Lanyue

The Lanyue lander, formerly known as the China crewed lunar surface lander (中国载人月面着陆器) or simply as the lunar surface lander (月面着陆器), is a spacecraft under development by the China Academy of Space Technology. The purpose of the lander is to carry two astronauts to the lunar surface and to return them to lunar orbit after a set period of time. The lander's initial lunar-landing attempt is envisioned to occur by 2029.

Nomenclature
The official names for both the crewed lunar lander and the next-generation crewed spacecraft, the Mengzhou (梦舟), were revealed by the China Manned Space Agency (CMSA) on 24 February 2024. One possible English translation for Lanyue is Embracing the Moon while the English translation for Mengzhou can be Vessel of Dreams or Dream Vessel.

Overview
Since at least August 2021, Western news media has reported that China's main spacecraft contractor was working on a human-rated landing system for lunar missions. On 12 July 2023, at the 9th China (International) Commercial Aerospace Forum in Wuhan, Hubei province, Zhang Hailian, a deputy chief designer with the CMSA, publicly introduced a preliminary plan to land two astronauts on the Moon by the year 2030. Under this plan, the astronauts will conduct scientific work upon landing on the Moon, including the collection of lunar rock and regolith samples. After a short stay on the lunar surface, they will carry the collected samples back into lunar orbit in their spacecraft and subsequently, to Earth.

The preliminary plan describes a 'landing segment' that consists of a new lunar-lander attached to a propulsion stage which together are to be launched autonomously into a trans-lunar injection (TLI) orbit by the under-development Long March 10 rocket. The lander-propulsion stage arrangement is somewhat analogous to the lander-orbiter architecture of the 2020 Chang'e 5 and the current Chang'e 6 robotic lunar sample-return missions; however, unlike the orbiters for the robotic missions, the propulsion stage for the crewed lander will descend from lunar orbit together with the lander rather than remaining in lunar orbit. (The propulsion stage will undergo a controlled impact landing on the Moon after it separates from the crewed lander during the final stages of the descent, while the lander itself will attempt a powered soft landing).

On 24 April 2024, Lin Xiqiang, deputy director of China Manned Space Agency (CMSA), stated that the initial development of various products for China's lunar missions, including the Lanyue lander, is complete; according to Lin, mechanical and thermal articles for the lander and other mission segments have been constructed and the requisite rocket engines are undergoing hot fire tests. Lin further elaborated that prototype production and tests are in full swing and that the crewed lunar exploration launch site is currently under construction near the existing coastal Wenchang spaceport in Hainan province.

Lander attributes
A model of the under-development lunar lander was unveiled at an exhibition to mark three decades of China's human spaceflight program on 24 February 2023 at the National Museum of China in Beijing.

The physical model of the under-development lander, when considered together with the presentation by Zhang Hailian on 12 July 2023, suggests the future spacecraft will have the following components: four 7500-newton main engines, numerous attitude-control thrusters for precise maneuvering, a stowed lunar rover capable of carrying two astronauts, docking mechanisms (for docking with the Mengzhou spacecraft), a crew hatch (for EVAs), a ladder attached to one of the landing legs, two solar arrays, various antennaes and sensors.

The estimated mass of the fully-fuelled landing segment (lunar-lander plus propulsion-stage) is 26000 kg.

Lunar rover
Models of the crewed lander includes a four-wheeled rover stowed on the lander's external wall. CMSA previously issued an open call to private, public, and educational institutions to submit development plans for the future lunar rover; according to CMSA, fourteen groups submitted proposals in response to the open solicitation and eleven of the fourteen proposals advanced to the expert-review stage. On 24 October 2023, CMSA announced that two of the remaining eleven submitted proposals have advanced to the detailed design phase while another six groups will receive continued support to enable them to continue research into innovative aspects of their proposals.

Survey of journal literature reveals that the planned lunar rover may incorporate "differential-braking" and "off-ground detection" technologies to enhance its anti-slip and steering-stability characteristics during high-speed traverse. Engineering prototypes have been built for design verification purposes.

The rover's planned mass is about 200 kilograms and will be able to carry two astronauts; it has a planned traverse-range of about 10 kilometres.

Lander mission architecture
Under CMSA's crewed lunar landing plan, the landing segment initially will be injected into an Earth-Moon transfer orbit via the Long March 10 carrier rocket, and subsequently acquire lunar orbit under its own power. It then will await a lunar orbit rendezvous with and docking by the separately launched Mengzhou spacecraft (formerly known as the next-generation crewed spacecraft, the analog to the Apollo program's Apollo command and service module) whereupon two astronauts will transfer to the lander, undock from Mengzhou, and maneuver the landing segment for a lunar-landing attempt.

