Chandrayan-2 Mission

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Re: Chandrayan-2 Mission

Postby juvva » 28 Sep 2019 06:57

Haridas wrote:
prasannasimha wrote:Gyroscopes could have had a Gimbal lock

You mean IMU gimble lock? As the gyros sensors are solidstate. But for that exact reason one always has one more axis ; ie 4 axis.

What is the 4th axis? ( I thought, Einstein was the only guy, who believed in the 4th axis ).

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Re: Chandrayan-2 Mission

Postby UlanBatori » 28 Sep 2019 07:27

Vikram lander could have sailed on the lunar electric field like a "ballooning" spider?

2 solar panels and 4 legs outstretched: just like a spider minus 2 legs.

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Re: Chandrayan-2 Mission

Postby Haridas » 28 Sep 2019 12:29

juvva wrote:
Haridas wrote:You mean IMU gimble lock? As the gyros sensors are solidstate. But for that exact reason one always has one more axis ; ie 4 axis.

What is the 4th axis? ( I thought, Einstein was the only guy, who believed in the 4th axis ).

A means to keep the 3 gimbles away from getting near lockin orientatuon.

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Re: Chandrayan-2 Mission

Postby SSSalvi » 28 Sep 2019 12:44

There are NO images.... Orbiter orbit does not pass over intended Landing Site.

If it has to image the area then they have to make the ORBITER look across track .. have they planned for that capability vis a vis onboard fuel budget of what they are claiming of 7 years lifetime?

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Re: Chandrayan-2 Mission

Postby SaiK » 28 Sep 2019 21:55

https://www.indiatoday.in/science/story ... 2019-09-27
Image
The LRO passed over the landing site on September 17 and acquired a set of high-resolution images of the area; so far the LROC team has not been able to locate or image the lander.

LRO will next fly over the landing site on October 14 when lighting conditions will be more favourable, John Keller, Deputy Project Scientist Lunar Reconnaissance Orbiter Mission, Goddard Space Flight Centre, told PTI via email.

"It was dusk when the landing area was imaged and thus large shadows covered much of the terrain; it is possible that the Vikram lander is hiding in a shadow. The lighting will be favourable when LRO passes over the site in October and once again attempts to locate and image the lander," Nasa said.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 28 Sep 2019 23:11

This thread is now more repetitive than an orbit by the LRO. As long as nothing new is discussed v should b fine. Maybe post a few pics of the launch?

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Re: Chandrayan-2 Mission

Postby Amber G. » 29 Sep 2019 00:11

ashbhee wrote:If ISRO has images of Vikram why not release it, why are they waiting for NASA to do it?

Both CY2, and Nasa's LRO are near polar orbit.., LRO's next pass will be in October over the site in better lightning condition. CY2 will also pass through (about once a month) over the course of the year. (Per ISRO the orbiter is functional and it is scheduled to send back observations over the year..) More eyes in the sky better it is.

>> Current orbits (Green LRO, other CY2). (Remember, moon surface below is spinning)

(Moon's North is thin vertical line - as you can see CY2's orbit is pretty close to exact polar orbit)
Image

One part, some of do not understand that it is not that simple - For example, LRO's recent image - approximately 900 million illuminated pixels were examined for the target area (about 1km x 1 km) .. If I understand correctly each pixel is slightly bigger than a meter ([NASA/GSFC/Arizona State University has more details.).

ISRO's CY2 camera, is supposed to have a have a slightly better resolution but It is further than LRO's closest approach (which is about 50 km). I believe that CY2's slightly elliptical orbit is such that, it is slightly closer to the surface than average near the Vikram landing sight. .. As said before other conditions such as light etc are also a factor. In any case looking for Vikram is more complicated than many think,

Hope this is helpful.

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Re: Chandrayan-2 Mission

Postby prasannasimha » 29 Sep 2019 14:24

UlanBatori wrote:This thread is now more repetitive than an orbit by the LRO. As long as nothing new is discussed v should b fine. Maybe post a few pics of the launch?

