Chandrayan-2 Mission

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Mort Walker
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Re: Chandrayan-2 Mission

Postby Mort Walker » 07 Sep 2019 04:08

^^^He's talking about doing it on earth. Then there is the question of wind too.

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Re: Chandrayan-2 Mission

Postby Dasari » 07 Sep 2019 04:08

vnms wrote:
Amber G. wrote:Trusting my eyesight and memory, the last I saw the telemetry data from the screen :

Horizontal velocity 48.1 m/s
Vertical velocity 59.8 m/s
Downrange distance: 1.09 km
Earth communication: OFF

That's exactly what I recollect.


Even if the engines shut off after this, a free fall from 2.1km would give a terminal velocity before crash at 102m/second. No craft will survive that crash.

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Re: Chandrayan-2 Mission

Postby Gagan » 07 Sep 2019 04:09

They can use cushioning balloons like the ones used while landing on Mars

Or they should have a Single gimbaled engine, or throttle down 4 engines.
I am no rocketery expert, other than the Diwali Rockets, but 2 engines seems like a lot of balancing to do.
And the transition from 4 to 2 to 1 was going to be difficult.
Things were fine until the 4 engines were firing. A little gimbal by the engines can compensate if one engine's thrust is sub par

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Re: Chandrayan-2 Mission

Postby Dasari » 07 Sep 2019 04:12

Gagan wrote:If it was inverted or horizontal, and its engines burning, that will cause deviation from the flight path laterally, which possibly seems to have happened.
Also descent velocity which was coming down, will start to now increase


I agree. Then the crash would have happened within 20 seconds. By the time they realized communication stopped, it already crashed.

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Re: Chandrayan-2 Mission

Postby Mort Walker » 07 Sep 2019 04:15

Master 3 axis stabilization in low earth orbit. It can be done with PSLV for low cost.

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Re: Chandrayan-2 Mission

Postby Cain Marko » 07 Sep 2019 04:15

Amber G. wrote:
Indranil wrote:
Why not? You just need something which exerts a vertical upward force of 5/6 times that of weight of the lander. For example, in a tethered experiment, you can use a helium balloon.

Helium balloons will not work in vacuum as the way you think.. it will only increase the weight of the lander (+ mass of helium)..:)
(There is NO practical way we know to simulate low gravity except going in earth's orbit (or vomit-comet type rides which are essentially the same).
(Swimming is water may make you feel "weightless" but it is not exactly what you need to simulate zero g, for obvious reasons)

What about using chutes for deceleration and landing? Fighters do it all the time. And so do manned modules. Of course it might be very challenging to keep the lander upright but just wondering...

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Re: Chandrayan-2 Mission

Postby sanjaykumar » 07 Sep 2019 04:16

This is not a big hurdle. The problem is the next mission may be years from now.

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Re: Chandrayan-2 Mission

Postby Rishi_Tri » 07 Sep 2019 04:22

Dasari wrote:
vnms wrote:That's exactly what I recollect.


Even if the engines shut off after this, a free fall from 2.1km would give a terminal velocity before crash at 102m/second. No craft will survive that crash.


I saw 0.335 KM.

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Re: Chandrayan-2 Mission

Postby Indranil » 07 Sep 2019 04:22

Amber G. wrote:
Indranil wrote:
Why not? You just need something which exerts a vertical upward force of 5/6 times that of weight of the lander. For example, in a tethered experiment, you can use a helium balloon.

Helium balloons will not work in vacuum as the way you think.. it will only increase the weight of the lander (+ mass of helium)..:)
(There is NO practical way we know to simulate low gravity except going in earth's orbit (or vomit-comet type rides which are essentially the same).

Yes, a helium balloon will not work in vacuum. But, why do we need vacuum? And you can replace it anything that exerts that force. The 800N engines were not tested in vacuum AFAIK.
Image
Image

I know that ISRO used it to simulate lower gravity.
Image

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Re: Chandrayan-2 Mission

Postby Amber G. » 07 Sep 2019 04:23

Dasari wrote:
vnms wrote:That's exactly what I recollect.


