Chandrayan-2 Mission

SaiK · Post by **SaiK** » 10 Sep 2019 00:40

prasannasimha wrote:The small thrusters are 25 N ones

should be enough for the 1/6th place. no? the weight of Vikram should be that much less. But then, we are assuming everything is intact per reports [no visuals we have seen yet].

---

another stupid question on pattern matching.. was this IR or pure visual range pattern matching? IOW, did we land with lights on?

suryag · Post by **suryag** » 10 Sep 2019 00:42

The dsn guys are not calling ch2l

chetak · Post by **chetak** » 10 Sep 2019 00:43

Amber G. wrote:
chetak wrote:

The lag in the signal reaching the lander would have caused some difficulties and its presuming that the lander antenna was correctly/optimally oriented
Time lag in signals reaching lander does NOT cause landing difficulties. (Lander does not depend on any out-side signals from earth or CY2 for its precision landing). Hope this is helpful.

Amber ji,

That has become clear now, especially the fully autonomous part.

This forum is an education by itself.

Your posts are insightful and make for interesting reading.

Thanks for taking the trouble. Much obliged.

JayS · Post by **JayS** » 10 Sep 2019 00:44

UlanBatori wrote:@JayS : Yes, but what happened to all the 100m-hover and the pattern-matching? Pls read the aiaa paper sections I posted above, thanks.

Have read it Saar. I was expecting hover phase. But it was not mentioned in any references I had read, so was bit confused. This reference makes things quite clear.

I am just thinking aloud here, due to unexpected attitude changes, it hit the ground too early to have gone through all that hovering and all. From what I remember from the live telecast, about 200 sec or so were expected for the remaining part (after 2.1 km altitude), giving the Lander enough time to hover and do scanning of the site. Short downrange for given Altitude suggests too fast horizontal velocity drop, which in turn suggests the thrusters didn't become vertical quick enough. Even if one of the thrusters overperformed, the auto control system should have been able to compensate for it by making thrusters vertical a bit earlier than the ideal case and compensating the imbalance in rotational motion with those small attitude control motors. Guess this part did not happen, may be the imbalance was too much for the control system to negate in short enough time.?

UlanBatori · Post by **UlanBatori** » 10 Sep 2019 00:45

Wonder what such software does when it encounters a command that is simply not possible to execute. Like "Hover at 100m, take survey, make sure no big stone below"
Arre, hover kaise karoonga? Phiphy metar per second par girta hum, hain?
I HOPE it was not written by MacroHard or else i know the answer. Nor by the ppl who approved the Ophishial Pharm IT-2 of Income Tax Division, or the Account Opening Pharm for On-line of State Bank (mongolia).
Since it is a guvrmand agency written software it should just say

chalta hai

ignore the memo and go about its bijnej.

SaiK · Post by **SaiK** » 10 Sep 2019 00:45

Another Q: What was the logic if it fails to find any pattern within given time?

SaiK · Post by **SaiK** » 10 Sep 2019 00:48

If the thrusters were too powerful, then it can't be our control system not fast enough to control the navigations. It can't be just the thrusters. [assume: 1/6th gravity means it requires faster controls]

UlanBatori · Post by **UlanBatori** » 10 Sep 2019 00:49

SaiK wrote:Another Q: What was the logic if it fails to find any pattern within given time?

"KYC rejected".

SaiK · Post by **SaiK** » 10 Sep 2019 00:50

JayS · Post by **JayS** » 10 Sep 2019 00:50

prasannasimha wrote:The small thrusters are 25 N ones

From the paper that ramana gave link to:

Chandrayaan-2 Lander will employ a clustered configuration of four 800N engines along with 50N attitude control
thrusters placed at the bottom of spacecraft, to decelerate the spacecraft for braking and soft landing on lunar surface

NRao · Post by **NRao** » 10 Sep 2019 00:55

On cell phone, unable to post properly. An article in ToI claims a NASA payload on the lander may help. There is some tech talk in the article

viewtopic.php?f=3&t=7248&p=2379135#p2379135

SaiK · Post by **SaiK** » 10 Sep 2019 00:56

I am trying to first rule out the case earlier reported in ToILet. "Too much Thrust"!!..

if we have our navs and controls pucca, then too much thrust can't be on the ground is my best assumption

UlanBatori · Post by **UlanBatori** » 10 Sep 2019 01:04

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!

