Chandrayan-2 Mission

[disha]

Is the objective of Chandrayaan our viewing pleasure?

Not necessary for C-2 itself, but a resounding *yes* that the future planetary missions *must* think of enhanced visual and aural coverage.

If exploration is not made fun, it is useless. Exploration has to be fun and must touch the very base of our monkey brains - curiosity. It has to give the feeling to masses on being there. To that there should be no argument!

I do hope ISRO launches a lander to Mars and two of its components will be stereoscopic cameras showing the depth as perceived by humans and a microphone that captures sounds from the martian surface.

On moon we do we have to rule out "sound"? What sound does the solar wind produce? Of course a stereoscopic HD colour camera will also help!

[RonyKJ]

I think the issue of determining velocity and position may not be as complicated.
The orbiter can send out signals with a time stamp which can be received by the IDSN.
The time lag between transmission and receipt of signal can be used to calculate distance to orbiter
Subsequent signals can be similarly used to calculate a new distance.
Using the above, velocity can be calculated.
If multiple receivers of the IDSN, located at say SHAR and Australia are used, then by triangulation,
position can also be calculated.
Looks like there is no need for laser or doppler.
Does this make sense?

[ldev]

Is the objective of Chandrayaan our viewing pleasure?

Not necessary for C-2 itself, but a resounding *yes* that the future planetary missions *must* think of enhanced visual and aural coverage.

If exploration is not made fun, it is useless. Exploration has to be fun and must touch the very base of our monkey brains - curiosity. It has to give the feeling to masses on being there. To that there should be no argument!

I do hope ISRO launches a lander to Mars and two of its components will be stereoscopic cameras showing the depth as perceived by humans and a microphone that captures sounds from the martian surface.

On moon we do we have to rule out "sound"? What sound does the solar wind produce? Of course a stereoscopic HD colour camera will also help!

+1

[RonyKJ]

I really hope that ISRO has got high definition cameras in the lander/rover. Does anyone know the specs of these cameras, their resolution? If it is DD like coverage/resolution of their launches, it will be a disaster.

I know data transfer rates are the bottleneck for transmitting high resolution pictures, but still.......

Is the objective of Chandrayaan our viewing pleasure?

I think it is very important to have high resolution images. The better the images, the more the public will be captivated
by the mission. So, from a purely PR point of view, it would be invaluable.
ISRO made a mistake with the methane sensor on MOM which wasn't sensitive enough to find any trace of methane
on Mars. If it were sensitive enough, we could have scored another big success. Unless of course, there is no methane
on Mars, but scientists think there is.

[Amber G.]

Have been away from this dhaga for some time... Have not seen all the messages so please ignore if you find something already discussed. Will comment on a few posts which may interest those who are interested in serious science and understanding. Of course, this is to inspired people to look up further for reputable resources.

Another question I have is regarding the orbits. If I am not mistaken, there is not much inclination between the equatorial planes of earth and moon.

Inclination between equatorial planes and earth and moon is about 24-25 degrees. This varies, and is a little more complicated than straight-forward ddm newspapers like to put.
To be clear, and help us understand the kinematics, let us take ecliptic as our reference plane.
- The earth's equatorial plane is tilted about 23.5 degree.
- The moon's equatorial plane is tilted about 1.5 degrees.

The moon's orbit (around earth) is tilted about 5 degrees. The points the orbit crosses ecliptic is called moon's nodal point -(Rahu and Ketu grah in Indian astronomy) are not fixed but rotates making one revolution in about 19 years. Also the math here is 3D trigonometry (or vectors) so one may need a good 3D model to do real "calculation".

*****
The earth's equatorial plane comes in calculations mainly to determine launch window (azimuth angle etc) - remember earth is spinning so points fixed on earth's surface are not "fixed' wrt to earth/moon position etc (which determines lunar orbit insertion etc).

The moon's equatorial plane comes into calculation mainly to determine precise timing for Vikram's descend so it reaches the right place on the moon at the right light condition. (Remember moon is spinning).

The moon's orbit around earth comes into calculation mainly to determine precise timing to fire rockets to "leave" earth.. and later achieve lunar orbit.

It is, obviously a lot complicated than what I say here .. (I will more time and equations etc ) but Lunar orbit insertion has flexibility in the sense that once the original orbit (it's perigee / nodal point are at the right point wrt to moon -- see my old message for details) one could reduce number or orbits etc with less of a headache. Even if we had Saturn rockets the timing/sequence of landing part will not change - if you miss that window you may have to wait for months.

