Moon Monday #144: On the most precise planetary landing attempt by SLIM, sprawling SLS rocket costs, and more

Japan launches the SLIM lunar lander with an unprecedented aim

Left: Launch of JAXA’s XRISM X-ray observatory and SLIM Moon lander on the MHI-built H-IIA rocket; Top right: SLIM’s flight model at the Spacecraft and Fairing Assembly Building at Japan’s Tanegashima launch complex; Bottom right: Illustration of SLIM’s trajectory to the Moon. Credits: Kyodo News / AP / JAXA

On September 7, Japan launched the 2012-proposed SLIM lander to the Moon. Shortly after separating from the upper stage of its H-IIA launch vehicle in Earth orbit, SLIM completed sun acquisition control and JAXA reported its health to be normal. Much like the Advanced Space-led CAPSTONE and South Korea’s KPLO spacecraft, SLIM will take a longer but highly fuel-efficient route to the Moon, only targeting entering into lunar orbit about four months later. SLIM will then spend a month in lunar orbit before attempting its 20-minute descent and lunar landing.

The compact SLIM lander aims to demonstrate pinpoint touchdown, which for lunar landings means achieving a touchdown within 100 meters of the targeted spot. For SLIM, that spot lies on a slope within the rocky ejecta of the 300-meter wide Shioli crater at 25.2°E, 13.3°S. SLIM aims to directly land in this otherwise mobility-inaccessible region and analyze its composition using SLIM’s near-infrared, multi-band spectroscopic camera to glean insights about our Moon’s mantle and its formation.

SLIM’s target landing location, marked as orange dots, in the Moon’s globe view, against the large Cyrillus and Theophilus craters, and besides the 300-meter wide Shioli crater. Image credits: LROC Quickmap / Graphic: Jatan Mehta

As a cherry on top, SLIM aims to achieve the daring first of a pinpoint planetary landing with a low spacecraft mass of only 730 kilograms. To that end, SLIM touts a number of novel mass reduction technologies and approaches such as an integrated fuel and oxidizer tank, which doubles as the lander’s structure base, foldable thin-film solar cell sheets, an integrated digital power control unit, and 3D printed parts like those in its five legs.

Lunar landing accuracies compared

To truly appreciate the tight landing ellipse of 100 by 100 meters that SLIM will target a touchdown within, let’s compare it to some other Moon landings:

In other words, SLIM’s mission doesn’t afford it to have any considerable errors beyond the most precise planetary landing to date. Such gripping precision isn’t for the sake of a demonstration. The upcoming US Artemis crewed missions, China’s Chang’e robotic craft, and the majority of other government as well as private endeavors plan to explore the Moon’s rocky south pole, where such demanding touchdowns would be indispensable in order to access the water ice lying inside permanently shadowed regions.

Elevation and slope maps at the Moon’s south pole. The terrain is very rocky, requiring missions to use precision landing technologies. Credit: LPI

For its next Moon mission launching before the end of decade, Japan is partnering with India to have its LUPEX rover directly study the nature, abundance, and accessibility of water ice at the lunar south pole at 89°S. The lander delivering LUPEX will be built by ISRO, and Chandrayaan 3’s success as well as hopefully that of SLIM will feed into the lander’s ability to safely touchdown amid unforgiving polar terrain. The Japanese government has already approved the LUPEX mission but India is yet to, and so that will be the green light to look out for next now that Chandrayaan 3 is successful.


Many thanks to Epsilon3, Open Lunar Foundation and Arun Raghavan for sponsoring this week’s Moon Monday.


The SLS rocket remains a critical cost concern for Artemis Moon missions

In a scathing report published on September 7 and delivered to the US House and Senate appropriators, NASA’s Government Accountability Office (GAO) has criticized the agency for continuing to be not transparent enough about the true cost of the SLS rocket central to the nearly $100 billion Artemis Moon program. NASA’s Office of Inspector General (OIG) had estimated in 2021 that separately from development costs, the first three SLS flights will cost $2.2 billion per launch. And now the GAO notes seeing cost growth even as the SLS moves into production:

Based on our analysis of the contract, the cost to produce successive core stages is increasing over time.

This report follows the OIG’s May 25 report, which criticized the agency’s handling of the SLS rocket engine contracts to Aerojet Rocketdyne and Northrop Grumman who provide the vehicle’s $146 million-per-piece RS-25 core engines and the twin boosters respectively. The OIG had noted a $6 billion cost increase and a delay of more than six years in receiving said hardware for the designated initial Artemis missions. The report added:

NASA and its contracts will continue to exceed planned cost and schedule, resulting in a reduced availability of funds, delayed launches, and the erosion of the public’s trust in the agency’s ability to responsibly spend taxpayer money and meet mission goals and objectives—including returning humans safely to the Moon.

The latest GAO report says related NASA officials acknowledge that the SLS is “unsustainable” at its current level, and that they’re trying to find short-term as well as long-term cost reduction strategies. To that end, NASA is preparing to award a contract for future SLS rocket launches to Deep Space Transport LLC, a joint venture between two major SLS contractors Boeing and Northrop Grumman. In hopes to reduce SLS’s cost by up to 50%, NASA will transfer the ownership of its production and associated facilities into a single launch service contract. The baseline contract would be for Artemis V–IX missions, and likely extend to Artemis X–XIV later.

More Moon

Illustration of Australia’s first lunar rover, shown here with its robotic arm in action trying to sample lunar soil. Credit: ASA

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