A 1-stage, absolutely reusable lunar lander makes the best sense of human return to the moon

When astronauts return to the moon for the first time since the Apollo era, they will rely on a number of mission elements to get them there and back safely. These include the Space Launch System (SLS) and the Orion spaceship, which are used to launch a four-person crew and take them to the moon. Until recently, the question of how they get to and from the surface remained unsolved as there were a few options.

To find out which ones are best in terms of performance and cost, researchers at the Skolkovo Institute of Science and Technology (Skoltech) in Moscow and the Massachusetts Institute of Technology (MIT) examined several dozen proposals. In the end, they found that a single-stage reusable lunar lander that could transport astronauts to and from the orbiting moon gate was the best option.

Their findings were published in an article titled “Lunar Human Landing System Architecture Tradespace Modeling”, which was recently published in Acta Astronautica magazine. The study was conducted by Skoltech researchers Kir Latyshev, Nicola Garzaniti, and Associate Professor Alessandro Golkar, which was attended by Edward Crawley – an MIT professor of aerospace and engineering systems.

During a speech at the Marshall Space Flight Center, VP Mike Pence urged NASA to land U.S. astronauts on the moon by 2024. Photo credit: NASA / White House

The question of what type of landing system would be best arose from NASA’s accelerated schedule announced by VP Pence at the fifth session of the National Space Council at the Marshall Space Flight Center on March 26, 2019.At the time, Pence dismissed the NASA advises astronauts to return to the moon by “whatever means” by 2024 (four years later than originally planned).

This new schedule forced NASA to undertake a series of reorganizations, as well as a review of its budget and operational plan. Previously, NASA had planned to mount the Lunar Gateway in orbit around the moon before landings were made. This should begin in 2022 with the deployment of the power and propulsion element (PSA) of the gateway, which was to be launched as part of the Artemis II mission.

The other elements – the HAbitation and Logistics Outpost (HALO), the ESPRIT service module, and the International Habitation Module (iHAB) – would be delivered between 2024 and 2027. By then, a Human Landing System (HLS) would be added by a crewed mission to the surface by 2028. However, a 2024 deadline for the crewed mission forced NASA to reconsider using the gateway at all.

By March 2020, NASA decided that the Lunar Gateway was not required to meet Project Artemis’ new schedule and stated that it was no longer a priority. The decision was made by Doug Loverro, then Associate Administrator of NASA’s Directorate for Human Exploration and Operations Mission (HEO-MD), as part of their plan to “reduce the risk” of the mandatory tasks associated with Artemis.

These views were expressed by Doug Loverro, who replaced William Gerstenmaier in July 2019 as part of a reorganization to accelerate progress on the SLS and the Artemis program in general. As Loverro stated during a NASA advisory board science committee (Friday March 13th), he has been working to make Artemis “risk-free” so NASA can focus on meeting Artemis’ mandatory targets and the 2024 deadline to reach.

This meant that NASA and its trading partners had to come up with a new strategy for landing astronauts on the moon. One of the options now on the table was a disposable lander that could be integrated into the Orion capsule or station. To develop this HLS, NASA commissioned SpaceX, Blue Origin and Dynetics as part of the Next Space Technologies for Exploration Partnerships (NextSTEP-2).

Currently, NASA plans to send astronauts back to the moon in 2024 and then deploy the Lunar Gateway with subsequent Artemis missions. In this way, they can send the “first woman and the next man” to the moon by 2024 while achieving the long-term goal of creating a program for “sustainable lunar exploration” (ie regular missions of longer duration).

To assess which HLS system would be optimal for the Artemis missions, Latshyev and his colleagues developed a number of mathematical and architectural screening models to evaluate the various options for sending a crew of four on a seven-day mission to the moon. This included a two-tier architecture for the lander, similar to the lunar module used by the Apollo astronauts.

Artist’s concept of the optimal strategy for the “last mile” to the moon. Image credit: Skoltech

These landers consisted of a descent and an ascent module, the former of which would remain on the lunar surface. Latshyev and his colleagues then took into account the gateway’s orbit, which NASA plans to station in a near-straight-line L2 half-orbit, and the amount of propellant needed. In total, they examined 39 variants of a future HLS and weighed the potential benefits against the possible costs.

Ultimately, they came to some conclusions depending on whether the lander would travel with the Orion spaceship (consumable) or integrated with the Lunar Gateway (reusable). Overall, they found that the best option for short missions to and from the lunar surface was a single-stage reusable module that relied on liquid oxygen and liquid hydrogen (LOX / LH2) propellants. As Latyshev stated in a recent Skoltech article:

“Interestingly, our study finds that even in orbit, when completely dispensable vehicles are taken into account, the two-stage (Apollo-like) landing system is still expected to have lower masses and therefore lower costs – which kind of confirms the Apollo decision again. However, reusability changes this.

“Although 1-tier and 3-tier vehicles are still heavier than the 2-tier vehicles in this case, they can reuse more of the ‘vehicle mass’ (around 70-100% compared to around 60% for the 2-tier vehicles Vehicles) option) over and over, saving money on manufacturing and delivering new vehicles to the orbit station and potentially making lunar missions cheaper. “

Artist illustration of the new spacesuit NASA is designing for Artemis astronauts. It’s called xEMU, or Exploration Extravehicular Mobility Unit. Photo credit: NASA

However, Latysev and colleagues also noted that this is a preliminary analysis that does not take into account other factors. These include crew safety, the likelihood of mission success, and project management risk considerations. An assessment of a mission architecture that takes this into account requires more detailed modeling at a later stage in the program.

The team hopes to expand their analysis to include this in the future. This will be possible as more mission parameters are defined. As Latysev explained, crew safety is the number one consideration when designing an HLS, or human-rated space system.

“This safety factor can influence the results in both cases. For example, multi-level solutions in an emergency could offer safer return options in the parking orbit before descending to the surface than our “winner”, the single-level system: Either the descent or the ascent vehicle can be used in the case of 3-level and 2-level systems in return In contrast to the one-step system of the 1-step system At the same time, it is expected that two-tier and three-tier systems will be more complex and therefore have a higher risk of failure in contrast to the simpler single-tier solution. So there is another compromise. “

Given the recent political change, certain details of the Artemis program could be in the air. However, earlier this month the Biden administration announced the approval of the Artemis program. In February they had already authorized NASA to start building the gateway in May 2024 at the earliest, in which the PSA and HALO elements were to be used together with a single Falcon Heavy rocket.

If successful, it means that the gateway’s core will be in orbit around the moon about five months before the Artemis III mission arrives. So it’s a good bet that the “first woman and next man” to walk on the lunar surface will use a reusable HLS to get there. If not, if not, the reusable lander will have to wait for subsequent missions while the Artemis III crew uses a consumable system.

In either case, Project Artemis will not be done without a reusable HLS that will appear sooner or later.

Further reading: Skoltech, Acta Astronautica

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