Then please desist from posting if noncontributory

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Re: Chandrayan-2 Mission

Postby Amber G. » 29 Sep 2019 21:59

Amber G. wrote:
ashbhee wrote:If ISRO has images of Vikram why not release it, why are they waiting for NASA to do it?


For example, LRO's recent image - approximately 900 million illuminated pixels were examined for the target area (about 1km x 1 km) .. If I understand correctly each pixel is slightly bigger than a meter ([NASA/GSFC/Arizona State University has more details.).
.

Just to give a sense, this is one picture from LRO ..( CY2 images will be similar too).. the circled part (and in real life, there were thousands such candidates) was suspected by some as possible Vikram.. One literally does that by comparing 'before' and 'after' pictures to see if there is anything new in the land-scape at the right point.
Image

(ISRO does NOT have, neither expected to have pictures like: Image :) :)

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Re: Chandrayan-2 Mission

Postby prasannasimha » 29 Sep 2019 22:55

To put it into perspective the expected image even of the CY2 orbiter would be 3 pixels wide and that of LRO 1 pixel in size. The shadow analysis may give more information. As Amber G said it will require comparing of before and after images.

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Re: Chandrayan-2 Mission

Postby fanne » 29 Sep 2019 23:01

did CY2 record before picture of the area? Could it have, given that it was in orbit just few days ago?

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Re: Chandrayan-2 Mission

Postby Amber G. » 29 Sep 2019 23:25

fanne wrote:did CY2 record before picture of the area? Could it have, given that it was in orbit just few days ago?

Yes, of course. One of the *main* task was to take as many high-resolution pictures of the landing site, analyze to make final pinpoint the landing area, load those images in Vikram's memory bank (for it's final navigation). CY2's one of the main purpose is to do the detailed study of the moon as was never done before. I hope you remember that CY2 was orbiting moon for days before the Vikram landing. (and it was orbiting moon about every two hours)

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Re: Chandrayan-2 Mission

Postby fanne » 29 Sep 2019 23:29

Thanks, makes me feel better. It makes sense, so they can also do comparative before and after analysis. I think ISRO has all the pics, analysis (finding needle in hay stack) is taking time and thus not officially released. The shadows etc. only came some days after the 'landing'. Trying to find 3 pixels worth of difference in a 900 million pixel maze must be time consuming.

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Re: Chandrayan-2 Mission

Postby Amber G. » 29 Sep 2019 23:44

^^^ And all this "mapping" was not only in visual light frequency - to study moon (and these may help locate Vikram).. among other things on CY2 we have -
:
- Terrain Mapping Camera-2 (TMC-2) for preparing a three-dimensional map essential for studying the lunar mineralogy - (can detect metal objects standing "up")

- Large Area Soft X-ray Spectrometer (CLASS) X-ray fluorescence spectra helps to determine the elemental composition of the lunar surface - metal objects can be located from other background)

- PRL's XMM (Solar X-ray monitor) also helps mapping metal and other elements present.

- Dual Frequency L and S band Synthetic Aperture Radar (DFSAR) - It can probe meters below the surface and does not need sun-light. (Was primarily to locate ice and other constituents. L-band can, if I am not mistaken, penetrate about 5 meters.

- IIRS (Imaging IR Spectrometer - thermal images etc) SAC) wide wavelength range (0.8 μm to 5 μm)

- ChACE- Can detect minute gases (lunar atmosphere) uses Quadrupole Mass Analyzer to carry out a detailed study of the lunar exosphere.

– RAMBHA-DFRS( Dual Frequency Radio Science experiment) can study electron density in the Lunar ionosphere.

