Interview: K. Radhakrishnan, ISRO

‘The challenge starts now’

Print edition : November 15, 2013

K. Radhakrishnan in his office in Bangalore. Photo: K. BHAGYA PRAKASH

Integration of the five payloads in the space bus of the Mars orbiter under way at the ISRO Satellite Centre in Bangalore. Photo: ISRO

The spacecraft underwent a battery of tests at a facility at the ISRO Satellite Centre where vaccuum conditions in space and the solar radiation that would fall on it were simulated to check the orbiter's space-worthiness and its performance level under such conditions. Photo: By Special Arrangement

Interview with K. Radhakrishnan, Chairman of the Indian Space Research Organisation.

IN THE RUN-UP TO THE LAUNCH OF THE MARS Orbiter Mission (MOM), which is scheduled from the Satish Dhawan Space Centre in Sriharikota on November 5, K. Radhakrishnan, Chairman of the Indian Space Research Organisation (ISRO), spoke to T.S. Subramanian and R. Ramachandran of Frontline separately and at different times, with the former in October and with the latter in September. Excerpts from the two interviews combined:

T.S. Subramanian: Are things on course for the Mars Orbiter Mission? What kind of preparations have you made for it?

We are ready for the Mars Orbiter Mission. On October 14, we completed the fuelling of the orbiter. Nearly 852 kg of fuel, that is, a combination of mono methyl hydrazine (MMH) and mixed oxides of nitrogen (MON3)—fuel and oxidiser respectively—has already been pumped into the orbiter.

As for the PSLV [Polar Satellite Launch Vehicle], the launch vehicle has been assembled. We had earlier completed the phase 3, level 2 checks, that is, electrical checks, on the entire vehicle. The spacecraft has been mated with the launch vehicle. The launch window for the MOM from SHAR is open up to November 19.

There are two activities: one is the integrated check of the vehicle and the spacecraft together and we call it phase 3, level 3. In this test, all ground stations—SHAR and ISTRAC [ISRO Telemetry, Tracking and Command Network]—will take part. We check out all the systems, and after everything is clear we will do the launch rehearsal. The launch rehearsal will be for all the activities of the countdown. We will go through this simulation and after that, we will again have a Mission Readiness Review [MRR] and the Launch Authorisation Board [LAB] meetings to give the authorisation for the launch.

We have one ground station at Byalalu [near Bangalore] as our deep-space ground station, which has been augmented from 2 kilowatt to 20 kw of power. There is a set of operations to be done by ISTRAC once the PSLV injects the orbiter into an elliptical orbit. That elliptical orbit will have an apogee of 23,500 km and a perigee of 250 km. So all the operations to be performed in the subsequent weeks on the orbiter to raise its apogee and for its trans-Mars injection are to be performed by the ISTRAC and then there is a long voyage of 300 days. [During that voyage], there will be at least three mid-course corrections, which means the firing of the small thrusters on board the orbiter. Then, finally, on September 21, 2014, we will have the crucial Mars orbit insertion.

Another important part of it is the navigation of the Mars orbiter from the earth-bound phase to the heliocentric phase and then the final Martian phase. So all the calculations done for this have been reviewed and this has been another advancement in this mission. That is, the Mars orbiter being taken through this long distance, passing the earth-centric phase, the heliocentric phase and the Martian phase.

As compared with Chandrayaan-1, where we were in the sphere of influence of the earth which extends to 9.6 lakh km from the earth, we have to get out of the earth’s sphere of influence in this mission and enter a long heliocentric phase. To do this, we have to understand the influence of the solar pressure and the influence of other planets on the orbiter and get into the sphere of influence of Mars, which extends over a distance of six lakh kilometres from Mars.

[To enable the Mars orbiter to get into the sphere of influence of Mars, the orbiter has to be slowed down by firing the thruster on board. Otherwise, the orbiter will end up as a fly-by]. While doing so, we have to ensure that even during the trans-Mars injection, we should be able to estimate the expected position of the orbiter in September 2014 within a very close tolerance level or close band of plus or minus 50 km accuracy. In between, we will have three mid-course corrections. That is why the trans-Mars injections we are planning to do from ISTRAC in the last week of March are a crucial operation. The entire calculation, which has gone into this flight path through these three phases, is very critical for this purpose.

Secondly, we are keeping three levels of autonomy in the Mars orbiter. It is essential because of the communication delay.

