WASHINGTON — Modifications to a large deployable antenna on a joint U.S.-Indian radar spacecraft will delay its launch, likely to the second half of the year.

In a March 22 statement, NASA said a new launch date for the NASA-ISRO Synthetic Aperture Radar (NISAR) mission will be set at the end of April because of work to protect the spacecraft’s reflector, an antenna that is 12 meters across when fully deployed, from temperatures when in its stowed configuration.

“Testing and analysis identified a potential for the reflector to experience higher-than-previously-anticipated temperatures in its stowed configuration in flight,” NASA said in the statement. To prevent those increased temperatures, a “special coating” will be applied to the antenna so that it reflects more sunlight.

That work, NASA said, requires shipping the antenna, currently with the rest of the NISAR spacecraft in India, to a facility in California that can apply the coating. NASA did not state how long the process of applying the coating, as well as shipping the antenna to California and then back to India, will take.

NASA officials had previously stated they expected a launch of NISAR in the spring. During a town hall about the mission at the Fall Meeting of the American Geophysical Union in December, project officials projected the mission to launch at the end of March.

In a recent interview with the Times of India, S. Somanath, chairman of the Indian space agency ISRO, said that the launch of NISAR would be delayed from the first quarter of the year, but offered few details about why other than it was not linked to the Geosynchronous Satellite Launch Vehicle (GSLV) Mark 2 rocket that will launch it.

“NISAR is still undergoing testing. It looks like the satellite may be delayed,” he said. Asked when the launch would take place, he said the “second half” of the year.

NISAR is the first Earth science spacecraft collaboration between NASA and ISRO and represents one of the biggest partnerships between the agencies in general, with NASA alone spending more than $1 billion in formulation and development of the mission. NASA is providing an L-band radar and engineering payload, while ISRO is providing the S-band payload, spacecraft bus and launch vehicle.

The radars on NISAR will be capable of advanced radar imaging to support a wide range of Earth science needs, from measuring the flow rates of glaciers to volcanic activity. The spacecraft will be able to map the entire Earth every 12 days.

Development of what would become NISAR started in response to recommendations from an Earth science decadal survey in 2007, but the mission is now playing a key role in NASA’s implementation of the latest Earth science decadal survey in 2018. That study recommended pursuing five “designated observables” with various missions, including one for surface deformation and change, or SDC, that would include a radar imaging payload.

NASA had been studying concepts for SDC as part of its overall Earth System Observatory, a suite of missions to implement those designated observables, but had planned to delay any development of that mission in order to incorporate lessons learned from NISAR. However, as part of a restructuring of the Earth System Observatory announced as part of the fiscal year 2025 budget request released March 11, NASA will no longer develop an SDC mission, instead using data from NISAR to fulfill that designated observable.

“We knew if that mission kicked off, it would be towards the end of the decadal period,” Karen St. Germain, director of NASA’s Earth science division, said of SDC during a March 20 presentation at a meeting of the National Academies’ Committee on Earth Science and Applications in Space.

“Given that we are going to be launching NISAR later this year and we want to learn from NISAR, we terminated that study” for SDC, she said, “with the idea being that, in the next decadal, we would determine if we want to restart an effort along those lines.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...