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YM COLUMN ARCHIVE

September 9, 2009

Chandrayaan mission of India coming to the end

I suppose you must have heard the news that the satellite control center abruptly lost the radio communication with Chandrayaan, Indian lunar orbiter, of which cause seems to be deeply relevant with thermal problem.

Some of you must have thought more or less “why?” when you heard the announcement that Indian Space Research Organization (ISRO) would raise the orbital altitude of the satellite from 100km to 200km. I am one of them. According to ISRO’s explanation, they had confronted the necessity to study more about perturbation of the orbit and variations of lunar gravitation, and at the same time to observe lunar surface with broader view. “Why now? Wasn’t it taken for granted?” was my candid feeling, but in fact they seem to have mistaken in estimating temperature in the vicinity of the moon, which caused malfunction on thermal control of the explorer to have led to the unexpected loss of communication.

Those involved in this mission at ISRO assumed at first of the temperature 100km above moon as 75 degrees C, but the truth is that actually it was much higher as to have caused malfunction to onboard instruments so that they had to raise the orbital altitude to 200km.

According to the latest explanation of ISRO, malfunction of onboard instruments occurred at the earlier phase on Nov. 25 last year, and so they had no other choice but to switch off some of the payloads. The thermal vacuum test conducted, prior to the launch, at ISRO Satellite Center at Bangalore was already seriously questioned of its result.

Early this year the situation improved to a certain degree, but the main sensor went out of order on April 26 followed by another trouble of backup sensor in the second week of May. Having faced the trouble with two star sensors due to the unexpected high temperature so as to cause uncontrollability in attitude of spacecraft, ISRO mission team urgently turned to attitude control skillfully maneuvered by gyrocompass as an emergency measure, which did not last long enough for ISRO to finally give up the mission on August 30. Thus Chandrayaan came to close its mission with achievements said to be successfully completed 96% of its scientific objectives.

At any rate under such difficult situation with trouble of star sensors, Chandrayaan really did good jobs as to have sent splendid images including those of total solar eclipse on July 22, and Chandrayaan also successfully achieved the mission task of observing North Polar ice of moon on August 21 in teamwork with NASA’s Lunar Reconnaissance Orbiter (LRO). It was at 1:30am on August 29 when the ground station abruptly lost communication with Chandrayaan.

India must have gained precious experience out of Chandrayaan mission. An engineer concerned with the project said that Chandrayaan II slated for launch in 2013 would be built with thermal design endurable up to 100 degrees C. Some of the eleven payloads onboard Chandrayaan from India, USA, England, Germany, Sweden and Bulgaria might not successfully left the satisfactory achievements, of which attained results will be gradually analyzed with hard efforts for clearing the data. Meanwhile, I’m looking forward to the International Astronautical Congress to be held at Daejeong city in Korea in October, where I expect to hear what kind of report will be made by Japan, India, China and USA of the performances by KAGUYA, Chandrayaan, Chang’e and LRO respectively.

I welcome your opinions on this column to the following E-mail address.
matogawa@planetary.or.jp

(Translated by The Planetary Society of Japan)