Chandrayan-2 Mission

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Re: Chandrayan-2 Mission

Postby SSridhar » 12 Sep 2019 07:50

sudarshan wrote: . . .is this in hours:minutes, or minutes:sec

It is hh:mm because rough braking lasted 10 minutes and the graph corresponds to that. It says Time (UTC).

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Re: Chandrayan-2 Mission

Postby UlanBatori » 12 Sep 2019 07:59

All speculation based on very incomplete data. NASA data support theory that Godzilla stood up and grabbed the lander. Those data are also quite likely to be wrong. I think ISRO has optical pictures, but taken with special Raa camera whose resolution cannot be revealed.

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Re: Chandrayan-2 Mission

Postby sudarshan » 12 Sep 2019 08:00

SriKumar wrote:1. The x-axis in the plot by Amber.G is min:sec. If you look at the leftmost point, it is 19:55. At the next gradation, it becomes 20:00; and the next is 20:05. The only way this is possible with all the gradations on the x-axis being equally wide is if the xy in 19:xy is in seconds. (Added later: it also works if xy is in minutes...but that's well, less likely :) ).


Seems to be hh:mm (thanks SSridhar).

4. It was puzzling to see the velocity shoot up from 400 m/s to 1400 m/s just 12 seconds before it was braking. Not clear to me why that should be the case. Before it brakes, it is in orbit, and not sure if that rapid increase was due to change in orbital velocity- does it change that drastically, or did it change its attitude first, and then started braking. The other possiblity is that the line-of-sight of the receiving station changed at 1400 m/s due to......change of direction of the lander. This confused me, so I did not attempt any calcs from this plot.


Not at all puzzling - it's ~12 mins, not 12 secs (see above). So ~1000 m/s (400 to 1400 m/s) in ~720 secs (12 mins) is around 1.4 m/s^2. Could just be free fall on moon (moon's gravity is like 1.6 m/s^2 - but recall - we are seeing only line-of-sight vel/acc from earth, so what we see as acceleration will be somewhat less than moon's gravitational acceleration).

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Re: Chandrayan-2 Mission

Postby SSridhar » 12 Sep 2019 08:13

Looks like there is a higher thrust by the throttleable engines followed by an overcompensation. Goes back to what an ISRO scientist said about overperformance.

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Re: Chandrayan-2 Mission

Postby Dileep » 12 Sep 2019 08:17

The X axis is indeed Hour:Minute in UTC. Multiple indicators show this.

1. It says UTC and the time actually matches.
2. Rough braking and fine braking are marked, and the time gap between them matches.
3. Look at the initial part of the graph and see the acceleration. around 1000 m/s in 13 minutes. Around 1.28m/s^2. Corresponds nicely to the profile. The glitch acceleration also kind of parallel to that segment, but slightly higher.

So, if the initial segment was simple 'coasting', the glitch seems to be 'downward push' rather than a free fall. Of course it maybe because the initial vector was at a shallower angle.
Last edited by Dileep on 12 Sep 2019 08:28, edited 1 time in total.

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Re: Chandrayan-2 Mission

Postby NRao » 12 Sep 2019 08:19

SSridhar wrote:Looks like there is a higher thrust by the throttleable engines followed by an overcompensation. Goes back to what an ISRO scientist said about overperformance.


Vikram, if I am not mistaken, was on "auto-pilot". So, for Vikram to "overperform" there should have been some inputs that asked it to "overperform".

The "overperformance" was not an accident. ???????

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Re: Chandrayan-2 Mission

Postby sudarshan » 12 Sep 2019 08:36

Dileep wrote:So, if the initial segment was simple 'coasting', the glitch seems to be 'downward push' rather than a free fall. Of course it maybe because the initial vector was at a shallower angle.


That's how I'm reading it too. So how about this scenario:

One rocket overperforms. So thrust is higher, meaning slowdown (deceleration) is higher (velocity goes lower than expected, which is seen in the curve at the start of the anomaly). But the overperformance by this one rocket also causes a turning moment. So the lander turns upside-down. Now the thrust is downwards. So this matches your "downward push rather than free fall" observation. The lander rights itself somehow, maybe the turning moment (due to imbalance in thrust) continues, so it comes right-way-up again. Now thrust is upwards, so another slowdown in velocity (also seen in the curve). That's the point where communication is lost.

