Chandrayan-2 Mission

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UlanBatori
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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 03:12

Increasing chance of Vikram saying "kaun bolta hai?" until Sep. 15, and then... nothing. But that is a week away.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 03:24

ramana, to answer an earlier question: If it wasn't more or less upright 100 m above the surface, and its thrusters were operating, it would have splattered all over the surface. So I think the craft WAS "more or less" right side up. Which means it was decelerating, but maybe wandering all over the place. The controller was trying its best to center it properly. Given its being in one piece, it cannot have fallen very far. I suspect that it actually LANDED, but maybe one leg failed, or it came down on a slope and keeled over (pretty difficult, look how wide the legs are pointed).

All these say that it is recoverable when the sun is sufficiently up (over the next week!)
But if the comms are destroyed, then it cannot be instructed to correct itself. So the original comm failure is still the big catch. There HAD to be one more error after the fully automatic system took over, as I explained a few pages ago. Maybe something else got shaken loose by the same thing that killed the comms.

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Re: Chandrayan-2 Mission

Postby Vayutuvan » 10 Sep 2019 04:00

ramana wrote:UB, JayS pointed out that the thrust control valve is a spool valve.
My old Hydraulic Control systems text book says its a mass(spool) and spring(fuel line) system and often resonates.
....

First lesson on spool valves
Second lesson on spool valves

chetak
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Re: Chandrayan-2 Mission

Postby chetak » 10 Sep 2019 04:01

UlanBatori wrote:UBCN diagnosis (posted b4) of "Too Much Thrust" (on one thruster was the quote) means combustion instability. Liquid fuel is metered through a choked nozzle with sufficient pressure ratio to prevent feedback from the combustor to the fuel source. So it is probably not because of too much fuel flow.
Combustion intability is amplitude of oscillation rising, sometimes without bound until the thing explodes. But it gives lots of thrust as the liners, housing all burn.
Average thrust may be high, but vibration level may be extreme. Enough to knock comm. electronics out, maybe? Though a single solder joint breaking should not bring down a mission of this sort!


All components are MIL grade at the very least and so will the soldering be to aerospace standards.

If the level of vibration is as high as you are suggesting than very little would have survived even on vikram despite the shock isolation between the lander and its guest

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Re: Chandrayan-2 Mission

Postby ramana » 10 Sep 2019 04:34

Need a NG&C expert here.

The AIAA paper says in 2nd para page 5, that
The INS after updating the state vector is used for the first burn. During the long coast phase also, the attitude and gyro drifts are updated using star tracker. The accelerometer bias is also updated during the long coast phase. The INS state vector is used during the second burn. During vertical descent...."



Basically the INS and the other two instruments have to be in sync before vertical descent...

What if the attitude and gyro drifts did not get updated during the long coast from the star tracker and errors accumulate leading to the extra thrust being commanded to make up for the shortfall?
This would show up as extra thrust being felt during the switch over to fine burn.

Maybe this is the start of the violent movement during the switch over?

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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 04:52

^^
I KNEW it! Next time they should relay the ground controller's soothing voice back to the lander:
2.1 km to go.. Situation Naarmal!

That would keep out all doubt aka oscillation.

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Re: Chandrayan-2 Mission

Postby ramana » 10 Sep 2019 04:54

Give your comment minus the Lahori speak.

UlanBatori
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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 04:59

chetak wrote:All components are MIL grade at the very least and so will the soldering be to aerospace standards.
If the level of vibration is as high as you are suggesting than very little would have survived even on vikram {U mean Aar-Biter} despite the shock isolation between the lander and its guest

Good point. Maybe the comm failure was just a freak of freaks. May even have repented its evil ways and be ready to start as soon as sun comes up. This is what happens to kitchen faucets in Ulan Bator. Drip-drip drip... despite hajaar attempts to re-tighten etc. Then say "Phoeey!" and next day it is Hey! Leak stopped!
It does seem to be true that the Orbiter is doing well. Which discounts the possibility of any explosion.

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Re: Chandrayan-2 Mission

Postby chetak » 10 Sep 2019 05:17

ramana wrote:Need a NG&C expert here.

The AIAA paper says in 2nd para page 5, that
The INS after updating the state vector is used for the first burn. During the long coast phase also, the attitude and gyro drifts are updated using star tracker. The accelerometer bias is also updated during the long coast phase. The INS state vector is used during the second burn. During vertical descent...."



Basically the INS and the other two instruments have to be in sync before vertical descent...

What if the attitude and gyro drifts did not get updated during the long coast from the star tracker and errors accumulate leading to the extra thrust being commanded to make up for the shortfall?
This would show up as extra thrust being felt during the switch over to fine burn.

