Chandrayan-2 Mission

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UlanBatori
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Re: Chandrayan-2 Mission

Postby UlanBatori » 11 Sep 2019 07:19

SSSalvi wrote:The boys,girls and oldies who are sitting at consoles are the same guys who designed and tested and qualified their respective systems.
There is no separate group dedicated to operations. And to use the analogy: the knowledge is passed on from generation to generation.... hands on knowledge. It is an involved knowledge not found even in scientific journals so has to be documented and passed on.

Fabulous way of operating. Lifecycle attention and care. Some were praying, maybe giving thanks. I mean before the anxious wait started.

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Re: Chandrayan-2 Mission

Postby SSSalvi » 11 Sep 2019 09:17

Rx freq from orbiter:2.23Ghz
Rx power :-130 dbm
Data rate : 1 kbps

Other antenna trying for lander:Tx signal
Freq 2.28 GHz
Plain carrier

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Re: Chandrayan-2 Mission

Postby Mort Walker » 11 Sep 2019 09:33

SSSalvi wrote:Rx freq from orbiter:2.23Ghz
Rx power :-130 dbm
Data rate : 1 kbps

Other antenna trying for lander:Tx signal
Freq 2.28 GHz
Plain carrier


For how long was this observed?

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Re: Chandrayan-2 Mission

Postby symontk » 11 Sep 2019 09:57

UlanBatori wrote:
disha wrote:
UB'ji, it is not humour if it crosses a limit. The above comes in that category. The above is a non-question since the answer to it has no material impact.


Sorry, it is a serious question. I do not see why anyone should get offended, but apologies if they choose to be that prickly, because I do not have the sensitivity to see why. Certainly no disrespect intended. Anyone who works for ISRO is by definition a "Rocket scientist" to the outside world. Remember Kaleem Khawaja the Sultan of the NRI-SAHI etc? IIT-KGP grad, his job was in the construction dept which built the small buildings and machine rooms and pakistans at a NASA Center. He was called a NASA Scientist. If he was that, then so is every ISRO employee a Rocket Scientist. If you work at Boeing at the security office checking vehicle license numbers, you are a Boeing employee, and that 787 is yours as much as it is that of the VP in a suit sitting in a tower in Chicago flipping PPT charts. In fact the security guard is much closer to reality than the VP is. Fully deserving of the Pride, which the VP probably has none.

If there is only like 1 launch every year, I would ask people all over the organization to step in and do Mission Control. If I have one launch every month, then there is enough work to keep them busy as full-time specialist Controllers.

This has a huge impact on the economics of space operations: the primary cost of space ops is the salaries, not the hardware or fuel or lease of the facilities. IOW it takes a "standing army" of expert people to get a rocket up there and back. You cannot just hire and fire them like software companies do: their expertise is very special.

An outfit like Kennedy Space Center has launches practically every week ( guessing) with numerous launch pads and numerous customers. So they will have full-time controller army, I suppose. But I had no idea that ISRO had enough launches to occupy so many controllers. Apparently I was wrong: ISRO seems to have many more launches than what makes the newspapers in Mongolia.

Also, are the controllers shared between defence and civilian missions? Except for the duration (so far), the processes are pretty similar, so the skill-sets should be similar down to the expert who scans all system reports in a flash (no joke that!) and updates "Situation Naarmal".

So how does ISRO operate? Trained specialist controllers, who have to be taught each different mission? Or do the scientists, engineers, machinists, everyone, get trained for mission control? Each has its advantages and disadvantages.

Specifically now: when something goes wrong, and is not in the Mission Control Manuals, what happens? Do the scientist-turned controllers get to solve the problem? Or does it just get tossed back into the labs while the expert mission controllers wait?

Please answer if you can. Yes, it is a serious question.