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Re: Chandrayan-2 Mission

Postby sudarshan » 12 Sep 2019 08:40

SaiK wrote:wow! so, the increase in velocity, then followed by loss of signal, and then thud! the saffron line looks like it made a screeching halt like a jet w/ landing gears down.


No no, the saffron line (I presume you mean at the very end) isn't a "screeching halt," it means the lander is at rest with respect to the moon, so the saffron line and blue line (moon's path) merge. The difference between these two lines is zero - i.e. the lander has no velocity with respect to the moon.

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Re: Chandrayan-2 Mission

Postby ramana » 12 Sep 2019 08:45

AmberG and UB

https://www.thehindu.com/sci-tech/scien ... ssion=true

Looks like scale model was tested in 2018.

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Re: Chandrayan-2 Mission

Postby Amber G. » 12 Sep 2019 10:12

ramana wrote:S^3, What would make the lander gain velocity before the communication was lost?
And what was the fuel margin for the lander?
Could it have exhausted as it corrected for the maneuver?

AmberG,
From the graph can we calculate the sudden acceleration during that maneuver?

To my eye it looks like Delta V= 360m/sec- 220m/sec = 140 m/sec
Delta T = 20.19=20.18 = 0.01 sec

X2dot = 140/0.1 = 1400 m/sec^2

That's quite a bit of sustained shock.
In Gs= 1400/(9.81*1/6) ~ 850 gs in moon environment?

Is this less than the lander qual shock and vibration spectra?

If its greater could be reason the comms were lost.

Have not followed the thread here .. sorry if missing some posts but a quick note - Some of us were checking this out..
and some calculations gives me less hope.. OTOH , all thing considered CY2 is/was awesome...

Here is the last position .. from JPL/Horizon animation .. (hard to put video, so the situation is around the last known position of Vikram.. (Green orbit is NASA LRO orange/blue is CY2, Vikram ).
Image

By comparing the position estimated by JPL/Horizon estimation based on doppler shifts etc.. I think (Let us wait till there is some more people who are expert give it another look and calculations to check)..

According to this calculation/estimation - (which can be easily wrong as all data is fuzzy and has to be analyzed more which ISRO is doing and let us wait for that) ..

- The time the communication lost was *not* 2.1 Km from the target but when Vikram landed on the surface. (Makes the landing pretty hard.
- The speed is about 50 m/s (110 mph) again hard.

But as I said, this was done with very fuzzy data.. so if we here from Vikram obviously our fuzzy data/calculation is wrong. Anyway we will know .

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Re: Chandrayan-2 Mission

Postby JayS » 12 Sep 2019 11:19

ramana wrote:I assumed its sec:hundredths of second.

Usually telemetry is in millisecs
that is reported as Secs: xxx
So here they are reporting as secs: 0.xx0
Eg. 19 Secs 550 millisecs, 20.000, 20 secs 050 millisecs

They probably have better data but the graph divisions are like that

Hours minutes is very slow.

Lets hear from AmberG what is x-axis units?


Its clearly hh:mm. 15 min for whole decent. Thats the clue.

Seems like 50 m/s jump in velocity. But this doesnt tell vector direction.

This picture also fits with the observation from the graph - It is possible Vikram went head down due to issue during alttitude control for a short while and the thrusters, instead of slowing it down, speeded it up towards moon surface before the control system wrestled back the correct attitude and speed started dropping. But too late, it hit the surface by then.

Just thinking aloud -
By eyeballing, it looks like 50m/s jump in 20sec time. Thats is 2.5m/s2 avg acceleration. Given 1200kg is a good number for Vikram considering fuel loss in decent, that would be a force of 1200x2.5 = 3000 N. The instantaneous acceleration likely was bit higher. Then the number of 4x800N total thrust approximately correlates to the Force magnitude. But in fine breaking only two thrusters were suppose to be working. If we subtract Moon's g of 1.6m/s2 from 2.5m/s2 we get the force of 0.9x1200 ~ 1100N. This is within the capability of 2x800N thrusters. So if we assume only two 800kN thrusters were working, then them assisting the gravitational acceleration can give some sensible numbers. This means Vikram going heads down.