The landing segment's powered descent phase will employ a "staged-descent" concept. Under this concept, the combined lander and propulsion stage will begin descending from lunar orbit with the latter providing the necessary deceleration; when the stack is close to the surface, the lander will separate from the propulsion stage and proceed to complete the powered descent and a soft-landing under the lander's own power (the discarded propulsion stage meanwhile will impact the lunar surface a safe distance away from the lander). At the conclusion of the surface portion of the mission, the full lunar lander will act as the ascent vehicle for the astronauts to return to lunar orbit. According to a report by the Xinhua News Agency, the lander also will be capable of autonomous flight operations.

As of 2022, the landing system is envisioned to enable a six-hour stay on the lunar surface by two astronauts. It is unclear from the source if the quoted 'six-hour stay on the moon' references the lander's total time on the lunar surface or the astronauts' surface-EVA duration; if the latter, then the proposed surface mission duration would be comparable to those carried out by the United States' Apollo 11 and Apollo 12 missions. During the previously-cited 2023 aerospace forum in Wuhan, Zhang Hailian also stated that a lunar surface-EVA spacesuit with an endurance period of no less than eight hours is currently under development.



Potential landing sites
Members of the Chinese Academy of Sciences have begun site selection research ("suggestions") for the anticipated crewed lunar exploration program. Thirty prime landing sites have been identified (narrowed down from a preliminary list of 106 and an interim list of 50); the thirty sites are located in both the lunar north and south polar regions as well as in the lunar near and far sides. Numerous criteria, intended to maximize mission scientific value while taking into account crew safety and engineering feasibility, were considered by the team. Examples of the 30 prime sites include the following: Ina crater/depression, Reiner Gamma, and Rimae Bode on the lunar near side, Apollo basin, Aitken crater, and Mare Moscoviense on the lunar far side, Shackleton crater in the lunar south polar region, and Hermite crater in the lunar north polar region.

Earth-Moon trajectory design
Preliminary trajectory designs based on specific landing sites and landing periods have also been carried out by a team from the Nanjing University of Aeronautics and Astronautics and from the China Astronaut Research and Training Center. In particular, the team analyzed possible Earth-Moon transfer trajectories based on seven potential landing sites, including Rimae Bode, a series of lunar rilles west of the Bode crater, and Mare Moscoviense, covering the period from 2027 until 2037. The analysis employed a dynamic weighting method that quantified mission efficiency factors and engineering constraints, combined with the application of a pseudostate trajectory model to optimize the computational efficiency of trajectory design and landing site/time selection.

The pseudostate model was first proposed by J.S. Wilson in 1969 to study Earth-Moon spacecraft transfer trajectories. In the context of an Earth-Moon-spacecraft three-body system, the pseudostate method usually is more computationally efficient than the traditional patched-conic method of trajectory design.

The patched-conic method essentially seeks to "patch" together two (Keplerian) two-body ellipses (the conics) at a point of intersection defined by the Moon's gravitational sphere of influence, while taking into account the various physical constraints. This method can result in large errors that may be controlled by a possibly unstable and time-consuming iterative computational process. The pseudostate model modifies the conic-patching method by defining a pseudostate transformation sphere (PTS), a region in which the spacecraft trajectory is calculated as an approximate solution to the restricted three-body problem. The method starts by calculating an initial simple two-body Earth-spacecraft ellipse and using it to propagate the spacecraft's position to a point within the Moon's PTS (the spacecraft's pseudostate), next the approximate restricted three-body solution is applied and the pseudostate is backward propagated to a point on the surface of the Laplace sphere, which defines the beginning of the Moon's gravitational sphere of influence, and finally a two-body Moon-spacecraft conic is calculated and the spacecraft location is forward propagated from the surface of the Laplace sphere to an arbitrary perilune point. The Laplace sphere and the gravitational sphere of influence concepts used in the two models, when applied to Earth-Moon system with an approximately circular orbit, is given by

$$R_\text{Laplace} \; = \; D \; \left( \frac{m}{M} \right)^{2/5},$$

where $$R_\text{Laplace}$$ is the radius of Laplace sphere, $$D$$ is the average Earth-Moon distance, $$m$$ is the mass of the Moon and $$M$$ is the Earth's mass. Strictly speaking, the Laplace sphere is not a sphere but a changing hypersurface defined at each point of the path of a gravitational mass. The criterion for calculating the Moon's Laplace sphere is to analyze the Moon's gravity as the primary force acting in the region under consideration while the Earth's gravity is treated as a perturbing force. The Laplace sphere differs from the Hill sphere because the calculation of the latter sphere requires the presence of stable orbits while the former does not..