SLIM landed on the Moon softly, but upside down!
Click for original image.
We now know why SLIM’s solar panel was not facing the Sun after the Japanese lunar lander touched down. When it was only 10 to 15 feet above the ground, preparing to land, one of its two descent engines failed, causing the spacecraft to tumble as it softly touched down. As a result, it landed softly, but upside down, thus putting the panel on its west side instead of its east side as planned.
The image to the right, cropped to post here, was taken by one of the two tiny rovers released by SLIM just prior to landing. It shows SLIM upside down, but essentially undamaged.
The lander however still apparently achieved its primary goal, landing within a small zone only 300 feet across, or 100 meters.
Analysis of the data acquired before shutting down the power confirmed that SLIM had reached the Moon’s surface approximately 55m east (180 feet) of the original target landing site. The positional accuracy before the commencement of the obstacle avoidance maneuver (at around a 50m altitude) which indicates the pinpoint landing performance, was evaluated to be at approximately 10m or less, possibly about 3 – 4m.
…Under these circumstances, the SLIM onboard software autonomously identifies the anomaly, and while controlling the horizontal position as much as possible, SLIM continued the descent with the other engine and moved gradually towards the east. The descent velocity at the time of contact with the ground was approximately 1.4 m/s or less, which was below the design range., but conditions such as the lateral velocity and attitude were outside the design range, and this is thought to have resulted in a different attitude than planned.
In other words, when that engine failed, SLIM was only about 10 to 30 feet from its pinpoint landing target, but then drifted eastward as its dropped those last few feet because of the unbalanced engine burn caused by only one engine.
That the spacecraft is still operating and can communicate with Earth, even though it is upside down, is remarkable. Moreover, SLIM did achieve its main goals quite successfully. It landed within its tight target zone, it released two mini-rovers which operated successfully, and has been able to send its own pictures back to Earth. It was not able however to test its crushable landing legs, as they remain in the air.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Click for original image.
We now know why SLIM’s solar panel was not facing the Sun after the Japanese lunar lander touched down. When it was only 10 to 15 feet above the ground, preparing to land, one of its two descent engines failed, causing the spacecraft to tumble as it softly touched down. As a result, it landed softly, but upside down, thus putting the panel on its west side instead of its east side as planned.
The image to the right, cropped to post here, was taken by one of the two tiny rovers released by SLIM just prior to landing. It shows SLIM upside down, but essentially undamaged.
The lander however still apparently achieved its primary goal, landing within a small zone only 300 feet across, or 100 meters.
Analysis of the data acquired before shutting down the power confirmed that SLIM had reached the Moon’s surface approximately 55m east (180 feet) of the original target landing site. The positional accuracy before the commencement of the obstacle avoidance maneuver (at around a 50m altitude) which indicates the pinpoint landing performance, was evaluated to be at approximately 10m or less, possibly about 3 – 4m.
…Under these circumstances, the SLIM onboard software autonomously identifies the anomaly, and while controlling the horizontal position as much as possible, SLIM continued the descent with the other engine and moved gradually towards the east. The descent velocity at the time of contact with the ground was approximately 1.4 m/s or less, which was below the design range., but conditions such as the lateral velocity and attitude were outside the design range, and this is thought to have resulted in a different attitude than planned.
In other words, when that engine failed, SLIM was only about 10 to 30 feet from its pinpoint landing target, but then drifted eastward as its dropped those last few feet because of the unbalanced engine burn caused by only one engine.
That the spacecraft is still operating and can communicate with Earth, even though it is upside down, is remarkable. Moreover, SLIM did achieve its main goals quite successfully. It landed within its tight target zone, it released two mini-rovers which operated successfully, and has been able to send its own pictures back to Earth. It was not able however to test its crushable landing legs, as they remain in the air.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Going forward, it appears landers will need solar cells on both top and bottom!
One minor nit: “in the air” is an obvious expression for the situation with the lander upside down, but of course the moon does not have air.
Is it bad that I laughed at the picture?
I wonder how many anachronistic expressions will make their way into our space-traveling future. There are plenty of them still around on Earth: Hair of the dog [that bit you], hang up the phone, squeaky wheel gets the grease (I’m old and I’ve never greased a wheel; hurrah for sealed bearings), never look a gift horse in the mouth, fall off the wagon, etc…
Keep hitting it with the rovers until it tips over! :)
markedup2 asked: “I wonder how many anachronistic expressions will make their way into our space-traveling future (?)”
I’d say the first was when JFK exhorted us to ” . . . set sail on these new seas.”
‘Up in the air’ may not be technically accurate, but does provide an immediate, understandable, grasp of the situation. It’s good communication.
I’d like to point out that *anyone* can land a spacecraft right-side up, although I would have expected this orientation from an Australian operator.
Any landing your rovers can walk away from is a good landing.
Robert wrote: “It was not able however to test its crushable landing legs, as they remain in the air.”
If it survived landing on its roof, how much does it need those crushable legs?
I had assumed that it touched down, then rolled over from too steep of an angle on the landing site.
My reading of the article is that it set down in correct orientation but due to its eastward speed it tipped over after soft touchdown.
From the press release:
Blair Ivey,
I’m still laughing.
To be precise:
It was nominally planned that the SLIM lander, shortly before touchdown, would turn or tilt 90° from the starting position with engines downwards, so that it would come to rest on one of its side surfaces, on which a kind of small legs are attached.
Due to the engine failure (the expansion nozzle of one of the two 400N engines blowed off), this planned movement was now not just 90° but 180°. In the spirit of the device’s designers, the lander is not upside down, but on its side.
Questioner wrote: “so that it would come to rest on one of its side surfaces, on which a kind of small legs are attached.”
How wonderful. My recollection is that is how the ship landed on the Moon in the book Rocket Ship Galileo, my second science fiction book, right after I Robot.
Scott Manley has an analysis of what happened. It depends upon a translation from Japanese, and about a third of the way through the video he notes a difficulty of mechanical translators, such as Google Translate.
https://www.youtube.com/watch?v=7bFiJvbKyPs (14 minutes)
Apparently, a major problem was that one of the two main thrusters failed, as its bell section departed the spacecraft, as Questioner noted. The root cause may be associated with an excess of oxidizer supplied to that thruster. He compared it to a similar problem, a faulty valve in Akatsuki, a Japanese probe to Venus.
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Speaking of applicable expressions, we could say “thrusters up,” similar to “Tango Uniform,” derived from “belly up,” which is what happens to dead fish. Maybe we don’t want to compare a fairly successful lunar probe to a dead fish.
Or, “flamey end up, point end down” could be appropriate, although there aren’t any flames, anymore, and the pointy end isn’t really pointy.
Upside-down does not really fit, because as Questioner pointed out, the solar arrays were supposed to be on top, after landed, so it is really upside-sideways.
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Getting space right is not easy. We have a lot of trouble with newly designed launch vehicles, despite them being similar to well established rockets (Starship and Super Heavy are trying to do very new things, which makes them even more difficult to get right). We have a trouble landing on the Moon, despite the many successful landings over a half century ago. Probes to Mars still go awry. When I was building and testing satellites and satellite instruments, the darnedest things went wrong, although we were able to fix the problems we knew about before launch. The concepts of rocket science may be simple, but executing them successfully is still difficult. We seem to still be in a steep learning curve, where space is concerned.
Then again, getting aviation right took a century, and yet we’re still learning.