Chandrayan-2 Mission

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sudarshan
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Re: Chandrayan-2 Mission

Postby sudarshan » 07 Sep 2019 07:04

Dasari wrote:Even assuming that the last communication was at 300m (based on the last point on graph), the concern we have is that the rate of descent from 2.1km to 300m was too fast for the craft to survive. As per ISRO's plan from 500m altitude the decent has to be 1m/sec. Leaving aside the path between 2.1km to 500m, it should have taken 200 seconds to come down from 500m to 300m. But that didn't happen. Only hope is that it somehow corrected itself after 300m and didn't crash too hard. As Gagan eludes there is still slight chance for miracle that it may revive itself.


The plot that Gagan posted doesn't show speed in the sense of "distance over time" it shows vertical speed relative to horizontal speed. Something happened to affect this ratio. The same graph can be generated if the horizontal speed was reduced a lot, without affecting the rate of descent. Need some way to get a time axis on the graph, then rates of descent can be inferred, and that would indicate whether or not rockets fired or shut off correctly.

EDIT: Ah wait, it's a video, not a picture. OK, that changes things (assuming the video is real-time - probably is). Will get back on this.
Last edited by sudarshan on 07 Sep 2019 07:10, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby SriKumar » 07 Sep 2019 07:08

Amber G. wrote:
SriKumar wrote:Clearly communication was not lost at 2.1 km. The track of the lander was broadcast live upto about 300 m above the surface. There is public domain data of altitude and range well below 2.1 km altitude in the video linked by gagan.

What I remember hearing from ISRO's chairman -

- All things were normal till altitude of 2.1 Km
- Subsequently (some time later but they did not say when) they lost contact.
- They are analyzing the data.
Yes, this is also there in the video linked by gagan (very end). This was a carefully-worded public statement prepared by ISRO for the public. But this is what happens when everything is broadcast live to public. The public knows a bit more than the official statement. We were seeing the same data that ISRO scientists were seeing in their control room. The telemetry (and therefore the communication) was clearly operative well below 2.1 km. altitude. THe public knows that the craft started to depart from the expected trajectory (the red line) at this altitude, so maybe bad things began to happen from this height downward, but telemetry was working, and is in the public domain now.

(In some ways this reminds me of the very first test of the desi cryogenic engine. It ignited ...and there was applause. And the ignition did not sustain beyond a second or so...and there there was silence. This is the risk one takes in broadcasting everything live.).
Last edited by SriKumar on 07 Sep 2019 07:16, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby Dasari » 07 Sep 2019 07:15

sudarshan wrote:
Dasari wrote:Even assuming that the last communication was at 300m (based on the last point on graph), the concern we have is that the rate of descent from 2.1km to 300m was too fast for the craft to survive. As per ISRO's plan from 500m altitude the decent has to be 1m/sec. Leaving aside the path between 2.1km to 500m, it should have taken 200 seconds to come down from 500m to 300m. But that didn't happen. Only hope is that it somehow corrected itself after 300m and didn't crash too hard. As Gagan eludes there is still slight chance for miracle that it may revive itself.


The plot that Gagan posted doesn't show speed in the sense of "distance over time" it shows vertical speed relative to horizontal speed. Something happened to affect this ratio. The same graph can be generated if the horizontal speed was reduced a lot, without affecting the rate of descent. Need some way to get a time axis on the graph, then rates of descent can be inferred, and that would indicate whether or not rockets fired or shut off correctly.



Agreed. Since the vertical speed is proportionately higher than horizontal speed, the plausible assumption is that it is descending faster which is in line with the data that communication stopped. It is possible that horizontal speed reduced much faster but vertical speed also reduced and it soft landed, but communication lost. Possible not probable.

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Re: Chandrayan-2 Mission

Postby Dasari » 07 Sep 2019 07:19

sudarshan wrote:
Dasari wrote:Are you saying it didn't have that much fuel?. How does it waste it when its purpose was getting over in few more minutes?

