Chandrayan-2 Mission

[Amber G.]

One can see "Mitra" (Named after Indian Physicist Sisir Kumar Mitra

(Dr. Mitra, among other things was JC Bose's student, and worked with Mme Curie).

[Amber G.]

<snip> see post above..
Ain't it remarkable that such minor speed changes can be detected from earth, so far away, on such a relatively small object?

Thanks. Nice analysis by you.
Another remarkable thing to me is ordinary scientists/engineers using routine equipments can enjoy/verify CY2's aspects.
Here one (or anyone with ability to listen to CY2's transmissions) can see delta-V (in radial direction) is consistent with ISRO's postings.

[ranneel]

^
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 .)

The problem with DBS is that the power gets distributed over both the sidebands which is inefficient against single sideband especially if the transmitter is very far which inturn affects signal to noise ratio. Modern cellular access technology use SSB taking advantage of quadrature modulation during up conversion. Probably something to do with legacy specifications so that signal is decodable by any Earth based receiving antennas as you mentioned.

[prasannasimha]

Not everything in military and space engineering is the latest or most efficient but often most reliable or time tested.For eg the processors for both space missions and military are slower than the fastest chips available(in fact many times slower) but things like radiation hardening etc etc are more important. So often a true and tested legacy common standard is often used than the latest methodology.

[prasannasimha]

The US Navy has run into problems with touch screens in some of their naval ships and they are now rethinking of going back to push button type. They had a ship collision recently because the jing bang touch screens failed to respond.

[Amber G.]

Not everything in military and space engineering is the latest or most efficient but often most reliable or time tested.For eg the processors for both space missions and military are slower than the fastest chips available(in fact many times slower) but things like radiation hardening etc etc are more important. So often a true and tested legacy common standard is often used than the latest methodology.

Some computers used by NASA on space probes , IIRC even around space shuttle time in early 80's, had magnetic core memories - (kind IITK's computers had in 1960's or 1970's) - not solid-state ones. Reason was time/tested and reliability. The OS was, again time tested one, not the latest version of MS Windows or such thing .

Richard Feynman did an excellent review of hardware/software used for Challenger (post Challenger disaster presidential review) and writes in detail. One of the positive part was their computer/software - which used old (much old) hardware/software but did not cut corners in reliability and testing. (Details - official Challenger review).

(Note added later: Magnetic core memories do not get affected by radiation (cosmic rays etc) and were tested to be reliable. Solid state memories (unless radiation hardened etc) were not that reliable. Point there was - if the thing works, don't "fix" it with something not tested, even if it is the latest fad.)

[Amber G.]

The US Navy has run into problems with touch screens in some of their naval ships and they are now rethinking of going back to push button type. They had a ship collision recently because the jing bang touch screens failed to respond.

One of my student, (A EE PhD) who is with US Navy (pretty high up rank) told me about the time a aircraft career lost *all* systems (including warning systems) due to, someone's bright idea of migrating the system to new OS (Windows based). The system came down, as the investigation found, due to a non-critical (application) program running which had a bug. This did wake up USN - not to install new (or latest) OS/Hardware without thorough testing and not doing "integration" just because it is the latest fad.

[ranneel]

Not everything in military and space engineering is the latest or most efficient but often most reliable or time tested.For eg the processors for both space missions and military are slower than the fastest chips available(in fact many times slower) but things like radiation hardening etc etc are more important. So often a true and tested legacy common standard is often used than the latest methodology.

I understand your argument regarding radiation hardened processors running at low speeds but if it was in reference to the communication technology regarding SSB thats not an equivalent analogy as SSB is as old as 1915. Looks like a trade-off for a simple detector and cost at the receiving side over efficiency.

[Amber G.]

Posting LOI in 3-D.. (HT: Sankara Viswanathan)

[Amber G.]

Xposting from the other thread - Some serious people may find this interesting.
**

Just to clear up for lay people like myself - there is no perigee and apogee with Chandrayaan-2 at this time, right? It is headed straight for the moon. Then there is the 'lunar capture', which leads to a new set of perigees and apogees around the moon, until it sets in at a more or less 100km orbit indefinitely.

CY-2 is still in elliptical orbit around the earth, this orbit will get it close to the approaching moon around 20th August and enable lunar capture.

