Chandrayaan 3: Launch and Discussions

[Amber G.]

To the experts on here, I love reading all your posts. Please keep them coming. I'm a biochemist but love all sciences. Amber G, how I wish I had instructors like you when I was in university!

Thanks.
For those who are curious, and are willing to use an ordinary calculator and not afraid to use simple mathematical formulas using very basic physics .. ( I posted simplified version in my previous post)... Here is how one calculates:
For example CY3's latest orbit: "Chandrayaan-3's orbit is reduced to 174 km x 1437 km following a manuevre performed today."


p = perigee = 174+1737.4 = 1911.4 (Km) (Radius of Moon = 1737.4 Km)
q = apogee = 1437+1737.4 = 3174.4 (Km)
semimajor axis = a = (p+q)/2 = 2543 Km.
semiminor axis = b = √(a*b) = 2463

4 sig, figures only (same as ISRO's published numbers). This gives how circular the orbit is, e = √(1-b^2/a^2) = .25

For Moon as I mentioned in the past post μ = 4.905×10¹² in SI units (length in meters, time in seconds etc)
This gives: velocity at anypoint in the orbit which is r from the center of the moon =
v = √(μ (2/r-1/a))

And time period T = (2*pi/√μ)* a^(3.2) = (for moon) = 2.8370*10^(-6)* a^(1.5)

So when a = 2563000 meters, T= 11505 seconds = 3.2 hours
(4 fig accuracy here -- more accuracy needs better values which is not necessary here)

It is the time period value which can be observed by doppler shift .. (along with velocity measurements in the line of sight) which can determine the orbit parameters ..

This can also enables one to estimate (even without pen/paper if one is quick in doing calculation) to see how fast Vikram will be movin in say 100x30 Km orbit..near the closest point of the moon..

[Ashokk]

Current Space Situation around the Moon – An assessment

As of July 2023, there are 6 active lunar orbiters (see Fig-1). Two of the five probes of NASA’s THEMIS mission have been re-purposed under ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun) as ARTEMIS P1 and ARTEMIS P2, both operate in eccentric orbits of low inclination. NASA’s Lunar Reconnaissance Orbiter (LRO) orbits the Moon in a nearly polar, slightly elliptical orbit. Chandrayaan-2, the second lunar mission of ISRO and Korea Pathfinder Lunar Orbiter (KPLO) also operate in polar orbits of 100 km altitude. NASA’s Capstone operates in a 9:2 resonant southern L2 NRHO, its perilune passes over the lunar North pole at 1500-1600 km altitude, while the apolune is over the South pole at a distance of nearly 70,000 km. The Japanese spacecraft Ouna which was placed in lunar orbit as part of Kaguya/SELENE mission in 2009 and Chandrayaan-1 launched in 2008 are the two defunct spacecraft. All the other orbiters have been either moved out of the moon-bound orbital regime or have landed/impacted the lunar surface, either deliberately or due to failure to land softly. For example, Chang’e 4 mission’s data relay satellite Queqiao, launched by China in May 2018, was later moved to a halo orbit near the Earth-Moon L2 point. Currently, the only operating rover is China’s Yutu-2 rover released by Chang’e 4, which operates on the far side. From the available media sources, it is expected that Luna-25 of Russia with a Lander and Rover will be in Lunar orbit of 100 km by August 16, 2023 and will be landing on South pole of the moon by August 21-23, 2023.

Risk of Close Approaches in Lunar Orbits and its Mitigation

Even with a handful of orbiting spacecraft, frequent conjunctions are experienced by LRO, KPLO, and CH2O as their orbital regimes in LLO overlap. Sometimes such conjunctions even warrant collision avoidance manoeuvres to be executed to be on the safer side because of the uncertainty associated with orbital estimates. Till July 2023, Chandrayan-2 has performed 3 collision avoidance manoeuvres to mitigate critical close approaches with LRO and KPLO. It is noteworthy that effective coordination is taking place among the agencies to avoid critical conjunctions in the Lunar orbit. For Chandryaan-3 (CH3) mission, the propulsion module is expected to orbit around the moon in a circular LLO of about 150 km altitude for many years to come. Majority of the lunar landers are also likely to temporarily reside in LLO (typically for a few days or weeks) before landing.

