One of the most important media outlets in China, the South China Morning Post, has been echoed from a peer-reviewed study that was published last March in the journal Chinese Space Science and Technology. In it, a team of Chinese researchers criticized the propulsion system of NASA’s Artemis lander and praised the one designed by their own engineers. With what is said in this study, of course, it seems that NASA is taking a gamble ahead of its next landing on the Moon. However, there is a detail that is not discussed in this article and that makes it clear that, in reality, it is a criticism with little foundation.
Doesn’t anyone think about the HLS? Broadly speaking, the Chinese article criticism that NASA’s lander uses only one engine for the two critical maneuvers of the moon landing: descent and subsequent ascent. If this fails, there is no backup to bring the Orion ship to port.
This is true. It would be a big problem to use a single engine, as they already did in the Apollo missions. However, with Artemis, NASA is not going to resort to the traditional two-stage system used in previous moon landings. On this occasion the Orion spacecraft will dock in lunar orbit with the Human Landing System (HLS) of SpaceX either Blue Origin. None of them have only one engine, so the problem that China points out does not really exist.
The background of the Apollo missions. On the Apollo missions The ship used consisted of two stages. One remained orbiting the Moon, with one person on board, and the other separated to embark on the moon landing with the rest of the crew inside. This lander heading to the Moon effectively had a single engine for each critical phase. That is, there was an ascent engine and a descent engine. For Artemis, it was decided that this system could be risky, so the Orion spacecraft has a single stage, which never lands on the moon. In exchange, it docks with an external lander that should be waiting for it when it reaches lunar orbit.
SpaceX or Blue Origin. NASA has contracted the services of SpaceX and Blue Origin to develop its HLS. If everything goes well, both must show their viability in Artemis IIIalthough SpaceX’s HLS will be the first to land on Artemis IV, introducing Blue Origin to later missions. Of course, if there were incidents with SpaceX and Blue Origin if it arrived on time, there would be no problem with reversing the order. Be that as it may, the key here is the propulsion used by the HLS of these companies.
SpaceX’s HLS-Starshipfor example, has six engines: three sea-level and three vacuum, all fueled by subcooled liquid methane and liquid oxygen in a full-flow, staged combustion cycle. This enables high thrust-to-weight ratios and efficiency in vacuum conditions essential for lunar descent and ascent. For its part, Blue Moon Mark 2, Blue Origin’s HLShas three engines to descend to the Moon from lunar orbit. Of course, although the data may vary, at the moment it is only known that for the ascent it has a single separate stage, with a hypergolic propulsion system. If this fails, there could be a problem like those pointed out by China.
SpaceX engine in a test prior to Starship Flight 12
The China option. Of course, the lander proposed by China is also a great option. On the one hand, it has a primary system that includes four variable thrust engines, so that if one fails, the other three continue to generate thrust comparable to that of the classic NASA engine. In addition, it has an additional layer with six smaller orbital control thrusters, which could be ignited on the lunar surface for an emergency ascent in case the main ones fail.
The weight problem. Seen this way, the more engines, the better. But of course, it is not something that simple. More engines mean more weight, which reduces the ship’s efficiency and payload capacity. All the extra weight that the engines represent can be less materials to build lunar bases or supplies for astronauts, for example. This is why NASA’s traditional design included a single engine.
China solves this problem by using a tank in which the fuel and the oxidizer used to start the combustion reaction are separated by a wall. Traditionally two tanks are used, instead of just one with a wall. Therefore, each extra tank meant much more weight. This type of tank results in a saving of hundreds of kilograms in the weight of the ship, which can be used to introduce more engines.
China has good tools to go to the Moonbut NASA too. For now, China has tested its proposal in a hot ignition test, in which the engines are tested in real conditions, but without taking off. Everything has worked correctly, although the importance of very precisely controlling the tank pressure has been proven. It is a country that is preparing very well in its own race to the Moon. But that does not invalidate the steps that NASA is taking. Artemis is not Apollo. This time the single-engine moon landing will not be at stake, so the chances of success are greater than in the past.
Image | Patricia Moore (Wikimedia Commons) | SpaceX
In Xataka | China’s most ambitious space project: an advanced hyperspectral satellite to make a “CT” of the Earth
GIPHY App Key not set. Please check settings