Chandrayan-1 moon mission

SSridhar · Post by **SSridhar** » 04 Nov 2008 08:44

The title that Chandrayaan has entered 'lunar space' is misleading. It will take another 5.5 days for the spacecraft to enter 'lunar space', assuming everything goes well. ISRO generally makes a press release after accurately determining orbital parameters which takes some time.

Singha · Post by **Singha** » 04 Nov 2008 08:57

some imagery of earth released. 5m res B&W.

http://isro.org/pressrelease/Oct31_2008.htm

Nitesh · Post by **Nitesh** » 04 Nov 2008 09:24

http://timesofindia.indiatimes.com/Chan ... latestnews

Chandrayaan enters lunar space for final journey
4 Nov 2008, 0920 hrs IST, IANS

BANGALORE: India's first moon mission Chandrayaan-I entered the lunar space early Tuesday for its final journey into the lunar orbit Saturday, an official of the Indian Space Research Organisation (ISRO) said.

"The operation to put Chandrayaan into lunar space went off very well. The complex manouvre was carried out around 5am by firing the liquid apogee motor (LAM) on board for about I50 seconds to place the unmanned spacecraft 380,000 km away from earth (apogee) and I,000 km from the moon," ISRO director S. Satish said.

The distance between earth and moon is about 384,000 km.

Preparations for the next major manoeuvre will begin soon to enable the spacecraft enters lunar orbit November 8 and positions itself about 100 km from the moon's surface.

"Chandrayaan has commenced its final journey towards the moon and will be inserted into the lunar orbit Saturday through complex manoeuvres from the space control centre of ISRO's telemetry, tracking and command network (Istrac) here," Satish said.

Even as the spacecraft gets ready for its rendezvous with the moon, its terrain-mapping camera (TMC) will shoot pictures of the earth and moon orbiting in 380,000 km (apogee) by 1,000 km (perigee).

"The images will be beamed to Istrac's space centre through electrical signals for processing and developing into high resolution pictures of one-five metres," Satish added.

All functions on board the satellite are performing well and its health parameters are normal. It is also able to send and receive signals from ISRO's deep space network (DSN) at Byalalu, about 40km from here.

Chandrayaan is carrying 11 scientific instruments, including six foreign payloads - two from the US, three from the European Space Agency (ESA) and one from Bulgaria. The remaining five are indigenously designed and developed by various centres of the state-run ISRO.

The spacecraft was blasted off October 22 on board the 316 tonne polar satellite launch vehicle (PSLV-CII) from the Satish Dhawan space centre at Sriharikota spaceport, about 80km north of Chennai.

Raj · Post by **Raj** » 04 Nov 2008 09:26

Looks like the firing went off successfully.

"The operation to put Chandrayaan into lunar space went off very well. The complex manouvre was carried out around 5 a.m. by firing the liquid apogee motor (LAM) on board for about 150 seconds to place the unmanned spacecraft 380,000 km away from earth (apogee) and 1,000 km from the moon," ISRO director S. Satish told media.

http://economictimes.indiatimes.com/New ... 671298.cms

The title of the above economictimes report is misleading.

As SSridhar explained it will reach Moon around November 8th.

K Mehta · Post by **K Mehta** » 04 Nov 2008 10:27

Chandrayaan-1 enters Lunar Transfer Trajectory-ISRO Press Release
The fifth and final orbit raising manoeuvre of Chandrayaan-1 spacecraft was successfully carried out today (November 4, 2008) morning at 04:56 am IST. During this manoeuvre, the spacecraft’s 440 Newton liquid engine was fired for about two and a half minutes. With this, Chandrayaan-1 entered the Lunar Transfer Trajectory with an apogee (farthest point to Earth) of about 380,000 km (three lakh eighty thousand km).

The health of the spacecraft is being continuously monitored from the Spacecraft Control Centre at ISRO Telemetry, Tracking and Command Network (ISTRAC) in Bangalore with support from Indian Deep Space Network (IDSN) antennas at Byalalu. Since its launch on October 22 by PSLV-C11, all systems onboard Chandrayaan-1 spacecraft are performing normally. Chandrayaan-1 will approach the Moon on November 8, 2008 and the spacecraft’s liquid engine will be fired again to insert the spacecraft into lunar orbit.

sumishi · Post by **sumishi** » 04 Nov 2008 10:30

lakshmic wrote: It is a question of sensor fidelity (or sensitivity) and need. Note that ability to sense all regions of the spectrum is different from the ability to discriminate between them. Let me explain....

Angre wrote: The HySI captures 80m resolution imagery in visible & near- IR bands (64 contiguous) ...

