USA got it wrong 6 times…
But India got it right, purrrrrrrrrfect, in the very first attempt!!!
This is again about Chandrayaan… but the focus is not on exploiting the resources, its on what we have managed to achieve, scientifically… We had a talk by Ranganath Ekkundi, the Group director of Power systems group of ISRO, yesterday, in our office.Listening to him talk, of the 5 year long project, the road blocks, complexities and the challenges faced, humbled me to the maximum possible extent. We believe we are doing great being in IT industry, writing programs, debugging, and earning loads… But in reality, in over 6 years of my experience I haven’t seen anything anywhere close to what he was talking about!! We are no where near what they have done. Here I intend to put down certain points that I felt were exemplary…
USSR’s Luna missions 1 to 8 failed to get to moon –
Luna 1 – Completely missed the moon’s orbit and never reached it
Luna 2, 4, 5, 7, 8 – Crashed on Moon surface
Luna 3 – Was a fly-by, meaning it didn’t go around or land on moon
Luna 6 – Missed moon and went into wrong trajectory
Luna 9 – Successful Landing
USA Ranger missions –
Ranger 1 and 2 – Were declared as test launches, meaning their launches actually failed :-)
Ranger 3 and 5 - Missed moon
Ranger 4 – crashed on moon
Ranger 6 landed but the camera’s didn’t function
Of course, we are about 30 years ahead of them in technology today, but still, that doesn’t make the ‘first attempt success’ any less of an achievement.
As I mentioned in one of my previous posts, main idea of the whole mission is to transform the discoveries into PROFIT, at some point of time… so much so that the ISRO director had said “can we afford not going to moon” when he was asked whether India can afford to spend so much for reaching moon. But the challenges faced were very real and very efficiently overcome…
1. The Fuel -
There was this big halla about how much money was spent just on fuel. But yesterday I heard how much planning went into deciding optimal amount of fuel for the mission. Too much fuel means wastage, too less means below optimal performance… or even mission failure!!
Fuel on PSLV - For 4 stages of launch
On the Chandrayaan space craft - For maneuvering the satellite to give it right direction with thrusters, so that it is always looking at the moon
On the Chandrayaan space craft (referred to as CSC from now on) - For sustaining all functions for about 2 years. (2 years is the expected life time of the satellite)
2. The Launch – Aim and Shoot?
Not quite…
It couldn’t be just as simple as aiming at the moon and shooting… Several points needed to be considered…
i. Orbit inclination of the earth as well as the moonii. The radius of the elliptical orbits and how much it needs to be raised to get the craft closer to moon.
iii. Positioning of moon and time matching… There was a gap of 2 weeks from the day of the launch, to when the CSC actually went into its specified place around the moon. So, the initial “aim” was directed to empty space; where the moon would ‘arrive’ in about 15 days, close enough to capture the CSC into its orbit. If the timing was late, the CSC would miss the moon; if it was too early, it would just fly into space, without being captured by moon’s gravity, probably fall into sun’s gravity.
Note: This was the first time point3 had to be considered. Before this, all we had done was send the satellites to orbits around the earth and timing never came into picture.
iv. Earth orbit burns – The craft was first spiraling around the earth. In fact it went around the earth 5 times, in an elongated elliptical orbit. Every time it came close to earth, an orbit raising maneuver was done by firing the engines, pushing the craft closer to moon in every orbit burn.
v. Lunar orbit insertion – Escape velocity of earth and that of moon. Escape velocity for earth is 11.2 km/sec where as that of moon is 2.6 km/sec. So if the craft reaches moon with the same velocity with which it left the earth, it would crash. Hence the craft was rotated, 180 degrees, when it came close to moon, hence decelerating the craft enough to be caught in the orbit around the moon
vi. The craft entered final position after 4 orbit reduction maneuvers around the moon. Chandrayaan-1 is now in its fixed polar orbit (rotating from pole to pole), about 100 kms from the moon and takes about two hours to go round the moon once.