Lot of people travel between trivandrum and sriharikota just for launching, there is a full fledged multi level hostel for visiting scientists, had a chance to stay there once too. Launch is an elaborate process, from transporting rocket parts to sriharkota and back to getting passess to vips

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Re: Chandrayan-2 Mission

Postby Arjun » 11 Sep 2019 10:16

LRO will be overflying the landing area on Sep 17th as per latest NYTimes article

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Re: Chandrayan-2 Mission

Postby SSSalvi » 11 Sep 2019 10:17

Right now lander wake up call is still on.
( Kumbjharna can wake up if alive.. Mara hua hoga to kaise uthega? )

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Re: Chandrayan-2 Mission

Postby Amber G. » 11 Sep 2019 10:24

Arjun wrote:LRO will be overflying the landing area on Sep 17th as per latest NYTimes article

Also my post almost a week ago.. After Sept 17th per this calculation it will be around Oct 18 or so..
Amber G. wrote:
Posting the same orbits from a slightly different perspective.
Image

Green is Nasa-LRO, Yellow CY2 Blue Vikram .. (Vikram's approx position is near the south pole etc)

(Trying to see what are the good times to look for Vikram from these two crafts which has very good cameras)


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Re: Chandrayan-2 Mission

Postby Amber G. » 11 Sep 2019 10:26

SSSalvi wrote:Right now lander wake up call is still on.
( Kumbjharna can wake up if alive.. Mara hua hoga to kaise uthega? )

Best suggestion is CY2 asking:
"How is the Josh!"
I am sure answer will be "High"..

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Re: Chandrayan-2 Mission

Postby Arjun » 11 Sep 2019 10:49

Presume ISRO will provide an update and share a snap or two over the next few days, else LRO will definitely do so

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Re: Chandrayan-2 Mission

Postby Amber G. » 11 Sep 2019 10:55

The NASA/JPL Horizons trajectory of the Vikram has been updated with the predicted descent trajectory .
Those who are interested can now compare directly the observed radiotelescope Doppler curve type with predictions.. ityadi. ..If there is interest, I may post some probable path of CY2 and Vikram..


Image

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Re: Chandrayan-2 Mission

Postby Haridas » 11 Sep 2019 10:56

Dileep wrote:Except the range safety officer. He sure will have the red button!


Back in 1989 I was working with xxx for range safety computer that can communicate with a dozen different optical sensors types at far off places on specialized serial like interfaces. Computation speed was limited due to US embargo (MTCR) on anything that is above 20 MegaFLOP.

So scientists will do custom micro instruction coding of new CPU instructions set for the HP1000-A900 series bit slice processor. Those were the days....

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Re: Chandrayan-2 Mission

Postby Amber G. » 11 Sep 2019 11:04

Arjun wrote:Presume ISRO will provide an update and share a snap or two over the next few days, else LRO will definitely do so


Hope so soon, but in the meanwhile let us be patient and wait.. till they are sure and ready so as not to jump on conclusion.

Meanwhile a few points from my limited knowledge and what I have seen:
Official ISRO tweet says nothing about ‘intact’.

#VikramLander has been located by the orbiter of #Chandrayaan2, but no communication with it yet.
All possible efforts are being made to establish communication with lander.


I suspect that ‘intact’ is an interpretation of some scientists - may be

an incorrect one. (But I hope I am wrong :) )

It is unlikely that a hard impact will leave Vikram intact.. but we will wait and know soon enough meanwhile from what I know.. thermal imager most likely does not have necessary resolution to establish ‘intactness’. Also Vikram to be in thermal equilibrium with its surroundings (no power) making it probably ‘fuzzy’. Any contrast would arise due to reflectivity differences but whole thing may be covered in Lunar dust.

FWIW: this is my extrapolation. I have not seen the thermal image...

Optical images are probably comparison of before/after moonscape and painfully looking for anything different..morning part so long shadows might have help..



Another serious thought given is to bring CY2 to a 50 km orbit .. This may be done after a year after all experiments are done (and powers to be agree etc) and we may map moon with much higher resolution.

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Re: Chandrayan-2 Mission

Postby Arjun » 11 Sep 2019 11:14

Amber G. wrote:I suspect that ‘intact’ is an interpretation of some scientists - may be

an incorrect one. (But I hope I am wrong :) )

It is unlikely that a hard impact will leave Vikram intact.. but we will wait and know soon enough meanwhile from what I know.. thermal imager most likely does not have necessary resolution to establish ‘intactness’. Also Vikram to be in thermal equilibrium with its surroundings (no power) making it probably ‘fuzzy’. Any contrast would arise due to reflectivity differences but whole thing may be covered in Lunar dust.