Few comments. For lay people as well as serious ones (with good background in physics/math).

- Juvva is basically correct but let me add and amplify:

1. Like everything in physics, NO orbit is *exactly* elliptical but it is a *very* good approximation and sufficient to *understand* basics. Just like we say earth is a sphere but closer we get (or more details) there are mountains and other irregularities. This does not matter if we are looking from space but can matter a lot if we are climbing the mountain.

2. For most planets, (or moon or sats around earth) we can simplify by not considering complications and treat it as a two body problem. Thus we can say moon goes around an elliptical orbit (nearly circular orbit) around earth. But there are perturbations due to effect of Sun, (and even Jupiter and Venus which are quite noticeable.

3. If we look from earth, the orbit of CY2 looks like figure 1 (figure constructed from actual data). Each part of the "orbit" is ellipse (or nearly an ellipse). After each rocket firing, there is different ellipse.
4. When CY2 reaches moon - before LOI, - ignoring moon - the path is such that perigee is where TLI was rocket was fired and apogee is pretty close to moon.
5. After moon's "disturbance"+ LOI rocket - the orbit changes to near circular orbit virtually identical to moon.
(Or course all those ellipses have little "ripples/perturbations/variation" from true ellipse)
Figure 1:


Hope this helps.

If you are looking from the Moon..
(See figure 2 - Sorry, the data for last 3 rocket firings are not available for this picture.. so posting a picture but *not* zooming in for the "orbits" around moon.. so they look like a point only) (You have to imagine that at the end point CY2 is going into elliptical orbit around the moon).

- CY2 looks like a sat orbiting earth (closely at first and then "escaping" and reaching towards moon.
- It is approaching the moon in nearly hyperbolic orbit.
- Near perigee (closest approach to moon) LOI starts.
- The nearly hyperbolic orbit becomes elliptical orbit with very large e.
- After a few more rocket firings - the orbit becomes more circular ending in a circular orbit. (about 100 Km)
- Vikram separates and assumes a elliptical orbit (perigee 30 km or so)
- Vikram soft lands etc..

Figure 2.

-
***Added later: I zoomed on the CY2 orbit from Moon's perspective. (I am using a plane where north pole of the moon is pointing upwards. In previous picture, north pole of the moon is coming towards you - perpendicular to the plane of the computer screen)

From this point of view - CY2 is approaching from right -( almost a straight line, but it is a part of ellipse in X-Y plane -- I am showing Y-Z plane). After the first burn, the orbit now is ellipse, it changes inclination.. almost polar wrt to moon now.. and the orbit is less elliptical after the second burn.



****
If you are looking from Sun:
Nothing much happens - small ripples - everything within few hundred thousand Km over the elliptical orbit of earth (about 150 million Km).

[Amber G.]

The landing point ..( (-70.90267°, 22.7811°) (Bottom of the picture - slightly left from the middle)

[Amber G.]

Added this to my previous message:
>>>
Added later: I zoomed on the CY2 orbit from Moon's perspective. (I am using a plane where north pole of the moon is pointing upwards.)

From this point of view - CY2 is approaching from right -( almost a straight line, but it is a part of ellipse in X-Y plane -- I am showing Y-Z plane). After the first burn, the orbit now is ellipse, it changes inclination.. almost polar wrt to moon now.. and the orbit is less elliptical after the second burn.

[disha]

The landing point ..( (-70.90267°, 22.7811°) (Bottom of the picture - slightly left from the middle)

That area looks so pockmarked with craters, it will be an immense feat to pull this landing off.

[Varoon Shekhar]

What is the LI4 camera, what distinguishes it from the Terrain Mapping Camera aboard Chandrayaan-2? The first photo of the moon was taken by the LI4, the pics of all the craters came from the TMC. Are they distinct? There is no mention of the LI4 as one of the payloads.

[SSSalvi]

The landing point ..( (-70.90267°, 22.7811°) (Bottom of the picture - slightly left from the middle)
----

That area looks so pockmarked with craters, it will be an immense feat to pull this landing off.

It is due to the projection. Actually it is as pockmarked as the equatorial region butdue to the prjection it appears like that.

View of the landing area when seen from directly above is as seen in my earlier post. Regenerated below.



=====
Added later:

The area is relatively flat compared to surroundings.



