Chandrayaan 3: Launch and Discussions

ramana · Post by **ramana** » 17 Jul 2023 22:57

S^3, Glad you are following the program.
Thanks for that insight.
Makes sense.

sanman · Post by **sanman** » 18 Jul 2023 01:51

vimal wrote: ↑17 Jul 2023 22:19 Chandrayaan 3 Launch LIVE Sriharikota ISRO 2023
How to reach the launch area with mass of traffic.

Heh, check upthread some posts back - I already posted it

juvva · Post by **juvva** » 18 Jul 2023 05:21

SSSalvi wrote: ↑17 Jul 2023 21:05

If I remember correctly the problem explained that time was ( Trying to explain in my language ):
1. Large deviations were not expected
2. So after ( suppose it is a 16 bit processor ) FFFF Hex, the value (say ) was 10000 Hex.
3. Since the processor was not programmed to handle beyond FFFF ( because deviation beyond that was not expected ) the system interpreted it as 0000 ( ignored the carry 1. ) and thought that more power needs to be pumped, and fired the engines more while it was expected to reduce the power.

Logically seems to be correct analysis.

sounds like pslv-d1, all over again...

madhu · Post by **madhu** » 18 Jul 2023 10:36

question for gurus,

https://twitter.com/coastal8049/status/ ... 93249?s=20

Scott Tilley has plotted the residuals for the Doppler data and the JPL Horizons data. the error is consistently reducing for each burn. the question is the increase in perigee from 173 to 221 is to reduce this error? any information on this please.

madhu · Post by **madhu** » 18 Jul 2023 11:34

Here is the recap of the trajectory of vikram detailing all the deviations and to some extent orientation of vikram.

disha · Post by **disha** » 18 Jul 2023 12:01

juvva wrote: ↑18 Jul 2023 05:21
SSSalvi wrote: ↑17 Jul 2023 21:05

If I remember correctly the problem explained that time was ( Trying to explain in my language ):
1. Large deviations were not expected
2. So after ( suppose it is a 16 bit processor ) FFFF Hex, the value (say ) was 10000 Hex.
3. Since the processor was not programmed to handle beyond FFFF ( because deviation beyond that was not expected ) the system interpreted it as 0000 ( ignored the carry 1. ) and thought that more power needs to be pumped, and fired the engines more while it was expected to reduce the power.

Logically seems to be correct analysis.
sounds like pslv-d1, all over again...

At first blush, sounds like PSLV-D1 but I do not think that is what SSSalvi'ji is saying in his inimitable style.

I think the issue is not buffer overflow of PSLV D1. It is definitely a software algorithm issue.

Here is what the C3 has over C2

1. Removal of the central thruster.
2. Addition of Laser doppler velocimeter

For the moment lets assume that In C2, the velocity must have been a derived value. Based on various calculations on the rocket burn time, the initial rate of approach etc. Keep this as derived_velocity attribute.

The lander was given a specific target, and as it approached the target, its parameters were to approach it at a specific velocity and angle. Keep this as intended_target attribute.

Now from here there are two paths that open up:

1. As the lander descends, it needs to know how much burn it has to do to reach the intended target.

2. And approach the intended target at the correct velocity

For item #1, it has to increase the burn and that will increase the velocity. However it has to reach that particular spot and the increased velocity is not desirable since

3. It will overshoot the intended_target AND

4. The derived_velocity of approach will be very high and over the margin.

That means that the braking rockets need to fire to bring the lander under the velocity limit. However doing the same will mean the thrusters have to fire more to approach the intended_target.

This back & forth firing increased the attitude deviations which led to a circular lock in to more thruster firing. Think of it as locked into a thrust/counterthrust "outward" loop. That is the errors now build up leading to more errors (attitude deviations) and this overwhelms the computing unit while the lander runs out of fuel. Thus a crash land.

The changes in C3 is now significant. First of all, the algorithm is "opened up". Instead of going to a particular target, it gets a set of targets and parameters, all achievable. This set of targets are identified by the excellent survey carried out by C2.

Second, with the laser doppler velocimeter, at any point the lander knows its true velocity. So now the algorithm, just has to calculate what targets are reachable given its current velocity and approach one of the priority and as it reaches it, fire the reverse thruster and hover over the target and land.