3. Positioning and direction –
Once in the orbit, the CSC should always know its position, w.r.t. to moon and the earth. Star maps are mainly used for this. That is, there is a map of all stars and star clusters that will be visible to the craft, at all positions around the moon. This is fed into the onboard computers. And based on this map, the craft orients itself properly. If this fails for some reason, there are gyros (Gyroscopes) which will help orient the craft.
If this also fails, only then the craft refers to the position of sun, the final and ever present point of reference.
4. Experiments on board the CSC –
There are 5 Indian and 6 international devices on board the Chandrayaan. There is a terrain mapping camera (TMC), developed in our own Ahmadabad, which creates 3D map of moon and has a swath range of about 20 km. There are also many others, solar wind interaction mappers, chemical mapping, mineral mapping, radiation monitors etc.
5. The Power –
Main power source is the sun… and there is a battery too, a light weight lithium ion battery which gets charged when sun light is available. But there is lot to consider here… the craft experiences varying sun illumination over the year.
> The panels come under the moon’s shadow, & the earth’s shadow several times during the weeks, months and years. Considerations thus include all the eclipses expected to occur over next 2 years, calculations on what would be the longest interval when the satellite WONT get any sun light, can the battery hold on for that long… when will it be in umbra, when in penumbra, which is partial eclipse and which is total…
> Everything needs power on board the CSC. There are the communication devices, the data transfer, deep space antennae, the functioning for the 11 scientific experiments on board the craft. All of these need power, and all of these have to be considered, for 2 year long functioning. When to operate which pay load is hence critical. From the ground stations, the load on the battery is reduced to minimal during maximum discharge periods.
> There are essential functions though, which always need power and cant be shut down. There is a propulsion system, which needs to be powered. The CSC is “3-Axis Stabilized space craft”, meaning its orientation compared to moon is always constant. But moon, unfortunately, has a tilted axis. Therefore, ultimately, to ensure the constant orientation, the propulsion system has to kick in at regular intervals, for orbit raising and maintenance.
6. The MIP –
It seems, Dr. APJ Abdul Kalam was the one that suggested ‘We are going so close anyway, why not drop something from India on to the moon?’ Hence the MIP. The Moon impact probe, our little gift to the moon, crash landed on the south pole of the moon on 14th November. It was in free fall for 25 mins, after being detached from the CSC, and took several images of moon on its way down. When the MIP was closer to the surface, rockets were fired to slow down its speed and to soften impact.
7. Communication –
Communication with the craft all through its journey and also after reaching its orbit is vital. For this there were
more than 10 tracking centers setup all over the globe… CSC was visible form one station or the other, at all times. This includes Byalalu, a village 40 kms from Bangalore with an ISDN antenna setup.
8. Softwares –
Softwares, as one can imagine, played a very important role, both on board CSC and at the ground station. Here are the few points about the programming that struck me the most…
- They used waterfall model for development, since the specification and requirement kept changing all the time… :-) sounds familiar.
- There were reviews and walk-through done at the end of every stage, but by different agencies. This starts with decision on which language and which OS would suit best for the mission at hand -> to design, coding, testing and reviews...
- All the programming for onboard softwares was done with Fortran, C, ADA, assembly languages. All with base OS as red hat linux, all embeded on the micro processor chips.
- For onboard software – there is provision of remote programming. Empty buffers have been left on the chip with pointers placed against them. The code can be written on ground, when required and inserted at the specified positions using the pointers.
- For ground software – Fortran, C, C++, Oracle (RDBMS) were used for real time programming. Again the OS was red hat linux.
- Error rate was – 1.5 per million lines of code!! Now “precision” seems less of word to describe this…
That’s about it… 5 year long work, narrated in very few words… I am surely proud we have such intellectuals among us… this is as close to a real scientist work as I have got in my life… It was all just simply awesome! I was standing all through the 1.5 hr talk and was too awestruck to even notice or think about the pain creeping into my legs. They deserve all the applause they are getting.