Maybe this is the start of the violent movement during the switch over?


would anyone know if the stabilization system is 3 axes or 6 axes

suryag
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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 05:23

Wtf Lander talking ???

Have screen shot

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 05:24

Check website

https://eyes.nasa.gov/dsn/dsn.html

Had my eyes pasted on the dl signal seems some activity

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 05:27

Frequency - 8.41 GHz

Power received - -123.98dBm

But now it’s gone :((

Was that a glitch swear I saw it and took screenshot took

Idiosyncrasies

In off-nominal scenarios when a project may be attempting to recover a spacecraft that is in safe mode or experiencing other operational challenges, an antenna may wrongly report that is receiving data from the spacecraft in question. While the ground station is searching for a signal, it may ‘lock on’ to a signal from a different spacecraft and wrongly identify it as the spacecraft being searched for. This is particularly common with spacecraft at Mars as multiple spacecraft are within the field of view of a single DSN antenna. For example, attempts to recover the Opportunity Rover (MERB) may appear successful when the antenna has actually locked on to a signal from one of the orbiters around Mars such as MAVEN or MRO. When this occurs, engineers ask the antenna to ‘drop lock’ and the hunt for the spacecraft continues.“

chetak
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Re: Chandrayan-2 Mission

Postby chetak » 10 Sep 2019 05:29

ramana wrote:Need a NG&C expert here.

The AIAA paper says in 2nd para page 5, that
The INS after updating the state vector is used for the first burn. During the long coast phase also, the attitude and gyro drifts are updated using star tracker. The accelerometer bias is also updated during the long coast phase. The INS state vector is used during the second burn. During vertical descent...."



Basically the INS and the other two instruments have to be in sync before vertical descent...

What if the attitude and gyro drifts did not get updated during the long coast from the star tracker and errors accumulate leading to the extra thrust being commanded to make up for the shortfall?
This would show up as extra thrust being felt during the switch over to fine burn.

Maybe this is the start of the violent movement during the switch over?


to minimize the risk of appreciable drift, the INS would have been fired up as late as possible but still given it enough time to settle and stabilize.

the orbiter INS would probably be used correct the lander INS a short while before the separation and give it an initial position as it were so that the lander INS would know where it was when it woke up and thus be "aware" of its IP at the start of the descent phase

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Re: Chandrayan-2 Mission

Postby ramana » 10 Sep 2019 05:31

Stabilization is six axis during the descent phase. They have 4 800N engiens for braking or retro rockets and eight 50N thursters at the four corners two each for attitude control.

The G&NC systems and the throttle capability can accommodate accumulated errors at end of rough braking phase.

See page 9 of the AIAA paper.

Looks like all this worked except for the extra thrust during switch over which caused the landing 500m away.
We need more insight into the terrain that caused the lander on its side.

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 05:59


UlanBatori
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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 06:39

ramana: I can't believe that just a bit of "extra thrust" would throw the mission like that. That's a DC bias for a controller, hain? At the handover to fine positioning the craft was still at least 500m up as I recall?

The scenario was to come down to 100m and hover briefly for decision-making. If that was possible, then the lander could have easily coasted back 500m if it knew where it was. So the comm failure must have been compounded by loss of position data.

OK, even then, the pattern recognition must have had a zoom-out feature if what it saw was not what it expected (like we do when we look at a map). It would have realized that it was looking at the ground 500, too far out. Still time to drift back. So I don't believe it was controller failure.
Propulsion system was the untested part: think about it. First space flight test of the engines on the lander.

Nothing to agonize about. The first 3 or 4 tests should have been in LEO, but that would have been 3 useless launches. Instead they packed everything into one, and "almost had it all". So now that we know what kinds of people make the decisions at ISRO....

Still a week to go for Sep. 14. (not 15th: we just looked up the calendar for the full moon). Maybe still Sep. 13 where u r. No reason to give up hope: they should keep trying with as much amplitude for the sender and as much sensitivity for the receiver as they can.

I think it is going to wake up, I think they will retract 2 legs and rock it upright (OK, main nozzles will be kaput but who cares). Then they will be able to open the door for the BLC to roll out. And then they are going to find that come October 8, it wakes up again - and stays on for the next 5 years. I bet they overdesigned, and that it will survive the lunar night. No real reason why any component should fail just because it gets a bit cold. And if it survives one night it will survive indefinitely.

UBCN prediction. Most accurate Predictor of the Indian Elections, remember?
Last edited by UlanBatori on 10 Sep 2019 06:44, edited 1 time in total.

suryag
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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 06:41

Ubcn garu please see my screenshot unless it was a glitch it shows the base station was receiving the ch2l carrier at a decent power

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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 06:45

^^ Is it confirmed that it is not a mirage or whatever they were saying? It should get stronger by the minute as the sun rises higher!

suryag
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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 06:49

well i had my eyes pasted on this and and it held for about 1 min or so(couldnt believe my eyes, pulled over and stopped on the freeway shoulder and took screenshot) they seem to be changing the azimuth slowly and after that it didnt happen(no more DL signal) btw received power is decent hoping against hope ...

