Chandrayan-2 Mission

Vayutuvan · Post by **Vayutuvan** » 17 Sep 2019 11:30

UB sir, both tangential and negative normal velocities are important. say normal velocity is zero. the vikram would have made a touch and go a few times and landed safely. I remember trying to skip flat pebbles in local watering hole.

SaiK · Post by **SaiK** » 17 Sep 2019 20:35

we can't use parachutes on moon, but we could use throw-away cushions. just thinking ahead on safety devices for the next landing.

chetak · Post by **chetak** » 17 Sep 2019 20:52

NASA’s Moon Orbiter Will Photograph Chandrayaan-2 Landing Site Today: Here’s What To Expect

by Prakhar Gupta

Sep 17, 2019,

Snapshot
Here’s what to expect as NASA’s lunar orbiter gets ready to photograph the landing site of Chandrayaan-2’s Vikram lander later today.

As the window of restoring communication with Chandrayaan-2’s Lander continues to shrink, NASA’s Lunar Reconnaissance Orbiter (LRO) will make an attempt to spot Vikram at its landing site during a flyover that will take place later today.

The Lander had hard-landed on the lunar surface on 7 September while attempting the closest ever soft-landing to the south pole of the Moon. Since then, ISRO and NASA have failed to establish communication with the Lander.

LRO’s flyover comes days after Chandrayaan-2’s Orbiter had managed to spot the Lander around 500 meters away from its designated landing site. The Lander is believed to have hit the lunar surface at a much higher velocity than it should have and is not in the orientation that it was supposed to be, making communication difficult.

There is no clarity on the state in which the Lander is — whether it has disintegrated due to the high-velocity impact with the lunar surface or not. There are many more questions like those regarding its orientation on the lunar surface that are still unanswered.

Moreover, it isn’t clear if the pictures taken by the Chandrayaan-2 Orbiter give answers to these questions. ISRO hasn’t released images of the landing site that the Orbiter took when it spotted Vikram at the landing site.

Therefore, this is what makes LRO’s flyby important.

“Per NASA policy, all LRO data are publicly available,” Noah Petro, LRO’s project scientist at NASA’s Goddard Space Flight Center, has said, confirming that LRO is due to fly over the Vikram landing site on Tuesday, 17 September.

“NASA will share any before and after flyover imagery of the area around the targeted Chandrayaan 2 Vikram lander landing site to support analysis by the Indian Space Research Organisation,” he told spaceflightnow.com.

This will not, however, be the first time that LRO will turn its sensors towards Vikram.

LRO was monitoring the Chandrayaan-2 Lander as it started descending towards the surface of the Moon in the early hours of 7 September.

NASA’s Orbiter was “observing the changes in the exosphere as a result of the rocket effluence coming down,” Jay Jenkins, program executive for the Office of Exploration at NASA's Science Mission Directorate, has been quoted as saying.

The LRO, launched by NASA in 2009, has been orbiting the Moon for a decade now. It carries a system of three high-resolution cameras, two of which are narrow-angle cameras providing images with 50 centimeter (19.7 inch) resolution.

Over the years, LRO has managed to produce high-resolution images of the Moon for various applications, including those of the Apollo landing sites. Most recently, it had captured images of China’s Chang’e 3 and Chang’e 4 Landers on the Moon’s surface, and located the Israeli Beresheet Lander earlier this year.

ArjunPandit · Post by **ArjunPandit** » 17 Sep 2019 21:01

https://quickmap.lroc.asu.edu/?extent=- ... AsjZwLrc0A
this is what i found on the nasa's site for LRO...is there any way to identify the actual landing points?

i also found that nasa has released the images, which run into TB..this release has been on every month on 9 or 10...

https://www.lroc.asu.edu/posts/1127

last one was on september 10...but before the CY2 landing.( 2019-05-16 through 2019-06-15).i dont have that much space to download all this in oneplace...anyone having space to filter this out?