Touch down at 10m/sec?. Are you crazy? Doesn't matter what the gravity is. When we say 10m/sec, we mean 10m/sec. That would be hard crash. Last 10 meters, the actual plan was to take 25 seconds.


You're right about 10 m/s being 10 m/s anywhere (regardless of gravity). However - a human descending by parachute on earth has a landing speed of about 20 kmph, or 6 m/s. So 10 m/s for a much harder (than human I mean) lander isn't that excessive. Kinetic energy (and thus impact force) goes up as square of speed, so from 5 m/s to 10 m/s is four times the force. If human feet (in shoes) can take 5 to 6 m/s, I think a metal lander with specially designed cushion pads can take 10 m/s.

Great job, ISRO, you should be proud of what was achieved. Tried for something which nobody has ever tried before, and almost made it.

Y'know, now that the haters in the western media have something new to (gleefully) focus their bile on, the Kashmir coverage should drop off a bit.


We can debate whether it survives 10m/sec or not or what survives, but 10m/sec or 36km/hour is not what is called soft landing. :D

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Re: Chandrayan-2 Mission

Postby SaiK » 07 Sep 2019 07:26

vnms wrote:
Amber G. wrote:Trusting my eyesight and memory, the last I saw the telemetry data from the screen :

Horizontal velocity 48.1 m/s
Vertical velocity 59.8 m/s
Downrange distance: 1.09 km
Earth communication: OFF

That's exactly what I recollect.

viewtopic.php?f=3&t=7725&start=1040#p2378188

yes, that is what I posted as well.
Last edited by SaiK on 07 Sep 2019 07:27, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby sanjaykumar » 07 Sep 2019 07:27

To the ISRO people reading this thread, we are proud of you.

There is a wealth of telemetry, laser altimeter, visual ?stereoscopic, doppler shift scanning, orbiter visuals of crash site wreckage and soil dispersion pattern, radar ?, perhaps even spectrometer/spectrophotometer analysis from the orbiter. A through crash analysis, isolation of the fault after reconstruction of the mission, then to the moon again.

There is no alternative.

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Re: Chandrayan-2 Mission

Postby sudarshan » 07 Sep 2019 07:27

^^^ Fair enough.

^^^^ Well if the video is real-time, then the craft was at ~1.8 km height around 2:57, then by 3:06, it was down to ~0.6 km (just by eye-balling). So 1.2 km drop in 9 secs :eek:. 130 m/sec? So the rockets were accelerating it down instead of decelerating - must have turned upside down, what?

IOW, Vishwamitra, rather than halting Trishanku mid-air, actually aided Indra in propelling him down.

The red curve would have been a slow float, so in 9 secs, the craft wouldn't have moved much down that red curve. On the green curve, the craft was traveling way faster down the curve itself - meaning, horizontal velocity about the same, vertical much higher than planned.

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Re: Chandrayan-2 Mission

Postby SaiK » 07 Sep 2019 07:33

^I was thinking the same.. it flipped, and little time to recover.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 07 Sep 2019 07:51

I thought landing was a straightforward thing: Decelerate the horizontal speed; keep turning the thrusters downward as horizontal speed decreased. Thrust downwards to reduce the downward speed, reaching nearly zero relative speed at touchdown (I didn't say 10m/s, I said something under, but significantly higher than 1m/s all the way from 500m as someone had posted). If you hang around too long at a distance above the ground you just kick up more stones etc. Better to maintain a very positive downward speed. But all this is no reason for comm cutoff at 2.1km above ground. I thought the curves being shown were from anticipated trajectory vs. data received with a couple of seconds of delay if it was 'real-time'. But could have been much more delayed than that, as ppl who watch cricket games know. Maybe 20 seconds to 1 minute delayed even in Earth transmission.

So by the time the display on the screen that we saw, updated, the show may have been over.
Wonder if the AutoPilot yelled "AoA!" or "YeeeeeeeeHaaaaaaaW!"
This should teach ISRO and Republic TV not to show these things without the Apostle of Calm saying:
"Situation Naaaaarmal".

