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.

The story began around 2007, when NASA actively began 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. Greenland and Antarctica, whose disappearing ice sheets have been linked to the global average increase in sea-levels over the years, would be among the vulnerable hotspots to come under surveillance. 

Traditional remote sensing satellites are limited in their need for sunlit conditions and clear skies for imaging. 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)

Mutual benefits

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. 

NASA and ISRO share expertise

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.

Then NASA administrator Charles Bolden (left), and ISRO chairman K. Radhakrishnan (right), signed documents which included a charter on NISAR, in Toronto | Photo Credit: NASA

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 few hours.

• MIT physicists perform the most idealized double-slit experiment to date, using individual atoms as slits.
• Experiment confirms the quantum duality of light: light behaves as both a particle and a wave, but both behaviors can’t be observed simultaneously.
• Findings disprove Albert Einstein’s century-old prediction regarding detecting a photon’s path alongside its wave nature.

In a study published in Physical Reviews Letters on July 22, researchers at MIT have realized an idealized version of the famous double-slit experiment in quantum physics yet.

The double-slit experiment—first devised in 1801 by the British physicist Thomas Young—remains a perplexing aspect of reality. Light waves passing through two slits, form interference patterns on a wall placed behind. But this phenomenon is at odds with the fact light also behaves as particles. The contradiction has lent itself to a paradox, which sits at the foundation of quantum mechanics. It has sparked a historic scientific duel nearly a century ago, between physics heavyweights Albert Einstein and Niels Bohr. The study’s findings have now settled the decades-old debate, showing Einstein’s predictions were off the mark.

Einstein had suggested that by detecting the force exerted when a photon passes through a slit—a nudge akin to a bird brushing past a leaf—scientists could witness both light’s wave and particle properties at once. Bohr countered with the argument that observing a photon’s path would inevitably erase its wave-like interference pattern, a tenet since embraced by quantum theory.

The MIT team stripped the experiment to its purest quantum elements. Using arrays of ultracold atoms as their slits and weak light beams to ensure only one photon scattered per atom, they tuned the quantum states of each atom to control the information gained about a photon’s journey. Every increase in “which-path” information reduced the visibility of the light’s interference pattern, flawlessly matching quantum theory and further debunking Einstein’s proposal.

“Einstein and Bohr would have never thought that this is possible, to perform such an experiment with single atoms and single photons,” study senior author and Nobel laureate, Wolfgang Ketterle, stated in a press release. “What we have done is an idealized Gedanken (thought) experiment.”

In a particularly stunning twist, Ketterle’s group also disproved the necessity of a physical “spring”—a fixture in Einstein’s original analogy—by holding their atomic lattice not with springs, but with light. When they briefly released the atoms, effectively making the slits “float” in space, the same quantum results persisted. “In many descriptions, the springs play a major role. But we show, no, the springs do not matter here; what matters is only the fuzziness of the atoms,” commented MIT researcher Vitaly Fedoseev in a media statement. “Therefore, one has to use a more profound description, which uses quantum correlations between photons and atoms.”

The paper arrives as the world prepares for 2025’s International Year of Quantum Science and Technology — marking 100 years since the birth of quantum mechanics. Yoo Kyung Lee, a fellow co-author, noted in a media statement, “It’s a wonderful coincidence that we could help clarify this historic controversy in the same year we celebrate quantum physics.”

A team of MIT scientists has developed a theory-guided strategy to directly measure an elusive quantum property in semiconductors — the electron-phonon interaction — using an often-ignored effect in neutron scattering.

Their approach, published this week in Materials Today Physics, reinterprets an interference effect, typically considered a nuisance in experiments, as a valuable signal. This enables researchers to probe electron-phonon interactions — a key factor influencing a material’s thermal, electrical, and optical behaviour — which until now have been extremely difficult to measure directly.

“Rather than discovering new spectroscopy techniques by pure accident, we can use theory to justify and inform the design of our experiments and our physical equipment,” said Mingda Li, senior author and associate professor at MIT, in a media statement.

By engineering the interference between nuclear and magnetic interactions during neutron scattering, the team demonstrated that the resulting signal is directly proportional to the electron-phonon coupling strength.

“Being able to directly measure the electron-phonon interaction opens the door to many new possibilities,” said MIT graduate student Artittaya Boonkird.

While the current setup produced a weak signal, the findings lay the groundwork for next-generation experiments at more powerful facilities like Oak Ridge National Laboratory’s proposed Second Target Station. The team sees this as a shift in materials science — using theoretical insights to unlock previously “invisible” properties for a range of advanced technologies, from quantum computing to medical devices.