Chandrayaan 3: Launch and Discussions

[madhu]

S^3 , I am not very clear. here is a plot of Lagrange Points of the Earth-Moon System.



so what you are saying is CY3 during TLI, will be pushed to L1 and further just a nudge to orbit the moon? which means during TLI it is just a huge ellipse whose perigee apogee matches with L1.

is my understanding correct?

[SSSalvi]

In case of Earth-Moon pair The L1 distance from earth centre is 323050 Kms.( 316672 kms above Earth. )
For TLI orbit Apogee is 362000 kms, way beyond L1.







Moon is away when CH3 is in the Apogee. In fact the CH3 is moving away from Moon initially. But its speed is more so it comes towrds CH3.
As time passes, Moon comes near CH3, pulls the Ch3 towards it ( ie reversing of CH3 direction of movement ) and soon CH3 enters in Moon orbit about 18000Kms X 200 Kms.

This ppt tries to emulate the movement .. I could not ( yet ) been able to create the orbit around moon so celetial movie could not be generated.
https://youtu.be/qP4eu72ptNM

[sanman]

[madhu]

so what you are saying is CY3 during TLI, will be pushed to L1 and further just a nudge to orbit the moon? which means during TLI it is just a huge ellipse whose perigee apogee matches with L1.

is my understanding correct?

Moon is away when CH3 is in the Apogee. In fact the CH3 is moving away from Moon initially. But its speed is more so it comes towrds CH3.
As time passes, Moon comes near CH3, pulls the Ch3 towards it ( ie reversing of CH3 direction of movement ) and soon CH3 enters in Moon orbit about 18000Kms X 200 Kms.

if green line is CY3 then it has to move reverse its direction which means we need more fuel and not efficient. more over even the video above at ~2.10min shows that CY3 keeps moving forward as i have shown.

[SriKumar]

Interesting conversation. My original question was triggered by the thought that the Orbital Plane of the CY3 when orbiting the earth i.e prior to (and ever during) trans lunar injection is a different plane from its orbital plane around the moon. To go from an earth orbital plane (roughly equatorial plane, but with some declination angle which I did not check) into a polar orbital plane around the moon takes some high force.

Now gravity of the moon (or any object) will apply a force that will pull it to the center of that object (moon). So crossing the Lagrangian point will definitely pull it into a lunar orbit, but I dont think this alone will alter the orbital plane. The change in velocity vector will be in the same plane as its original orbital plane.

This was my thought process earlier but as I wrote the above, I realized that if the trajectory of CY2 is such that it 'enters' the lunar gravity field near its poles, I can see how this would change the orbital plane. Need to mull this over.....

Madhu: your diagram above assumes that all the orbits (around earth and the moon) happen in the same plane. I think this may not be exactly right becausethe CY3 orbit around the moon is about its poles (and moon's axis of rotation is generally parallel to earth's axis, but not exactly. The exact angles can be googled but they are not 90 degrees apart)

[madhu]

Madhu: your diagram above assumes that all the orbits (around earth and the moon) happen in the same plane. I think this may not be exactly right becausethe CY3 orbit around the moon is about its poles (and moon's axis of rotation is generally parallel to earth's axis, but not exactly. The exact angles can be googled but they are not 90 degrees apart)

Yes my diagram is highly simplified also not considering time. The main point is to discuss efficient path as I could not understand S^3 diagram. My understanding is to approach L1 such that forward movement will be in polar orbit of moon. My point is moving from leading edge is more efficient than trailing edge.

[arvin]

In case of Earth-Moon pair The L1 distance from earth centre is 323050 Kms.( 316672 kms above Earth. )
For TLI orbit Apogee is 362000 kms, way beyond L1.

Moon is away when CH3 is in the Apogee. In fact the CH3 is moving away from Moon initially. But its speed is more so it comes towrds CH3.
As time passes, Moon comes near CH3, pulls the Ch3 towards it ( ie reversing of CH3 direction of movement ) and soon CH3 enters in Moon orbit about 18000Kms X 200 Kms.

Thanks Salvi sir for the above info.

Plotting with above figures with everything in straight line, we get CY3 5th orbit apogee is almost 40000 km inside earth moon langrange point L1 which is 61350 km from center of moon.