Even if the engines shut off after this, a free fall from 2.1km would give a terminal velocity before crash at 102m/second. No craft will survive that crash.

FWIW, on moon the speed it will hit (assuming free fall from horizontal-V=48 km etc..) will be about 74 m/s (26o Km/Hr).. The impact will be sort of glancing (about 45 degree horizontally) so it will bounce and impact may be be about half as damaging as pure vertical fall.. something like head-on collision of 120 Km/hr car with a tree.

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Re: Chandrayan-2 Mission

Postby Indranil » 07 Sep 2019 04:24

Mort Walker wrote:Master 3 axis stabilization in low earth orbit. It can be done with PSLV for low cost.

I would focus on the ADMIRE project.
Image

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Re: Chandrayan-2 Mission

Postby Supratik » 07 Sep 2019 04:27

Chute? Where is the atmosphere? Watching the sequence I was wondering whether they are going too fast and if there was a slow alternative.

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Re: Chandrayan-2 Mission

Postby Amber G. » 07 Sep 2019 04:29

Cain Marko wrote:
Amber G. wrote:Helium balloons will not work in vacuum as the way you think.. it will only increase the weight of the lander (+ mass of helium)..:)
(There is NO practical way we know to simulate low gravity except going in earth's orbit (or vomit-comet type rides which are essentially the same).
(Swimming is water may make you feel "weightless" but it is not exactly what you need to simulate zero g, for obvious reasons)

What about using chutes for deceleration and landing? Fighters do it all the time. And so do manned modules. Of course it might be very challenging to keep the lander upright but just wondering...

1. VERY VERY difficult to simulate vacuum ..Design would be very simple for earth (or even Mars) but not for moon. No parachutes or simple tech to slow down and **control**.
2. Yes with helium one can simulate (low gravity) for some forces but **very** little. The additional frictional forces makes testing too complicated.
You may be able to do some *static* stress testing but no testing of rockets etc.
Hope this helps.

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Re: Chandrayan-2 Mission

Postby Najunamar » 07 Sep 2019 04:32

Do you mean a rapid deceleration instead of stepwise braking as was attempted? Why would it be any different? Perhaps the new motors after the Israeli crash are the culprit, any case we'll know soon.

However, looks like all the calcs were on the dot till the very last 2.1 km... so if the cause is identified perhaps another mission with modified lander + rover can be launched as has been suggested by other posters.

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Re: Chandrayan-2 Mission

Postby Supratik » 07 Sep 2019 04:36

No they did it stepwise but I felt the sequence was too fast.

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Re: Chandrayan-2 Mission

Postby ldev » 07 Sep 2019 04:37

If there is a single PSU in India that is a text book example on how to do it, it is ISRO. And to achieve all their objectives they need and deserve a massive increase in funding commitments. This would be a great time to make that commitment so that ISRO can re-double it's efforts and achieve success in it's moon landing mission.

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Re: Chandrayan-2 Mission

Postby disha » 07 Sep 2019 04:40

It will not be a hardware error. I think it is a software error.

Terrain mapping and navigating was always going to be challenging. Terrain mapping kicks in during the soft landing phase and that is where things did not work out.

One would never know what kind of hazards it will find there and the hazard avoidance, guidance, terrain mapping - all of it had to work it in sync.

This points to a software error.

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Re: Chandrayan-2 Mission

Postby Gagan » 07 Sep 2019 04:46

Its angle is already close to horizontal as it is firing its retro rockets to slow down, there is a risk that it can tip over completely at that point.
Its angle is carefully controlled and it is progressively brought to a more vertical attitude from an angle that is closer to horizontal.

It is possible that either a software error, or glitch in attitude control or telemetery data, or even a hardware failure.
So many possibilities.

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Re: Chandrayan-2 Mission

Postby Varoon Shekhar » 07 Sep 2019 04:50

What data and/ or pictures would Vikram have sent before the malfunction. It was a fairly long descent, wouldn't there be more than telemetry transmitted?

