Japan’s SLIM aims to be the first ‘moon sniper’ with high-accuracy landing

Japan has launched a lunar exploration spacecraft on Thursday aboard a homegrown H-IIA rocket, hoping to become the world’s fifth country to land on the moon early next year. The spacecraft, named Smart Lander for Investigating Moon (SLIM), is dubbed the ‘moon sniper’ for its ability to land within 100 metres of its target site on the lunar surface.

SLIM’s mission objectives and challenges

SLIM’s primary goal is to test advanced optical and image processing technology that will enable high-accuracy landing on the moon. This will allow Japan to achieve ‘landing where we want’ on the lunar surface, rather than ‘landing where we can’, according to Japan Aerospace Exploration Agency (JAXA) President Hiroshi Yamakawa.

Japan’s SLIM aims to be the first ‘moon sniper’ with high-accuracy landing
Japan’s SLIM aims to be the first ‘moon sniper’ with high-accuracy landing

SLIM will also analyse the composition of olivine rocks near the landing site in search of clues about the origin of the moon. Olivine is a mineral that is believed to be abundant in the moon’s mantle, but rare on its surface. Finding olivine rocks could indicate that they were exposed by an ancient impact event that excavated deep layers of the moon.

SLIM faces several challenges in its mission, such as:

  • Navigating through a long, fuel-efficient approach trajectory that will take about five months to reach the moon
  • Performing autonomous guidance and control during the descent phase using a laser altimeter and a camera
  • Avoiding hazards such as craters and boulders on the lunar terrain
  • Surviving the harsh environment of the moon, which has extreme temperatures, radiation, and dust

SLIM’s launch and status

SLIM was launched on Thursday from Tanegashima Space Center in southern Japan as planned and successfully released by the H-IIA rocket. The launch was delayed three times in a week last month due to unfavourable weather conditions.

Hours after launch on Thursday, JAXA said it picked up signals from SLIM showing it was operating normally. The spacecraft is expected to start the landing by February 2023 after orbiting around the Earth and the moon.

SLIM is set to touch down on the near side of the moon close to Mare Nectaris, a lunar sea that, viewed from Earth, appears as a dark spot. The landing site is about 600 kilometres south of Apollo 11’s landing site.

SLIM’s significance and future prospects

SLIM is Japan’s first attempt to land a spacecraft on the moon since 2008, when it sent an orbiter called Kaguya (SELENE) that mapped the lunar surface in high resolution. SLIM is also Japan’s first lunar lander developed entirely by JAXA, without any international collaboration.

SLIM is a low-cost mission that cost about $100 million to develop and launch. It is part of JAXA’s Lunar Exploration Program (LEP), which aims to establish Japan’s presence and leadership in lunar exploration.

SLIM’s success could pave the way for more ambitious lunar missions by Japan in the future, such as:

  • Sending a rover called Lunar Cruiser (formerly known as SLIM-2) that will explore polar regions of the moon and demonstrate wireless power transmission technology
  • Sending a sample return mission called MMX (Martian Moons eXploration) that will collect samples from Phobos and Deimos, the two moons of Mars
  • Participating in NASA’s Artemis program that plans to send humans back to the moon by 2024

SLIM’s comparison with other lunar missions

SLIM is not alone in its quest to explore the moon. Several other countries and entities have launched or planned lunar missions in recent years, such as:

  • China, which has landed four spacecraft on the moon since 2013, including Chang’e-4, the first to land on the far side of the moon in 2019, and Chang’e-5, the first to return lunar samples since 1976 in 2020
  • India, which became the fourth nation to successfully land a spacecraft on the moon with its Chandrayaan-2 mission in 2019, and is planning to launch Chandrayaan-3, a repeat attempt of the same mission, in 2023
  • Russia, which attempted to land Luna-25, its first lunar mission since 1976, in 2023, but failed due to a malfunction during the descent phase
  • Israel, which attempted to land Beresheet, the first privately funded lunar mission, in 2019, but crashed due to a communication error during the final moments of landing
  • United States, which plans to launch several robotic missions to the moon under its Commercial Lunar Payload Services (CLPS) program, such as Peregrine, Nova-C, and Viper, in 2023 and beyond

SLIM stands out from these missions for its high-accuracy landing capability, which could enable more precise and diverse exploration of the lunar surface. SLIM is also one of the smallest and lightest lunar landers ever built, weighing only about 150 kilograms and measuring about 2.5 metres in diameter.

SLIM’s companion: XRISM

SLIM was not the only payload on board the H-IIA rocket that launched on Thursday. The rocket also carried the X-Ray Imaging and Spectroscopy Mission (XRISM), a joint project of JAXA, NASA and the European Space Agency.

XRISM is a space telescope that will observe X-rays emitted by hot and energetic phenomena in the universe, such as black holes, supernovae, and galaxy clusters. XRISM will use a cutting-edge instrument called Resolve that can measure both the position and energy of X-rays with high accuracy.

XRISM’s mission objectives are to:

  • Investigate the formation and evolution of cosmic structures and black holes
  • Study the physical processes and chemical compositions of hot plasmas
  • Explore the diversity and history of astronomical objects through X-ray spectroscopy

XRISM is a successor to Hitomi (ASTRO-H), a previous X-ray observatory that was launched by JAXA in 2016 but lost contact shortly after due to a technical failure. XRISM will inherit Hitomi’s scientific goals and instruments, but with improved design and performance.

XRISM was successfully deployed by the H-IIA rocket and confirmed to be operating normally by ground stations in Hawaii and Japan. The satellite will undergo a series of tests and calibrations before starting its scientific observations in mid-2024.

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