Japan Takes Another Shot at the Moon

[Yazata]

Japan is trying again. Their last try was a Japanese "new space" company called I-Space. Sadly it didn't succeed in landing its lander.

This time its the government space agency JAXA.

This lander is called SLIM (Smart Lander Investigating Moon). It proposes to use a rather peculiar method of landing. It will brake from lunar orbit, locate a suitable landing spot using AI, then come to a hover about 3m/9ft above the lunar surface. Then instead of propulsively landing (hard) it will just shut off its engine and fall (easy) that last 9 feet. (The Moon has 1/6G, so falling 9 feet on the Moon is like falling 18 inches on the Earth.

SLIM is scheduled to launch from Japan tomorrow August 27 on a Japanese H-2A rocket.

https://twitter.com/SpaceNosey/status/16...3780963810

[Yazata]

After some delays, the Japanese lunar lander SLIM got off successfully today aboard a H2A rocket from their Tanegashima Space Center.

https://global.jaxa.jp/press/2023/09/20230907-1_e.html

JAXA photos

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[Yazata]

Japanese reports are confirming that JAXA's SLIM lander has landed on the Moon!

But... it isn't entirely successful. SLIM soft-landed and the lander is communicating with Earth. But unfortunately, the solar cells on SLIM aren't producing power and the lander is currently operating on batteries. They are trying to conserve battery life by shutting off instruments. Right now they are prioritizing downloading descent and landing engineering data so they can perfect their landing methods for future flights. If possible, they will download scientific data and maybe some photos after the engineering data.

They say that SLIM's battery life is probably a matter of hours so their time is limited.

They don't know why the solar panel isn't generating power. They say that there's a small chance the lander is currently in shadow and might regain power when the Sun is in a different place in the Lunar sky. But that's a very faint hope.

It's probably just a loose connection. A human astronaut could probably fix it quickly and easily, which is an advantage of crewed flights. A robot spaceprobe is doomed if even a small thing fails to work as designed.

[Yazata]

SLIM has shut down after its battery reached 12%. But JAXA is hoping that the reason its solar panels aren't working is that the lander is in shadow and that the panels will start producing power when the Sun is in a different place in the lunar sky. (A 'day' on the Moon is the same as an Earth 'month' since it's tidally locked with one face always facing the Earth.)

SLIM did land close to the Lunar south pole, where the Sun is always low in the sky. It's where some craters are permanently in shadow such that water ice might form in them.

Artist's conception from JAXA

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[Yazata]

SLIM released a couple of smaller probes, one of which captured this photo from the Moon's surface, transmitted through SLIM before it had to shut down due to depleted batteries.

The biggest thing I notice is that SLIM isn't sitting on the Moon's surface in the planned manner. It was supposed to shut off its engine about 3 m above the surface, fall the rest of the way, then end up on its side with its solar panels on top.

The photo suggests that it bounced and ended up resting on its nose (opposite the engines) rather than its bottom side. In the photo, I think the bottom is to the left, meaning the solar panels are pointing to the right. Given that the sunlight appears to be coming from the left, that means the solar panels are pointing away from the Sun and hence are in shadow.

That gives me hope that SLIM might revive when the Sun moves to shine on the right side, perhaps in a week or two.

JAXA photo (the grey lines appear to be data transmission artifacts, or perhaps they are for color calibration)

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[Zinjanthropos]

Looks like SLIM hit with a little forward momentum. The front landing pad dug in and halted the craft but not before the back end continued its forward progress and left the ground, tilted, but did not fall back down. Looks hilly there so maybe that contributed.

Seems like piss poor way to land. The artist depiction shows what looks like four small landing gear tucked under an office coffee wagon. I think they’re lucky it didn’t tip over on one side. Shouldn’t the landing gear be spread out beyond the sides, kind of tripod-like? Millions of yen payload with two cent landing pads.

Maybe some day the shock wave of a nearby meteor hit or of some tectonic nature will jar it enough so that rear end falls back down to surface. Easy fix if you can get to it so I wonder if there is currently any unmanned mobile lunar surface machines roaming nearby to give it a nudge? What about using the released probe?

[confused2]

I suspect the pic will become a textbook example of "This is what happens when you try to land on a slope".

BBC have some news (before Yazata!)..

"An abnormality in the main engine affected the landing attitude of the spacecraft," the Japanese space agency Jaxa said in a statement.It seems one of the two big thrusters on Slim (Smart Lander for Investigating Moon) stopped working during the descent.

https://www.bbc.co.uk/news/science-environment-68091389

[Yazata]

Scott Manley has a great little video analyzing what happened with SLIM, based on JAXA's Japanese language briefing. (no, Scott doesn't understand Japanese, but got his hands on a computer translation)

The landing software worked great, but something made one of its two main engines fail (its rocket nozzle came off!) at a low altitude. The other engine kept working, had enough thrust to complete the landing, but the computer had to compensate which gave SLIM more lateral velocity than expected. So it ended up on its nose with its solar panels pointed sideways, rather than on its legs with the solar panel pointed skywards.

It did release its two little rovers and managed to get some great photos of the Lunar surface. And yes, JAXA is hopeful that SLIM will start charging when the Sun moves to shine on the panels, and more of the mission can be salvaged.

Scott thinks that JAXA engineers are rather pleased with how it went, despite the problems. It did soft land on the Moon, its navigation system worked as designed and it set down in the 'box' where they planned it to land, and the control software reacted to the loss of the engine very well and saved the vehicle.

Scott mentions that the first Indian lander Chandrayaan 1 failed because its flight computer threw up its hands (if it had hands) and said in effect "I don't know what to do!" and the lander crashed, when the computer could have saved it had it been able to adjust. (India's second lander, Chandrayaan 2, was a great success.)

https://twitter.com/DJSnM/status/1750588159975657896

[Yazata]

The two little rovers that SLIM released are cool little things:

One is a little grasshopper like thing that jumps in the Moon's low gravity. The other is a ball that gets thrown out as SLIM lands, then pops open to expose a little cellphone-like camera and then rolls around. They aren't powerful enough to communicate with Earth directly and use SLIM as a communications relay. They proved their functionality in the short time SLIM was working, including producing that photo of SLIM upended on the surface.

JAXA photo

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[Yazata]

JAXA has announced that they have reestablished contact with SLIM and they immediately fired up SLIM's multiband camera and started making scientific observations. They don't say what's happening with the solar panel, but the fact that SLIM seems to be back in action suggests that the panel is producing power.

https://twitter.com/SLIM_JAXA/status/175...5810556340