Starship & Artemis: The Infrastructure of Return

The Artemis program is the current framework for human lunar exploration. This program utilizes a multi-component infrastructure to facilitate the return of personnel to the lunar surface. The primary elements of this infrastructure include the Space Launch System (SLS), the Orion spacecraft, and the Starship Human Landing System (HLS).

Starship Human Landing System Engineering Specifications

The Starship HLS is a modified variant of the SpaceX Starship vehicle. It is designed to function exclusively in space and on the lunar surface. Because it does not return to Earth, it lacks heat shielding and aerodynamic control surfaces such as grid fins or body flaps. This design decision reduces the overall dry mass of the vehicle.

Dimensions and Mass

The Starship HLS stands approximately 52 meters (171 feet) in height. The vehicle has a diameter of 9 meters. The dry mass is estimated at 100,000 kg. This mass budget supports a significant payload capacity to the lunar surface, with the potential to deliver up to 200 tons of cargo in a cargo-only configuration.

Propulsion Systems

The vehicle utilizes two distinct propulsion systems:

1. Main Propulsion: The base of the Starship HLS is equipped with six Raptor engines. These engines utilize sub-cooled liquid methane (CH4) and liquid oxygen (LOX). Three engines are sea-level variants for high-thrust maneuvers, and three are vacuum-optimized variants (Rvac) with larger nozzles for increased efficiency in space.

2. Landing Engines: For the terminal phase of the lunar descent, the Starship HLS utilizes a ring of high-thrust landing engines located mid-body. These engines burn gaseous oxygen and methane. The placement prevents high-velocity engine plumes from disturbing the lunar regolith, which can cause cratering and damage to the vehicle's base or nearby infrastructure.

Propellant Transfer and Orbital Depots

The Starship HLS requires more propellant than a single launch can provide to reach the Moon and return to lunar orbit. This necessitates an orbital refueling infrastructure in Low Earth Orbit (LEO).

The Refueling Sequence

The mission profile begins with the launch of a Propellant Depot variant of Starship. This vehicle remains in LEO to store methane and oxygen. Subsequently, a series of tanker Starships are launched to transfer propellant to the depot.

• Tanker Capacity: Each tanker is expected to deliver approximately 100 to 150 tons of propellant per flight.

• Mission Requirements: An Artemis III mission may require between 6 and 15 tanker flights to fully fuel the HLS, depending on boil-off rates and delivery efficiency.

• Cryogenic Management: The storage of LOX and CH4 for extended periods requires active thermal management and insulation to minimize propellant loss due to boil-off.

Docking and Transfer Mechanics

Propellant transfer occurs via a specialized docking interface. The vehicles dock tail-to-tail or side-to-side, using settled acceleration to move the liquid from the tanker to the receiver. This process is critical for heavy-lift missions beyond LEO.

Orbital Mechanics: The Near Rectilinear Halo Orbit (NRHO)

The Artemis architecture utilizes a specific lunar orbit known as the Near Rectilinear Halo Orbit (NRHO). This orbit provides a stable staging point for lunar operations.

Characteristics of NRHO

The NRHO is a highly elliptical orbit that passes over the lunar North and South poles. It provides several technical advantages:

• Constant Communication: The spacecraft maintains a direct line of sight with Earth for the majority of the orbit.

• Thermal Stability: The orbit avoids long periods of shadow, ensuring constant solar power availability.

• Accessibility: It requires minimal delta-v (velocity change) for spacecraft arriving from Earth or ascending from the lunar surface.

Rendezvous and Docking

During the Artemis III mission, the Orion spacecraft, carrying four astronauts, will launch on an SLS rocket and travel to the NRHO. Simultaneously, the pre-fueled Starship HLS will transit from LEO to the NRHO. The two vehicles will perform an automated rendezvous and docking.

Lunar Surface Operations

Upon docking in lunar orbit, two members of the crew will transfer from Orion to the Starship HLS. The HLS then undocks and initiates the descent to the lunar South Pole.

Descent and Landing

The descent is managed by the onboard guidance, navigation, and control (GNC) systems. These systems utilize terrain-relative navigation (TRN) to identify safe landing zones and avoid hazards such as craters or large boulders. The mid-body engines activate in the final 100 meters to ensure a soft touchdown.

Surface Stay and Infrastructure

The Artemis III mission plan includes a surface stay of approximately 6.5 days. The Starship HLS serves as the primary habitat during this period.

• Elevator System: Due to the height of the Starship HLS, an elevator system is integrated into the side of the hull to transport astronauts and equipment from the airlock to the surface.

• Life Support: The internal volume of Starship HLS provides over 1,000 cubic meters of pressurized space, which is significantly larger than previous lunar landers.

• Power: A solar array encircles the upper section of the HLS to provide electrical power during the lunar day.

Artemis IV and the Lunar Gateway

The infrastructure for Artemis IV expands to include the Lunar Gateway. The Gateway is a small space station that will remain in NRHO.

Gateway Components

The initial Gateway configuration consists of the Power and Propulsion Element (PPE) and the Habitation and Logistics Outpost (HALO). These modules provide:

• Command and Control: Centralized management of lunar surface sorties.

• Docking Ports: Multiple ports for Orion, HLS, and logistics resupply craft.

• Scientific Research: External and internal payloads for deep-space research.

Mission Integration

In Artemis IV, the Orion spacecraft will dock directly with the Gateway. The crew will then transition to a waiting Starship HLS that is also docked at the station. This permanent orbital infrastructure reduces the complexity of individual missions and facilitates long-term presence.

Technical Challenges in Infrastructure Development

Several engineering hurdles remain for the successful implementation of this infrastructure.

1. Cryogenic Long-Term Storage: Preventing the boil-off of liquid methane and oxygen over the 90-day loiter period in lunar orbit is a primary concern.

2. Raptor Engine Reliability: The Raptor 2 engines must demonstrate high reliability during multiple relights in vacuum and during the critical landing phase.

3. Dust Mitigation: Lunar regolith is abrasive and electrostatically charged. Infrastructure must be designed to prevent dust from entering seals, docking ports, and mechanical systems such as the elevator.

The integration of Starship into the Artemis program represents a shift toward high-mass payload delivery and reusable lunar infrastructure. The technical specifications of the HLS, combined with the logistics of orbital refueling and the stability of the NRHO, form the engineering foundation for the return to the Moon.