Hope this answers or makes few points clear ..

There were a couple of occasions when Dr Sivan was asked about how the landing date was maintained even though the launch date slipped by a week.
It was my understanding that this would be done by reducing the number of orbits around the moon after LOI was achieved. But Dr Sivan did not mention that at all, instead he talked about the time of TLI being adjusted. I wonder what is the real situation.
***
... .. Since we need to be in polar orbit around the moon, if we launch into polar orbit around the earth and then do the transfer to moon, we will arrive very close to polar orbit around the moon. Is this what was done? Was Chandrayaan 2 launched into polar orbit around the earth? This would make sense of what the chairman said regarding correction at perigee to achieve exact polar orbit around moon.
Another piece of info is that there is some possibility that systems on rover and lander may survive beyond 1 lunar day, since they have been tested to that temperature, but it is not guaranteed.

To add, "perigee" etc are important but not that much as "nodal points".. actually all are important but it is complicated math and not some rules of thumb.

Chandrayaan was launched such that at TLI could be done with right time window and availability of fuel.. It is NEITHER polar orbit or equatorial orbit around earth but its inclination is such that it reaches moon (which could be as much (but not more) 28 degrees inclination (wrt t earth's equatorial plane.)

Similarly after reaching moon, the orbit is "adjusted" (by firing rockets at precise timing windows) to achieve a "polar" orbit of the moon - how much the change in "inclination" depends on lot of factors.. (it is not addition/subtraction of angles.. more a vector calculation)

Hope this helps.

Edited later: Removed unneeded part. (Thanks Indranil for pointing out)

[prasannasimha]

From the calculations that I made (and I may be wrong about it) the Orbiter high resolution camera is 11,25,00,000‬ pixels from my calculation = 21.45 Megapixel camera and resolution of 0,32 meters
Terrain mapping camera From ISRO website
TMC 2 is a miniature version of the Terrain Mapping Camera used onboard the Chandrayaan 1 mission. Its primary objective is mapping the lunar surface in the panchromatic spectral band (0.5-0.8 microns) with a high spatial resolution of 5 m and a swath of 20 km from 100 km lunar polar orbit. The data collected by TMC 2 will give us clues about the Moon's evolution and help us prepare 3D maps of the lunar surface.

The camera on Pragyaan may be HD
The thing is while ISRO may bet HiDef images it may not necessarily be released to public till analysis and publications are made by the science teams

[prasannasimha]

There are Doppler Inertial navigation systems and star sensors that are used for navigation

[Indranil]

I think the issue of determining velocity and position may not be as complicated.
The orbiter can send out signals with a time stamp which can be received by the IDSN.
The time lag between transmission and receipt of signal can be used to calculate distance to orbiter
Subsequent signals can be similarly used to calculate a new distance.
Using the above, velocity can be calculated.
If multiple receivers of the IDSN, located at say SHAR and Australia are used, then by triangulation,
position can also be calculated.
Looks like there is no need for laser or doppler.
Does this make sense?

Is that is possible, but
1. It would become a single point of failure.
2. One has to make sure that the transmitter is facing earth even during orbit modifications which is fuel consuming.
3. This method has a lag which is too significant for station keeping operations. I am VERY SURE that onboard navigation systems are used for orbit raising/station keeping automatically. ISRO has terrestrial override capability. But, intervention is not required for planned operations.

[Amber G.]

Talked to an actual space engineer and the three body problem and involvement of Lagrangian points are not used except for actual missions to Lagrangian points. The ellipse assumption is enough for modeling for lunar missions

Yes..To be precise using elliptical orbit (newton's calculation) with Euler/Gauss etc "perturbation" method and slightly good computer any one (good/interested enough to study elliptical orbits) do that with more than enough accuracy needed here/

Basically calculate elliptical orbit (using two body problem) and take perturbations.. For example for orbit around moon you use two body problem (moon and orbiter) and then add perturbation due to earth, sun, and other planets as well as perturbation due to finite size and non-uniformity of the moon ityadi..computer programs do that ..

[Amber G.]