Mort Walker · Post by **Mort Walker** » 10 Sep 2019 01:05

suryag wrote:The dsn guys are not calling ch2l

They may be out of line sight at this time. Let's see layer tonight.

Amber G. · Post by **Amber G.** » 10 Sep 2019 01:06

I have been ignoring UB's posts. I find them bizarre, scientifically inaccurate to the point of being silly, off topic and plain weird. But in order to clarify and remove some confusion here are a few comments. Hope this helps people in understanding physics and encouraging people to look up and think for themselves. It is very easy to make fun of others but more satisfying part is to learn. Anyway two comments on something which he commented on my posts.

Full Moon is Sep. 14, so right now should be half-way there per madarssa math. Which is why the timing was what it was. Maybe just coming over the horizon at the South pole -

Really?

Madrasa math or no madrasa math.. when "sun comes over the horizon" (IOW morning/noon/evening etc) has NOTHING to do with -- when is the full moon!

(Take any time, there is a place on moon, when the sun is "rising" , or at "noon" etc. Sunrise/Sunset depends on longitude not when it is full moon or not.)

UlanBatori wrote:Atmosphere or not is a small part of the solar cell efficiency issue. ...
<Rest of "madarasa math skipped >

REALLY???? (BTW I was not talking about solar cell efficiency is abstract sense .. it is how much power Vikram can generate from sunlight on moon)

Solar panels in mid day generate more electricity than in the morning/evening. (Or for that matter high latitude places are less suitable than places near equator on earth)

Why? It is not an "angle" issue.. It is just that sun's photons passes through longer layers of atmosphere when sun is low on horizon than when the sun is high.(BTW that was I already pointed out in my original message).-- More photons get scattered, you have less photons. Even in madarasa math

.

Hope this is helpful for some.

SaiK · Post by **SaiK** » 10 Sep 2019 01:11

interesting UB ji, we could then assume comms failure can't be because of that sudden /extreme vibration due to some nozzle having too much fuel. [assuming we have fault tolerance is the comms bus]

SaiK · Post by **SaiK** » 10 Sep 2019 01:19

amber ji, wouldn't be mid day for at least 7 earth days on moon?

UlanBatori · Post by **UlanBatori** » 10 Sep 2019 01:27

I have been ignoring Ulan Batori's posts

Someone could perhaps show this postor how to use the "ignore" key and how to operate it so that she does not ever again sully a friendly discussion with her sneering. Some of us are humble yak-herders, we didn't memorize high-school textbooks.. but once in a while, as Haridasji kindly pointed out once.. (never mind).

Madrasa math or no madrasa math.. when "sun comes over the horizon" (IOW morning/noon/evening etc) has NOTHING with when is the full moon!

I did not say it did (perhaps someone could help with reading). What I was trying to figure out is whether the landing site is already at peak sunlight, in which case there is no hope, or it is still early morning, in which case there IS hope. Requires a bit of imagination and optimism...

So, not having Sears-Roebuck memorized, I approximate.

Since the place can be seen from Earth, full Moon is a good indication of when the place is in the middle of the lunar day. Not to 16 decimals precision and relativistic string theory perhaps, but good enough for an Internet Forum discussion. Given the latitude and longitude, I hope the day is not off by more than 1, but it is too much trouble for me to go check with the correct Lat/Long, precession rate, 10-body dynamics etc. It is also unnecessary if one has a slight amount of imagination, not limited to mugging textbooks.

Let's see....

The lander was supposed to land on .. Sep. 7. If one were designing a mission where the expected lifetime is the 2-week Lunar Day, when would one land? At the fag end of the Lunar Day? At the middle? Or at the start?

I would land at the start, if I were on the equator.
But at the poles the sun does not come up very high.

