Chandrayaan-3 Soft-landing [video]
isro.gov.in
isro.gov.in
What made them make that decision? Was it like "lets be as precise as we can because we want to get to the spot X because X is special" and thus "Lets let the software always compensate for any errors to get to X". I am assuming that even at this point they tested the software for extreme conditions. It is most likely that once this assumption was made the Software was built that way, i.e: "Lets test the Software can always correct for any issues to get to X with feedback(like thrust)". It trades off Safety for Accuracy(to hit X).
This time the idea was "Lets select a trajectory to X" but this time "We will let the software prioritize safety(altitude, speed and heading) to be within norm once we start descending towards X". And additionally "Not make any corrections if we are somehow too far off X if it exceeds safety limits". It trades off Accuracy(to hit X) for Safety.
Video has captions
- CY2 lander had limited leeway in fixing issues, by design. CY3 has more and has landed itself, no assistance from base.
- CY2 lander had limited time to fix itself, apparently it was just a few seconds short of making it fine
The video provides an explanation for why India's Chandrayaan 2 lunar landing mission failed in 2019. The landing craft Vikram experienced issues during the camera coasting phase where instruments were being calibrated. Specifically, the engine thrust was higher than expected and thrust control couldn't be adjusted to correct the trajectory. As a result, errors accumulated and Vikram's trajectory deviated significantly from the planned path. For Chandrayaan 3, ISRO has implemented changes like adding instantaneous thrust control, increasing the allowed attitude change rate, and enlarging the landing zone to make the mission more robust to errors. The video offers an insightful technical look into what went wrong and how ISRO is addressing it for the next lunar mission.
Hopefully they have upgraded software to just gracefully attempt a landing, and hopefully they won't be off course.
With new one, they did couple of things. Larger area to be selected for landing based on camera input. Escape sequence to more achievable points, if something like this happens again. They increased the tolerance from 10 degrees to 25 degrees and guessing fixed the bug in code. They also did some smoothening of the trajectory for different phases to make it more continuous. I think they also made other changes in engines among other things and a whole host of testing.
I did like seeing the live images captured during descent, I also hope those get made into a video and posted online.
Looking forward to the rover deployment too.
While we think "this cannot ever happen" in a lot of cases it can, in ways you did not consider. Both for good and bad
Edit: here, at least, is a mention of the thing with her daughter in a Google Blog article: https://blog.google/products/maps/margaret-hamilton-apollo-1...
Turns out it just flew over a cliff edge that actually does that. Completely by accident.
It was in there.
A lot.
This can't even come from the software engineering, but must be some kind of managerial failure (e.g. we're short on time, but have to report great progress to my boss, so skip this scenario).
Almost all space mission code only ever has the so-called 'happy path'. We rely on extremely tight mechanical and aerospace engineering tolerances to achieve that happy path.
The Hubble Space Telescope's primary mirror grinding was off by a matter of micrometres, and resulted in blurry images.
Consider all the Mars rovers. Imagine some wind gust threw the descending module off course, or a retro-rocket failed because of vibrations.
Writing code for space missions isn't like writing a CRUD app. Developers can't just teleport to a space probe millions to billions of kilometres away to rectify errors and debug running code on the fly.
For the record, the 'failure path' for Apollo 11 was to get the US President to announce to the world that the two astronauts would likely be marooned on the Moon. Apollo 13 very nearly failed, too.
If Apollo 11 had followed the "happy path", they would have crashed and died.
Hubble was also the "failure path". The main mirror was flawed and had to be corrected.
Same reason you can't program a self driving car to save a person by sacrificing a squirrel. It's just going to run over the squirrel when it didn't need to.
Writing only happy path code as a standard practice in the space sector seems quite absurd. You won't ever achieve absolute precision and errors do happen, yet it seems like systems recover most of the time.
Recently, the antenna of Voyager 2 got misaligned, but it is expected to recover from that. That was only the last problem it encountered over its very long mission - and it managed to recover from all of those so far!
Or, are you saying that it's expected that the mission did not count with this scenario, and that future missions don't need to account for that either?
