads with dedicated liquid oxygen, liquid methane, and liquid nitrogen tank farms insulates the refueling campaign against single-pad weather delays or pad refurbishment turnarounds.

Stage Three and Stage Four Across the Final Tanking Orbit

Rather than completing the entire refueling process in a single low parking orbit, NASA’s updated Artemis IV refueling architecture introduces a two-orbit staging strategy captured in Stages three and four of the mission project chart. In Stage three, titled HLS Launch and First Refill, the uncrewed Starship Human Landing System lifts off from Earth atop a Super Heavy booster and enters Low Earth Orbit. The lander tracks down the partially or fully loaded propellant depot, docks with it, and takes on its initial propellant load in what mission planners describe as a first orbital pit stop.

After receiving this initial fuel transfer in Low Earth Orbit, the Starship lunar lander undocks from the depot and fires its engines to climb into a higher-altitude elliptical or intermediate staging trajectory known as the Final Tanking Orbit (FTO). Raising the lander’s orbit midway through the refueling campaign accomplishes two engineering objectives. First, climbing to the Final Tanking Orbit stores a portion of the mission’s required energy as orbital potential energy before the final top-off occurs. Second, moving the lander to a higher altitude reduces the thermal heating load from Earth’s infrared radiation and albedo, slowing the rate of cryogenic boil-off inside the lander’s tanks while it waits for the final fuel transfer.

With the lunar lander parked in the Final Tanking Orbit, Stage four of the sequence, Tanker Wave Two and FTO Top-Off, gets underway back in Low Earth Orbit. A second wave of Starship tankers launches from Texas and Florida to replenish the propellant depot in its lower orbit, where each tanker can deliver maximum payload mass without expending extra propellant to reach the higher staging altitude. Keeping the individual tanker flights restricted to Low Earth Orbit preserves their payload fraction and shortens their orbital phasing windows.

Once the second wave of tankers has refilled the depot in Low Earth Orbit, the depot itself fires its Raptor engines to ascend from Low Earth Orbit into the Final Tanking Orbit. There, the depot conducts a second rendezvous and docking maneuver with the waiting Starship Human Landing System. As outlined in reports on NASA’s Artemis IV diagram, the depot transfers the remaining propellant required to top off the lander’s tanks right at the threshold of High Earth Orbit, leaving Starship HLS with full propellant margins for its outward lunar push.

Stage Five and the Revised Earth-Orbit Rendezvous With Orion

Stage five of the project chart, Orion Docking and Trans-Lunar Burn, reflects the most consequential change in NASA’s 2026 lunar architecture overhaul. Under NASA’s earlier baseline from 2021 through 2025, a fully fueled Starship HLS was supposed to depart Earth orbit alone, travel to the Moon, and wait inside an elongated lunar trajectory called a Near-Rectilinear Halo Orbit (NRHO) for astronauts arriving aboard Orion. Following a February 2026 program restructuring announced by NASA Administrator Jared Isaacman and Associate Administrator Amit Kshatriya, and detailed further in an October 2026 lander architecture revision, NASA moved the meeting point between Orion and Starship from lunar orbit back to Earth orbit.

Under this updated sequence, once Starship HLS completes its final top-off in the Final Tanking Orbit, it maneuvers to its rendezvous altitude in High Earth Orbit and completes a readiness checkout before the crew leaves the ground. Four astronauts then launch from Launch Complex 39B at Kennedy Space Center aboard NASA’s Orion spacecraft atop a standardized Block 1 Space Launch System rocket (SLS). By canceling earlier plans to introduce the upgraded Block 1B Exploration Upper Stage immediately after Artemis III, NASA kept the Earth-ascent rocket in a standardized configuration and shifted the outward trans-lunar propulsion task onto the commercial lander system.

After Orion reaches High Earth Orbit, it performs a nose-to-nose rendezvous and docking maneuver with the fueled Starship lander, using a docking adapter derived from SpaceX’s flight-proven Dragon 2 mechanism that completed more than 200 qualification test scenarios at Johnson Space Center. To validate these hardware and software interfaces before a crewed lunar landing attempt, NASA restructured the 2027 Artemis III mission into an Apollo 9-style demonstration in Low Earth Orbit. During Artemis III, Orion is scheduled to dock with a Version 3 Starship test article in Earth orbit to verify connected-spacecraft flight control, communications, and docking dynamics before the first crewed surface landing on Artemis IV, targeted for 2028.

