Chandrayan-2 Mission

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Suresh S
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Re: Chandrayan-2 Mission

Postby Suresh S » 08 Sep 2019 08:51

Eswarji clearly has written what I felt.Two great organizations of India both public institutions where desh bhakti and seva of Bharat Ma is what drives them, India,s armed forces and ISRO. I am proud of both like most Indians. May Lord Vishnu bless both of them and take them to greater heights in the future.

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Re: Chandrayan-2 Mission

Postby saip » 08 Sep 2019 08:52

If it is in line of sight from earth now, won't it be always in line of sight from earth as the Moon ALWAYS presents the same side to earth all the time. Parts of it may not be lit.

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Re: Chandrayan-2 Mission

Postby SaiK » 08 Sep 2019 09:25

So it was the orbiter relaying then

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Re: Chandrayan-2 Mission

Postby arvin » 08 Sep 2019 09:28

Article by tarmak. Good info on final moments.

https://english.manoramaonline.com/news ... phase.html

Up to 2.1 km all was fine. Soon the rotation rates increased and the engine thrust went up to 100 per cent in place of around 70 per cent. The velocity too shot up indicating tumbling and crashing. At this stage, the telemetry link was lost,” says another top scientist part of the crucial mission activities.


So lander had radar altimeter to determine height. Thrusters would be firing based on this input.

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Re: Chandrayan-2 Mission

Postby ramana » 08 Sep 2019 09:30

From a friend


Ramana pls see at 6:55 mark, where during tumble no lift, and then lift comes back again, albeit not as agressive as before.
https://youtu.be/5xKJG00-S_c

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Re: Chandrayan-2 Mission

Postby chetak » 08 Sep 2019 09:35

arvin wrote:Article by tarmak. Good info on final moments.

https://english.manoramaonline.com/news ... phase.html

Up to 2.1 km all was fine. Soon the rotation rates increased and the engine thrust went up to 100 per cent in place of around 70 per cent. The velocity too shot up indicating tumbling and crashing. At this stage, the telemetry link was lost,” says another top scientist part of the crucial mission activities.


So lander had radar altimeter to determine height. Thrusters would be firing based on this input.


not the only input, saar.

they would also need inputs from accelerometers and gyroscopes to determine the deceleration and vehicle orientation at the very least

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Re: Chandrayan-2 Mission

Postby Amber G. » 08 Sep 2019 09:43

sudarshan wrote:Hmm, scratch what I said above about near and far side, I might be guilty of spreading disinformatsiya. It seems, looking at crater maps, that the moon's south pole is on the far side as seen from earth? Will check and get back. But then, like UB said, I fail to see how a radio telescope from earth can pick up signals from the moon's far side.

Note: Ignoring silly non-sense and/or obvious scientifically incorrect other posts - (Not answering everything mentioned in this dhaga).. but a few points, just to make basics clear: (For more clarity see any good book) Hope this is helpful.

Looking from earth:

1 - About Half the moon's surface is always visible from earth, and about half is not. The side visible is called the near side and other is far side of the moon.
2 - As day/month/year passes some part which was not visible before can be visible. Thus about 59% of the moon's area is visible some time or the other.
3 - T Vikram landing site) is always visible. It's direction moves a little: (About 7 degree due to elliptical nature of the orbit and about 8 degrees due to the fact that moons equator is tilted about 5-6 degree wrt to it's orbit. Another 1 degree could be due to earth's elliptical orbit) .. But that particular landing site is always visible. (Of course you have to be on earth at the time and place when moon is visible :) )

4 . South pole (or North pole) will *not* be on far side *all* the time. At least half of the month they are visible (and thus have been mapped in old times by earth based telescopes).
saip wrote:If it is in line of sight from earth now, won't it be always in line of sight from earth as the Moon ALWAYS presents the same side to earth all the time. Parts of it may not be lit.

That is correct.
Just to add some part of the moon do go in/out of the site. So instead of 50% one can see about 59% or the area of the moon from earth if you watch is over the months.

***
Vikram's landing site (and things on Moon in general) - if you are looking through telescopes -- Best time is right now (astami - half full moon. This is because things (like mountains) cast a long shadow and one can see 3-d view (higher mountains cast longer shadow) -- something all astronomors knwo

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Re: Chandrayan-2 Mission

Postby saip » 08 Sep 2019 09:55

Amber G, I know we need a min of Three Geosynchronous satellites to cover earth. But to cover moon how many we need (I mean receive signals from any spot on the farside of the moon and retransmit them uniterrupptedly)? Only two? Is there something called luno-synchronous orbit? Thanks.