.those might have been used by ISRO folks to train their CV models....but again huge caveats involved with optics.not an expert in CV, but it is still better than just using images by ISRO orbiter

ArjunPandit · Post by **ArjunPandit** » 17 Sep 2019 21:27

curious what is it...i am sure isro would have requested it in advance..
https://mare3.actgate.com/fcgi-bin/fpro ... est.msh%22

Varoon Shekhar · Post by **Varoon Shekhar** » 17 Sep 2019 21:40

"There is no clarity on the state in which the Lander is — whether it has disintegrated due to the high-velocity impact with the lunar surface or not."

I thought the possibility of disintegration of the lander has been excluded. ISRO was quoted by several media outlets including India Today, that the lander is intact, but tilted.

ArjunPandit · Post by **ArjunPandit** » 17 Sep 2019 22:14

^^^didnt isro base this by the thermal image rather than the optical image?? i am not able to find anything on the landing site or within the images close by...not sure if the displayed images are the latest ones..although the player says latest images as of today..but seems like latest images have not been updated..

SSSalvi · Post by **SSSalvi** » 17 Sep 2019 23:29

Stale subject ... stillllllll posting for records:

Showing the Lander path while descending ( LO in image below ) and the lander position at 20:19 UTC ( 1:40 IST ).

Inset shows thae same situation but in detail.

Also shows the ORBITER ground trace and its position when the Lander was lost. I doubt if the Orbiter will view crash site unless the satellite is moved in Roll axis to ' see ' the site.

Notice that the Landing position that we had assumed is not in the path that the Lander had taken .. So ISRO had a different position in mind for landing the Lander.

Current orbit of ORBITER ( Orange line in image below, termed Orbiter3 ) is fixed in repeativity and the orbital period is about 119 minutes. So it passes in the vicinity of crash site but not over it.

By the way US craft LRO might have obtained the image of area near crash site a few hours back.

Vayutuvan · Post by **Vayutuvan** » 17 Sep 2019 23:33

SaiK wrote:we can't use parachutes on moon, but we could use throw-away cushions. just thinking ahead on safety devices for the next landing.

Increases the weight as well as the volume of the lander. That is why I was talking about a honeycomb structured metamaterial (with directional properties) skin on the lander. Just before landing, the skin can be inflated using compressed air that is kept in a cylinder.

Numbers have to be worked out to see whether this is possible at all. One can also unfold a folded sacrificial honeycomb structure with proper orientation depending on how the lander is landing.

ArjunPandit · Post by **ArjunPandit** » 17 Sep 2019 23:36

https://www.nytimes.com/2019/09/10/scie ... ikram.html
i know its nyt but stil...

Consider NASA’s Mars Polar Lander, which vanished as it was trying to land near the Martian South Pole in 1999. An investigation found several possible explanations, including that when the landing legs unfolded, sensors inadvertently interpreted the vibrations as the spacecraft arriving on the surface and shut the engine down.

For NASA’s Phoenix Mars and Mars InSight missions, the spacecraft were largely the same design as Polar Lander, but they were modified to avoid potential pitfalls. For example, the computer was told to ignore any vibration signals that occurred as the landing legs unfolded. Through testing, the engineers verified that everything would work. Both Phoenix and InSight made it to the surface without problem.

Amateurs used an old 25-meter radio telescope owned by the Netherlands Institute for Radio Astronomy to track Vikram’s descent. The frequency of the lander’s radio transmissions shifted based on its speed relative to Earth. That phenomenon, known as the Doppler effect, is similar to the changing pitch of train whistles and police sirens as they speed by.

Cees Bassa, an astronomer at the Dutch institute who participated in the effort, calculated the lander’s velocity, which matched predictions during the first phase of the firing of the engines.

He could not say what caused the oscillations, but he now believes that the end of the radio transmissions coincided with Vikram hitting the ground. It was supposed to touch down at less than five miles per hour.

The Doppler data indicate that Vikram was instead moving at more than 110 miles per hour.