@AmberG
Very good images in your post 2 posts below ... Great and thanks for sharing

[Amber G.]

^^^One can also see a little more detail and background etc, for example here.
https://www.hou.usra.edu/meetings/lpsc2019/pdf/1493.pdf
For the "landing ellipse" (20-30Km area around the site)

Topography and morphology. The slope map (Figure 2a) generated using
LOLA topography data (~60 m/pixel) reveals that ~94% of the area within the ellipse have slope within 15˚. The remaining 6% of the ellipse have locally steep slopes (>15˚)

images reveals that there are 13600 craters whose diameter is >10 m and only 11 craters with diameter>500 m (

[Amber G.]

I like these images too .. (Primary landing site blue dot, secondary left blue dot)

Wide:

Zoom:

[Mort Walker]

^^^

Are those last two images from CY2?

[Amber G.]

^^^ No, these were mapped using LROC Quickmap, and published in a magazine.

[SSSalvi]

CY2 can't give clean image right now. Camera calibration has to be done after it reaches its final orbit.

Absence of shadows in above images means this could be Radar image.

[juvva]

August 28, 2019

Third Lunar Orbit Maneuver
Third Lunar bound orbit maneuver for Chandrayaan-2 spacecraft was performed successfully today (August 28, 2019) beginning at 0904 hrs IST, using the onboard propulsion system. The duration of the maneuver was 1190 seconds. The orbit achieved is 179 km x 1412 km.
All spacecraft parameters are normal.
The next Lunar bound orbit maneuver is scheduled on August 30, 2019 between 1800 - 1900 hrs IST.

From isro update page.

[Amber G.]

^^^ FRom ISRO Tweet: Third Lunar bound orbit maneuver for Chandrayaan-2 spacecraft was performed successfully today (August 28, 2019) at 0904 hrs IST.

[juvva]

179km x 1412km -achieved
Vs
178km x 1411km -planned

right on the mark !!!

[Amber G.]

HatTip: Sankaranarayana Viswanathan
Want to take a Joyride on CY2..and look out the window: (From actual ephemerides).
Ride so far: First part looking at Earth - then at Moon ...

[SaiK]

Is the next orbit-lowering to go 100x100 circular?

[Vivek K]

179km x 1412km -achieved
Vs
178km x 1411km -planned

right on the mark !!!

I guess the accuracy shows that all is going well with calculations and control. Great job thus far!!

[Vips]

Is the next orbit-lowering to go 100x100 circular?

Next manuever tomorrow is planned to achieve orbit of 126 X 164 and the planned orbit for the final maneuver on Sep 1 is 114 X 128

[Amber G.]

Sharing a few images (From actual data): (For nice animation, see Sankara's animation posted before)

First phase: From Earth to Moon.

[ldev]

Sharing a few images (From actual data): (For nice animation, see Sankara's animation posted before)

First phase: From Earth to Moon.

Thank you for bringing the orbits alive!! Much appreciated. And it is based on actual data so we can see the change in velocity at apogee and perigee!!.

[SriKumar]

In looking at the orbits, it seems like getting into a lunar orbit is more challenging task than getting grabbed by Martian gravity into a Martian orbit (the distance and time delay notwithstanding). Per my memory, the orbit of Mangalyaan did not involve the sharp turns seen above with chandrayaan just prior to getting captured in a circumlunar orbit. CY after goes in moon's circum-earth path for a little bit, and does a double-curve into a circum-lunar orbit. Mangalyaan's was much more like a single smooth elliptical curve with no sharp turns. Same for Maven that went into a polar martian orbit. Myaan was traveling at 31 km/sec i.e. faster than Mars at 24 km/sec and came from behind tangential to Mars' orbit around sun, braked and entered martian orbit. Orbit seemed less complex than the gyrations cyaan had to go through.

[Amber G.]

In looking at the orbits, it seems like getting into a lunar orbit is more challenging task than getting grabbed by Martian gravity into a Martian orbit (the distance and time delay notwithstanding). Per my memory, the orbit of Mangalyaan did not involve the sharp turns seen above with chandrayaan just prior to getting captured in a circumlunar orbit. CY after goes in moon's circum-earth path for a little bit, and does a double-curve into a circum-lunar orbit. Mangalyaan's was much more like a single smooth elliptical curve with no sharp turns. Same for Maven that went into a polar martian orbit. Myaan was traveling at 31 km/sec i.e. faster than Mars at 24 km/sec and came from behind tangential to Mars' orbit around sun, braked and entered martian orbit. Orbit seemed less complex than the gyrations cyaan had to go through.

