Chandrayan-1 moon mission

[sumishi]

Sumishi,

Pl. go thru the paper above.

" However, with the moon’s gravity field heavily dependent on longitudinal variations, it becomes necessary to include non-zonal terms also in the orbital evolution process."

Perhaps what U were saying in your earlier posts ( Moon's gravity is NOT 1/6 ) may be the average of all the variable intensities of Gravity w.r.t Lattitudes.

Also note that the paper is by ISRO scientists in 2005.

SSSalvi, many thanks for that info! Yeah, u have an important point there regarding the average.

BTW, let me admit that I have learned a lot from this forum since the time I chimed in -- there are a number of real experts here. Quite unlike a lot many forums I have seen. Cheers!

[manoba]

In elliptical orbit the pictures will be distorted. No doubt you can see the shapes but that will be without any accuracy ( Technically called as RAW Image ) and the image processing software will fail to work with so much of distorted Raw Image. Surely no satellite operator would like to publish distorted pictures and then keep on giving excuses for its inaccuracies.

Eh... what logic is this? A camera is supposed to click correct image no matter what orbit it follows, elliptical, triangular, multi-gonal..., unless and otherwise its lens surfaces changes from circular curve to an elliptical one. Or, am I missing something?

Wasn't those two pictures of earth were clicked when the CY-I was following an elliptical orbit? I didn't see any distorted image...

[Lalmohan]

so, ssalvi - are you assuming that CY will be bent over during elliptical orbit or that images will be distorted due to doppler shift or differential refraction from lunar atmosphere and/or solar wind interference?

[SSSalvi]

In the satellite imagery world, the image is not acquired in one single shot... there is a linear array which images a line of image at a time and the sat movement pushes the array to next line when it acquires second image and so on.

To acquire the correct image the distance between sat and moon surface has to be constant for all lines so the orbit has to be essentially circular for mathematically correct image acquisition.

Of course the image looks ok for people like us but a trained eye can detect the variation especially because there are people who know lunar surface features like their 'hasta-rekhas'.

The Earth image that is being circulated in various forums is a raw image and everybody was elated to see it but Emily Lakdawalla posted a image which is partly corrected.

She has made very balanced comments as are expected from an authority:

How could they make such a mistake? It's like I said when I pointed out the error with the Rosetta image. Data doesn't come down from spacecraft in familiar formats like JPEG or TIFF; it's a stream of ones and zeroes, with a format unique to the science instrument, and scientists and engineers write their own software for translating that into raw image data. There are varying conventions for whether bits are written right or left, and if you take that raw image data and open it up in a piece of off-the-shelf image processing software, the image might be backwards. (I have this problem when I try to open up Mars Reconnaissance Orbiter CTX images.)

If you're in a hurry, and you don't yet have a lot of experience working with your spacecraft's data -- as is certainly the case for a newly launched spacecraft that you're trying to ballyhoo to your taxpayers with quick press releases and status reports -- it'd be easy to make that mistake. It's actually much more understandable for ISRO to have made this mistake with a spacecraft launched only a week before, and whose camera was being tested for the first time, than it was for ESA to make the mistake with Rosetta, a spacecraft that had been launched more than three years prior, whose camera had been used during two previous flybys.

The error is not really important. Kudos to the Chandrayaan-1 team; the image is absolutely gorgeous in its detail, and bodes well for the spacecraft's images of the Moon, which will be taken from a much closer distance.

http://www.planetary.org/blog/article/00001721/

An example of how the corrected image looks like see:

Post No 163 in
http://www.unmannedspaceflight.com/inde ... &start=150

Notice the image stretching at top.

[manoba]

In the satellite imagery world, the image is not acquired in one single shot... there is a linear array which images a line of image at a time and the sat movement pushes the array to next line when it acquires second image and so on.

To acquire the correct image the distance between sat and moon surface has to be constant for all lines so the orbit has to be essentially circular for mathematically correct image acquisition.

Of course the image looks ok for people like us but a trained eye can detect the variation especially because there are people who know lunar surface features like their 'hasta-rekhas'.

The Earth image that is being circulated in various forums is a raw image and everybody was elated to see it but Emily Lakdawalla posted a image which is partly corrected.

Yes, SSSalvi, but in satellite imagery world, a single capture of a frame, a single image/picture will not get distorted due to the orbit. But ONLY the stitching of several single shots and arranging them in a band of images will give distorted result, if the satellite/camera follows a noncircular orbit. In an elliptical orbit, in aposelene, the camera captures bigger portion of lunar surface with less detail. In periselene, the camera covers smaller portion with high resolution. So, only the mapping of the lunar surface will get distorted, but not the individual images themselves for Pete's sake.