To summarize, with CY3 moving away from 5th orbit apogee, the capture of CY3 in moon orbit happens somewhere in the range of 20000 to 40000 km above the moons surface?

[SSSalvi]

https://sankara.net/chandrayaan3.html
A nice 3d fine grain rendering by Shankar brings out the details ( My diagram is a coarse rendering. )

The inflection due to Moon is clearly seen.

[SSSalvi]

To summarize, with CY3 moving away from 5th orbit apogee, the capture of CY3 in moon orbit happens somewhere in the range of 20000 to 40000 km above the moons surface?

You are on dot!
CH3 moves in Last earthbound orbit upto 30000 kms from Moon. Orbital velocity is already as low as about 0.2 kms/s because CH3 is at Apogee.
Now even a small tug from Moon is sufficient to pull CH3 in its direction. And .. that exactly is what is seen.
Ch3 was moving along last apogee from Left to right in the view seen in last diagram.
Then because of pull by Moon, the velocity reduces and after a momentary 0 it reverses and starts increasing.
It is a treat to watch distances and speeds being displayed at Left Bottom of window.

A mistake in timing and distances could throw CH3 to surface of Moon or in a very large Apogee orbit.

You could see a last correction ( a kink in the path after Perigee near Earth ) in TLI orbit to manage these conditions.

[SriKumar]

https://sankara.net/chandrayaan3.html
A nice 3d fine grain rendering by Shankar brings out the details

The inflection due to Moon is clearly seen.

[[/img]

Thanks for posting this. Very impressive piece of work...a service to the public. Wonder where he got the trajectory data. The level of detail is amazing, the lunar axis is shown, as is the approaching moon. Effectively, ISRO will bring CY3 in front of the approaching moon and essentially 'park' it there in its path (zero velocity for a brief period of time). With this approach (both figuratively and literally speaking), CY3 can be placed into any orbit about the moon in any plane they want, using only small thrusters to adjust the orbit, but this needs a high level of precision in placement and timing of the 'placement' of CY3. ISRO could have taken a different strategy....wonder why this one was chosen (to come to zero velocity).....maybe its allows them to reset/calibrate the velocity instruments, and perhaps gives them more control over CY3's movement.

[madhu]

Sssalvi, never thought CY3 would stop and reverse the direction. None of the animations shown in TV show this.

[SSSalvi]

Wonder where he got the trajectory data

ISRO ( and for that matter all responsible Space operators ) posts planned trajectories ( at least for non standard Launch activities ) on NASA's Horizons data base.

https://ssd.jpl.nasa.gov/horizons/app.html#/

Upto Launch full program was available ( even Lander activities ).

But, post Launch only the realized data is available. ( e,g, presently data available only till next correction ).

Because it is purely scientific data , only enthusiasts wander that heaven.

[disha]

SSSalvi'ji, Thanks for the above image and also the site

https://sankara.net/chandrayaan3.html
A nice 3d fine grain rendering by Shankar brings out the details

The inflection due to Moon is clearly seen.

----

Coming to the image, think of the lines as contour lines on a terrain map. One will get concept of the Earth's gravity well and within that the Moon's gravity well.

Put it this way, take a sand box and make a wide bowl into it and take a big blue marble called Earth and put it in the center of the bowl. Think of that as the Earth's gravity well. In that gravity well (The sand bowl), create another smaller sand bowl. Let's say at 2/3rd the distance from the Earth. In that smaller bowl, put a white marble called Moon and it is the moon's gravity well.

Here C3 is a bead that circles around Earth several time, at each circle, it is trying to reach the edge of the Moon's gravity well, such a way that at one point it will just have enough momentum that it will fall into Moon's gravity well and then start circling around the moon.

That's one way to visualize it.

Another way is to look at the 3D link of above and rotate it such a way that the RBG axis are orthogonal to each other. At that point you are looking top down (or bottom up) to the Earth-Moon system.

Now visualize yourself as a chef who is throwing rumali roti called C3 up towards the moon. Each time you are imparting some velocity for it to reach it higher and higher and at one point it reaches just high enough while the moon is ahead of it that while falling down the roti (C3) starts falling towards the moon. That is when C3 is captured into Moons' orbit.

