What’s in Today’s Article?

• Background (Context)
• About SLIM Mission (Objective, Features, Comparison with Chandrayaan-3, Significance)

Background:

• On 25^th December, 2023, Japan’s Smart Lander for Investigating Moon (SLIM) spacecraft entered into the orbit around the moon after a months-long journey.
• Its planned moon-landing attempt is scheduled for 19^th January, 2024.
• If the attempt succeeds, Japan will become only the fifth country to soft-land a robotic craft on the natural satellite, months after India succeeded with its Chandrayaan-3 mission in August, 2023.
• Perhaps more importantly, SLIM’s success or failure will also affect the upcoming Chandrayaan-4 mission.

About SLIM:

• SLIM is a spacecraft built and launched by the Japan Aerospace Exploration Agency (JAXA) on September 7, 2023, from the Tanegashima spaceport.
  • It weighed only 590 kg at launch, which is almost one-seventh of Chandrayaan-3, which weighed 3,900 kg at launch.
• SLIM was launched together with XRISM, a next-generation X-ray space telescope, onboard an H-2A rocket.
• On December 25, SLIM entered into an elliptical orbit around the moon. Its apogee (farthest point) in this orbit is 4,000 km and perigee (closest point) is 600 km above the lunar surface.
• SLIM will also mark the second Japanese attempt this year to soft-land on the moon.
  • The HAKUTO-R M1 lander crashed in late April after its engines shut down too soon during the landing.

Comparing Trajectories of SLIM &Chandrayaan-3:

• Compared to Chandrayaan-3, SLIM is lighter because it carries less fuel.
  • Of Chandrayaan-3’s 3.9 tonnes, the propulsion module alone weighed 2.1 tonnes.
  • This is why the mission was launched on July 14 and could reach the moon less than a month later, by following a route called the Hohmann transfer orbit.
  • On the other hand, SLIM took four months because it followed a longer but more fuel-thrifty route based on weak-stability boundary theory.
• Once it got close to the moon, Chandrayaan-3 applied its brakes – which consumes fuel in space – so that it could slow down enough to be captured by the moon’s weaker gravity.
  • SLIM got near the moon, instead of slowing down and being captured by the moon’s gravity, it allowed itself to be deflected in the moon’s direction even as it shot past lunar orbit, deeper into space.
  • This deflection is the result of the combined forces exerted by the earth and the moon.

What will SLIM do on the Moon?

• On January 19^th, the SLIM mission will try to land within 100 metres of its chosen landing site.
  • This is an unusually tight limit given the history of moon-landing missions.
  • For example, the ‘Vikram’ lander of Chandrayaan-3 was designed to descend in an elliptical area that was 4 km long downrange and 2.5 km wide cross-range.
• SLIM, in effect, will set the record on January 19 for attempting to soft-land with the smallest ever area tolerance on the moon.
• Just before it lands, SLIM will deploy two small rovers called Lunar Excursion Vehicle (LEV) 1 and 2.
• LEV-1, LEV-2, and SLIM will together study the lunar surface near the landing point, collect temperature and radiation readings, and attempt to study the moon’s mantle.

How will SLIM affect Chandrayaan-4?

• Scientists are interested in the moon’s south pole region at large because parts of some of the craters here are always in shadow.
  • These parts contain water-ice, and a lunar surface mission could potentially explore these sites and attempt to extract water.
• When ISRO successfully executed its Chandrayaan-3 mission by soft-landing a robotic craft on the moon’s surface, on August 23, it also concluded the second phase of its lunar exploration programme.
• The first mission of its third phase is the Lunar Polar Exploration (LUPEX) mission, a.k.a. Chandrayaan-4.
• LUPEX/Chandrayaan-4 will be an Indian-Japan joint enterprise (however, while JAXA has approved LUPEX, India is yet to) with an earliest launch date in 2026.
• It will explore an area closer to the moon’s south pole than Chandrayaan-3 did.
• The technologies JAXA will test with SLIM, but especially a feature-matching algorithm and navigation systems, will be crucial for LUPEX/Chandrayaan-4.
• For now, JAXA is expected to provide the launch vehicle and the lunar rover while India will provide the lander module.
• The landing site is yet to be fixed; to compare, the ‘Vikram’ lander of Chandrayaan-3 mission landed 600 km from the south pole.