Notr that we dont know velocity vector direction so above can be totally wrong speculation. But it seems logical that velocity increase was because the thrusters were assisting the g acceleration rather than opposing it.

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Re: Chandrayan-2 Mission

Postby Amber G. » 12 Sep 2019 11:31

Sorry if already posted: From TOI:
Nasa’s deep-space antennas sending hello messages to 'motion ..
t


Meanwhile per Twitter: (Orbat_editor sor something like that) Vikram Lander is transmitting in Safe Mode. Signal Strength should show improvement with increased sunlight over the next week..ityadi ... Their cited source is BRF :)..

BTW: the DSN live site is https://eyes.nasa.gov/dsn/dsn.html
Last edited by Amber G. on 12 Sep 2019 11:41, edited 3 times in total.

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Re: Chandrayan-2 Mission

Postby SSSalvi » 12 Sep 2019 11:36

Goldstone DSN on with CH2
Orbiter :Tx. 2.05 Ghz. & 7.18 Ghz. Tx Pwr 0.25 kw
Rx. 2.23Ghz

Lander attempt :
Tx Frq 2.1Ghz. Power: around 10Kw

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Re: Chandrayan-2 Mission

Postby Haridas » 12 Sep 2019 12:17

ramana wrote:I assumed its sec:hundredths of second.

Usually telemetry is in millisecs
that is reported as Secs: xxx
So here they are reporting as secs: 0.xx0
Eg. 19 Secs 550 millisecs, 20.000, 20 secs 050 millisecs

They probably have better data but the graph divisions are like that

Hours minutes is very slow.

Lets hear from AmberG what is x-axis units?

Remember the dopper data (for such short duration) needs scaling factor, bcoz only radial (wrt earth) component of velocity contribute to dopper shift. The scaling factor can be determined from geometry.

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Re: Chandrayan-2 Mission

Postby Amber G. » 12 Sep 2019 12:29

Per New York Times: NASA will actually share before and after images, if any, of the area where Vikram lander was supposed to land. NASA’s Lunar Reconnaissance Orbiter, a spacecraft currently orbiting the moon, will soon be flying over the lander’s landing site on 17 September, and it could help ISRO with images of the area to help with its analysis.

This story also has their analysis of astronomers who used an old 25-meter radio telescope owned by the Netherlands Institute for Radio Astronomy to track Vikram’s descent, and has some analysis of Cees Bassa (His data/graph was used/mentioned by me in earlier post)

NYTimes article says "The Doppler data indicate that Vikram was instead moving at more than 110 miles per hour" (Which is consistent with 50 m/s figure I gave)

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Re: Chandrayan-2 Mission

Postby UlanBatori » 12 Sep 2019 16:46

ramana: subscale test maybe with small number of real engines, from airplane. Yes, if that occurred (which is not totally clear) it proved that a carefully prepared sample of the engines would work once. Theory says that back pressure does not matter for choked nozzles so test from airplane == test in Space. But heat transfer is very different (nozzle walls and throat will last longer) in air, but hopefully they have tested the engine in a vacuum chamber.

Of course the real engines would have been made/selected as carefully. But so are engines for nuclear missiles and human-rated fighter engines.

Combustion/ rocket instability hits more or less randomly, per the Pershing SRBM missile (post-deployment, dozens built) and the F100 jet engines (thousands built). The mid-1980s incidence for the F-100 was cited as 1 in 6, brand-new off the production line. Pershing was more than 1 in 20.
ISRO is having to make do with absolute minimum of test flights, witness the CY-2 trying out so many new and risky things in one mission. That is what enrages some of us about these pompous so-called "journalists" sneering at ISRO "built on failure" etc. Have they ever typed 100 words without a typo?

In any other agency, the lander would have been tested 3 times in space before attempting an actual moon mission (test surviving the boost to GTO, the separation and re-orientation, performance of automatic control and comms around the Moon). At least 100 of the engines would have been tested to failure. Some 10 landers would have been tested to destruction, with at least 3 in Space. So present test should be considered as just that: a first test in a series. ISRO just prefers to lay out the whole thing, which is a test-till-failure philosophy of the full system. Respect for taxpayer.

