The Indian Space Research Organisation (ISRO) is preparing to launch the NASA-ISRO Synthetic Aperture Radar (NISAR) satellite aboard a Geosynchronous Satellite Launch Vehicle (GSLV) Mk. II rocket from the Satish Dhawan Space Centre launch site in southeast India. The mission comes just over two months after its EOS-09 mission failed aboard a different rocket type.
This launch is just the third ISRO orbital flight of 2025, and the second flight of the GSLV Mk. II this year after the successful NVS-02 mission on Jan. 28. The NISAR satellite is scheduled to launch aboard GSLV F16 from the Second Launch Pad on Wednesday, July 30, at 12:10 UTC, and the rocket will take a southerly trajectory over the Bay of Bengal to place NISAR into a Sun-synchronous 98.4-degree inclination orbit.
The 52 m tall GSLV Mk. II, capable of flying up to around 3,000 kg to Sun-synchronous orbit (SSO), is a three stage launch vehicle with four liquid-fueled strap-on boosters that stay attached to the first stage throughout its flight. The first stage is solid-fueled, while the second stage, like the four strap-on boosters, is powered by a Vikas engine using storable but highly toxic liquid hypergolic propellants.
GSLV F12 at the Second Launch Pad ahead of the NVS-01 mission (credit: ISRO)
The third stage uses cryogenic propellants — liquid oxygen and liquid hydrogen — and an indigenous Indian-made CE-7.5 engine. This stage will place the 2,392 kg NISAR payload into a circular SSO at 743 km altitude. Despite its name, the GSLV has launched missions to different types of orbits, and NISAR’s orbit will allow it to pass over any given point on Earth at the same time each day.
The 5.5 m long NISAR, incorporating hardware from NASA and ISRO, will observe Earth’s surface using a pair of synthetic aperture radars (SAR) over a planned mission duration of three years for NASA and five years for ISRO. The mission has enough consumables for at least five years in space, including 265 kg of hydrazine propellant, with its solar arrays generating five kilowatts of power.
NISAR will undergo a 90-day commissioning phase on orbit before science operations can begin. The reflector antenna deployment process, a major highlight of this phase, will start 10 days after launch with pre-deployment checkouts and last up to eight days.
One day will be dedicated entirely to the all-important reflector deployment, to be done around 17 days after launch, and which will finish the sequence. Without the reflector, NISAR’s mission will be dramatically affected.
Illustration of NISAR in orbit. (Credit: NASA/JPL/Caltech)
The NISAR satellite project started in 2019, but the groundwork for this joint collaboration was started as early as 2007. The National Academy of Sciences decadal survey prioritized greater insight into ecosystems, solid Earth, and cryosphere sciences in 2007, and in 2014, NASA and ISRO signed an agreement to collaborate on NISAR.
Over the intervening years, teams from both agencies collaborated despite the vast distance between the United States and India and the worldwide COVID-19 pandemic. Both nations contributed hardware to the project, and the agencies conducted work in major facilities in both countries.
NASA contributed NISAR’s L-band SAR instrument along with the high-rate telecommunications system, GPS receivers, a solid state recorder, and a payload data subsystem. Northrop Grumman’s business unit Astro Aerospace, based in California, provided the 12 m deployable mesh reflector antenna that both SAR instruments will use.
The IRIS assembly at the Jet Propulsion Laboratory in Pasadena, California. (Credit: NASA/JPL/Caltech)
ISRO contributed a modified I3K satellite bus, based on a standard bus for 3,000 kg-class satellites used for INSAT and GSAT class satellites, as well as the Chandrayaan-3 propulsion module. The Indian space agency also provided the S-band SAR instrument and the GSLV Mk. II launch vehicle and associated launch services.