Under the ambit of ISRO System for Safe and Sustainable Space Operations Management (IS4OM) critical analyses of each of the Lunar Bound Manoeuvres for orbit loweringare being performed to assess potential risks of close approaches with the other lunar orbiters before executing the manoeuvres.

[sanman]

Will we lose a record to the Russians?

[sanman]

[ramana]

Have we already seen this video?

https://www.youtube.com/watch?v=gGv4qpSSl3w

[ramana]

This was before the launch. Very candid interview.

[disha]

^Sanman'ji, Well we will wish Ruskies the best. South pole is not going away and yes there are always bragging rights on who reached to moon first and who reached to south pole first, it all boils down to successful exploitation of Moon's resources for upliftment of Indians & humanity.

There are few cases where I do think ISRO needs to look and improve. One is their inability to do proper PR. It is important and it is an art that needs to be mastered. The other is the severe under confidence and sometimes an inability to take risk and go and explore an area even if the outcome is certain failure. For example, ISRO spent decades trying to procure a semi-cryogenic. And the result is still *zero*.

On the Chandrayaan, ISRO went to Roscosmos for the lander and after much delay, Roscosmos screwed ISRO. They changed their lander parameters which impacted the Chandrayan-2 design and cut into the weight budget of rover, making a wash of all the plans and designs.

https://www.spacesafetymagazine.com/spa ... r-mission/

Eventually ISRO had to re-design C2 and launch it with LVM3 and it gained immense experience. Now behind the scenes Roscosmos/Russia were developing their Luna-25 and are now trying to undercut ISRO/India.

ISRO's experience with Russia on the cryo- episode should have thought them a lesson. But no, they still went to Russia and Ukraine for C2 and Semi-Cryo and got screwed over. Again. And again. And now maybe fourth time screwed over.

At this point any ISRO/DOS official talks about "Russia collaboration or NASA collaboration" where they think those furrin agencies will let us ride their horse or give access to their technology or algorithms must be summarily fired.

Even for C3, ISRO is doing NASA a favour by sticking their laser reflector on the C3 orbiter to measure the earth-moon distance. That is, NASA wants to ride ISRO horse and yes we should accomodate such requests since we may need help to save our people in future or salvage a crucial operation or simply want to use their deep space network. There is a difference between "Co-opetition which is part cooperation and part competition" and outright genuflection. There will be people and I am sure even on this forum who will sing paens about NASA's payload on C3.

Point is nothing comes free and atmanirbharta is way to go. ISRO has to forget riding other agencies horses and learn to pay for what it needs and build what it cannot get. And others will come to ISRO for cooperation when they see ISRO's capabilities. Also, ISRO has to come back and say 20% of their budget will be to blow up things. We will fail. May fail again and maybe fail again. But we will not give up on a goal. And continue trying. And try it fast.

Part of the problem is not ISRO, but Indians in general. We would rather listen to a moron Jean Druize and whine why do we need a space program when so many do not have paneer (yes, the paneer part was mentioned in LS yesterday) everyday but not spend money on a space program.

In a way, let it be a lesson to Indians in general and ISRO in particular, that apart from science, bragging rights do matter. Since it helps motivate. Human psyche is that, jo jeeta woh sikandar. We cannot fight against human psyche, we have to learn to work with it.

[disha]

Have we already seen this video?

https://www.youtube.com/watch?v=gGv4qpSSl3w

Yes. This is linked I believe in the second or third page. Following that there was some discussion on C2 failures and then the lecture at IISc which has very very good details. It will take time to unspool and discuss those details.

[Prem Kumar]

Disha: it beats me why ISRO is taking so much time to master semi-cryo. Agnikul (the space startup) is using semi-cryo engines for their 1st and 2nd stages. Agnikul is yet to launch, but their basic design and initial tests are done. If they can do it, why not ISRO?

Also, the Jean Drieze argument is bogus even on purely economical grounds. Take one single example the recent Gujarat cyclone. It was the equivalent of a Category-3 hurricane easily. Almost zero lives lost. Literally Billions of $$ saved - all because we had satellites that gave the Govt/people 3 weeks notice about the incoming storm. Just this one incident alone provided ROI for several years of satellite & launch-vehicle development costs! Not to mention other uses like telling fishermen where to fish, preventing deforestation, warning farmers of locust/pest attacks etc.

