The Hindu : National : 'India's moon orbiter mission to have new facet'

Online edition of India's National Newspaper
Thursday, Nov 25, 2004

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National

'India's moon orbiter mission to have new facet'

By R. Ramachandran

UDAIPUR, NOV. 24. The Chairman of Indian Space Research Organisation (ISRO), G. Madhavan Nair, said here that a new facet would be included to the Indian moon orbiter mission, Chandrayan-1.

Besides the 55-kg payload (in a total in-lunar orbit mass of 523 kg) of on-board instruments, the spacecraft will carry an impactor weighing about 25 kg as an add-on module. The payload at present includes four Indian instruments weighing 45 kg and (possibly) five international instruments weighing 10 kg.

The actual nature, configuration and objective of the impactor are being studied, according to Mr. Nair who spoke to mediapersons after his address yesterday at the inauguration of the five-day Sixth International Conference on the Exploration and Utilization Moon (ICEUM-6) being held here since November 22. Basically, the impactor will be dropped in free-fall from the spacecraft's 100 km x 100 km orbit on the moon surface. Roughly, such an impactor will impact the surface at a velocity of about few km per second.

The instruments will make measurements during its fall under gravity as well as after impact. The impactor will be destroyed after crashing on the surface. "The idea is to demonstrate certain technologies that could be useful for future missions," Mr. Nair said. "It may even carry an instrument like a mass spectrometer to measure material ejected from impact."

Kalam's suggestion

The ISRO Chairman's announcement, however, came as a bombshell even to the scientists associated with Chandrayan-1. According to some, the suggestion to include some such technology demonstrator component came from the President, A.P.J. Abdul Kalam, some time ago and Mr. Nair hinted this in his address as well.

Apparently, a feasibility study and discussions on the possibility of incorporating an impactor as part of the payload have been on in the ISRO for the past six months or so. However, the scientists are far from arriving at any consensus on the matter. "There is a deep division between the technical people and the scientists," said a key scientistassociated with the mission. "The basic question is what is it meant to do?" he added.

Delivering such an increased payload into the proposed lunar orbit is apparently not a serious problem. At present, the launch profile for putting a 520-kg lunar satellite into a circular 100 km polar orbit is as follows. ISRO's work-horse Polar Satellite Launch Vehicle (PSLV) will be the rocket that will be used to deliver a 1050-kg spacecraft (identical to the METSAT/Kalpana-1 mission) in a nominal 240 km x 36,000 km elliptical geostationary transfer orbit (GTO) from where it will be boosted to a highly elliptical 240 km x 100,000 km parking orbit. From here, after appropriate manoeuvres at the perigee (240 km), it will be injected into a lunar transfer trajectory where it will coast (but for two mid-course corrections) till it is captured into an initial lunar orbit of 1000 km altitude from where it will wind down to a 100 km circular orbit.

According to Dr. V. Adimurthy of the Vikram Sarabhai Space Centre (VSSC), the same launch profile will be adequate for the increased payload requirement as well except that instead of the base configuration PSLV, a higher performance PSLV - XL will be used. PSLV-XL has improved strap-on solid motors. PSLV carries six strap-on solid motors, which have been of SLV-3 heritage all along. The improved ones will deliver a higher thrust.

Additional payload

"There is margin for accommodating an additional 25 kg payload if need be," said Dr. M. Annadurai, Project Director of Chandrayan-1. "Only the mission sequence may have to be changed a little. The strategy will be to reduce the apogee of the GTO from the present 36,000 km to 25,000 km. From a lower apogee, a higher payload can be delivered into the lunar orbit. This, combined with PSLV-XL's capacity to deliver 50 kg more in the GTO gives an increased payload capacity of about 25 kg in the lunar orbit," he said. This means that the dry mass of the spacecraft will now be 465 kg instead of the present 440 kg.

But what about its objectives? The possibility of such an impactor doing any meaningful science or demonstrating any technology appears limited. As far as science is concerned, the impactor has about 15-18 minutes of flight before it impacts the surface. If any science is to be done it has to be done in this time.

"In fact, the spacecraft itself will crash after two years on the lunar surface and it will provide a bigger impactor. If there is any possible new science, one can add a suitable instrument on-board and wait for two years. Nothing is going to be lost on the moon in two years. I would rather have more on-board instruments if there is indeed a 25-kg margin available, " said another top scientist.

Dr. George Joseph, a former scientist of the Space Applications Centre (SAC), Ahmedabad, refused to comment on the advantages of including an impactor over adding more useful on-board instruments. Dr. Joseph is the key man behind the identification of payload instruments and author of the mission's feasibility report

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