When astronauts return to the Moon for the first time since the Apollo Era, they will be relying on a number of mission elements to get them there and back safely. This includes the Space Launch System (SLS) and Orion spacecraft that will launch a crew of four and carry them to the Moon. But until recently, the question of how they will get to and from the surface remained unresolved, as there were a few options.
To determine which would be best in terms of performance and cost, researchers from Skolkovo Institute of Science and Technology (Skoltech) in Moscow and the Massachusetts Institute of Technology (MIT) reviewed several dozen proposals. In the end, they determined that a one-stage reusable lunar lander that could transport astronauts to and from the orbiting Lunar Gateway was the best option.
Their findings appeared in a paper titled “Lunar human landing system architecture tradespace modeling,” which recently appeared in the journal Acta Astronautica. The study was conducted by Skoltech researchers Kir Latyshev, Nicola Garzaniti, and Associate Professor Alessandro Golkar, who were joined by Edward Crawley – an MIT Professor of Aeronautics and Astronautics and of Engineering Systems.
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The question of what type of landing system would be best emerged as a result of NASA’s expedited schedule, which was announced by VP Pence during the fifth meeting of the National Space Council at the Marshall Space Flight Center, which took place on March 26th, 2019. It was at this time that Pence directed NASA to return astronauts to the Moon by 2024 (four years soon than originally planned) by “any means necessary.”
This new timetable forced NASA to undergo a series of shake-ups, as well as a review of their budget and deployment schedule. Previously, NASA planned to assemble the Lunar Gateway in orbit around the Moon before making any landings. This was to be begin in 2022 with the deployment of the Power and Propulsion Element (PPE) of the Gateway, which would 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. A Human Landing System (HLS) would be added by this time, followed 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 of 2020, NASA decided that the Lunar Gateway wasn’t necessary for the fulfillment of Project Artemis’ new timeline and declared that it was no longer a priority. The decision was issued by Doug Loverro, the Associate Administrator of NASA’s Human Exploration and Operations Mission Directorate (HEO-MD) at the time, as part of their plan to “de-risk” the mandatory tasks associated with Artemis.
These sentiments were expressed by Doug Loverro, who replaced William Gerstenmaier in July of 2019 as part of a shakeup designed to expedite progress with the SLS and the Artemis program in general. As Loverro explained during a NASA Advisory Council science committee (held on Friday, March 13th), he has been working to “de-risk” Artemis so NASA can focus on meeting the mandatory goals of Artemis and its 2024 deadline.
This meant that NASA and its commercial partners needed to come up with a new strategy for landing astronauts on the Moon. The options that were now on the table included an expendable lander that could be integrated with the Orion capsule or the station. To develop this HLS, NASA contracted SpaceX, Blue Origin, and Dynetics, as part of the Next Space Technologies for Exploration Partnerships (NextSTEP-2).
As it stands, NASA plans to send astronauts back to the Moon in 2024 and then deploy the Lunar Gateway with subsequent Artemis missions. This will allow them to send the “first woman and next man” to the Moon by 2024 while fulfilling the long-term goal of creating a program for “sustained lunar exploration” (i.e., regular missions that are longer in duration).
To assess which HLS system would be optimal for the Artemis missions, Latshyev and his colleagues developed a series of mathematical and architectural screening models to assess the various options for sending a crew of four on a seven-day mission to the Moon. This included a 2-stage architecture for the lander, similar to the Lunar Module used by the Apollo astronauts.
These landers consisted of a descent and ascent module, the former of which would be left on the lunar surface. Latshyev and his colleagues then factored in the orbit of the Gateway, which NASA plans to station in an L2 near-rectilinear halo orbit, and the amount of propellant needed. In total, they reviewed 39 variations of a future HLS and weighed the potential benefits against the possible costs.
Ultimately, they came to a few conclusions, depending on whether the lander would be traveling with the Orion spacecraft (expendable) or integrated with the Lunar Gateway (reusable). Overall, they found that the best option for making short ‘sortie’-type missions to and from the lunar surface was a single stage reusable module that relied on liquid oxygen and liquid hydrogen (LOX/LH2) propellant. As Latyshev explained in a recent Skoltech news article:
“Interestingly, our study finds that, even with the orbiting station, if fully expendable vehicles are considered, then the 2-stage (Apollo-like) landing system is still expected to have lower masses and, therefore, lower costs – which sort of reconfirms the Apollo decision. However, reusability changes that.
“Though 1-stage and 3-stage vehicles in this case are still heavier than the 2-stage one, they allow to reuse more of the ‘vehicle mass’ (approximately 70-100% compared to around 60% for the 2-stage option) over and over again, thus saving money on producing and delivering new vehicles to the orbiting station and making lunar missions potentially cheaper.”
However, Latysev and his colleagues also noted that this is a preliminary analysis that does not take into account other factors. These include crew safety, probability of mission success, and considerations relating to project management risks. An assessment of a mission architecture that takes these into account will require more elaborate modeling at a later stage of the program.
The team hopes to expand their analysis in the future in order to take these into account, which will be possible as more of the mission parameters are defined. But as Latysev explained, crew safety is the most important consideration when it comes to the design for an HLS – or any human-rated space system, for that matter:
“This safety factor can affect the results in either way. For example, multi-stage solutions might offer more safe return opportunities in case of emergency in the parking lunar orbit prior to descent to the surface than our ‘winner’, the 1-stage system: either the descent or ascent vehicle can be used for return in case of 3-stage and 2-stage systems as opposed to the single stage of the 1-stage system. At the same time, 2-stage and 3-stage systems are expected to be more complex and therefore to have more risks of breakdowns, as opposed to the simpler 1-stage solution. So there is a trade-off again.”
Given the recent shift in politics, certain details about the Artemis Program could be up in the air. However, earlier this month, the Biden Administration announced its endorsement of the Artemis Program. Back in February, they also authorized NASA to begin building the Gateway in May of 2024 (at the earliest), which would involve deploying the PPE and HALO elements together using a single Falcon Heavy rocket.
If successful, this will mean that the core of the Gateway will be in orbit around the Moon about five months before the Artemis III mission arrives. As such, its 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, then the reusable lander will have wait upon subsequent missions while the Artemis III crew use an expendable system.
Either way, Project Artemis will not be happening without a reusable HLS making an appearance sooner or later.
Further Reading: Skoltech, Acta Astronautica