At this place, per someone's post, the sun only rises to 10 degrees above the horizon (think Antarctic summer day). So there is no light even by the equivalent of say, 8AM (earth-day equivalent, one might need a SLIGHT bit of imagination to imagine that..). So I would land at the equivalent of 9AM (equatorial mid-morning on Earth) so that my solar panels would get SOME power as I started to roll out the rover.

So it is reasonable to guess that ISRO, being at least as smart as I PLUS having read the kindergarten textbooks, did exactly that, to within plus or minus one day.

So I checked the lunar phase. Sure enough, ISRO is smart: it IS close to the equivalent of 9AM at the landing site. We expect to find out in the next week whether Vikram can be powered up.

I am here to pass the time, don't know about other postors... but PLEASE feel free to use the IGNORE POSTOR key to avoid having to strain your imagination. *** edited***

UlanBatori · Post by **UlanBatori** » 10 Sep 2019 01:40

SaiK wrote:interesting UB ji, we could then assume comms failure can't be because of that sudden /extreme vibration due to some nozzle having too much fuel. [assuming we have fault tolerance is the comms bus]

Can't say. Rocket combustion (or combustion+acoustic) instability is so severe that it causes 10% or more thrust oscillation and basically shakes the vehicle to failure. In the 1950s through 80s there were lots of spectacular failures.

So maybe by 2.1 km, the comm ckts were destroyed? In which case I wonder how it can communicate even when the sun comes up and it wakes up.

The thing to note here is that all parts of the GSLV-CV2 propulsion architecture had been flight-tested **EXCEPT*** the lander propulsion. I am sure it was tested many times on Earth, but never in Space AFAIK. And like that Armstrong video of the lander going berserk on Test Flight #21, I guess this one simply hit the unlucky number. This is one reason why I keep saying that the papparazzi who criticize DRDO for missiles that have to be tested more TEN times and conclude "lazy DRDO" are toxic enemy agents. Missiles are tested in the THOUSANDS before being accepted into NATO inventories, for instance. Why? Because some of these failures are still seemingly random. These are all systems operated at the fine edge between peak performance and instability, to save weight.

So the one lesson is that b4 any human-carrying flight there have to be MANY flights, damn the cost.

Amber G. · Post by **Amber G.** » 10 Sep 2019 01:42

SaiK wrote:amber ji, wouldn't be mid day for at least 7 earth days on moon?

Full day will be about 14.5 days ... (unlike earth, sun will almost be as bright at "mid day" as in the "evening")

SaiK · Post by **SaiK** » 10 Sep 2019 01:43

UlanBatori wrote: So the one lesson is that b4 any human-carrying flight there have to be MANY flights, damn the cost.

108++

Amber G. · Post by **Amber G.** » 10 Sep 2019 01:45

SaiK wrote:
another question on pattern matching.. was this IR or pure visual range pattern matching? IOW, did we land with lights on?

From what I know, it is purely (or mostly) visual pattern matching.

Mort Walker · Post by **Mort Walker** » 10 Sep 2019 01:45

UBji,

Yourself and AmberG are a wealth of information coming from your respective fields of expertise. Please go easy on each other. I would have flunked your post graduate course computational fluid dynamics and I would have flunked AmberG’s course in electrodynamics. What do onlee when one like me and others are complete duffers? We still need you to educate some of us who are willing to listen.

Mort Walker · Post by **Mort Walker** » 10 Sep 2019 01:47

Amber G. wrote:
SaiK wrote:amber ji, wouldn't be mid day for at least 7 earth days on moon?
Full day will be about 14.5 days ... (unlike earth, sun will almost be as bright at "mid day" as in the "evening")

My question was what is the angle of the sun on lunar south pole at this time? Are there tables or references anywhere? Is this to imply full sun for nearly 15 days from the beginning of the lunar day?

NRao · Post by **NRao** » 10 Sep 2019 02:00

Try this applet:

http://www.jgiesen.de/SME/details/seDetails.htm

Complex for me. Hope it helps.