<This is the guy whose github code we ran into..>
did i miss few pages back?

ramana · Post by **ramana** » 17 Sep 2019 23:38

S^3, Yellow marks actual landing spot?
They reported lander was 500m away from intended landing spot.

ramana · Post by **ramana** » 17 Sep 2019 23:41

Also S^3 and UB, I think the four engines for braking could have caused the tumble due to thruster over/under performance.
Such behavior will cause in one of the off-center engines will cause a moment and tumble the lander.
Then the oscillations to correct the attitude.

SaiK · Post by **SaiK** » 18 Sep 2019 00:26

math guru, perhaps we need to inflate it with something lighter than what is in moon's atmo.

Vayutuvan · Post by **Vayutuvan** » 18 Sep 2019 02:24

SaiK wrote:math guru, perhaps we need to inflate it with something lighter than what is in moon's atmo.

That is the rub. Moon doesn't have any atmosphere. But that is also a blessing in that we require very little air to inflate the reticulated structure, assuming it is possible at all.

SaiK · Post by **SaiK** » 18 Sep 2019 05:00

wouldn't then be cheaper to have all air cushioned landing inside a big inflated ball [it ain't going up for sure] - say co2 or o2 is good enough for cushioning some spring loaded soft-joints to the the balloon periphery. it would also take care of any accidental tumbling etc (mechanicals). I guess, the only critical mechanism is to get the ground sensors right, so that on deflation, the bottom side is facing down for pragyan (2nd version) to roll out.

?

ramana · Post by **ramana** » 18 Sep 2019 08:04

SaiK, Please discuss in ISRO thread.
This is about Chandrayan-2.

SSSalvi · Post by **SSSalvi** » 18 Sep 2019 08:11

Ignore for now ... will post updated

@Ramana

Here is a closeup of situation. Showing the craters referred by ISRO.
ISRO says ( Prior to Launch of CY2 ) the site is 'between' the craters. But the Lander path ( Based on jpl/nasa data base ) and the landing ( CRASHHHHH) site around location marked as 2019 ( Pertaining to lander position at 20:19 UTC) are way apart.

Now ISRO says the debris ( Sorry to use that word ) is just 500M away from intended landing spot.

What does it mean? Either they had a different location in mind than what was published ... OR......?????

They never disclosed the exact location.

The midway point 'between the craters' and the 'crash site' are at least 80 Kms apart ... with simple visual calculation taking the dia of Menzius C to be 25 kms across.

Vayutuvan · Post by **Vayutuvan** » 18 Sep 2019 09:14

SaiK wrote:wouldn't then be cheaper to have all air cushioned landing inside a big inflated ball [it ain't going up for sure] - say co2 or o2 is good enough for cushioning some spring loaded soft-joints to the the balloon periphery. it would also take care of any accidental tumbling etc (mechanicals). I guess, the only critical mechanism is to get the ground sensors right, so that on deflation, the bottom side is facing down for pragyan (2nd version) to roll out.

?

SaiK avare, as per the bradmin directive, let us continue in ISRO thread. CY2 thread is for immediate (knee jerk?) reaction it seems.

prasannasimha · Post by **prasannasimha** » 18 Sep 2019 09:28

^ It was done by US for the one if the Mars landers. I think spirit and opportunity but was given up subsequently

UlanBatori · Post by **UlanBatori** » 18 Sep 2019 09:52

I wonder what is the delay in sharing images that ISRO has, if any.

juvva · Post by **juvva** » 18 Sep 2019 13:02

NASA’s LRO Fails To Spot Chandrayaan-2 Lander

As scheduled, NASA’s Lunar Reconnaissance Orbiter Camera (LROC) on Sept. 17 imaged the intended lunar south pole landing site for India’s Chandrayaan-2 Vikram lander, but long shadows in the area may be obscuring the silent lunar explorer. It was near dusk as the region prepares to transition from a two-week lunar day to and equally long lunar night, so shadows covered much of the region and Vikram may not be in the LROC’s field of view, NASA said Sept. ...

https://aviationweek.com/awinspace/nasa ... n-2-lander

UlanBatori · Post by **UlanBatori** » 18 Sep 2019 18:16

So much for nasalro woo hooo.

