Chandrayan-2 Mission

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Re: Chandrayan-2 Mission

Postby SSSalvi » 05 Sep 2019 08:16

ramana wrote:Do that for having raised the issue.
And AmberG will correct your answer.
Our folks have forgotten basic physics.

:) Well said! :)

BTW Good Morning from Landing site.
Seeing first light of day.
Waiting to Dilboo the avenger.
Last time fellow dropped a heavy missile .. not this time .
Dilboo, Help!

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Re: Chandrayan-2 Mission

Postby SwamyG » 05 Sep 2019 08:18

Mort Walker wrote:
SwamyG wrote:1. So are the considerations to heat; a political/administrative task of taking isotopes up in the air (somebody mentioned ISRO did not make a request), or is it scientific/engineering one (essentially a weight issue)?

2. 35 x 101KM is nearly a circular orbit, curious why it is not "perfect" circular orbit? After all the orbiter is powered, unlike the natural planets and moons orbiting Sun and planets respectively.


Let Vikram land first, then we can discuss RTG. There is a lot which can go wrong come 7 September. Success rates are around 50%.

It is an elliptical orbit in polar configuration as AmberG. pointed out above. The moon’s gravity is not uniform. It’s mass is lumpy and a shallow circular orbit would require more use of thrusters to keep it in position.

I am aware of the 52% success rate, and the recent Israeli mishap. I am not counting chickens before they hatch. I am not asking about circular vs elliptical orbits. Considering the numbers an additional 60kms comes with that perspective.
Last edited by SwamyG on 05 Sep 2019 08:33, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby SSSalvi » 05 Sep 2019 08:21

Rony post ..
Care ... He has computed for Earth.

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Re: Chandrayan-2 Mission

Postby SwamyG » 05 Sep 2019 08:40

Amber G. wrote:(There is an old joke about Indian parents who, when their child gets 99% in a test, ask the child "what happened to 1 point?" :) - In this case Chandrayaan is getting 100%!!!)


. (Short answer: No, it is not weight issue, ISRO did not think it needed/wanted it. We will use it when our antriksh-yatris land on moon.)
Please click on the link
https://twitter.com/i/status/1168614557427699712


Thanks for the answers. I am aware of the elliptical and circular. Was curious to know if they had gone for say a 30x40, or 50x55 (all arbitrary numbers), would that, have required more energy. Like I replied to Mort, considering the large numbers in play....this is very close. Just wanted to see why a 30x30 could not be attempted. Thanks again. Also thanks for the answer on weights. That answers my interest; I did not have the intention to debate or discuss the reasons in depth here.

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Re: Chandrayan-2 Mission

Postby juvva » 05 Sep 2019 09:08

juvva wrote:I remember reading somewhere ( need to dig up the source), that the landing strategy is now changed. The engine in the center will be on and firing all the way to touch down(no free fall).


ISRO animations on youtube show the central engine, thrusting all the way down to the surface, upto touch down....

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Re: Chandrayan-2 Mission

Postby Amber G. » 05 Sep 2019 09:53

juvva wrote:
juvva wrote:I remember reading somewhere ( need to dig up the source), that the landing strategy is now changed. The engine in the center will be on and firing all the way to touch down(no free fall).


ISRO animations on youtube show the central engine, thrusting all the way down to the surface, upto touch down....

FWIW: (Disclaimer: I do not know exact details of landing strategy but..)
- Landing strategy basics hasn't changed from months of extensive calculations/testing/checking/double_checking etc..As we know, it is not changed at spur of the moment or as we go - not the basic strategy.
- Particulars, of course, will change, as designed by last phase calculations after camera(s) has found the exact 'suitable site' within the landing-site ellipse (pre selected area of about 10-20 km area of ellipse shape land). No one knows the exact place yet and no one will know before Vikram decides.
- Calculate exact velocity vector, distance, and gravitation acc of moon at that point from on-board navigational computer.
- Feed exact delta-V data needed to on-board inertial guidance system so that impact velocity is zero (or as close to zero as possible). (For this, the engine can run all the way to touch-down or switch off a little earlier (in case the velocity is negative and lunar acc will make it zero at height=0).
Everything has to work nearly perfectly as there is very little room for error. There is very little time to react and try it again. (In Apollo's language, IIRC they called is "dead man's curve" .. after that you do not have luxury to go up and try again.. if you did not get it right then you will be dead).