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Re: Chandrayan-2 Mission

Postby ramana » 08 Sep 2019 10:07

Folks don't mind lekin don't get irritated by posts. They reflect the anxiety of lot of people.
Let's be NaMo squirrels and try to answer every doubt. It's our kartavya.

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Re: Chandrayan-2 Mission

Postby ramana » 08 Sep 2019 10:11

To me the lander ad rover are about 15 % of the mission. ISRO has said its more like 5%.
So over all the mission is quite successful.
The video posted above shows anomaly started during switch over of rough to fine braking.
But recovered. There was a significant delay velocity and about 500m from target landing point.

That's a great first achievement.

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Re: Chandrayan-2 Mission

Postby Dasari » 08 Sep 2019 10:15

saip wrote:Amber G, I know we need a min of Three Geosynchronous satellites to cover earth. But to cover moon how many we need (I mean receive signals from any spot on the farside of the moon and retransmit them uniterrupptedly)? Only two? Is there something called luno-synchronous orbit? Thanks.



Geometrically it is not possible to cover with less than three, unless they relay it with three other Geo Sync satellites of the earth.

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Re: Chandrayan-2 Mission

Postby Amber G. » 08 Sep 2019 10:23

Dasari wrote:
saip wrote:Amber G, I know we need a min of Three Geosynchronous satellites to cover earth. But to cover moon how many we need (I mean receive signals from any spot on the farside of the moon and retransmit them uniterrupptedly)? Only two? Is there something called luno-synchronous orbit? Thanks.



Geometrically it is not possible to cover with less than three, unless they relay it with three other Geo Sync satellites of the earth.

The Relay sat is Queqiao. It is in a "halo" orbit near the Earth-Moon L2 point.
For details, do a search on "halo" orbit, or "Lagrangian" points of Earth-Moon system.

(Basically A relay sat in such a halo orbit would be in continuous view of both the Earth and the far side of the Moon (most of the far side) so it can be used as a relay station. Actually NASA was thinking of such a sat in 1960-70's but they thought they will not need it as they restricted themselves to the near side of the moon)

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Re: Chandrayan-2 Mission

Postby saip » 08 Sep 2019 10:40

Thanks. So, I guess we only need ONE satellite if it is at L2 point (some 65000 km from the moon)

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Re: Chandrayan-2 Mission

Postby chola » 08 Sep 2019 11:48

ramana wrote:To me the lander ad rover are about 15 % of the mission. ISRO has said its more like 5%.
So over all the mission is quite successful.
The video posted above shows anomaly started during switch over of rough to fine braking.
But recovered. There was a significant delay velocity and about 500m from target landing point.

That's a great first achievement.


Indeed it was. I think people were spoiled by the flawless success of Mangalyaan. Both the US and Russia had many failures in their space programs. This is very hard business and we are one of only a handful who are in it.

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Re: Chandrayan-2 Mission

Postby Neela » 08 Sep 2019 11:50

Simple question.
Simulating lander on earth is one aspect which ISRO must have done. However, without an actual flight testing on earth you are taking a lot of risk. Now I dont know if ISRO has done it or not. If software was to blame, what kind of testing should have been done to avoid sensor inputs messing attitude, acceleration etc.

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Re: Chandrayan-2 Mission

Postby EswarPrakash » 08 Sep 2019 12:05

Neela wrote:Simple question.
Simulating lander on earth is one aspect which ISRO must have done. However, without an actual flight testing on earth you are taking a lot of risk. Now I dont know if ISRO has done it or not. If software was to blame, what kind of testing should have been done to avoid sensor inputs messing attitude, acceleration etc.


Neelaji, I think you are forgetting the unforgiving conditions in the outer space, and uneven gravity which will be really hard to simulate anywhere.

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Re: Chandrayan-2 Mission

Postby varshar » 08 Sep 2019 12:11

EswarPrakash wrote:When Rama asked for the moon

I could not stop myself from writing what I felt


Very beautiful tribute Mr. Prasad... captures what most of us are feeling.

I've taken the liberty of sharing within my network.