Thanks lakshmic and Angre for clearing matters up!!
laksmic, that was one hell of an exposition.

sumishi · Post by **sumishi** » 04 Nov 2008 10:35

K Mehta wrote:Chandrayaan-1 enters Lunar Transfer Trajectory-ISRO Press Release

Way to go, ISRO!!

SaiK · Post by **SaiK** » 04 Nov 2008 11:05

great news to hear that we are just 4k km away from moon. one more thruster to do the elliptical orbits around the moon.

we could also look at other engine techs like ION engine etc.

prashanth · Post by **prashanth** » 04 Nov 2008 11:14

Congrats ISRO

. A great anxiety has been removed. Things are probably easier ahead.

added later: oops. 5 more days to go.

sumishi · Post by **sumishi** » 04 Nov 2008 11:16

prashanth wrote:Congrats ISRO . A great anxiety has been removed. Things are probably easier ahead.

I think the lunar capture is the most critical part of the mission.

Abhijit N · Post by **Abhijit N** » 04 Nov 2008 12:11

Nitesh wrote: "The images will be beamed to Istrac's space centre through electrical signals for processing and developing into high resolution pictures of one-five metres," Satish added.

Is the resolution actually higher than 5 meters then ..

Singha · Post by **Singha** » 04 Nov 2008 13:03

I think he meant printed sheets of size 1m - upto 5m.

Shivani · Post by **Shivani** » 04 Nov 2008 14:25

If it's the size of the print (one to five meters, fifteen meters, 1.5 meters....) it does not tell anything about the resolution. But he specifically uses the word resolution in that statement. I do not think you get into his kind of position at ISRO by being flippant about resolution and size.

I think Mr. S. Satish is definitely talking about resolution and not print size. One to five meters. Does the distance from the surface (moon, earth) affect resolution? The atmosphere and lack of it?

sumishi · Post by **sumishi** » 04 Nov 2008 15:21

p_saggu wrote:......
Meanwhile, from ISRO's website itself:

Any ideas why the originally planned apogee of 386,194 km (overshooting the moon's orbit?) has been reduced to 380,000 km (undershooting!!)

SSSalvi · Post by **SSSalvi** » 04 Nov 2008 16:04

sumishi wrote:
p_saggu wrote:......
Meanwhile, from ISRO's website itself:
Any ideas why the originally planned apogee of 386,194 km (overshooting the moon's orbit?) has been reduced to 380,000 km (undershooting!!)

The figure is only for illustrating the structure of planned orbits and not the physical view. In fact it is simply not possible to draw real orbits in 2 dimensions. Refer my earlier post showing 5 orbits ... notice that the orbits are not on a plane surface but that the orbital ellipse is inclined to equator and ( apsidal line ) is continuously rotating.

So what has been depicted as a single orbit in ISRO's drawing are in reality several orbits ( or rather several revolutions in each orbit ) and they are not retracing the same points as shown in the drawing.

Add to that the FOURTH dimension: TIME

Spacecraft takes finite time to travel and so although you may command it to point to moon you have to consider the delay for the spacecraft to reach that point and so you have to aim in space to a future hypothetical position of moon whereas at the time of firing moon may be lakhs of miles away.

In fact that could be the reason of why they have planned to approach moon in several intermediate orbits so that successive delta corrections can be applied in each orbit.

If you miss the moon in one big slingshot then the whole mission will go 'phut'.

The transfer between Earth orbit and Moon orbit will be through an inclined orbit ( In space how do you specify 'inclined' ) that is from the apogee of Earth orbit to the moon not in 'perpendicular' orbit as shown in ISRO drawing.

BTW.. y2no is a highly respected website and calculations are accurate. There is always a gap ( at least a day ) between the orbital measurements carried out by the satellite operator ( ISRO in CY case ) and published in public domain in sites such as y2no and celestrak. It is not intentional but that much of delay is inevitable because the reporting agencies have to get those elements and put them on their website. They do not update it online... they do it once in a day or two. That is the reason why I said in my post mentioned above that CY may not be in the orbits shown therein.

sumishi · Post by **sumishi** » 04 Nov 2008 16:22

SSSalvi wrote:
sumishi wrote: Any ideas why the originally planned apogee of 386,194 km (overshooting the moon's orbit?) has been reduced to 380,000 km (undershooting!!)
...
Add to that the FOURTH dimension: TIME

Spacecraft takes finite time to travel and so although you may command it to point to moon you have to consider the delay for the spacecraft to reach that point and so you have to aim in space to a future hypothetical position of moon whereas at the time of firing moon may be lakhs of miles away.

In fact that could be the reason of why they have planned to approach moon in several intermediate orbits so that successive delta corrections can be applied in each orbit.
....

