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IRS-1A: India's Initiation to Remote Sensing | 1st IRS satellite
India's First Remote Sensing Satellite, IRS-1A paved the path of many new technologies, ground segment and managerial aspects of ISRO as we know it today.
It's the year 1975. India just launched its first satellite, Aryabhata. The satellite operated only for a few months, but ISRO learned a lot during the journey for achieving this dream. The Aryabhata mission's success resulted in new programs for communication satellites (APPLE/INSAT) and remote sensing satellites. Let us learn about the first operational satellite fully designed and developed by ISRO, IRS-1A: India's Initiation to Remote Sensing.
Background: A legacy of Aryabhata, Bhaskara and APPLE
Over the next few years, to continue Vikram Sarabhai's vision, the agency built two more experimental satellites called Bhaskara 1 and Bhaskara 2. While Aryabhata was a scientific satellite, Bhaskara(s) were remote sensing satellites in some sense. They had camera payloads but lacked the strict parameters of operational remote sensing satellites like a fully stable satellite. The Bhaskara satellites, therefore, were a step forward in the right direction. ISRO tested some key technologies while leaving out some advanced ones.
On the communication satellites front, APPLE again was an experimental satellite, whereas the first operational satellites INSAT-1 series were procured. Therefore, when the design and development of the first operational satellite, IRS-1A, started, ISRO ventured into unknown territory on many fronts: control systems, deployable solar panels, ground station, quality control protocols and data utilisation, to name a few.
The Bhaskara satellites launched in 1979 and 1981, respectively. Around the same time, the idea of an operational remote sensing satellite was going around in ISRO. The National Natural Resources Monitoring and Management System (NNRMS) of Govt of India considered essential areas of application of satellite-based remote sensing data as
Agriculture, where the extent of crops and their yields were required to be monitored over the growing seasons,
Monitoring of the different types of land/land use,
Monitoring of water resources,
Monitoring of drought and floods,
Monitoring of the forestry in the country, and
Geological applications like mineral prospecting.
The agricultural applications gained priority over other areas. In India, a typical agricultural field had a 30 m length. Therefore, a 36 m resolution payload was selected for the satellite. Other applications could work with a course resolution which resulted in the inclusion of a separate 72 m resolution payload.
With these payloads finalised, the Space Commission submitted a proposal to the Government of India, giving full details of the mission. ISRO included a list of new technologies to be developed, specifications of satellite and ground segment, budget, import requirements, schedule and project management aspects in the report. Finally, the GOI approved the IRS-1A satellite in 1981.
IRS-1A Development: Realising new technologies
The imaging systems, along with fine resolutions, require multispectral data. Different frequency range channels help classify various features such as water bodies, green covers, and construction. Therefore, ISRO included four bands (blue, green, red, and infrared) in each of the two cameras.
Next came the decision of orbit selection. To observe the growth of crops in a season, a repetitiveness of 22 days was set. This requirement meant ISRO selected a 900 km Polar Sun-synchronous orbit. Therefore, two LISS (Linear Self Scanning Scanner) payloads were developed for the IRS-1A satellite.
The satellite needed a lot of new technologies to support the imaging system.
A three-axis stabilised satellite with cameras mounted appropriately to take images of the Earth's surface with pointing accuracies of ± 0.3 degrees about pitch and roll axis and ± 0.4 degrees about the yaw axis,
Power system to provide the required conditioned power,
Telemetry, Tracking and Command (TT&C) system working in S-band,
Data handling and radiofrequency transmit systems for transmitting the camera data, and
The mechanical system consisting of a structure, thermal control and solar panel deployment mechanism.
An aluminium honeycomb structure was realised to support different instruments. Special considerations meant that the satellite bus was compatible with different launch vehicles, including the upcoming PSLV. A passive (no electrical power needed) thermal system evolved where the cameras remained at the standard room temperature.
All prior ISRO satellites had permanent mounted solar panels. An imaging satellite like IRS-1A needs high power. Therefore deployable solar panels are required. The team developed a mechanism that underwent more than 50 tests, including zero-gravity testing.
Being the first three-axis stabilised satellite, IRS-1A needed many new control systems. Attitude sensors, dynamically tuned gyroscope, reaction wheels and mono-propellant based propulsion system were developed. Digital microprocessors was a new technology in the world. This lead ISRO to use a hardware-based control system with a safe mode inbuilt.
