Key Takeaways

• The Human Landing System transports astronauts from lunar orbit to the surface and back using commercial architectures.
• SpaceX utilizes a modified Starship vehicle requiring multiple Earth-orbit refueling missions before departing for the Moon.
• Blue Origin employs the Blue Moon lander with liquid hydrogen propulsion focused on sustainable high-performance operations.

Introduction

The National Aeronautics and Space Administration (NASA) established the Artemis program to return humans to the lunar surface. A central component of this architecture is the Human Landing System (HLS). This system serves as the vehicle that transports crew members from the lunar orbit – specifically a Near Rectilinear Halo Orbit (NRHO) – to the lunar surface and subsequently returns them to orbit. Unlike the Apollo Lunar Module, which was designed and operated directly by the government, the HLS is procured through a Public-Private Partnership model. Commercial partners design, build, and operate the landers, while the government purchases the service of landing crew on the Moon.

The HLS integrates into a broader infrastructure that includes the Space Launch System (SLS) rocket and the Orion spacecraft. The operational flow involves the crew launching on SLS/Orion, traveling to the Moon, and docking with the HLS in lunar orbit. The HLS then performs the descent, surface operations, and ascent. The program emphasizes sustainability, aiming for recurring missions to the lunar South Pole, a region known for challenging lighting conditions and potential water ice resources. Two providers currently hold contracts to develop these landers: SpaceX and Blue Origin.

Procurement and Program Structure

The procurement strategy for the HLS falls under the Next Space Technologies for Exploration Partnerships (NextSTEP-2) Appendix H broad agency announcement. The selection process occurred in phases. Initially, three teams led by SpaceX, Blue Origin, and Dynetics received funding for design work. In April 2021, the government selected SpaceX as the sole provider for the initial crewed demonstration mission, known as Artemis III. This decision utilized the Option A award.

Following this selection, the program expanded to ensure redundancy and competition for future missions. This expansion, termed the Sustaining Lunar Development (SLD) phase, sought a second provider for a recurring service. In May 2023, the government selected a team led by Blue Origin to develop a second lander system for the Artemis V mission. Consequently, the HLS program now manages two distinct vehicle architectures operating in parallel to support long-term lunar exploration.

SpaceX Starship HLS Architecture

The Starship HLS is a specialized variant of the core Starship transportation system. It represents a significant departure from traditional capsule-based landers due to its massive size and integrated design. The vehicle serves as both the transit module and the surface habitat. The design leverages the reusable architecture of the Starship system but incorporates modifications specific to the lunar environment.

Vehicle Structure and Materials

The primary structure consists of 304L stainless steel. This material offers high strength at cryogenic temperatures and a high melting point, although the lunar variant does not require the thermal protection system tiles found on the Earth-return versions. The vehicle stands approximately 50 meters tall with a diameter of 9 meters. This volume provides substantial habitable space for the crew and payload capacity for scientific equipment.

Propulsion Systems

Propulsion relies on Raptor engines, which utilize liquid methane (CH4) and liquid oxygen (LOX) as propellants. This methalox combination offers advantages in terms of specific impulse and storage density compared to hypergolic fuels. The HLS variant includes two distinct engine configurations:

• Vacuum Raptors: These large-nozzle engines provide high efficiency for orbital maneuvers and the majority of the descent and ascent burns.
• Landing Engines: To mitigate the risk of kicking up high-velocity lunar regolith (dust) that could damage the vehicle or surrounding hardware, Starship HLS features a set of smaller, elevated thrusters located mid-body. These thrusters perform the final descent and touchdown maneuvers, placing the plume impingement point higher above the surface.

Power and Thermal Control

Power generation on the lunar surface presents unique challenges due to the extended darkness periods at the South Pole. The Starship HLS employs a band of solar panels wrapped around the circumference of the vehicle body. This orientation ensures continuous power generation regardless of the vehicle’s orientation relative to the sun during transit. For surface operations, the vertical height of the solar array keeps it above local terrain shadows for longer durations.

Thermal control relies on radiators and active cooling loops. The use of cryogenic propellants requires active Cryogenic Fluid Management (CFM) to prevent boil-off during the transit and loiter phases. The stainless steel hull is polished or painted white to reflect solar radiation and minimize passive heat absorption.