Also the central thruster which was added to clear the moon dust away is eliminated. And does not compete for its share of fuel.

In nutshell, the algorithm locked in and tried to manage its "approach" parameters instead of "given the approach parameters", which target can be achieved.

disha · Post by **disha** » 18 Jul 2023 12:10

madhu wrote: ↑18 Jul 2023 10:36 question for gurus,

Scott Tilley has plotted the residuals for the Doppler data and the JPL Horizons data. the error is consistently reducing for each burn. the question is the increase in perigee from 173 to 221 is to reduce this error? any information on this please.

Nothing to be concerned off. See my note:

disha wrote:Now ISRO will raise the apogee to ~143000 km and the perigee may come to ~275 km. Any inclination trimming is carried out at the apogee in that highly elliptical orbit, C3 will be slingshot at perigee burn to 400000 km for the trans-lunar injection.

As the apogee increases, there will be change in the perigee (increase in perigee) and here it went from 173 (175) to 221. What Scott is trying to say is that there is error in tracking because of the changes in perigee (it is like, hey I was looking at 175 and now C3 is at 221 and my plots does not account for it).

rahulm » 16 Jul 2023 12:07 pm wrote:
A new data point (for me) from this page: Chandrayaan 2 will also be used as a backup relay for comms with Earth.

Comms and deep space network and relay stations are the most boring but most important stuff. I suspected C2 will be used as a relay station (or even a monitoring & observation platform) and thanks for confirming the above.

arvin · Post by **arvin** » 18 Jul 2023 17:53

3rd orbit raising maneovure performed successfully as per ISRO.

https://twitter.com/isro/status/1681236 ... 74850?s=20

NRao · Post by **NRao** » 18 Jul 2023 18:09

rahulm » 16 Jul 2023 12:07 pm wrote: A new data point (for me) from this page: Chandrayaan 2 will also be used as a backup relay for comms with Earth.

C2 consisted of an orbiter, lander, and a rover. Of which they lost the last two, leaving an orbiter behind.

C3 is an improved C2. However since a healthy orbiter from C2 was already there, C3 was designed minus an orbiter. With C3 they just filled in the blanks with improved units.

madhu · Post by **madhu** » 18 Jul 2023 18:38

arvin wrote: ↑18 Jul 2023 17:53 3rd orbit raising maneovure performed successfully as per ISRO.

https://twitter.com/isro/status/1681236 ... 74850?s=20

orbital data is not updated. havens-above is showing that 184km x 41642km x 21.31deg inclination from 221km x 41610km x 21.28deg inclination
which means are they just adjusting the perigee height?

SSSalvi · Post by **SSSalvi** » 18 Jul 2023 18:51

^^^
Heavens Above is using data of 17 July 2023 20:50:24 UT.
Latest data to generate new orbit is still not in public.
I , like many others , is checking for updates every hour

arvin · Post by **arvin** » 18 Jul 2023 18:57

https://twitter.com/isro/status/1681293 ... 62499?s=20

Its 51400 km x 228 km.

madhu · Post by **madhu** » 18 Jul 2023 18:58

SSSalvi wrote: ↑18 Jul 2023 18:51 ^^^
Heavens Above is using data of 17 July 2023 20:50:24 UT.
Latest data to generate new orbit is still not in public.
I , like many others , is checking for updates every hour

Ya, now it's updated
@isro
Chandrayaan-3 Mission::
The spacecraft has attained a 51400 km x 228 km orbit, as planned.

SSSalvi · Post by **SSSalvi** » 18 Jul 2023 19:29

ISRO tweeter has just written the orbit size ( that too after someone commented for it !).

It does not serve the purpose of those who do detailed computation. A few more hours to get the full details.

But of course for the majority , the given info is good.

BTW, nice presentation about CH3 descent,Madhu.