And of course - Orbiter High Resolution Camera (OHRC) to prepare high-resolution topographic maps and digital elevation models of the lunar surface. OHRC has spatial resolution of 0.3 m from 100 km polar orbit.
Last edited by Amber G. on 29 Sep 2019 23:47, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby prasannasimha » 29 Sep 2019 23:47

fanne wrote:Thanks, makes me feel better. It makes sense, so they can also do comparative before and after analysis. I think ISRO has all the pics, analysis (finding needle in hay stack) is taking time and thus not officially released. The shadows etc. only came some days after the 'landing'. Trying to find 3 pixels worth of difference in a 900 million pixel maze must be time consuming.

ISRO has the imagery but will not release it( or may never release it) till the failure analysis team finishes its review.Very likely they will be confirming by multiple passes to compare with all the previous imagery that was obtained during landing site selection

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Re: Chandrayan-2 Mission

Postby fanne » 30 Sep 2019 00:23

Oh so you are insinuating that ISRO has already located Vikram/Pragnya?

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Re: Chandrayan-2 Mission

Postby ramana » 30 Sep 2019 05:52

We don't know what they know. Rest is speculation till FAB is done.
If we persist on inanities will be forced to lock thread.

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Re: Chandrayan-2 Mission

Postby prasannasimha » 30 Sep 2019 23:26

fanne wrote:Oh so you are insinuating that ISRO has already located Vikram/Pragnya?

There is already mention of thermal imaging .There are sources mentioning that imaging by the orbiter has been done. Further information will be got after failure analysis. They will not put out any more information till it is done .

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Re: Chandrayan-2 Mission

Postby Amber G. » 01 Oct 2019 00:41

For many of us, the soft-landing was the *most* critical part - something we were doing for the first time and by no means easy.
This is what I said on in July
Amber G. wrote:
SwamyG wrote:Amber and other gurus, which part of the entire journey from lift off to landing the rover would be cause for concerns & celebrations? From a mission perspective, that is.

For me the most critical part will be Vikram's soft landing on the moon. As there is no air, the inertial guidance based retro-rockets have to be extremely accurate. India has impressive and proven technology (used in MoM) here so I am quite hopeful.


***
Meanwhile as ISRO has pointed out, scientifically speaking, as output from the scientific equipments is concerned - I will agree with 98% success.

As far as Vikram - the site will be located/confirmed with more details in near future (few months). True, no details has been published publicly (not unusual at al), Images of Vikram has been captured by CY2 - and more will be captured - in thermal (IR), and visual range.

What we (scientists) all know and some of my thoughts -

==> Images and analysis of even a hard impact can and will provide many clues. For example, the debris around the actual vehicle can indicate the angle at which it fell as well as its speed. Clearer images can of course reveal what the status and position of the lander still is. It may take some time but questions would eventually be answered ...whether it is in one piece, whether it crashed at the spot it was supposed to or away from it, and whether it is in an inverted position or leaning slightly.. ityadi. It may take many passes of CY2/LRO , and many different wavelengths but that is what science and ISRO is all about.

==> I think (and most scientist will agree) most likely is that clear images will enable to see displacement of lunar soil (called regolith) at the crash site. ( Lunar regolith is a fine and powdery. When CY-1 intentionally crashed on the lunar surface around the same region a decade ago, it had displaced the regolith water ice under it - The biggest discovery of CY1)
==> Vikram would have displaced the regolith as well when it hit the surface. This would enable Chandrayaan-2’s orbiter to study the water ice using IIRS (Imaging Infrared Spectrometer) and DFSAR ( Dual Frequency Synthetic Aperture Radar) (As said above IIRS is an infrared imager that can perform a full mineralogical mapping of the moon. It’s purpose is to map water ice. The DFSAR will also perform lunar mapping in the process of measuring the thickness of the crust. It will calculate how thick the regolith is.

===> Scientists can also figure out what direction the antenna was pointing to and if the lander still was in one piece to be able to communicate again. (Unlikely because if it was, it would respond - I don't think it is in one piece - my estimation is minimum 50 m/s impact -- but who knows :))

Hope this is useful. IMO, this thread ought to focus more on CY2, science rather than pseudo science and off-topic silliness.

