Chandrayaan 3: Launch and Discussions

[Amber G.]

Chandrayaan3 orbit data has been updated at @NASAJPL HORIZONS post TLI. (So in Sankara V. data - so the animation link posted here is also been updated now. Looks like LOI seems to be around 5th August, 7:19 pm IST.

Meanwhile when I look out in our front yard, I see:


Of course, If I was on CY3, this would have been the view:


--- If you click on the above picture, you can see how moon looked, from CY3's perspective for last few weeks... you can even see liberation..

[vimal]

UAE is much smaller than us, and yet they also sent a mission to Mars not long after us. It shows they are not small on ambition, howsoever small their size. Meanwhile I see that indian tendency is to strut a lot in advance, and then stumble on execution.

Usually I ban a poster for posting claptrap like this. sanman, since this is the first time you are catching attention, a warning issued. Keep your opinions about UAE’s technology awesomeness or India’s shameful behavior off this forum. Use some personal social media profiles for such posts

Serious OT but I think we need to set the record straight w.r.t UAE Mars probe.

A casual Google search tells me that UAE Mars probe was built with the help of 3 American entities and launched from Japan. So basically a green paint job over phoren maal like our green biraders from west. This with endless amount of money unlike ISRO.

I can go out on a limb to say that UAE is mission is basically a NASA mission.

[Ashokk]

https://twitter.com/isro/status/1686327939280035840

Chandrayaan-3 Mission:

The spacecraft’s health is normal.

Today’s perigee burn has successfully raised Chandrayaan-3 orbit to 288 km x 369328 km.

In this orbit, the spacecraft enters the moon’s sphere of influence.

A crucial maneuvre at perilune would achieve the Lunar Orbit Injection (LOI).
12:48 PM · Aug 1, 2023

[vnms]

Since I have not seen too many pictures taken from CY3, yet, let me share this
#Chandrayaan3 journey from 14th July through TLI later today and initial lunar orbits until 8th August -
25 days packed into an 80 second video
HT: Sankar V. animation, JPL, Horizon .. (Video is posted here with permission).
This video, I think has been shared in a few SM platforms.

The perspective, including star background is mathematically correct.
(You see time-period of orbit getting longer... the camera position switches from looking towards earth to the moon in the later part of the video)

Enjoy.

Great simulation.

A quick question. Is CY3 supposed to be in a polar orbit. From the vid, it does not look so. Or I might be mistaken

[nitzter]

Great simulation.

A quick question. Is CY3 supposed to be in a polar orbit. From the vid, it does not look so. Or I might be mistaken

Draw a straight line from CY3 to the centre of the moon and fix the observer at a set distance away from the moon on that line. You will get the perspective this video suggests...

Not a perspective of an observer moving in the direction of the flight path.

[disha]

A quick question. Is CY3 supposed to be in a polar orbit. From the vid, it does not look so. Or I might be mistaken

CY3 *will* be in polar orbit around Moon. It will be similar to C2. Check the mission profile of the C2 on page 83 https://web.archive.org/web/20160304201 ... 014-15.pdf

The simulations are good learning tools and provide excellent perspectives with respect to a reference frame. Remember in space there is no top or down or east or west or north or south. For example, the video view is with a reference of an observer sitting on top of the C3 with the top pointing to a celestial North, the celestial North is from the perspective of the frame of reference of Earth.

If all of this gets confusing, just sit on top of the C3 and enjoy the ride.

[SSSalvi]

A quick question. Is CY3 supposed to be in a polar orbit. From the vid, it does not look so. Or I might be mistaken

Lander is supposed to hover the South Pole of Moon .. so orbit around Moon has to be Polar, For dropping of Lander.

Yes, It will be a Polar orbit.

Rover will communicate with Lander.
Lander will communicate with CH2 Orbiter and also with DSN network on Earth.

[Amber G.]

^^^ To add to above ... orbit will be polar, circular .. about 100 Km finally...

Since I have not seen too many pictures taken from CY3, yet, let me share this
#Chandrayaan3 journey from 14th July through TLI later today and initial lunar orbits until 8th August -
25 days packed into an 80 second video
HT: Sankar V. animation, JPL, Horizon .. (Video is posted here with permission).
This video, I think has been shared in a few SM platforms.

The perspective, including star background is mathematically correct.
(You see time-period of orbit getting longer... the camera position switches from looking towards earth to the moon in the later part of the video)

Enjoy.