Thruster overperformance may explain temporary attitude changes and the antenna may have gone out for seconds, but persistent comm loss is best explained as impact. What was the altitude at "2.1km out" I wonder.

So far all data shown are very approximate/1 or 2 components of 3-component vectors, very low-resolution observations by people/machines from very far away. Someone who has access to the best stuff is surely synthesizing all these, and I hope they do it with patience and without harassment. Then we might be able to get some clarity. Meanwhile, given the new assurance of 50m/s impact, what was the basis for the initial statement that it "looks intact, just toppled"? With all mass-saving efforts I doubt very much whether anything other than the legs were designed for any impact, crash-absorbing features etc. So they should have seen many different "intact landers" scattered all over.

Maybe this is what was behind the Hundi article (that ISRO knows that the lander died instantly). The journo may have had inside info and written lifafa. Maybe they hope that just the comm part is lying out there, and may respond, in which case they can claim: Aha! First Soft-Enough Landing so far south!! Just trying to be charitable, the best spirit of conspiracy theorists.

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Re: Chandrayan-2 Mission

Postby SwamyG » 12 Sep 2019 19:01

https://www.forbes.com/sites/robinandre ... 9a3afe13c7

If the orbiter was lost too, then sure, this mission would be a devastating, but not unforeseeable, failure. Space is hard. But the ingenuity of India’s scientists and engineers means that ISRO will now be able to conduct a myriad of phenomenal, cutting-edge lunar research regardless of whether or not they can salvage Vikram.

The orbiter, connected with the Indian Deep Space Network – a collection of antennas and relays to support its interplanetary missions – is absolutely packed with top-notch tech. Here’s a taste of what that little orbiter will be able to accomplish as it spins around the moon in glorious solitude.


Don’t let that crash-landing get you down, though; the moon still has a brand-new robotic friend, one that will, in time, reveal more of its secrets than anyone can possibly imagine.


Hmmmm coming from Forbes such positivism. Very interesting.

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Re: Chandrayan-2 Mission

Postby fanne » 12 Sep 2019 19:22

The handle that announced Chand Rayan in one piece is not official. The only thing Isro has said is that they have thermal image

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Re: Chandrayan-2 Mission

Postby UlanBatori » 12 Sep 2019 20:38

The other snippet was the concern that "no nation releases near-Moon data". What could that mean? There are no tall mountains that might have hit the lander as it zoomed along.

So what WAS different about this lander's trajectory? Did previous ones (Apollo, Luna, Chang-e) just decelerate to zero tangential speed at 1 or 2km above surface, then retro-thrust all the way to the surface? Was ISRO trying to be too smart by using orbital mechanics to get very close in altitude, zooming along, then do a smart Pogachev Cobra Maneuver and descend only about 300 meters (makes a big difference in fuel requirement, probably; I am too poor to have STK running on my YakPowerGizmo).

IOW, in the process did Vikram come close enough to the surface to get seriously hit by anomalies in the magnetic field? I can't think of anything else. Any Dust Devils that have electrostatic charge hence could form an ion layer. But I thought they hang around below 100m, and are extremely low-density. Maybe at dawn at such a latitude the situation is different and density is higher? But surely that would at best cause a bit of sparks on the outside, nothing to get excited about since the lander would land as scheduled?

But if there is a very strong local magnetic field, perhaps bad things might happen. I don't know how ferromagnetic a lander is, but I know that my cordless screw driver now insists on hugging screws and moving them around although they LOOK like gold (probably Chinese iron with brass coating).

What else could happen? Surely gravity anomalies have to be spread out over a very large area unless there is a tiny Black Hole at 70.9 deg. S. lat. Wonder why LIGO hasn't detected that yet. OK, let's not go there. :shock:

So the question is why the Cobra Maneuver led to oscillations, and was it so violent because of unanticipated EXTERNAL forces? Did Blofeld Khan, Number 2 at ISI-SPECTER, send the command to crash? (JUST KIDDING!!!)

Did Vikram get hit by a passing NEO or piece of Anthropogeinc Space Junk (ASJ)? Any CashMori stone-throwers at 70.9 deg. S.?

