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ramana wrote:Do that for having raised the issue.
And AmberG will correct your answer.
Our folks have forgotten basic physics.
Well said! I am aware of the 52% success rate, and the recent Israeli mishap. I am not counting chickens before they hatch. I am not asking about circular vs elliptical orbits. Considering the numbers an additional 60kms comes with that perspective.Mort Walker wrote:Let Vikram land first, then we can discuss RTG. There is a lot which can go wrong come 7 September. Success rates are around 50%.SwamyG wrote:1. So are the considerations to heat; a political/administrative task of taking isotopes up in the air (somebody mentioned ISRO did not make a request), or is it scientific/engineering one (essentially a weight issue)?
2. 35 x 101KM is nearly a circular orbit, curious why it is not "perfect" circular orbit? After all the orbiter is powered, unlike the natural planets and moons orbiting Sun and planets respectively.
It is an elliptical orbit in polar configuration as AmberG. pointed out above. The moon’s gravity is not uniform. It’s mass is lumpy and a shallow circular orbit would require more use of thrusters to keep it in position.
Amber G. wrote: (There is an old joke about Indian parents who, when their child gets 99% in a test, ask the child "what happened to 1 point?"
Thanks for the answers. I am aware of the elliptical and circular. Was curious to know if they had gone for say a 30x40, or 50x55 (all arbitrary numbers), would that, have required more energy. Like I replied to Mort, considering the large numbers in play....this is very close. Just wanted to see why a 30x30 could not be attempted. Thanks again. Also thanks for the answer on weights. That answers my interest; I did not have the intention to debate or discuss the reasons in depth here.. (Short answer: No, it is not weight issue, ISRO did not think it needed/wanted it. We will use it when our antriksh-yatris land on moon.)
Please click on the link
https://twitter.com/i/status/1168614557427699712
ISRO animations on youtube show the central engine, thrusting all the way down to the surface, upto touch down....juvva wrote:I remember reading somewhere ( need to dig up the source), that the landing strategy is now changed. The engine in the center will be on and firing all the way to touch down(no free fall).
FWIW: (Disclaimer: I do not know exact details of landing strategy but..)juvva wrote:ISRO animations on youtube show the central engine, thrusting all the way down to the surface, upto touch down....juvva wrote:I remember reading somewhere ( need to dig up the source), that the landing strategy is now changed. The engine in the center will be on and firing all the way to touch down(no free fall).
Further, Isro also carried out another manoeuvre of the orbiter on Tuesday, which the space agency did not officially announce. Sources said that the orbiter’s orbit was further reduced after a 36-second burn of the onboard propulsion systems. The orbiter reduced the distance closest to Moon to reach an orbit where the perigee was 96km.
“This was done so that the orbiter is right on the head of the lander when the landing happens,” a source added. Vikram is expected to touchdown on the lunar surface between 1.30am and 2.30am on September 7. Isro had announced that it would be at 1.55am. "We are looking at starting the powered descent at 1.40am or 1.45am. The landing must happen 15 minutes after that," Sivan explained.
It could be vice versa. Unless one sees the full gravitational map of moon, it will be difficult to call that out generically.dada wrote:Is the gravitational pull near lunar pole stronger than at lunar equator ?
Moon is nearly spherical (compared to earth) - flatting factor of about .0012 (1/3 or earth). This means polar and equatorial radius are almost same (diff about 2 Km). It also spins much slower than earth, hence effect due to "centrifugal" is much smaller. Thus the gravitational pull is - within say 1-2% - same. (Equatorial g will be less due to this theory but not by much) Moon is relatively less homogeneous than earth so there is more random fluctuation in the value of "g" but all within 1-2% or so of the value = 1.62 m/s2 ( about 0.1654 g) (The maximum variation due some mascons is about .02 m/s^2)dada wrote:Is the gravitational pull near lunar pole stronger than at lunar equator ?
Here is map of "g" at moon: (From Wiki - As I said in above messages the max variation is about .025)disha wrote:It could be vice versa. Unless one sees the full gravitational map of moon, it will be difficult to call that out generically.dada wrote:Is the gravitational pull near lunar pole stronger than at lunar equator ?
For example, Apollo landings on Moon's equator were on basalt plain which are generally denser and hence prospectively can be termed as one with larger gravitational pull.