Regards,
Varun

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Re: Chandrayan-2 Mission

Postby Indranil » 08 Sep 2019 12:22

It is unlikely to be a software error. It went into a state that the software did not know to correct from.

I was thinking how to simulate the lander on earth. While it is not possible to simulate the entire experiment on earth it can be simulated to an imaginary point on the top of the atmosphere. The "lander" has to have a mass which is 1/6th that of the moon lander and use the same engines. This would provide the same TWR as on moon. The landing point will also not be stationery. A stationary point on the "top" of the atmosphere has an angular velocity that is not the same as that of a point on the surface of the moon. Therefore, the landing point will moving is a moving point on the top of earth's atmosphere. The lander has to be able to land on this point.

If we speaking of a lander mass of about 300 kgs, PSOM-12 should be able to launch do it.

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Re: Chandrayan-2 Mission

Postby Ashokk » 08 Sep 2019 13:21

Extra brake thrust may have sent Vikram out of control in home stretch
BENGALURU: When silence descended on the Isro mission control and millions of Indian homes minutes before Vikram was to touch down on the Moon at 1.53am on Saturday, many thought the lander had too little thrust to brake to a halt. A day later, Isro scientists are looking at whether Vikram had too much braking thrust, which spun it out of control.
"We thought one of the thrusters may have underperformed," said an Isro scientist. "But after some preliminary analysis, it looks like a thruster overperformed."
Descending from its orbit 30km from the Moon, Vikram had achieved perfect roughbraking for 10 minutes, reducing its velocity from 1,680 metres per second to 146 metres per second. Soon after the fine-braking that signalled Vikram's last 5km descent to the Moon, mission control lost contact with the lander.
Officially, Isro maintained that data was still being analysed. However, a scientist told TOI, "Vikram's legs were to be horizontal during the roughbraking and had to be rotated by 90 degrees to bring them vertical to the landing surface before fine-braking. At this point, the thrust might have been more than optimal, impacting the lander's orientation. It's like a car losing direction due to sudden braking at high speed."
When Vikram went silent, Isro mission control searched for links from Nasa's deep space network centre in Madrid and the Indian station in Mauritius, but to no avail.

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Re: Chandrayan-2 Mission

Postby mridulmm » 08 Sep 2019 14:09

https://twitter.com/timesofindia/status ... 0054627329

ISRO Chief, K Sivan to ANI: We've found the location of #VikramLander on lunar surface and orbiter has clicked a thermal image of Lander. But there is no communication yet. We are trying to have contact. It will be communicated soon.

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Re: Chandrayan-2 Mission

Postby prashanth » 08 Sep 2019 14:24

Indranil wrote:It is unlikely to be a software error. It went into a state that the software did not know to correct from.

I was thinking how to simulate the lander on earth. While it is not possible to simulate the entire experiment on earth it can be simulated to an imaginary point on the top of the atmosphere. The "lander" has to have a mass which is 1/6th that of the moon lander and use the same engines. This would provide the same TWR as on moon. The landing point will also not be stationery. A stationary point on the "top" of the atmosphere has an angular velocity that is not the same as that of a point on the surface of the moon. Therefore, the landing point will moving is a moving point on the top of earth's atmosphere. The lander has to be able to land on this point.

If we speaking of a lander mass of about 300 kgs, PSOM-12 should be able to launch do it.


Indranil Ji, yes.
An ISRO scientist has now indicated that one or more of variable thruster braking engines may have not functioned as intended. That apart, in the scenario you have described it would be perhaps not be possible to use radio and laser altimeters which require a solid surface to measure the altitude, which is critical during the last phase of lunar descent.
I was comparing the braking methods used by Surveyor, Luna and Chang'e Missions. One difference is (based on initial reading) is that the former three used fewer engines for descent and landing compared to 5 of Vikram. Surveyor used 3 vernier engines for final descent phase, Luna 9 seems to have used one main retro-rocket engine with a few smaller ones, and Chang'e 3 used 1 (source, wikipedia). Wikipedia says that the 800 N engines used in Vikram are derived from workhorse 440 N LAM. I could not also find out if variable thrust functionality of the 5 engine cluster was tested during orbit-lowering manoeuvres.

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Re: Chandrayan-2 Mission

Postby Indranil » 08 Sep 2019 14:30

There were smaller 25 N engines too.