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Re: Chandrayan-2 Mission

Postby SaiK » 12 Sep 2019 21:31

UlanBatori wrote:..but taken with special Raa camera whose resolution cannot be revealed.

obfuscation is possible :).. and we can reduce the resolution as well! :)

in another discussion, I was joking we landed on a pond and got drowned. :) water proved in one shot!

So present test should be considered as just that: a first test in a series. ISRO just prefers to lay out the whole thing, which is a test-till-failure philosophy of the full system. Respect for taxpayer.


beautiful narrative! :)

Any CashMori stone-throwers at 70.9 deg. S.?
:rotfl: AoA~

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Re: Chandrayan-2 Mission

Postby UlanBatori » 13 Sep 2019 03:48

Gee! Interest dropped faster than the term "Kashmir" from the news. Sep. 15 is still far away.

Question: How do they know the altimeter was not off? That is what happened to Gary Powers, the USAF U-2 pilot who took off from (where else) Peshawar to overfly the Soviet Union. Altimeter said 80,000, actual was 40,000, within missile range.
Last edited by ramana on 13 Sep 2019 05:06, edited 1 time in total.
Reason: Edited by ramana

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Re: Chandrayan-2 Mission

Postby suryag » 13 Sep 2019 04:16

Saar mourning :(

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Re: Chandrayan-2 Mission

Postby Nalla Baalu » 13 Sep 2019 04:48

UB saar, please to refer below from yak's mouth. Lander carried 3x redundant altimeters onlee, 2x ka-band and 1x laser.

UlanBatori wrote:Gee! Interest dropped faster than the term "Kashmir" from the news. Sep. 15 is still far away.

Question: How do they know the altimeter was not off? That is what happened to Gary Powers, the USAF U-2 pilot who took off from (where else) Peshawar to overfly the Soviet Union. Altimeter said 80,000, actual was 40,000, within missile range.



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Re: Chandrayan-2 Mission

Postby SriKumar » 13 Sep 2019 05:05

UlanBatori wrote:Gee! Interest dropped faster than the term "Kashmir" from the news. Sep. 15 is still far away.
Well, no new information means no new material to chew on and dissect. Couple of unrelated general comments:

1 Considering that the lander maintained its telemetry lock (with Orbiter? DNS-Madrid?) even while it was upside down, while righting itself, and then while rightside up (and it was even sideways just before braking) there would have been multiple antenae on the craft pointing multiple directions. For it to lose telemetry may not have been just a matter of wrong orientation.

2. About the craft hitting lunar ground when telemetry was lost- I think it is unlikely (pure espekulashun onlee) because the area would have been well-photographed with hi-res cameras. The ISRO scientists, per Madhanan Nair (IIRC) looked over the photos, picked a landing area the previous day and then Vikram went to the spot a day later. Now granted that Vikram did not land on the intended target, but 500 m away (if the report is to be believed). If indeed there is a 100 meter high hillock 500 m from the designated landing spot, that is not a good landing spot- I guess it means that the entire area (200 km x 200 km) or whatever area was scanned for a landing zone, is full of hilly features then. Speculation to fill a slow newsday.....
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Re: Chandrayan-2 Mission

Postby ramana » 13 Sep 2019 05:12

So there was altimeter redundancy and can rule that out.

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Re: Chandrayan-2 Mission

Postby ramana » 13 Sep 2019 05:13

Srikumar during violent maneuvers usually such packages experience electric short.

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Re: Chandrayan-2 Mission

Postby ramana » 13 Sep 2019 05:23

Nalla Baalu, Thanks. Wish we had that video early on to understand the descent phases.

So did the lander did land and did it deploy those three other experiments which are external to the lander?
Could they see the pictures?

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Re: Chandrayan-2 Mission

Postby Amber G. » 13 Sep 2019 05:36

There have been a few posts asking about and wondering about the position and angles of Sun on the moon .. and just some basic questions which people, it seemed, were not clear.. Hope these two animation helps to get bearing straight.

I can get some more specific for Vikram's point of view but I am trying to figure out how to upload/share a high-resolution animation on brf. Meanwhile, I am using some Nasa/dropbox or other such resources..