FWIW: this is my extrapolation. I have not seen the thermal image...

Optical images are probably comparison of before/after moonscape and painfully looking for anything different..morning part so long shadows might have help..



Another serious thought given is to bring CY2 to a 50 km orbit .. This may be done after a year after all experiments are done (and powers to be agree etc) and we may map moon with much higher resolution.

If they knew for sure that Vikram was in pieces they would not have talked about trying to communicate...so either they know it is in one piece or they are not sure of the precise situation.

CY2 I guess overflew the spot yesterday and would have been able to provide more clarity.....ISRO has not shared this so far, for some reason

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Re: Chandrayan-2 Mission

Postby Ashokk » 11 Sep 2019 12:05

Vayutuvan wrote:What is the carrier frequency?

2.2 GHz

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Re: Chandrayan-2 Mission

Postby SSSalvi » 11 Sep 2019 12:11

My Take.. albight harsh:
This is only a show op ... To show that 'we are trying.'

Is it possible that those who have spent years in designing every component and subsystem will not know what has happened at exactly the moment the failure has happened?

Ok, identification of exact faulty component or software routine may take some time... but the final outcome must have been deduced.

When you clearly see that that the force which was to oppose the fall has in fact aided it , what is there to conclude?

Saying that systems were autonomous and so they would have landed the craft like a baby is impossible.. go-nogo logic would not allow the system to enter that state unless suitable conditions are achieved.
.

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Re: Chandrayan-2 Mission

Postby AdityaM » 11 Sep 2019 12:34

would the presence of charged surface particles disrupt communication signals ?
i assume that the poles would have presence of charged particles ...

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Re: Chandrayan-2 Mission

Postby SSSalvi » 11 Sep 2019 12:44

Not to the extent that the communication would be stopped.
There is always a extra margin of 3 to 4 db to overcome eventuality.. this margin is sufficient to at least a very very feeble hearing of signal by a 30 footer of DSN

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Re: Chandrayan-2 Mission

Postby chetak » 11 Sep 2019 12:54

Frozen screens tell story: Chandrayaan-2’s Vikram Lander fell silent 335 m from Moon



Frozen screens tell story: Chandrayaan-2’s Vikram Lander fell silent 335 m from Moon

It is likely that touchdown occurred at a much higher velocity than the “stringent touchdown requirement of 5 m/s in vertical and horizontal velocity” or less, as specified by ISRO in the planning phase.

Johnson T A | Bengaluru |
September 11, 2019



ISRO Mission Control display shows point when contact was lost
Data frozen on giant screens at the Mission Operations Complex at ISRO’s Telemetry Tracking and Command Centre early on Saturday are the basis on which the space agency has begun its analysis of the Vikram lander’s failure to soft-land on the Moon.

The data suggest a failure in the “Fine braking phase” in the final part of Vikram’s journey (an altitude of 5 km to 400 m), which kicked in when the lander was 5 km from the surface of the Moon.

In its statement, ISRO said that “normal performance (of Vikram) was observed up to an altitude of 2.1 km”, and “subsequently, communication from Lander to the ground stations was lost”.

The frozen screens at mission control have shown that communication was lost when the lander was barely 335 metres (0.335 km) from the surface of the Moon. The screens show that the green dot representing the lander started to deviate from the time its altitude was just above 2 km, and continued to deviate before stopping at a point that was clearly below 1 km altitude, and somewhere near or below 500 m.

At that time, the module was still moving with a vertical velocity of 59 metres per sec (or 212 km/hr) and a horizontal velocity of 48.1 m/sec (or 173 km/hr). The lander was at that point around 1.09 km from its designated landing spot on the Moon.

As per plan, Vikram should have lost most of its velocity by the time it was 400 m from the surface of the Moon, and should have been hovering above the intended landing site — set to make a soft vertical descent at “walking pace”.