Amber G. · Post by **Amber G.** » 18 Jul 2023 21:37

At the time of posting (8 minutes ago) CYIII is 56,382 Km from earth (center), ~ 440,000 Km away from the Moon .. moving in the orbit at 1.32 Km/sec .. and if you look towards earth it will look like:

(Some past orbits are being shown too)

madhu · Post by **madhu** » 18 Jul 2023 23:05

AMSAT-DL is going to live telecast CY3 when it is in it's field of view. One can watch here

https://twitter.com/amsatdl/status/1681 ... 40704?s=20

Is this movement of frequency is what Scott Tilley plotting as running doppler summary?

Thanks SSSalvi sir.

sanman · Post by **sanman** » 18 Jul 2023 23:17

madhu wrote: ↑18 Jul 2023 18:58 Ya, now it's updated
@isro
Chandrayaan-3 Mission::
The spacecraft has attained a 51400 km x 228 km orbit, as planned.

So is the next burn going to be TLI? Or are there one or more orbit-raising burns required first?

madhu · Post by **madhu** » 18 Jul 2023 23:24

sanman wrote: ↑18 Jul 2023 23:17
So is the next burn going to be TLI? Or are there one or more orbit-raising burns required first?

There is 2 more I think. One is planned for July 20, 2023, between 2 and 3 pm IST.

vsunder · Post by **vsunder** » 19 Jul 2023 04:57

The recent immense solar flare activity is a bit worrying. Sensitive electronics can get affected. Satellites have been fried in the past and this one caused serious disruptions in communications.

https://www.livescience.com/space/the-s ... ow-july-18

https://www.scientificamerican.com/arti ... lar-flare/

https://www.reuters.com/science/russian ... 023-07-17/

Flares of this type knocked out Space-X satellites in the past in 2022. The current one is a M class flare so below the worst an X class flare, nevertheless M class flares have done damage in the past to satellites and disrupted telemetry. So second level of intensity, with X being the highest intensity.

sanman · Post by **sanman** » 19 Jul 2023 11:06

vsunder wrote: ↑19 Jul 2023 04:57 The recent immense solar flare activity is a bit worrying. Sensitive electronics can get affected. Satellites have been fried in the past and this one caused serious disruptions in communications.

https://www.livescience.com/space/the-s ... ow-july-18

https://www.scientificamerican.com/arti ... lar-flare/

https://www.reuters.com/science/russian ... 023-07-17/

Flares of this type knocked out Space-X satellites in the past in 2022. The current one is a M class flare so below the worst an X class flare, nevertheless M class flares have done damage in the past to satellites and disrupted telemetry. So second level of intensity, with X being the highest intensity.

Oh damn - that's the last thing we need. Don't they usually check the solar weather forecast before launching these missions?

Does it help to be on the other side of the Earth at the time? Maybe we'll be lucky and the Earth will get in the way, to shield us.

madhu · Post by **madhu** » 19 Jul 2023 17:05

I am tiring to recreate the doppler summary from ScottTilley data. I see that Burn-2 and 3 matches exactly at the peak and the timing of them is more or less accurate from various sources. I do not have the exact time of Burn-1.

please correct me, my understanding is peaks in the plot corresponds to apogee and perigee right? and firing for orbit-raising maneuver should match the peaks?

any one know exact firing time?

madhu · Post by **madhu** » 19 Jul 2023 20:10

vsunder wrote: ↑19 Jul 2023 04:57 The recent immense solar flare activity is a bit worrying. Sensitive electronics can get affected. Satellites have been fried in the past and this one caused serious disruptions in communications.

https://www.livescience.com/space/the-s ... ow-july-18

https://www.scientificamerican.com/arti ... lar-flare/

https://www.reuters.com/science/russian ... 023-07-17/

Flares of this type knocked out Space-X satellites in the past in 2022. The current one is a M class flare so below the worst an X class flare, nevertheless M class flares have done damage in the past to satellites and disrupted telemetry. So second level of intensity, with X being the highest intensity.

https://twitter.com/TamithaSkov/status/ ... 44192?s=20
Twitter handle has posted the picture of flare.

Any update on health?

disha · Post by **disha** » 19 Jul 2023 20:25

madhu wrote: ↑19 Jul 2023 17:05
I am tiring to recreate the doppler summary from ScottTilley data. I see that Burn-2 and 3 matches exactly at the peak and the timing of them is more or less accurate from various sources. I do not have the exact time of Burn-1.

please correct me, my understanding is peaks in the plot corresponds to apogee and perigee right? and firing for orbit-raising maneuver should match the peaks?

any one know exact firing time?