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Re: Chandrayan-2 Mission

Postby Dasari » 07 Sep 2019 04:53

If it is terrain mapping software issue, it would have landed in some ditch or something along those lines which would not have been this bad. According to ISRO that terrain mapping comes into play at 500m altitude when craft was descending at a velocity of 1m/second with both thrust engines slowing it down. Here we didn't reach that phase. From 2.1km, it descended much faster than the intended speed. It appears when they realize they lost the communication ( that is 20-30 seconds after 2.1 altitude), the craft already crashed.

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Re: Chandrayan-2 Mission

Postby Najunamar » 07 Sep 2019 04:53

How difficult or easy is it to simulate (virtually)the various possibilities and correlate the actual telemetry to the simulated cases? I know it may not be feasible to get actual performance with only limited data in the descent phase but now they have some data (also would have had some details from the Chandrayaan 1 MIP uncontrolled descent).... I am sure they're augmenting the RCA that they are doing with supporting data from such simulations already -but curious as to how close it gets.

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Re: Chandrayan-2 Mission

Postby NRao » 07 Sep 2019 04:56

Gagan wrote:The final moments of Vikram Lander:

The graph deviates at 2:17 seconds. At 2:42, Vikram is nearly inverted !!! It recovers, then over corrects !!!
It tumbled at the critical juncture when soft landing phase was started. This indicates perhaps that one engine shut off later than the other, causing an imbalance.


I suspect during the recovery from this deviation that the antenna got disoriented. I would not be surprised if Vikram has landed, but the antenna is pointing is some odd direction, thus unable to communicate.

14 days to correct a problem if it is correctable.

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Re: Chandrayan-2 Mission

Postby Gagan » 07 Sep 2019 05:03

All that is knows is that there is a comms cut off.
It still had several seconds before it should have landed.

<Conspiracy Theory> PM, Dr Sivan, Other senior ISRO officials go to Dr Sivan's office, where they look at encrypted photos of the landing site taken by the orbiter in near real time. They know, have proof already. The site of the cloud, some debris if visible is a few KMs off from where it was supposed to be.</conspiracy theory>

Since there is no atmosphere of any significance, and thus no winds, and gravity 1/6 of earth, the cloud of dust will just hang out in that area, until it gradually settles. When it does, it will bury some of the lander as well, which might be partly underground due to the speed of the impact.

Of course, it could have landed safely, but that video is ominous

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Re: Chandrayan-2 Mission

Postby Dasari » 07 Sep 2019 05:10

Based on above chart, the craft was descending too fast. Unless the horizontal speed got reduced by the engines, the graph clearly shows the craft was gathering vertical(downward) acceleration.

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Re: Chandrayan-2 Mission

Postby SriKumar » 07 Sep 2019 05:16

Gagan wrote:All that is knows is that there is a comms cut off.

Since there is no atmosphere of any significance, and thus no winds, and gravity 1/6 of earth, the cloud of dust will just hang out in that area, until it gradually settles.
Since there is practically no atmosphere, the dust cloud will settle immediately. No hangin' out. A feather and a coin (or stone and a mote of dust) will fall at the same speed in absence of air resistance.

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Re: Chandrayan-2 Mission

Postby Amber G. » 07 Sep 2019 05:17

Najunamar wrote:How difficult or easy is it to simulate (virtually)the various possibilities and correlate the actual telemetry to the simulated cases? I know it may not be feasible to get actual performance with only limited data in the descent phase but now they have some data (also would have had some details from the Chandrayaan 1 MIP uncontrolled descent).... I am sure they're augmenting the RCA that they are doing with supporting data from such simulations already -but curious as to how close it gets.

I dare say we have **plenty of data**. We will know every minor detail and will learn. (Data analysis takes time, and professionals do not jump tp conclusion till they study all the data).. Heck there is data from various other radio telescopes which were "watching" it to add to ISRO's .

There will be no ambiguity where Vikram landed and which path it actually followed.. this can also tells us exactly what thrusts (vectors) were applied and even if we did not get other data about rockets well being we can determine what went wrong.
Let us wait.

Meanwhile we know about GSLV works.. 95% of the scientific experiments are with the orbiter and that is working fine.

As some one said, I will not be too surprised if we found that glitz could be easily corrected and our basic design was fine. We will see.