“Data received at mission control showed that the landing was going as intended until the 2 km altitude. The communication link was lost when the lander was a few metres from touchdown,” a former head of an ISRO centre, who was at mission control on September 7, said.

As per plan, Vikram should have lost most of its velocity by the time it was 400 m from the surface of the Moon, and should have been hovering above the intended landing site.

It is likely that touchdown occurred at a much higher velocity than the “stringent touchdown requirement of 5 m/s in vertical and horizontal velocity” or less, as specified by ISRO in the planning phase. “In the final touchdown phase, the velocity should have been only 1 or 2 metres per second, something like a walking pace,” the former senior ISRO scientist said.

Early analysis suggests that Vikram began to experience a “high pitch rate” (spinning rate) after it attempted — around an altitude of 7 km — to manoeuvre into position to pick up images of the lunar surface in order to select a place to land, the scientist said.

Snatches of conversation that occurred in mission control among the mission director and the centres monitoring the parameters of the lander through the landing process, also indicated that a glitch occurred in the final “fine braking phase” of the descent.

“Please confirm the parameters,” mission director Ritu Karidhal radioed several minutes after the screens froze up indicating loss of communication with the lander. “Braking ended at around two km,” was the message radioed back to mission control.

The 15-minute process of reducing the velocity of the lander from 1680 m/sec (6048 km/hr) to zero m/sec was in the 13th minute when the screens at mission control froze. Until that point, the Navigation Guidance and Control System — working in auto mode on the basis of final data fed into its systems (including data fed around four hours before the descent, at a distance of 30 km from the Moon’s surface) — had performed precisely to plan.

A “rough braking phase” had reduced the velocity of the lander from 1680 m/sec to 146 m/sec, when it was 7.42 km from the Moon’s surface — resulting in screens at mission control showing the mission was going as per “pre flight indications”.

From 7.42 km to 5 km, the lander coasted in the “attitude and absolute navigation control phase”, reducing velocity almost to the intended 96 m/sec (346 km/hr). Around 9.52 minutes into the landing operation, Vikram’s imager is understood to have been switched on.


When ISRO Chairman K Sivan approached Prime Minister Narendra Modi to convey the status of the mission after the loss of the communication link, he said “the telemetry link has been lost to the ground”. P Kunhikrishnan, the director of the U R Rao Space Centre, told officials that “they are getting data only from Madrid (ground station), no other telemetry links”.

The braking thrust for reducing the speed of the lander from 1680 m/sec to the range of zero m/sec was being provided by four 800 N liquid fuel engines (each having eight thrusters) on board, using new “throttleable technology” developed at ISRO.

The lander was being guided to the surface of the Moon by an Inertial Navigation System onboard, in which Vikram was taking decisions by itself, without intervention from ground stations, on the basis of data obtained from cameras, sensors, and altimeters on board

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Re: Chandrayan-2 Mission

Postby Dileep » 11 Sep 2019 17:49

For all we chair scientists analyzing DSN reports, the guys may already know exactly what happened.

One of the most uncomfortable processes in this line of work is to sit through the RCA sessions. We (the tech team) already know what obviously happened, but still have to go through the 'neti, neti' arguments with people full of 'indeligence' and multiple chips on the shoulders.

Some of the arguments go similar to this well known lawyer joke
An attorney, cross-examining the local coroner, queried, "Before you signed the death certificate had you taken the man's pulse?"

"No," the coroner replied.

"Well, then, did you listen for a heart beat?"

The coroner answered, "No."

"Did you check for respiration? Breathing?", asked the attorney.

Again the coroner replied, "No."

"Ah," the attorney said, "So when you signed the death certificate you had not taken any steps to make sure the man was dead, had you?"

The coroner rolled his eyes, and shot back "Counselor, at the time I signed the death certificate the man's brain was sitting in a jar on my desk. But I can see your point. For all I know he could be out there practicing law somewhere."

