Chandrayan-2 Mission

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 08:20

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


Did you see a data rate even for a short time?

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Re: Chandrayan-2 Mission

Postby sudarshan » 10 Sep 2019 08:27

No data rate (the data rate was "-"). It seemed like just the carrier signal on the downlink. I guess the lander won't send data to any old donkey who asks for it?

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 08:31

UlanBatori wrote: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... ??


-141 dBm is power in decibels per miliwatt reference. It is the power at the receiver of the ground station after passing through filters, low-noise amplifiers and down converters.

antilog(-141/10) = 7.94E-15 mW or 7.94E-18 Watts.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 08:37

sudarshan wrote:No data rate (the data rate was "-"). It seemed like just the carrier signal on the downlink. I guess the lander won't send data to any old donkey who asks for it?


It means one of two things. One, the transmitter and/or antenna on Vikram was destroyed. Two it could mean that Vikram is transmitting, but it is below the noise floor of the ground station receiver due to Vikram's antenna being pointed somewhere else.

The noise floor, as a rough rule of thumb is -174 dBm + 10log(receiver bandwidth). A receiver with 1 Hz bandwidth has a noise floor of -174 dBm and at 1 KHz it would be -144 dBm. See: https://en.wikipedia.org/wiki/Johnson%E ... uist_noise

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Re: Chandrayan-2 Mission

Postby sudarshan » 10 Sep 2019 08:42

It was briefly at -115 dB (around the time of suryag's post saying to "go check on the website"). At that time I was so excited about the dB value, that I didn't notice the data rate or whether the downlink signal was just the carrier or actual data. Didn't get a screengrab either. Kicking myself for it now. We'll see if it comes back.
Last edited by sudarshan on 10 Sep 2019 08:42, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby SSSalvi » 10 Sep 2019 08:42

Right now ( 0820 IST ) Goldstone is transmitting 11 kw @2.1 GHz using ant#24 to CY2. Data rate is not there in status panel.

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 08:44

sudarshan wrote:It was briefly at -115 dB (around the time of suryag's post saying to "go check on the website"). At that time I was so excited about the dB value, that I didn't notice the data rate or whether the downlink signal was just the carrier or actual data. Didn't get a screengrab either. Kicking myself for it now. We'll see if it comes back.

Screenshots please, saar :). I am also trying to monitor it to see if anything changes. Will share if I spot something.

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Re: Chandrayan-2 Mission

Postby prasannasimha » 10 Sep 2019 08:46

The plane sune wavd is the carrier wave. The modulated wave pic is tge data transmission occuring.

No terrestrial telescope has the resolution to even image Apollo landing sites and can only be imaged by LRO and now Chandrayaan.
This is dictated by optics. Our largest telescope does not have the two point discirimination capability to even image the Apollo lander let alone the much smaller Vikram so lets not have flights of fancy.
The signals we are getting can be still due to a wrong lock. We have to see. Even if ruggadized ( all satellites undergo thermoacoustic testing) we need to see of the lander rolerated the unscheduled hard landing. Getring just some communicarion on itself would be big as we would get the crucial data wrt what happened in the last phase.
There is no self righting mechanism for the Lander so we will not be able to kick and jiggle it open . The 0eople at ISTRAC have salvaged previous missions but problem for reorientation is that the lander is on a surface so refiring will not help . They will be thinking of out of the box things. If lander awakens it will be an Apollo 13 type of thing of problem solving pr more like Hitens salvage.
The

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 08:57

sudarshan wrote:It was briefly at -115 dB (around the time of suryag's post saying to "go check on the website"). At that time I was so excited about the dB value, that I didn't notice the data rate or whether the downlink signal was just the carrier or actual data. Didn't get a screengrab either. Kicking myself for it now. We'll see if it comes back.

Per this tweet (not sure how genuine it it is, it claims to be a bot that monitors NASA's DSN site):

Deep Space Network
‏ @dsn_status
2h2 hours ago

DSS 24 carrier lock on Chandrayaan-2 Lander
Frequency: 2.2846GHz
Signal strength: -138dBm
IDLE OFF 1 TURBO

https://twitter.com/dsn_status/status/1 ... 9194380289

The Goldstone antenna name is indeed DSS 24.