Gagan · Post by **Gagan** » 18 Sep 2019 21:43

No way ISRO is going to put up 32 cm resolution images to the public domain
Images will be downgraded, such that public won't be able to see very fine details.

But should be enough to keep us busy till the next launch

ramana · Post by **ramana** » 19 Sep 2019 01:47

A question: Do we know the spacing of the 500N engines on the lander?
I am assuming they are mounted in a square configuration.

Also whats the rotational moment of inertia of the lander along its principal axes?

I want to calculate how much the engine has to over perform in order to tumble the lander?

ashbhee · Post by **ashbhee** » 19 Sep 2019 01:57

The Chandrayan-3 is suppose be a sample return with JSA. Doesn't it make sense to do a repeat Chandrayan-2 before that? Maybe just with the lander like NASA's Mars mission (Curiosity, Spirit, opportunity etc). Since it just a lander it will cheaper and Chandrayn-2 in orbit, suppose be in orbit for 7 year will work as communication satellite.

Since it is just the lander, we can launch using PSLV or even the new SSLV.

ramana · Post by **ramana** » 19 Sep 2019 02:05

If you read press reports by eg. Chengappa, that's the plan as the CY2 Orbiter has long life of 7 years.
But before that need to find the root cause and ensure its corrected.

Amber G. · Post by **Amber G.** » 19 Sep 2019 03:43

Not keeping up with recent posts .. but just posting CY2 orbits .
(Was watching the moon and other planets with home telescope with the with kids - and was trying to explain how CY2 orbits will look like around the moon)

The first picture shows Chandrayaan_2's 90 km orbit around the recent भाद्रपदा पूर्णिमा - full moon. Note how close to the surface the trajectory is in relation to moon's diameter. Obviously this orbit was chosen to keep the spacecraft in constant sunlight.

>> Other plane:

***** Added Later:
Some comments: (Scientifically accurate, but not from ISRO's (or NASA's) official sources. (Also these may be different ddm's silly comments also)

- The above orbits are calculated - not from ISRO's data (which I was not able to get the latest data), but rather than other data and the orbit is about 91km (rather than 100 per ISRO), perhaps in a few days, when we get better (and more orbit data) data hope we can get more detail orbit.

- The "low angle" from CY2, In my opinion is good for thermal image, and even photographs as Vikram, if in one piece is going to cast long shadow visible from CY2 .. OTOH, if behind some rock/mountain it can be hidden from that perspective.

- The "pictures" (form ISRO or NASA's LRO) are going to be a "few pixels" .. Millions (or more) pictures have to be examined (before and after) so "see" it. One way to think about it is to looking for a key (few cms in dimension) in a vast rocky plane from a plane flying 1Km high.

- The LRO's polar orbit is elliptical but similar to CY2 in some respects, but it comes as close as 50 km above the surface... Here is one month's plot from Doppler data:

Sun is going to set in about 2 days ..

Amber G. · Post by **Amber G.** » 19 Sep 2019 07:46

^^^ Sankara dot net and NASA/JPL/Horizons gives a very good tool if one is interested in seeing the orbits/terrain etc.
Sankara has included CY2, Vikram and LRO too..

LRO's data base has a very detail map of moon publicly available.. If some one is good in CGI etc. one can even make good animation with *actual* data.

Amber G. · Post by **Amber G.** » 19 Sep 2019 08:02

Meanwhile, as expected LRO was pretty active recently. It was in contact with DSN and non-DSN ground stations. The signal was visible even when DSN Now wasn't showing a contact. Of course, my guess is it will take some time to do image analysis and may e some time before before we will see a result regarding Vikram lander.

Two more days till sun sets near Vikram .. LRO will again have a near pass with this site in a month or so.

Amber G. · Post by **Amber G.** » 19 Sep 2019 08:16

I will look but if someone has the current/latrest orbit data for CY2 from ISRO, can you post link here.