This obviously sets back the human-carrying mission a lot. Expectations had been driven too high by the flawless record, but there is a reason why people esp. Disaster Photographers come to watch these events. We saw that today. Years of preparation and work, gone in a flash for no apparent reason. They must have simulated that phase 10,000 times. I remember John Young, commander of the first Space Shuttle, being asked: "When will the Shuttle become Routine, Commander?"
"When you guys stop coming to watch the launches."

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Re: Chandrayan-2 Mission

Postby UlanBatori » 07 Sep 2019 08:05

But all said and done, kudos to the organizers of the open broadcast. What a terrific experience for the youngsters to be sitting there right behind the mission control people, living those moments with them! I hope the tragic end never happens again, but that was all the more a valuable experience for the youngsters. I assume that many of them were ISRO kids, there to watch their parents' work.

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Re: Chandrayan-2 Mission

Postby Karthik S » 07 Sep 2019 08:07

Better luck next time ISRO, am sure RCA will be done and we will shoot for the moon again.

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Re: Chandrayan-2 Mission

Postby Karthik S » 07 Sep 2019 08:08

BTW have you guys seen the way a so called journo was shouting at one of ISRO's scientists ?

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Re: Chandrayan-2 Mission

Postby SaiK » 07 Sep 2019 08:19

UlanBatori wrote:..I assume that many of them were ISRO kids, there to watch their parents' work.
Yes. Kids were little disappointed and when Modi tried to cheer the elder kids, they were in still-shocked state. The TV wala did say, many of those kids were there because they won some competition.

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Re: Chandrayan-2 Mission

Postby SSSalvi » 07 Sep 2019 08:23

Appears to have started tumbling ( could be due to firing or misfiring of one of the thrusters ) and so pushed it into the moon rather than applying elevation force.

------
Bagala has become a commentary terrorist.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 07 Sep 2019 08:26

ACtually an inflated huge balloon around a lander might not be a bad idea. Not so much on the Moon except to go bouncing around, but I know this is a great way for low-ballistic entry to, say, Venus.

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Re: Chandrayan-2 Mission

Postby NRao » 07 Sep 2019 08:28


sanjaykumar
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Re: Chandrayan-2 Mission

Postby sanjaykumar » 07 Sep 2019 08:43

The first Soviet Luna to soft land on the moon did have nitrogen inflated bags and it did bounce 3 or 4 times.

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Re: Chandrayan-2 Mission

Postby SaiK » 07 Sep 2019 08:51

Losing Vikram is not unbearable.. not able to know what happened is unbearable.

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Re: Chandrayan-2 Mission

Postby sanjaykumar » 07 Sep 2019 09:03

ISRO has already done the hard work, rocketry, orbital transfer and insertion, deorbit scheme and hardware, payloads . There should be full engineering models of every piece of equipment available. The GSLV III Performed flawlessly. Perhaps they can be ready to go in short order. Perhaps in months.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 07 Sep 2019 09:06

The PM's speech was inspiring, but he did not commit to any new additional moon mission, and in that sense very disappointing. ISRO can do it, but political and economic backing must be there. Chandrayaan 3 for 2024 is in the planning stages, but not funded. It was supposed to be an Indian lander aboard a Japanese rocket. This failure means the Japanese will back out since the lander design is flawed as seen with Vikram.

Modi in his speech said nothing about a Chandrayaan 3. IMHO, I think the Indian dream of landing on the moon has now been set back by at least a decade if not more.

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Re: Chandrayan-2 Mission

Postby sudarshan » 07 Sep 2019 09:14

So if I understand right, the first stage of the descent was with four retro-rockets, then it was supposed to go down to two? What is the reason for that? Why not keep the four rockets, and manipulate their thrust?

Four rockets is like a quadcopter drone. Easier to manage the turning moments. With two, it becomes way more critical. Since each rocket is basically providing thrust equal to half the weight of the craft, the turning moment becomes pretty excessive when there is an imbalance (depending on the distance between the rockets - I assume a greater distance provides greater stability against gravitational moments, but also acerbates imbalances between the rocket thrusts).