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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 06:54

It will get better. Only 4E-16 W that time. How do they calculate that power: is that source assuming omni-directional?

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 07:11

Quickly goto dsn, goldstone is able to get DL signal from CH2L :) earlier it was Madrid station

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Re: Chandrayan-2 Mission

Postby sudarshan » 10 Sep 2019 07:13

suryag wrote:Quickly goto dsn, goldstone is able to get DL signal from CH2L :) earlier it was Madrid station


I see it, seems like two-way communication. Moon must be visible from California now. In Madrid it would be close to setting or already set. Is there any significance to the shape of the wave form? Seems like the signal from CH2L is just the carrier frequency with no data (pinging?).

-116 dB.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 07:21

Does that mean it has risen by 7dB already? Is this a measure of source or receiver?

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Re: Chandrayan-2 Mission

Postby ramana » 10 Sep 2019 07:23



Awesome..10^-19

Maybe once batteries charge up.

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Re: Chandrayan-2 Mission

Postby sudarshan » 10 Sep 2019 07:24

Erratic - down to -143 dB now. Dies occasionally and then comes back.

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Re: Chandrayan-2 Mission

Postby arvin » 10 Sep 2019 07:26

power received was varying from -139 to -141 db.

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Re: Chandrayan-2 Mission

Postby ramana » 10 Sep 2019 07:27

It's on ICU.

Still excellent.

Maybe should let rover stay in lander as thermal protection and come out after next lunar day?

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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 07:36

That's weird: that you can actually look step outside and look directly at the lander (without seeing it so far). Aren't the big telescopes capable of zooming right in at this short distance? Even amateurs might see a flash from the metal foil?

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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 07:38

ramana wrote:Maybe should let rover stay in lander as thermal protection and come out after next lunar day?

To get an additional half day?
Maybe if they manage to right it, with the legs retracted, the ramp may be shallow enough to get the BailGadi roll back up before nightfall. I doubt if they can close the door though: wouldn't they have built that in if they anticipated going past 1 day?

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 07:42

This is awesome news! Any further screenshots?


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Re: Chandrayan-2 Mission

Postby TandavBrahmand » 10 Sep 2019 07:47

UlanBatori wrote:That's weird: that you can actually look step outside and look directly at the lander (without seeing it so far). Aren't the big telescopes capable of zooming right in at this short distance? Even amateurs might see a flash from the metal foil?


UBji - Nope. No ground-based telescope, not even Keck or others have the resolution required to "see" anything.

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 07:48

I am able to see an up signal only...

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Re: Chandrayan-2 Mission

Postby UlanBatori » 10 Sep 2019 07:52

Pingreji pls: what is an up signal and what does -141 dB mean? Compared to 1 watt? And is that the source (because receiver power should depend on solid angle of capture), hain? Like if I got this much power with this much area, and I know it came from this source, then the omni-directional source should have a power of... ??

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 07:54

Up means an outgoing signal from the ground station I suppose? Down signal indicates a response from the spacecraft. Happy to be corrected.

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 07:59

Still seeing only one way transmission to the lander (CH2L). Only the orbiter CH2O is showing two way communications. I hope you guys were able to get screenshots of what you saw :)

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Re: Chandrayan-2 Mission

Postby Vayutuvan » 10 Sep 2019 08:06

UlanBatori wrote:Pingreji pls: ... ??


Sire, why "pingreji"? Naarmal mul mul roomaal would do naa?!

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Re: Chandrayan-2 Mission

Postby Najunamar » 10 Sep 2019 08:07

I see blue lines for the up signal - is the white one for down signal? If so there are times when I do see the white wave...

Also, yes can see the moon clearly in CA sky now (sigh...)

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 08:11

This is the description panel fir the NASA DSN page :

Below is the current state of the Deep Space network as established from available data updated every 5 seconds. Click a dish to learn more about the live connection between the spacecraft and the ground. The legend (below) shows the various connections between spacecraft and the ground. A carrier is a pure radio 'tone' used to establish communications or for navigation. Data is commands, scientific measurements or housekeeping engineering information. Uplink is commands being sent 'up' to a spacecraft. Downlink is data received from a spacecraft.

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Re: Chandrayan-2 Mission

Postby gashish » 10 Sep 2019 08:19

I did see downlink signal on Gladstone receiver. Forget to take the screenshot :oops:


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