Great simulation.

A quick question. Is CY3 supposed to be in a polar orbit. From the vid, it does not look so. Or I might be mistaken

Thanks. The simulation is mathematically correct.. up till the Next LOI (5th August, 7:19 pm IST).. There will be about 4 or 5 more burns till it achieves a 100 Km Polar orbit. .. .. After new data (post LOI) more accurate orbit will be available to plot using JPL/Horizon/Sankar V...
At present.the orbit (wrt to moon) is quite elliptical...



--- To get the orientation right ..(seeing the correct direction etc).. star background has been added in the picture..(again mathematically correct .. so those who are familiar with stars could get the perspective correct)

[Amber G.]

To be clear, the simulation I posted above ... posting it again, as I think it is quite nice one.. (Click on image to see the video:


This is what if we look at the moon from CY3..

By the way at the time of the post the orbits are: (CY3 is still some distance away from the moon ...)

Wrt to Earth (Moon goes around Earth too)


Wrt to Moon:

[Amber G.]

Per Horizon/JPL data update for Chandrayan3 it looks like he closest lunar approach upon insertion seems to be 202 km altitude occurring at 7:29 pm IST on 5th August. (I have not seen any recent updates from ISRO)

[Amber G.]

Above post (The closest approach 202 Km (at 7:29 PM IST)) - per JPL/Horizon data , is consistent with ISRO's following Tweet/post

Chandrayaan-3 Mission:
The spacecraft has covered about two-thirds of the distance to the moon.
Lunar Orbit Injection (LOI) set for Aug 5, 2023, around 19:00 Hrs. IST.
(The closest lunar approach upon insertion seems to be 202km altitude occurring at 7:29 pm IST on 5th August)

The present orbit (per ISRO's post I saw) is 288 Kms perigee (altitude) and 369,328 Kms apogee - if you want to do your own calculations (simultations) -- (The orbit is still earth-centric if you want to use the formulas I posted here ..)

[ramana]

Disha and SS Salvi et al can you guys write an article showing the complex orbit pictures so lay people can understand?
And attribute AmberG as a mentor.
The S//M hardly has the intricacies we discuss.
Nor does ISRO!

[Amber G.]

While waiting for LOI, just for fun doing some calculations ..remembering classical Newtonian mechanics (I had fun teaching those graduate courses with central force and elliptical orbits).. Playing with JPL/Horizon data/ Sankar V's excellent app..

(The closest lunar approach upon insertion seems to be 202 km altitude occurring at 7:29 pm IST on 5th August
I don't have official ISRO ephemeris but ist should be close )

Sharing some positions/orbits as I post: (All on scale - HT Sankar V)
(Some pictures have stars/constellations in the background - Again accurately so one can get the directions correctly -- for those who are familiar with stars and constellations - There are no up or down like we use on Earth but star background is same if you look from earth or the moon and unlike Sun or Moon etc, there position do not change with time... )

(At present, as I post, (11:24 EDT = GMT -4) CY3 is about:

From Earth - 362,000Km (from center) , speed 0.25 Km/sec (wrt to earth)
From Moon - 83,250 Km (from center, about 81,510 from surface), speed = 0.90 Km/sen (wrt to moon)
From Sun - Of course, ~ 150 Million Km, speed = 30 Km/sec (wrt to Sun) etc
Date and Time stamp:

Orbit XY- Plane (Earth Perspective) (This is 2-D plane - in which moon orbits around Earth - Most(almost all) orbits of CY3 are roughly in this plane though it does a do a small amount of up-down ( direction of North Pole of Earth/Moon is up here) on this plane -- final orbit of CY3 will be perpendicular to this plane)

At present:

In 3D - At the time of LOI (Closest approach to the Moon)



Different perspective Orbit: YZ Plane:


Moon Perspective:



If all goes well, at LOI if you look out the window of CY3:


-- After LOI ( Tomorrow) - after last update on the burn and new orbit(s) will be more precisely calculated - Probably there will be 4- 5 burns, (all carefully planned and calculated by ISRO - I am still impressed with how accurate they can manage the burn) before a nice polar circular orbit is achieved.

[disha]

Disha and SS Salvi et al can you guys write an article showing the complex orbit pictures so lay people can understand?
And attribute AmberG as a mentor.
The S//M hardly has the intricacies we discuss.
Nor does ISRO!

