While a lot of hype surrounds Isros first interplanetary mission the Mars Orbiter Mission (MOM) to be launched aboard the tried and trusted PSLV-C25 Tuesday,there is also criticism that the mission does nothing to push the frontiers of space science. There is even talk that it is a political tool going into the election season,much like the 2008 Chandrayaan mission ahead of the 2009 polls. Isro chief K Radhakrishnan answered some of the criticism in an interview to Johnson T A. He also explained the complexities in the mission.
Could Isro not have waited for the GSLV to fly the mission since this would take the orbiter closer to Mars?
In August 2010,we formed a study group on what we should do,whether we should do a fly by or an orbiter. Fly by means we can carry large instruments but the observation time is very short but we can be successful because it will always pass somewhere near Mars. But we decided there is no point. We were clear we should do an orbiter. We then put up a team and they worked up to June 2011. They came out with a report with all the options. After looking at the vehicle that we have and what is required,a decision was taken.
There are two types of orbits we have chosen a 365-by-80,000 km orbit which will require 855 kg of fuel. If I have to put it in a circular orbit of 1,000 km,we need 2,000 kg of propellant. That means the fuel itself is two tonnes at present it is 850.8 kg. If you take the spacecraft,it is in the range of 500 kg to 600 kg. That means for a circular 1,000 km orbit,you are talking a 2,600-kg spacecraft. With a 1,350-kg satellite I am now getting a 350-by-80,000 km orbit.
Now if you are at 1,000 km orbit like Maven you need a couple of tanks,couple of liquid apogee motors,so you have to devise a different configuration for the orbiter spacecraft. Then there is the question of launcher. Even GSLV cannot lift it because its capacity is 2,200 kg. We are talking of 2,600 kg,plus the instrument. We decided to go for the elliptical orbit,365-by-80,000.
There were launch opportunities for 2013,2016 and 2018. Because of the geometries involved,2016 would be costlier. You need a vehicle like GSLV at that time. In short,what we have done is that we have availed the best available opportunity 2013 November.
How different would the Mars mission be if Isro were to wait for the GSLV?
If we had GSLV,two things would have happened,this transfer that we are talking of if you had the same mass of spacecraft,1,350 kg,the initial orbit could have been bigger. Instead of 250 km-by-23,000 km,it could have been 36,000 km or 40,000 km. That means the number or orbit raisings could have been reduced. Secondly,we could have carried more payload. Now we are carrying 15 kg,it could have carried a few 100 kg but where is the payload for it. There is no instrument,so there was no need. What we now have is a prudent strategy. GSLV would need more fuel for achieving the 1,000-km orbit around Mars (which is closer than the 350-by-80,000 km orbit for MOM) and it would need a different spacecraft. Though there is criticism there are clear parameters that have helped us decide.
Between the Mars mission and the GSLV development,which has suffered setbacks,which would you categorise as being the key to Indias space programme?
Both are important. In the launch vehicle,GSLV is essential. If you look at GSLV,the first launch was aborted in 2001 because there was a problem. Within 22 days we corrected that and we had a flight. It injected a satellite but there was under-performance in the last cryogenic stage and the satellite did not last more than two months. Second and third were successful flights. The fourth flight was a failure and in the fifth,there was a problem in the control system. These were component problems. After nearly two-and-a-half years,we had a flight in April 2010 but last-stage cryo did not perform. It was the first flight for the indigenous cryo. In December 2010,the Russian cryogenic stage developed problems. The vehicle had to be destroyed. We went back to testing,reviews and we came back to launch earlier this year but there was a leak. GSLV is essential. We have been working on an indigenous cryo stage for the last 20 years,we have to stick with it. GSLV MK III is another advanced vehicle that we are developing. Now we are going to have the ground test of the cryogenic stage also. We had a small test last week that was successful. When you talk priorities you must understand these are two different areas. A Mars mission has no conflict with the development of GSLV.
The elliptical orbit of 365-by-80,000 km around Mars is considered too far to carry out meaningful experiments. Also,much of what MOM intends to do like look for methane is being done by missions like NASAs rover Curiosity. What does the MOM do different?
NASAs Curiosity makes in situ measurements. It may be detailed measurement of that place but it will not give you what we are looking for such as methane in the atmosphere. Our instruments will do that. You are also looking at methane which is in parts per billion,so the instrument must have sufficient sensitivity. Our instrument has that. One criticism is that the elliptical orbit does not take us close enough. If you are doing a remote-sensing,mapping mission like we had in Chandrayaan where we wanted to have a terrain map at five metres spatial resolution,altitude is important. Here,our objective is to measure the atmospheric column. For this,the MOM orbit is sufficient. It will provide enough time to carry out measurements.
As the time for the launch approaches what is the general feeling in Isro?
We have understood and worked on all these systems over the years. But in a complex mission one should not cut any corner. We have to do all the tests. We had to do additional testing as well. People have worked 24×7 because this D Day cannot be changed. In the Chandrayaan mission we could change the date. Here,we cannot change the date because the opportunity comes only once in 26 months.
Of the 51 attempted missions to Mars only 21 have been successful. How has Isro used learning from past missions?
Of the 30,some were launch failures where there were problems in the initial part itself. Some are because of lack of understanding of the gravity of Mars. When you say you are at a distance of 500 km from Mars and if your calculations are wrong you may crash. Otherwise,you may miss the orbit. You get from all these past studies better and better gravity models. Nasa has its calculations,so we give them our initial calculations and our final calculations and ask them to run them and then we check.
Which part of the mission is the most complex for Isro the launch,the main journey to Mars from December 1 or the insertion into Martian orbit in September 2014?
The trans Martian injection of December 1 is the most crucial part. Then there is the Martian insertion of September 21,2014. These things we are doing for the first time. We have to calculate that at the given time,at the given velocity what position the spacecraft will be in when it reaches Mars after 300 days.