Moon landings

The Luna programme was a multi-billion two-decade-long programme that consisted of more than 40 launches, however, only 24 have official Luna numbers as the others failed to leave Earth's orbit. The programme achieved several "firsts", namely the first lunar impactor, the first lunar flyby, the first spacecraft to take a picture of the far side of the moon, the first soft landing, the first lunar orbiter, and lastly first circumlunar probe to return to earth. The programme was divided into 3 generations of spacecraft.

Luna 1-3

The first generation of spacecraft was Luna 1 through 3. Luna 1, intended as an impactor, missed the moon and was the first spacecraft to do a lunar flyby. Luna 1 released one kg of sodium gas in space making it visible and allowing it to be tracked by astronomers from the Earth. There was no propulsion on board and it was powered using mercury oxide batteries. It also discovered the existence of solar winds and the lack of a magnetic field on the moon. Luna 2 was similar to Luna 1 and was successful in impacting the moon. Luna 3 was a flyby mission that clicked 29 photos of the far side of the moon. Unfortunately, only 17 of those images could be transmitted back to Earth.

Luna 4-14

The second generation of spacecraft was Luna 4 through 14. Luna 4-8 were landers that failed at soft landing. Luna 8 completed the development of a star tracker and failed because a puncture in the airbag led to a landing failure. Luna 9 was the first successful lander on the moon. It also debunked the fear that the surface of the moon was too soft, and the lander would sink in.

Luna 10 was the first spacecraft to successfully orbit a planetary body other than Earth. The “Internationale” was broadcast from Luna 10 during its first orbit and played in front of the Twenty-third Congress of the Communist Party of the Soviet Union. Luna 11 was an orbiter who amongst other things tested the efficiency of lubricants for gear transmission in vacuum for future rover missions. Luna 13 was a lander which was very similar to Luna 9. It took panorama pictures that took 100 minutes to transfer each. Luna 14 was an orbiter to test communication systems in lunar orbit and earth and engineering test of gear transmission systems in a vacuum.

Luna 5-24

The third generations of spacecraft were Luna 15 through 24. Luna 15 was a sample return mission that took place at the same time as Apollo 11. It is suspected to be a last-ditch attempt at getting lunar samples back to Earth before the US. Unfortunately, the landing wasn't successful. Luna 16 was the first successful Soviet sample return mission. The lander had a drill and robotic arm to load the samples into the rocket. The spacecraft was able to drill to a depth of 35 cm before encountering hard rock. 101 grams of sample were returned to earth. There was no control system on the return rocket and there was only one burn to set it on the trajectory of Earth.

Luna 17 was the first successful rover mission by the Soviet Union. Rover Lunokhod 1 used solar cells for power, travelled more than 10 km and lasted 11 days. It sent over 20000 pictures and 200 panoramas. Luna 19 was the first third-generation lunar orbiter. Luna 20 was a sample return mission that sent back 30g of moon regolith. Luna 21 was the second successful rover mission that landed Lunokhod 2. It had a top speed of 2 km/hr and used polonium-210 as a heat source. It operated for 4 months and travelled 37 km. The Lunokhod retroreflector is still used for lasers ranging from Earth.

Luna 22 was an orbiter mission similar to Luna 19. It tested lubricants on different frictional surfaces and studied different coatings with varying reflective properties. Luna 23 was a sample return mission that landed successfully but the sample return apparatus didn’t work, so no samples were obtained. Luna 24 was a successful sample return mission. It landed only a few hundred meters from Luna 23 and sent 170.1 g of samples.

The Luna 25 mission was launched in August 2023 on top of a Soyuz-2.1b rocket. The mission is targeting a lunar landing at the end of August 2023. The mission is the first moon mission of Russia since Luna 24 and the first moon mission flown since the fall of the soviet union. The mission has been in development for quite some time, at least since 2010 when Phobos Grunt was launched. Originally the mission was to include the ESA Pilot-D and the Swiss  LINA-XSAN payload, but these were removed in the wake of the Russian invasion of Ukraine. 

Luna 25 crashed during its landing attempt. From the last updates, it seems that a malfunctioning thruster caused the spacecraft to hit the moon prematurely. The satellite was first placed in a 100km polar orbit and it was intended to be placed in an elliptical orbit with a periapsis of only 18km above the surface of the moon. When the thruster fired too long this orbit started to intersect the moon [187].

Currently, it is unclear how this mission failure impacts the planned Luna 26, 27, and 28 missions.

The laser altimeter is a device that emits laser pulses and measures the time it takes for them to bounce back from the ground. This allows SLIM to determine its altitude and velocity relative to the lunar surface.

The terrain camera is a device that captures images of the landing site and compares them with a pre-loaded map of the area. This allows SLIM to identify its position and orientation on the map, and to avoid any obstacles or hazards.

The navigation camera is a device that tracks landmarks on the lunar surface, such as craters or mountains, and uses them as reference points. This allows SLIM to estimate its location and trajectory, and to correct any errors or deviations.

The guidance, navigation and control system is a software that processes the data from the sensors and computes the optimal commands for the thrusters and attitude control system. This allows SLIM to autonomously adjust its attitude and velocity during the landing phase, and to achieve a soft and accurate landing.