Ack.

[sanman]

Could Chandrayaan-3's lander do another short hop later on after landing?
An interesting idea worth pondering.

https://notes.jatan.space/p/will-chandr ... er-landing

[Amber G.]

As I post, ISRO: Chandrayaan-3 should begin its Lunar Orbit Insertion maneuver any time now.

Good luck, Chandrayaan3 for a successful LOI. I will post post LOI orbit, once it is available from JPL/Horizons.


Here is the what is calculated right-now from the orbit (These are not official ISRO figures, but calculated from orbit elements available)

Closest approach: Aug 5, 9:59 AM (Ohio, AmberG's Time (EDT) = GMT -4)
Distance from Earth's Center: 366,741 Km, Velocity 2.52 Km/Sec
Distance from Moon: 1939.47 Km (from Center of the Moon), Altitude: 202.07 Km, Velocity 2.41 Km/sec


(Anyone who gets TLE from Isro or other sources please post it here, TIA>)

Meanwhile
.NASA has reestablished full communications with Voyager 2. From 19.9 billion km into interstellar space, instructing it to turn its antenna back to Earth – and after 37 hours, it worked.

[Amber G.]

^^^ The burn has started and seems to be going well..
Hearing that there would be an official update from ISRO at 745 pm.. that's minutes from now..



(I am watching live stream)

[Ashokk]

https://twitter.com/isro/status/1687829587018100736

Chandrayaan-3 Mission:
“MOX, ISTRAC, this is Chandrayaan-3. I am feeling lunar gravity ”

Chandrayaan-3 has been successfully inserted into the lunar orbit.

A retro-burning at the Perilune was commanded from the Mission Operations Complex (MOX), ISTRAC, Bengaluru.

The next operation - reduction of orbit – is scheduled for Aug 6, 2023, around 23:00 Hrs. IST.

[Amber G.]

FWIW: This live stream may be interesting to some people here:

[Ramesh]

Data showing some variation from the planned graph.

[SSSalvi]

Status as at 8PM IST



All seems to be going on well ... the deviation seems to be not abnormal - Predicted data is about 3 4 days days stale ( on Horizons ).

Of course this display is not official but surely mathematically authentic.

[Amber G.]

S^3 .. thanks. Hope, ISRO publishes/tweets new orbit data officially.

Congratulations ISRO on the LOI milestone! From all accounts, the burn was very successful and impressive. (The doppler data etc looks extremely good and except for the final landing of Pragyan and Vikram - which is challenging - all remaining orbit burns s seems to be routine for ISRO).

(No there is NO sense in noting "Data showing some variation from the planned graph" type statements. The burn was extremely successful).

Plugging in the numbers available now - looks like the perigee, or altitude (distance from surface of the moon) of the current orbit is about 115 Km - which is very good.

Again, orbits are mathematically correct, (but not official )

[SSSalvi]

Meanwhile
.NASA has reestablished full communications with Voyager 2. From 19.9 billion km into interstellar space, instructing it to turn its antenna back to Earth – and after 37 hours, it worked.

Great news fo the grey hair... Missed in the glare of CH3 .
Thanks

[Amber G.]

^^^^ Yes, more details - Perhaps slightly OT for this thread - but probably not as to see how accurately we can predict orbits, and reestablish communications even with old electronics after decades, and to give some idea how powerful radio telescopes (in tracking CY3 etc) are ...... here is the story many will find interesting...
NASA Mission Update: Voyager 2 Communications

UPDATE, Aug. 4, 2023: NASA has reestablished full communications with Voyager 2.

The agency’s Deep Space Network facility in Canberra, Australia, sent the equivalent of an interstellar “shout” more than 12.3 billion miles (19.9 billion kilometers) to Voyager 2, instructing the spacecraft to reorient itself and turn its antenna back to Earth. With a one-way light time of 18.5 hours for the command to reach Voyager, it took 37 hours for mission controllers to learn whether the command worked. At 12:29 a.m. EDT on Aug. 4, the spacecraft began returning science and telemetry data, indicating it is operating normally and that it remains on its expected trajectory.

[juvva]

am I correct in thinking that cy3 is always in radio visibility of earth, and is never occulted by the moon, because of polar orbit ?

[Ashokk]

https://twitter.com/isro/status/1687859829803466753

Today's maneuver has resulted in an orbit of 164 km x 18074 km, as intended.

