HENNAI, August 16: Seventeen days after the launch of world’s costliest Earth observation satellite NASA-ISRO Synthetic Aperture Radar ( NISAR), its 12- metre antenna reflector was successfully unfurled in orbit on August 15 when India was celebrating its Independence Day, said Jet Propulsion Laboratory (JPL) part of USA’s National Aeronautics and Space Administration (NASA) said.
On August 15, small explosive bolts that held the reflector assembly in place were fired, enabling the antenna to begin a process called the “bloom”, its unfurling by the release of tension stored in its flexible frame while stowed like an umbrella. Subsequent activation of motors and cables then pulled the antenna into its final, locked position, JPL said.
The drum shaped antenna reflector spanning 39 feet or 12 metres is an essential piece of science hardware in NISAR was unfurled in Low Earth Orbit (LEO).
Weighing about 142 pounds (64 kilograms), the reflector features a cylindrical frame made of 123 composite struts and a gold-plated wire mesh.
On August 9, the satellite’s boom, which had been tucked close to its main body, started unfolding one joint at a time until it was fully extended about four days later. The reflector assembly is mounted at the end of the boom.
The reflector had been stowed, umbrella-like, until the 30-foot (9-meter) boom that supports it could be deployed and locked in place, JPL said on August 15.
Launched by ISRO on July 30 from the Satish Dhawan Space Centre on India’s southeastern coast, NISAR will track the motion of ice sheets and glaciers, the deformation of land due to earthquakes, volcanoes, and landslides, and changes in forest and wetland ecosystems down to fractions of an inch. It also will aid decision-makers in fields as diverse as disaster response, infrastructure monitoring, and agriculture.
“The successful deployment of NISAR’s reflector marks a significant milestone in the capabilities of the satellite,” said Karen St. Germain, Director, Earth Science Division at NASA Headquarters in Washington.
“From innovative technology to research and modeling to delivering science to help inform decisions, the data NISAR is poised to gather will have a major impact on how global communities and stakeholders improve infrastructure, prepare for and recover from natural disasters, and maintain food security,” Karen St.Germain added.
The mission carries the most sophisticated radar systems ever launched as part of a NASA mission.
In a first, the satellite combines two synthetic aperture radar (SAR) systems: an L-band system that can see through clouds and forest canopy, and an S-band system that can see through clouds as well but is more sensitive to light vegetation and moisture in snow. The reflector plays a key role for both systems, which is why the successful deployment of the hardware is such a significant milestone, JPL said.
“This is the largest antenna reflector ever deployed for a NASA mission, and we were of course eager to see the deployment go well. It’s a critical part of the NISAR Earth science mission and has taken years to design, develop, and test to be ready for this big day,” said Phil Barela, NISAR Project Manager at JPL in Southern California,
which managed the US portion of the mission and provided one of the two radar systems aboard NISAR.
“Now that we’ve launched, we are focusing on fine-tuning it to begin delivering transformative science by late fall of this year,” Barela added.
To image Earth’s surface down to pixels about 30 feet (10 meters) across, the reflector was designed with a diameter about as wide as a school bus is long. Using SAR processing, NISAR’s reflector simulates a traditional radar antenna that for the mission’s L-band instrument would have to be 12 miles (19 kilometers) long to achieve the same resolution.
“Synthetic aperture radar, in principle, works like the lens of a camera, which focuses light to make a sharp image. The size of the lens, called the aperture, determines the sharpness of the image,” said Paul Rosen, NISAR’s Project Scientist at JPL.
“Without SAR, spaceborne radars could generate data, but the resolution would be too rough to be useful. With SAR, NISAR will be able to generate high-resolution imagery. Using special interferometric techniques that compare images over time, NISAR enables researchers and data users to create 3D movies of changes happening on Earth’s surface,” Rosen said.
The NISAR satellite is the culmination of decades of space-based radar development at JPL. Starting in the in the 1970s, JPL managed the first Earth-observing SAR satellite, Seasat, which launched in 1978, as well as Magellan, which used SAR to map the cloud-shrouded surface of Venus in the 1990s.
The NISAR mission is a partnership between NASA and ISRO spanning years of technical and programmatic collaboration.
The successful launch and deployment of NISAR builds upon a strong heritage of cooperation between the US and India in space.
Indian rocket Geosynchronous Satellite Launch Vehicle-F16 (GSLV-F6) on July 30 orbited the NISAR.
The data produced by NISAR’s two radar systems, one provided by NASA and one by ISRO, will be a testament to what can be achieved when countries unite around a shared vision of innovation and discovery.
The ISRO Space Applications Centre provided the mission’s S-band SAR. The U R Rao Satellite Centre provided the spacecraft bus. Launch services were through Indian Space Research Organisation’s (ISRO) Satish Dhawan Space Centre.
After launch, key operations, including boom and radar antenna reflector deployment, are being executed and monitored by the ISRO Telemetry, Tracking and Command Network’s global system of ground stations.
Managed by Caltech in Pasadena, JPL leads the US component of the project. In addition to the L-band SAR, reflector, and boom, JPL also provided the high-rate communication subsystem for science data, a solid-state data recorder, and payload data subsystem. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the Near Space Network, which receives NISAR’s L-band data.
The spacecraft is built around ISRO’s I-3K Structure. It carries two major Payloads viz., L & S- Band Synthetic Aperture Radar (SAR).
The S-band Radar system, data handling & high- speed downlink system, the spacecraft and the launch system are developed by ISRO.
The L-band Radar system, high speed downlink system, the Solid-State Recorder, GPS receiver, the 9m Boom hoisting the 12m reflector are delivered by NASA.
Further, ISRO takes care of the satellite commanding and operations and NASA will provide the orbit maneuver plan and Radar operations plan.
NISAR mission will be aided with ground station support of both ISRO and NASA for downloading of the acquired images, which after the necessary processing will be disseminated to the user community.
The data acquired through S-band and L-band SAR from a single platform will help the scientists to understand the changes happening to Planet Earth.
Built at a cost of about $1.5 billion, the 2,400 kg NISAR’s mission life will be five years.
(UNI)
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