Thanks SSSalvi! Much appreciated.

Rahul M · Post by **Rahul M** » 04 Nov 2008 16:38

SSS, what is the source of data for sites like n2yo ?

Raj · Post by **Raj** » 04 Nov 2008 18:00

Frontline has a series of articles on ISRO/Chandrayaan
http://www.hinduonnet.com/fline/index.htm
http://www.hinduonnet.com/fline/stories ... 300400.htm

sumishi · Post by **sumishi** » 04 Nov 2008 19:18

SSSalvi wrote: BTW.. y2no is a highly respected website and calculations are accurate. There is always a gap ( at least a day ) between the orbital measurements carried out by the satellite operator ( ISRO in CY case ) and published in public domain in sites such as y2no and celestrak. It is not intentional but that much of delay is inevitable because the reporting agencies have to get those elements and put them on their website. They do not update it online... they do it once in a day or two. That is the reason why I said in my post mentioned above that CY may not be in the orbits shown therein.

That might be true, but they did slip up royally this time. On 02/11/2008, with their Chandrayaan's orbit updated to "262,004.5km apogee / 582.3km perigee" (the one prior to this recent firing), not only were they showing data like -- altitude: 203,710 km; speed: 14.97 km/s (a speed which S Sridhar said is wrong) -- but the next day, I saw the site display data approx. like -- altitude: 150,000 km; speed: 10.9 km/s !! Chandrayaan slowing down from apogee to perigee??

Unless I am missing something here...

SaiK · Post by **SaiK** » 04 Nov 2008 19:29

can some gurus jot what is the plan ahead?, especially how the spacecraft would be brought down to circular orbit around the moon from an elliptical one? the gravity is three times less than earth, is it easier or difficult?

especially on two important events

EBN-5 -> LC and
LBN-3 -> LBN4

transfers.

sumishi · Post by **sumishi** » 04 Nov 2008 19:48

Just putting up the following interesting graphic depicting the orbital trail of SMART-1 spacecraft which was sent by ESA to the moon in 2003. Chandrayaan follows a similar strategy as SMART-1 did. In the image, it appears that SMART-1 "attaches" itself to a lunar orbit towards the top (slightly right) -- the darker blue trail.

Bade · Post by **Bade** » 04 Nov 2008 21:17

That might be true, but they did slip up royally this time. On 02/11/2008, with their Chandrayaan's orbit updated to "262,004.5km apogee / 582.3km perigee" (the one prior to this recent firing), not only were they showing data like -- altitude: 203,710 km; speed: 14.97 km/s (a speed which S Sridhar said is wrong) -- but the next day, I saw the site display data approx. like -- altitude: 150,000 km; speed: 10.9 km/s !! Chandrayaan slowing down from apogee to perigee??
Unless I am missing something here...

In an elliptical orbit with large eccentricity the orbital speed is not a constant like in a perfect circular obit. The speed of Chandrayaan at apogee (closest point to earth) is much larger than at perigee. No surprises there.

Bade · Post by **Bade** » 04 Nov 2008 21:20

what is the source of data for sites like n2yo ?

The source very likely is the "two-line element" with orbital parameters kept by NORAD and made public with some delay. So with large orbital changes during transfer orbits changes n2yo will not have the latest numbers as has been mentioned before. Do a google for more details on the two-line element set.

Added later:

http://celestrak.com/NORAD/elements/

Lots of details for those interested.

sumishi · Post by **sumishi** » 04 Nov 2008 21:43

Bade wrote:
That might be true, but they did slip up royally this time. On 02/11/2008, with their Chandrayaan's orbit updated to "262,004.5km apogee / 582.3km perigee" (the one prior to this recent firing), not only were they showing data like -- altitude: 203,710 km; speed: 14.97 km/s (a speed which S Sridhar said is wrong) -- but the next day, I saw the site display data approx. like -- altitude: 150,000 km; speed: 10.9 km/s !! Chandrayaan slowing down from apogee to perigee??
Unless I am missing something here...
In an elliptical orbit with large eccentricity the orbital speed is not a constant like in a perfect circular obit. The speed of Chandrayaan at apogee (closest point to earth) is much larger than at perigee. No surprises there.

errr.. isn't apogee the farthest from earth, and perigee the nearest?

Bade · Post by **Bade** » 04 Nov 2008 21:46

Oops I mixed it up again. It is fastest at closest point to earth and slowest at farthest point.