Crew Interface and Egress

The crew cabin resides in the upper section of the vehicle. It includes sleeping quarters, a galley, sanitation facilities, and science stations. Because the cabin sits dozens of meters above the surface, a traditional ladder is impractical. The Starship HLS utilizes a mechanical elevator system to transport crew and cargo from the airlock down to the lunar surface. This elevator deploys through a side hatch and travels along a track on the exterior of the hull. The system includes redundancy features to ensure crew can return to the cabin in the event of a mechanical failure.

Blue Origin Blue Moon Architecture

The Blue Moon lander represents a different approach, focusing on high-specific-impulse hydrogen propulsion and a dedicated cislunar architecture. The Blue Origin National Team initially included partners such as Lockheed Martin, Boeing, and Draper. The design has evolved into the MK2 configuration for the SLD contract.

Vehicle Structure and Design

The Blue Moon MK2 is a single-stage reusable lander. It stands approximately 16 meters tall and fits inside a 7-meter payload fairing. The structure utilizes aluminum and composite materials to minimize dry mass. Unlike the massive Starship, Blue Moon is sized more specifically for the ferry mission between NRHO and the surface, although it still offers significant payload capability.

Propulsion and Power

The core propulsion system uses the BE-7 engine. This engine burns liquid hydrogen (LH2) and liquid oxygen (LOX). The hydrolox propellant combination delivers high specific impulse, making it highly efficient for the energy-intensive maneuvers required for lunar descent and ascent. The BE-7 features deep throttling capabilities, allowing it to reduce thrust significantly for a precise, soft touchdown.

The choice of liquid hydrogen introduces technical complexities regarding storage. Hydrogen has a very low boiling point, making it susceptible to boil-off. To address this, Blue Moon incorporates advanced cryocoolers and multi-layer insulation (MLI) to maintain the propellant in a liquid state for extended mission durations.

Power is provided by hydrogen fuel cells, which supplement solar arrays. Fuel cells are particularly effective for surviving the lunar night, as they can generate electricity from boil-off gases or stored reactants without reliance on solar flux.

Crew Systems and Operations

The crew module sits atop the propellant tanks. It provides a pressurized environment for four astronauts. The lower height of the vehicle compared to Starship allows for a shorter ladder or simpler lift mechanism for surface access. The lander is capable of docking with the lunar Gateway or the Orion spacecraft directly.

Concept of Operations (CONOPS)

The operational profiles for both landers differ significantly in their deployment but converge during the lunar phase.

Aggregation and Refueling

The Starship HLS requires a significant campaign of Earth-orbit aggregation. The concept involves:

1. Launch of the Starship HLS Depot to Low Earth Orbit (LEO).
2. Launch of multiple Starship Tanker flights to transfer propellant to the Depot.
3. Launch of the Starship HLS vehicle.
4. Docking of the HLS with the Depot to load full propellant tanks.
5. Trans-Lunar Injection (TLI) burn to send the HLS to the Moon.

This architecture necessitates rapid launch cadences and automated docking technologies. The high number of launches is a trade-off that allows the HLS to arrive at the Moon with a massive payload capacity.

The Blue Moon architecture also utilizes refueling but may employ a Cislunar Transporter. A tug or propellant carrier ferries fuel from LEO to the lander in NRHO or an intermediate orbit.

Lunar Orbit Rendezvous

Both landers operate in Near Rectilinear Halo Orbit (NRHO). This orbit is a stable, highly elliptical path that balances the gravitational pull of the Earth and Moon. It offers continuous line-of-sight communication with Earth and low delta-v access to the lunar surface.

1. Orion launches with the crew on SLS.
2. Orion travels to the Moon and enters NRHO.
3. Orion docks with the waiting HLS (Starship or Blue Moon).
4. Crew transfers from Orion to the HLS.

Descent and Surface Operations

Following crew transfer, the HLS undocks and performs a descent burn. The vehicle lowers its periapsis and initiates the braking phase. Advanced guidance, navigation, and control (GN&C) systems utilize Terrain Relative Navigation (TRN) and Lidar to identify safe landing sites in real-time. The target sites are located at the lunar South Pole, where lighting conditions create long shadows and high contrast, complicating visual navigation.

Upon landing, the HLS transitions to surface mode. It provides life support, power, and communications relay for the crew. EVAs (Extravehicular Activities) are conducted using the HLS airlock. The duration of the surface stay for initial missions is approximately one week.