As I understand, orbit raising burns are always performed at Perigee and Orbit inclination changes are optimal around apogee.

I think the chart is trying to say that the peak is post perigee burn OR the doppler peak corresponds to the perigee, as the craft approaches Earth, the doppler peak rises.

disha · Post by **disha** » 19 Jul 2023 20:29

vsunder wrote: ↑19 Jul 2023 04:57 The recent immense solar flare activity is a bit worrying. Sensitive electronics can get affected. Satellites have been fried in the past and this one caused serious disruptions in communications.

We wait for good news with baited breath. And hope that the craft is at Perigee and <400 Km when the storm arrives and the Earth's magnetosphere can protect it to some degree.

As mere mortals on this forum, all we can do is ask Dilbu to chant Hanuman Chalisa.

disha · Post by **disha** » 19 Jul 2023 20:31

madhu wrote: ↑19 Jul 2023 20:10 https://twitter.com/TamithaSkov/status/ ... 44192?s=20
Twitter handle has posted the picture of flare.

Any update on health?

That's a major flare and shows the might of our Sun. One can fit in half-a-dozen of Earth's under the arc of the flare! Thanks for the link to a cool pic!

SSSalvi · Post by **SSSalvi** » 19 Jul 2023 21:03

@Madhu
Here is a set of TLEs , if it helps
CHANDRAYAAN-3
1 57320U 23098A 23195.17804341 .00000480 -64874-6 00000+0 0 9994
2 57320 21.3150 8.8322 7350849 178.0282 188.8377 2.24991467 04
CHANDRAYAAN-3
1 57320U 23098A 23195.17845806 .00000480 -64965-6 00000+0 0 9996
2 57320 21.2842 8.8622 7354357 177.9705 189.0585 2.25106015 02
CHANDRAYAAN-3
1 57320U 23098A 23195.54389961 .00000473 -66941-6 00000+0 0 9990
2 57320 21.2463 8.7581 7349791 178.2157 125.1928 2.25009678 04

Also , if you zoom ( with a slider at bottom ) in https://celestrak.org/NORAD/elements/gr ... ATNR=57320 you will see a heavy activity between 1300 and 1500 hrs UT on 14th ... if it helps.

Sorry that I did not do it myself. Attempted , but seems lost, after having no touch with subject for over a decade.

madhu · Post by **madhu** » 19 Jul 2023 22:03

SSSalvi wrote: ↑19 Jul 2023 21:03 @Madhu

Also , if you zoom ( with a slider at bottom ) in https://celestrak.org/NORAD/elements/gr ... ATNR=57320 you will see a heavy activity between 1300 and 1500 hrs UT on 14th ... if it helps.

Sorry that I did not do it myself. Attempted , but seems lost, after having no touch with subject for over a decade.

thanks for the reply SSSalvi. i found some armature radio astronomers quoting the time burn time as '15-07-2023 12:17:00' IST or T06:47 UTC. which makes the line close to peak but not exact peak. error may be due to the use of Doppler and not radar data.

currently i am using

Code: Select all

    '15-07-2023 12:17:00', # The first orbit-raising maneuver (Earthbound perigee firing-1) 
                           # source:https://twitter.com/coastal8049/status/1680090422335655936?s=20 
    #
    '17-07-2023 13:14:00', # The second orbit-raising maneuver (Earthbound apogee firing) 
                           # source:https://twitter.com/isro/status/1680845817903722497?s=20 ( from time stamp)
    #
    '18-07-2023 14:14:00' # The third orbit-raising maneuver (Earthbound perigee firing) 
                          # source:https://twitter.com/amsatdl/status/1681234136814559232?s=20
                          # but isro tells its at 14-15 hrs https://twitter.com/isro/status/1680845817903722497  
    #

happy to update if i get better data. where did you get the TLE data from? is ISRO publishing it anywhere?

SSSalvi · Post by **SSSalvi** » 20 Jul 2023 08:47

where did you get the TLE data from? is ISRO publishing it anywhere?