First one is moon (looking from outside.. earth) in year 2019.
- You can see north-pole/south pole, Moon equator, meridian etc are shown and also subsolar and sub-Earth points. for 2019.
(The subsolar and sub-Earth points are the locations on the Moon's surface where the sun or the Earth are directly overhead, at the zenith. A line pointing straight up at one of these points will be pointing toward the sun or the Earth.

The sub-Earth point is also the apparent center of the Moon's disk as observed from the Earth.

The blue dot is the sub-Earth point, and the yellow dot is the subsolar point. The lunar latitude and longitude of the sub-Earth point is a measure of the Moon's libration. For example, when the blue dot moves to the left of the meridian (the line at 0 degrees longitude), an extra bit of the Moon's western limb is rotating into view, and when it moves above the equator, a bit of the far side beyond the north pole becomes visible.

At any given time, half of the Moon is in sunlight, and the subsolar point is in the center of the lit half. Full Moon occurs when the subsolar point is near the center of the Moon's disk. When the subsolar point is somewhere on the far side of the Moon, observers on Earth see a crescent phase.

An animated diagram of the subsolar and sub-Earth points for 2019.

The second one is Phases of Moon seen in 2019 (hourly intervals) -Nasa/JPL has some high resolution images which can be uploaded/shared by aam junta..
Here is one:
2019 Phases of Moon

Date/Time, names of important landscapes on the moon, and distance from earth is animated

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Re: Chandrayan-2 Mission

Postby Amber G. » 13 Sep 2019 08:54

For quick reference: Keep your eyes open..
Image

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Re: Chandrayan-2 Mission

Postby Arjun » 13 Sep 2019 11:19

Wokaay...looks like ISRO has no desire to preempt any LRO 'before after' with their own photu from CY2

Wonder what to make of it

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Re: Chandrayan-2 Mission

Postby Varoon Shekhar » 13 Sep 2019 18:39

https://economictimes.indiatimes.com/ne ... s?from=mdr

Term "15 minutes of terror" is a disservice to science

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Re: Chandrayan-2 Mission

Postby SSSalvi » 13 Sep 2019 19:41

^^^
From same report some useful snippets: ( It seems to have been written before the catastrophe.

the moon lander Vikram’s operation from the time it started its journey towards soft landing on the moon on September 7 early morning: “The lander Vikram was horizontal at 30 km altitude at a speed of 1.66 km/sec. When it is brought to lunar surface, lander will be vertical and its velocity will be maximum 2 m/sec.

It follows a curved track during this operation. “The height is reduced by firing thrusters in opposite direction. As the velocity is reduced, because of loss of energy, the lander loses height due to lunar gravitational attraction, roughly one sixth of gravity on earth.

“There were two phases of lunar descent -- Braking and hovering.

The lander Vikram has five big (800 Newton) thrusters and eight small thrusters.
“The five big thrusters are positioned as: four at corners and one at centre. The resultant thrust of four corner ones, if fired equally, will combine in vertical direction, providing opposing force and the resultant vertical axis of vector will pass through centre of gravity, providing stability.

“If an imbalance is created by throttling four engines, i.e. by varying fuel injection rate, the resultant force vector is not aligned to vertical axis of lander, creating one horizontal and vertical component.

generally, operation of four corner thrusters and the central thrusters is made exclusive to make things simple. Thrust vector of central one will also pass through centre of gravity, aiding stability. “Let us assume operation of simultaneous operation of four corner thrusters. Now if one or more of them are not operating simultaneously or there is imbalance in thrust output among them, the resultant uncompensated horizontal force will spin the lander in horizontal plane.

“In that case, the resultant vertical force vector will also not pass through centre of gravity and resultant couple will trigger spinning in vertical plane.

In fact, the controlled spinning by throttling is used to aid programmed tilting of the lander in the braking phase. “If spinning in two orthogonal plane goes out of control, it will essentially tumble down the lander. Tumbling of lander with thrusters on, will make things very complex, like firework burnt in Diwali, called spinning wheel or ‘Charki’. “The result will be simultaneous tumbling and zig zag random motion of lander, beyond the control of on-board control system. So, throttling of the four thrusters is a critical activity.