Few comments:

I think the issue of determining velocity and position may not be as complicated.
The orbiter can send out signals with a time stamp which can be received by the IDSN.
The time lag between transmission and receipt of signal can be used to calculate distance to orbiter
Subsequent signals can be similarly used to calculate a new distance.
Using the above, velocity can be calculated.
If multiple receivers of the IDSN, located at say SHAR and Australia are used, then by triangulation,
position can also be calculated.
Looks like there is no need for laser or doppler.
Does this make sense?

Is that is possible, but
1. It would become a single point of failure.
2. One has to make sure that the transmitter is facing earth even during orbit modifications which is fuel consuming.
3. This method has a lag which is too significant for station keeping operations. I am VERY SURE that onboard navigation systems are used for orbit raising/station keeping automatically. ISRO has terrestrial override capability. But, intervention is not required for planned operations.

- Knowing the position and velocity while in orbit is quite easy.. laser, radio, optically (just using stars) are fairly well understood and is, of course, no challenge. This is true for computers inside the space-craft with no input from earth.
- In fact, since accurate orbit is known (or parameters transmitted to space-craft's computer) the velocity, position could be known very accurately in real time by just knowing the accurate time only.
- For orbital changes (once desired orbit is calculated - done in advance and this does require help from earth computers/scientists etc) one calculates necessary delta-V and fuel requirement etc..
- The critical part is for how long, which direction, with what thrust etc the rockets have to be fired to achieve precise delta-V. Not a bit less, not a bit more (except for some later correction).
- For this, obviously, one does/can not depend on radio, communication to earth and rely on their computers, or other "external" navigational systems ityadi. For example if there is an atmosphere (which will be the case on earth or Mars) while rockets are firing ionization of the air will make any navigation depending on radio waves unreliable. For this reason this part is *all* (or virtually all) inertial. ==> depends ONLY on onboard systems - without "looking"/talking/listening out.

- Typically this is done by accelerometers - (similar to iPhone's accelerometers which detects iPhone's movement). Integration of acceleration over the time gives you delta-V. (Remember basic physics -- dV/dt = Acceleration).
- Typical accelerometers measure acceleration by measuring electric current produced. For chandrayaan etc one uses other basic physics . (dq/dt = current).. so if you integrate the current you get charge. Measuring accumulated charge accurately gives you delta-V.
- In fact, whole system is one (thus providing extreme reliability) integrated with throttle of the rocket. The system keeps rocket running accurately and shuts off automatically when the desired delta-V is reached.
- This above mechanism still impresses me a lot. I saw a sample (actually borrowed from JPL by Feynman and shown in a physics lecture) many decades ago - things used to cost a lot. The system used/produced by India is developed by Indian Engineers with fraction of the cost.

In summary, the critical orbit changes - specially the last one when Vikram does soft landing on Moon - are all depend primarily on inertial guidance and it matters a little if the system can talk to earth's computer. While rockets are firing during the critical phase, the feedback l does not depend on external navigational equipments.

Hope this helps.

[Amber G.]

how do they determine distance at such large distances esp when everything is moving?

By dopppler shift measurement. It is an involved theory.
At least l can't explain in simple terms.

Regarding accuracy, in 1975 , with the then technology, which was contained in the size of 5 racks of 6 ft height , the ranging equipment ( that is the technical name ) could measure geosync satellite ( 36000 kms altitude ) position with an accuracy of 1 mtr.

Now this function can be achieved with a laptop.

At present, with laser rangefinders the accuracy is about an inch or so, over the distance of the moon!
With LIGO type interferometers - believe it or not - the accuracy is better than diameter of an electron over the distance of the moon. Not that we are using these LIGO type interferometers but this type of precession is truly mind boggling.
Anyway accuracy is more than sufficient even with ordinary equipments.

[Amber G.]

how do they determine distance at such large distances esp when everything is moving?

Allow me to add here - What a person like me will find perigee/apogee ityadi which you may like and impress friends..

One can do that even without a calculator (if you are good to do simple math on paper) or with a calculator and simple formula for moon/chandrayaan...

- If you know the orbital time period (=T): Use this formula
(All units are SI that is, distance in meters, time in seconds etc..)
k ≈ 5x10^12 (if you do it without calculator) (or more accurately ≈ 4.90487 x 10^12
use kT^2 = 4*pi^2*a^3
This gives you a which is average of perigee and apogee. (also called semi major axis, or equal to radius of a circular orbit)

The geometric mean is semi-minor axis of ellipse, so if you know this, you can get both apogee and perigee.