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Re: Chandrayan-2 Mission

Postby Amber G. » 01 Oct 2019 01:39

prasannasimha wrote:
There is already mention of thermal imaging .There are sources mentioning that imaging by the orbiter has been done. Further information will be got after failure analysis. They will not put out any more information till it is done .

Just to add: Per ISRO: "Every data or image will be analyzed. It will go through due process of review and approval and after that this will go to public domain" Link

By the way, AFAIK (I am watching this since Apollo 11), apart from LRO no one has put all the data in public domain right away - makes no sense. Apart from other issues, sheer logistics - how do you make terabytes of unformatted/raw data available to ddm's misinterpretation) - makes it very hard.

I remember people like Carl Sagan, in his lectures in schools, had lot of pictures not officially released by NASA - even then there were some very funny results when ddms misinterpreted pictures and wrote articles :(.

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Re: Chandrayan-2 Mission

Postby SSSalvi » 03 Oct 2019 20:42

Waiting for the images of shattered DreamLander.

Next Lunar day begins midnight bet 4th and 5th Oct.

CH2 Orbiter will cover the landing sight between 9th and 10th Oct with good Sunlight.

LRO is not a good candidate to image polar areas. It will cover the Landing Site between 16th and 17th Oct .. but the lighting conditions are not very helpful. It will give a similar situation seen in last cycle : Long shadows and low Illumination apart from the fact that it has a inferior spatial resolution compared to CH2 Orbiter. ( Of course the LRO has a different role than imaging small items ).

Only advantage of LRO images is that we are SURE to see those in public domain within hours of its pass over the area.

No such possibility with CH2 Orbiter images .. SURE for that.

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Re: Chandrayan-2 Mission

Postby Amber G. » 04 Oct 2019 10:42

CY-2's CLASS, in its first few days of observation, detected charged particles and their intensity variations on the lunar soil!
Chandrayaan 2’s Orbiter payload detects charged particles on Moon

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Re: Chandrayan-2 Mission

Postby somdev » 04 Oct 2019 18:55

Amber G. wrote:CY-2's CLASS, in its first few days of observation, detected charged particles and their intensity variations on the lunar soil!
Chandrayaan 2’s Orbiter payload detects charged particles on Moon


Finally some interesting science news is trickling out :)

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Re: Chandrayan-2 Mission

Postby Amber G. » 04 Oct 2019 21:09

^^^ For more detailsStudying Earth’s extended magnetosphere (geotail)plasma around Moon

>>>
ISRO reports that the intensity of these particles changed as much as ten times the levels outside the geotail, indicating the complex interaction of these particles with the magnetic field.

Image

(This geotail crosses the Moon’s orbit and extends beyond it during its rotation around Earth. The Moon passes through this geotail region for almost six days around the full moon day. Therefore, during the full Moon in September, CLASS was able to detect the charged particles and their intensity variation.)


(Note:) Earth’s magnetic field obstructs the solar wind plasma resulting in a magnetic envelope around Earth, called the magnetosphere. While this magnetosphere is compressed to around 22,000 km on the side facing the sun, it stretches into a long tail on the opposite side, known as the geotail.
Image
***
CLASS is designed to measure direct signatures of elements such as Sodium, Calcium, Aluminium, Silicon, Titanium and Iron, on the lunar surface using the secondary x-ray radiations from the Moon.

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Re: Chandrayan-2 Mission

Postby Varoon Shekhar » 04 Oct 2019 21:28

https://frontline.thehindu.com/science- ... epage=true

Pretty good article in Frontline by T.S.S Makes it clear that Vikram's issue was a software one, not propulsion.

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Re: Chandrayan-2 Mission

Postby Amber G. » 04 Oct 2019 21:57

Here are some awesome pictures taken by OHRC of CY2's
Image

Image location:
Image

and this:
Image

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Re: Chandrayan-2 Mission

Postby sanjaykumar » 04 Oct 2019 22:50

Remarkable.