UlanBatori · Post by **UlanBatori** » 10 Sep 2019 02:02

I avoid computation fluid dynamics, the Plague etc at the same level, thanks. Associating CFD with me is like calling Hafeez Saeed an Ahmadiya.
I am just minding my own business, so don't see what I can do to reduce the incidence of terrorist attacks. See this statement for instance:

Full day will be about 14.5 days ... (unlike earth, sun will almost be as bright at "mid day" as in the "evening")

Yes. But if you place a solar panel so that the sun's un-scattered rays come parallel to the surface, you won't get diddly-squat as power, which is the problem I was trying to figure out (as stated slowly and clearly several times..) Actually I happen to suspect that there is no air above the lunar surface, though there IS a haze layer that DOES scatter sunlight, so the statement above is quite terminologically inexact. Shocking.

I bet about 0.003 percent of the sunlight DOES get scattered.

Look at this picture: Clear proof that day-night on the moon is **NOT** an exact sharp line in space or time. There IS scattering and you CAN see sunlight before any part of the Sun is visible over the horizon. A fact that you can probably verify by looking up at a partial Moon. The spatial inexactitude is seen if you look carefully. Or you can just look up at the moon because your eyes have much more dynamic range than a JPEG image. This is the problem with strutting textbook knawlidj around (which I don't mind) and using that to sneer at others, which I think can become slightly educational sometimes.

Reminds me of the scene from "Men In Black" where the uncultured entity is grabbed off the tossed into the room where a Squad of Special Fauj are standing at stiff attention. No idea why the FBI grabbed him and told him he was needed for a Classified Mission
Entity: "Hey dude, why were YOU selected for this mission?"
Squad Leader: "BECAUSE WE ARE THE BEST OF THE BEST OF THE BEST, SSSIIRRRRR!"
Entity: "Oh, so you got no clue neither, huh?"

Amber G. · Post by **Amber G.** » 10 Sep 2019 02:08

Mort Walker wrote:
Amber G. wrote: Full day will be about 14.5 days ... (unlike earth, sun will almost be as bright at "mid day" as in the "evening")
My question was what is the angle of the sun on lunar south pole at this time? Are there tables or references anywhere? Is this to imply full sun for nearly 15 days from the beginning of the lunar day?

I can look up, it is fairly easy, data or calculate but within 1.5 degrees, sun is at "horizon" at south pole at this time (and always).

The more detail position of the sun depends on the local geography.. Theoretically there can be a peak (near or on south pole) where sun *never sets* .. (There are few peaks like that on Moon where some parts of the year there is is eternal light)

So angle of the sun at Vikram's landing is what I said it was - Foe more accuracy one needs actual geographical location (and near by ground, peaks, valleys etc), even more than moon's astronomical.. ephemeris - to see if Vikram can see the sun or not.

Hope it is clear what I am saying here.

( Earth is tilted 23.5 degrees, we need tables (or know how to calculate) to find angles of sun, time of sunrise etc. At moon it is much easier)

Amber G. · Post by **Amber G.** » 10 Sep 2019 02:12

NRao wrote:Try this applet:

http://www.jgiesen.de/SME/details/seDetails.htm

Complex for me. Hope it helps.

This is more from observer on earth. There is not much market for such tables for the perspective from moon as not too many people live on the moon

.
(BTW, if moon's orbit, earth's orbit, and earth's equator were in the same plane, we might not even need some tables

)

UlanBatori · Post by **UlanBatori** » 10 Sep 2019 02:13

And the intended Chandrayaan-2 Landing spot is/was **NOT** at the south pole of the Moon. It is at 70.9 degrees south.
I think the pole is 90 degrees per my madarssa math.

t doesn't have a name, at least not yet. But in just a few days, if all goes well, it could become one of the most important places on the moon's surface.
That spot is a highland that rises between two craters dubbed Manzinus C and Simpelius N. On a grid of the moon's surface, it would fall at 70.9 degrees south latitude and 22.7 degrees east longitude. It's about 375 miles (600 kilometers) from the south pole.
And it's the preferred landing site for India's moon mission, Chandrayaan-2,

Read above re: (never mind). If people could read, there would be no riots and no war. One COULD use imagination and common sense in lieu of complex programs and charts and tables, as I indicated above, to solve a given problem to enough accuracy to know whether there is hope.