Hell, you can run a few thousand simulators for every scenario you can think of during descent, including lost of burner, propellant leak, etc, and then during the actual descent a chip get burnt because of a stray cosmic ray. There will still be somebody on HN call you out for cutting corner.
This wouldn't be the first time that a mission failed due to embarrassing failures in basic software practices (eg Starliner's initial software bugs emerging from a lack of integrated testing).
Main difference is that you aren't triggering a billion overly sensitive nationalistic folks when you point out similar embarrassing errors in most other countries' programs. Eg the time NASA lost a probe due to miscommunicated units, the Apollo 1 disaster, the space shuttle disasters, or the tape around the wiring in Starliner, which was intended to be fire retardant actually turning out to be flammable...
Hell, Japan's Hakuto-R also failed because the software's error detection was buggy, and they openly admitted as much without any bluster about how no one but other people with experience writing code for space probes can criticize them.
What do you mean by "they haven't officially straight-up announced the issue." ? They did so - several times actually.
One of the big things they changed with this lander compared to Chandrayaan-2 was to increase the landing zone from 500mx500m to 4000mx4000m and adding more sensors and cameras to help the computer find a good landing site.
For those who didn't watch live, there was another hover phase (0 m/s descent) at 150m above the lunar surface before final commit.
Great outcome and I look forward to the pictures sent back by the rover!
Most missions have several different scientific systems on board. If any one fails well the others still make the mission a partial success. If the landing system fails they all become a failure.
Can you elaborate on this? Presumably it could land...anywhere on the moon, so what exactly does it mean to increase the landing zone? What determines where it can or can't land?
It obviously can't land on mountains and certain rocky or steep terrain. They know its limitations. These limitations determine where it can or can't land.
During target selection they will find an adaquet place on the surface that meets the criteria.
By increasing from 500m^2 to 4000m^2 they need to find a larger area that meets those same needs.
This also helps during the actual landing. It can aim anywhere inside that 4000m^2 area instead of being limited to just a 500m^2 area.
I'm also curious
- Why the south pole of the moon? does it have an added significance vs other locations on the moon?
- Is a landing on the south pole more difficult to achieve? Seems so according to this article: https://www.reuters.com/science/why-are-space-agencies-racin...
> It is of special interest to scientists because of the occurrence of water ice in permanently shadowed areas around it. The lunar south pole region features craters that are unique in that the near-constant sunlight does not reach their interior. Such craters are cold traps that contain a fossil record of hydrogen, water ice, and other volatiles dating from the early Solar System
I haven't read specific reasons for choosing that site, but we have never landed that far south, and it will be interesting to see what differences (if any) there are from the more central latitudes, which is a good enough reason on its own.
However, the first direct evidence of water vapor near the Moon was obtained by the Apollo 14 in 1971 [0]. A series of bursts of water vapor ions were observed by the instrument mass spectrometer at the lunar surface near the Apollo 14 landing site.
[0]: https://www.planetary.org/articles/water-on-the-moon-guide
Very well done, India. Respect!
The point was about we could be doing so much more with the resources we have. That is what I got out of it - and I agree.
edit: lets goo!!!
Which is disappointing. India should have their own video sharing/livestream platform.
Had the same issue with JWST for example.
So it's good to see it work both ways.
(To be clear, I am happy for India, just think it could be presented better)
But I'm proud of the people that worked on and executed that mission for them. Obviously a moment of immense national pride, well deserved.
ISRO is primary arm of the Department of Space which is headed by the Prime Minister. So in essence, the Prime Minister is the boss. It is not an independent federal agency like NASA.
https://www.theguardian.com/science/2019/jul/14/apollo-11-ci...
Most British news outlets really are a scourge on our society.
Another clocks are labeled "GHY," "HAW," and "BIK." What do they indicate?
So, likely the current time at the location of the radio antennas they're using to communicate with the lander.
[1] https://www.isro.gov.in/Chandrayaan3.html
[2] https://www.thehindu.com/sci-tech/science/chandrayaan-3-miss...
[3] https://www.nytimes.com/live/2023/08/23/science/india-moon-l...