Once Orion and Starship HLS are securely docked in High Earth Orbit during the lunar landing mission, Starship fires its six rear Raptor engines – comprising three sea-level Raptor engines for gimballing control and three large-nozzle Vacuum Raptor engines optimized for spaceflight – to execute the trans-lunar injection (TLI) burn for the combined stack. Pushing Orion toward the Moon with Starship allows the mission to enter a Low Lunar Orbit (LLO) rather than the distant Near-Rectilinear Halo Orbit. According to NASA’s October 2026 operational summary, staging through Low Lunar Orbit reduces the total propellant Starship must aggregate for lunar descent and ascent and shortens the transit time required for astronauts leaving the surface to rejoin Orion.

The table below summarizes the six sequential stages of the Starship refueling and lunar landing project chart across their orbital zones, participating vehicles, and primary operational milestones.

Stage Six Descent to the Lunar South Pole and Ascent Back to Orion

After the joined Starship and Orion stack arrives in Low Lunar Orbit, Stage six of the project chart – Lunar Landing and Ascent – begins. Two of the four Artemis astronauts transfer through the docking tunnel from Orion into the upper crew cabin of Starship HLS, leaving the other two crew members aboard Orion to monitor orbital operations. Starship then undocks from Orion and initiates its powered descent toward the rugged, cratered terrain of the lunar South Pole region, where permanently shadowed craters harbor water-ice deposits alongside sunlit peaks.

Landing a 50-meter-tall cylindrical vehicle on unprepared lunar regolith presents distinct engineering challenges involving plume-surface interaction and center-of-gravity stability. Firing Starship’s main rear-mounted Raptor engines all the way to touchdown would blast a crater into the unconsolidated lunar soil, kicking up high-velocity rock fragments that could damage the spacecraft’s engines or cause the tall lander to tilt beyond its stability envelope. As examined in engineering analyses of Starship landing stability, SpaceX must pair automated hazard-avoidance lidar and shock-absorbing landing legs with a specialized terminal propulsion system.

During the final 100 meters of descent above the lunar surface, Starship HLS shuts down its main bottom-mounted Raptor engines and switches to a ring of high-thrust gaseous oxygen and methane thrusters mounted mid-way up the spacecraft’s barrel. Placing these landing thrusters tens of meters above the ground reduces the exhaust pressure striking the regolith, limiting dust excavation and rock ejecta during touchdown. Once the lander settles onto its shock-absorbing legs, the two astronauts live inside the spacious upper cabin for several days and ride an external motorized crew elevator from the high airlock deck down to the lunar surface to collect geological samples and evaluate Axiom Space extravehicular activity suits.

Before NASA permits a crewed landing on Artemis IV, SpaceX is contractually required to execute a complete uncrewed lunar landing and ascent demonstration mission to prove that the refueling campaign, mid-body landing thrusters, and landing gear function reliably in lunar conditions. Should an emergency arise in deep space during early missions, independent studies have even evaluated adapting SpaceX Dragon for lunar rescue to provide dissimilar redundancy. At the conclusion of the surface expedition, the two astronauts ride the elevator back to the cabin, lift off from the Moon using the propellant remaining in Starship’s tanks, redock with Orion in Low Lunar Orbit, and transfer back into the capsule for reentry and splashdown in the Pacific Ocean.

Commercial Competition and Industrial Supply Chain Implications

SpaceX’s high-cadence methalox refueling campaign operates within a competitive dual-provider procurement structure managed by NASA. After selecting SpaceX under Option A in 2021, NASA awarded a $3.4 billion Sustaining Lunar Development contract in May 2023 to a Blue Origin-led National Team that includes Lockheed Martin, Boeing, Draper, and Astrobotic Technology to build the Blue Moon Mark 2 crewed lander. Under NASA’s realigned 2026 contract terms, whichever commercial provider completes its uncrewed lunar demonstration and safety certification first can be assigned to the targeted 2028 Artemis IV landing.

