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Japan’s SLIM Lunar Orbit Entry


Japan’s Smart Lander for Investigating Moon (SLIM) successfully entered lunar orbit on December 25, marking a crucial step before its planned moon landing on January 19. This development positions Japan to potentially become the fifth country to achieve a soft landing on the moon, following India’s success with Chandrayaan 3 in August. The outcome of SLIM’s mission carries significance, as it may impact the upcoming Chandrayaan 4 mission.


GS III: Science and Technology

Dimensions of the Article:

  1. SLIM: Japan’s Lunar Mission
  2. SLIM’s Lunar Mission Objectives
  3. SLIM’s Impact on Chandrayaan 4 Mission

SLIM: Japan’s Lunar Mission

Overview of SLIM
  • Developed and launched by the Japan Aerospace Exploration Agency (JAXA) on September 7, 2023.
  • Weighs 590 kg at launch, significantly lighter than Chandrayaan 3.
  • Launched alongside XRISM, a next-gen X-ray space telescope, onboard an H-2A rocket.
  • Entered an elliptical orbit around the moon on December 25.
Comparison with Chandrayaan 3
  • SLIM’s launch closely follows the success of Chandrayaan 3’s surface component and Luna 25’s failure.
  • SLIM marks Japan’s second attempt in 2023 for a lunar soft landing.
Journey to the Moon
  • SLIM’s lighter weight is attributed to carrying less fuel.
  • Utilized a longer but fuel-thrifty route based on weak-stability boundary theory.
  • Built up kinetic energy around Earth through multiple swings, allowing for a more fuel-efficient journey.
  • Sacrificed time for fuel efficiency, reaching lunar orbit after four months.
  • December 25 marked SLIM’s orbital capture around the moon.
Innovative Approach
  • SLIM’s deflection toward the moon, rather than slowing down, utilized the combined forces of Earth and lunar gravity.
  • Physicists developed this approach in the late 1980s during the ‘Hiten’ mission.
  • SLIM’s unique trajectory prioritized fuel efficiency over a faster journey to the moon.

A diagram illustrating SLIM’s path from the earth to the moon, spanning four months. | Photo Credit: JAXA

SLIM’s Lunar Mission Objectives

Precision in Lunar Landing

  • SLIM is known as the “moon sniper” for its remarkable precision in landing.
  • Scheduled to attempt a landing within 100 meters of its chosen site on the moon.

Historical Context

  • Past moon-landing missions had more lenient area tolerances for landing spots.
  • For example, the Vikram lander of Chandrayaan 3 had a 4 km x 2.5 km area tolerance.
  • China’s Chang’e 3 holds the record for the most precise moon landing, 89 meters away from its chosen spot within a 6 km x 6 km ellipse.

Landing Site and Data Utilization

  • SLIM’s landing site is near the Shioli Crater at 13.3º S and 25.2º E.
  • Similar to Chandrayaan 3, SLIM will use data from JAXA’s SELENE orbiter to guide its descent.

Technical Specifications

  • SLIM’s lower mass, only 120 kg excluding fuel, contributes to its maneuverability.
  • Its small size tests the efficiency of its design.

Additional Exploration

  • Before landing, SLIM will deploy two small rovers, Lunar Excursion Vehicle (LEV) 1 and 2.
  • LEV-1, LEV-2, and SLIM will collectively study the lunar surface, gather temperature and radiation readings, and attempt to explore the moon’s mantle.

SLIM’s Impact on Chandrayaan 4 Mission

Targeting Moon’s South Pole

  • Scientists aim for the moon’s south pole region due to perpetually shadowed craters containing water-ice.
  • Chandrayaan 3’s success marked the conclusion of the second phase of India’s lunar exploration program.

Lunar Polar Exploration (LUPEX) Mission

  • LUPEX, or Chandrayaan 4, is the first mission of the third phase.
  • Joint venture with Japan (pending Indian approval) and scheduled for a potential launch in 2026.
  • LUPEX will explore an area closer to the moon’s south pole compared to Chandrayaan 3.

Challenges and Technologies

  • Moon’s polar terrain is rocky with craters and steep slopes, requiring precise landing.
  • Downrange and cross-range limits for LUPEX will be lower, demanding advanced navigation systems.
  • SLIM’s tested technologies, including a feature-matching algorithm, are crucial for LUPEX’s success.

Collaboration Details

  • JAXA expected to provide the launch vehicle and lunar rover; India contributes the lander module.
  • The landing site for LUPEX is yet to be determined.

JAXA’s SLIM Mission Timing

  • SLIM’s mission launch closely follows Chandrayaan 3’s success and precedes Russia’s Luna 25 spacecraft failure.
  • SLIM’s success on January 19 sets a record for the smallest-ever area tolerance in a moon landing.

-Source: The Hindu

February 2024