SSridhar · Post by **SSridhar** » 04 Nov 2008 22:09

sumishi, it is Kepler's Second Law. Earth is one of the foci of the elliptical orbit. The Law states that the radius vector connecting the centre of the earth to the satellite sweeps equal areas in equal times. Since the apogee is farthest and the perigee is nearest this is not possible unless the velocity at perigee is the highest and that at the apogee is the slowest.

sumishi · Post by **sumishi** » 04 Nov 2008 22:17

SSridhar wrote:sumishi, it is Kepler's Second Law. Earth is one of the foci of the elliptical orbit. The Law states that the radius vector connecting the centre of the earth to the satellite sweeps equal areas in equal times. Since the apogee is farthest and the perigee is nearest this is not possible unless the velocity at perigee is the highest and that at the apogee is the slowest.

Exactly! And so what I was referring to was that the n2yo data was doing something very anti-Keplerian. According to the site, CY was losing speed when coming from apogee to perigee.

p_saggu · Post by **p_saggu** » 04 Nov 2008 23:01

Sumishi,
That graphic you posted of CY's orbital maneuvers, the ESA video on the chandrayaan shows the ISRO chaps modelling something similar on the computer screen

RavinM · Post by **RavinM** » 04 Nov 2008 23:15

Dear Gurus,

my question is, if moon's gravity extends over 60,000 odd kms, why do u need lunar orbit insertion, as any object after the nuetral point must be automatically, "caught" under lunar gravity.

'slowcapture' is not a valid username on this forum. A human sounding name must be used. I have changed it to RavinM.

Jayram · Post by **Jayram** » 04 Nov 2008 23:27

This graphic explains what ISRO is trying to do rather well I thought

http://www.hinduonnet.com/fline/stories ... 300700.htm

Courtsey the hindu. article here http://www.hinduonnet.com/fline/stories ... 300600.htm Orbital Challenges

Jayram

sumishi · Post by **sumishi** » 04 Nov 2008 23:29

p_saggu wrote:Sumishi,
That graphic you posted of CY's orbital maneuvers, the ESA video on the chandrayaan shows the ISRO chaps modelling something similar on the computer screen

I checked what you mentioned, and yes, it is so. Thanks for the info.
Anyways, the graphic I posted was of the SMART-I spacecraft's maneuvers. Since SMART-I did it successfully, it stands to reason why ISRO should follow the same strategy instead of the earlier "potshots" tactics of the 60s by the Americans/Russians.
Although, I must admit, I am not sure whether SMART-I was the first to try this kind of maneuver.

Angre · Post by **Angre** » 05 Nov 2008 00:05

SSridhar wrote:... it is Kepler's Second Law. Earth is one of the foci of the elliptical orbit. The Law states that the radius vector connecting the centre of the earth to the satellite sweeps equal areas in equal times. Since the apogee is farthest and the perigee is nearest this is not possible unless the velocity at perigee is the highest and that at the apogee is the slowest.

SSridhar,
How is the CY speed, orientation and exact placement in the orbital plane determined? Is it solely by the orbital motion laws or is there something else CY has (star sensor?) that is used to plot the position?

Gerard · Post by **Gerard** » 05 Nov 2008 03:46

Chandrayaan 96 hours from moon's orbit

SwamyG · Post by **SwamyG** » 05 Nov 2008 03:55

Gerard wrote:Chandrayaan 96 hours from moon's orbit

From the above:

"The return key in a keyboard
is hit and the message is processed by the computer and transmitted to the spacecraft. Let me assure you that the person who will be hitting this return key on Saturday for the LOI is under no pressure," he said.

Aha aha....what a simplicity, what a simplicity. You can not make it sound more trivial

JaiS · Post by **JaiS** » 05 Nov 2008 04:06

Detailed article on Chandrayaan testing.

Gruelling tests

CHANDRAYAAN-1 underwent a series of tests for several weeks at the ISRO Satellite Centre (ISAC), Bangalore. It was broiled at temperatures of above 120 degrees Celsius, subjected to freezing conditions below minus 120 degrees Celsius and put in vacuum before it was declared flight-worthy and transported to Sriharikota.

During the thermo-vacuum trials, the spacecraft underwent “soak and shock” tests. It was subjected to high temperatures for a long duration in the “soak” test and went through high and low temperatures in quick succession in the “shock” test. Besides, Chandrayaan-1 faced a high level of noise and vibration tests to check whether its instruments held together. Elaborate tests were done on the solar panel to ensure that it unfolded like an accordion and that its antenna pointed in the right direction.

Of the 11 scientific instruments, five are from India. They “were built for the first time in India”, said T.K. Alex, Director, ISAC. After the spacecraft was fully integrated with its payloads, it was tested for almost three months for technical interfaces, communication between the instruments, and communication with the ground. For these and the thermo-vacuum tests, special facilities such as a space simulation chamber and an ultra clean room were set up at ISAC.

