EVENTS & ISSUES

New Delhi, 20 July 2009

Chandrayaan-I Snag

SPACE AGENDA MAY NOT BE HIT

By Radhakrishna Rao

The snag that hit India’s ambitious maiden lunar mission, Chandrayaan-1 resulting in the curtailment of the scope of some of the experiments and a possible reduction in its active lifespan is by no means an isolated incident. Due to the uncertainties in outer space environment, highlighted by violent fluctuations in temperature, many of the deep space missions, including planetary probes meet their premature end. However, sources in the Indian Space Research Organization (ISRO) say that Chandrayaan-1, India’s first deep space probe, has accomplished most of the mission objectives set for it and the upcoming space projects will by no means be affected by the glitch.

What is that went wrong with the Rs 4,000-million fully home-grown Chandrayaan-1 spacecraft featuring 11 mission payloads—five Indian and six international? As pointed out by ISRO, the failure of the vital star sensor designed to determine the position and attitude of Chandrayaan-1 spacecraft, detected on April 26, forced the space scientists to devise an alternative strategy to keep the lunar probe in a “safe and stable mode”. As it is, by looking at stars, this important sensor, which is basically an electronic device, can determine the position of the spacecraft. The loss of this sensor has been attributed to the excessive thermal radiation.

Following the loss of the star sensor, ISRO activated the onboard gyroscopes, an electro mechanical system, to stabilize the orientation of Chandrayaan-1 spacecraft. However, gyroscopes, which are also used in IRS earth observation and INSAT multi-purpose spacecraft constellation not only need regular intervention but are also far more vulnerable to extremes of outer space environment vis-à-vis the star sensor.  ISRO has stated that “other than the failure of the star sensor and one of the bus management units, the health of the spacecraft is normal”.

All said and done, the use of gyroscopes along with antenna pointing information and images of specific location of the lunar surface for determining the orientation of Chandrayaan-1 spacecraft is considered far from foolproof strategy. Whether the failure of the star sensor could lead to a reduction in the lifespan of Chandrayaan-1, no clear-cut indications are available. However ISRO Chairman G.Madhavan Nair points out that the life of Chandrayaan-1 is not dependent on the star sensor but is determined by a number of factors including onboard fuel availability.

Even so, the loss of the star sensor nudged ISRO to boost the orbit of Chandryaan-1 to 200-km from 100-km. This exercise was aimed at sheltering the spacecraft in a “more benign environment”, and in the process help reduces the extent of maneuvers which involve the use of onboard fuel. However, the drawback is that the data and images transmitted from this orbit will not be of “expected quality”. Incidentally, in early 2009, when the temperature within the Chandryaan-1 spacecraft had touched 80 degrees Celsius, the Indian moon mission had faced the problem of thermal heating.

Meanwhile, ISRO scientists have shared good news that Chandrayaan-1 data is stored safely and images transmitted by the lunar craft are received on a regular basis. However, of one of the Indian payloads onboard Chandrayaan-1, the High Energy X-ray Spectrometer could not accomplish its mission due to the low solar activity at the time Chandryaan-1 was placed in its 100-km orbit around the moon. For this, the payload is dependent on solar radiance for its operations. But then as observed by Nair, the three other Indian payloads --- the Terrain Mapping Camera, the Hyper Spectral Imager and Moon Mineralogy Mapper --- have already collected much of the data.

“We have completed 90 per cent of the observation. Going by the orbital plans, nine months are enough to complete the mission. But we decided on keeping the mission on for 18 months and set satellite’s lifespan for two years,” explained a confident Nair. The other Indian payload, the Moon Impact Probe (MIP) weighing over 30kg with Indian flags painted all around, made a successful crash landing on the lunar surface on the night of November 14.

The 1380-kg cuboid shaped Chadnryaan-1, originally designed for a lifespan of two years was launched by means of an augmented version of the four-stage Indian trusted space work horse PSLV(Polar Satellite Launch Vehicle) on the morning of October 22 from the Satish Dhawan Space Centre (SDSC) in Sriharikota island, about 100-kms to the north of Chennai. This one single achievement made India the third Asian country after China and Japan to send a probe to the moon.

Further, the launch and positioning of Chandrayaan-1 spacecraft into a 100-km orbit around the moon catapulted India into the ranks of the elite league of space faring nations---the US, Russia, European Space Agency (ESA) and China and Japan—which have a wherewithal for the successful accomplishment of a lunar mission.

The point to be driven home is that the lessons learnt from the snags that affected Chandrayaan-1 would provide valuable inputs for hardening the instrumentation packages and electronics devices going into the follow-on lunar mission Chandrayaan-II, slated for launch in 2013. Chandrayaan-II, which will be launched by means of the three-stage Geosynchronous Satellite Launch Vehicle (GSLV) featuring an indigenous upper cryogenic engine stage, will carry a robotic rover that would land on the lunar surface to study samples of soil and rock. In contrast to Chandrayaan-1, Chandrayaan-II will be an Indo-Russian project.

However, the biggest hurdle involved in the successful accomplishment of Chandrayaan-II mission is to find a way to ensure that robotic rover lands safely on the lunar surface. Due to the absence of atmosphere in the moon’s periphery, the option of parachuting the rover is ruled out. The Rs.4250-million Chandrayaan-II will also carry international payloads along with the Indian experimental packages.

Meanwhile, Chandrayaan-1 has completed 3,000 orbits around the moon and has made available more than 70,000 high-quality imageries some of which provide a breathtaking view of lunar mountains and craters, especially craters in the permanently shadowed regions of the moon’s poles. Going further ISRO also claims that Chandrayaan-1 has successfully accomplished most of its mission goals, including building and launching spacecraft followed by the insertion of the spacecraft into a circular orbit of 100-km around the moon.

Other achievements of Chandrayaan-1 were: placing the Indian tricolor on the moon, carrying out the imaging operations of the lunar surface and collection of data on the minerals on lunar surface and realizing the deep space tracking network as well as the operational procedures for travel into deep space. There is a silver lining after all. ---INFA

(Copyright, India News and Feature Alliance)