Mort Walker · Post by **Mort Walker** » 10 Sep 2019 02:15

Yes. It’s clear. Geographical or lunagraphical features at the location are the limitation here. If Vikram is tilted, the solar panels may not be getting direct light which complicates this whole situation.

vinod · Post by **vinod** » 10 Sep 2019 02:39

How will the space craft do pattern matching if the craft's orientation changed and camera is not pointing downwards to the ground?

ramana · Post by **ramana** » 10 Sep 2019 02:44

JayS, We should be able to calcutate if the side thrusters can tilt the lander back to normal.

We know the lander mass.
We approximate its CG.
We approximate the lander legs.
Maybe the thruster orientation is outwards and not helpful!

First we need Vikarm to wake up
Next do system check and fuel inventory.
Then see if a combination of main thurster and side thursters can be fired up to provide righting moment.

ramana · Post by **ramana** » 10 Sep 2019 02:45

Any way we know the anomaly was corrected and the lander made to rotate to vertical.
But it landed intact 500 m off and is on its side.

ramana · Post by **ramana** » 10 Sep 2019 02:46

Folks don't get hot under the collar we have a lot of guest reading here and hopefully getting hope.
No need for scholarly umbrage.
Both of you are eminent experts in your fields.

UlanBatori · Post by **UlanBatori** » 10 Sep 2019 02:47

Camera not pointing would be a problem. In-plane rotation is not a problem for pattern-matching. At its roots it is a cross-correlation, implemented with 2-D Fast Fourier Transforms (I am sure now greatly modified!) It will give a result that says,

This looks like Abdul Gujranwali coming over the LOC, but turned 90 degrees after a disagreement with INSAS bullet.

The phase info (imaginary part of the complex transform function) will give the rotation which the pattern-matching will use instantly.
But yes, the camera has to be looking in the general direction, and the camera has to be working.

I am sure that should sound like gibberish, but don't worry, it probably is.

But all that is irrelevant. If pattern matching fails, the autopilot would just say, OK< this is my best guess of where I need to be, I am going to sit down here although it is dark. Maybe ground-pointing radar will say: ooops! reflection from a rock right below! And it will move a bit to avoid that. All those had plenty of redundancies.

ramana · Post by **ramana** » 10 Sep 2019 02:49

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.

Could that have driven the combustion instability?

ramana · Post by **ramana** » 10 Sep 2019 02:50

Right now we can let ISRO think of RCA but other teams are probably burning midnight oil to recover the mission.

UlanBatori · Post by **UlanBatori** » 10 Sep 2019 02:53

No speculation on these things. I am sure the designers read papers and attend reviews with far nastier (not 2 mention knowledgeable) ppl than me shooting at them. Fact is that after all the $$T in development, US research in rocket instability shifted from Preventing Instability to Using Pulsating Combustion. My Evil 6th Coujin was slide operator at one of those military meetings way back where they were throwing missiles over his head at each other:

After 40 years of funding you guys, you STILL don't know how to stop this problem that is costing us billions of dollars a year in failures!

And the funding that you put into our research wouldn't pay for ONE of your ignorant tests!

This is why I said that broadcasting ISRO Mission Control was a heck of a lot better PR than broadcasting real technical "discussions".
Now they are all happy because they are into pulsating combustion.
That should tell you all you want to know. Point is that you are operating systems at the very edge of instability. If you want to be safe, go conservative, back off in Isp and pay the cost.

B4 anyone asks WHY DIDN'T ISRO DESIGN SAFELY? I will point to the song: "Fly high and proud, and if you should fall" etc.

If you look carefully the payload carried by the launcher was almost exactly at the limit of what the launcher could carry. Which means that they had to hack away at the payload until it was just feasible. It's like "Yes, you MUST carry grandma and the 15 kids AND this SMALL tiffin-carrier AND this SMALL bag of coconuts in the Ambassador". which can only be done by leaving the spare tyre behind....
As the old song goes..

Just a song b4 i go..
A lesson 2 b learned..
Traveling twice the speed of sound..
It's EZ to get burned!

If it was easy others would have done it.

suryag · Post by **suryag** » 10 Sep 2019 02:55

Dsn trying now kuch bolo Vikram please ...

UlanBatori · Post by **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.