Notably, NASA’s October 2026 architecture update gave Blue Origin a very different path to the Moon that eliminates in-space cryogenic propellant transfer from its initial crewed landing missions. As detailed in coverage of the revised Blue Moon plan, Blue Origin plans to use four launches of its heavy-lift New Glenn rocket to place three liquid hydrogen and liquid oxygen transfer stages and one Blue Moon Mark 2 lander into Low Earth Orbit. Those four spacecraft elements dock together in Earth orbit and operate like a multi-stage rocket, discarding each transfer stage as its propellant is depleted on the way to an elliptical polar lunar orbit.

International competitors have also designed lunar landing architectures specifically to avoid the operational complexity of multi-tanker orbital refueling. China’s crewed lunar program targets a landing near the lunar South Pole before 2030 by launching its Mengzhou crew spacecraft and Lanyue lunar lander separately aboard two expendable Long March-10 super-heavy rockets, which then dock directly in lunar orbit. Even as NASA and international agencies refine their flight trajectories, policy analysts note that lunar program flight-plan revisions address technical transportation readiness rather than resolving international legal frameworks governing lunar resource extraction or permanent base jurisdiction.

As reported in the July 2026 GAO major projects assessment and earlier GAO reviews of Artemis schedules, turning SpaceX’s orbital refueling chart from an engineering diagram into a routine operational capability requires industrial-scale manufacturing and launch operations. Launching 10 to 22 Starships for a single lunar sortie demands continuous production of Raptor engines, automated stainless-steel ring welding, dedicated air-separation plants producing tens of thousands of metric tons of liquid oxygen and liquid methane, and rapid Federal Aviation Administration launch licensing across Texas and Florida. If SpaceX validates rapid tanker reuse and low-loss cryogenic storage in 2027 the same orbital propellant depots built for Artemis IV will establish a reusable in-space transportation network capable of moving 100-ton payloads across cislunar space and onward to Mars.

Summary

The journey of a Starship lunar lander from Earth to the Moon depends on replacing the single-rocket paradigm of the 1960s with a coordinated six-stage orbital supply chain. Because a Starship upper stage expends nearly its entire propellant load reaching Low Earth Orbit, filling its 1,200-metric-ton tanks requires an orbital depot supplied by multiple reusable tanker flights. Whether a single lunar landing ultimately takes SpaceX’s optimistic projection of six to eight tanker launches, the baseline 10 to 14 tankers, the Government Accountability Office’s 16-launch total, or the NASA Aerospace Safety Advisory Panel’s conservative 22-launch estimate will be determined by how much payload Version 3 tankers deliver to orbit and how effectively thermal insulation suppresses cryogenic boil-off.

By organizing the refueling campaign across two Earth orbits – a Low Earth Orbit depot aggregation phase followed by a Final Tanking Orbit top-off – and docking Starship directly with Orion in High Earth Orbit before the trans-lunar burn, NASA’s revised 2026 architecture reduces the propellant needed in lunar orbit while testing hardware interfaces early on Artemis III in 2027. If SpaceX proves automated ship-to-ship cryogenic fluid transfer and precision landing at the lunar South Pole, high-cadence orbital refueling will shift from the primary schedule risk of the Artemis program into the foundational logistics system of the cislunar economy.

Appendix: Useful Books Available on Amazon

• Rocket Propulsion Elements
• Design of Rockets and Space Launch Vehicles
• Escaping Gravity: My Quest to Transform NASA and Launch a New Space Age
• Moonrush: Improving Life on Earth with the Moon’s Resources
• Space Mathematics: Problems in Aeronautical and Space Engineering

Appendix: Top Questions Answered in This Article

Why Must SpaceX Refuel Starship in Earth Orbit Before Going to the Moon?

A Starship upper stage burns almost all of its onboard liquid methane and liquid oxygen propellant just to overcome Earth’s gravity and reach Low Earth Orbit. Without refilling its 1,200-metric-ton tanks in space, the spacecraft lacks the velocity change needed to travel to the Moon, land, and ascend back to orbit. Orbital refueling resets the rocket equation in space and allows Starship to deliver up to 100 metric tons of payload to the lunar surface.

Why Do Refueling Launch Estimates Range From Six to 22 Flights?

Neither NASA nor SpaceX has published a binding final tanker count because the total depends on three evolving engineering variables: tanker payload capacity, cryogenic boil-off rates, and orbital transfer efficiency. SpaceX Chief Executive Officer Elon Musk projects six to eight tanker flights assuming high-capacity Version 3 tankers and minimal evaporation. Conversely, NASA’s Aerospace Safety Advisory Panel estimates up to 22 launches when factoring in conservative boil-off margins and multi-orbit staging losses.