Once in the orbit, the CSC should always know its position, w.r.t. to moon and the earth. Star maps are mainly used for this. That is, there is a map of all stars and star clusters that will be visible to the craft, at all positions around the moon. This is fed into the onboard computers. And based on this map, the craft orients itself properly. If this fails for some reason, there are gyros (Gyroscopes) which will help orient the craft.
If this also fails, only then the craft refers to the position of sun, the final and ever present point of reference.
4. Experiments on board the CSC –
There are 5 Indian and 6 international devices on board the Chandrayaan. There is a terrain mapping camera (TMC), developed in our own Ahmadabad, which creates 3D map of moon and has a swath range of about 20 km. There are also many others, solar wind interaction mappers, chemical mapping, mineral mapping, radiation monitors etc.
5. The Power –
Main power source is the sun… and there is a battery too, a light weight lithium ion battery which gets charged when sun light is available. But there is lot to consider here… the craft experiences varying sun illumination over the year.
> The panels come under the moon’s shadow, & the earth’s shadow several times during the weeks, months and years. Considerations thus include all the eclipses expected to occur over next 2 years, calculations on what would be the longest interval when the satellite WONT get any sun light, can the battery hold on for that long… when will it be in umbra, when in penumbra, which is partial eclipse and which is total…
> Everything needs power on board the CSC. There are the communication devices, the data transfer, deep space antennae, the functioning for the 11 scientific experiments on board the craft. All of these need power, and all of these have to be considered, for 2 year long functioning. When to operate which pay load is hence critical. From the ground stations, the load on the battery is reduced to minimal during maximum discharge periods.
> There are essential functions though, which always need power and cant be shut down. There is a propulsion system, which needs to be powered. The CSC is “3-Axis Stabilized space craft”, meaning its orientation compared to moon is always constant. But moon, unfortunately, has a tilted axis. Therefore, ultimately, to ensure the constant orientation, the propulsion system has to kick in at regular intervals, for orbit raising and maintenance.
6. The MIP –
It seems, Dr. APJ Abdul Kalam was the one that suggested ‘We are going so close anyway, why not drop something from India on to the moon?’ Hence the MIP. The Moon impact probe, our little gift to the moon, crash landed on the south pole of the moon on 14th November. It was in free fall for 25 mins, after being detached from the CSC, and took several images of moon on its way down. When the MIP was closer to the surface, rockets were fired to slow down its speed and to soften impact.7. Communication –
Communication with the craft all through its journey and also after reaching its orbit is vital. For this there were
more than 10 tracking centers setup all over the globe… CSC was visible form one station or the other, at all times. This includes Byalalu, a village 40 kms from Bangalore with an ISDN antenna setup.8. Softwares –
Softwares, as one can imagine, played a very important role, both on board CSC and at the ground station. Here are the few points about the programming that struck me the most…
- They used waterfall model for development, since the specification and requirement kept changing all the time… :-) sounds familiar.
- There were reviews and walk-through done at the end of every stage, but by different agencies. This starts with decision on which language and which OS would suit best for the mission at hand -> to design, coding, testing and reviews...
- All the programming for onboard softwares was done with Fortran, C, ADA, assembly languages. All with base OS as red hat linux, all embeded on the micro processor chips.
- For onboard software – there is provision of remote programming. Empty buffers have been left on the chip with pointers placed against them. The code can be written on ground, when required and inserted at the specified positions using the pointers.
- For ground software – Fortran, C, C++, Oracle (RDBMS) were used for real time programming. Again the OS was red hat linux.
- Error rate was – 1.5 per million lines of code!! Now “precision” seems less of word to describe this…
That’s about it… 5 year long work, narrated in very few words… I am surely proud we have such intellectuals among us… this is as close to a real scientist work as I have got in my life… It was all just simply awesome! I was standing all through the 1.5 hr talk and was too awestruck to even notice or think about the pain creeping into my legs. They deserve all the applause they are getting.
Hmm… I seem to be stuck on moon quite a lot eh… lets see if I can get out!!
BTW, please forgive the photo quality. They were taken with the mobile camera in the dimly lit conference room.
