Bharat Rakshak

They say DSN has received signals from Vikram.
https://eyes.nasa.gov/dsn/dsn.html

Click on Madrid -> CH2L.

SPACECRAFT
NAME
Chandrayaan-2 Lander

RANGE
-

ROUND-TRIP LIGHT TIME
-

ANTENNA
NAME
DSS 54

AZIMUTH
106.22 deg

ELEVATION
11.84 deg

WIND SPEED
15.43 km/hr

MODE
-

DOWN SIGNAL
SOURCE
CHANDRAYAAN-2 LANDER

TYPE
DATA

DATA RATE
1.00 kb/sec

FREQUENCY
2.28 GHz

POWER RECEIVED
-127.74 dBm
(1.68 x 10-19 kW)

Lander separated from orbiter.
There is media coverage of Chandrayaan-2 lander
Landing from 1:30 AM IST onwards on Sept 7 and Pragyan rover rolling out from the lander from 5:30 AM IST.

Excellent! What would be the challenge of detaching the Vikram lander from the main orbiter, vis-a-vis more or less the same operation on the moon impact probe( MIP) onboard Chandrayaan-1? Is it just a question of more bolts to be sheared, or not even that?

SwamyG wrote:They say DSN has received signals from Vikram.
https://eyes.nasa.gov/dsn/dsn.html

Click on Madrid -> CH2L.

The LRO antenna seems to be tracking the orbiter.

Varoon Shekhar wrote:Excellent! What would be the challenge of detaching the Vikram lander from the main orbiter, vis-a-vis more or less the same operation on the moon impact probe( MIP) onboard Chandrayaan-1? Is it just a question of more bolts to be sheared, or not even that?

Vikram must not collide with the Orbiter after separation and separation must be clean

Varoon Shekhar wrote:Excellent! What would be the challenge of detaching the Vikram lander from the main orbiter, vis-a-vis more or less the same operation on the moon impact probe( MIP) onboard Chandrayaan-1? Is it just a question of more bolts to be sheared, or not even that?

Vikram has already separated. Are you asking the separation of Pragyan from Vikram? Read that Pragyan will roll out of Vikram. I wish there was a video of it later. At least pictures.

No, I was asking what the difference is between the MIP separation on board Chandrayaan-1 in 2008, and the separation of the Vikram lander from Chandrayaan-2. Were there any extra technological challenges in the latter? So, it's avoiding a collision between Vikram and the main orbiter. Since the MIP on Chandrayaan-1 is more of a 'free fall' one supposes. Thanks!

Yes. Until the deorbit test tomorrow where the engines on Vikram will be fired for 3 seconds, Vikram and Orbiter will be in the same orbit. The animations were a little confusing to me about which craft will be ahead. One of the animations had Vikram ahead, in another behind. Or maybe I misread the animation.

And in all the justified excitement and anticipation about the lander/rover, let's not lose sight of the orbiter! It must now be in a functioning mode, or close to it. With all its 8-9 payloads. Okay, soon enough.

Varoon Shekhar wrote:And in all the justified excitement and anticipation about the lander/rover, let's not lose sight of the orbiter! It must now be in a functioning mode, or close to it. With all its 8-9 payloads. Okay, soon enough.

we are monitoring.

The health of the orbiter and lander is being monitored from the Mission Operations Complex (MOX) at Isro Telemetry, Tracking and Command Network (ISTRAC) in Bengaluru with support from Indian Deep Space Network (IDSN) antennas at Bylalu, near Bengaluru," Isro said.

If I understand correctly, Vikram has to be flipped around 180 degrees before firing its engines to deorbit. Then it has to be flipped back again for the landing.

I didn't understand the flipping here. Can you please explain

prasannasimha wrote:

Amber G. wrote: From what I know, the main reason was existing restrictions/policy/GOI rules about RTG/RHU (Radioisotopic generator or heating units). ISRO did not decide to plan for RHU because they did not think that they will get clearance in the short time they were shooting for. (Weight etc was not the factor it is mostly that people don't like "nuclear" anything being sent into space. - politically it is quite difficult).. Better to design with what they can use. (
I hope there is new thinking there, and they use Pu238 as RHU unit for future space probes.

Currently Pu238 is only being produced in Russia (In fact US had to get it from Russia for an RTG some time back) Strontium, Polonium and Americium have also been used. I think one iof the recent RTG's sent had Americium.
The original plan was to ahve a Rover from USSR but after Phobos Grunt mishap Russia backed out so we did not plan one with an RTG.

From what I know, this is not exactly true. True that US stopped (just like US is not opening new reactors, and even many isotopes, there was shortage it was cheaper to import from outside US) producing Pu238 but it has started again (within last few years) as there are plans and needs for RTG in some of the NASA probes. Again from what I know, US has few Kg of stockpile - enough for 4-5 missions - and current rate is about a Kg or so per year but it is going to increase as Nasa again has more plans for space probes.