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Re: Chandrayan-2 Mission

Postby tandav » 08 Sep 2019 14:35

mridulmm wrote:https://twitter.com/timesofindia/status/1170611250054627329

ISRO Chief, K Sivan to ANI: We've found the location of #VikramLander on lunar surface and orbiter has clicked a thermal image of Lander. But there is no communication yet. We are trying to have contact. It will be communicated soon.

Massive flights of imagination penned down below but hey we can all hope...

Both the Vikram lander and the Pragyan Rover do not have RTG onboard, in the off chance that the internal control systems worked and only the communication module has failed. If so perhaps miraculously the Lander actually landed safely and automatically deployed the Rover without input from Mission control. If Vikram can automatically take initiative without guidance from ISRO mission control (perhaps coded in if comms fail). ISRO will have its task cut out and re-establish contact before the extreme cold of the lunar surface degrade electronic parts.

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Re: Chandrayan-2 Mission

Postby nits » 08 Sep 2019 15:07


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Re: Chandrayan-2 Mission

Postby UlanBatori » 08 Sep 2019 17:32

Quoting Mort Walker:

Chinese put up a satellite for communication with the far side


I know, hence the pooch. Orbiter could relay messages in "burst mode" when it comes back around to the Near Side (based on the spy novels that are my main source of knowledge on these things). But Chinese put up the satellite where they can do telepresence, I think. That cuts delay down to the 3 seconds or so (signal has to travel much longer distance than direct to Moon and back).

Fortunately Rover speeds on the Moon are like 1 cm per second so if cheen decide to go explore Vikram ruins, they won't be able to do much else for the next couple of months.

I think ISRO should send a quick mission with a rubber ball as Lander (omi-orientation capability). Thrusters at all orientation, ability to survive a 100 mph impact with resilience, and bounce-mode locomotion giving unprecedented surface motion speeds. Name it Jaspreet.. White ball is OK.

Imagine the impact (no pun intended) of a bouncer on the Moon. Swing is probably more difficult because no air. Maybe the Surface Layer dust haze? Naah, too low-density for swing unless you get up to supersonic speeds.

Wonder why this design has not been used extensively in the past. I know: trouble is all these Science Mission pressures to send Test-Tubes and Pipettes and Burettes and "Explore the Origins and Manifest Destiny of All Humankind" garbage instead of some rugged explorer stuff. An AK-47 might not be out of place: the Escape Velocity, if you aim straight at Earth, should be quite low because you only need to get past the L-1 point, but pls kindly aim at LaHore. First Indian Lunar Return Vehicle. Useful too.

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Re: Chandrayan-2 Mission

Postby ldev » 08 Sep 2019 17:44

So this is what ISRO is planning for a future moon landing mission. A moon landing in partnership with Japan including a rover and bringing back samples of moon dust. To be implemented in 2024 after the human spaceflight mission. Under discussion since 2017 and discussed during Modi's visit in 2018.

India's next moon shot will be bigger in collaboration with Japan Aerospace Exploration Agency (JAXA)

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Re: Chandrayan-2 Mission

Postby UlanBatori » 08 Sep 2019 18:17

There will now be very tough questions b4 any human spaceflight. A failure occurred, that slipped past the best checks and redundancies.
May be worth considering whether to hand over that phase to military as was done in the old days for the first 5 human-carrying missions.

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Re: Chandrayan-2 Mission

Postby ldev » 08 Sep 2019 18:29

Was reading that the first level crew selection for the human spaceflight program has been completed. About 10 potential candidates, all IAF pilots. They will undergo basic training in Russia.

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Re: Chandrayan-2 Mission

Postby arshyam » 08 Sep 2019 18:29

Gagan wrote:Guys is this confirmed?

https://twitter.com/vasudevan49/status/ ... 3610146816
Vasudevan Iyengar wrote:Latest update:
Lander found 500m away from the actual landing spot. But almost upside down. Seen from OHRC image and it is intact!
Trying to send commands from Bangalore control center...

Looks like it is?

mridulmm wrote:https://twitter.com/timesofindia/status/1170611250054627329

ISRO Chief, K Sivan to ANI: We've found the location of #VikramLander on lunar surface and orbiter has clicked a thermal image of Lander. But there is no communication yet. We are trying to have contact. It will be communicated soon.


Would love to see that lander image.