NISAR is the first observation satellite to use two different bands for SAR observations. The L-band SAR instrument, built at NASA’s Jet Propulsion Laboratory (JPL) in California, operates at 24 cm wavelength and can penetrate deeper into vegetation. The L-band observations are useful for studying biomass, and the L-band’s sensitivity to larger features and slower movements make it ideal for studying land and ice changes.
The S-band SAR instrument, built by ISRO’s Space Applications Centre in Ahmedabad, India, operates at 10 cm wavelength and is more sensitive to moisture, light vegetation, and changes in smaller features. This makes the S-band instrument suited for studying agriculture, wetlands, changes in soil moisture, and changes in vegetation growth.
NASA and ISRO personnel posing by NISAR in Bengaluru, India. (Credit: ISRO)
Both bands, as well as other bands used by different SAR satellites, allow observations through cloud cover and at night. The two radar instruments were integrated into the Integrated Radar Instrument Structure (IRIS) at JPL, with the S-band instrument being transported from India.
After integration, IRIS was shipped to India for integration into the NISAR satellite at the U R Rao Satellite Centre (URSC) in Bengaluru. URSC finished NISAR before ISRO moved the satellite to the launch site, and the payload arrived at the Satish Dhawan Space Centre on June 12.
The NISAR satellite, with a radar swath 242 km wide, will be able to observe surface motion on Earth down to one centimeter. In addition, the satellite will measure the motion of Earth’s land and ice from 77.5 degrees north to 87.5 degrees south latitude twice every 12 days.
The NISAR spacecraft and key elements. (Credit: NASA/JPL/ISRO)
The satellite will use SweepSAR technology, which allows for fine spatial resolution as well as wide area coverage, and NISAR will be the first space-based application of SweepSAR.
SweepSAR, developed by JPL and German Space Agency engineers, works by bouncing a transmitted narrow beam of microwave energy off of the antenna’s large reflector, illuminating an entire 242 km swath on the ground. The signals that strike the ground return to the spacecraft at slightly different times, depending on the nature of the surface.
NISAR was built at a cost of $1.5 billion USD, making it one of the most expensive Earth observation satellites ever built. It will generate more data on a daily basis — 80 terabytes per day — than any other observation satellites that NASA or ISRO have operated, and this data will be freely available to the public.
NISAR prior to encapsulation in its payload fairing. (Credit: ISRO)
NISAR’s data and products will be hosted by the Alaska Satellite Facility Distributed Active Archive Center. S-band products will be processed by the National Remote Sensing Centre (NRSC) in Hyderabad, India. Data products in both bands will be made available to Indian government users, distributed through the NRSC’s Bhoonidhi portal.
NISAR did not have an entirely smooth path to the launch pad. The U.S.-provided antenna reflector needed to be sent back to California to apply a thermal coating that would mitigate potential temperature increases during its stowed configuration in flight. After the coating was applied, the reflector was sent back to URSC for integration into the spacecraft.
The two space agencies have a long history of developing Earth observation satellites and SAR technology. NASA launched the first civilian SAR observation satellite, Seasat, in June 1978 from what was then Vandenberg Air Force Base, while India launched its first dedicated SAR observation satellite, RISAT-1, in 2012.
Illustration of the Seasat SAR satellite in orbit. (Credit: NASA)
A follow-up satellite, RISAT-1A, was launched in 2022, while RISAT-1B, also known as EOS-09, was lost in a launch failure aboard a Polar Satellite Launch Vehicle (PSLV)-XL on May 18 of this year. The PSLV-XL’s solid-fueled third stage failed during its burn and the mission was lost. As the GSLV doesn’t use this stage it was cleared to fly NISAR.
The NISAR mission is a major Earth science mission for both agencies, as India develops greater space capabilities. ISRO already sent an astronaut to the ISS aboard the private Axiom-4 mission this summer, and plans additional flights aboard its GSLV Mk. II and LVM3 rockets in the coming months.
(Lead image: GSLV F16 rolling out with the joint US-Indian NISAR payload. Credit: ISRO)
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