For example see here: http://large.stanford.edu/courses/2018/ph241/shi2/

In 2013, Pu-238 was produced in the United States for the first time in 25 years at the Oak Ridge National Laboratory in Tennessee. ... .

Interesting part is with NaMo's backing and good relations between India and US (and the nuclear deal), it may be India at present which has the best capability to produce Pu238 and India and US may help each other out.

(From what I heard, it was around 2016 when India (or at least some of ISRO scientist) was seriously thinking about Pu238 based RHU (it does not generate electricity - it is just a heating unit which keeps the batteries warm) and DAE thought it could provide the necessary amount ityadi but they dropped the idea thinking it will not be ready as they might need more time just to get all clearance etc)

SSSalvi wrote:Lander separated from orbiter.
There is media coverage of Chandrayaan-2 lander
Landing from 1:30 AM IST onwards on Sept 7 and Pragyan rover rolling out from the lander from 5:30 AM IST.

Do we know if images or video will be sent by Vikram during the landing phase? At least a few images prior to landing attempt would be nice.

SaiK wrote:I didn't understand the flipping here. Can you please explain

Flip once, fire the lander engine to reverse thrust, then flip the lander back agaiin

SaiK wrote:I didn't understand the flipping here. Can you please explain

The main thruster probably needs to be fired shortly to correct the final orbit of Vikram and to push into descent phase. The smaller thrusters will probably correct orientation for landing (flipping), then gravity will pull Vikram down and the main thruster will slow down the fall.

SaiK wrote:I didn't understand the flipping here. Can you please explain

Dr Sivan in his press conference https://youtu.be/njzOans5P-c mentioned that on Sep 3, Vikram will be rotated 180 degree and there will be a small burn. Then it will be rotated back. Then again on Sep 4, it will be rotated again 180 degree and there will be another burn and then rotation back by 180 degree. The reason given was to change orbit from 100 x100 to 100 x 35. I assume this will also be a test of the landing engines.
I don't know if the orbit numbers are correct, but I think that by doing these burns, you change from a circular orbit to an elliptical one where the closest point is 35 km from where the landing will start.

Some insights here:
https://www.quora.com/What-is-the-most- ... -satellite

SwamyG wrote:Soft landing at the polar site calls for group lungi dance.

+72. That would be an immense achievement and a first by any nation.

Mort Walker wrote:

SSSalvi wrote:Lander separated from orbiter.
There is media coverage of Chandrayaan-2 lander
Landing from 1:30 AM IST onwards on Sept 7 and Pragyan rover rolling out from the lander from 5:30 AM IST.

Do we know if images or video will be sent by Vikram during the landing phase? At least a few images prior to landing attempt would be nice.

Observing the current trend ISRO seems to be not shy to publish some raw images to quench the thirst of general audience.
There are two pushdowns.. 120*110 kms. And. 110*36 kms.
And finally intelligent autonomous soft landing at intended location near South Pole.
As the system will be busy with active decision making process it will not communicate with Earth during that time.( In addition to the fact that the communication antenna will not be pointed to Earth).

ISRO faced this communication void during Mangalyaan twice .. once during insertion to Martian orbit because the insertion occurred when the yaan was behind Mars blocking radio connectivity .. and another when the yaan passed through the tail of the comet .. this was for a different reason , the tail generate very high radio noise which could override the radio signal from yaan.

thanks, got it. reverse thrusting!

Lalbagcha Raja is space themed for this year: https://youtu.be/pYnwCeQ1K1c

There will be no real time transmissions till the Lander actually lands and the rover panel/slide is opened. We will probably be getting telemetry data. DrSivan told about one cause of Beresheets failure - human interference caused issues and muddled up things so they will allow the Lander to do the entire decision making.

Mort Walker wrote:^^^Yes, I remember playing with some isotopes as an undergraduate that were primarily alpha emitters, But I didn't know that Pu238 had no gammas. I would still think any RTG would create noise in radio transmit-receive, as many digital transmissions are near thermal noise levels at a given bandwidth.

Alpha emitting isotope does NOT affect radio communication noise floor. Noise floor is established by Antenna temperature and NF (noise figure) of LNA (low noise amplifier) stage of the radio only.

prasannasimha wrote:

SwamyG wrote:Amber G, ISRO is known for what it has achieved. So are the isotopes the only way to get power? I understand the power source has to be light in weight. So I am not wondering why we not have a giant battery pack.

Battery has to be recharged and where and how will the recharging happen = from Solar panels and again this will prove to be a problem as the thermal amplitude is so wide that they aren not sure if the electronics will resist these fluctuations. They have done some tests and think it may work but can only say if Pragyaan rewakes.

Very big battery size needed to balance the energy density spread over 14 days versus size of thermal insulation of a cavity that houses battery and electronic circuits. Almost no electronic IC part will survive 4deg Kelvin (-270 deg C) cold cycle.