The way kids need to be thought is via the sand models above or by visualizing Sun and other planetary bodies in a vertical stack (Sun at Bottom, Neptune at top) and show how one can launch sats to Mars by throwing the sat up and up and then get it captured into the Mars' orbit. And do the same for Earth-Moon system.

This will also help visualize what happens if Earth' suddenly looses gravity. We will be all superhumans hurtling down (or up towards Sun).

[disha]

Sssalvi, never thought CY3 would stop and reverse the direction. None of the animations shown in TV show this.

I do not think it stops and reverses the direction.

Let's take the approach from Image above (with all the L* points)

C3 is a falling object, depending on perspective, it goes towards the L1 point and its velocity is almost zero and falls into the Moons gravity well from that point, as it falls towards the moon, its orbit (as depicted from Image 1) goes retrograde to its initial orbit on Earth. And starts falling towards moon.

If you take the 3D animation chart, it appears that C3 is firing its motors such a way that its apogee will be at L2, and the orbit is aligned on the edge of the moon's gravity well, such a way that when it starts falling, a small motor burn makes it fall towards the moon. Think again of this as taking your extended right arm in an high arc over your head (which is Moon) and goes over and while coming back down, on the other side is captured into Moons orbit (or the tip of your right arm is just few inches away from your left ear).

It could be that my interpretation of the 3D animation chart may be off and instead of L2, it is indeed C3 @ L1 and captured into Moon's orbit. Which will be same as the image depicts.

Either way, it is a nice & delicate dance and whole load of calculation and mastery of trajectories.

---

PS: DDM is going to kill science in next few days.

[SriKumar]

The data plotted on https://sankara.net/chandrayaan3.html is from Horizon- a JPL website which received data from ISRO. The level of detail is extra-ordinary and could have come only from ISRO or completely made up (which is less likely given that they have data for past ISRO missions- CY2 and MOM, and not been debunked).

The CY3 TLI trajectory clearly places it well beyond the L1 point and right in the middle of the moon's orbital path around earth, and in fact, a little past that. It gets to this point before the moon gets there. The moon, at this point, is still quite far away and has not yet reached the rendezvous point. As moon gets closer, it pulls CY3 towards itself in the process, negating its forward velocity (already very low) and then pulling CY3 towards itself with ever-increasing velocity permitting it to orbit the moon.

[SSSalvi]

Horizons is a sophisticated and accurate astro calculator.
You could get output even upto 0.5 sec interval. It is your choice. All scientific and authentic.
Shankar's ( or mine ) graphics were made days before CH3 was launched and they are accurately matching with actuals.
I had made several educational blogs in almost real time during MOM ( Mangalyaan ) to make common man aware of science ( and to remove misconceptions - even now some said India takes a month while other countries take much less to reach Moon ).
Sharing a few images made using output generated through Horizons:

[madhu]

Sssalvi hi, whats ur blog? Can u post the like. Thx
Disha hi thanks for clarification.

[Amber G.]

Interesting conversation. My original question was triggered by the thought that the Orbital Plane of the CY3 when orbiting the earth i.e prior to (and ever during) trans lunar injection is a different plane from its orbital plane around the moon. To go from an earth orbital plane (roughly equatorial plane, but with some declination angle which I did not check) into a polar orbital plane around the moon takes some high force..."

FWIW: (For those who are interested in Technical details - need basic math/physics - look up in any text book for more details) . SriKumar, hope this helps.

To make it clear - (Basic astronomy/physics) the 'planes' here:
Earth - (Earth's Equatorial Plane) - Plane of Earth's equator Most people use this coordinate system to locate the position.
For orbits near the earth you measure the distance from center of earth of the sat. The plane of the orbit is defined by inclination of the orbit. (You also need the position of the node and the position of perigee and time to calculate the position)

Ecliptic - This is about about 23.5 deg. from Equatorial plane . (as you said)
Moon's Orbit plane - this is tilted about 5 degree from ecliptic --- This is roughly the orbital plane of CYIII for almost all of it's journey.... (Except beginning and end when CYIII will change the inclination to go in polar orbit)
Moon's Equatorial plane. - This is tilted about 1.5 degree wrt to ecliptic and (and about 6.7 degree to CYIII orbit plane up till now) so CYII has to do some major change in orbit inclination once it starts orbiting the moon.

