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Chandrayaan-3 Soft-landing [video]

isro.gov.in

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Re: Chandrayaan-3 Soft-landing [video]

#281

Post by balozi »

the-dude wrote: post #184

If the lander flipped over and exploded, it seems nobody would have noticed.

I don't know much about landing extraterrestrial missions, but I would imagine that the moment of touchdown is exactly the moment everyone in the control room should be keenly paying attention to their assignment instead of jumping up to celebrate (or at least try not to distract those that are). Because if that thing sunk into a pool of moon water or landed on top of another lunar lander, it would be 15 minutes before anyone realized. Just a minor layman observation.

Anyhow congratulations to this team and to the people of this great nation.

Re: Chandrayaan-3 Soft-landing [video]

#282

Post by rqtwteye »

Philip-J-Fry wrote: post #204
sva_ wrote: post #201

Earlier quoted context omitted.

I can imagine that this is a HN-bubble thing. Most people would probably get bored from just seeing some live footage.

SpaceX livestreams didn't get super popular for having a politician on them. They got popular for showing exactly what's happening with enthusiastic presenters narrating it. Most people find speeches and politicians boring. They wanna see rockets flying, robots moving, etc.

“enthusiastic presenters narrating it.”

I seriously hate their narrators and all the cheering.

Re: Chandrayaan-3 Soft-landing [video]

#283

Post by sumodm »

jvm___ wrote: post #12

Scott Manly has a video on why he thinks the last one failed. It sounds like their landing software didn't have "oh crap, we're way off course, just land wherever". It only had the happy path of "fly to here and land", so when it switched to the landing phase it tried valiently (including flying upside down) to try to fly back to the landing zone, but the landing zone was much further than fuel supplies allowed. Hope…

Yes, this seems to be one of the issues. Here is a talk by ISRO Chairman S Somanath at Indian Institute of Science (IISc) about the same and what they added. He goes into details of what went wrong. These are based on my limited understanding. One of the thrusters had an issue and got activated for longer (or may be activation profile of thrusters at its extreme's were different from modeled). They had a narrow landing region selected as final position (even one possible point). So now their control system tried to correct this but the algorithm had a bug and that caused it to be further delayed. At this point the correction required, i.e; thrusters to be activated, was outside the tolerance levels. So finally ended up with 50m/s vertical speed. https://www.youtube.com/watch?v=fZ2sNRP1opY&t=1440s

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.

Re: Chandrayaan-3 Soft-landing [video]

#284

Post by suyash »

NKosmatos wrote: post #60
the-dude wrote: post #11

Does anybody know if we will be watching a simulation or actual footage? I am asking because the livestream of the last failed moonlanding this year didn't feature a single second of footage. None.

The lander external view is simulation, but they have a camera (Lander Imager Display) looking downwards that is transmitting live photos every couple of seconds (center, top right on the main screen).

Though it's disappointing to see simulation, it makes sense as there is no external vehicle to capture the live video and stream it. The lander cameras are showing realistic video though.

In principle, it should be clearly stated which is real and which is sim.

Re: Chandrayaan-3 Soft-landing [video]

#287

Post by goku12 »

the-dude wrote: post #148
shivdeepak wrote: post #129

Earlier quoted context omitted.

That's probably because the image data being larger than the on-board sensor data would take longer to reach earth, thus the latency.

Obviously I am not a golfer, but I would have waited until the onboard stabilized, sensors be damned.

The sensor data is a reliable low-entropy indicator. The engines are probably cutoff based on the same data (most probably a set of load sensors on the legs). If the data indicates that the engine has cutoff, the craft is stationary and if the data is still streaming, then it's a pretty good indicator that it worked as expected. I would trust it more than the video - especially when the video is lagging heavily.

PS: I have worked extensively on something related. Video is good to have and helps in post-flight analysis. However, it can also mislead sometimes. Sensor data gives you a much clearer initial picture.

Re: Chandrayaan-3 Soft-landing [video]

#289

Post by contrarian1234 »

thyrox wrote: post #47

Not asking rhetorically but why is this a big deal? Is it because it's going to the south pole? What are some other benefits to be gained from this?

I'd be curious if it's at all interesting from a technical perspective. It was impressive in the 60s and 70s because a lot of new things needed to be discovered and understood to make it happen. But now a days.. are there really technical aspects that would not be covered in a typical engineering course?

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)

Re: Chandrayaan-3 Soft-landing [video]

#290

Post by seatac76 »

shri_krishna wrote: post #151
seatac76 wrote: post #146

Earlier quoted context omitted.

The speech after had a weird order I was expecting ISRO to speak first, thought that was not needed but idk

Because: https://news.ycombinator.com/item?id=37235089

I cracked up at the little flag waving by who I assume was the prime minister/president. The duality is interesting serious Indian scientists doing great work and a politician on the screen for no good reason. Here’s to the tribe of scientist prevailing and taking the country forward, prob true everywhere now that I think of it.
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