---- More details snipped ---

a_kumar · Post by **a_kumar** » 05 Nov 2008 05:28

sumishi wrote:Anyways, the graphic I posted was of the SMART-I spacecraft's maneuvers. Since SMART-I did it successfully, it stands to reason why ISRO should follow the same strategy instead of the earlier "potshots" tactics of the 60s by the Americans/Russians.
Although, I must admit, I am not sure whether SMART-I was the first to try this kind of maneuver.

That picture is a nice find. Chandrayaan isn't taking the pot-shot approach and it doesn't seem like it is taking SMART-1 approach either.

SMART-1 approach was first tried on Japanese first lunar mission (Infact, this approach somewhat salvaged a failed mission). Uses something called low energy orbits.. blew my mind when I read it.

First Japanese Lunar Mission : Hiten - 1991

Low Energy Transfers

The transfer used by Hiten is a revolutionary new type of low energy transfer to the Moon derived from Weak Stability Boundary Theory. See Capture Dynamics and Chaotic Motions in Celestial Mechanics. Unlike the standard three day transfer to the Moon this low energy route does not require large rocket engines to slow down to be captured into lunar orbit. It also takes three months instead of three days.

A picture of interplanetary "superhighway" from wiki link below.

Interplanetary Transport Network

The ITN makes particular use of Lagrange points as locations where trajectories through space can be redirected using little or no energy.

I have gained a lot more respect for Japanese space efforts, unlike Chinese efforts which have less signal/noise ratio.

SriKumar · Post by **SriKumar** » 05 Nov 2008 06:55

"The operation to put Chandrayaan into lunar space went off very well. The complex manouvre was carried out around 5 a.m. by firing the liquid apogee motor (LAM) on board for about 150 seconds to place the unmanned spacecraft 380,000 km away from earth (apogee) and 1,000 km from the moon," ISRO director S. Satish told media.

Question for gurus: How is the attitude of a spacecraft known when it is in deep space, such as CY just prior to the most recent LAM firing? One has to assume that the spacecraft has to be oriented very, very precisely prior to LAM firing. So, it is a 2-fold question: how precisely is the orientation needed to be known (1 degree? 1 minute?) ; and how is the attitude/orientation of the satellite determined in deep space? (alignment with Star sightings? Gyroscopes?).

Arun_S · Post by **Arun_S** » 05 Nov 2008 11:47

Optical means to determining orientation is the only way. All gyros have drift that after few hours makes them useless, unless corrected by correlation with stars OR when on earth by sensing force generated by gravity or precession of gyro when its orientation is different from earth's axis of rotation.

So all satellites (comm sats in GSO as well as surveillance sats) and spacecrafts have a sun and earth seekers for initial orientation lock and star seekers for fine orientation lock. After the orientation is locked then one can as well measure angular position of specific stars that are favorable for spatial position determination.

FYI back in 1900 -1980 ships used celestial navigation fixes using manual sextant measurement to determine ships position to within half nautical mile. IAF transport aircraft's were equipped with port holes to take star fixes as part of the stellar navigation gear carried on board. ( As a middle school kid I was amazed to see those star gazing ports and gear aboard IAF's No-6 Squadron's Superconnies in Poona). Clearly with modern onboard seekers spacecrafts can determine their position more accurately, specially if they are coupled with a on board INS, so that error due to discrete star fixes can be compensated to reduce the third and forth order effects.

vina · Post by **vina** » 05 Nov 2008 12:13

Dont know Arun_S.. But I would think that in this day and age, mechanical gyros will not used and it would be ring laser gyros, which have no mechanical parts /moving parts, so the drift should be next to zero or very very small indeed. Yeah, stuff like accelerometers, momentum wheels and other stuff, will have mechanical losses and drift, but a true INS systems (not the open loop strap down one, where you would start integrating measured readings would have far less drift and errors. I think the sun and star sensors should be vital for attitude control and pointing and orienting etc, rather than for navigating through space..

Usual disclaimers about not being an expert, just armchair speculator etc, seriously apply here.

Neshant · Post by **Neshant** » 05 Nov 2008 12:14

I was reading briefly about Ion thrusters that are used aboard some spacecraft for repositioning them. Its looks like it needs more research to make it smaller and more efficient. Its stuff like this that Indian space program should be investing in.

By comparison, spending a ton of money to put a man on the moon will not result in a significant technological gain. Even Russians have left this till 2025 which means it has low priority for them. That money would be better spent on smaller projects like the one above which are of greater scientific challenge to industry.

http://en.wikipedia.org/wiki/Ion_engine