Ascent and Return

At the conclusion of the surface mission, the HLS ascends back to NRHO.

1. The vehicle performs a powered ascent.
2. It executes rendezvous maneuvers to locate Orion.
3. The HLS docks with Orion.
4. Crew and samples transfer back to Orion.
5. Orion departs for Earth.
6. The HLS remains in orbit or is disposed of, depending on the mission profile (expendable vs. reusable).

Technical Challenges and Risks

The development of these systems involves overcoming several significant engineering hurdles.

Cryogenic Fluid Management (CFM)

Storing cryogenic propellants (methane, hydrogen, oxygen) for months in space is a primary technical risk. Heat from the sun and the spacecraft’s electronics causes propellants to boil into gas. Without active cooling (cryocoolers) or passive mitigation (sunshades, orientation), the fuel tanks would empty before the mission begins. Zero-gravity fluid transfer is also complex; settling the fuel to the bottom of the tank without gravity requires ullage motors or rotational maneuvers.

Dust Mitigation

Lunar regolith is abrasive, electrostatically charged, and sharp. During landing, engine plumes accelerate this dust to high velocities. This ejecta can damage sensors, solar panels, and the vehicle structure. It also poses a threat to the Orion spacecraft or Gateway if the HLS is not sufficiently cleaned before docking. The Starship’s high-mounted thrusters and Blue Moon’s deep-throttling capabilities are specific design responses to this problem.

Precision Landing

The South Pole features rugged terrain with craters and boulders. The landing ellipse (the margin of error for the landing spot) must be small – often less than 100 meters. This requires autonomous hazard detection and avoidance systems that function faster than human reaction times. The systems process optical and Lidar data to map the terrain underneath the vehicle during descent and adjust the trajectory to find a flat spot.

Eclipse Survival

The lunar South Pole experiences periods of darkness, although shorter than the 14-day night at the equator. However, the HLS must survive orbital eclipses where it passes through Earth’s shadow. During these periods, solar power is unavailable, and temperatures drop drastically. Batteries and fuel cells must bridge these gaps, and thermal heaters must keep electronics and propellants within operational limits.

Comparison of Technical Approaches

Interface with External Systems

The HLS does not operate in a vacuum but connects with multiple other architecture elements.

The Gateway

The Lunar Gateway is a small space station planned for NRHO. While early Artemis missions may involve direct docking between Orion and HLS, later sustainable missions will utilize Gateway as a transfer hub. The HLS must support the International Docking System Standard (IDSS) to mate with Gateway ports. This station provides a safe haven for HLS between missions and facilitates data relay.

Extravehicular Mobility Units (EMUs)

The HLS must interface with the next-generation spacesuits, known as Exploration Extravehicular Mobility Units (xEMUs). The lander provides the cabin pressure, oxygen recharge, and scrubbing capabilities to support these suits. The airlock design must accommodate the bulk of the suits and allow for dust mitigation protocols, such as vacuum cleaning the suits before the crew re-enters the main cabin. Axiom Space and Collins Aerospace have been involved in the development of suit technologies that will interface with these landers.

Summary

The Artemis Human Landing System represents a paradigm shift in lunar exploration hardware. By leveraging commercial competition and differing technical architectures, the program seeks to establish a resilient and redundant capability for accessing the lunar surface. SpaceX’s Starship offers massive scale and payload capacity through a methalox-based, LEO-refueling architecture. Blue Origin’s Blue Moon focuses on high-efficiency hydrolox propulsion and cislunar sustainability. Both systems face significant technical challenges regarding cryogenic fluid management, automated precision landing, and operation in the extreme environment of the lunar South Pole. Success depends on the validation of these subsystems and the reliable execution of complex concepts of operation involving orbital rendezvous and fueling.

Appendix: Top 10 Questions Answered in This Article

What is the Artemis Human Landing System?

The Human Landing System (HLS) is the spacecraft component of NASA’s Artemis program responsible for carrying astronauts from lunar orbit to the surface of the Moon and back. It is built and operated by commercial partners rather than being a government-owned vehicle.

Which companies are building the landers for Artemis?

SpaceX and Blue Origin are the two primary companies under contract. SpaceX is developing the Starship HLS for the initial landing, while Blue Origin is developing the Blue Moon lander for subsequent sustainable missions.