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Re: Chandrayan-2 Mission

Postby Mort Walker » 11 Sep 2019 18:16

IMHO, the 335m reading was extrapolated from last telemetry at 2100m. At 335m calculation, there was no data and telemetry could no longer be extrapolated. So the above story looks like speculation. I’m inclined to believe what Dr. Sivan has said.

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Re: Chandrayan-2 Mission

Postby kvjayan » 11 Sep 2019 19:03

So, ISRO is trying to 'hide setbacks with the cellophane of national pride'!

https://www.thehindu.com/opinion/op-ed/ ... epage=true

And the author is upset with 'social media-fuelled national pride'. However, this rag takes pride calling itself "India's National Newspaper". Hyrocrisy at its worst.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 11 Sep 2019 19:45

ISRO’s successes are built on the altar of multiple failures improved over five decades. It still has a long way to go — from successfully grooming a private sector industry capable of providing many more jobs to ensuring that it maintains its meritocratic work, culture and ability to hire talented engineers who can be invested in its work. While getting the world to share in its success is important, ISRO only needs to explain its setbacks, not hide them with the cellophane of national pride.


Could someone try educating this 3-star-King Jackass? Copy to the whole world, please?

jacob.koshy@thehindu.co.in

Al Haj Field Marshal Abdul Bin Kabul has already posted comment: may be short-lived.

I was wondering what had happened to Naxal Ram's "Hundi". But Jacob Koshy's article today removes my fears: the stable of traitors is alive and the humanoid jackasses are kicking. Sorry to insult gentle donkeys by comparison.

ISRO has a record of success-to-failure that leaves every other space agency in the dust, if this jeenius could be educated on such complex topics. They have done it with a minuscule budget and having to put up with anti-national media where such fools get jobs. This mission should have been a mission to Low Earth Orbit to simply test out components, at any other National Agency. Instead ISRO chose to reach out all the way and test all the way to the surface. What a fabulous, brave culture!!! And all you so-called "resident Indian" traitors can do is to sneer with utter ignorance compounded by the malice of born losers.

The Hindu is back to its Chinese-backside-kissing hate propaganda against India. Low IQ, High TQ (traitor quotient)

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Re: Chandrayan-2 Mission

Postby SSridhar » 11 Sep 2019 21:26

The Hindu has chosen not to publish rebuttal comments for that silly article. Sometimes, they publish them a few days later just to show they are neutral while the article itself has become stale by that time.

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Re: Chandrayan-2 Mission

Postby sanjayc » 11 Sep 2019 21:59

UlanBatori wrote:Could someone try educating this 3-star-King Jackass? Copy to the whole world, please?
jacob.koshy@thehindu.co.in


Being in the PR industry, I know him well. In fact, met him earlier this week. He is soft spoken, quiet and humble. His writing style will change once he joins some other paper.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 11 Sep 2019 22:14

And we would like to speed him on his way. Let him take his editor with him and drop him/her in a pakistan

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Re: Chandrayan-2 Mission

Postby Indranil » 11 Sep 2019 22:49

I am still trying to understand how the lander is intact. For this to happen, it had to slow down considerably from the time of the anomaly. That can only happen if the lander is right side up for most of the rest of the descent.

I am more interested in the final moments now.

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Re: Chandrayan-2 Mission

Postby chetak » 11 Sep 2019 22:53

twitter


An update on the Dwingeloo Telescope observations of the isro #Chandrayaan2 landing attempt. If we assume that the Madrid (Deep Space Network)ground station compensated for the Doppler of the pre-burn orbit,these are the approximate line-of -sight velocities during the descent.


Image


Image

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Re: Chandrayan-2 Mission

Postby chetak » 11 Sep 2019 23:03

twitter


Here's a eerie recoding of the searcher's signal reflected of the moon & back to Earth via EME on 2103.7MHz.
DSN 24 BEEMS~12KW of RF at the #Moon in hopes of stimulating #Chandrayaan2 's #VikramLander DSN24 in southern California is presently transmitting a 'hello are you there Vikram?' message to the moon.The moon acts as a radio reflector and sends back a small portion of that signal that can be detected here on Earth after the ~800000km round trip.-Scott Tilley .



https://twitter.com/hasi_iafjohari/status/1171660851327176704

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Re: Chandrayan-2 Mission

Postby prasannasimha » 11 Sep 2019 23:03

Indranil wrote:I am still trying to understand how the lander is intact. For this to happen, it had to slow down considerably from the time of the anomaly. That can only happen if the lander is right side up for most of the rest of the descent.