***
To find velocity (if you know the position) or vice-versa use this formula: (v= velocity in m/s)
v^2 = k (2/r - 1/a)

"a" you just found out, r is distance of space-craft (or vikram or orbiter) and the center of the moon.
(to get elevation above the moon's surface, subtract the radius of moon = (see wiki) = 1737000 meters,

That's all folks. For *any* lunar orbit (while rockets are not firing) if you know the time-period of revolution ==> you can calculate "a" and thus velocity if you just know the distance from the moon.

[Vips]

[SSSalvi]

I really hope that ISRO has got high definition cameras in the lander/rover. Does anyone know the specs of these cameras, their resolution? If it is DD like coverage/resolution of their launches, it will be a disaster.

I know data transfer rates are the bottleneck for transmitting high resolution pictures, but still.......

1. They would surely use the cameras of REQUIRED resolution. One just can't compare commercial cameras with Space cameras. Both are different technologies.

2. As far as ISRO is concerned, they have technology which is no less than the best space-tech cameras worldwide. AND the most important is to know that they have in-house optics development division so they KNOW the technology in and out.

3. Current images what you are seeing are from large ( one image says from 2650 kms ) distance using a camera which has a specific design to work from about 100 kms orbit ... it is just bonus images .. not the real mission intent images. Just imagine : We have cameras which give at least 5M resolution from a 1000 kms orbit ( for any general user like you and me. ) . ( Published specs of Cartosat-2 )
They are RAW images ... in actual usage each image is used only after corrections applied on every pixel.

AND FINALLY, No one uses images now a days for VIEWING, they use it for analytical purposes .. rarely for enjoying a ' Ah, what a nice scene ' moment.

[ldev]

2. As far as ISRO is concerned, they have technology which is no less than the best space-tech cameras worldwide. AND the most important is to know that they have in-house optics development division so they KNOW the technology in and out.

3. Current images what you are seeing are from large distance using a camera which has a specific design to work from about 100 kms orbit ... it is just bonus images .. not the real mission intent images. Just imagine : We have cameras which give at least 5M resolution from a 1000 kms orbit ( for any general user like you and me. )
They are RAW images ... in actual usage each image is used only after corrections applied on every pixel.

AND FINALLY, No one uses images now a days for VIEWING, they use it for analytical purposes .. rarely for enjoying a ' Ah, what a nice scene ' moment.

Thank you SSSalvi. I believe you about the resolution+ that ISRO is capable off I know even a color picture will look B&W on the moon, but it will be nice to see it.....

Actually, I had not thought of what you said. At launch DD may provide coverage but fortunately DD cannot reach the moon as yet It will as you said cameras with the required resolution under ISRO's control.

[SSSalvi]

^
Why should there be no color on Moon? ( noob question .. not comment )

[disha]

^
Why should there be no color on Moon? ( noob question .. not comment )

It will not be colorless for sure. However given the basalt (iron rich), magnesium & titanium content in the moon dust, and the harsh sunlight (no atmosphere to disperse the light) dark blues, green blue, dark rusts, grey and white will be the dominant colors.

On high def photos/videos, they are definitely useful for science. But how do you excite a 5 year old?

[ldev]

^
Why should there be no color on Moon? ( noob question .. not comment )

What I meant is that the surface of the moon will look B&W in comparison to the vivid colors of earth i.e. color photography will not add vivid colors because they are inherently not there unlike say a photograph of the earth as taken by Apollo 11 astronauts from the surface of the moon Apollo 8 astronauts from lunar orbit. It looks bright, blue in contrast to the colorless moon surface.


By the way, it will be nice if Chandrayaan 2 took a picture of the earth from moon orbit. Wonder if ISRO has any plans for that?

[sanjaykumar]

https://www.popularmechanics.com/space/ ... -the-moon/

[Amber G.]

Simple - orbital velocity formula is v = SQRT(G*M/R)., where R is radius of orbit, which will be avg. radius of moon + height above moon

Plugging in the numbers, for G, M and R for 10 Km at moon orbit, I think it will be around 70 Km/sec. Raising it to 100 km will be @22 Km/Sec. (I might have eaten a zero here or there so please do not quote me or correct me on the numbers calculated ...)

As you suspected - Formula is correct but calculation is not. The value is about 1.7 Km/Sec for 10 Km (or 100 Km for that matter - it is only about 3% less - R is essentially same 1737 Km adding 10 or 100 Km changes a few percentage only in the calculation).