****
I do remember watching Apollo 11 - when they landed the famous "Houston, Tranquility Base here. The Eagle has landed." was answered "Roger, copy that.." but the tension in even the mission control's voice was audible for people to notice. (Normally people there speak without emotion but that relief in the voice was noticeable in this case)

***

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Re: Chandrayan-2 Mission

Postby SSSalvi » 05 Sep 2019 09:59

As an ex insider:

Every single step ( like, how to route a cable in a particular way ) is discussed, discussed and discussed in at least 4 5 meetings plus in at least 3 review meetings involving intercenter personnel from various specialities.
Views are fought tooth and nail and after meeting same guys eat lunch together in harmony.
But technical discussions are Paramount till finalized and frozen.

Even for changes in real-time operation all the experts are huddled together for hours fighting over pro cons must shouldn't ...

---------

Interesting?

ttps://m.timesofindia.com/india/chandrayaan-2s-second-de-orbiting-maneuver-executed-isro/articleshow/70969698.cms

Further, Isro also carried out another manoeuvre of the orbiter on Tuesday, which the space agency did not officially announce. Sources said that the orbiter’s orbit was further reduced after a 36-second burn of the onboard propulsion systems. The orbiter reduced the distance closest to Moon to reach an orbit where the perigee was 96km.

“This was done so that the orbiter is right on the head of the lander when the landing happens,”
a source added. Vikram is expected to touchdown on the lunar surface between 1.30am and 2.30am on September 7. Isro had announced that it would be at 1.55am. "We are looking at starting the powered descent at 1.40am or 1.45am. The landing must happen 15 minutes after that," Sivan explained.

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Re: Chandrayan-2 Mission

Postby dada » 05 Sep 2019 10:21

Is the gravitational pull near lunar pole stronger than at lunar equator ?

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Re: Chandrayan-2 Mission

Postby disha » 05 Sep 2019 10:34

dada wrote:Is the gravitational pull near lunar pole stronger than at lunar equator ?


It could be vice versa. Unless one sees the full gravitational map of moon, it will be difficult to call that out generically.

For example, Apollo landings on Moon's equator were on basalt plain which are generally denser and hence prospectively can be termed as one with larger gravitational pull.

Hence to equivocally say gravitational pull near lunar pole(s) is stronger than at lunar equator is not plausible.

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Re: Chandrayan-2 Mission

Postby Amber G. » 05 Sep 2019 10:40

dada wrote:Is the gravitational pull near lunar pole stronger than at lunar equator ?

Moon is nearly spherical (compared to earth) - flatting factor of about .0012 (1/3 or earth). This means polar and equatorial radius are almost same (diff about 2 Km). It also spins much slower than earth, hence effect due to "centrifugal" is much smaller. Thus the gravitational pull is - within say 1-2% - same. (Equatorial g will be less due to this theory but not by much) Moon is relatively less homogeneous than earth so there is more random fluctuation in the value of "g" but all within 1-2% or so of the value = 1.62 m/s2 ( about 0.1654 g) (The maximum variation due some mascons is about .02 m/s^2)
For more details check out, say https://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html

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Re: Chandrayan-2 Mission

Postby Amber G. » 05 Sep 2019 10:59

disha wrote:
dada wrote:Is the gravitational pull near lunar pole stronger than at lunar equator ?


It could be vice versa. Unless one sees the full gravitational map of moon, it will be difficult to call that out generically.

For example, Apollo landings on Moon's equator were on basalt plain which are generally denser and hence prospectively can be termed as one with larger gravitational pull.

Hence to equivocally say gravitational pull near lunar pole(s) is stronger than at lunar equator is not plausible.

Here is map of "g" at moon: (From Wiki - As I said in above messages the max variation is about .025)
Image

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Re: Chandrayan-2 Mission

Postby Amber G. » 05 Sep 2019 11:13

Posting a photo of CY2 .. (Saw in a newspaper)
Image
This strange, bright light that appeared in skies over the Northern Territory and Queensland on launch night, left hundreds of people mystified... It turned out to be CY2.

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Re: Chandrayan-2 Mission

Postby Dileep » 05 Sep 2019 14:04

Slightly OT, but we had a few occasions of senior retired ISRO scientists working with/for us. The attention to details, the deep probing and the tenacity drilled into those bright minds is extraordinary (from POV of us engg service folk).

The only problem was, we couldn't get anything done to OUR schedule, and they couldn't get anything done to THEIR satisfaction.

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Re: Chandrayan-2 Mission

Postby sooraj » 05 Sep 2019 15:10

Chandrayaan 2 - Landing on Moon - LIVE from ISRO



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Re: Chandrayan-2 Mission

Postby SaiK » 05 Sep 2019 22:03

SSSalvi wrote:..forgotten basic physics...