What Is the Difference Between a Starship Tanker, a Depot, and Starship HLS?

All three vehicles share the common nine-meter-diameter stainless-steel Starship airframe and Raptor engine propulsion system, but each is modified for a specific role. Tankers are reusable ships equipped with heat shields and aerodynamic flaps that haul surplus propellant from Earth to Low Earth Orbit and return to land. The depot is a stretched orbital storage vessel without reentry hardware, and Starship HLS is an unshielded lunar lander equipped with a crew cabin, landing legs, and mid-body landing thrusters.

What Is Cryogenic Boil-Off and How Does It Affect the Launch Schedule?

Liquid oxygen boils at minus 183 degrees Celsius and liquid methane boils at minus 161 degrees Celsius at standard pressure. When an orbital depot circles Earth, solar radiation and thermal infrared glow from Earth warm the tanks and cause a fraction of the stored liquid to evaporate into gas that must be vented. To outpace these evaporation losses, SpaceX plans to launch refueling tankers on a rapid six-day cadence from two separate launch complexes in Texas and Florida.

Why Does the Refueling Sequence Use Both Low Earth Orbit and a Final Tanking Orbit?

Splitting the refueling campaign across two orbital altitudes optimizes tanker payload mass while reducing thermal evaporation losses on the lunar lander. Individual tankers deliver maximum surplus fuel by flying only to Low Earth Orbit to fill the depot. After Starship HLS receives an initial refill in Low Earth Orbit and climbs to the higher Final Tanking Orbit, the refilled depot ascends to top off the lander in a cooler thermal environment closer to trans-lunar departure.

How Did NASA Change the Orion and Starship Rendezvous Plan in October 2026?

Under NASA’s original architecture, Starship HLS was supposed to fly uncrewed to the Moon and wait in a Near-Rectilinear Halo Orbit for astronauts arriving separately aboard Orion. Under the revised October 2026 plan, Orion docks with the fueled Starship lander in High Earth Orbit instead. Starship then fires its Raptor engines to push both joined spacecraft toward the Moon, inserting them into Low Lunar Orbit before two astronauts descend to the surface.

What Role Will the 2027 Artemis III Mission Play Before the Moon Landing?

In February 2026, NASA restructured Artemis III from a surface landing mission into a 2027 crewed systems demonstration in Low Earth Orbit modeled on Apollo 9. During the flight, astronauts aboard Orion will rendezvous and dock in Earth orbit with commercial lander test articles from SpaceX and Blue Origin to validate flight software, docking adapters, and communications. The first crewed lunar South Pole surface landing is scheduled to follow on Artemis IV in 2028.

Why Does Starship HLS Use Mid-Body Thrusters Instead of Raptor Engines for Touchdown?

Firing Starship’s powerful rear-mounted Raptor engines close to the lunar surface would excavate a deep crater in the loose lunar soil and spray high-speed rock debris against the base of the rocket. To prevent regolith erosion and landing instability, Starship shuts down its main Raptor engines roughly 100 meters above the ground. It completes touchdown using a ring of gaseous oxygen and methane thrusters mounted mid-way up the spacecraft’s hull.

How Do Astronauts Return to Earth After Completing Lunar Surface Operations?

Starship HLS is designed SOLELY for space and lunar operations and lacks the thermal heat shield and aerodynamic flaps required to survive reentry into Earth’s atmosphere. After spending several days exploring the lunar South Pole, the two surface astronauts launch from the Moon aboard Starship HLS and redock with the waiting Orion capsule in Low Lunar Orbit. All four astronauts then ride Orion back to Earth for a parachute-assisted splashdown in the Pacific Ocean.

How Does Blue Origin’s Revised Blue Moon Architecture Differ From SpaceX’s Plan?

Under NASA’s October 2026 architecture update, Blue Origin deferred in-space cryogenic propellant transfer for its initial crewed lunar missions. Instead, Blue Origin plans to launch three fueled propulsion transfer stages and one Blue Moon Mark 2 lander across four New Glenn rocket flights. Those four elements dock in Low Earth Orbit and fire sequentially like a multi-stage rocket on the way to an elliptical polar lunar orbit, avoiding ship-to-ship fluid transfer during the initial landing campaign.