Edited later: Some one has already pointed it out.. For Moon, convenient is to use GM = 5*10^12 (in SI units) to do quick calculation in your head. If you want more accuracy use GM= 4.90487 x 10^12 - accurate 4-5 significant figures.

[disha]

Edited later: Some one has already pointed it out.. For Moon, convenient is to use GM = 5*10^12 (in SI units) to do quick calculation in your head.

Thanks!

PS: Doing it with my thumbs and in process eating couple of more zeroes became easier for me now ...

[SaiK]

By the way, it will be nice if Chandrayaan 2 took a picture of the earth from moon orbit. Wonder if ISRO has any plans for that?

Does Vikram or Pragyan payload carries a camera?

another silly question: Pragyan says it can communicate only with Vikram, and Vikram is designed for one lunar day. So, the whole mission needs to wrap up by a fortnight.

is it possible to extend this?

[UlanBatori]

^
Why should there be no color on Moon? ( noob question .. not comment )
surface of the moon will look B&W in comparison to the vivid colors of earth i.e. color photography will not add vivid colors because they are inherently not there

Where there are deposits of metal ores close to the surface (like Manganese), there are colors: Orange, black, grey. Trouble is, IMO, that during the day it is so bright that it was hard to take photos that were not over-exposed in the Apollo days.

There could be diamonds and bits of platinum lying around from asteroid impacts.

[Amber G.]

Does Vikram or Pragyan payload carries a camera?

another silly question: Pragyan says it can communicate only with Vikram, and Vikram is designed for one lunar day. So, the whole mission needs to wrap up by a fortnight.

is it possible to extend this?

Vikram and Pragyan carry camera (very good ones too - Carries, among others things like Orbiter High-Resolution Camera (OHRC) (on orbiter), Lander Position Detection Camera (LPDC) Lander Hazard Detection and Avoidance Camera (LHDAC). ityadi)
Pragyan/Vikram can communicate directly (also) with earth -- (Vikram Lander will be constantly communicating with the Indian Deep Space Network (IDSN) in Byalalu near Bengaluru. (This is also the network used by the Orbiter and Rover too.. point is, since Vikram/Pragyan will be sort of "fixed" on moon so with big antennas it is not that hard .. I guess, even for other radio telescopes, one may be able to eves-drop on the conversation if it is not encrypted -- (most of the communication will be encrypted, of course. )

[ldev]

Does Vikram or Pragyan payload carries a camera?

another silly question: Pragyan says it can communicate only with Vikram, and Vikram is designed for one lunar day. So, the whole mission needs to wrap up by a fortnight.

is it possible to extend this?

I found a helpful article which answers these questions:

India heads to the moon with Chandrayaan 2

Chandrayaan 2 will eventually attain an orbit 62 miles (100 kilometers) above the lunar surface, mapping the Moon and the proposed landing site with its Orbiter High Resolution Camera (OHRC).

We know this because the photographs of the earth and the moon released so far are from the Orbiter camera.

During descent, the lander will use two onboard cameras to autonomously assess its final landing site.

So Vikram the lander has at least 2 cameras.

The Pragyan rover includes a ........... along with two 1-megapixel stereo NAVCAMs.

So the rover has two stereo navigation cameras. I wonder whether ISRO will release any pictures taken by the rover cameras, they will be pretty low resolution.

The solar-powered rover and lander will arrive near lunar sunrise, and are expected to last until local lunar sunset two weeks later, though there are plans to try and wake them both up after the long lunar night. The orbiter's primary mission should last one year.

ISRO will try to wake up the lander and rover after the 14 day lunar night when temperatures go down to -175degC to -200degC. But the orbiter has a mission life of 1 year.

[Amber G.]

is it possible to extend this?

Some of the items left behind (like laser reflectors) will be there for years to come ..Pragyan's system is *not* designed to last lunar night but who knows .. some possibility that system may come back. (This has been discussed in this dhaga .. see my (among others) post wrt to this some times ago. Orbiter will last for years (or longer) - official life is about a year but it does not need much to survive.

[Amber G.]

The solar-powered rover and lander will arrive near lunar sunrise, and are expected to last until local lunar sunset two weeks later, though there are plans to try and wake them both up after the long lunar night. The orbiter's primary mission should last one year.

ISRO will try to wake up the lander and rover after the 14 day lunar night when temperatures go down to -175degC to -200degC. But the orbiter has a mission life of 1 year.

