JAXA's Smart Lander for Investigating Moon (SLIM) is getting ready for landing on the lunar surface tomorrow Friday Jan 19 at 15:20 UTC.
The spacecraft, nicknamed the “Moon Sniper,” will demonstrate precision landing in a target area less than 100m in diameter, using real-time image recognition technology.
The spacecraft will land on a sloping surface near the crater Shioli.
SLIM carries a number of science instruments and will also deploy 2 rovers.
SLIM was launched on Sep 6, 2023 and it took an unusual 110-day path to get to the moon.
Instead of traveling straight to the moon (like the Apollo missions), which requires a lot of fuel to slow down once it gets near the moon, SLIM went way past the moon, used the moon's gravity and that of earth, to enter an elliptical orbit whose perigee was close to the Moon's orbit. It was injected into lunar orbit on Dec 25, 2023, followed by a few orbit lowerings.
Where will JAXA's Smart Lander for Investigating Moon (SLIM) land?
The landing area is just to the east of Shioli, a small lunar impact crater, that is located within the much larger Cyrillus crater on the near side of the Moon.
See maps below for the location of the landing area. The last 3D map shows the slope on which Shioli resides and where SLIM will attempt to land on Jan 19.
SLIM will begin its final descent from an altitude of 15 km, during Perilune of its final 600x15 km elliptical orbit.
Besides traditional inputs to its navigation and control system, SLIM will utilize radar and vision based systems to precisely estimate position and velocity and to avoid obstacles during landing.
Interestingly, SLIM will land, tilt over and rest on its side, using shock absorbing legs, on the sloping landing surface.
Humankind's success rate at robotic landing on the moon over the past 5 years has been less than stellar. Out of 8 attempts, only 2 have been successful, as shown in the chart below.
We wish the best of luck and happy landing to SLIM, the Smart Lander for Investigating Moon.
Similar to Chandrayaan-3, SLIM will operate for one lunar day, about 14 earth days, since it does not carry a radioisotope heater unit to keep its electronics warm during the long cold lunar night.
The graphic below shows the phase of the moon tonight and on Jan 30 and the location of SLIM's landing area near Shioli crater. After Jan 30, SLIM will no longer receive sunlight to charge its batteries.
SLIM will deploy a couple of small rovers just before touchdown.
Lunar Excursion Vehicle 1 (LEV-1) is a hopping rover equipped with cameras, direct-to-Earth UHF comms. and a few instruments.
LEV-2 is a baseball-sized, spherical rover with a pair of cameras. It will communicate via LEV-1. It will use its two independently controlled wheels to crawl along the lunar surface.
Both rovers will operate for a few hours on Li-ion batteries.
Check out the rest of this thread for more info on this fascinating mission that will attempt to land with a precision of 100m on a sloping lunar surface. https://fosstodon.org/@AkaSci/111777585745262427
Here is chart of the elevation angle of the Sun at the SLIM landing site until the end of this month.
After Jan 31, the long cold solar night will begin, which SLIM is not designed to last.
Unlike Chandrayaan-3 which landed in the south polar region, SLIM's location is close to the equator and hence the sun elevation angle will be quite high during local noon.
The SLIM landing webcast has been suspended.
We will have to wait for the press conference (on the same webcast) which will begin sometime in the near future.
😢
This video shows how a successful landing would have looked like if you were there watching it from near the landing site.
Some bright news - DSN Madrid is showing a signal from LEV-1, the hopping rover, which must have hopped off and is now sending data via its UHF omnidirectional antenna.
Can't tell if the signal is good and if the data is being decoded.
But no signal from the SLIM lander itself, which was being shown earlier this morning.
AMSAT-DL reports that the signal from SLIM stopped at 17:57 UTC (the 17:00 in the tweet below is an error which they later corrected).
DSN is not showing a signal at this time either.
@ISibboI I'm not sure if it was on the press conference or I read this elsewhere, but I thought I saw mention that they might try to communicate when they determine the sun angle is correct for generating electricity.
Here is my simplistic take on what likely happened.
