Mission mode

The dish antenna installed at Byalala village, 40 km from Bangalore-K. MURALI KUMAR

With the launch date set for Chandrayaan-1, installation of a massive dish antenna to track the spacecraft is complete.

PROJECT Chandrayaan-1 has picked up speed with four out of 11 instruments of the spacecraft having been integrated and the installation of a dish antenna with a diameter of 32 metres to track the spacecraft completed. If the current momentum is sustained, a new and more powerful version of the Indian Space Research Organisations (ISRO) Polar Satellite Launch Vehicle, PSOM-XL, will lift off from Sriharikota in Andhra Pradesh on April 9, 2008, and put Chandrayaan-1 in orbit on its 3.84 lakh-km journey to the moon. Chandrayaan-1 will weigh 525 kg in lunar orbit and will have a mission life of two years.

The objectives of the mission are to investigate the moons minerals and chemical properties, detect the presence of water, if any, on the lunar surface, systematically map the entire lunar surface, look for clues on the origin and evolution of the moon, create expertise in the development of detectors and sensors for future programmes to explore planets, and develop miniaturised spacecraft technologies.

With a resurgence of interest in the moon, India will be the third country in 2007-2008 to send a spacecraft to investigate it. Japan launched its Selene mission on September 14, 2007, and China sent the Change-1 spacecraft on October 24, 2007. Russia is planning a moon mission and the United States has declared its intention to set up a base on the moon by 2024.

Since the date for the launch has been set, activities relating to the Chandrayaan-1 project have revved up at the ISRO Satellite Centre (ISAC), Bangalore. In a spacious, ultra-clean, high-purity hall at the ISAC, spacecraft engineers are busy assembling and integrating the 11 payloads from six countries, including Indias six.

Four payloads the Moon Mineralogy Mapper from the U.S. National Aeronautical and Space Agency; the Miniature Synthetic Aperture Radar, also from NASA; the Radiation Dose Monitor (RODOM) experiment from the Bulgarian Academy of Sciences; and the Near-Infrared Spectrometer from Max Plank Institute, Germany, have already been assembled. Elements of the propulsion system and power system of the spacecraft have also been integrated and tested.

The integration of the remaining payloads the Sub Atom Reflecting Analyser (SARA) experiment through the European Space Agency (ESA) from the Swedish Institute of Space Physics, and the Indian payloads will begin in the fourth week of January and be completed in February.

M. Annadurai, Project Director, Chandrayaan-1, calls it a national mission with international participation and with India as the captain. Chandrayaan-1 is the first step for India in planetary science Although ISROs earlier satellites formed its bread and butter missions, Chandrayaan-1 has fired us with enthusiasm because the unknown is always exciting, he said.

At Byalalu village, 40 km from Bangalore, there is a sense of fulfilment among the engineers of the ISRO Telemetry, Tracking and Command Network (ISTRAC), where the massive dish antenna has been installed. The dish, weighing 60 tonnes, can rotate both horizontally and vertically. The antenna is the centrepiece of the International Deep Space Network (ISDN) at Byalalu. It will track not only Chandrayaan-1 but also Chandrayaan-II and ISROs mission to Mars. It will send commands to Chandrayaan-1 to perform various manoeuvres during its journey and receive information about the health of the spacecraft, its sub-systems and the payloads, and also scientific data about lunar soil, its chemical properties, and so on. Thus, communication through deep space is the backbone of this mission, and high-end software plays a crucial role in this.

S.K. Shivakumar, Director, ISTRAC, called the dish antenna an all-out Indian effort with key contributions coming from ISTRAC and the ISAC, Electronics Corporation of India (ECIL), Hyderabad, the Bhabha Atomic Research Centre, Trombay, the Space Applications Centre, Ahmedabad, and several private industries, including Godrej and Vamshi Electronics, Hyderabad. The installation of the antenna has been completed in all aspects, he said, and described it as a dream project for radio frequency engineers.

The entire technology for the antenna was developed indigenously. All its advanced mechanical systems were designed and developed in India. Shivakumar said: We have reached the limit in the state-of-the-art technology available in 2007 for an antenna of this class. It is meant not only for one mission but many missions into deep space that we plan in the future.

The entire antenna can be divided into three parts: the dish, also called the reflector; the mount, the driving system that can rotate the dish; and the pedastal on which the entire system is erected.

The credit for designing and developing the dish goes to ECIL. We chose ECIL as the prime contractor for the development of the system, Shivakumar said. The big petals of the dish were manufactured and assembled in Hyderabad. Then the dish was dismantled into petals. The individual petals were brought to Byalalu and they were assembled on the ground on a trial basis. The petals were separated again, hoisted by tall cranes and reassembled into a dish on top of the mount at a height of 27 metres from the ground. Fitting the petals precisely into a dish at that height was a challenging job because each petal weighed several tonnes.