SLIM's scientific objectives are to conduct investigation of the Moon's origins by landing near the Marius Hills Hole, a possible skylight of a subsurface lava tube that could provide clues about the Moon's volcanic history and potential habitability. SLIM will also test technology fundamental to exploration in low-gravity environments, such as wireless power transmission, optical communication, and miniaturized instruments.

Ranger Block 2

The second block of Ranger spacecraft had a lot more scientific instruments than the first block such as Gamma Ray Spectrometer, TV Camera, Radio Altimeter, etc. It also had a Lunar Impacting Capsule which was meant to survive a 100 mile/hr impact and make measurements for 30 days. The capsule has a seismometer to measure moonquakes. The instrument was housed around two layers of liquids, liquid Freon and water respectively. Additionally, the liquids were housed inside a Balsa wood shell. The iconic stripe paint pattern was chosen to minimise thermal variance in the instrument environment.

Ranger 3 missed the moon by 38,800 km and is still orbiting the Sun. Ranger 4 had a perfect launch, but spacecraft communications got disabled. The capsule impacted the lunar far side. Ranger 5 missed the moon by 725 km

The Apollo Lunar Excursion Module, LEM, was the moon lander of the Apollo project. The LEM was stored in the Saturn V and extracted by the command module after launch. For transit, the LEM would be attached to the forward docking port of Apollo. When the stack was in lunar orbit, two crew members would transfer to the LEM and prepare for landing. The LEM consisted of two parts, the descent and ascent stage. The descent stage was on the bottom of the stack and was powered by a hyperbolic engine with a throttle range of 65 to 92.5%. This allowed for sufficient control for a safe landing. The descent stage also housed the landing legs. These legs would dampen the final landing and housed probes to help the astronauts determine their distance to the lunar surface. The "upper stage" or ascent module also used a hyperbolic engine. It would allow the two astronauts to return to lunar orbit, where they would dock with the orbiting Apollo command module. 

The video on the right shows the lift-off of Apollo 17 filmed by the lunar rover. The descent stage is left on the moon and the ascent stage flies off. Note how the exhaust of the N2O2-Aerozine 50 combustion is clear and no flame can be seen. A similar phenomenon was observed in the 2021 Perseverance lander. 

The LK lander was the Russian alternative to the Apollo LM. The Lk would have launched onboard the N1 rocket below the Soyuz module much like Apollo and LEM were launched. The LK would be extracted after launch and when the combination was around the moon a single cosmonate would space walk over to the Lk. The LK was quite a bit smaller, weiging between 5560 and 6525 kg compared to 15200 and 16400 for the LEM. The Lk only had one hypergolic engine that would be usedo n both ascent and descent flight. The landing legs would stay behind on the moon. Later LK landers would be upgraded to two crew members

On ISRO's first moon mission, Chandrayaan-1, was a small piggyback lander. This lander, the Moon Impact Probe, was designed to impact the moon sometime after being released from the main vehicle. After separation from the main mission, the probe spun up for stability and fired its retro rocket motor. This caused the orbit of the lander to decrease and thus intersect the surface of the moon. After a 25-minute descent phase the probe "hard landed" with a velocity of 1.69 km/s.

Even though the mission was short it showed ISRO's capabilities of reaching the surface of the moon. Marking India to be the fourth nation to do so. Furthermore, the mission discovered the presence of water just before it hit the ground. This discovery was not made public until the Moon Mineralogy Mapper, a NASA experiment onboard Chandrayaan-1, confirmed this discovery. 

After the crash of Chandrayaan-2, ISRO officials announced a new moon lander. This lander was to learn from the mistakes of Chandrayaan-2. The main updates included a redesign of the landing engines and the landing software. The software now allowed for attitude corrections in all phases of flight and the control of the attitude was provided by four downwards-facing rockets. 

The lander landed successfully on November 23 2023, after which it deployed a moon rover. This landing makes India the fourth nation to soft land on the moon and the first lander on the lunar south pole. 

OMOTENASHI is one of the CubeSats flying onboard the Artemis 1 mission to the moon. The objective of OMOTENASHI is to demonstrate low-cost landing techniques for the moon. After separation, the satellite will spin up and ignite a small solid rocket motor. The burn will last for about 15 to 20 seconds.  It will then separate the lander from the motor and inflate a 50cm airbag. This airbag ensures a safe landing. The final free-fall is about 100 meters and the final impact will be between 20 and 30 m/s.

After the successful launch in November 2022, the satellite was separated from the Orion spacecraft. Unfortunately, the team on the ground was not able to establish communications with the lander and were thus not able to start the landing sequence. The satellite remains in Lunar orbit. 

The Hakuto-R lander has a long history starting in the days of the Google Lunar X Prize to kickstart the moon landers in 2007. Even though the Hakuto lander did not reach a flight-ready state during the competition it managed to fly in November 2022. This launcher included the Rashid rover, the first moon rover of the UAE.

After the launch in 2022, the lander reached the moon. On the 25th of April, the landing attempt was started but ended

with the lander not responding. Currently, the lander is considered lost.