Once in orbit around the moon, using Moon as center would be easier to calculate the orbit...

With Horizon system (see links posted here), one can calculate the orbit/plane etc.. Here the position will be post TLI.. (Orbits projection on two different planes. ... to make it clear..)

[Amber G.]

The data plotted on https://sankara.net/chandrayaan3.html is from Horizon- a JPL website which received data from ISRO. The level of detail is extra-ordinary and could have come only from ISRO or completely made up (which is less likely given that they have data for past ISRO missions- CY2 and MOM, and not been debunked).
<snip>

Sankaranarayanan Viswanathan's (a fellow IITian ) simulation - has been posted here before --- In fact with CYII and MOM etc..

--- To be clear The orbit calculations/simulation can be done for any object from Horizon/JPL system.. Interesting thing about it (for me) is all the calculation is being on on your browser .. and anyone can use it. (ISRO supplies the orbit elements and the rest of the calculation is done fairly accurately. ( new date is needed only when orbit corrections are applied and new orbit elements are loaded in this simulation) Since it has *large* amount of data for all planets (and how the surface looks) and *many* other satellites, it can produce very impressive simulation...one can actually take a 'joy ride' and see what it will look like if you are able to look out of the window...

[Amber G.]

Sssalvi, never thought CY3 would stop and reverse the direction. None of the animations shown in TV show this.

Probably I don't understand the context - FWIW: In strict sense it does not exactly , 'stop and reverse' ... This is how I will explain to my students:
Basically: CYIII after TLI, burn, is on highly elliptical orbit --- perigee is quite near the earth, while apogee is as far as moon..in fact when it reaches the apogee moon happen to be also close by - the timing is right.

-- If no rockets are fired, CYIII may come back to earth (or become a sat going around the Sun - orbit will be deflected a little (or more - depending on a few factors ) by Moon's gravity but CYIII, I think will not be captured or orbit the moon.... (It depends on many factors but I think this is most likely ... I may have to do actual calculations using actual TLI data). (In fact US's Men Moon Mission, depended on this -- if something goes wrong -- not enough fuel - they can return back to Earth)

--- When it is near the moon ( or in case of MOM near Mars), the rockets fires to *slow* down .. (In case of MOM , orientation has to be changed to put the rockets in the right direction).. the orbit around the moon becomes less 'elliptic' (wrt to moon and goes around orbit of moon. Few corrections later, the orbit around the moon becomes circular (and plane of the orbit changes close to 85 deg to make it polar wrt to moon).

(LOT depends on timing, and actual velocities etc -- so let us wait till TLI to show more accurate prediction).


-

[sanman]

Sssalvi, never thought CY3 would stop and reverse the direction. None of the animations shown in TV show this.

Best to just see this in terms of gravitational capture. CY-3 is passing close enough to the Moon, so that firing its rockets will slow it down enough to allow it to be captured by Moon's gravity.

Forget about zooming out and seeing some larger trajectory map in relation to Earth. Once you start getting close to the Moon, its frame of reference becomes more important, because that's what you're trying to orbit around. So switch to the Moon's reference frame, and leave the past behind - the Moon becomes your new centre for you to orbit.

[sanman]

[Tanaji]

Amberg:

What does the red triangle indicate in your pictures?

[SSSalvi]

Best to just see this in terms of gravitational capture. CY-3 is passing close enough to the Moon, so that firing its rockets will slow it down enough to allow it to be captured by Moon's gravity.

Forget about zooming out and seeing some larger trajectory map in relation to Earth. Once you start getting close to the Moon, its frame of reference becomes more important, because that's what you're trying to orbit around. So switch to the Moon's reference frame, and leave the past behind - the Moon becomes your new centre for you to orbit.
[/quote]

When you are at zero speed and there is an increasing pull in Backward and UP direction what else will happen? Either orbit in NS orbit or crash into it ( very very unlikely , seeing the past track record of drama producers/directors ).

[SSSalvi]

so CYII has to do some major change in orbit inclination once it starts orbiting the moon.