Dilboo, Help!

moi not dilboo, but on conditional note, if we had already flight tested to specs on Earth, the dilboonetics kicks in with this post. /whoever doesn't want to land on moon, please stay out of this dhaaga. :)

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Re: Chandrayan-2 Mission

Postby Amber G. » 05 Sep 2019 22:29

With latest data: Vikram's and orbiter's orbit..
Image

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Re: Chandrayan-2 Mission

Postby juvva » 05 Sep 2019 23:09


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Re: Chandrayan-2 Mission

Postby rsingh » 05 Sep 2019 23:18

NASA guy twitted that they are helping us with deep space communication for CY2. Kuch parkash daliye. Is it a US sat that relay signals or what?

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Re: Chandrayan-2 Mission

Postby Ashokk » 05 Sep 2019 23:27

ISRO uses NASA's dish antennas which are located at different parts of the world to communicate with Chandrayaan when it is not visible from India. As per the DSN website, currently an antenna located in Madrid is in use.

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Re: Chandrayan-2 Mission

Postby Amber G. » 05 Sep 2019 23:34

^^^ There are many (even non-official) who are/will_be watching this with their radio telescopes. Madrid antenna is at good spot as moon will be visible from here when Vikram lands. Perfect spot to watch.
(Nothing unusual - ISRO, NASA all help each other in communication and observations etc - Even armature ham-radio types (with good radio telescopes) will be watching/listening)

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Re: Chandrayan-2 Mission

Postby ramana » 05 Sep 2019 23:51

SaiK wrote:
SSSalvi wrote:..forgotten basic physics...

Dilboo, Help!

moi not dilboo, but on conditional note, if we had already flight tested to specs on Earth, the dilboonetics kicks in with this post. /whoever doesn't want to land on moon, please stay out of this dhaaga. :)



And hold off on intelligent questions till landing is over please!

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Re: Chandrayan-2 Mission

Postby disha » 06 Sep 2019 00:30

Here is Sri Madhavan Nair explaining the complexities of C-2

https://www.firstpost.com/tech/science/chandrayaan-2-is-a-very-very-complex-operation-says-isro-ex-chief-madhavan-nair-7280851.html

On-board cameras will be mapping the terrain, sending the pictures to us. Then we will have to select the appropriate location and see that in the exact location it descends slowly to the surface", Nair said in an interview to PTI.

"It's a very, very complex operation. I don't think any nation has done a similar operation trying to have real-time pictures and then try to have an on-board computer implement autonomously the function of the landing. It's going to be a remarkable event and we are all looking forward to that event. I am sure it will be a 100 percent success", he said.

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Re: Chandrayan-2 Mission

Postby Vivasvat » 06 Sep 2019 01:25

disha wrote:https://www.firstpost.com/tech/science/chandrayaan-2-is-a-very-very-complex-operation-says-isro-ex-chief-madhavan-nair-7280851.html

trying to have real-time pictures and then try to have an on-board computer implement autonomously the function of the landing.

This sounds quite like Balakot SPICE. Probably involves more than that.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 06 Sep 2019 04:45

Ashokk wrote:ISRO uses NASA's dish antennas which are located at different parts of the world to communicate with Chandrayaan when it is not visible from India. As per the DSN website, currently an antenna located in Madrid is in use.


As of the time of this posting it appears to be Goldstone Deep Space Communications Complex (GDSCC) in the Mojave desert in California.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 06 Sep 2019 04:51

From Nair's interview it appears there will be real-time pictures during the descent and landing. But would it be broadcast to the world soon?

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Re: Chandrayan-2 Mission

Postby SriKumar » 06 Sep 2019 06:33


https://www.firstpost.com/tech/science/chandrayaan-2-is-a-very-very-complex-operation-says-isro-ex-chief-madhavan-nair-7280851.html

On-board cameras will be mapping the terrain, sending the pictures to us. Then we will have to select the appropriate location and see that in the exact location it descends slowly to the surface", Nair said in an interview to PTI.

"It's a very, very complex operation. I don't think any nation has done a similar operation trying to have real-time pictures and then try to have an on-board computer implement autonomously the function of the landing. It's going to be a remarkable event and we are all looking forward to that event. I am sure it will be a 100 percent success", he said.
In reading the full article, it seems that the Vikram lander will first take pictures of the lunar surface for potential landing sites, which it must be doing right now as it orbits in very close proximity to surface. The people (ISRO) on earth will study the pictures and designate a landing site based on the pictures. Then as Vikram descends, the onboard camera and image recognition systems (in addition to laser and other sensors) guide the craft to the selected landing site.