The following panels from the webcast show the orientation of SLIM near touchdown. Each panel has two views. left view looking up the slope, right view from the side.
In Panel 1, SLIM was oriented correctly and planning for a final orientation as in panel 5.
But starting in panel 2, SLIM rotated right 90° and rotated 180° vertically.
It is now lying upside down, solar panels on the side. There is likely some damage too.
Let's keep in mind that after the legs touched the sloping lunar surface, SLIM was supposed to gently tilt/rotate towards the slope.
Perhaps, the rotation started too early and the spacecraft over-rotated. Maybe, one or more thrusters failed. The sideways rotation might have been caused by the spacecraft head jamming into the surface, thrusters still firing.
This is of course very coarse analysis based on what was displayed on the webcast. JAXA will figure it all out shortly.
@AkaSci I know it’s easy to second-guess after the fact, but the landing process did seem rather complicated and untested to me. Have any other landers used this kind of approach?
@michaelgemar I'm not aware of anything quite like that. Most things tend to land with flame side down. NASA broke many molds w/Pathfinder-esque airbags and Curiosities Sky Crane. But I don't recall a sideways tilt on purpose of any lander.
Assuming that the SLIM lander is near upside down on the lunar surface, which way are the solar panels facing?
One likelihood is South, in which case, they will see very little Sun, given that the Sun stays on the North side in the sky (SLIM is at latitude 13.33 S).
Facing west would be more advantageous as the Sun would light them up later in the lunar day after Jan 24.
Scott Manley in a YouTube video says that the panels are facing west, as indicated in the diagram above.
Also, around 15:19:50, according to the data shown in the webcast, all thrusters on the SLIM lander were firing at abnormally high rates and the spacecraft was rotating along all 3 axes.
The clock on the display was frozen at 15:18:50 and then jumped to 15:19:03, indicating perhaps a loss of telemetry during that interval.
Things certainly did not look healthy around touchdown time. Although, this could be a telemetry glitch.
SLIM was indeed powered down at 17:57 UTC (which is when AMSAT-DL reported loss of signal; see post #27). Battery level was 12% at that time, 2.5 hours after touchdown.
Telemetry shows that the solar panels are facing west and there is hope that later in the lunar day, the system may revive. Many of us concluded that from the webcast images.
This photograph of the JAXA SLIM spacecraft taken by the LEV-2 rover was released today. It confirms that the lander ended up upside down on the lunar surface.
A press conference is in progress which will provide more details on the anomaly that caused this issue even though SLIM achieved its goals of landing within a very tight target area and deploying the two rovers.
The tiny crawling rover LEV-2 successfully sent this image via LEV-1.
These two b/w images of the lunar surface near the landing area were taken and sent by the JAXA SLIM lander itself in spite of its unfortunate landing orientation.
The first image was taken by the CAM-PX camera. It also shows the slope of the landing area.
The 2nd image was taken by the geological survey spectroscopic camera. The 1st image is overlaid in the inset.
Both images show small rocks on the relatively smooth terrain.
This slide from the briefing, translated using Google lens and posted on twitter, indicates that one of SLIM engine nozzles fell off during landing.
Yikes 😱
It shows an image of the falling nozzle captured by one of the cameras around 00:19:20 JST, just when it lost telemetry.
With one nozzle missing, the lander would have started rotating, while the software tried to compensate using the other thrusters.
Here is another translated slide from the JAXA SLIM briefing.
It states that the main engine was operated at higher load during 8 orbit changes and during the power descent phase, but there were no signs of abnormality in the main engine until the event occurred.
The the -X side (failed) engine had rather mild combustion conditions compared to the +X side engine.
The team believes that some external factor other than the main engine affected the the -X side main engine.
This slide shows that around 00:19:18 JST, when the JAXA SLIM lander was hovering around 50 m, one of the two main engines (the one on the -X side) experienced a failure, as shown by the green line in the graph; the total thrust fell by about 50%, the -X side engine temperature did not rise as expected.
Translated slide 17 states that the JAXA SLIM lander is believed to be oriented upside down, the main engine facing upwards and the solar panels facing west.