The standard source : CElestrak

You have to make a special data request for the date range of any sat to them... reply comes within a day.

ISRO will never divulge their 'secrets' of data base .. and they have a right to do that. But, when it is available in open there is no point in not sharing.

In fact interested persons may just enjoy that. I hope someone from ISRO will be reading this.

One problem ( having talked to the concerned person long back ) may be because they believe more ( or traditionally developed their tools before TLE came around ) in State Vector or Ephemeris format rather than TLE.

But now that should not be a problem because both way converters are available online.

SSSalvi · Post by **SSSalvi** » 20 Jul 2023 10:46

Just for fun!
1st Image : Part of Earth orbit ( Light Yellow ) and Moon ( Green ) during initial period of Ch3.
2nd Image : Orbit raising period track of CH3 ( Pink )

3rd Image Earth to moon transfer and subsequent movement of CH3 around Moon ( Yellow )
4th Image : Deatailed view of Moon snatching away CH3 from Earth orbit

ramana · Post by **ramana** » 20 Jul 2023 15:31

Fourth orbit raising done.

https://twitter.com/ANI/status/16819638 ... DU_Bw&s=19

juvva · Post by **juvva** » 20 Jul 2023 16:01

from the earth bound orbits diagram shared earlier, looks like next burn will be for TLI (?)

SSSalvi · Post by **SSSalvi** » 20 Jul 2023 16:38

No, You have to do some more waiting.
Apogee now about 71000 Kms, Period 1 day.
At the end of 4th such orbit next Orbit raising to about 127000 kms apogee, 3+ days orbit period.
There will be 3 such orbits after which the actual transfer orbit will start.
So another 7 orbits for TLI orbit.
Transfer orbit has a orbital period of about 8.5 days, but before 1/2 of orbit is completed ( just before Apogee of about 362000 kms ), Moon will take away the the CH3.
( Its a plain boundary issue like any nations. Moon will claim that beyond Lagrange1 ( 323050 Kms ) point it is my territory , if I am around , and your ISRO has presented it to me on platter

)

drnayar · Post by **drnayar** » 20 Jul 2023 19:41

https://pbs.twimg.com/media/F1eEUhwaMAA ... ame=medium

juvva · Post by **juvva** » 20 Jul 2023 20:31

SSSalvi wrote: ↑20 Jul 2023 16:38 No, You have to do some more waiting.
Apogee now about 71000 Kms, Period 1 day.
At the end of 4th such orbit next Orbit raising to about 127000 kms apogee, 3+ days orbit period.
There will be 3 such orbits after which the actual transfer orbit will start.
So another 7 orbits for TLI orbit.
Transfer orbit has a orbital period of about 8.5 days, but before 1/2 of orbit is completed ( just before Apogee of about 362000 kms ), Moon will take away the the CH3.
( Its a plain boundary issue like any nations. Moon will claim that beyond Lagrange1 ( 323050 Kms ) point it is my territory , if I am around , and your ISRO has presented it to me on platter )

ok thanks!
but the orbital diagrams from isro show only 5 earth bound orbit sizes (inluding the initial launch orbit).
maybe they over simplified in their illustration

SSSalvi · Post by **SSSalvi** » 20 Jul 2023 20:56

I wanted to tabulate for my reference. Doing it now.
1st Burn : July 15 06:47 UTC 41762 km x 173
2nd Burn : July 16 41603 km x 226 THis seems to be unplanned so confusion .... To raise Perigee from 173 to 226
3rd burn : July 17 51400 km x 228 km
4th Burn : July 20 71351 km x 233

madhu · Post by **madhu** » 20 Jul 2023 22:00

SSSalvi wrote: ↑20 Jul 2023 20:56 I wanted to tabulate for my reference. Doing it now.
1st Burn : July 15 06:47 UTC 41762 km x 173
2nd Burn : July 16 41603 km x 226 THis seems to be unplanned so confusion .... To raise Perigee from 173 to 226
3rd burn : July 17 51400 km x 228 km
4th Burn : July 20 71351 km x 233

thx S^3 ji, adding source will help in long run. i know you are taking it from ISRO tweet but a link will be handy so adding it for your help