(Hope this helps S^3 to plot)

From the latest I can see from observed data (NASA/JPL/Horizon's elements+ my calculations ) I am seeing
perilune(perigee - moon's radius) = 84 Km,
apolune (apogee - moon's radius) = 140 Km,
eccentricity = 0.0153
That makes a period of ~7131 seconds. (Can some one tell me this data accurately as ISRO will have this)

Amber G. · Post by **Amber G.** » 19 Sep 2019 08:30

Someone mentioned Queqiao ..

Amber G. wrote:
Dasari wrote:

Geometrically it is not possible to cover with less than three, unless they relay it with three other Geo Sync satellites of the earth.
The Relay sat is Queqiao. It is in a "halo" orbit near the Earth-Moon L2 point.
For details, do a search on "halo" orbit, or "Lagrangian" points of Earth-Moon system.

(Basically A relay sat in such a halo orbit would be in continuous view of both the Earth and the far side of the Moon (most of the far side) so it can be used as a relay station. Actually NASA was thinking of such a sat in 1960-70's but they thought they will not need it as they restricted themselves to the near side of the moon)

Small tidbit .. Quequiao's and CY2's path sort of crossed on 9/12.. we could (or perhaps did) use Chinese relay sat at L2 too

Vayutuvan · Post by **Vayutuvan** » 19 Sep 2019 12:46

Gagan wrote:No way ISRO is going to put up 32 cm resolution images to the public domain
Images will be downgraded, such that public won't be able to see very fine details.

But should be enough to keep us busy till the next launch

32 cm resolution, really?! If so, I don't care what ISRO does as long as it doesn't put out an image at that resolution.

Vayutuvan · Post by **Vayutuvan** » 19 Sep 2019 12:55

prasannasimha wrote:^ It was done by US for the one if the Mars landers. I think spirit and opportunity but was given up subsequently

what was done? in anycase, who says we shouldn't do something similar with a variation? amreeka attempted and failed doesn't mean nobody else should attempt the same or attempt a variation.

we wouldn't have had a mangalyan if we trudged the well trodden path.

Vayutuvan · Post by **Vayutuvan** » 19 Sep 2019 13:04

ramana wrote:A question: Do we know the spacing of the 500N engines on the lander?
I am assuming they are mounted in a square configuration.

square configuration with a center fifth engine is very stable.two diagonal engines and the anti-diagonal engines can be pulsed while the center engine is firing continuously. as long as the pulsing frequency is high enough, it is as good as firing all five engines. ISRO had a good design.

Dileep · Post by **Dileep** » 19 Sep 2019 16:27

The "X cm" resolution of the camera is associated with the "distance to object" (or altitude for land imaging) na? So, 30cm was for what altitude?

ramana · Post by **ramana** » 19 Sep 2019 19:44

CY2 Orbiter is in 91 km orbit from Moon surface if you scroll up and see AmberG posts.

sudarshan · Post by **sudarshan** » 19 Sep 2019 20:18

ramana wrote:A question: Do we know the spacing of the 500N engines on the lander?
I am assuming they are mounted in a square configuration.

Also whats the rotational moment of inertia of the lander along its principal axes?

I want to calculate how much the engine has to over perform in order to tumble the lander?

The spacing might be obtainable from public sources, but the moment of inertia is not something easy to obtain.

But - we don't really need the exact values for either of these.

Technically, even a tiny force will eventually cause a large velocity change and a large displacement. So if a 10 ton object is subject to a nano-newton of force, it will eventually accelerate to great speeds, and cover large distances (if there are no opposing forces).

In the same way, even a minute over-performance by one engine will eventually tumble the lander head-over-heels, just a question of time. It could be a year, or a million years, if the over-performance was like 1 ppm or 1 pp-trillion.

So we can use this to get a good estimate of tumbling time.

As below - assume a mass for the lander, assume a "diameter" (with cylindrical lander assumption), and calculate the maximum moment of inertia (which is the value if all of the lander's mass was situated at half the diameter away from its rotational axis).