Chutiyas like Drieze can be defeated by economic arguments alone, let alone aspirational ones

[arvin]

^^^
ISRO's semi cryo is staged combustion cycle, which is far more difficult to master.
Agnikul might be using gas generator I guess. Their chamber pressure is only 10 bar

[disha]

Disha: it beats me why ISRO is taking so much time to master semi-cryo. Agnikul (the space startup) is using semi-cryo engines for their 1st and 2nd stages. Agnikul is yet to launch, but their basic design and initial tests are done. If they can do it, why not ISRO?

Its the scale. What Agnikul is doing with semi-cryo is basically equivalent of diesel engines on the lawn mowers that may get scaled up to tractor engines. What ISRO needs to build is engines for a super tanker.

I hope to post the entire problem with semi-cryo in the space thread when I get the chance. Sanman already pointed out to the coking issue of the semi-cryo. That is part of the problem. There are several nuances.

Also, the Jean Drieze argument is bogus even on purely economical grounds. Take one single example the recent Gujarat cyclone. It was the equivalent of a Category-3 hurricane easily. Almost zero lives lost. Literally Billions of $$ saved - all because we had satellites that gave the Govt/people 3 weeks notice about the incoming storm. Just this one incident alone provided ROI for several years of satellite & launch-vehicle development costs! Not to mention other uses like telling fishermen where to fish, preventing deforestation, warning farmers of locust/pest attacks etc.

Chutiyas like Drieze can be defeated by economic arguments alone, let alone aspirational ones

+72 to above. You have put it far better than I could.

Ppl like Jean Druize's do not value Indian lives. And they will shift the goal post on the need to explore Mars or Moon and call it pride mission. There are counters to it and it needs to be articulated.

I would like to do 999 things to Jean Druize and whoever advances his line of thinking. If I put even 0.72 items of things to do to Jean Druize here on this pages, I will be mothballed. So I will just froth at the mouth and keep quite and point out only one aspect, there are significant Jean Druize'es type mafiosis within India and they need to be countered at every step. There was a time in the early part of past decade and a decade prior where this mafiosis were calling the shots. Some still continue with significant nuisance value even now and they need to be countered again and again.

So we wait for C3 to make a landing. Keeping the fingers crossed.

[disha]

^^^
ISRO's semi cryo is staged combustion cycle, which is far more difficult to master.
Agnikul might be using gas generator I guess. Their chamber pressure is only 10 bar

Arvinji, yes scale is different. As you correctly point out, agnikul is a baby engine. The chamber pressure of CE7.5 (GSLV Mk2 CUS) goes up to 75 bar. But that's not the thing or maybe the only thing, one aspect is how you cool the nozzles. And higher burn means hotter the nozzle etc...

[SSSalvi]

Chupa Rustom!

Went un-noticed

Earth viewed by Lander Imager (LI) Camera on the day of the launch & Moon imaged by Lander Horizontal Velocity Camera (LHVC) a day after the Lunar Orbit Insertion.
When everyone is looking at ISRO handle , SAC Ahmedabad, who developed these cameras published on their handle

[SSSalvi]

https://www.isro.gov.in/Current_Space_S ... sment.html

[Amber G.]

Chupa Rustom! Indeed!

LI & LHV cameras are developed by SAC & LEOS.
https://www.isro.gov.in/SAC.html
https://www.isro.gov.in/LEOS.html
ISRO: Tweet'a link: https://twitter.com/isro/status/1689501 ... 60128?s=20

[Amber G.]

Meanwhile:
There is this Opportunity under ISRO's Capacity Building in Space-Based Disaster Management Support Program:

Indian scientists, engineers, and faculty members are invited to empower disaster response using space technology.
May apply by August 20 for financial support.