If I got this right, the four-rocket phase went pretty well, and it was during the transition to two rockets that something went wrong.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 07 Sep 2019 09:17

^^^ Correct.

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Re: Chandrayan-2 Mission

Postby suryag » 07 Sep 2019 09:22

Sivan sir crying :(( I feel like crying too

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Re: Chandrayan-2 Mission

Postby Rishi_Tri » 07 Sep 2019 09:25

As told by so many, this mission accomplished:

Heaviest successful payload launch to GTO - means lift capacity for Gaganyaan available.
First attempt, and successful, at separation of Orbiter and Lander.
First attempt at Lander orbit lowering maneuvers.

But Unsuccessful - Lander perhaps crash landing. Perhaps in control till about 335 mts from Moon.

Already looking forward to next crack at this. Just thinking aloud: Six months to do RCA. Another six months to present proposal for another attempt. One Year for approval. Two years for preparation. Attempt in 4+ yrs.

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Re: Chandrayan-2 Mission

Postby Rishi_Tri » 07 Sep 2019 09:26

Mort Walker wrote:The PM's speech was inspiring, but he did not commit to any new additional moon mission, and in that sense very disappointing. ISRO can do it, but political and economic backing must be there. Chandrayaan 3 for 2024 is in the planning stages, but not funded. It was supposed to be an Indian lander aboard a Japanese rocket. This failure means the Japanese will back out since the lander design is flawed as seen with Vikram.

Modi in his speech said nothing about a Chandrayaan 3. IMHO, I think the Indian dream of landing on the moon has now been set back by at least a decade if not more.


I read PM's speech differently. He was exhorting people to have another go at it and he mentioned that. He said,"we shall embrace the moon and very soon". That part was in Hindi.

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Re: Chandrayan-2 Mission

Postby ramana » 07 Sep 2019 09:37

Looks like around 2.1 km one of the four retro rockets under performed or shut off. This caused the other three to increase thrust but as the only three thrusters, cause the lander to rotate. That adds velocity and it crashed.
So it was in-flight issue. Nothing to do with South pole, rocky terrain etc.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 07 Sep 2019 09:40

ramana wrote:Looks like around 2.1 km one of the four retro rockets under performed or shut off. This caused the other three to increase thrust but as the only three thrusters, cause the lander to rotate. That adds velocity and it crashed.
So it was in-flight issue. Nothing to do with South pole, rocky terrain etc.


It seems the telemetry data indicated the rough braking with 4 engines completed, but switching to 2 engines for fine braking did not. Maybe a single or dual engine that is gimbaled with thrust vectoring? How did the Chinese do it back in late 2018?

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Re: Chandrayan-2 Mission

Postby sudarshan » 07 Sep 2019 09:52

I guess the Chinese were under pressure to get it right, if they didn't want to be breaking rocks in Heilongjiang or Inner Mongolia :P. Contrast with how Modi treated ISRO with consummate respect even with what happened.

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Re: Chandrayan-2 Mission

Postby juvva » 07 Sep 2019 10:03

one other possibility is a problem with throttle control of one or more engines ( h/w or s/w), remember that ISRO is trying out throttle-able engines for the first time.

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Re: Chandrayan-2 Mission

Postby Mollick.R » 07 Sep 2019 10:19

I was taking live snaps of TV screen as mission was progressing.
Following two images are few second before glitch (whatever it was) took place. .

Image


Image


It says altitude 335 m

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Re: Chandrayan-2 Mission

Postby SSSalvi » 07 Sep 2019 10:32

One of the reasons why communication failed is a mispointing of antenna due to sudden rotation of the yaan... Even before crash.

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Re: Chandrayan-2 Mission

Postby Philip » 07 Sep 2019 10:39

There was some bedlam at MC.Unfortunate.However, like Robert the Bruce and the spider, " if at first you don't succeed, try, try, try again". There were many successes
in the mission.The new GSLV launcher and beautifully navigating the craft from an earth orbit to a lunar orbit without a hitch.