“A very large component of lander is fuel tank. When lander accelerates, decelerates, because of inertia, the liquid fuel gets into sloshing, akin to splashing of water in a tub.
If( Sloshing becomes severe as more and more fuel depletes in fuel tank) ------ It may so happen that engine nozzle feed will be starved of fuel resulting in uncontrolled throttling.
“The first phase of braking phase lasts from 30 km altitude to 400 m altitude where velocity is reduced from 1.66 km/sec (6,000 km/hr) to 60 m/sec (200 km/ hour). “Orientation of lander is changed from horizontal to vertical. Throughout this period four corner thrusters are operated to brake and central thruster is switched off.
“At 400 m height, the second phase of braking starts. The lander is vertical, two of four corner thrusters are switched off simultaneously and two diagonal thrusters are switched on.

“By the time lander descends to 100 m, these two thrusters brake lander to reduce vertical speed from 60 m/sec at 400 m height to less than 2 m/sec at 100 m height. “The braking control from 30 km height to 100 m is carried out by a series of time tagged commands, loaded in the lander a few hours before operation from ground. They are generated based on precise measurement of lander orbit, prior to de-orbitting.

“When lander reaches 100 m height, the lander is three axis stabilised and it essentially floats. Moon’s gravity is compensated by upward thrust of two diagonal thrusters. “Small thrusters are used to move lander sidewise. The camera on lander takes photograph of lunar surface below. “The resultant image is matched with stored images of landing site (captured by high resolution camera of orbiter earlier) and horizontal movement of lander is controlled. By slowly reducing vertical thrust by central thruster, lander is slowly descended. “Radar altimeter keeps an eye on true altitude of the lander. This mode is called hovering mode. This is the most complex mode and fully autonomous.

“The ( hovering mode ) software is loaded prior to launch and it cannot be changed afterwards as in the case of braking mode which can be changed even a few hours before operation. “Just five seconds before landing, the two diagonal thrusters are switched off and central thruster is switched on. “It was apprehended that two corner thrusters, if active will blow the moon dust and it will create a centre jet upwards, covering the lander with dust. “So central thruster will reduce this upward jet. All landers need to be prepared to operate under dusty condition at the last moment of landing.”

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Re: Chandrayan-2 Mission

Postby ramana » 13 Sep 2019 20:10

Varoon Shekhar wrote:https://economictimes.indiatimes.com/news/science/15-mins-of-terror-is-disservice-to-science-scientist/articleshow/71098222.cms?from=mdr

Term "15 minutes of terror" is a disservice to science


Its a disservice to the forum to post that one liner when its chock full of technical information on the Lander attitude and control system.
:( :twisted:

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Re: Chandrayan-2 Mission

Postby ramana » 13 Sep 2019 20:17

So S^3 we can postulate when things went awry now that we know the planned operation of the lander?

That velocity gain shows the lander spun and there was build up of vertical component and this occurred before the shift from horizontal to vertical.
However lander recovered as it went into fine braking mode.

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Re: Chandrayan-2 Mission

Postby Gautam_2 » 13 Sep 2019 20:50

Arjun wrote:Wokaay...looks like ISRO has no desire to preempt any LRO 'before after' with their own photu from CY2

Wonder what to make of it


What is the the resolution of photos from CY2O? I read somewhere VL would appear as a 3x3 pixel object in the pic from CY2O.

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Re: Chandrayan-2 Mission

Postby Varoon Shekhar » 13 Sep 2019 21:01

Still waiting for that richly detailed article about all the technologies/ systems on board Vikram, that worked very well, before the mishap. So far, it's just general stuff like rough breaking and variable propulsion. Usually, Frontline's T.S Subramanian and R.Ramachandran provide superb write-ups on events like these. And that's the only reason I read that mag these days!

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Re: Chandrayan-2 Mission

Postby SaiK » 13 Sep 2019 21:18

We still have no actual data shared after the signal loss. ISRO only said it has identified, which I assume is the orbiter shot, and we know it is still in one piece. NASA (per that article) says they will share both before and after pics...if both pics remains same with some markers, then there is a possibility of loose moon sand as well. water if any in the crater would be frozen anyway and no likelihood of a drown.

let's wait.