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Re: Chandrayan-2 Mission

Postby SriKumar » 08 Sep 2019 19:35

A final note on the velocities from this video that Gagan had linked. THe graphs at 3:00 onwards is actual test data (albeit limited accuracy- one has to extraploate manually from the very grainy graph).
https://www.youtube.com/watch?time_cont ... XbJLhMb8aE

In looking at the altitude, and range positions at 3:06 to 3:15, and assuming that the timescale is actual time (i.e. data updates all happened at the same speed), the final 2 telemetry data points suggest that the final vertical velocity is 20.4 m/s eyeballed calc.(not accurate to even 1 m/sec let alone 0.4 m/s) and reducing. The range is just within 1 km of the landing spot, and closing.

The two 'error bars' that bounded the trajectory is very interesting. It is about 2 km uprange and about 0.75 km down range. This seems to suggest that anywhere in this wide swath of atleast 2.5 km was an acceptable landing spot ? Maybe I am reading too much into the trajectory bound. If so, it definitely came down within the bounds set, even the velocity might have been OK if a tad high- the craft was clearly decelerating at this point. Orientation is a different story- the graph does not show orientation. The visitor janta sitting in the control room would have gotten to see all the screens (including orientation).

It is interesting ISRO says they took a thermal image of the lander. I am quite sure they would have taken all images possible with the instrumentation on the orbiter including optical camera. Perhaps the optical camera did not show the details they want to see.

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Re: Chandrayan-2 Mission

Postby fanne » 08 Sep 2019 20:08

@ 30 cm resolution, I think they can see anything/everything on the lander.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 08 Sep 2019 20:09

Place must have been well-lit unless it came down inside a crater/ slope of a hill and that's why it toppled. Thermal image: why would the exterior surfaces have different thermal signature in daytime I wonder. If it was night they could be checking for signs of life, but daytime? Did they expect to see nozzles that haven't cooled down to the ambient? (there is no conduction/convection to the outside, only radiation, so cooldown may be slower)

VERY interesting that Dr. Sivan says they are trying to establish contact. Sounds like there is some hope, not just wishful thinking, there. A rugged Android BSNL phone (<20m/s landing speed is nothing! It is like being on a KSRTC Fast Passenger bus) owned by Vikram's AI system trying to send WhatsApp to the ISRO Group?
I am in the well on the Moon onlee! Slight knee prablem from laang travel. Hope u r in the well. Did PeeEm like our laddoos? Manju's nephew's friend's B'Din Party go OK yaar?

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Re: Chandrayan-2 Mission

Postby Gagan » 08 Sep 2019 20:27

Indranil wrote:There were smaller 25 N engines too.

50 N engines, multiple ones for attitude correction, yaw-pitch correction

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Re: Chandrayan-2 Mission

Postby Varoon Shekhar » 08 Sep 2019 20:48

After the success of the 'rough braking", for how many minutes did the 'fine braking' work flawlessly, before the mishap?

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Re: Chandrayan-2 Mission

Postby Gagan » 08 Sep 2019 20:48

A word about the TV transmission of ISRO launches and possible measures to improve it. I have repeated some things ad-nauseam multiple times in the past.
1. Doordarshan as an socialist era TV broadcaster is poorly motivated to do 21st century transmission. Period.

2. A high quality transmission will need a lot of money in the form of a fleet of dedicated cameras on the ground, in the air, on the rocket launcher or the lander, gyro stabilization, special telescopes. All will need to be imported. The broadcaster will have to give out a contract to develop software to allow on-screen telemetry, and develop VERY high quality animation, that is synced to telemetry.
3. VERY close coordination with ISRO - which is itself a government organization with at least some ethos that remain in bygone era. ISRO seems to be struggling between the demands for secrecy, and log-kya-kahenge syndrome. I suggest that they explode forward with confidence. I for one love them, warts and all, and expect nothing more than NAAAARMAL PARFAARMANCE from them !!!
4. ISRO will have to install cameras on all launchers, at multiple places, which they already do, but will have to dedicate a lot of band width to the transmission. Further they will perhaps have to deploy a parallel system to collect audio-visual data and re-transmit to the TV broadcaster.
5. ISRO and India will have to deploy special ships in the IOR, or use french islands in southern IOR, or further equip our station in Antarctica for this

One reason why all this isn't happening is the expense. I don't agree that this expense is unjustifiable. It is of primary importance now.
In fact there is now a VERY NOTICEABLE difference between ISRO launch transmission and what other space powers are doing. And ISRO and India comes across as uncaring and callous.