Which means that the solar panels should start receiving sunlight and hopefully charging the batteries starting today, as shown in the graphs below (graphs created by me).
The image of the lander with the lunar background is computer generated, not an actual photo.
SLIM did not land upside down. In spite of one failed engine, SLIM touched down upright and with nominal speed. It was the lateral leftward speed that caused it to rotate post touchdown.
The final resting place is 55m east of the target landing site.
At the 50 m hover mark, the positional accuracy was within 10m!
SLIM sent back data and images until it was shut down after 2.5 hours.
Here is some info on the orientation of the JAXA SLIM lander's solar panels.
The solar panels are facing southwest. NW would have been better, since SLIM is at 13.3°S. In the image taken by LEV-2, the solar panels are not visible.
So, there is some hope of a revival as the Sun moves farther west.
This is based on matching an image from a similar location (but from a much higher angle) using the lunar map at LROC. The shadows imply it too.
NASA's Lunar Reconnaissance Orbiter (LRO) today published this image and location of the JAXA SLIM lander on the lunar surface. The image was taken on Jan 24, five days after landing.
The 1st image below shows the new LRO image. SLIM is a tiny dot in this image. The 3 other images below it zoom out of the area to provide more context. I extracted them from the LROC map site and a NASA site.
A note about that iconic image of the upside down JAXA SLIM lander taken by the LEV-2 rover.
The lander appears to be in quite good shape. It is not visibly damaged, shattered or crushed, which a hard landing or a soft landing on its head would cause. As stated by JAXA, the spacecraft must have landed upright, its legs absorbing the vertical speed of 1.4 m/s and then gently rolled over due to its lateral speed.
Instruments and comms were up for 2.5 hours until shut down.
👏👏
Confirmation from JAXA that the team has succeeded in establishing communications with the SLIM lunar lander and has resumed operations!
They have successfully obtained an image using SLIM's Multi-band Camera.
As expected, the batteries are getting charged by the afternoon Sun. They only have a few days left for science operations before the Sun sets and the lunar night begins.
Check out the rest of this thread to learn more about the SLIM lunar mission.
The reference to the "toy poodle" in the tweet by JAXA most likely refers to the rock named "Toy Poodle" in the image below taken by SLIM's Multi-Band Camera on Jan 25.
JAXA assigned nicknames to several rocks in the image as shown below.
An acknowledgement and a thank you note from the JAXA SLIM team to NASA's Lunar Reconnaissance Orbiter (LRO) and ISRO's Chandrayaan-2 missions.
The two missions have provided valuable data to make SLIM's pinpoint lunar landing objective a reality.
Note that even though the Chandrayaan-2 lander crashed during landing on 6 Sept. 2019, the Chandrayaan-2 orbiter has stayed operational and continues to provide hi-res science data.
There is but a slim chance that SLIM can survive the lunar night, which starts tomorrow. It does not have radioisotope thermoelectric generators (RTG) to provide heat and power to its electronics. Nighttime temperatures can fall to a chilly -130° C, 140 K.
Also, due to the solar panel's SW orientation, batteries won't get recharged until late afternoon on the next lunar day, i.e., around Feb 26.
It is a bitter-sweet Good Night for the JAXA SLIM lander as its transmission was turned off by ground station at 00:29:40 UTC. There is hope that it may wake up about 3 weeks from now as the Sun lights up its solar panels again. There is also the realization that this was probably the last transmission from SLIM.
The Sun sets at the SLIM site tomorrow morning around 09:00 UTC.
Come to think of it, SLIM managed to meet most its objectives, in spite of the failed engine.
👏 🙏 #SLIM#Space
52/n
Here is a parting gift by the JAXA SLIM lander as night fell around it earlier today.
It is an image taken by the CAM-PX camera just before the sun set. The sun is at such a low elevation that only the tops of the small rocks and the hills in the background are lit up. This is the same scene whose image was taken on Jan 19 in the morning sun, as shown in the 2nd image below.
Wishing you and your two rover buddies - sweet dreams.