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Mahesh

28/12/23 06:52 AM IST

SLIM lunar landings

In News
  • Recently,Japan’s Smart Lander for Investigating Moon (SLIM) spacecraft entered into orbit around the moon after a months-long journey, and ahead of its planned moon-landing attempt on January 19.
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. Of course, the latter mission also carried a larger suite of instruments.
  • SLIM was launched together with XRISM, a next-generation X-ray space telescope, onboard an H-2A rocket.
  • JAXA had planned to launch SLIM and XRISM together, so delays in readying XRISM pushed SLIM’s launch date from 2021 to 2023.
  • On December 25, SLIM entered into an elliptical orbit around the moon over three minutes or so. 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, built by Japanese company ispace, crashed in late April after its engines shut down too soon during the landing.
SLIM v/s Chandrayaan
  • SLIM is lighter because it carried much 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.
  • SLIM took four months because it followed a longer but more fuel-thrifty route based on weak-stability boundary theory.
  • Once it was launched into an orbit around the earth, SLIM swung around the planet multiple times, building up its kinetic energy with each swing.
  • Once it was travelling fast enough, it shot up towards the moon’s orbit.
  • Chandrayaan 3 followed a qualitatively similar path until this point. 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.
  • But once 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.
Functions of SLIM
  • SLIM, in effect, will set the record on January 19 for attempting to soft-land with the smallest ever area tolerance on the moon.
  • The chosen site is near the Shioli Crater, at 13.3º S and 25.2º E. Just as the ‘Vikram’ lander of the Chandrayaan 3 mission used data from the Chandrayaan 2 orbiter to help guide its descent, SLIM will use data from JAXA’s SELENE orbiter, which ended in 2009.
  • Its lower mass – only 120 kg excluding fuel – will help in this endeavour by rendering it more manoeuvrable while its small size will be a test of its economical design.
  • 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.
LUPEX mission
  • LUPEX 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 – and this makes all the difference.
  • The terrain near either of the moon’s poles is rocky, pocked with several craters, and full of steep slopes.
  • Axiomatically, if there is a suitable landing spot for a (relatively) large landing module or rover, its downrange and cross-range limits will be lower than they were for Chandrayaan 3.
  • The craft will have to land as close to the site as possible, if not at the site itself.
Source- The Hindu

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