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 09:01

Speculation from an armchair satcomm(am a cellular RF engineer by training) as to what is being trained

1. On the Uplink frequency the DSN transmits tone and data(some inane data not like asking to send pictures) because it doesnt know if the receiver is good, we dont want the lander to transmit at high power and exhaust the battery if the DSN is not getting any good signal
2. Once Tone and data is received by the receiver the receiver tries to initiate comms by transmitting tone
3. The DSN looks for a tone on the DL
4. Once power above noise floor is measured(noise floor is very subjective and based on link budget, so we dont know what Vikram's noise floor would be configured at the DSN receiver) then freq errors, phase drifts are measured to see if this is indeed coming from the intended party or some background noise
5. At this point if the receiver parameters are good the DSN may transmit another separate command to start receiving some data because you now know that the lander can transmit something meaningful and will not rail on TX power and exhaust batteries

What ISRO engineers might do is
1. collect the data from Madrid/Goldstone where tone was being seen at, check the parameters and lock the azimuths of the antennas(?) because i see that the DSN azimuth was changing which i believe is their attempt to try different orientations to get through
2. Once they lock the azimuths they can possibly transmit at higher power around the same time and orientation and get something back

literally, the chances are slim but miracles often happen on the RF side. I just want to hear "Bengaluru this is goldstone we have your bird" this was the dialogue in that johnny walker mars mission video

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 09:05

Thanks for the explanation saar. Any idea on what that tweet I posted above means? What's a carrier lock - is it a lock on to an incoming signal?

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 09:05

suryag wrote:I just want to hear "Bengaluru this is goldstone we have your bird" this was the dialogue in that johnny walker mars mission video

Yeah, that was a very well done video. Fingers crossed onlee.

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Re: Chandrayan-2 Mission

Postby sudarshan » 10 Sep 2019 09:09

arshyam wrote:Per this tweet (not sure how genuine it it is, it claims to be a bot that monitors NASA's DSN site):


That tweet might be genuine, it seems to be around the same time that suryag said to go check the site.

I've been monitoring the site so far, but now I have to knock it off and go attend to something else. I'll leave it to you other guys.

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 09:11

Got it!

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 09:11

Sir carrier lock means we are mostly seeing power which is above noise floor and the lock signifies that there are no runaway frequency errors or phase drifts. The tone is generally the easiest to transmit as there is generally no modulator/demodulator involved and the transmitter + power amplifier can be pre-programmed to send a sine wave without baseband(modulator/demodulator) being involved. Data transmission needs more SNR than tone, also i dont know the antenna architecture of the lander do they have 2xRX-TX antennas or 4xRX-TX antennas, but if there is no transmit diversity on the lander then you need to really hit the right orientation if it is not an omnidirectional antenna

If we indeed received tone and it is consistent it tells a lot about the health of the craft - first it didnt burn or suffer fire internally, all components are in their places along with connections, most likely the antennas lost orientation or were broken by yakherders

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 09:12

Down Signal
Type:Carrier
Data Rate: 0.00 b/sec
Frequency: 2.27GHz
Power Received: -132.38dBm (5.78x10^-20 kW)

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Re: Chandrayan-2 Mission

Postby sudarshan » 10 Sep 2019 09:12

Woo hoo! -118 dB. Who's going to be first with the screenshot?

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 09:14

The power received went up to -134.19 dBM and then the down signal went off, came back for a sec and again went off.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 09:19

I wonder if Goldstone can switch to the higher gain antenna?
Best downlink power seen about -114 dBm.
Last edited by Mort Walker on 10 Sep 2019 09:20, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby sudarshan » 10 Sep 2019 09:19

Image

OK I'm out for now.
Last edited by sudarshan on 10 Sep 2019 09:24, edited 2 times in total.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 09:21

No data rates yet.

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 09:21

-118 is definitely encouraging

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 09:22

Mort sir they have to look at the received tone characteristics before they request data

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 09:22

I saw -111 dBm now. A 7 dB improvement.