Some of our TV anchors and their guests were simply deplorable though.Trying to make cheap jibes at Pak and belittle them, drawing comparisons which are universally known. Pak is a nuisance and the less we have anything to do with that pestilential entity the better.Jousting with Pak is like trying to wrestle with a pig in the drains.You get filthy too.Simply ignore Pak, give it no bandwidth unless it is during a conflict situation.Now Paki anchors will be gleefully enjoying the discomfiture of our jingos.

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Re: Chandrayan-2 Mission

Postby ramana » 07 Sep 2019 10:45

CY2 Had many phases. For simplicity: launch, sat to Geo-Transfer, lunar orbit , lander and rover.
I would assign 10% to lander and 5% to rover.
As you can see over all success was 85%.

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Re: Chandrayan-2 Mission

Postby ramana » 07 Sep 2019 10:47

What was the them for the lander retro rockets?

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Re: Chandrayan-2 Mission

Postby Suraj » 07 Sep 2019 10:53

In my opinion it is just as well that Modi did not announce CY3 in a rush of emotion . These things happen . ISRO had its chance and will have another, just not right away . Their next goal is the manned space mission in two years. The Chinese similarly lost Mars probe in 2012 and are not due to attempt another trip until 2022 . There will be a CY3 but GY1 comes next. I’m sure ISRO will find out what caused the lander to lose contact mere seconds from its destination.

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Re: Chandrayan-2 Mission

Postby Varoon Shekhar » 07 Sep 2019 11:00

Philip, very well said. No need to take cheap shots at Pakistan constantly or make much of them. They are obnoxious and a nuisance, and should be dealt with that way. We should hail the superb effort of ISRO, and the overwhelming success of the mission as a whole. Feeling moved right now at the vulnerability of ISRO to criticism. There is a need to speak up for them at this juncture.
Last edited by Varoon Shekhar on 07 Sep 2019 11:41, edited 3 times in total.

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Re: Chandrayan-2 Mission

Postby Amber G. » 07 Sep 2019 11:02

As a scientist I will wait till the root cause is determined (and that will be done) but a few points to keep in mind
-It is still possible that @isro may locate the Vikram lander intact or semi intact state on the Moon, despite loss of contact. I hope they find it soon.
-We lost communication (not confidence, not commitment, not courage, not challenge)
I really liked NaMo's address.

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Re: Chandrayan-2 Mission

Postby chetak » 07 Sep 2019 11:15

Karthik S wrote:BTW have you guys seen the way a so called journo was shouting at one of ISRO's scientists ?



nothing out of the ordinary for this paki channel and its rundee, presstitute and sold out employees.


twitter

Just for everyone information this

Pallava Bagla works for NDTV (an unofficial Pakistan channel in India)

Keeping up the tradition of NDTV & showing everything in India in a very poor light

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Re: Chandrayan-2 Mission

Postby chetak » 07 Sep 2019 11:18

ramana wrote:What was the them for the lander retro rockets?


If true, about shifting to two retro rockets during the last stages

four retro rockets would have been a better way to go, especially in the final stages.

the general principle being a risk is reduced as the criticality increases
Last edited by chetak on 07 Sep 2019 11:21, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby vishvak » 07 Sep 2019 11:20

If you define success as lander dropping to a designated spot (and THEN losing comms) then you only win perception battle (nothing succeeds like success) but is perception enough in space science - as what a race to land rowers on top of others?

The 85% success (with orbiter in place) says something - that all phases till then succeeded at least. And then 'failure' (actually crash/comm-fail) indicates that we are doing something unique (like Intellectual Property worthy) instead of sitting with one lander on top of another.

This is what Japanese space probe to asteroid Ryugu did for 'hopping' but that's only an asteroid and wouldn't prolly work on moon landing. Just to state that choosing path less traveled means doing something different.
Like the Japanese-built MINERVA-II1A and MINERVA-II1B, the autonomous MASCOT can move by hopping, which it does by manipulating a metallic "swing arm" inside its body. The lander can also use this arm to right itself on Ryugu's surface — an important feature, because MASCOT needs to be right side up to gather data and beam it up to Hayabusa2.

From Space.com website on probe Hayabusa to asteroid Ryugu
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