[Amber G.]

p = perigee = 174+1737.4 = 1911.4 (Km) (Radius of Moon = 1737.4 Km)
q = apogee = 1437+1737.4 = 3174.4 (Km)
semimajor axis = a = (p+q)/2 = 2543 Km.
semiminor axis = b = √(a*b) = 2463

4 sig, figures only (same as ISRO's published numbers). This gives how circular the orbit is, e = √(1-b^2/a^2) = .25

For Moon as I mentioned in the past post μ = 4.905×10¹² in SI units (length in meters, time in seconds etc)
This gives: velocity at anypoint in the orbit which is r from the center of the moon =
v = √(μ (2/r-1/a))

And time period T = (2*pi/√μ)* a^(3.2) = (for moon) = 2.8370*10^(-6)* a^(1.5)

So when a = 2563000 meters, T= 11505 seconds = 3.2 hours

For record: Keplerian elements (Not Official figures but observed via doppler shift and correct) if one wants to draw/calculate the orbit - or want to know precisely where CY3 is at (or how fast it is moving) any given time)
Time of Epoch: August 9, 2023 08:17:28.000 (UTC) - Lunar reference
SMA = 2542.65
ECC = 0.2484
INC = 89.77 (Polar orbit!)
RAAN = 268.096
AOP = 288.236
TA = 0.0

[sanman]

On a related note, Luna 25 has just launched out of Vostochny in Russia, on Soyuz 2.1B Fregat-M



The nuclear-powered Luna 25 will land at the lunar south pole just ahead of Chandrayaan-3

[Amber G.]

^^^ To be clear, Luna-25 is not nuclear-powered in the conventional sense, it does have radioactive isotope to give (Radioisotope power systems (RPS))it power even when there is no sunlight..
For fun, here is estimate of Luna-25 trajectory - as usual projected on two different planes. (Aug 15, 8PM UTC) - (Not official but most likely correct):
TLI has been done.



--- Meanwhile, CY3, orbits looks stable according go Doppler ..No drama!

[Amber G.]

From ISRO:

[SSSalvi]

Russian craft Tweet:

Roscosmos reported that #Luna25 successfully separated from the Fregat upper stage and is on its way to the Moon: https://t.me/roscosmos_gk/10427


https://twitter.com/katlinegrey/status/ ... 4161192960
https://twitter.com/katlinegrey/status/ ... 60/photo/1

[Amber G.]

Posting the 'official' Mission profile of Luna-25:

[SSSalvi]

^^^
Luna 25 descent starts from 18 kms altitude against 30 Kms of CH3

and Congrats from CH3

https://twitter.com/isro/status/1689845 ... D32948.200

[SSSalvi]

deleted

[SSSalvi]

Some Info about Luna 25 Goal and Landing site:

[SSSalvi]

Location of Russian craft LUNA25 landing site ( Indicated as TEST_PLACE ) as on 21st August.

It is in sunlight so craft can be set there ( although it is not necessary ... It has a nuclear powerpack so it can work for months without sunlight [ my guess] ) on 21st before CH3 scheduled for 23rd.

Some Brownie Points attempt by Rus

[Prem Kumar]

^^^
ISRO's semi cryo is staged combustion cycle, which is far more difficult to master.
Agnikul might be using gas generator I guess. Their chamber pressure is only 10 bar

Arvinji, yes scale is different. As you correctly point out, agnikul is a baby engine. The chamber pressure of CE7.5 (GSLV Mk2 CUS) goes up to 75 bar. But that's not the thing or maybe the only thing, one aspect is how you cool the nozzles. And higher burn means hotter the nozzle etc...

Agnikul 2nd stage chamber pressure is 10 bar. This has been tested
1st stage chamber pressure is 150 bar. This is yet to be tested

Their payload is 100 Kgs to LEO

I was told that LOX+Kerosene semi-cryo is basically a WW2 concept, though a lot of tech-development has happened since then. I fully agree that at a much larger scale (100X that of Agnikul), there will be a host of other problems to be solved. But I am wondering why ISRO, instead of trying to solve that, went the full-cryo route, which was tougher? Is it because that's what Unkil & the Rooskies had and we wanted to play it safe?

[drnayar]

Why india did not go for a Semi cryogenic engine is worthy of a spy thriller !!.. it was there and it wasnt. If it had gone full throttle we would have saved nearly a decade of development of medium and heavy lift launch vehicles.

[disha]

quote="Prem Kumar" post_id=2597262 time=1691757340 user_id=15621]
I was told that LOX+Kerosene semi-cryo is basically a WW2 concept, though a lot of tech-development has happened since then. I fully agree that at a much larger scale (100X that of Agnikul), there will be a host of other problems to be solved. But I am wondering why ISRO, instead of trying to solve that, went the full-cryo route, which was tougher? Is it because that's what Unkil & the Rooskies had and we wanted to play it safe?
[/quote]

^ OT for this thread, we will carry more discussions in space thread. Wanted to put a quick response:

Prem'ji, full cryogenic is not tougher. ISRO has two different cycled cryo- engines to prove that. And one was in-situ replacement of a very powerful Russian engine!