R. Ramachandran: Given the long duration between the launch and the trans-Mars injection that the spacecraft has to remain in the earth’s influence, do considerations about radiation impact on the devices and their radiation hardening require any revision? Are there any additional precautions required? What kind of exposure do you expect during the Mars mission?

In the Mars mission, not because of Mars but, before leaving the earth orbit, we have to take so many orbits around the earth. And when you go in for longer ellipses, the number of crossings of the Van Allen radiation belts will be more. So what we do is to calculate how many crosses the spacecraft is going to see, what is the total radiation expected on each component, and accordingly decide on the radiation hardening of the components or provide appropriate radiation shielding to the devices. We have designed for a maximum of 60 such crosses. Because of our mission planning, you have to go through a process of five orbit raising manoeuvres and since the date for the trans-Mars injection is fixed, the earlier you launch, the greater the gap. This is the maximum number that we have put for an October 21 launch. [Given the revised schedule, the number of crosses will correspondingly come down.] But the later you launch, since October-November is prone to cyclones and adverse weather, the higher the risk of not being able to launch within the available launch window until November 19.

RR: But beyond the earth’s influence during the nine-10 month journey to Mars…

Compared to this, that is less.

RR: What kind of radiation do you expect during the long journey?

Once in a while cosmic ray particles can come. The damage potential is much more in Van Allen belts.

TSS: You are using a PSLV-XL version to put the Mars orbiter into orbit.

This is the fifth flight of the PSLV-XL version with the extended strap-on configuration. When compared with previous PSLV missions, we have defined its trajectory this time to meet the specific requirements of the Mars Orbiter Mission. If you look at the altitude profile of the PSLV in this mission, you will see a different pattern. There is a long coasting phase between the third stage burn-out and the ignition of the fourth stage.

The coasting phase lasts nearly 20 minutes and the mission is designed in such a way that the “argument of perigee” is around 270° as compared with 180° that we were keeping in the previous flights. This is to ensure that minimum energy is transferred when the spacecraft is transferred from the earth-orbit to the Martian orbit. So, this flight is different. Owing to the long coasting phase, we require the ground stations in the Pacific Ocean to monitor the important events performed by the fourth stage, namely the fourth stage ignition, the engine burn-out and the spacecraft injection. So we are placing two ship-borne terminals in the Pacific Ocean. They will be 3,000 nautical miles from Fiji. One terminal is called Nalanda and the other Yamuna. The vessels are from the Shipping Corporation of India [SCI] and the ground terminals belong to the Defence Research and Development Organisation [DRDO]. You essentially require a stabiliser system for the antenna [and hence the ship-borne terminals].

To get the argument of perigee, which is specific to the lift-off time, the ships will have to be moved accordingly. For each day, there is a launch window and the ships will have to move according to the trajectory we are deciding for that day. For each day, there is a trajectory which is unlike the previous missions. We will have one attempt a day. The next day, there will be another trajectory. This is to optimise the energy required to transfer the spacecraft from the earth-orbit to the Martian orbit. The launch window is open up to November 19. We will take into account the forecast about rain, thunderstorm, cyclones, etc. The LAB will take a view of all this and fix the launch window. [Earlier, in an interview to RR] Because every day the relative positions of the planets are changing, depending on the day of the launch, depending on the time of the launch, the argument of perigee will slightly change. So for the mission management it is going to be a challenge. Supposing there is a half-hour hold, the entire steering programme has to be changed. So for that we are going to have a catalogue of such programmes.

TSS: After the trans-Mars injection, the Liquid Apogee Motor [LAM] on board the Mars orbiter will be idle for about 300 days. How confident are you that it will bounce back to life after this long gap?

You have the fuel and the oxidiser, which should be injected into the combustion chamber at a given pressure and temperature. In our geostationary missions, once the LAM engine completes the initial-phase firing, we close that line and ensure that there is no fuel loss.

Secondly, the rubber materials we use in the components could show deterioration in performance if they remain longer in contact with the propellants. These two aspects have been taken into account.

The third aspect is we have to ensure the efficiency of the LAM engine after a long gap. The propulsion system on board the spacecraft has to perform after a gap of 300 days [in September 2014] after doing its first phase of activity in November 2013. So at the Liquid Propulsion Systems Centre [LPSC] at Mahendragiri, [Tamil Nadu], we have a test facility where the two engines were subjected to firing after prolonged gaps. We went through that process. We have tested the propulsion system on the ground over a long duration to understand its performance degradation over a period of time.

