Dr M Annadurai served as project director for ISRO’s first mission to the moon Chandrayaan 1 and also worked on the Chandrayaan 2 project, scheduled to be launched on July 15 for ISRO’s first soft landing on the moon. He was closely linked to the mission as director of the U R Rao Satellite Center in Bengaluru until his retirement last year. He spoke to Johnson T A on the similarities and differences between ISRO’s first and second moon missions:
You were project director for the Chandrayaan 1 mission undertaken in 2008 and the first project director for the Chandrayaan 2 mission. How different are the two projects?
Overall, the project is more or less the same — it is a logical extension of whatever we have done with Chandrayaan 1. The only thing is that in Chandrayaan 1 we had the 35 kg moon impact probe which we released after getting to the moon. It crashed on a targeted spot. Now we are going to have a controlled soft landing. Previously, it was like passive throwing of the moon impact probe from the orbiter. The orbiter in Chandrayaan 2 is the same as the Chandrayaan 1 — that is why we were ready with the Chandrayaan 2 orbiter some three or four years ago. Unfortunately, the Russians dropped out (of making a lander and rover). That was the orbiter that was eventually used as the Mars orbiter in the Mars mission (2013-14). That is the secret behind how we were able to do the Mangalyaan project in 13 months. The lander is totally new.
The Chandrayaan 1 launch was on the lightweight PSLV but the Chandrayaan 2 is on the powerful GSLV Mk III. What difference does this make to the project?
The GSLV will put a heavier payload further into space. This is how it was originally planned as well. We now have the Mk III instead of the Mk II. Once you put it in an orbit, it will be more or less what was done with the Chandrayaan 1 mission. We were the first people in the world to use a launcher like the PSLV and do a mission like Chandrayaan 1. We launched on October 22, 2008 and we reached only on November 8. We took so many days because we gradually increased the orbit (firing on board engines) to finally reach the orbit of the moon. A similar thing is happening here but we will land softly on the moon instead of throwing an impacter. The lander has its own intelligence and will land on its own.
In Chandrayaan 1, there were issues with lunar heat radiation which caused damages to the orbiter leading to a premature end to the project. Have those issues been addressed in the Chandrayaan 2 programme?
Although the heat radiation was identified initially as the cause of the shortening of the Chandrayaan 1 mission, we found an inherent issue with one of the imported dc/dc converters used in the spacecraft itself. We used some 757 of them in Chandrayaan 1. That was used worldwide but unfortunately the batch we used developed problems. Heat was generated internally as a consequence of the faulty converters and along with the heat environment, a hot spot was created. This is the major reason it failed. Initially, when the project was on, we thought external heat caused the problem but we later found that it was the internal heat. We made a correction in Mangalyaan orbiter. We removed the imported dc/dc converters and made our own dc/dc converters which will not have this problem. The Mangalyaan has gone on for five years now. These indigenous products will help the system. Over and above that, whatever inputs we got from Chandrayaan 1 are going into Chandrayaan 2. This is especially for the orbiter which will be used for more than a couple of months. The lander we are landing for the first time. The life of the rover is only one lunar day (14 earth days) but we have made some things that can help it survive longer. It is called a sleep and wake up solar-powered circuit which will help it revive after a long night once the sun comes out and it will be used to heat the system. If it works, we may get a bonus of couple more lunar days. In the case of the orbiter, we are talking of a life of six months to a year. I am hopeful it will live for a long time given the Mangalyaan experience which is living beyond its expected life span.
What is the communication network between the rover, the lander, orbiter and earth?
The rover can communicate only to the lander (for power optimisation) but the lander and orbiter can communicate with each other and earth. Lander is more like a relay. Prime part is to the ground. If for some reason we are not able to land at the spot we have chosen and if that spot is not visible from earth, then we have to rely on the rover to lander to orbiter to earth chain which is a back-up chain. In case we land as planned, then we will have direct contact with the lander.
The Chandrayaan 2 project now has a woman project director. How significant is it?
It is not something new. You know there is T K Anuradha (who has headed some of ISRO’s communication satellite programmes). There was Vallarmathi for the RISAT project. We have other women as well. Nowadays equal opportunity is given to all.
How would you describe the Chandrayaan 2 project director Dr Muthayya Vanitha?
For some time, she worked with me. When I was moved up, she was brought in as an associate project director and was working with the then project director Nagesh. Around a year-and-a-half ago, she was made project director. This is her first project. She is a systems engineer and as project director, she needs to know about all the systems. She picked up her knowledge in the period she was the associate director and was then made the project director. She has done well as project director.