Still wondering about video of these events. What limits real time transmissions. Weight penalty, power management, transmission bandwidth?

Does the decision making systems used for landing use Automated Planning area of AI?

sanjaykumar wrote:Still wondering about video of these events. What limits real time transmissions. Weight penalty, power management, transmission bandwidth?

HD video requires few Mbit/sec bandwidth. Similar to Geo Sat satellite that are very heavy compared to orbiter. Now the distance is 10 times more, so link budget Signal to Noise Ratio(SNR) is 100 times lower. So solar panel (transmit power) and/or antenna size (Ant Gain) need to increase 100 times for same SNR.

Space fairing craft are optimized for 1 to 100 Kbit/sec bandwidth.far cry from multi-Megabit needed for live video.

Thanks for providing some very good reasons.

Haridas wrote:

Mort Walker wrote:^^^Yes, I remember playing with some isotopes as an undergraduate that were primarily alpha emitters, But I didn't know that Pu238 had no gammas. I would still think any RTG would create noise in radio transmit-receive, as many digital transmissions are near thermal noise levels at a given bandwidth.

Alpha emitting isotope does NOT affect radio communication noise floor. Noise floor is established by Antenna temperature and NF (noise figure) of LNA (low noise amplifier) stage of the radio only.

I understand that LNAs are usually well shielded. What aren’t as well shielded are A/D converters used for downconversion. If the error rate is low and intermediate frequencies are less than 100 MHz, it may not be a problem.

Haridas wrote:

sanjaykumar wrote:Still wondering about video of these events. What limits real time transmissions. Weight penalty, power management, transmission bandwidth?

HD video requires few Mbit/sec bandwidth. Similar to Geo Sat satellite that are very heavy compared to orbiter. Now the distance is 10 times more, so link budget Signal to Noise Ratio(SNR) is 100 times lower. So solar panel (transmit power) and/or antenna size (Ant Gain) need to increase 100 times for same SNR.

Space fairing craft are optimized for 1 to 100 Kbit/sec bandwidth.far cry from multi-Megabit needed for live video.

Don’t need HD video at 1920x1080. NTSC video would be sufficient. It was done for the Apollo program in the 1960s. Seeing video would be beneficial for the scientists and major inspiration for Indians and the world.

In the 1960s, digital video didn't exist, but today don't see why something like 250 Kpixels in black and white couldn't be transmitted at 1/2 or 1/3 data rates. This would involve another antenna, electronics, camera and power. This would add weight, but I suspect not as much as thought.

Basic cause of no video coverage during descent is the antenna pointeing to Earth. If you try to orient the antenna it will create mechanical disturbance confusing the landing decision.

But I am sure that they will record the whole video onboard ( for post descent analysis of the decision making process to refine it for future missions ) and receive it after the rover is stabilized.

Hopefully they will release it afterwards.

BTW even though the orbiter can now technically start its observational activity they may delay it till the lander/rover stabilize ( or dilboo happens ). Was there dilboo during launch? I missed him then.

I am not That greedy, a video afterwards is well appreciated. Like Mort said, it will galvanize Indians. But that is cherry on the cake. Mission is most important show off in itself. Video or not. Just us fellows are a little greedy.

On a 2nd thought.. they may not release it .. it will expose the proprietory algorithms developed for this and they may not want to make it public at least till some protection ( read patent/publication in scientific community) is in place.

SSSalvi wrote:On a 2nd thought.. they may not release it .. it will expose the proprietory algorithms developed for this and they may not want to make it public at least till some protection ( read patent/publication in scientific community) is in place.

The competitors and enemies will determine the algorithm based on visuals? I can understand them reading the steps. Even if the steps are broken down into functions, is that secretive? Like you mentioned earlier some sanitization can help a bit.

This is one of those moments which will inspire millions of India's brightest kids into aerospace engineering and astrophysics. Having post video shortly after landing would have immense benefits in the long run which would outweigh any potential proprietary algorithm (as some parts could be edited) loss.

It also gives pause to the rest of the world that India is not a country to be messed with. The developed countries will seek space exploration partnership with India.

To get the most bandwidth, it might be possible for Vikram to transmit the video data to Chandrayaan and then from there to earth.

What's the likely genre of video compression algorithm? And, FEC for DL?

Mort Walker wrote: To get the most bandwidth, it might be possible for Vikram to transmit the video data to Chandrayaan and then from there to earth.

Yaan will be visible to rover/lander only for a small part of orbit of yaan.
Moreover the antenna should have been designed for this operation.( Pointing to yaan )

If there is no live streaming...what is it that Modi and apparently some 60 other kids from cross India specially flown in to Bangalore will be watching live during the landing on the 7th? I presume there must be some facility for regular updates during the last one hour?

Dhoti shiver started for me