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Re: Chandrayan-2 Mission

Postby Amber G. » 07 Sep 2019 05:25

SriKumar wrote:
Gagan wrote:All that is knows is that there is a comms cut off.

Since there is no atmosphere of any significance, and thus no winds, and gravity 1/6 of earth, the cloud of dust will just hang out in that area, until it gradually settles.
Since there is practically no atmosphere, the dust cloud will settle immediately. No hangin' out. A feather and a coin (or stone and a mote of dust) will fall at the same speed in absence of air resistance.

Moon dust is VERY messy and in true sense it is nightmare, serious danger. (ISRO, of course, knows it) Vikram type landers capable of spewing out gas at around 2-3 Km/sec — can propel rocks and gravel-sized particles up to 10 to 100 meters per second, sending them tremendous distances (up to half a Km away). Fine dust and sand can speed up to 1 Km/sec , propelling them hundreds of kilometers away — even distributing them all over the Moon.. as Apollo astronauts learned the hard way. (As ISRO knows, dust is definitely a possible cause).

Any machinery in the path of these high-speed particles could suffer some serious blasting or damage. It could ruin a spacecraft in orbit around the Moon if it just happens to be in the wrong place at the wrong time... (Some space crafts were seriously damaged in the past and many Apollo astronauts had bad things to say about it -- IIRC it "ate up" one of guys rugged shoes (in space suit and all - as the dust is quite sharp)
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Re: Chandrayan-2 Mission

Postby Dasari » 07 Sep 2019 05:27

Isro lost contact with Vikram when it was just 2km from lunar surface

This heading could be misleading. Did communication with Vikram lost before crash or after crash? The heading implies the communication was lost before the crash. Why? An explosion? The most plausible explanation is that it already crashed by the time we found that it was not communicating. Which will be true when the descent from 2.1 km to surface was super fast.

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Re: Chandrayan-2 Mission

Postby SriKumar » 07 Sep 2019 05:50

Clearly communication was not lost at 2.1 km. The track of the lander was broadcast live upto about 300 m above the surface. There is public domain data of altitude and range well below 2.1 km altitude in the video linked by gagan.

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Re: Chandrayan-2 Mission

Postby Gagan » 07 Sep 2019 06:07

Lunar soil is negatively charged, and too much dust will hamper comms
If it is buried in a dune, its solar panel won't charge it and it will not communicate

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Re: Chandrayan-2 Mission

Postby ramana » 07 Sep 2019 06:16

Amber G. wrote:Just a reminder to all here: that on its way to put this lander down on the moon, India did put its second space craft on the orbit of the moon. Chandrayaan-2 will be doing science for next year or longer. (Lander would have lasted about 2 weeks only).


And whole mission cost $87M
Less than a Rafale.

ISRO should get ready another mission once technical is understood.

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Re: Chandrayan-2 Mission

Postby ramana » 07 Sep 2019 06:16

BTW very good discussion.

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Re: Chandrayan-2 Mission

Postby Amber G. » 07 Sep 2019 06:22

SriKumar wrote:Clearly communication was not lost at 2.1 km. The track of the lander was broadcast live upto about 300 m above the surface. There is public domain data of altitude and range well below 2.1 km altitude in the video linked by gagan.

What I remember hearing from ISRO's chairman -

- All things were normal till altitude of 2.1 Km
- Subsequently (some time later but they did not say when) they lost contact.
- They are analyzing the data.

My advise to the chairman and other higher-up would be.. (I actually told them this :))
- Take a well deserve rest and have a wonderful week end.
- The scientists/engineers know their job, they will analyze the data and will update you when they are ready. Let them do their work.
This should be investigated like a engineering/scientific problem and NOT like a investigative reporters or busy-bodies or lawyers or politician's problem.