To add: By "waking up" , they mean : Next day wait .. warming and bringing them in the range of working temperature and re-establishing contact. The machines have to be tested after the freezing and heating cycle.

This battery system for Pragyan and Vikram is quite innovative - I don't think anyone has used such system before - basically they put everything is a "sleep" mode before the cold night. Almost all older systems had nuclear powered heater's (Radioisotope heating) to make sure the electric system/batteries do not get too cold. India does not have radioisotope heating for the batteries. Some of the scientists/engineers involved in designing think (or hope) that the system will wake up.. others don't think it will and official life, of course, is one solar day.

[SaiK]

dhanyavad amber g and others

[Shalav]

MOM and Chandrayaan 2 oribital animations

http://sankara.net/

[Amber G.]

The animation above ( <created by
Sankaranarayanan Viswanathan )) is really good. Thanks Shalav for posting it.

BTW, This is generated by NASA/JPL's Horizons system using ephemerides of CY2. Anyone can use this and one can generate 2D - 3D graphics of any object in solar-system..(Brf posts some time have used this - IIRC I also posted Sankaranarayanan Viswanathan's created animation around Mangalyaan's time )

(Million times better than using old Newcomb's tables and month's of cpu to calculate the orbit -- and nice/fast graphics card to show the animation)

From their site:

There is a limited web-based interface (to JPL's system) which can be used to generate ephemerides for solar-system bodies. Full access to and features are available via the primary telnet interface.

A web-interface tutorial is available to assist new users.

I really wished our ddm's, TV shows use that kind of resource to show (and zoom in) it at important stages to make things much more easy to understand.

Added later: For those who are interested the site is at:
https://ssd.jpl.nasa.gov/horizons.cgi

[SSSalvi]

Numerical data input used to generate one of the graphics that I post is based on jpl horizon .

[Amber G.]

^^^ @SSSalvi @prasannasimha @Indranil and others -
Anyone has source/site which will publish Vikram's orbital ephemerides as soon it is available. ( Vikram's orbital data is not likely to be available easily as ISRO would plan it just it time so we have to wait - It will be fun to put the animation of this landing on the moon with realistic images .. I know the landing site, and approximate (possible) path etc.. request to share ISRO site(s) which has up-to-date detail data etc..

[SaiK]

^^^ I thought it reached too early in the animation, but it made sense later.

[Amber G.]

^^^ In Sankara's animation, from what I know, the data/ephemerides is actual (from Launch, EBN#1, EBN#2, EBN#3, EBN#4, EBN#5, EBN#6(LOI), LBN#1 (TLI), LBN#2.. We are now between LBN#2 and LBN#3 .(post LBN#3 we will get new actual data) LBN#4 and LBN#5 data, obviously have not been loaded as we don't know the actual position.

I like to see from Moon's point of view..
(Moon is at the center, Earth is shown in its apparent motion going around the moon)



The three version is nice too..
https://www.facebook.com/kvsankar/video ... 117336741/

[Amber G.]

There were a few posts about measuring distances/velocities .. using radio telescopes ..doppler effect etc..

Apart from ISRO many others (some aam scientists with access to radio-telescope) are watching CY2 too. Sharing some typical activity of this type here.

Other eyes are watching CY2 -- From Dwingeloo radio-telescope .. This time to track the Chandrayaan2 lunar insertion burn. This is the Doppler curve of the 2230.8MHz radio signal from the lunar orbiter during the insertion burn.


(Some notes: - From their reports and my understanding)

The central curve is the carrier frequency, which was ground locked to the Madrid
tracking station (except for a brief unlock around 03:22UTC). The two other curves are sidebands. Full spectrum, with data sidebands at 32.5kHz offset from the carrier is not shown here.



From the Doppler curves alone it is not immediately obvious that the insertion burn has happened. (Pretty hard - the fact that the orbit changes from a hyperbolic trajectory to a very eccentric one. so scientifically it was hard to check that)

But they compared/plotted data.. with Doppler measurements (blue), against the predictions (orange) if no insertion burn had occurred. The observed Doppler curve breaks off the prediction around 03:30 to 03:40UTC... so they confirmed that "some thing" happened .. and by this time ISRO had confirmed that the burn was 100% successful.

They say, their radio-telescope will be at right place to observe the landing burn (at that time the moon will be up in Europe where this radio telescope is) and can track the landing.

[Amber G.]