What Lakdawalla has pointed out is that the image is flipped not distorted. That is due to how the raw bytes of images are stored in the memory (top-down or bottom-up as per the camera specs, and perhaps may be the problem of little/big endian thing about which I am not sure) and how they are treated by the receiver and how he restored them in the image formats, which we are convenient of.

[sumishi]

Here is that media channel moon image, as released by ISRO: (Why is it not sharp?)

[SaiK]

the image properties says 682x1024 pixel.. still there is no reason to be blur. perhaps, chandrayaan didn't get focus/exposure correct? or intentionally blurred by isro!?

[krishnan]

no autofocus

[SaiK]

http://www.isro.org/chandrayaan/htmls/tmc.htm

[rachel]

So today is Tuesday.. two more firings over the next two days to bring it down to 100km circular...so by Thursday it is in 100km circular orbit... then probe dropped on Friday (or possibly Saturday).

Xciting stuff!

[sivab]

http://www.hinduonnet.com/thehindu/holn ... 112031.htm

Chandrayaan-1 gets further closer to moon

Bangalore (PTI): Chandrayaan-1 spacecraft on Tuesday moved closer to the Moon with ISRO scientists carrying out orbit reduction manoeuvre at 18:30 hours for a duration of 31 seconds.

"The current orbit of Chandrayaan-1 is 255.3 km (the farthest distance from the moon) X 101.3 km (nearest distance to the moon). The orbital period is 2.09 hours", ISRO spokesperson S Satish told PTI.

Further manoeuvres are planned in the coming days to bring the spacecraft to its final circular orbit of 100 kms above the moon's surface, Satish said.

[sumishi]

Chandrayaan nudged closer to moon

"The spacecraft is at 187 km from the moon (periselene) and 255 km away (aposelene), orbiting elliptically once in every 2 hours and 16 minutes over the polar regions of the lunar planet," Indian Space Research Organisation (ISRO) director S Satish said.
"The complex exercise enabled Chandrayaan to move swiftly from 7,500 km aposelene late Sunday to 255 km, which is a remarkable feat. All sub-systems and instruments onboard are functioning satisfactorily," Satish said.

Chandrayaan-I will undergo two more orbit-lowering manoeuvres over the next two days to enter into its designated slot of 100 x 100km from the lunar surface for a two-year rendezvous with the moon.

Why isn't there a press release of ISRO of this lowering of orbit from LO-1 to LO-2 (Nov. 10th night about 10:00 pm), even though isro.org was last updated on November 11, 2008 4:50 PM?

[sumishi]

http://www.hinduonnet.com/thehindu/holn ... 112031.htm

Chandrayaan-1 gets further closer to moon

Bangalore (PTI): Chandrayaan-1 spacecraft on Tuesday moved closer to the Moon with ISRO scientists carrying out orbit reduction manoeuvre at 18:30 hours for a duration of 31 seconds.

"The current orbit of Chandrayaan-1 is 255.3 km (the farthest distance from the moon) X 101.3 km (nearest distance to the moon). The orbital period is 2.09 hours", ISRO spokesperson S Satish told PTI.

Further manoeuvres are planned in the coming days to bring the spacecraft to its final circular orbit of 100 kms above the moon's surface, Satish said.

Only the Final orbit lowering remains!!

[rachel]

So just one more firing?

[Vipul]

http://www.hinduonnet.com/thehindu/holn ... 112031.htm

Chandrayaan-1 gets further closer to moon

Bangalore (PTI): Chandrayaan-1 spacecraft on Tuesday moved closer to the Moon with ISRO scientists carrying out orbit reduction manoeuvre at 18:30 hours for a duration of 31 seconds.

"The current orbit of Chandrayaan-1 is 255.3 km (the farthest distance from the moon) X 101.3 km (nearest distance to the moon). The orbital period is 2.09 hours", ISRO spokesperson S Satish told PTI.

Further manoeuvres are planned in the coming days to bring the spacecraft to its final circular orbit of 100 kms above the moon's surface, Satish said.

Only the Final orbit lowering remains!!

Chandrayaan-I will undergo two more orbit-lowering manoeuvres over the next two days to enter into its designated slot of 100 x 100km from the lunar surface for a two-year rendezvous with the moon.

[sumishi]

Chandrayaan-I will undergo two more orbit-lowering manoeuvres over the next two days to enter into its designated slot of 100 x 100km from the lunar surface for a two-year rendezvous with the moon.