Appendix: Glossary of Key Terms

Low Earth Orbit

An orbital region around Earth typically situated at altitudes between 160 kilometers and 2,000 kilometers above the surface. Because spacecraft can reach this region with the lowest energy expenditure from launch pads, it serves as the primary staging zone for orbital propellant depots and initial tanker deliveries.

Human Landing System

The commercial spacecraft program managed by NASA under the Artemis campaign to transport astronauts between lunar orbit and the Moon’s surface. SpaceX holds contracts to develop the Starship lunar lander variant, and Blue Origin holds a parallel contract to develop the Blue Moon crewed lunar lander.

Tsiolkovsky Rocket Equation

The fundamental mathematical formula of astronautics that calculates how much velocity change a rocket can achieve based on the effective exhaust velocity of its engines and the natural logarithm of its initial total mass divided by its final dry structural mass after burning propellant.

Delta-V

A standard astrodynamics measure representing the change in velocity required for a spacecraft to execute an orbital maneuver, such as climbing into Earth orbit, departing for the Moon, braking into lunar orbit, landing on the surface, or launching back into orbit.

Trans-Lunar Injection

A high-energy propulsive engine burn executed by a spacecraft in Earth orbit to place it onto a trajectory that intersects the Moon. Under NASA’s revised 2026 architecture for SpaceX, the fueled Starship lander performs this maneuver while docked with the crewed Orion spacecraft.

Aerospace Safety Advisory Panel

An independent federal advisory committee established by the United States Congress in 1968 after the Apollo 1 fire to evaluate safety performance, technical risks, and management practices across NASA human spaceflight programs and report its findings directly to agency leadership and lawmakers.

Government Accountability Office

An independent, nonpartisan legislative branch agency that audits federal spending, evaluates government program schedules and cost risks, and adjudicates federal contract bid protests for the United States Congress, including periodic oversight reports on NASA’s Artemis lunar exploration portfolio.

Methalox

A bipropellant rocket fuel combination consisting of liquid methane as the fuel and liquid oxygen as the oxidizer. Both liquids must be stored at cryogenic temperatures well below minus 160 degrees Celsius and are burned by SpaceX’s full-flow staged-combustion Raptor engines.

Cryogenic Boil-Off

The gradual evaporation of super-cold liquid propellants such as liquid oxygen, liquid methane, or liquid hydrogen into gas when external heat from sunlight or planetary radiation warms a spacecraft’s storage tanks in the vacuum of space, requiring venting or active refrigeration.

Ullage Gas

The pressurized gas occupying the empty volume inside a propellant tank alongside the liquid fuel or oxidizer. In microgravity, engineers must settle the liquid at the tank outlet so ullage gas does not enter transfer pipes and cause pump cavitation during orbital refueling.

Final Tanking Orbit

An intermediate staging Earth orbit at a higher altitude than Low Earth Orbit used in NASA’s Artemis IV refueling architecture. Starship HLS climbs to this orbit after its initial refill in Low Earth Orbit and receives a second and final fuel transfer from the ascending depot.

Near-Rectilinear Halo Orbit

A highly elongated seven-day orbit around the Moon that balances the gravitational pull of Earth and the Moon. Earlier Artemis plans designated this trajectory as the rendezvous point for Orion and commercial landers before NASA introduced provider-specific orbits in October 2026.

High Earth Orbit

An orbital region at high altitude above Low Earth Orbit where NASA’s Orion crew spacecraft is scheduled to rendezvous and dock with the fully fueled Starship Human Landing System before the combined spacecraft stack fires its engines to depart for Low Lunar Orbit.

Space Launch System

NASA’s government-owned super-heavy-lift expendable launch vehicle designed to launch four astronauts aboard the Orion crew capsule from Kennedy Space Center in Florida, using two solid rocket boosters and a core stage powered by four Space Shuttle-derived RS-25 liquid hydrogen engines.

Low Lunar Orbit

A circular or near-circular trajectory typically located roughly 100 kilometers above the surface of the Moon. Operating from this low altitude reduces the propellant required for a lunar lander to descend to the surface and shortens the ascent transit time back to the orbiting crew capsule.