[Amber G.]

ISRO: CHANDRAYAAN3 HAS JUST ENTERED LUNAR ORBIT!!

As expected here is Official Announcement from ISRO (Ⓒ BRF)

[Amber G.]

am I correct in thinking that cy3 is always in radio visibility of earth, and is never occulted by the moon, because of polar orbit ?

No, Obviously not, while going around the moon in circular orbit, about half the time it is behind the moon. (True for any circular orbit orbit around the moon.. polar or not. (For elliptical orbit, time for invisibility due to occulted by the moon depends on where the perigee is - CY3 moves faster near perigee - so the invisibility duration may be less (or more) than half but it is never zero if the altitude is few hundred Km's )

This is why one needs orbiter as relay station. When Vikram/Pragyan is on the surface of the moon it will always be visible (or invisible if it landed on the 'other' side) from earth -- but signals will be weak.

[Amber G.]

https://twitter.com/isro/status/1687859829803466753

Today's maneuver has resulted in an orbit of 164 km x 18074 km, as intended.

Thanks. (Estimate I calculated/estimated (~115 Km) is quite accurate from very spotty initial data from doppler).. )..Important point is next few burns CY3 will be in as ideal position as anyone hopes for.

(Sankar V's web page will be updated soon with the updated data as soon as JPL?Horizons updates it.

[Amber G.]

For those who are familiar with Moon's geography -
From what I know one of the best candidate for touchdown on August 23 is within the southern region of the Moon’s near side is Manzinus U crater - soft landing about 20 kilometers west of the rim. CY3 will take its time to select the best landing site so that it gets full 'day' (about 14 earth days) of sunlight. (Again, if they do not find good site, they may wait a few weeks for the next opportunity).

[Tanaji]

Stupid q: Is the firing to reduce the orbit done at apogee or perigee? Why? Does it reverse for increasing the orbit?

[Amber G.]

^^^ IMO not stupid question at all! Orbit correction can happen, of course, at anypoint but in general, *most* fuel efficient is near the perigee. This is true (generally - there are few complexities) in both cases:
Case 1: When you want to give a boost (Sometimes called gravity assist), to go to higher orbit.
Case 2: When you want to get captured by a planet (or a smaller satellite like moon). (in this case you want to bring the speed with respect to moon even lower --- remember wrt earth both Moon (in circular orbit) and CY3 (In elliptical orbit) are moving..but moon is faster and catching up.. wrt to Moon the relative velocity of CY3 wrt to moon was only about 2.4 Km/sec.. it got reduced (due to burn) and thus the apogee (and thus semi-major axis of orbit) got reduced.

HTH.

-- Simple formula (as I posted before) is:
v^2 = μ ( 2/r - 1/a)

--- FWIW - (Check out any good reference if I am not clear - I am avoiding complexities):
The choice between perigee/apogee depends on the desired outcome of the orbital maneuver.

Increasing Orbit:

To increase the orbit's size (altitude), a spacecraft typically fires its thrusters at apogee. This is because when the spacecraft is at apogee, it is moving slower in its orbit, and applying thrust at this point increases its kinetic energy. This results in a higher perigee and apogee, effectively raising the orbit's altitude.

Decreasing Orbit:

To decrease the orbit's size (altitude), a spacecraft typically fires its thrusters at perigee. When the spacecraft is at perigee, it is moving faster in its orbit, and applying thrust at this point decreases its kinetic energy. This results in a lower perigee and apogee, effectively lowering the orbit's altitude.

In the case of Chandrayaan firing rockets at perigee to increase the orbit might seem counterintuitive, but it's actually a result of the specific dynamics of lunar missions and the way they leverage gravity assists.

When CY3 is on its way to the Moon (or any other distant celestial body), it often uses a technique called a gravity assist or gravitational slingshot. This involves flying close to a planet (usually Earth) to gain energy from its gravitational field, which helps increase the spacecraft's velocity and alter its trajectory. This allows the spacecraft to reach its destination with less fuel and in a more efficient manner.

ForCY3 firing the rockets at perigee to increase the orbit is related to the use of gravity assists. Here's how it works:

Initial Launch: The spacecraft is launched into an Earth orbit, often an elliptical orbit, with a perigee and an apogee.

Gravity Assist Maneuver: To reach the Moon, the spacecraft performs a gravity assist maneuver by flying close to Earth. During this maneuver, the spacecraft gains energy from Earth's gravity, which increases its speed and changes its trajectory.