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Re: Chandrayan-2 Mission

Postby somdev » 05 Oct 2019 00:13

Amber G. wrote:^^^ For more detailsStudying Earth’s extended magnetosphere (geotail)plasma around Moon

>>>
ISRO reports that the intensity of these particles changed as much as ten times the levels outside the geotail, indicating the complex interaction of these particles with the magnetic field.

Image

(This geotail crosses the Moon’s orbit and extends beyond it during its rotation around Earth. The Moon passes through this geotail region for almost six days around the full moon day. Therefore, during the full Moon in September, CLASS was able to detect the charged particles and their intensity variation.)


(Note:) Earth’s magnetic field obstructs the solar wind plasma resulting in a magnetic envelope around Earth, called the magnetosphere. While this magnetosphere is compressed to around 22,000 km on the side facing the sun, it stretches into a long tail on the opposite side, known as the geotail.
Image
***
CLASS is designed to measure direct signatures of elements such as Sodium, Calcium, Aluminium, Silicon, Titanium and Iron, on the lunar surface using the secondary x-ray radiations from the Moon.


Amber G@ I had posted some of my apprehensions earlier in this thread around lunar physics but that did not resonate well :)

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Re: Chandrayan-2 Mission

Postby Vayutuvan » 05 Oct 2019 06:49

Somdev ji, let us discuss in the physics thread which is better.

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Re: Chandrayan-2 Mission

Postby somdev » 05 Oct 2019 14:50

Vayutuvan wrote:Somdev ji, let us discuss in the physics thread which is better.


Sure no problem. I had put it here in the first place because any spacecraft failure analysis cannot be in isolation of its operating environment. I guess I was coming from a system-of-systems perspective.

But yes point taken :)

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Re: Chandrayan-2 Mission

Postby SSSalvi » 08 Oct 2019 12:28

Not much light on what exactly went wrong .. but the compounding of problems well summerized.

https://frontline.thehindu.com/science-and-technology/article29477285.ece?homepage=true

It descended to about 33 km above the moon. As Vikram entered the fine braking phase with only 2 km to go before touchdown, it seemed to encounter a problem with its control. One of the four throttleable engines seemed to have produced a higher thrust than it should have. So Vikram’s velocity of descent started increasing instead of reducing. Vikram, therefore, tumbled out of control. Instead of turning 90 degrees before coming down to soft-land on the moon, it swung 180 degrees. It “twisted”, or deviated from its fine trajectory, came down fast and crash-landed on its side.


Opinion is sharply divided among ISRO engineers on whether one of the four throttleable engines produced more thrust than required, leading to an increase in the velocity of descent.


the four throttleable engines should have worked in a balanced manner during the fine braking phase. However, an engine produced a higher thrust than required, so the velocity of descent shot up. Vikram, therefore, started deviating from its path and it did so fast. Instead of turning 90 degrees to land on its four legs, the lander turned 180 degrees. The engineer said: “Owing to the twist from 90 degrees to 180 degrees, communication with the lander was lost. The higher thrust from one of the engines led to Vikram coming down fast and it crashed.


an “anomaly in the performance of one of the four throttleable engines’’, an error in the overall software configuration, and the sloshing around of the liquid fuel in the tank on board Vikram as the fuel was getting depleted—could have led to the crash-landing on the moon


Since the software was not robust enough, the problems got compounded.


on September 8 when ISRO was able to locate the lander, which was lying a few hundred metres close to its intended touchdown spot on the moon’s South Pole. ISRO was able to locate it with the help of the thermal images taken by a high-resolution camera on the orbiter.


And an unrelated problem:

What is worrying space specialists is that with ISRO fully concentrating on the Chandrayaan-2 mission in the past few months, there has been no launch of remote-sensing, communication or navigation satellites. The last lift-off that took place before the Chandrayaan-2 launch was of PSLV-C46, which put a radar-imaging satellite called RISAT-2B into orbit on May 22, 2019. “A backlog has built up".