Isn't that an earlier news snippet you are referring to? It is already at 255.3km x 101.3km (LO-3), while in the article you specified, the orbit is 255km x 187km (LO-2).

[prao]

I am beginning to doubt that the CY1 cameras are of the pushbroom type (or the Linear Imaging & Self Scanning - LISS sensors as ISRO normally terms it). I wonder if they are more like normal digital camera sensors that capture an image over an area i.e. across and along the direction of travel. The INSAT cameras are of that type since they have no relative motion with respect to the Earth. Here's why I am inclined to think that: (bear with me please - I know I could be waaaay off base here (I also found out that the Kaguya Terrain Camera is of the pushbroom type but it also has HDTV sensors with 2.2 M pixel resolution)

1. ISRO normally explicitly refers to pushbroom cameras as LISS sensors like they have for the IRS series including Resourcesat-1 but for CY1, there's no mention of linear sensors when refering to the TMC aboard CY1. They do mention a swath of 20 km and a resolution of 5 m but this is how they put it

It can image a strip of lunar surface which is 20 km wide and resolution of this CCD camera is 5 m.

2. The images captured of the earth - one partial earth image from 9000 km, one whole Earth image taken at 70000 km and a whole Moon image taken at 311200 km do not appear to be images taken by linear imaging cameras. some rough calculations:
To have a 5 m resolution at 100 km from the lunar surface, the angular resolution of the camera is 5.0E-5 radians. At 311200 km, the Moon would subtend an angle of 0.011 radians only and the relative motion of CY1 wrt the Moon would be very small. So to image the full moon, CY1 would have to be manually moved to be able to scan the full Moon in a minimum of 223 steps - too much trouble if you ask me just to take a poor quality image. As far as can tell, CY1 is not designed to be steerable - I couldn't find any mention of steerability which might mean that thrusters would be required to orient the satellite, no? Why waste all that fuel to no purpose? Then at 9000 km only a partial image appears to be captured. Using a globe I estimated that the area captured covers around 18 degrees of the Earth's surface (from somewhere below the Equator to roughly the Tropic of Capricon) . At 9000 km this is roughly 0.2 radians or 20 km at 100 km distance. This could simply confirm that the swatch of the TMC is 20 km or it might imply that the image area would be 20x20 km at 100 km altitude.

Like I said, I could be completely wrong, so if anyone has better info, please post!

[juvva]

I am beginning to doubt that the CY1 cameras are of the pushbroom type (or the Linear Imaging & Self Scanning - LISS sensors as ISRO normally terms it). I wonder if they are more like normal digital camera sensors that capture an image over an area i.e. across and along the direction of travel. The INSAT cameras are of that type since they have no relative motion with respect to the Earth. Here's why I am inclined to think that: (bear with me please - I know I could be waaaay off base here (I also found out that the Kaguya Terrain Camera is of the pushbroom type but it also has HDTV sensors with 2.2 M pixel resolution)

1. ISRO normally explicitly refers to pushbroom cameras as LISS sensors like they have for the IRS series including Resourcesat-1 but for CY1, there's no mention of linear sensors when refering to the TMC aboard CY1. They do mention a swath of 20 km and a resolution of 5 m but this is how they put it

It can image a strip of lunar surface which is 20 km wide and resolution of this CCD camera is 5 m.

2. The images captured of the earth - one partial earth image from 9000 km, one whole Earth image taken at 70000 km and a whole Moon image taken at 311200 km do not appear to be images taken by linear imaging cameras. some rough calculations:
To have a 5 m resolution at 100 km from the lunar surface, the angular resolution of the camera is 5.0E-5 radians. At 311200 km, the Moon would subtend an angle of 0.011 radians only and the relative motion of CY1 wrt the Moon would be very small. So to image the full moon, CY1 would have to be manually moved to be able to scan the full Moon in a minimum of 223 steps - too much trouble if you ask me just to take a poor quality image. As far as can tell, CY1 is not designed to be steerable - I couldn't find any mention of steerability which might mean that thrusters would be required to orient the satellite, no? Why waste all that fuel to no purpose? Then at 9000 km only a partial image appears to be captured. Using a globe I estimated that the area captured covers around 18 degrees of the Earth's surface (from somewhere below the Equator to roughly the Tropic of Capricon) . At 9000 km this is roughly 0.2 radians or 20 km at 100 km distance. This could simply confirm that the swatch of the TMC is 20 km or it might imply that the image area would be 20x20 km at 100 km altitude.