The imaging camera data was beamed back to Earth in real-time. There was no recorder onboard. This meant that the payload data needed an Earth-pointing antenna while the Telemetry and Telecommand antenna had to be omnidirectional.
ISRO imported Solar cells and Ni-Cd Batteries. A power system tested and qualified for space was designed around these imported components. The team developed power conditioners to convert raw power into regulated power voltage.
IRS-1A also paved the path for managerial aspects
By that time, ISRO had expanded a lot. There were multiple centres of the space agency spread throughout the country. IRS-1A became one of the first inter-departmental efforts. ISRO satellite centre (URSC) lead the project and coordinated with all other centres. The Project Management Council (PMC) chaired by Dr UR Rao and a Project Management Board (PMB) chaired by Dr K Kasturirangan were formed at URSC to guide the project and conduct higher-level mission analysis.
The Space Applications Centre, Ahmedabad, developed the imaging system and even the data products to analyse the remote sensing data. Teams developed the control systems and solar panel deployment at ISRO Inertial Systems Unit (IISU), VSSC. Liquid Propulsion Systems Centre (LPSC), Bangalore, developed the propulsive system needed to control the satellite.
While this inter-departmental effort was undergoing, ISRO formed a new centre. Until now, ISRO utilised a ground station at the Sriharikota Launch Range as a command station for its satellites. ISRO Telemetry Tracking and Command Network (ISTRAC) was developed as a Control Centre for IRS-1A and all upcoming Indian Remote Sensing (IRS) satellites. Bearslake station in Moscow, Fairbanks station in Alaska, Weilheim station in Germany, Malindi station located in Kenya, operated by ESA, were the stations identified for the network.
The National Remote Sensing Agency, Hyderabad (now NRSC), was already receiving payload data from NASA Landsat and French SPOT satellites. New ground systems evolved to receive IRS-1A satellite data.
Quality Assurance and Testing
The inter-departmental effort and multiple industries involved meant uniform quality assurance norms was needed across all centres. ISRO constituted a Product Assurance Board which catered to reliability apportionment of the satellite. The teams required to get every component checked with the board through checklist documents.
Each and every subsystem of the satellite was thoroughly tested through newly developed testing setups. The teams even developed multiple models such as a structural model for vibration testing, qualification model for testing and final flight model. ISRO first used this multiple model philosophy for the IRS-1A mission.
Launch and Operations
ISRO's Polar Satellite Launch Vehicle (PSLV) was still under development. This limited the agency to use a foreign launcher for the satellite. After the Soviets helped India launch the first satellite, Aryabhata, ISRO decided to approach them again. Soviet Union agreed to launch IRS-1A onboard a VOSTOK rocket at a "reasonable price tag".
There were multiple visits by Soviet Scientists to assist ISRO to design a compatible satellite. Even ISRO scientists AD Dharma S Kalyana Raman visited Baikonur Cosmodrome. A few days before launch, the satellite was flown onboard an Aeroloft IL-76 cargo aircraft on 24th January 1988.
After conducting some more tests, such as solar panel deployment and fuel loading, the satellite was integrated with the launch vehicle. IRS-1A launched at 12:13 IST on 17th March 1988.
The solar panels deployed without any hiccups after a few minutes. On 18th March, the satellite had acquired stabilisation, and the LISS-1 was switched on. A few more days later, the LISS-2 payload started sending images as well. Within three weeks, the satellite was operationalised and data made available to the scientists.
UR Rao had become the ISRO chairman by then. He constituted the Antrix Corporation to sell the IRS series data internationally commercially. Hence, the commercial arm of ISRO was formed. IRS-1A worked for almost nine years, much more than its three-year design life.
IRS series: The Road Ahead
IRS-1A had a paved path for numerous facilities and procedures at ISRO. Riding on the first remote sensing satellite's success, ISRO designed IRS-1B/C/D satellites in the coming years. In 1993, PSLV became operational, and India now launched the satellites on our own launch vehicle. The Indian Remote Sensing network is one of the largest nationally operated around the world. IRS programme has evolved to include many satellites such as Resourcesat, Cartosat and the latest EOS series satellites.