Hence to equivocally say gravitational pull near lunar pole(s) is stronger than at lunar equator is not plausible.
moi not dilboo, but on conditional note, if we had already flight tested to specs on Earth, the dilboonetics kicks in with this post. /whoever doesn't want to land on moon, please stay out of this dhaaga.SSSalvi wrote:..forgotten basic physics...
Dilboo, Help!
SaiK wrote:moi not dilboo, but on conditional note, if we had already flight tested to specs on Earth, the dilboonetics kicks in with this post. /whoever doesn't want to land on moon, please stay out of this dhaaga.SSSalvi wrote:..forgotten basic physics...
Dilboo, Help!
On-board cameras will be mapping the terrain, sending the pictures to us. Then we will have to select the appropriate location and see that in the exact location it descends slowly to the surface", Nair said in an interview to PTI.
"It's a very, very complex operation. I don't think any nation has done a similar operation trying to have real-time pictures and then try to have an on-board computer implement autonomously the function of the landing. It's going to be a remarkable event and we are all looking forward to that event. I am sure it will be a 100 percent success", he said.
This sounds quite like Balakot SPICE. Probably involves more than that.disha wrote:https://www.firstpost.com/tech/science/ ... 80851.html
trying to have real-time pictures and then try to have an on-board computer implement autonomously the function of the landing.
As of the time of this posting it appears to be Goldstone Deep Space Communications Complex (GDSCC) in the Mojave desert in California.Ashokk wrote:ISRO uses NASA's dish antennas which are located at different parts of the world to communicate with Chandrayaan when it is not visible from India. As per the DSN website, currently an antenna located in Madrid is in use.
In reading the full article, it seems that the Vikram lander will first take pictures of the lunar surface for potential landing sites, which it must be doing right now as it orbits in very close proximity to surface. The people (ISRO) on earth will study the pictures and designate a landing site based on the pictures. Then as Vikram descends, the onboard camera and image recognition systems (in addition to laser and other sensors) guide the craft to the selected landing site.
https://www.firstpost.com/tech/science/ ... 80851.html
On-board cameras will be mapping the terrain, sending the pictures to us. Then we will have to select the appropriate location and see that in the exact location it descends slowly to the surface", Nair said in an interview to PTI.
"It's a very, very complex operation. I don't think any nation has done a similar operation trying to have real-time pictures and then try to have an on-board computer implement autonomously the function of the landing. It's going to be a remarkable event and we are all looking forward to that event. I am sure it will be a 100 percent success", he said.
There is no doubt that the landing will be recorded, broadcast (to the orbiter) and stored, and then broadcast to earth. Not just visuals but all other data like distance from surface, attitude, orientation, velocity, deceleration etc. will be recorded for future use. Landing footage will likely be released once the landing is deemed successful, and at an appropriate time.Mort Walker wrote:From Nair's interview it appears there will be real-time pictures during the descent and landing. But would it be broadcast to the world soon?
Difference between an engineer and a scientist.Dileep wrote:Slightly OT, but we had a few occasions of senior retired ISRO scientists working with/for us. The attention to details, the deep probing and the tenacity drilled into those bright minds is extraordinary (from POV of us engg service folk).
The only problem was, we couldn't get anything done to OUR schedule, and they couldn't get anything done to THEIR satisfaction.
Correct. ISRO is the best example of the intersection of science and engineering. It is indeed a rare type of organization that gets the best of both.SSSalvi wrote:Cannot compare two different items which have their own different goals and targets.
Each is called excellent when the job is executed meticulously.
If the landing is successful, then it should be released immediately. The psychological impact will be the greatest among friend and foe alike. The boost for Indian youth in aerospace engineering and astrophysics will be huge!SriKumar wrote:There is no doubt that the landing will be recorded, broadcast (to the orbiter) and stored, and then broadcast to earth. Not just visuals but all other data like distance from surface, attitude, orientation, velocity, deceleration etc. will be recorded for future use. Landing footage will likely be released once the landing is deemed successful, and at an appropriate time.Mort Walker wrote:From Nair's interview it appears there will be real-time pictures during the descent and landing. But would it be broadcast to the world soon?
The only problem is not to aim high. Once the aim is high enough (and higher still), it's just situational.Ah, a man's reach should exceed his grasp, or what's a heaven for?