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Re: Chandrayan-2 Mission

Postby Vayutuvan » 13 Sep 2019 21:49

Amber G. wrote:For quick reference: Keep your eyes open..
[img...]https://miro.medium.com/max/615/0*_yEr9TO7nczK24uM[/img]


any idea about at what scale that picture is? what is the 500 meter radius circle, for example?

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Re: Chandrayan-2 Mission

Postby ramana » 13 Sep 2019 22:27

Gautam_2 wrote:
Arjun wrote:Wokaay...looks like ISRO has no desire to preempt any LRO 'before after' with their own photu from CY2

Wonder what to make of it


What is the the resolution of photos from CY2O? I read somewhere VL would appear as a 3x3 pixel object in the pic from CY2O.



The high resolution camera on CY2 Orbiter is 0.3M resolution.

viewtopic.php?p=2378930#p2378930

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Re: Chandrayan-2 Mission

Postby ramana » 13 Sep 2019 22:44

Thanks to @KK2Everest

https://www.manoramaonline.com/news/ind ... ssion=true


It is believed that the Vikram lander was thrown out of control only about 500 meters before the moon landed on the Thiruvananthapuram ന്ദ്ര Chandrayaan 2 mission. This conclusion is made after further evaluation of the optical images of the lander captured by the orbiter in the moon's orbit. Initial reports suggested that Vikram lost control over a height of 2.1 km. The mission failure committee (FAC) began its analysis of the scenarios.

The ISRO received thermal image footage of the lander, which was photographed by the OHRC camera on the orbiter. This was followed by images of ordinary sunlight. Both are being closely scrutinized by the ISRO expert team. The last indication is that Vikram fell 750 meters from the designated landing point.

The absence of a lander in the fall is proof that it has lost control of the Moon. All of Lander's key components are evident in the footage obtained. At the same time, sensitive sensors and batteries can shake and fall in the fall. This is likely due to the lack of communication. The lander is less likely to be activated automatically. At the same time, the reason for the loss of control at the last minute is still unclear.

The new lander may only be launched

ISRO is looking for the possibility of launching a new lander instead of a failed lander. The only plan to land the lander is because the orbiter is sure to remain in the lunar orbit for the next 7 years. The final decision on the matter will be finalized after the analysis of the last-minute failure of the Chandrayaan-2 mission. The design of the Lander will have to be modified to overcome the elements that have failed. There is also the possibility of adding new elements so that the mission can be completed even if it is thrown down.

chandrayaan-2-landing-signal-earth
If only the lander sends, the cost, including launch, can be reduced. The lander and rover of the Chandrayaan II weighs 1498 kilograms. Even if the lander had to add fuel to the lunar orbit from the Earth's orbit, the orbiter's 2379 kg would be eliminated.

Following the report from the FAC, the design and financial costs of the new project are expected to be considered. If the Center approves this, the preparation for the mission will begin. The plan may also change if the design of the Chandrayaan 3 mission is proposed to be implemented in 2024 with the cooperation of Japan.

Gagyanan may be late

The mission of landing the moon on the moon should be investigated as to the cause of the landing, so it may be too late for ISRO's Gaganyan to send people into space. The spacecraft is already scheduled to launch in 2022 using the GSLV Mark-3 rocket.

Chandrayaan-2: NASA to assist ISRO

NASA, the US space research agency, is working with ISRO to restore communication with Vikram Lander, which landed on the Bengaluru ∙ moon surface. Vikram, who is part of the Chandrayaan-2 mission, lost his signal during a soft landing on the Moon last night.

chandrayaan-2
Deep space network antennas from the NASA Jet Propulsion Laboratory in the US, California, Madrid, Spain, and Canberra, Australia, send frequent radio wave signals to connect the Vikram lander. These are large antennas capable of interacting with multiple artificial satellites at the same time. This is in addition to sending the signal for the last 7 days using the antenna of Bayalalu as the ISRO hub in Bengaluru Peenya.

Batteries and solar panels in Vikram Lander have a lifespan of only 14 days. As such, the Lander and the Pragyan Rover can only function for a further seven days.

English Summary : Crash landing for ISRO's plan for a new lander, having capacity



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