Kerosene based rockets are actually older than WW2. Goddard developed the first liquid fueled rockets in 1920s. It was gasoline and liquid oxygen because liquid hydrogen was not readily available in 1920s. So hundered years back itself, Goddard wanted to use LH2 but settled on gasoline (since it was readily available). Pressurization of the tanks was done by nitrogen, the concept of gas pressurization is still used today.

It is a mis-conception that cryo engine since it requires liquid hydrogen is tougher compared to semi-cry since kerosene does not need to be liquefied. If that was the case, the Saturn V upper stages would have been semi-cryo OR the latest NASA SLS would have been semi-cryo or even Arianne.

I would argue that apart from staged combustion engines (which is the current pinnacle of engineering), *staging* a LOX/LH2 Cryo engine based rocket is simpler than semi-cryo engine based.

drnayar'ji, ISRO did not have fuel to go full throttle. ISRO developed its own fuel called ISROSENE.

---

ISRO just went on a wild goose chase with semi-cryo and at this point, it is already too late when it arrives.

[disha]

...

Location of Russian craft LUNA25 landing site ( Indicated as TEST_PLACE ) as on 21st August.

It is in sunlight so craft can be set there ( although it is not necessary ... It has a nuclear powerpack so it can work for months without sunlight [ my guess] ) on 21st before CH3 scheduled for 23rd.

Some Brownie Points attempt by Rus

Looking at the mission profile, typical Ruskie approach. It is indeed a TEST_PLACE for their luna 25 craft which is actually Chandrayaan-1 vintage with some additional fuel to land.

Ruskie's first goal, "hey we reached first". Science, oh that is secondary. Let's do the engineering first.

Mission profile: just drop the Luna 25, it will slow down and it will slow down further. And then land, somewhere in the vicinity of where we intend to land. The Russian scientist says, but the crater is over there to study. Well, from the engineering perspective, that is the problem of the intertial navigation team. They were not precise enough.

Anyway, operation successful, even if the patient is dead. You see, we do not know if Luna 25 is carrying the radio isotope batteries. It is assumed that it does since it is renamed as Luna25 and sounds like Luna24 line. It might have the Radio-Isotope battery, but I have not found a definitive answer. I think it does not have Radio isotope batteries since their "TEST_PLACE" is in full sunlight all the time!

Meanwhile ISRO scientists, lets do some science while solving the engineering problems. Let's identify craters of interest. Let's put a rover over there. Heck we do not have radio-isotope batteries, lets calculate the orbits and get an orientation with maximum sunlight. Let's put the solar panel on Pragyaan in such a way that it shields the electronics from direct sunlight while generating energy. Let's orient the Vikram lander in such a way that it gets the maximum power.

Identify a set of craters where we can do useful science. Like C1 found water on moon, we find the mineral composition on craters which are in permanent shadow. What's the water content there? Hydrogen content? Oxy-hydrogen based minerals? What do we need to build a sustainable habitat there?

And then the ISRO scientist sets about identifying the craters, proper landing sites, so much so that C2 got a very challenging landing site on the first go.

No doubt Ruskies reach some places first and then their program stalls. Meanwhile the DDM will go ga-ga over how Ruskies have a powerful rocket (their fregat upper stage is a space junk for years to come) and why we are SDRE only, really - C3 is SDRE chubby and 3x the weight of Luna 25 and then the Soyuz 2b which launched Luna25 is no more powerful than LVM3. In fact our LVM3 is also SDRE and we also call it "Fat boy".

LVM3 that launched C3 has ~30% more throw weight than Soyuz2b which launched Luna25, with an additional responsibility to not turn the final cryo- stage into a space junk. And additional mission objectives like, land a rover near a crater that matters and do some science.

No doubt Ruskies lost the space race. So much so that they are cheaply competing with a 3rd world nation to get some brownie points.

[SSSalvi]

we will carry more discussions in space thread.

Thanks for moving to appropriate thread. This will be in continuation of other similar discussions already going on there.