How does SpaceX’s Starship HLS differ from the standard Starship?

The HLS variant lacks the heat shield tiles and flaps required for Earth reentry, as it remains in space. It also features landing legs, a solar array band around the body, and high-mounted thrusters to avoid kicking up lunar dust during touchdown.

What fuel does the Starship HLS use?

Starship HLS uses a combination of liquid methane and liquid oxygen, known as methalox. This fuel is chosen for its density and efficiency, and it is combusted in Raptor engines.

What fuel does the Blue Moon lander use?

Blue Moon uses liquid hydrogen and liquid oxygen, known as hydrolox. This combination provides a very high specific impulse (efficiency), which is beneficial for the high-energy demands of lunar ascent and descent.

How do astronauts get down to the surface from the Starship HLS?

Because the crew cabin is located near the top of the 50-meter vehicle, astronauts use a mechanical elevator system. This elevator lowers them and their equipment from the airlock to the lunar surface.

Why is orbital refueling necessary for these landers?

The landers are too heavy to launch directly to the Moon with full fuel tanks using current rockets. They must launch to orbit first and receive propellant from tanker spacecraft to have enough energy to reach the Moon, land, and take off again.

What is the Near Rectilinear Halo Orbit (NRHO)?

NRHO is a stable orbit around the Moon that passes over the poles. It is the staging ground where the Orion capsule (or the Gateway station) meets the HLS for crew transfer before the descent to the surface.

What are the main risks associated with cryogenic fuels in space?

The main risk is boil-off, where heat from the sun causes the liquid fuel to turn into gas and escape. Long-duration missions require active cooling systems (cryocoolers) and insulation to keep the fuel in a liquid state for months.

Why is landing at the lunar South Pole difficult?

The South Pole has extreme lighting conditions with long, shifting shadows that can confuse visual navigation sensors. The terrain is also rugged, requiring precise automated systems to identify safe, flat landing spots among craters and boulders.

Appendix: Top 10 Frequently Searched Questions Answered in This Article

Who won the NASA lunar lander contract?

NASA awarded contracts to both SpaceX and Blue Origin. SpaceX was selected for the initial Artemis III landing, while Blue Origin was selected for the Artemis V mission to provide a second, sustainable landing option.

How much did the Artemis lander cost?

The contracts are fixed-price awards. SpaceX received an initial award of approximately $2.9 billion for the first mission, while the Blue Origin-led team received a contract valued at roughly $3.4 billion for their development and demonstration mission.

Will Starship land on the Moon?

Yes, the Starship HLS variant is designed specifically to land on the Moon. It will not return to Earth but will ferry crew between lunar orbit and the lunar surface.

How many astronauts fit in the Artemis lander?

The landers are designed to support a crew of up to four astronauts on the surface. For the initial missions, two crew members are expected to descend to the surface while two remain in orbit on Orion.

When will humans land on the Moon again?

The timeline is subject to technical progress and schedule adjustments. The Artemis III mission, which intends to land the first humans since Apollo, is currently targeted for the latter half of the 2020s.

What is the difference between HLS and Orion?

Orion is the spacecraft that launches from Earth, carries the crew to lunar orbit, and returns them to Earth. The HLS is the specialized vehicle that takes the crew from Orion (in lunar orbit) down to the Moon’s surface and back up to Orion.

Why does Blue Origin use hydrogen?

Blue Origin uses liquid hydrogen because it is the most efficient chemical rocket fuel available in terms of specific impulse. This efficiency allows for a lighter vehicle or higher payload capacity for the demanding maneuvers required for lunar landing.

Does the Artemis lander have an airlock?

Yes, both lander designs incorporate an airlock. This chamber allows astronauts to put on their spacesuits and exit the pressurized cabin to walk on the moon without venting the entire atmosphere of the ship.

What happens to the lander after the mission?

For the initial missions, the lander may be disposed of in a heliocentric orbit or crashed into the lunar surface. In future sustainable architectures, the landers are designed to be refueled in orbit and reused for multiple trips to the surface.

Is the lunar lander reusable?

Both SpaceX and Blue Origin have designed their architectures with reusability in mind. The goal is to establish a system where landers remain near the Moon and are refueled by tankers, reducing the cost of subsequent missions.