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# NISAR had to unfold before it could measure a moving Earth
- URL: https://pvweekly.com/nisar-unfolding-earth-measurement/
- Published: 2026-10-27T19:29:58.000Z
- Updated: 2026-10-27T19:29:58.000Z
- Description: 2025 archive · The 2025 U.S.–India radar mission turned an orbital launch into a working instrument through deployment, checkout and calibration.
- Author: PV Weekly Editorial
- Tags: Technology & Defense, Archive 2025, #ledger-format, #archive-backfill-20261027

**2025 archive** · August 15, 2025Reporting prepared October 22, 2026\. This retrospective describes events and expectations from the period covered.[Browse the archive](https://pvweekly.com/archive/)

A 12-meter radar reflector cannot do its job folded against a spacecraft. For NISAR, reaching orbit on July 30, 2025, left a second, mechanically demanding operation ahead: extend a nine-meter boom, open the reflector and establish that the radars could make trustworthy measurements.

The joint NASA–Indian Space Research Organisation mission cleared that deployment on August 15\. Its subsequent commissioning supplied a useful account of what separates a successful launch from a scientific observing system. Hardware had to change shape, electronics had to pass checks, and the images had to be compared with references on Earth.

NISAR launched aboard India's GSLV from Satish Dhawan Space Centre. NASA described a mission intended to measure land and ice movement at centimeter scales, with applications ranging from ground deformation to changing forests and agricultural landscapes. Its planned observing pattern covered most land and ice twice in a 12-day cycle. Repeated measurements, rather than a single striking picture, were central to its value.

The two radar systems approached that task at different wavelengths. NASA's L-band instrument used a wavelength of about 24 centimeters; ISRO's S-band instrument used about 10 centimeters. The longer wavelength could penetrate forest canopies, while the shorter one was sensitive to smaller vegetation and certain agricultural features. Both could collect observations through clouds and precipitation and without daylight, according to NASA's August update.

That pairing gave the mission different ways to interrogate the same planet. A field, forest or moving ice surface interacts with radar signals according to its physical characteristics. Two wavelengths therefore supplied complementary information, rather than simply a backup copy of one image.

Getting the shared reflector into place required a sequence of joints to unfold. ISRO later reported that boom deployment began August 9 and proceeded over five days before the reflector opened. NASA announced on August 28 that the spacecraft and payload had passed preliminary checks and that orbit raising had begun two days earlier toward the operational mean altitude of 747 kilometers.

The next problem was measurement quality. In its November 28 account, ISRO said the S-band radar had begun acquiring images on August 19\. Teams used corner reflectors around Ahmedabad and elsewhere in India, as well as observations of Amazon forests, to calibrate imagery and spacecraft pointing. They adjusted acquisition settings using those comparisons. The first S-band image covered the Godavari River Delta, resolving different vegetation and land-use classes.

Calibration mattered because apparent change in a measurement can come from the observing system as well as the surface being observed. A radar product intended to support infrastructure or land-management decisions needs a defensible relationship between the signal and the ground. Deployment demonstrated that the antenna could operate; calibration addressed whether users could interpret what it received.

The 2025 milestones thus built on one another. Launch delivered the equipment. Unfolding established its observing geometry. Checkout and calibration began turning returns from Earth into useful evidence. The mission's enduring promise rested on repeating that last task reliably, across many landscapes and successive passes.

## Sources

- [NASA-ISRO Satellite Lifts Off to Track Earth’s Changing Surfaces](https://www.nasa.gov/news-release/nasa-isro-satellite-lifts-off-to-track-earths-changing-surfaces/?ref=pvweekly.com) — NASA · 2025-07-30.
- [NASA-ISRO Mission Aces Checkouts, on Track to Start Delivering Science](https://science.nasa.gov/blogs/nisar/2025/08/28/nasa-isro-mission-aces-checkouts-on-track-to-start-delivering-science/?ref=pvweekly.com) — NASA · 2025-08-28.
- [NISAR Mission enters Science Phase](https://www.isro.gov.in/NISAR%5FMission%5FScience%5FPhase.html?ref=pvweekly.com) — ISRO · 2025-11-28.