Code: Select all

orbitRaisingManeuver =[
    '15-07-2023 12:17:00', # The first orbit-raising maneuver (Earthbound perigee firing-1) 
                           # source:https://twitter.com/coastal8049/status/1680090422335655936?s=20 (2023-07-15T06:47 UTC)
    #
    '17-07-2023 13:14:00', # The second orbit-raising maneuver (Earthbound apogee firing) 
                           # source:https://twitter.com/isro/status/1680845817903722497?s=20 ( from time stamp)
    #
    '18-07-2023 14:30:00' # The third orbit-raising maneuver (Earthbound perigee firing) 
                          # source:https://twitter.com/amsatdl/status/1681234136814559232?s=20  (2023-07-18 08:22:00 ITC)
                          # but isro tells its at 14-15 hrs https://twitter.com/isro/status/1680845817903722497  
    #
    '20-07-2023 14:30:00' # The fourth orbit-raising maneuver (Earth-bound perigee firing)
                          # source:https://twitter.com/isro/status/1681960236347965440 (considered middle b/w 2 & 3)
                          #     https://twitter.com/isro/status/1682029955746770944?s=20 (71351 km x 233 km)
]

CY3Orbital = [
    ' 41762 km x 173 km orbit inc 21.3°', #orbit-raising maneuver - 1; spacecraft is now in 41762 km x 173 km xorbit
    ' 41603 km x 226 km orbit',           #orbit-raising maneuver - 2; spacecraft is now in 41603 km x 226 km orbit
    ' 51400 km x 228 km orbit',           #orbit-raising maneuver - 3; spacecraft is now in 51400 km x 228 km orbit
    ' 71351 km x 233 km orbit',           #orbit-raising maneuver - 4; spacecraft is now in 71351 km x 233 km orbit. ]

madhu · Post by **madhu** » 20 Jul 2023 22:18

AMSAT-DL

@amsatdl
#Chandrayaan3 time-lapse at the end of today's observation @SternwarteBO. JPL/Horizons trajectory data was good enough for tracking! Thanks @isro for the update.

shows the jumping of frequency as soon as the spacecraft approaches the perigee. I was following it from 12.00pm today till CY3 set at observatory.

SriKumar · Post by **SriKumar** » 21 Jul 2023 05:05

SSSalvi wrote: ↑20 Jul 2023 10:46 Just for fun!
1st Image : Part of Earth orbit ( Light Yellow ) and Moon ( Green ) during initial period of Ch3.
2nd Image : Orbit raising period track of CH3 ( Pink )

Nice plots. Especially the 3rd and 4th plots show the track of CY3 being injected into a lunar equatorial orbit and immediately being steered/forced into a lunar polar orbit. That's quite the 90 degree turn; the thrust generated by its on-board engines. The lander and its electronics must be seeing tremendous stresses from the drastic change in trakectory.

SSSalvi · Post by **SSSalvi** » 21 Jul 2023 10:08

That '90 deg turn' is not by rocket motors.

Actually after the Lagrange1 distance ( it is the distance between Moon and Earth in this case ) which is an equi-potential type of situation where the gravitaional forces of Earth and Moon are equal and depending on whether thw satellite is in Moon Gravity or Earth gravity it will be pulled by it, and will either crash into the body or orbit it depending on the situation.
Here is an image from my old blog ( It shows Sun L1 point though )

1.At that time the CH# is near Earth Apogee so its speed is very low
2. It is beyond L1 distance

So. as Moon comes near by CH3 gets 'pulled' in its gravity rather than it being pushed into Moon orbit using force onboard. And Handover Takeover is very smooth because CH3 is almost no speed at apogee..

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

And, we enjoying the multi party tussle.

madhu · Post by **madhu** » 21 Jul 2023 13:49

here is the updated trajectory monitoring plot. as per scott's tweet the spacecraft made a low pass just after the post burn-4. next challange is to see if i can calculate orbit parameters from the doppler data that I have. i know it will be off as i will be using simplified model but just fun doing it.

can i do it with this data? i have frequency and time so i should be able to there differences to know the drift. my understanding is right?