Like I said, I could be completely wrong, so if anyone has better info, please post!

prao

some details of TMC: http://www.ias.ac.in/jess/dec2005/ilc-16.pdf

Looks like this is a pushbroom type. But you do have a valid point on how the ~300K distance moon image was acquired without rotating CY. Is it possible that the mirrors in the TMC can be used for scanning? Though it looks like the mirrors are fixed from the above document.

[prao]

Juvva,

Thanks for the link - interesting paper. Yes it certainly looks like a pushbroom type system and like you said the mirrors appear fixed. So the question of how ISRO managed those images remains! Will having three linear sensors make assembling images like they've published any easier? Remember the three sensors are 25.2 degrees apart in their views according to the paper so they're certainly not close.

P

[SaiK]

From the above IAS pdf doc:-

The camera will have four gain settings to cover the varying illumination conditions of the Moon. Additionally, a provision of imaging with reduced resolution, for improving Signal-to-Noise Ratio (SNR) in polar regions, which have poor illumination conditions throughout, has been made. SNR of better than 100 is expected in the ±60◦ latitude region for mature mare soil, which is one of the darkest regions on the lunar surface.

Now, were there any improper selection as to which mode to use to shoot moon from 311K odd kms?

gurus to the rescue.

[Gerard]

Chandrayaan’s orbit reduced

On Wednesday evening, the Spacecraft Control Centre (SCC) at Bangalore will issue commands to the spacecraft’s engine, called the Liquid Apogee Motor (LAM), for reducing its aposelene from 255 km to 100 km. (It is powered by liquid propellants). When it is done successfully, the spacecraft will be in its final circular orbit of 100 km above the moon.

[prao]

Thinking about this TMC issue some more, perhaps the motion of CY1 along its orbit is enough to allow it to scan the moon with a pushbroom camera w/o having to steer. Depending on its period of revolution (about its own axis), it may not have to move very much along its orbit to scan the moon fully. For example if its orientation is fixed relative to the stars then assuming that a section of its highly elongated elliptical orbit as a straight line that is roughly perpendicular to a line drawn from the moon (at 311000 km distance), CY1 will have to travel only about 3500 km along its orbit to fully scan the moon with the TMC. This might take somewhere between half hour to 1 hour by my extremely rough calculations.

[juvva]

Thinking about this TMC issue some more, perhaps the motion of CY1 along its orbit is enough to allow it to scan the moon with a pushbroom camera w/o having to steer. Depending on its period of revolution (about its own axis), it may not have to move very much along its orbit to scan the moon fully. For example if its orientation is fixed relative to the stars then assuming that a section of its highly elongated elliptical orbit as a straight line that is roughly perpendicular to a line drawn from the moon (at 311000 km distance), CY1 will have to travel only about 3500 km along its orbit to fully scan the moon with the TMC. This might take somewhere between half hour to 1 hour by my extremely rough calculations.

Or if the attitude of CY is fixed relative to the stars, would the motion of the moon itself be enough to scan it in a reasonable time.

[prao]

Thinking about this TMC issue some more, perhaps the motion of CY1 along its orbit is enough to allow it to scan the moon with a pushbroom camera w/o having to steer. Depending on its period of revolution (about its own axis), it may not have to move very much along its orbit to scan the moon fully. For example if its orientation is fixed relative to the stars then assuming that a section of its highly elongated elliptical orbit as a straight line that is roughly perpendicular to a line drawn from the moon (at 311000 km distance), CY1 will have to travel only about 3500 km along its orbit to fully scan the moon with the TMC. This might take somewhere between half hour to 1 hour by my extremely rough calculations.

Or if the attitude of CY is fixed relative to the stars, would the motion of the moon itself be enough to scan it in a reasonable time.

Right, that's possible too I think! Perhaps a combination of the two with some intensive rearranging of the pixels after! Or it could be that at the relative positions when the Moon was imaged, one of the bodies in question could be assumed to be stationary. That would simplify the image processing.

[svinayak]

Please do not post irrelevant material. Thanks

[enqyoob]

Hi Saiji, pls help. I have a bet with someone that you will resume posting in clear language out of the goodness of ur heart. Can't afford to lose...

[SaiK]

Yes Sir! I 'll do so from next time onwards..

Questions about the push broom.

Would n't the frame itself being small (since the object in focus is small as well at a distance of 311k km)?, and needed very little time to sweep the scan lines? Assuming, TMC was in the direction of focus, and moving towards it. Should it be a few seconds, then there should'nt be any distortion, is my guess.

Even a fast point to shoot digital camera should work. In my guess, I am thinking TMC was not necessary to be used to shoot this picture.