I_max=m*r^2 (I_max=max. moment of inertia, m=mass, r=radius)

Then calculate the tumble times for various values of over-performance, like 1%, 2%, 5%, etc. Finally, apply a fudge factor for the moment of inertia. And we get a ball-park value of the tumble time.

Recall, (Turning Moment)=(Moment of Inertia)*(Angular Acceleration), just like (Force)=(Mass)*(Linear Acceleration).

If we have the angular acceleration, and we have the tumbling angle (assume 180 degrees, full head-over-heels), we get the tumble time from (Angle)=0.5*(Angular Acceleration)*(Time)^2,

just like (Distance)=0.5*(Linear Acceleration)*(Time)^2.

So in this vein, please see the calcs. below:

In the above, the tumble times are calculated for two different values of mass - 2000 kg and 5000 kg. Radius is assumed to be half a meter. As seen, even a 1% over-performance by one engine, with a moment arm of 0.125 m (or 5 inches), will tumble a 5 ton lander head-over-heels within 2 minutes, even if the moment of inertia were at its maximum possible value. With a realistic fudge factor on the moment of inertia like 0.5 or so, a 5 ton lander will tumble in 80 seconds with a 1% over-performance on one 500 N engine.

Hope there are no mistakes in the above.

Amber G. · Post by **Amber G.** » 19 Sep 2019 21:56

Sorry if already posted:
-During the Sept. 17 LRO flyover of the area, local lunar time was near dusk, ==> "poor lighting and a challenging imaging environment."
- Per NASA policy, all LRO data are publicly available. NASA is sharing any before and after flyover imagery of the area around the targeted Chandrayaan-2 Vikram Lander landing site to support analysis by the Indian Space Research Organization.
- Landing site photographs needs to be analyzed in detail but AFAIK lander itself has not been located.
LROC picture of the Vikram landing (We have posted this in BRF before but posting it again)

SSSalvi · Post by **SSSalvi** » 19 Sep 2019 22:16

About current orbit data:
ISRO never publishes orbit data. ( State Vector or
TLE are the correct terms. )

Celestrak is an authentic source for latest TLE for Earthbound Satellites . It doesn't include CY2 after it entered Moon gravity.

For crafts in non-stellar orbits jpl/nasa horizons is the only known source. But it doesn't give in TLE format and more importantly it gives derived output. .. not the official values from actual satellite operators.

Other source for Earthbound satellites is n2yo

Amber G. · Post by **Amber G.** » 19 Sep 2019 22:18

Dileep wrote:The "X cm" resolution of the camera is associated with the "distance to object" (or altitude for land imaging) na? So, 30cm was for what altitude?

Few comments about resolving power and resolution:

Yes, resolving power is actually measured in angle (radians). I can "resolve" 30 cm easily, without any aid, from a distance of 1 Km. My 20 cm home telescope can "resolve" 30 cm from a distance of 100 Km -- almost the same power as CY2's cameras..

- The "definition" or understanding of "resolving power of 30 cm" is this - if there are two LED's (point source of light) 30 cm (or more) apart one can see them as *two* separate light sources.. If they are closer than that they will look like one source.

- The resolving power depends on wavelength of the wave. It is about (wavelength) divided by (diameter_of_the_objective_lens/mirror).

- Though "resolving power of 30 cm" a good (very good) measure of what one can see clearly, BUT it is not everything. It certainly does not mean that any thing like 31 cm will be visible (seen/identified) and 29 cm will be not. MANY other factors (like lighting, surrounding, brightness/reflectivity of Vikram/ direction , shadows etc..) needs to be considered before one can identify Vikram.

- There are no "secrets" spilled if ISRO publishes high resolution photographs of the moon. The most likely reason it is not publishing it is NOT to protect it's technical secrets but because it is VERY difficult to identify Vikram from a few pixels.

Hope this helps in understanding and encourages people to learn more basics..