I am more interested in the final moments now.

One of the possibilities is it did correct itself(the attitude of the lander seemed to have corrected itself and descended till loss of signal) so it may have landed hard on its feet on an incline and tipped over due to inability for the telescopic legs and crush pads to compensate or a leg/legs may have even broken. Of course all this is conjectural

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Re: Chandrayan-2 Mission

Postby Vayutuvan » 11 Sep 2019 23:22

List of artificial objects on the moon

Look at how many crashed (unintentionally). This gives a better picture in terms of how after how many tries, each nation got it right. After one success, there were a string of failures as well.

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Re: Chandrayan-2 Mission

Postby SaiK » 12 Sep 2019 00:15

Amber G. wrote:The NASA/JPL Horizons trajectory of the Vikram has been updated with the predicted descent trajectory .
Those who are interested can now compare directly the observed radiotelescope Doppler curve type with predictions.. ityadi. ..If there is interest, I may post some probable path of CY2 and Vikram..


Image

wow! so, the increase in velocity, then followed by loss of signal, and then thud! the saffron line looks like it made a screeching halt like a jet w/ landing gears down.

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Re: Chandrayan-2 Mission

Postby prasannasimha » 12 Sep 2019 00:55

I think somewhere now the Chandrayaan Orbiter would have made a pass over the putative crash site . Leet us hope we get some more useful data about it.
I do not think we will get images from the orbiter wrt the lander so easily as it may give an idea about our two point discrimination capability or else it will be a significantly degraded image for general public usage. Currently its claimed resolution is the highest imaging capability declared around the moon.

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Re: Chandrayan-2 Mission

Postby ramana » 12 Sep 2019 01:37

S^3, What would make the lander gain velocity before the communication was lost?
And what was the fuel margin for the lander?
Could it have exhausted as it corrected for the maneuver?

AmberG,
From the graph can we calculate the sudden acceleration during that maneuver?

To my eye it looks like Delta V= 360m/sec- 220m/sec = 140 m/sec
Delta T = 20.19=20.18 = 0.01 sec

X2dot = 140/0.1 = 1400 m/sec^2

That's quite a bit of sustained shock.
In Gs= 1400/(9.81*1/6) ~ 850 gs in moon environment?

Is this less than the lander qual shock and vibration spectra?

If its greater could be reason the comms were lost.

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Re: Chandrayan-2 Mission

Postby ramana » 12 Sep 2019 01:45

Remember there is a 2 sec latency in the signal due to the distance to the moon.
So we could be seeing delayed data.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 12 Sep 2019 03:13

ramana: What in that neighborhood could CAUSE such an acceleration? Force or Impulse required seems massive. Vikram is over 1200kg IIRC. So we must consider that it was an explosion. Per Mullah New Ton, if you say 1400Gs,
Force = 1400*1200 Newtons, hain? 1680,000N?

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Re: Chandrayan-2 Mission

Postby sudarshan » 12 Sep 2019 03:21

ramana wrote:To my eye it looks like Delta V= 360m/sec- 220m/sec = 140 m/sec
Delta T = 20.19=20.18 = 0.01 sec

X2dot = 140/0.1 = 1400 m/sec^2

That's quite a bit of sustained shock.
In Gs= 1400/(9.81*1/6) ~ 850 gs in moon environment?



Numbers seem all over the place (no offense sir). 20:19-20:18 is 1 second, not 0.01 s (is this in hours:minutes, or minutes:sec - if hours:minutes, it would actually be 1 minute, not 1 sec).

If delta_T was 0.01 seconds (like you said) acceleration would be 14,000 m/s^2 (not 1400 m/s^2).

Assuming delta_T being 1 second:

X2dot = 140 m/s over 1 second = 140 m/s^2.