I urge ISRO to do their OWN transmission using Antrix corporation. Transmission should be purely scientific, with no room for sycophancy. There is NO NEED TO SHOW THE ISRO CHIEF, the PM or other dignitaries, or the gathered children. There IS NO NEED TO SHOW PEOPLE APPLAUDING, while cutting away from improtant scientific data being displayed. Comparable commentary done by videshis talks about rate of fuel burn, they descrbe how the launcher is rotating by X degrees along it axis to orient itself, they talk about stage separation in huge detail. They describe the events surrounding the pre-launch in much more detail. All these are done by people who are fluent in conversation.

We need a Harsha Bhogle for ISRO launch commentary. Not a cricketer himself, but very knowledgeable never the less, and able to give very detailed information and engross people with his speech.

Telemetery HAS TO BE ON SCREEN !!!! We as fans of ISRO's work, like to analyze in detail every step of the way. But have to rely on miserly snippets of information released by a media shy ISRO. ISRO has a lot of room to improve in media management. Do they or Antrix have a dedicated media manager? One can't send a senior scientist to tackle the media -that is not right. It is akin to sending someone unprepared in war into battle with a pack of hungry wolves, who's primary purpose to take one improper word and sensationalize it!

ISRO has to surge forward, and shed this 70s and 80s mindset and we have to have a more scientifically oriented, modern, high-tech TV coverage.

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Re: Chandrayan-2 Mission

Postby Gagan » 08 Sep 2019 21:03

ISRO can release more detailed telemetery data and timelines in its website if it is OK with the powers that be.

What happened to the lander? We know that the Moon's environment is super hostile. Did that environment have a role to play in the lander's failure?
Did one of the 800KN engines under perform? Was there a software glitch?

I understand that analysis of these things is ISRO's domain. But they have to add to humanity's knowledgebase by giving out accurate analysis results by a fairly detailed press-release that is on their website. Can't rely on the media to tell their story, and mix their bias in between

ISRO has to tell its story itself !!!!!

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Re: Chandrayan-2 Mission

Postby Mort Walker » 08 Sep 2019 21:35

arshyam wrote:

Looks like it is?

mridulmm wrote:https://twitter.com/timesofindia/status/1170611250054627329



Would love to see that lander image.


If ISRO is attempting to communicate with Vikram after getting images means it crashed mostly intact. If images revealed Vikram was completely destroyed, there would be no need to waste time and the Failure Analysis Committee could get on with its work.

The ToI tweet quotes Dr. Sivan as saying “It will be communicated soon”. What does that mean? Do we still have hope?
Last edited by Mort Walker on 08 Sep 2019 21:41, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby vijayk » 08 Sep 2019 21:38

Vigilante
@vigil_nte

So this guy @pallavabagla clicks pictures of ISRO scientists/Engineers and their workplaces and sells it on Getty images.
https://gettyimages.com/photos/pallava- ... st#license


Image

prashanth
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Re: Chandrayan-2 Mission

Postby prashanth » 08 Sep 2019 21:39

Varoon Shekhar wrote:After the success of the 'rough braking", for how many minutes did the 'fine braking' work flawlessly, before the mishap?


Here is my analysis based on this video:


After rough braking, there is the CAM coasting phase. Not sure what CAM means, but ISRO animation video indicates attitude correction from thrusters-sideways relative to moon surface to thrusters down. A slight deviation is observed between predicted and achieved trajectories between 5-6 KM altitudes. There is an abrupt loss of altitude at the initiation of fine braking at about 4 KM altitude, not expected in the predicted trajectory. At 38:59 timeline, the animation shows inverted lander with tumbling in progress. Looking at the roll-rate, it is likely that attitude control was lost at a higher altitude, perhaps immediately after fine braking commenced?

Despite the hard landing, ISRO has demonstrated excellent science so far, in locating the lander within a day using the orbiter and attempting to communicate with it. Let's hope for the best.

Varoon Shekhar
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Re: Chandrayan-2 Mission

Postby Varoon Shekhar » 08 Sep 2019 21:57

^
Thanks, so it is accurate to conclude that the 'fine braking' succeeded only for a very brief time, say only a minute or two. Or did it perform longer.


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