I am asking because the livestream of the last failed moonlanding this year didn't feature a single second of footage. None.
NASA reported locating the Vikram Lander's debris in Dec 2019: https://www.nasa.gov/image-feature/goddard/2019/vikram-lande...
Edit: They called this out now, it seems those are live pictures.
The only footage we have of any spacecraft landing anywhere other than Earth is either from Apollo or the Perseverance skycrane deployment. If they do have footage, it'll be like the latter, retrieved after the fact.
Congrats !
It is good that Indians are able to go aboard and bring a globalized knowledge back to India.
Dozens of major private companies focused on making this success making various spare parts including steel cranes by Tata steel, special alloys of Mishra Dhatu Nigam (The Alloy Company), wings by L&T Aero etc. etc. I know some people here and they were so proud and focused on "excellence" which I think is often missing in what we Indians normally do.
Space programs are important because of precision required. It created a discipline and desire for perfection not just for ISRO but for all their suppliers and vendors. Hope this habit spreads.
When I look at this, it seems it's a long-range optical feed of the moon surface with lander graphics laid over it. Has anyone found footage of the actual craft touching down? It would be amazing to see.
- 3 by China: All success
- 1 by Japan (along with a rover from UAE): Failed
- 1 by Israel: Failed
- 1 by Russia: Failed
- 2 by India: Previous one failed. This one succeeded
I can see why the entire world would be excited by something like this. I hope that there will be routine landings by different players and that the landing guidance would be perfected.
[1] https://en.wikipedia.org/wiki/List_of_missions_to_the_Moon#M...
1. No one has managed to make a landing on the moon's South Pole yet.
2. Since the South Pole doesn't get any sunlight at all, it's believed that there's a possibility of discovering ice/water there.
- Its landing on the south pole where nobody's ever landed before
- Russia failed to land on the moon a week or two back
Simultaneously capability development and demonstration for ISRO
How is that not a big deal?
I get it's very expensive and hence difficult to pull off - but this makes it comes off as mostly nationalism and a big display of disposable income (which for a country with so much poverty is .. something)
As a geek, I love the space program.
As a human, I don't think it makes sense given the poverty.
For me the most interesting part to watch personally was the telemetry. What's the latency involved here, do they have agency in terms of manual overrides and intervention in case things go wrong?
What does RTT look like, are there more efficient encoding of data to allow minimal information?
I'm not sure about the details of this mission and whether the Indians have negotiated usage of the Deep Space Network, but with the large antennas of the DSN multi megabit rates are quite achievable.
How will it fly? There is no atmosphere.
But yes, it’d be cool if it were possible.
The onboard has not been shown since.
EDIT: I went to re-watch the moment on youtube and it does seem like the lander moves slightly to the left!
Check the row for Chandrayaan-2. Why does it say Unsuccessful landing but main mission success and extended missing ongoing?
What exactly are main mission and extended mission and how can they succeed or be ongoing when the landing has been unsuccessful?
The complexity of landing on the moon is somewhere between that of launching a spacecraft and that of a self-driving car. It's sad that so many landers were lost - it would have been heartbreaking for those who built them. But I hope that they attempt it again and perfect this complex task.
It makes me wonder, what is it that ISRO does differently than most other government agencies in India that makes them so efficient.
Although, I do not have reference for what the exact budget was/is.
Anyhow congratulations to this team and to the people of this great nation.
PS: Will they share the data with opensource community for analysis?
13:34 BST
08:34 EDT
Congratulations, India!
The team deserves even more praise to be able to achieve these wins with limited resources.
Actually congratulations to all countries still running space programmes including Russia's failure.
The more the merrier.
This is a stupendously difficult thing to do, India is truly a superpower.
It also ironic that a country and population seen as backwards by the British Empire have overtaken the British in landing on the moon.
Would be nice to see the African and South American continent achieve a moon landing as well.
The country that first visited the Moon should have explored the lunar south pole decades ago. Then the dark side of the moon. Then a manned colony.
Instead we are beaten by a foreign nation to the south pole. And our next project is a manned landing on the moon, which we already accomplished in the 1960s.