Leonard David's INSIDE OUTER SPACE

A Japanese spacecraft has survived its landing on the Moon.

But Japan’s Smart Lander for Investigating Moon (SLIM) is on limited battery power, just for a few hours. However, the draining of the battery does not mean the end of the SLIM mission.

The solar cells on the craft at this time are not functioning, perhaps not aligned with the Sun. Even if battery power is no longer available, the solar cells may still gather sunlight given a spacecraft/Sun alignment in the near-term. If such is the case, SLIM could come back to life.

According to a Japan Aerospace Exploration Agency (JAXA) statement, ), once the spacecraft was situated on the  lunar surface, priority was quickly given to acquiring as much data as possible from SLIM on the Moon.

The solar cells were operating correctly before touchdown and suffered the problem after SLIM’s landing. 

SLIM cannot keep itself warm through the lunar night. However, the lander can resume its operation given that the battery is re-energized upon radio relay by controllers on Earth.

Payloads ejected

The Japan Aerospace Exploration Agency (JAXA) confirmed that SLIM successfully landed on the Moon surface on January 20 at 0:20 am (JST). Communication with the spacecraft was established after the landing. However, the solar cells were not generating power, and top priority was given to data acquisition from the SLIM on the Moon.

SLIM is on the Moon and was responding to Earth commands after its touchdown, according to officials at a January 19 (U.S. time) post-landing press meeting.

Two sub-payloads were ejected successfully by SLIM en route to its touchdown and they are relaying data.

More time will be required to fully-understand the overall health and situational position of SLIM on the Moon.

Touchdown

The SLIM project focused on the ability of a lander to pinpoint its touchdown using technology that transforms descending onto the lunar landscape where it is “easy to land” to touching down “where you want to land.”

Japan has become the 5th country to successfully soft land a spacecraft on the surface of the Moon.

SLIM was launched last year on September 7, departing Earth atop an H-IIA launch vehicle from the Yoshinobu Launch Complex at the Japan Aerospace Exploration Agency’s (JAXA) Tanegashima Space Center.

SLIM – also called “Moon Sniper” – made its touchdown near Shioli crater. This pinpoint landing approach appears to have been successful, but more data is being assembled to satisfy this checklist goal.

Technology-driven target

SLIM is a technology-driven mission and included a baseball-sized, spherical rover developed in Japan by space program experts and a toy manufacturer. This ball-shaped rover was to crawl across the harsh lunar surface, swinging from side to side to propel itself forward.

The SLIM project is led by members of the JAXA Institute of Space and Astronautical Science (ISAS), and researchers from universities and other institutions across the country.

The Moon landing target was to plop down within roughly 330 feet of the ejecta blanket of Shioli crater.

SLIM carries a NASA-provided Laser Retroreflector Array (LRA) that can work in tandem with the NASA Lunar Reconnaissance Orbiter’s (LRO) Lunar Orbiter Laser Altimeter (LOLA). An overflight by LRO of the SLIM touchdown area could yield imagery, a flyover that is to occur mid next week.

Special software

In dropping down over the site, the SLIM descended almost vertically while detecting the altitude with landing radar. During this vertical descent phase, obstacle detection was performed at low altitude, just above the target zone.

SLIM is outfitted with high-tech gear and special software to process images captured by its onboard camera gear. It spots and identifies those craters, and then compares those features with a pre-loaded map embedded in the spacecraft’s memory to precisely compute the probe’s own position.

SLIM engineers and software specialists developed a dedicated image processing algorithm with high computational efficiency to achieve both accuracy and processing time.

Coast to coast

SLIM’s landing was a sporty proposition.

Firing its main engine in the opposite direction of its travel direction around the Moon, SLIM went into a powered descent phase. During that time there was a total of four “coasting” periods of about 50 seconds.

During that coast period, SLIM used camera imagery for quick processing to estimate its position and speed with high accuracy. At the same time, the onboard computer was to redesign the trajectory toward the landing point.

At a little above 10 feet and with main engine shutdown, SLIM was to auto-pilot itself to landing. SLIM is equipped with a mechanism to absorb the impact during landing at its five touchdown legs.

What all this adds up to is putting the smarts into a smart lander weighing a little over 460 pounds when it sat down on the Moon.

Running modes

The SLIM lander achieved ejection of a small scale, lightweight probe system and apparently did use its pinpoint landing technology – but that’s not all.

SLIM deployed a palm-sized Lunar Excursion Vehicle 2 (LEV-2) jointly developed with toy manufacturer, Takara Tomy, along with the Sony Group Corporation and Doshisha University.

The ball-shaped vehicle — SORA-Q — is equipped with two cameras and can transform its shape to traverse the lunar surface.

SORA-Q’s wheels that move freely left and right can run in two types of running modes, “butterfly running” and “crawling running” because the rotating shaft is eccentric, according to the Takara Tomy company.

The popular toy manufacturer is scheduled to make available SORA-Q for public purchase.

Shioli: shining science

NASA’s Lunar Reconnaissance Orbiter spacecraft will use its super-powerful LROC system to image the landing site next week.

Moon explorer Mark Robinson at Arizona State University’s School of Earth and Space Exploration notes that Shioli crater formed a little over 7 miles away from the rim of the 62 mile diameter Theophilus crater on ejecta emplaced during the Theophilus-forming impact.

In the case of Shioli crater, Robinson says, the bright ejecta seen around the rim originated from over 60 feet beneath the Moon’s surface. “Since it comes from depth, the ejected material was protected from the effects of space weathering, which darkens and changes the color of the regolith. Over time, the bright ejecta will fade into the background as the surface weathers.”

Thus, all that tossed out material around Shioli crater originated from beneath the surface. “As a result, SLIM will provide an opportunity to explore a cross-section of the crust,” Robinson points out.

As JAXA and ISAS teams note, SLIM will be invaluable in honing future landing skills, not only for the Moon, but on other deep space locations. It’s a project they state to move from the era of “landing where we can” to “landing where we want.”