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Re: Chandrayan-2 Mission

Postby SriKumar » 06 Sep 2019 06:46

Mort Walker wrote:From Nair's interview it appears there will be real-time pictures during the descent and landing. But would it be broadcast to the world soon?
There is no doubt that the landing will be recorded, broadcast (to the orbiter) and stored, and then broadcast to earth. Not just visuals but all other data like distance from surface, attitude, orientation, velocity, deceleration etc. will be recorded for future use. Landing footage will likely be released once the landing is deemed successful, and at an appropriate time.

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Re: Chandrayan-2 Mission

Postby ramana » 06 Sep 2019 07:14

Folks please put any links to watch Vikram lander live.

Thanks.

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Re: Chandrayan-2 Mission

Postby fanne » 06 Sep 2019 07:28

watch for Sooraj post in this very thread and this very page. The live link is on standby

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Re: Chandrayan-2 Mission

Postby pravula » 06 Sep 2019 07:49

Dileep wrote:Slightly OT, but we had a few occasions of senior retired ISRO scientists working with/for us. The attention to details, the deep probing and the tenacity drilled into those bright minds is extraordinary (from POV of us engg service folk).

The only problem was, we couldn't get anything done to OUR schedule, and they couldn't get anything done to THEIR satisfaction.


Difference between an engineer and a scientist.

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Re: Chandrayan-2 Mission

Postby SSSalvi » 06 Sep 2019 08:36

Cannot compare two different items which have their own different goals and targets.

Each is called excellent when the job is executed meticulously.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 06 Sep 2019 08:44

SSSalvi wrote:Cannot compare two different items which have their own different goals and targets.

Each is called excellent when the job is executed meticulously.


Correct. ISRO is the best example of the intersection of science and engineering. It is indeed a rare type of organization that gets the best of both.

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Re: Chandrayan-2 Mission

Postby sanjaykumar » 06 Sep 2019 08:44

Getting to that time.


If the mission is successful, I will give 1.3 billion thank yous.
If not then I will repeat the finest line in all of the English corpus:

Ah, a man's reach should exceed his grasp, or what's a heaven for?

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Re: Chandrayan-2 Mission

Postby Mort Walker » 06 Sep 2019 08:54

SriKumar wrote:
Mort Walker wrote:From Nair's interview it appears there will be real-time pictures during the descent and landing. But would it be broadcast to the world soon?
There is no doubt that the landing will be recorded, broadcast (to the orbiter) and stored, and then broadcast to earth. Not just visuals but all other data like distance from surface, attitude, orientation, velocity, deceleration etc. will be recorded for future use. Landing footage will likely be released once the landing is deemed successful, and at an appropriate time.


If the landing is successful, then it should be released immediately. The psychological impact will be the greatest among friend and foe alike. The boost for Indian youth in aerospace engineering and astrophysics will be huge!

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Re: Chandrayan-2 Mission

Postby Vivek K » 06 Sep 2019 08:56

Should broadcast it 24 hours to Pakis!! Mandatory watching!

But agree with Mort! Need to Tell your story before someone else tells a distorted version.

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Re: Chandrayan-2 Mission

Postby vishvak » 06 Sep 2019 10:17

Ah, a man's reach should exceed his grasp, or what's a heaven for?

The only problem is not to aim high. Once the aim is high enough (and higher still), it's just situational.

As they say in desi, nishhan-chook maaf, nahi maaf neeche-nishaan. (It's unpardonable to have lower aim than possible but if unsuccessful higher aim is still pardonable or what's the word).

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Re: Chandrayan-2 Mission

Postby Bibhas » 06 Sep 2019 11:05

My predictions for tonight (and for the next 14 days):
1. Chandrayaan 2 Lander (Vikram) will make a picture perfect landing
2. There will be some initial communication glitch with Pragyan which will be sorted out soon. Very very tense moments.
3. Pragyan / Vikram will stop working due to one issue or other a day or two before the intended final day. Some rona dhona will happen.
4. But it will give us a pleasant surprise waking up one or two days after the next Lunar day cycle begins.

Thank you Amber G. for those insightful information in reply to my questions few pages back. It helped a lot understanding the basic issue.
I am just having a feeling like this. No logic.

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Re: Chandrayan-2 Mission

Postby Arjun » 06 Sep 2019 11:21

What kind of soil is expected around the lunar South Pole? Loose sandy type? Given the frigid temperatures and possibility of water can the surface be icy?

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Re: Chandrayan-2 Mission

Postby RKumar » 06 Sep 2019 13:25

Anti jinx ... before I am banned by Ad-minmuhlas

Lander mission will fail only!! :((

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Re: Chandrayan-2 Mission

Postby SSSalvi » 06 Sep 2019 14:21

If admin were negative, we would not have known that there is a dilboo.


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