According to N. Ramakrishna Reddy, engineer, ISTRAC, since the dish has to point towards the spacecraft it wants to track, it will move vertically from 0{+0} to 90{+0} and also horizontally. The total antenna system, including the dish, therefore, will rotate on four wheels in a circular manner on a track. It is called the wheel and track system. Each wheel is about 1.4 metres in diameter. The thickness is 20 cm and the weight two tonnes.

Ramakrishna Reddy said: All the four wheels have to be aligned with extreme precision. The wheels have to rotate through a planetary gear-box very slowly at a speed of 0.4{+0} a second. The elevation [of the dish from 0{+0} to 90{+0}] is done through a bull-gear, which is the rotating mechanism. It supports the dish. Inside the dish is a quarter-pod, a four-legged structure. It supports a sub-dish. The total height of the system from the ground level to the crown of the quarter pod is 32 metres, that is, 11 storeys tall. The entire antenna system weighs about 350 tonnes. The design of the antenna servo control system was done by BARC, Mumbai. A BARC team also developed the software for it. SLN Technology, Bangalore, fabricated and integrated the hardware for the control system.

A crucial challenge that ISTRAC met in the installation of the antenna was the erection of the beam wave guide system. It is through this system that commands are sent to the spacecraft for performing various manoeuvres, and telemetry signals are received from Chandrayaan-1. The system has seven highly polished mirrors inside. The mirrors were made in India. Ramakrishna Reddy, who is the core designer of the beam wave guide system, said its development involved the fundamentals of optics and microwave propagation.

The dish antenna system was readied within two and a half years of ISTRAC signing the contract with ECIL on March 24, 2005. The ground-breaking ceremony was on November 4, 2005.

A few hundred metres away, another dish antenna has come up. The diameter of its dish is 18 m. The installation of this antenna is a turn-key job. It was built by Vertex RSI, a German company, to ISROs specifications. This antenna will also be used to track Chandrayaan-1 and send commands to it or receive telemetry signals from it. The antenna has already been used to receive signals from Selene.In order to operate the antennae at Byalalu, a network control centre has been established at ISTRAC at Peenya in Bangalore.

Similarly, ISTRAC ground stations (the radars) at Sriharikota, Thiruvananthapuram, Lucknow, Port Blair, Mauritius, Brunei and Biak in Indonesia can be operated from Peenya. In my opinion, this is a good achievement of ISTRAC in terms of modernisation of network. We have built state-of-the-art systems and we have proved our remote-operations capability. The same will continue for the IDSN complex, said Shivakumar.

The entire IDSN project at Byalalu has so far cost Rs.200 crore. While the installation of both the dish antennae cost Rs.100 crore, Rs.50 crore was spent on the rest of the elements. Civil works such as the laying of roads, construction of several buildings and water supply cost another Rs.50 crore.

On December 19 and 20, 2007, the Chandrayaan-1 team completed the critical design review of the ground segment of the spacecraft, which is a milestone in the mission. The review was attended by ISRO experts and engineers from NASA and the ESA.

Chandrayaan-1 will carry six instruments of ISRO to achieve its scientific objectives. The instruments include cameras to take pictures of the lunar terrain to detect the presence of minerals and chemicals, a laser ranging instrument, an instrument to measure the X-rays emanating from the moons surface, and importantly, a moon impact probe (MIP), which will be released from Chandrayaan-1 to crash-land on the moon. The MIP will carry three instruments: a mass spectrometer, an altimeter and a video camera. The 20-kg, cube-shaped probe is positioned on top of the spacecraft.

Annadurai said: After Chandrayaan-1 reaches the lunar orbit, we will re-orient it and eject the MIP. There is a solid motor in the MIP, which will fire for two seconds to reduce the MIPs velocity to 75 metres a second. Once you reduce the velocity, it is no longer in the lunar orbit. It will keep falling under the influence of gravity and this free fall will last for 18 minutes. As the MIP hurtles towards the moons surface, its video camera will take pictures of the lunar surface. The altimeter will measure the instantaneous altitude of the MIP from the moon. The mass spectrometer will sniff the tenuous atmosphere above the moon to find out what it is made of. All this data will be sent to Chandrayaan-1 until the MIP crashes on the moons surface.

This crash-landing is a precursor to the soft-landing by the rover to be flown by Chandrayaan-2.

What is under way right now at the ISAC is Hardware Inlook Simulation (HILS). In other words, sensors, gyros and wheels and the four integrated payloads of Chandrayaan-1 are undergoing various manoeuvres, similar to those when Chandrayaan-1 journeys to the moon.

Annadurai said, During these tests, the spacecrafts manoeuvres are being simulated and its responses studied. This is one of the important tests to be performed before integrating other payloads. All these activities are progressing as per plan. The team is working diligently on a 24 x 7 schedule.