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Re: Chandrayan-2 Mission

Postby gauravsharma » 10 Sep 2019 09:25

SPACECRAFT
NAME
Chandrayaan-2 Lander
RANGE
404.77 thousand km
ROUND-TRIP LIGHT TIME
2.70 sec
ANTENNA
NAME
DSS 24
AZIMUTH
158.76 deg
ELEVATION
29.70 deg
WIND SPEED
27.78 km/hr
MODE
-
UP SIGNAL
SOURCE
CHANDRAYAAN-2 LANDER
TYPE
DATA
DATA RATE
-
FREQUENCY
2.10 GHz
POWER TRANSMITTED
11.58 kW
DOWN SIGNAL
SOURCE
CHANDRAYAAN-2 LANDER
TYPE
CARRIER
DATA RATE
0.00 b/sec
FREQUENCY
2.27 GHz
POWER RECEIVED
-110.00 dBm
(9.99 x 10-18 kW)
Last edited by gauravsharma on 10 Sep 2019 09:26, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 09:25

suryag wrote:Mort sir they have to look at the received tone characteristics before they request data


Yes, I guess they're just looking for a carrier. No data is being sent up.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 09:27

At -108 dBm now.

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 09:27

Long night for isro telemetry folks

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Re: Chandrayan-2 Mission

Postby Bibhas » 10 Sep 2019 09:29

I saw -108.5 dB right now.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 09:29

I wonder if it actually is Vikram or is it something else (some other satellite) at 2.27 GHz.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 10 Sep 2019 09:30

Gone now.

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Re: Chandrayan-2 Mission

Postby gashish » 10 Sep 2019 09:31

Here is the snapshot at 8:32pm pst

Image
Image
multiple image upload

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Re: Chandrayan-2 Mission

Postby NRao » 10 Sep 2019 09:32

What does all this mean?

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 09:32

Here's what I saw:

Image

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Re: Chandrayan-2 Mission

Postby disha » 10 Sep 2019 09:33

Thanks to all the RF warriors trying to get a lock on C2Lander.

Hoping for the best.

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Re: Chandrayan-2 Mission

Postby gauravsharma » 10 Sep 2019 09:35

On the other hand CHANDRAYAAN-2 ORBITER is sending data at the rate of 999.0 b/s with power level -125dBm to ANT26 (Goldstone)

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 09:35

Sir the Madrid one was at 8 GHz that would have definitely been Vikram again the tests would be to lock the azimuth angle and checknif you see tone only when you send tone ... fingers crossed and praying

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Re: Chandrayan-2 Mission

Postby arshyam » 10 Sep 2019 09:35

suryag wrote:Sir carrier lock means we are mostly seeing power which is above noise floor and the lock signifies that there are no runaway frequency errors or phase drifts. The tone is generally the easiest to transmit as there is generally no modulator/demodulator involved and the transmitter + power amplifier can be pre-programmed to send a sine wave without baseband(modulator/demodulator) being involved. Data transmission needs more SNR than tone, also i dont know the antenna architecture of the lander do they have 2xRX-TX antennas or 4xRX-TX antennas, but if there is no transmit diversity on the lander then you need to really hit the right orientation if it is not an omnidirectional antenna

If we indeed received tone and it is consistent it tells a lot about the health of the craft - first it didnt burn or suffer fire internally, all components are in their places along with connections, most likely the antennas lost orientation or were broken by yakherders

Thanks, so does this mean we are receiving tone?

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Re: Chandrayan-2 Mission

Postby suryag » 10 Sep 2019 09:37

From an armchair perspective yes

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Re: Chandrayan-2 Mission

Postby Ramnath » 10 Sep 2019 09:39

Was looking at the purported Bot feed on twitter.
It also had mentions about the CY Orbiter link.
Something to the effect that 7hrs ago, there was carrier lock at signal strength of -141dbm(only carrier) on dss65. Then 6 hours ago, there was a downlink ongoing at 1kbps. So the signal strength numbers of the lander don't seem to be so weak to be discounted as noise.


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