TSS: It will take 20 minutes for the command from the ground to reach the spacecraft and another 20 minutes to receive the signals from the orbiter.

Yes. Twenty minutes each way. There are three levels of autonomy on board the orbiter. One level will enable the spacecraft to monitor the health of its subsystems and switch over from the primary system to the secondary system as required. The second level is, there are a set of operations that the orbiter has to perform, which calls for a series of or a chain of commands. Instead of sending this chain of commands from the earth, we are building this facility within the spacecraft itself so that on a trigger, the chain can be activated.

TSS: Does it mean that no command will be sent from Byalalu to the spacecraft?

It will be there [commands will be sent]. The third level of autonomy is, when the spacecraft is in non-normal condition, it has to be brought to a “safe” mode, pointing towards the earth for communication and the solar panels should point towards the sun for generation of power and for creating a condition where we can make the right intervention from the ground. These facilities are in the spacecraft.

Of course, we are monitoring the health of the spacecraft from the ground. We can also send the signals from the ground. The spacecraft will check for commands from the ground as it progresses [in its voyage towards Mars]. But we will be receiving that information from the spacecraft with a delay. In the interim period, the orbiter will be in a position to take a decision by itself. The important point now is that these decision rules that we are putting into the spacecraft have to be checked thoroughly so that they do not get into the wrong stream. This has been done. If one were to identify two important elements in the Mars orbiter, it is its autonomy and its navigation towards Mars. Coming to the ground stations, one important measurement to be done is precise ranging, that is, the position of the Mars orbiter has to be determined precisely. So we have adopted a new technique this time.

It is called “one-way differential Doppler ranging”, where you require two ground stations, that are sufficiently apart and then you look at a known celestial object in the directional vicinity of the spacecraft and then look at the spacecraft again to get the precise measurements. This means you do a calibration of the stations and then look at the subject [spacecraft].

TSS: You had earlier told me that “the primary objective of the mission is to put the spacecraft into Martian orbit”. Can you elaborate on the functions of the five instruments on board the Mars orbiter?

In 2011, we had done a feasibility report on the Mars Orbiter Mission, which is available. We requested the Advisory Committee for the Space Science led by Professor U.R. Rao to define the instruments required for this mission. We received 30 ideas. We narrowed them down to 11 possible instruments and finally to five. They were all to be built by the various ISRO centres.

What we want to study about Mars is the likelihood of the presence of methane there [which is an indicator of possible life on the planet]. So we have a methane sensor on board the orbiter. The second part is the origin of the methane, whether it comes from a biological or a geological process. There is a thermal infrared sensor, which will give information on the geological activity on Mars. This is the second sensor.

The Space Applications Centre, Ahmedabad, has made the methane sensor and the infrared sensor. We will be studying the Martian environment, specifically the escape processes [of the gases] in the Martian atmosphere. There are two instruments [to do this]. The Lyman Alpha Photometer, made by the Laboratory for Electro-Optic Systems (LEOS), Bangalore, will look at the escape processes of deuterium and hydrogen. The other instrument, called the Martian Exospheric Neutron Composition Analyser, or MENCA, will look at the exosphere of Mars. This has been made by the Space Physics Laboratory, Thiruvananthapuram. We have the Mars colour camera [for optical imaging of the surface of Mars].

The orbit will be 377 km periapsis and 80,000 km apoapsis. Once the Mars orbiter is put into this orbit, there is a sequence of operations to be done on these instruments and we also have to do a systematic calibration process for these instruments. This is to ensure that the measurements we will make using these instruments are decipherable without confusion or ambiguity so that your background is clear.

We have another opportunity. Mars has two satellites and one of them called Phobos, is likely to be in the vicinity of the Mars orbiter and we will study Phobos from our orbiter. There is a comet likely to pass by the side of Mars at a distance of 50,000 km. NASA [National Aeronautics and Space Administration] scientists have forecast this. If this should happen, it will be another opportunity to observe the comet.

This is the profile of the entire mission and the bottom line is that this is a complex mission. Every day is important and we gain knowledge. If we are able to put our orbiter around Mars, 85 per cent of our objective is achieved. We will then be able to do scientific experiments. But there are several new, complex tasks to be performed. That is the challenge and excitement that this mission offers to the scientific and technical community.