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Re: Chandrayan-2 Mission

Postby CRamS » 07 Sep 2019 06:23

I am little concerned about this bold part in the HT report headline:


Chandrayaan 2 Moon Landing Live Updates: PM Modi to address nation at 8am from Isro HQ as speculations mount over Vikram lander


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Re: Chandrayan-2 Mission

Postby UlanBatori » 07 Sep 2019 06:26

UBCN has learned with usual 400% re-lie-ability that the lander was diverted to a raa mission, zooming over to the near side. ISRO analyzing CYN-1 data and after a couple of passes by the aar-biter confirmed the presence of a Platinum deposit there that is truly immense. Don't want to give away location, but VikRAAm is now happily sending data directly to Raa. 2.1km, finished rough braking... how do you know if it was in fact anywhere in that vicinity? It's the far side of the moon, remember. Just sayin'. If the engines were already working fine in the rough braking mode, there is no earthly reason why the comm should suddenly stop, hain? Did it blow a fuse or what? Besides the Aar-biter went by shortly thereafter, so why have we not seen images of the dust plume/ new crater? Remember that ISRO said all along that if the first site proved unsuitable VikRAAm would move over to the second. Well, it did. Except not where it was announced.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 07 Sep 2019 06:27

OK, I AM out of here, pls don't ban me. Just feeling not too good. All that work of all those good people....
And I am crying for those 15 momeen who will be killed tonight when their co-momeen fire AK-47s into the sky in celebrations in Pakistan. Revenge for Babri Masjid. And 1971. And Balakote. And 1999. And World Cup.
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Re: Chandrayan-2 Mission

Postby Dasari » 07 Sep 2019 06:28

SriKumar wrote:Clearly communication was not lost at 2.1 km. The track of the lander was broadcast live upto about 300 m above the surface. There is public domain data of altitude and range well below 2.1 km altitude in the video linked by gagan.



Even assuming that the last communication was at 300m (based on the last point on graph), the concern we have is that the rate of descent from 2.1km to 300m was too fast for the craft to survive. As per ISRO's plan from 500m altitude the decent has to be 1m/sec. Leaving aside the path between 2.1km to 500m, it should have taken 200 seconds to come down from 500m to 300m. But that didn't happen. Only hope is that it somehow corrected itself after 300m and didn't crash too hard. As Gagan eludes there is still slight chance for miracle that it may revive itself.

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Re: Chandrayan-2 Mission

Postby UlanBatori » 07 Sep 2019 06:31

1 m/s descent speed from 500m is way too low: waste of rocket fuel. It was going to touch down at somewhere under 10m/s or so IIRC. Remember gravity is only 1/6g so impact is not that great.

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Re: Chandrayan-2 Mission

Postby Dasari » 07 Sep 2019 06:47

UlanBatori wrote:1 m/s descent speed from 500m is way too low: waste of rocket fuel. It was going to touch down at somewhere under 10m/s or so IIRC. Remember gravity is only 1/6g so impact is not that great.


Are you saying it didn't have that much fuel?. How does it waste it when its purpose was getting over in few more minutes?

Touch down at 10m/sec?. Are you crazy? Doesn't matter what the gravity is. When we say 10m/sec, we mean 10m/sec. That would be hard crash. Last 10 meters, the actual plan was to take 25 seconds.

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Re: Chandrayan-2 Mission

Postby sudarshan » 07 Sep 2019 06:54

Dasari wrote:Are you saying it didn't have that much fuel?. How does it waste it when its purpose was getting over in few more minutes?

Touch down at 10m/sec?. Are you crazy? Doesn't matter what the gravity is. When we say 10m/sec, we mean 10m/sec. That would be hard crash. Last 10 meters, the actual plan was to take 25 seconds.


You're right about 10 m/s being 10 m/s anywhere (regardless of gravity). However - a human descending by parachute on earth has a landing speed of about 20 kmph, or 6 m/s. So 10 m/s for a much harder (than human I mean) lander isn't that excessive. Kinetic energy (and thus impact force) goes up as square of speed, so from 5 m/s to 10 m/s is four times the force. If human feet (in shoes) can take 5 to 6 m/s, I think a metal lander with specially designed cushion pads can take 10 m/s.

Great job, ISRO, you should be proud of what was achieved. Tried for something which nobody has ever tried before, and almost made it.

Y'know, now that the haters in the western media have something new to (gleefully) focus their bile on, the Kashmir coverage should drop off a bit.


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