On July 30th, NISAR — the NASA-ISRO joint space mission — launched to space aboard the GSLV Mark II rocket from Sriharikota, Andhra Pradesh. The satellite, now safely tucked into a sun-synchronous orbit around earth, will enter a commissioning phase over the next three months, to deploy all its instruments.
Perched at an altitude of 750 km, the three ton satellite will complete an orbit around the earth every 12 days, while studying the planet’s diverse geology with unprecedented detail.
NISAR, a portmanteau for the NASA-ISRO synthetic aperture radar mission, marks the culmination of a decade-long effort to build the most powerful earth observation satellite to date.
In 2007, NASA had begun actively exploring an ambitious undertaking to build a satellite, which could map the earth and the whole ecosystem. On the agenda were investigations into studying climate change and its role in exacerbating extreme weather events. These include surveillance over vulnerable hotspots, such as Greenland and Antarctica, where disappearing ice sheets have been linked to the global average increase in sea-levels over the years.
Remote sensing satellites traditionally used can’t capture the full picture, without uninterrupted sunlight exposure or obstructions namely cloud cover. But synthetic aperture radar is a fix to these problems. Clouds are transparent to radio and microwaves unlike visible light. As such, a synthetic aperture radar can work across any weather, whether sunlit or not alike.
That said, SAR technology isn’t new. They have been around for about seventy years, since the first proof of principle was proven in the 1950s. In 1978, the US launched the first SAR-equipped earth observation satellite, Seasat, to monitor oceans. Neither Seasat or for that matter any SAR-based successors, could bear resolutions as high as 1 cm, or map terrain across a swath area as wide as about 240 km, as NISAR can.
NASA engaged in a cost-effective strategy, opening doors for international partners to pool resources, and co-develop the satellite and the scientific campaigns.
(A) Melt pond in Greenland | Photo Credit: Michael Studinger (2008) (B) NASA administrator Charles Bolden and ISRO chairman K. Radhakrishnan sign documents, which included a charter on NISAR, in Toronto | Photo Credit: NASA (2014)
NASA and ISRO share expertise
NASA found an interested party in ISRO, which at the time was developing the Radar Imaging Satellite (RISAT), which had a smaller scope to study India’s geology. India, being especially vulnerable to floods, landslides and cyclones, couldn’t overlook the incentives an extra eye in the sky could provide.
NISAR can track and relay even the minutest of changes on the surface in near real-time. In principle, the satellite should detect a flooded area hidden from view to rescuers on-ground, or even traditional remote sensing satellites which use passive receivers. The satellite can serve a key role in an integrated multi-hazard early warning system.
In 2014, ISRO inked the NISAR agreement with NASA. The mission would only be their latest collaboration between the two space agencies. Previously, they had collaborated on 2008’s Chandrayaan-1. Back then, NASA’s Moon Mineralogy Mapper (M3) instrument and miniSAR radar onboard the Chandrayaan orbiter, led the famous detection of water ice on the moon.
Although NISAR was originally slated for launch in 2020, innumerable delays followed as they sorted technical challenges, and the abrupt global lockdown amid COVID pandemic.
Upon project completion last year, NISAR had become the most expensive satellite built, with NASA and ISRO pouring some $1.5 billion into development. The costs were unevenly split between them; with NASA spending some $1.3 billion, and ISRO bearing a modest amount at $91 million.
But a white paper details ISRO had contributed an equal value in engineering various components, re-establishing parity. ISRO engineered the spacecraft body, readied tracking stations on-ground, and developed the short wavelength S-band radar. The S-band (at 12 cm) complements NASA’s longer wavelength L-band (24 cm) radar.
The L-band can track changes under thick foliage or leaves, under forests. It can even measure land deformation rates as tiny as 4 mm/year. While the L-band serves as NISAR’s primary means of acquiring radar data, ISRO’s S-band radar will help provide details that concern Indian earth scientists, monitoring coastal erosion for example. Both radars work in tandem with NASA-designed radar receiver and reflector – a 12-meter wide meshed net, resembling a canopy attached to the spacecraft body via a boom.
Three months from now, once the commissioning phase is complete, NISAR will begin its observational runs, and beam radar data back to earth continuously. The National Remote Sensing Centre in Hyderabad, and Goddard Space Flight Centre in Maryland, will process the respective L & S-band data independently, and archive them online for the world to see, all in a matter of few hours.