China launches to the far side of the Moon with sample return

by Adrian Beil

In cooperation with France, China launched  the Chang’e 6 mission. The launch happened at Friday, May 3, at 09:27 UTC, and the mission’s main goal is a regolith sample return from the surface of the Moon. The launch happened during very rainy conditions, which did not affect launch criteria.

About the mission

In overall structure, Chang’e 6 is similar to the previously launched Chang´e 5 mission. The probe is expected to return up to two kilograms of lunar soil samples to Earth. The remarkable feature of this mission is the landing position. Previous missions to return Moon soil only targeted the Earth-facing side of the Moon, while Chang´e 6 is trying to return samples from the far side of the Moon.

The overall mission duration will be 53 days from launch to touchdown. The 8,200 kilograms heavy sample return vehicle will be launched on a Chang Zheng 5, China’s most capable rocket. Touchdown on the Moon will be at the southern edge of the Apollo Basin.

The location of the Chang’e 6 landing. (Credit: The Planetary Society)

The Apollo Basin is an enormous impact crater located in the southern area of the Moon. It is a double-ringed walled plain crater, which means it features an outer and an inner ring. Inside of the Apollo Basin are even more craters, which have eroded the primary structure of the impact crater.

The overall architecture of the vehicle is very similar to Chang’e 5, as this was the initial backup lander to the previous mission. With Chang’e 5 being successful, there is no need for the backup vehicle to fulfill that function, which means it can go on a dedicated mission.

This mission, together with the previous one, is part of the third phase of the Chinese Lunar Exploration Program. While the initial phase of reaching lunar orbit was completed by the second mission, and the second phase of landing on the Moon was completed by mission four, the third phase is all about returning and collecting lunar samples. This goal is to be accomplished by Chang’e 5 and Chang’e 6.

The final fourth phase of the program would then conduct robotic research of the Moon’s south pole. After completion, this program would then pave the way for crewed Chinese lunar landings in the 2030s.

The Payload for the Mission. (Credit: CASC)

The mission architecture consists of four major modules: the orbiter, the lander, the ascent vehicle, and the sample-return capsule.

The lander will conduct the main phase of the mission, land on the surface of the Moon, and then also perform the probe collection. The probes will each weigh roughly 2 kilograms and will be collected from roughly 2 meters below the surface. Of the whole mass of the mission, roughly 3,200 kg falls on the lander, while the ascent vehicle has a mass of 700 kg. The remaining 4,300 kg comprise the orbiter and return capsule.

After the drilling is complete, the payloads will be stored in the ascent vehicle, which will boost the payload to a lunar orbit, where it will dock with the orbiter. The orbiter also hosts the sample-return capsule, which will safely reenter Earth’s atmosphere.

The science

Next to the sample return, the mission features several Chinese and international science payloads. Part of this is a French instrument, but also contributions from Italians, a Swedish, and a Pakistani payload.

France is providing the Detection of Outgassing Radon (DORN), which will conduct studies of the transport of lunar dust and other interactions between lunar regolith, the lunar water, and more. DORN is being developed by the Research Institute of Astrophysics and Planetology (IRAP), in a tight relationship with CNES.

For this research, the outgassing from the lunar crust will be estimated. This outgassing includes elements such as helium-4, argon-40, and radon. Estimating these quantities and measuring the isotopes and their decay will help scientists understand particle transport on the lunar surface.

The concept behind the DORN payload. (Credit: CNES)

The Italian instrument, INRRI (INstrument for landing-Roving laser Retroreflector Investigations), will consist of two passive laser retro-reflectors that will be used in the future for laser range-finding of the lander.

The Swedish NILS (Negative Ions on Lunar Surface) will detect and measure the amounts of different negative ions at the landing site and during the descent to the lunar surface. Negative ions are not yet fully observed plasma components on the Moon, and NILS’ main aim is to better understand them. The primary goal of this research is to use this example to estimate the importance of negative ions for space, surface, and planetary bodies. It will operate for thirty minutes after landing, and at the latest, it will conclude with the launch of the sample return module.

The Icube-Q payload. (Credit: Institute of Space Technology)

The Pakistani CubeSat, called ICUBE-Q, will separate from the mission once it’s still in space. It is built by students in Pakistan and will take images of the orbiter, the Moon, and Earth. Secondly, it will also conduct studies of the Moon’s magnetic field.

The rocket

The Chang Zheng 5 for this mission. (Credit: CASC)

The rocket for this mission was the Chinese powerhouse, Chang Zheng 5. The most powerful of all Chinese rockets, usually used for high-profile and high-energy missions, was launched from the Wenchang Satellite Launch Center, on Hainan Island in China. It will use Launch Complex 101.

Since this is a mission beyond low-Earth orbit (LEO), it used the standard configuration of the rocket and not the LEO-optimized Chang Zheng 5B.

The rocket stands 56.97 meters tall, with a liftoff mass of 851,800 kilograms. Most of this mass is in the heavy first stage, and the four attached CZ-5-300 liquid-core rocket boosters.

The first stage, CZ-5-500, stands 33.16 meters tall, with a diameter of 5 meters. It features two YF-77 hydrogen engines, which ignited at the ground. While they are providing 1,036 kN at liftoff, the majority of the thrust at liftoff was provided by the four liquid rocket boosters, which each feature two YF-100 RP-1 engines. Each of these cores provided 2,400 kN at liftoff, and they burned until 2 minutes and 55 seconds into flight.

The sustainer first stage, based on hydrogen, then carried on the mission up until 481 seconds into the flight. With its high efficiency of 428 seconds of specific impulse in a vacuum, it helps to carry heavy payloads beyond LEO.

After this phase, the second stage, CZ-5-HO took over. It features two vacuum-optimized YF-75D engines, which are also based on liquid hydrogen and liquid oxygen. This stage can burn up to 700 seconds and has a maximum thrust of 176.72 kN.

On today´s mission, the rocket conducted two person. The first burn, just north of four minutes, raised the payload into a stable orbit, before the second burn, SEI-2, burned for another 7 minutes, to perform the trans-lunar injection. The spacecraft seperated from the rocket 36 minutes and 58 seconds after liftoff, and China confirmed the launch section of the mission to be succesful.

Liftoff during heavy rain from the Wenchang Satellite Launch Center. (Credit: CASC)

After launch, the payload will now coast for three days, until performing the Lunar Orbit Insertion (LOI). The planned seperation of the lander from the orbiter is planned after 29 days, with the ascent being planned just three days later.

After 48 days, the payload will then perform the Trans-Earth Injection (TEI) and return to Earth. Landing is planned for June 20, 53 days after launch.

The rocket carried the payloads all the way to translunar injection, where then the payload itself will start to navigate itself for the landing.

(Lead Image: Payload in the Clearnroom. Credit: Vony7/China News Media)

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