CY2's TLI was much more challenging but this is for a different reason.. (See note ***).
If one was entering *any* ordinary orbit (eg CY1 ) it will not be that challenging. Mangalyaan would be more challenging as delta-V needed (and V itself) would be larger. Moon has less mass and in general getting into its orbit *much* simpler than Mars. (Remember going to Mars and achieving the orbit in the first attempt was a *BIG* deal while for moon Luna-1 went in around 1966)

***
Note *** What makes CY2 TLI (and other adjustments for the orbit) challenging is that one is setting up Vikram to land at one particular place on the moon (that too near south pole) at one particular time (local morning). TLI achieved a lot of change in inclination (to get to Lunar polar orbit).. MUCH more complex task in the sense that calculations were about 100x time more challenging. ..

Too see this, let me post the TLI delta-V in XY plane (orbit of moon) and YZ and ZX Plane. (As BRF does not allow a hologram or three dim picture-- this is the best I can do ) .. This gives some idea of the challenges CY2 has to transfer the orbit to a polar orbit.

XY plane (orbit of moon's plane):


YZ plane projection:


ZX plane projection:

[Sonugn]

Fourth Lunar bound orbit maneuver for Chandrayaan-2 spacecraft was performed successfully today (August 30, 2019) beginning at 1818 hrs IST as planned, using the onboard propulsion system. The duration of the maneuver was 1155 seconds. The orbit achieved is 124 km x 164 km.

All spacecraft parameters are normal.

The next Lunar bound orbit maneuver is scheduled on September 01, 2019 between 1800 - 1900 hrs IST.

Target - 126 X 164
Achieved - 124 km x 164 km

The next Lunar bound orbit maneuver is scheduled on September 01, 2019 between 1800 - 1900 hrs IST.

https://www.isro.gov.in/update/30-aug-2 ... t-maneuver

[Sonugn]

On Sep 2, separation will happen, is there any time for this?

[ramana]

AmberG, Thanks for the explanation .
Its the corkscrew path to get there.
That accounts for the minor 1km variation in orbits achieved.

S^3 In such planetary travel/orbits 1km off is important no?

[Amber G.]

AmberG, Thanks for the explanation .
Its the corkscrew path to get there.
That accounts for the minor 1km variation in orbits achieved.

S^3 In such planetary travel/orbits 1km off is important no?

Ramana - to add, "corkscrew" part is obviously looking from earth's frame of reference. Here moon is is orbit and CY2 is going around the moon. So the orbit looks like "corkscrew".

Thing I was trying to show is the orbit around the moon is polar. The poles of the moon are tilted about 5 degrees to perpendicular to XY-plane. This is why one sees that the elliptical orbit is is not in the same plane as moon's orbit.

Looking from the moon, the orbits are regular elliptical orbits. These are polar orbits. Again looking through XY, YZ, ZX plane projection to view 3-D part:

Looking from moon - (Red triangle - part is when TLI firing was done)
In XY plane:



In YZ plane:


In Zx plane:

[prasannasimha]

AmberG, Thanks for the explanation .
Its the corkscrew path to get there.
That accounts for the minor 1km variation in orbits achieved.

S^3 In such planetary travel/orbits 1km off is important no?

Not really corkscrew. they are ellipses that are marked in space time to get a corkscrew

[Amber G.]

S^3 In such planetary travel/orbits 1km off is important no?

Perigee/apogee distance and minor variation here is not important. What's important is the orientation (inclination of the orbit) and phase (= timing -- where CY2 is at one particular point in the orbit relative to ground) so that final Vikarm orbit (30km x 100 km) is within the parameters of it heading towards the landing point. This is, actual timing issue as moon is spinning so your timing has to be exactly right so that the particular point on landing on the spinning moon is reached.

Actually final adjustment in the timing is done by adjusting (lowering or elevating) the orbit. If you are "behind" the spot you are supposed to, you actually "slow down" (less delta-V) ==> lower the orbit (thus increasing the angular velocity relative to moon) to "catch up". Pretty complicated and some times counter intuitive. When ISRO says "parameters normal" == much more than values of perigee/apogee.