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Re: Chandrayan-2 Mission

Postby ramana » 09 Oct 2019 01:36

S^3 A few questions and a comment:

1) If the extra thrust tilted the lander from 90 to 180 degrees then it will have more horizontal delta V?
2) can they simulate the effects in hardware-in-loop model on the ground?
3) How did the omni directional antenna lose communications when the lander tilted?
5) Why did the engine produce more thrust when it had that electro controlled valve?
5) last para is bokwas to put in the lander fault analysis report. Dr Sivan is quite capable to sort out the schedule and priorities. That's why he is in charge.


OK more in the article

The engineer described as “earlier thinking” the version that one of the four throttleable engines generated a higher thrust, which led to the velocity of Vikram’s descent increasing and its crash-landing. He asserted: “Vikram’s propulsion was perfect. It worked all right. Its sensors worked well. Its navigation was good. Everything worked well. But there was some software problem such as we had in ASLV [Augmented Satellite Launch Vehicle] flights [in 1987 and 1988] and the first PSLV [Polar Satellite Launch Vehicle] flight in 1993. It is definitely not a propulsion problem. It is an algorithm formulation problem. We are strong in propulsion. We are strong in sensors. We should have concentrated a bit on the software. We should have done more simulation.”

Another top ISRO official also said that both the liquid engine and the cryogenic engine on board the GSLV-Mk III M1, the propulsion system on the orbiter and the four throttleable engines of Vikram—all developed by the Liquid Propulsion Systems Centre—had worked perfectly during the mission.

A combination of several factors—that is, an “anomaly in the performance of one of the four throttleable engines’’, an error in the overall software configuration, and the sloshing around of the liquid fuel in the tank on board Vikram as the fuel was getting depleted—could have led to the crash-landing on the moon, a top spacecraft engineer said.

“When the orientation of Vikram changed drastically, its propulsion should not fire in that wrong orientation of the lander. This is the normal mission requirement. If the spacecraft goes to the wrong attitude [orientation], the propulsion should stop firing. When the lander is coming down, it should not accelerate,” he added. When a problem occurred in controlling the lander, “the control stability will not come on its own”, he explained. The stability should be created by the software. If a disturbance occurred in Vikram during its fine braking phase, the software should take care of it.


He summed up the issue thus: several things added up. The intended orientation of the lander went wrong because of an anomaly in the performance of an engine. The software was not able to take care of it. The fuel in the tank was getting depleted because Vikram had already completed two manoeuvres. The fuel in the tank was sloshing around, which created another problem. Since the software was not robust enough, the problems got compounded.

[i]{Cascading failure. But still not the root cause.
Why did the engine produce more thrust? Software is belt and suspenders to get you out of malfunction. However such a mission should not have malfunction.
Fuel sloshing does not make sense. What he is saying is the CG was changing due to fuel slosh.
But didn't they have baffles in the tank to mitigate fuel sloshing?}[/i

Hopes revived briefly on September 8 when ISRO was able to locate the lander, which was lying a few hundred metres close to its intended touchdown spot on the moon’s South Pole. ISRO was able to locate it with the help of the thermal images taken by a high-resolution camera on the orbiter. Despite valiant attempts, ISTRAC was not able to communicate with the lander up to September 18. Time was running out to communicate with the lander because its intended lifespan was only for 14 earth days, that is, up to September 21.


Even TSS uses flamboyant language.
"Shot out of orbit" etc!

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Re: Chandrayan-2 Mission

Postby Amber G. » 09 Oct 2019 02:15

Some comments about CLASS ( Chandrayaan-2 Large Area Soft X-ray Spectrometer):
- CLASS can provide some valuable data about the environment around Earth.. For about six days each month, the moon passes within Earth's geotail, -- distorted bubble of Earth's magnetosphere created by the constant push of the solar wind that spews out from the sun..