Does Vikram or Pragyan payload carries a camera?

Sorry if it was already posted but This picture was taken by LI4 Camera on Vikram.

[sudarshan]

There were a few posts about measuring distances/velocities .. using radio telescopes ..doppler effect etc..

Apart from ISRO many others (some aam scientists with access to radio-telescope) are watching CY2 too. Sharing some typical activity of this type here.

Other eyes are watching CY2 -- From Dwingeloo radio-telescope .. This time to track the Chandrayaan2 lunar insertion burn. This is the Doppler curve of the 2230.8MHz radio signal from the lunar orbiter during the insertion burn.

...

From the Doppler curves alone it is not immediately obvious that the insertion burn has happened. (Pretty hard - the fact that the orbit changes from a hyperbolic trajectory to a very eccentric one. so scientifically it was hard to check that)

But they compared/plotted data.. with Doppler measurements (blue), against the predictions (orange) if no insertion burn had occurred. The observed Doppler curve breaks off the prediction around 03:30 to 03:40UTC... so they confirmed that "some thing" happened .. and by this time ISRO had confirmed that the burn was 100% successful.

They say, their radio-telescope will be at right place to observe the landing burn (at that time the moon will be up in Europe where this radio telescope is) and can track the landing.

To put it in a slightly more lay perspective:

1. Before the insertion burn, CY-2 was in a hyperbolic path around the moon - which means, left alone, it would have hurtled away from the moon and never returned
2. The insertion burn changed the path into an elliptical one (which means - an orbit around the moon) - but this is a high-eccentricity orbit (kind of like a comet - e.g. Halley's comet - around the earth)
3. The Doppler plot shows a reduction in the Doppler shift from the pre-insertion-burn path
4. Assuming that the Doppler shift is in the direction of "receding from the earth":
5. This means, after the insertion burn, CY-2 is not receding radially from the earth as fast as it was before the burn
6. (Doppler shifts tell you nothing about tangential velocity component, so all of the below is applicable to the radial component only)
7. This means - the expected shift at around 03:42 was like 3000 Hz, but the measured one was like 2750 Hz - around a 250 Hz difference
8. Since the signal frequency is around 2230 MHz, the reduction in the Doppler shift is like 0.1 parts per million (ppm)
9. So the reduction in the radial velocity component is like 3*10^8 m/s (speed of light) *0.1 ppm, or around 30 m/s
10. Which means, the reduction in the radial velocity component as seen from the earth, from the maneuver which converted CY-2's orbit from a hyperbolic one WRT the moon into an elliptical one, is around 30 m/s, or 100 km/hr or 60 mph
11. So post insertion, CY-2's radial velocity as seen from the earth was less by about the top speed of a cheetah, or about the top (allowed) speed on Indian or US highways

Ain't it remarkable that such minor speed changes can be detected from earth, so far away, on such a relatively small object?

[Varoon Shekhar]

https://www.isro.gov.in/update/26-aug-2 ... ndrayaan-2

Quite a few new pictures of the moon's surface taken by the Terrain Mapping Camera of Chandrayaan-2

[ranneel]

The central curve is the carrier frequency, which was ground locked to the Madrid
tracking station (except for a brief unlock around 03:22UTC). The two other curves are sidebands.

why does isro use double sideband modulation over single side band....any ideas?

[SSSalvi]

^
Why double sideband?
The data bandwidth is very small. So it is not a big problem because the frequency band is specifically allotted for this purpose. ( There is a international body which allocates frequencies for different purposes. E.g. 2G, 4G are internationally assigned for frequency and modulation etc for cellphone communication purpose by that body .)

Moreover the telemetery freq and format is a universally agreed scheme that is why any station in such tasks can receive these signals ( there is a international network .. no one can see the satellites from his antenna round the clock - except Geo-Sync satellites - so the network)

==========================

Unrelated post....

There was a question of Camera resolution.

Just how do they test the cameras?

Here is the camera calibration site used to test ISRO satellite cameras. Both the images show same site.



Each square is made up of different characteristics: different land types, textures,reflectivity, color etc.

The site is imaged by the cameras after they are flown in orbit. Received image is checked for the characteristics as translated by camera in digital values and these values are compared with the expected characteristics. The difference is stored in a look up table and applied to the images received by camera in regular operation.

Now the interesting part: why two images above?

Image on right is captured by Indian Satellite while the image on left is from a US satellite. No comments .