Lunar Injection Burn: After the gravity assist, the spacecraft is on a trajectory that will intersect the Moon's vicinity. To get captured by the Moon's gravity and enter lunar orbit, the spacecraft performs a lunar injection burn at or near perigee. This burn is carried out at perigee to increase the spacecraft's velocity and allow it to reach the Moon.

Lunar Orbit Insertion: Once near the Moon, the spacecraft performs another burn to reduce its velocity, allowing it to be captured by the Moon's gravity and enter lunar orbit.

CY3 utilizes the energy gained from the gravity assist to reach the Moon, and the burn at perigee is specifically used for lunar capture. While it might seem like the spacecraft is increasing its orbit's altitude by firing at perigee, the goal is not to raise its Earth orbit but to reach the Moon. The terminology and approach can be a bit different for interplanetary missions compared to Earth-centric missions.

[sanman]

Chandrayaan-3 enters lunar orbit

Ajay Lele from IDSA comments

[Ashokk]

Increasing Orbit:

To increase the orbit's size (altitude), a spacecraft typically fires its thrusters at apogee. This is because when the spacecraft is at apogee, it is moving slower in its orbit, and applying thrust at this point increases its kinetic energy. This results in a higher perigee and apogee, effectively raising the orbit's altitude.

Dumb question: I thought that the use of the engine at higher speeds generates a greater change in mechanical energy and a hence higher orbit (Oberth effect), than its use at lower speeds. So would it not be more efficient to fire the engines at the perigee (highest velocity) than at the apogee or am I missing something?

[SriKumar]

Many/most of the shots of the lunar orbit of CY3 above (including the orginal ISRO brochure) do not show the lunar axis, hence difficult to judge if the current orbital plane of CY3 is polar (or close). The animation by Sankaranarayan (based on orbital elements) does show the axis of moon and the trajectory of CY3. Per this animation, CY3 trajectory at the end of TLI intersects the orbit of the moon around earth and gets there 'ahead of moon' and the approaching moon pulls it towards itself rightaway (roughly reversing its velocity vector) and CY3 goes into a polar orbit- going from south to north in the first orbit itself. Not sure how this aligns with what was shown in the satellete Tracking channel simulation- does not seem to, actually.

[Tanaji]

AmberG:

Sincere thanks for taking the time and effort to explain in such a lucid manner. I am off to read more about basic orbital mechanics…

[juvva]

iirc the apollo lunar missions used to execute a loi burn on the far side of the moon, but it looks like chandrayan_x missions execute the burn in radio visibility of earth.
why the difference?

[SSSalvi]

Just for general info:

Showing the significance of orbit attained.

Ground path that the orbit takes while the CH3 is orbitting.

Notice the Landing sight 'L' and the South pole 'P'

( Note: This is based on Planned orbit ... not on the achieved orbit. Will update when available including . How the sunlight illumination plays role in deciding the 14 days life of Lander. )

[SSSalvi]

iirc the apollo lunar missions used to execute a loi burn on the far side of the moon, but it looks like chandrayan_x missions execute the burn in radio visibility of earth.
why the difference?

Depends on the sight that you want to land on surface ... as well as specific requirements based on transfer point of 'Handover' of craft to Ms. Moon ( in English language regions ) or Mr, Moon ( India and Germany region ) .

[SSSalvi]

Stupid q: Is the firing to reduce the orbit done at apogee or perigee? Why? Does it reverse for increasing the orbit?

General rule dictated by Mr. Kepler .....Firing at one end changes the other end.
Fire to add velocity will increase other end altitude and Fire in reverse direction of motion to reduce the altitude of other end.

Added later : Example of two types of burn in CH3 mission

If you watch Launch Video https://www.youtube.com/watch?v=q2ueCg9bvvQ at 51:00 minute, just before separation the Perigee is nearly 170 kms. That is the limit imposed by GSLV capability.
This altitude has some atmospheric drag so this needed to be increased.

In the 1st orbit burn at Perigee, Apogee alt was raised to 41760 kms ( Perigee still about 170 Kms ).
Susequently, in 2nd orbit burn ( near apogee), raised perigee from 170 Kms to 226 Kms without significantly changing the Apogee alt.
Since this did not raise the Apogee, there was no much celebration for common man so this burn went almost un-noticed.