RR: With regard to the possible close encounter with the comet [C/2013 A1 (Siding Spring)], has ISRO done independent calculations on its probability? What will be its likely impact on the mission?

No. We will have to share the data [with NASA] and one possibility is to use it positively if it does happen. The important question is, will it pollute the Mars environment such that what you are going to study will be not from the Mars environment but from the comet environment. This is something we have to see. NASA made that statement a few months ago but it has not said anything further about it. But these are low-probability cases.

TSS: You obviously raced against time to get the orbiter ready. Prime Minister Manmohan Singh announced the mission on August 15, 2012. You hardly had a year and half to get the five payloads and integrate them into a bus. How did you do it?

The vision of the Advisory Committee for Space Science was to study the moon, Mars and the sun. These are the three targets. In August 2010, the ISRO Council set up a study team with our scientists and engineers drawn from various ISRO centres and the study was completed in June 2011. It brought out the possibility of doing this mission in 2013 or 2016 or 2018.

These were the three opportune windows available. The immediate opportunity was in 2013. For the 2013 window, it was clear that we can achieve this mission using PSLV-XL and that an orbiter of 1,350 kg can be used. We had consultations among our ISRO scientists and with the space community. In December 2011, we got the approval of the Space Commission. After the approval of the Union Cabinet, the mission was announced by Prime Minister Manmohan Singh. Time is of the essence in this project as we had to leave the sphere of influence of the earth on November 30, 2013. As of now, it has been satisfying to the entire ISRO team that we could build the Mars orbiter and the instruments, gear up the Deep Space Network at Byalalu, and carry out the analysis, calculations and the simulations for navigating the orbiter from the earth towards Mars. The challenging phase starts now.

TSS: Chandrayaan-1 had several instruments from abroad on board. It was called “an international mission with India as the captain”. But the Mars orbiter does not have any foreign payload. Why?

The basic reason is the time that was available from our decision to go ahead with the mission to the D-day. We had to build the scientific instruments within the ISRO family. That is the only way we can manage the schedule. If we had undertaken the mission during the subsequent opportunities, we could have looked for partners. Here, we are racing against time.

TSS: What kind of augmentation have you done at the Byalalu facility to track and communicate with the orbiter?

There are two basic antenna systems. One is the 18-metre system and the other is the 32-metre system. The 32-metre antenna was developed indigenously for the Chandrayaan-1 mission. Its power has been increased from 2 kilowatt to 20 kw. This is the basic augmentation. Plus we have introduced the one-way differential Doppler ranging. Apart from the Byalalu station, we are making use of the Deep Space Network of the Jet Propulsion Laboratory [JPL] of NASA.

TSS: There is a fear that the government shutdown in the U.S. would lead to the shutdown of NASA installations, including its Deep Space Network, and that this would impact on the Mars mission.

V. Koteswara Rao, Scientific Secretary, ISRO: We are interacting with NASA on a regular basis. Your fears that NASA may announce a shutdown will in no way impact our mission. The JPL staff belongs to Caltech University and so they are all working. So no shutdown.

Radhakrishnan: We are also talking at the level of the Director of the JPL and ISRO Chairman through videoconferencing.

TSS: During the International Astronautical Federation conference in Hyderabad in 2007, Michael Griffin, then NASA chief, predicted that man would land in Mars in 2037. Is it possible?

There was an indication that this might happen in 2030 or 2040, that humans would have a habitat on Mars. But there are changes. Mars certainly remains a planet of interest for the scientific community to explore and understand, essentially from the point of view of understanding the life on the earth.

TSS: NASA’s rover Curiosity has found water on Mars.

Curiosity’s was an in situ measurement. But we will be doing measurements from an orbiter. This is a basic difference. We are trying to find a column of methane…. There was a report that Curiosity did not find methane in Mars. Because there is no drinking water in Tamil Nadu, it does not mean that there is no water on the earth. It is not representative. The most important point in this mission, as it was in Chandrayaan-1, is to kindle young minds. The ISRO teams are excited about the challenges involved in this mission.

TSS: The MOM will be the 25th launch for the PSLV, a silver jubilee launch.

Every mission is a first mission. Each rocket is a new rocket. Each launch vehicle mission has its own challenges. There is no room for complacency.

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