Near Left Bottom in TLI orbit

[SSSalvi]

Amber G:

so CYII has to do some major change in orbit inclination once it starts orbiting the moon.

FRom Shankar animation. Left Bottom corner.
Already incorporated in planning ....



Plus the fact that 1st orbit is huge and is reduced by the time 2nd orbit starts.

[Amber G.]

Amberg:

What does the red triangle indicate in your pictures?

Direction towards z-axis (North)
(CYIII's orbital plane is tilted wrt to ecliptic (or Earth's equatorial plane). It is approx same as moon's orbit around earth)

Sankaranarayanan Viswanathan calculations gives projection (or 3D) on any plane)...

Waiting for looking out and see something like this in a few weeks...

HT: S Viswanathan

[Amber G.]

Sankaranarayanan Viswanathan have updated #Chandrayaan3 animation. This is to match with the most recent version of orbit data from JPL HORIZONS. This is dated 21st July and extends, (I think) up to 8th August. Lunar orbits beyond that time will depend on the new data....

New addition is stellar sky background .. from NASA data so star image (with a constellation outline image) is realistic


HT: S. Viswanathan,

[Amber G.]

Dup post.. deleted

[Amber G.]

Best to just see this in terms of gravitational capture. CY-3 is passing close enough to the Moon, so that firing its rockets will slow it down enough to allow it to be captured by Moon's gravity.

Forget about zooming out and seeing some larger trajectory map in relation to Earth. Once you start getting close to the Moon, its frame of reference becomes more important, because that's what you're trying to orbit around. So switch to the Moon's reference frame, and leave the past behind - the Moon becomes your new centre for you to orbit.

Having Moon as reference system makes sense in that phase...

[arvin]

Amber G, the quoted part in your above post is written by sanman. SSSalvi missed the "quote" while quoting him so its seen as a continuos post.

[Amber G.]

^^^ Thanks. (I had a chance to look at all the posts..,, pretty good.

It is the matching of timing and distances that the ISRO magicians are playing and then watching the fun.

Indeed! (There was a time - I did watch/followed Apollo 11 live - when months of calculation using best computers were used just to get the launch window correctly..-- of course the onboard computer on Apollo was using magnetic core memories - 4KB RAM, and 32KB (Yes Kilo-bytes) of hard disk -- (Weight about 30kg for the box) -- the burn which will let moon 'capture' and put it in the lunar orbit was quite tense - as the burn had to take place when astronauts could not contact with earth and have to depend on the onboard computer. If something went wrong (as it happened indeed for Apollo 13) they will not do the burn, and the trajectory (as planned carefully) will bring them back to Earth...

We have come a long way!

This was 54 Years ago..

[Amber G.]

Good Night!
Will leave you with:
Now, looking from CY3 back towards home:


Looking at CY3, Earth, Moon from far away:


Looking from Home at CY3: (Live stream - Tracked with the latest trajectory data from JPL/Horizons -- 0.4° beam width -- 20m antenna Bochum. They have been following CH3 2241.6 MHz 8K telemetry the whole time.

[Cyrano]

Nice discussion. Thank you guru log ! Keep it coming.

[ramana]

RahulM, I saw a ppt of 11 changes between CY-2 and -3 and one of them is less instruments due to using CY-2 as the relay.

If you are on TG can send the file.

Emailed TG id to you

check your id.

[Amber G.]

Also - ESA Kourou and Goonhilly (GES Ltd)' are also supporting Chandrayaan3 - alongside NASA and ISRO ground stations during the whole journey - during the lunar descent and through to the end of lunar rover surface operations roughly 14 days later. They are assisting ISRO with tracking, commanding and receiving data from the spacecraft.

[hgupta]

Can India set up her own independence by creating its own communication network that would basically sidestep the need to use US Deep Space Network and be subject to US's whims and requirements?

[SSSalvi]

^^^
It is not the technology that India has to depend on other countries , India has its own stations.

As you can see in Image above India location does not allow communication over locations 3 and 4... so it has todepend on stations in that region.

In fact these stations are used internationally by all responsible space entities round the world.

[Dilbu]

Is there a twitter handle where ISRO is providing live update on the status of CY3?

[SSSalvi]

Dilbu asking??????

https://twitter.com/isro/