[SSSalvi]

........ since their "TEST_PLACE" is in full sunlight all the time!
...... lets calculate the orbits and get an orientation with maximum sunlight.

Like CH3 landing site , "TEST_PLACE" , is also illuminated for 1 Lunar day of 14 Earth days. ( Only when Moon is above ( Northern half of ) ecliptic. )

For perennial sunlight we have to move to higher Latitudes like others with robust outer shield.

Of course rest of the wishful thinking is something to ponder on.

[Amber G.]

........ since their "TEST_PLACE" is in full sunlight all the time!
...... lets calculate the orbits and get an orientation with maximum sunlight.

Like CH3 landing site , "TEST_PLACE" , is also illuminated for 1 Lunar day of 14 Earth days. ( Only when Moon is above ( Northern half of ) ecliptic. )

For perennial sunlight we have to move to higher Latitudes like others with robust outer shield.

Of course rest of the wishful thinking is something to ponder on.

To add and Just to be clear:
Moon's axis is NOT tilted 23.5 degrees like earth so unlike earth it does NOT have places with significant 'maximum sunlight' like north (or south pole) on Earth. Moon's axial tilt is *only* about 1.5 degrees with respect to the ecliptic so it does not have pronounced 'summer' or 'winter' type variations as we have on Earth. The 'arctic circle' is above 88.5 degrees.

CH3 (or Luna25) landing site is still about 600 Km from the pole.. The Sun will be low on the horizon but day/night time will be about 14/14 days.

Interestingly (as I pointed out also in CY2 thread - but most people do not know/realize ), there are some areas (near the poles) deep in the canyons, where sunlight never reaches and they remain permanently dark.

There are are about 300 such known permanently shadowed regions (PSRs) ... they are always dark so difficult to observe. NASA’s ShadowCam (which orbits the moon aboard the Korea Pathfinder Danuri) first time took 'pictures' last year.. one area about 2000 metres wide inside Shackleton crater, near the lunar south pole was AFAIK was the first area observed in details.

OTOH - Peary crater near the north pole, there are peaks of eternal light (perhaps the only known region in our solar system (**see note below**) where the sun never sets. Not an idea place to land.

Added later: Okay did some research/calculations and find that there are a few such other places ...
Mercury: axial tilt (about 0.034 degrees), some crater floors near its poles are in perpetual shadow and experience extremely cold temperatures, while certain sunlit regions near the poles also receive near-constant sunlight.

Ceres (Dwarf Planet): Ceres an asteroid t between Mars and Jupiter, has areas near its poles that experience near-continuous sunlight.

Pluto: While not a planet, Pluto's axial tilt is quite significant (approximately 122.5 degrees). This means that certain regions near its equator can experience nearly constant daylight during parts of its year, despite being far from the Sun.

Triton (Moon of Neptune), Titan (Moon of Saturn) and Io (Moon of Jupiter) may be such other candidates..

[KL Dubey]

Like CH3 landing site , "TEST_PLACE" , is also illuminated for 1 Lunar day of 14 Earth days. ( Only when Moon is above ( Northern half of ) ecliptic. )

For perennial sunlight we have to move to higher Latitudes like others with robust outer shield.

Of course rest of the wishful thinking is something to ponder on.

Given the proximity of the two sites, I hope this is not some Chinese-inspired plan to show up there first and somehow jam CY3 communications during the crucial landing phase. Not sure if it is feasible to even load any such equipment into a small lander/rover, but I can't help "thinking the unthinkable".

[bala]

To add and Just to be clear:
Moon's axial tilt is *only* about 1.5 degrees with respect to the ecliptic so it does not have pronounced 'summer' or 'winter' type variations as we have on Earth.

The moon's orbit eliptic and the earth's orbit eliptic are tilted 5.16° (see https://en.wikipedia.org/wiki/Axial_tilt ). Rahu and Ketu are points of interception of the earth's eliptic to the moon's eliptic.

[Amber G.]

To add and Just to be clear:
Moon's axial tilt is *only* about 1.5 degrees with respect to the ecliptic so it does not have pronounced 'summer' or 'winter' type variations as we have on Earth.

The moon's orbit eliptic and the earth's orbit eliptic are tilted 5.16° (see https://en.wikipedia.org/wiki/Axial_tilt ). Rahu and Ketu are points of interception of the earth's eliptic to the moon's eliptic.