- ISRO released some initial data from CLASS (The device is designed to measure X-ray fluorescence, one can identify where on the lunar surface certain elements — like magnesium, aluminum, silicon and iron — are located. The instrument works best when the sun releases a solar flare - but even when there is no flare at the lunar surface but
when CY2 is inside Earth's geotail, the instrument can analyze how that environment differs from beyond the geotail. So this is a bonus, studying Earth's magnetosphere.

- CLASS did just that, measuring a sharp increase in particles that ISRO has identified as electrons.. Initial data but I think it is exciting as we get more data about their spectrum etc. Considering that CY2 is going to spend a lot of time this may be important data for us.

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Re: Chandrayan-2 Mission

Postby ramana » 09 Oct 2019 03:37

AmberG, i as listening to NPR about Lunar environment and how its bombarded with cosmic rays and has all sorts of particles emanating from the lunar surface This was a few weeks back and my memory could be wrong.

So are these X-Ray florescence a bye-product of that?

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Re: Chandrayan-2 Mission

Postby Vayutuvan » 09 Oct 2019 03:56

Amber G. wrote:- CLASS did just that, measuring a sharp increase in particles that ISRO has identified as electrons.. Initial data but I think it is exciting as we get more data about their spectrum etc. Considering that CY2 is going to spend a lot of time this may be important data for us.


What is the significance? in layman's language if you please.

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Re: Chandrayan-2 Mission

Postby ramana » 09 Oct 2019 04:08

You can tell the composition, atomic structure etc from the emitted electron particles.


AmberG are these electrons or beta particles?

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Re: Chandrayan-2 Mission

Postby Amber G. » 09 Oct 2019 11:02

Ramanaji, beta particles are nothing but electrons (+ positrons) . :).
Last edited by Amber G. on 09 Oct 2019 22:56, edited 1 time in total.

ramana
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Re: Chandrayan-2 Mission

Postby ramana » 09 Oct 2019 11:45

Thanks! You forgot a , after my name!

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Re: Chandrayan-2 Mission

Postby SSSalvi » 10 Oct 2019 15:20

ramana wrote:

1) If the extra thrust tilted the lander from 90 to 180 degrees then it will have more horizontal delta V?
2) can they simulate the effects in hardware-in-loop model on the ground?
3) How did the omni directional antenna lose communications when the lander tilted?
5) Why did the engine produce more thrust when it had that electro controlled valve?
5) last para is bokwas to put in the lander fault analysis report. Dr Sivan is quite capable to sort out the schedule and priorities. That's why he is in charge.


Trying some loud thinking :

1. If one of the thrusters misbehaves then it will in all probability keep rotating ( i.e. not just 90 to 180 deg ) because the misbehavior will not stop just as soon as it becomes 180 deg. So there will surely be a disturbance in both HOR and VERT components, and it may not be a monotonically increasing and decreasing .. it will cycle randomly original velocities + and - directions.

2. They surely can and I am sure they must have tried to simulate all possible anomalies the evaluation committees have asked them to try. Evaluation committee consists of multi-disciplinary real experts.

3. Omni is a misnomer .. in reality it is a Hemispherical coverage antenna which is blind below its mounting surface.

4. The control logic can misbehave and valve will just obey the command received from controller.

I was just thinking of one possibility.. we can debate on it:

Suppose that the craft is moving to its intended landing site ( before the last precision hovering stage ) maintaining a fixed ( or a downward travel ) distance from ground.
During this travel if it encounters the rim of a crater.. will it try to maintain the distance from ground ( now a sudden slope of rim rising continuously ) and so tilt and the craft will start rotating due to sudden jerk in a highly dynamic condition?
Trying to explain with a figure:
Image

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Re: Chandrayan-2 Mission

Postby ramana » 11 Oct 2019 02:14

Possible but not plausible.
Reason is the lander anomaly happened during the rough to fine braking transition and not during final vertical phase.

I have a question for you from rockets and controls aspect.
Once the lander tumbles along the pitch axis, what engines can return it to proper motion?
I don't see any small thrusters (50N) mounted at different planes of the lander.
I would expect at two different planes.
They all look in same plane.


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