[K Mehta]

First official moon image from chandrayaan
Images from Chandrayaan-1 -ISRO website
Mods plz format the pic if needed.
Sweeet image.

[K Mehta]

Guys please put the media spins in the psyops thread.
Request to mods to make this a technical discussion thread.

Done

[SSSalvi]

All the info we have says that the camera is pushbroom type so must acquire image using the forward motion of yaan for line by line image acquisition.

But then we can't get the image so geometrically correct in a non circular unplanned orbit without oriantation of attitude, which is unlikely.

ISRO must explain whether they have changed to a 2 dimensional CCD array .. It will be an achievement if they have. Anyway they must have realised from hi-res satellites ( Cartosats ) that pushbroom and 'step and stare' techniques have problems.

Incidentally , how is it that the Earth photo is clearer than Moon photo from almost the same distance? Just the angular size difference of both the objects from equal distance can't be attributed for out of focus image.

[sumishi]

...
Incidentally , how is it that the Earth photo is clearer than Moon photo from almost the same distance? Just the angular size difference of both the objects from equal distance can't be attributed for out of focus image.

The earth photo was taken from 70,000 km, while this moon image is from 311,200 km (if you add up, both photos seems to be taken from about the same/similar location in orbit, just pointing at different objects). Can it be that the moon image has been resized upwards, making it blurry?

[narayana]

Chandrayaan-I to hit the moon's surface
this reporter Seems like a Porki agent who cannot wish well,Boore nazar walle Tera Mooh kala,Touch wood

[SSridhar]

Chandrayaan-I to hit the moon's surface

That was a poor choice of words for a title by Times Now. I have written to them.

[p_saggu]

^ ^ ^
It has been corrected already
Chandrayaan enters final lunar path

[harbans]

BANGALORE: Chandrayaan-1 spacecraft is slated to reach about one km away from its final orbital home of 100 kms above the moon's surface this evening.

ISRO scientists are planning the final orbit reduction manoeuvre for about one minute at around 7 pm that would bring the lunar spacecraft to around 101 kms above the moon's surface, ISRO sources said.

The circular orbit is expected to be trimmed to 100 kms tomorrow, they added. - PTI

http://www.thehindubusinessline.com/blnus/14121935.htm

[sarulan]

Chandraayaan enters final orbit
http://economictimes.indiatimes.com/Mis ... 705375.cms

[harbans]

Chandrayaan-I reaches its final resting orbit
12 Nov 2008, 1915 hrs IST, AGENCIES

BANGALORE: Chandrayaan-1 spacecraft reached its final orbital home, about 100 kms above the moon's surface on Wednesday.

Chandrayaan-I will stay in the orbit for the next two years.

On November 9, India became the fifth member of the global moon club with Chandrayaan-1 entering the lunar orbit at 5.04 pm (IST). The other four members are the US, Russia (former Soviet Union), Japan, China and members of European Space Agency (ESA).

According to Isro officials, Chandrayaan's liquid engine was fired for 817 seconds when the spacecraft passed at a distance of about 500 km from the moon to reduce its velocity to enable the lunar gravity to capture it around the moon. Chandrayaan's speed was reduced to 366 metres per second when it flew into the moon's orbit.

Experts said it was a significant feat because India's moonshot was successful in the very first attempt — something that even major space powers like the US and Russia could not achieve. The man who launched the Indian moon mission, Krishnaswamy Kasturirangan, had said, "It's undoubtedly a great moment for India because nearly 50% of the moon missions of other countries have not been successful."

Chandrayaan-1, the two-year Rs 386 crore Indian moon mission launched from Sriharikota on October 22, will draw a three-dimensional map of the moon, carrying out its chemical mapping and hunting for water or ice.

Kasturirangan said the lunar orbit insertion (LOI) was a nail-biting moment because two objects — the moon and Chandrayaan — moving at a high speed had to have a successful rendezvous. At a certain point, the gravity of moon and that of earth cancel each other out, making LOI very challenging.

http://timesofindia.indiatimes.com/Chan ... 705426.cms

[Nitesh]

^ ^ ^
It has been corrected already
Chandrayaan enters final lunar path

some goof up here

The spacecraft performance is normal.Further orbit reduction manoeuvres are scheduled in the coming days to take Chandrayaan-1 to its final operational orbit of 100 kms height from the lunar surface.After this, the moon impact probe, one of the eleven scientific instruments (payload) of Chandrayaan-I, will be released to hit the moon's surface, the statement said.

[neeraj]

http://www.isro.org/pressrelease/Nov12_2008.htm
Final orbit reached.

[nishug]