Just some basic geometry and basic astronomy:

Ecliptic - is the plane where earth (and Moon - and almost all the planets - except comets etc) goes around Sun. (Earth's ecliptic is not different than Moon's 'ecliptic' -- *all* planets move more or less in the same plane).

Earth's Axis (Line joining North Pole- south Pole) line is tilted around 23.5 degrees) and Moon axis (Line Joining Moon's North Pole and South Pole is 1.5 degrees with respect to ecliptic.

So like on earth, we have summers/winters, and as go go at higher latitudes length of day could be longer than night (or vise-versa), including places above arctic circle where sun, depending on the time of the year, never sets (or rises) --- On Moon this kind of situation is not pronounced. For most of the moon, day and night are roughly equal (each around 14.7 earth-days).

-------

Rahu and Ketu are nodal points - point where orbit of Moon (around earth) touches the ecliptic. This orbit plane (Orbit of moon around earth) is tilted around 5.1 degrees wrt to the ecliptic (BTW Rahu and Ketu are not fixed, they make a complete cycle in around 18,6 years.

This also means - the Moon's *maximum* possible declination (position above or below equatorial plane) can vary from 18.5 to about 28.5 degrees (with in time span of 18,6 years).. at present this inclination is about 28 degrees.
(This means, at present (this whole year) one can see Moon at zenith at its highest point in the sky at some time of the month from any latitude below 28 degrees - say from Florida or Jaipur India. For Sun, you have to be lower than 23.5 degree lattitude, About 9 years from now, the situation will change and you have to go below 18 degrees to see moon at zenith)

Since all these are vectors the inclination/angles calculation is not simple but requires spherical trigonometry -- Or needs three dimensional mode to understand.

Hope this helps.

[Amber G.]

^^^ Decided to put an animation to show it clearly -- Since many have questions about this..( Hard to 'draw' 3-dimensional models on 2_D dhaga )

The animation below shows the geometry (not to scale) of the orbit and rotation of the Moon. The grey plane is the ecliptic plane. The yellow axis is the normal to this plane. The inclined orbit takes the Moon above and below the ecliptic plane. (The points where it crosses the ecliptic plane is where Rahu and Ketu are - Nodes - When moon is close to these points eclipsed can take place

The blue axis is in the direction normal to the plane of the Moon's orbit. The red axis is the direction of the rotation axis of the Moon: over the course of one Lunar orbit, it points in the same direction in space. The red, yellow and blue axes remain on the same plane, and this defines a Cassini state.

Geometry of the lunar orbit/rotation vector. The plane of the Moon's orbit is inclined by 5.14 deg with respect to the normal to the ecliptic plane - the plane about which Earth rotates around the Sun. But just like the Earth’s rotation axis is inclined by 23.5 deg in space, the Moon’s rotation axis is also inclined, by about 1.54 deg in space.

<click for animation>

Hope this is helps.

[SSSalvi]

LUNA26 has 1 Targeted location and 2 standby locations.

It is interesting to see the spread of these locations on Moon surface.



First target is L25_A ( in subsequent video post I will show how these targets get illuminated with sunlight ), which will get twilight from 21st Aug, CH3 will get twilight on 22nd , L25_B will get twilight on 23rd and L25_C on 23rd.

So, Rus has kept some risk margin if 1st attempt is not executed and taking care that L25 will not clash with CH3 location.

[SSSalvi]

Here is support video for last post.

It shows how the 4 locations get sunlight one after another with timegap of one day between each.

The arrow from South Pole is the Sun direction.

[Amber G.]

The doppler data is showing some difference from the expected orbit of CY3. There may have been a minor orbit adjustment around Aug 11th . ISRO (to my knowledge) have not made any burns.. but it may make minor burns without announcing.
(If I can get data from some other sources too would be nice)..Have not seen Horizon data,,

ISRO definitely have flexibility on Vikram's planned landing ..and perhaps ISRO will stick to it's original date but I wonder if Luna25 is affecting the time table. (If I was them -- I will stick to original plan unless I have *scientific* reason to change)..

The anomaly is there.. orbit has changed slightly but measurable ..(The doppler data taken by aam-abduls may be not as accurate as others so I will wait)... Let us see if this is just some error or something is really going on.

Will update the post, after consulting with other techies ...