But it seems likely delta_T is actually 1 minute (if the x-axis is in hours:minutes). So much less drastic acceleration, like 2.33 m/s^2.

Also note that this is Doppler, so only gives line-of-sight numbers. It says nothing about the other velocity component, tangential to the earth-based observer.

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Re: Chandrayan-2 Mission

Postby ramana » 12 Sep 2019 03:40

I assumed its sec:hundredths of second.

Usually telemetry is in millisecs
that is reported as Secs: xxx
So here they are reporting as secs: 0.xx0
Eg. 19 Secs 550 millisecs, 20.000, 20 secs 050 millisecs

They probably have better data but the graph divisions are like that

Hours minutes is very slow.

Lets hear from AmberG what is x-axis units?

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Re: Chandrayan-2 Mission

Postby sudarshan » 12 Sep 2019 05:52

ramana wrote:I assumed its sec:hundredths of second.

Usually telemetry is in millisecs
that is reported as Secs: xxx
So here they are reporting as secs: 0.xx0
Eg. 19 Secs 550 millisecs, 20.000, 20 secs 050 millisecs

They probably have better data but the graph divisions are like that

Hours minutes is very slow.

Lets hear from AmberG what is x-axis units?


Ramana-ji, let's look at it this way. Assume the x-axis is in secs:hundredths-seconds. Then what is the deceleration from 20.08 secs to 20.18 secs? If you look at the graph - velocity drops from 1400 m/s to 400 m/s. Time delta is 20.18-20.08=0.1 seconds. Calculate the deceleration:

1000 m/s over 0.1 seconds=10,000 m/s^2. Just as spectacular as the speed-up, no? So if it is secs:centisecs like you said, then the deceleration from 1400 m/s to 400 m/s is equally drastic as the acceleration from 220 m/s to 360 m/s that you noted. So that deceleration from 1400 m/s to 400 m/s would also have to be an explosion.

Not to belabor my point, but as a gentle reminder again, this is why I keep saying: a) get the units right, and b) do some sanity checks after the calcs.

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Re: Chandrayan-2 Mission

Postby Dasari » 12 Sep 2019 06:07

Do we have picture of Vikram on the moon surface? ISRO officially announced that Vikram is in one piece, not disintegrated, and landed on its side. That rules out any explosion or rapid acceleration. How do we explain this?

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Re: Chandrayan-2 Mission

Postby SriKumar » 12 Sep 2019 07:17

1. The x-axis in the plot by Amber.G is min:sec. If you look at the leftmost point, it is 19:55. At the next gradation, it becomes 20:00; and the next is 20:05. The only way this is possible with all the gradations on the x-axis being equally wide is if the xy in 19:xy is in seconds. (Added later: it also works if xy is in minutes...but that's well, less likely :) ).
2. I dont think the 2-second delay will contribute to an error (if anyone thinks it might) since the 2-second delay applies to all transmission uniformly. Now, if the time delay is non-uniform, it is a different story.
3. The plot did not clarify line-of-sight as per what- CY2 orbiter? Madrid (The station that could see CY2 at that time). If Madrid, then one has to know the angle of Madrid-to-Vikram landing spot to do a velocity calculation for estimating absolute magnitudes. Otherwise we are seeing a plot that is velocity*cos(90-angle) (per first order simplistic trig.). Need to draw it.
4. It was puzzling to see the velocity shoot up from 400 m/s to 1400 m/s just 12 seconds before it was braking. Not clear to me why that should be the case. Before it brakes, it is in orbit, and not sure if that rapid increase was due to change in orbital velocity- does it change that drastically, or did it change its attitude first, and then started braking. The other possiblity is that the line-of-sight of the receiving station changed at 1400 m/s due to......change of direction of the lander. This confused me, so I did not attempt any calcs from this plot.
5. I feel that the plot shown in the Mission Control seconds before and after the telemetry stopped might be the most accurate velocity data released, since (I assume) it came from the lander itself. That said, the scale was really large: 2 km per gradation of the plot. At that large least count, even a dot would be 10 m wide, so the error builds up.


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