One analogy I like to give: Hitting a wicket with pin-point accuracy is impressive but imagine a wicket where the cylinder shaped wicket is spinning fast and there is a small dot on the wicket. And one hits that fast spinning dot with pin-point accuracy. (And that too when dot is facing one particular direction -aka morning at a point on moon )
-- Landing a rover on a preselected point is *many* times more difficult than putting a space-craft in a random orbit.

[prasannasimha]

S^3 In such planetary travel/orbits 1km off is important no?

Perigee/apogee distance and minor variation here is not important. What's important is the orientation (inclination of the orbit) and phase (= timing -- where CY2 is at one particular point in the orbit relative to ground) so that final Vikarm orbit (30km x 100 km) is within the parameters of it heading towards the landing point. This is, actual timing issue as moon is spinning so your timing has to be exactly right so that the particular point on landing on the spinning moon is reached.

Actually final adjustment in the timing is done by adjusting (lowering or elevating) the orbit. If you are "behind" the spot you are supposed to, you actually "slow down" (less delta-V) ==> lower the orbit (thus increasing the angular velocity relative to moon) to "catch up". Pretty complicated and some times counter intuitive. When ISRO says "parameters normal" == much more than values of perigee/apogee.

One analogy I like to give: Hitting a wicket with pin-point accuracy is impressive but imagine a wicket where the cylinder shaped wicket is spinning fast and there is a small dot on the wicket. And one hits that fast spinning dot with pin-point accuracy. (And that too when dot is facing one particular direction -aka morning at a point on moon )
-- Landing a rover on a preselected point is *many* times more difficult than putting a space-craft in a random orbit.

That was actually Bizz Aldrin's PhD Thesis where he showed that you need to be at a lower orbit to catch up and higher orbit to slow down which is used in various rendezvous maneuvers in space(V bar/X bar approaches)

[Amber G.]

Perigee/apogee distance and minor variation here is not important. What's important is the orientation (inclination of the orbit) and phase (= timing -- where CY2 is at one particular point in the orbit relative to ground) so that final Vikarm orbit (30km x 100 km) is within the parameters of it heading towards the landing point. This is, actual timing issue as moon is spinning so your timing has to be exactly right so that the particular point on landing on the spinning moon is reached.

Actually final adjustment in the timing is done by adjusting (lowering or elevating) the orbit. If you are "behind" the spot you are supposed to, you actually "slow down" (less delta-V) ==> lower the orbit (thus increasing the angular velocity relative to moon) to "catch up". Pretty complicated and some times counter intuitive. When ISRO says "parameters normal" == much more than values of perigee/apogee.

One analogy I like to give: Hitting a wicket with pin-point accuracy is impressive but imagine a wicket where the cylinder shaped wicket is spinning fast and there is a small dot on the wicket. And one hits that fast spinning dot with pin-point accuracy. (And that too when dot is facing one particular direction -aka morning at a point on moon )
-- Landing a rover on a preselected point is *many* times more difficult than putting a space-craft in a random orbit.

That was actually Bizz Aldrin's PhD Thesis where he showed that you need to be at a lower orbit to catch up and higher orbit to slow down which is used in various rendezvous maneuvers in space(V bar/X bar approaches)

Not to go OT, but Buzz Aldrin, AFAIK, is the only PhD (that too from MIT) astronaut. His nickname in old days was "Dr. Rendezvous" for his work... The theory and methods are also used as basically landing of CY2 is a kind of "rendezvous maneuver" with the moon.

For perspective, With respect to Apollo 11's path and time windows for launch -- where one has to land on a particular point on the moon (I knew some of the people involved in calculations):
- It took months of calculations (using best computers and scientists) to calculate time windows and path specifics.
- If they miss the launch window, next launch would not take place for months (or more).

We now know methods, data (or all planets and their gravity wells) and fast computers, and precise controls (to deliver delta-V with high degree of accuracy) so we take all this for granted. For CY2 , we missed the first window but we were still able to launch CY2 etc and kept most of the landing parameters same.

[Amber G.]

I think there ought to be a crater on moon named after Kalam. (ISRO should lobby for it)
(We have Aryabhatta, Sarabhai, Mitra etc but I don't think there is a crater named after Sri Kalam)