TOI explains: How Nisar was built - why it'll take 90 days before any data comes in

NEW DELHI: The India-US Earth observation satellite , Nasa-Isro Synthetic Aperture Radar (Nisar), is set for launch on July 30 from Isro’s spaceport in Sriharikota aboard the GSLV-F16 rocket. But the mission’s real work begins after it enters orbit. Over the next several weeks, the satellite will go through a carefully sequenced set of actions before it starts sending data. In all, Nisar will need at least 90 days to enter its “science phase”.

How Nisar was built

Before we get to what happens after launch, here's how the satellite came together: Nisar is the result of nearly a decade of collaboration between Isro and Nasa. Over 8–10 years, both agencies separately developed and tested key systems, which were then brought together into one observatory.

The core radar payload was built in parts — Isro developed the S-band synthetic aperture radar (SAR), and Nasa’s Jet Propulsion Laboratory (JPL) built the L-band SAR. These were integrated into a shared structure called the Integrated Radar Instrument Structure (IRIS).

Assembly of IRIS and other payload elements took place at JPL. The structure was then shipped to Isro, which had in parallel developed the satellite’s mainframe at the UR Rao Satellite Centre (URSC) in Bengaluru. Isro then carried out the final assembly, integration and testing of the complete satellite.

And now that the satellite is ready for launch, let’s look at what will happen in the starting Wednesday:

Phase 1: Launch

At 5.40pm on Wednesday (July 30), the GSLV-F16 rocket will place the 2.8-tonne satellite into a Sun-synchronous polar orbit. This means the satellite will pass over the same part of Earth at roughly the same local solar time every day — ideal for tracking changes on the surface.

Phase 2: Deployment (Post-launch Days 10-18)

Nisar carries a massive 12-metre-wide mesh reflector, which acts as a radar antenna. Since it is too large to launch fully open, it will be folded and stowed during launch and then deployed in space using a complex multistage boom system.

The process begins on the 10th day from launch — “Mission Day 10” which becomes “Deploy Day 1”. Here’s how the deployment unfolds: On Deploy Day 1 (DD-1), engineers initiate pre-deployment checks and unlock six ‘launch restraints’ that keep the system secure during launch.

Two more restraints are released, and the first hinge (called the ‘wrist hinge’) is activated on DD-2. This starts the unfolding motion of the boom.

On DD-3, the shoulder hinge is extended, swinging the boom further outward and on DD-4, the elbow hinge opens, continuing the arm-like movement. The root hinge is deployed on DD-5, bringing the boom to full extension, and on DD-6, a pause is built into the schedule to allow for analysis and verification of earlier steps.

And, DD-7 will be a buffer or ‘margin’ day in case any delays or issues need to be addressed. Once this is through, on DD-8, the satellite performs a ‘yaw manoeuvre’ (rotation) to correctly orient itself, and then finally opens the circular radar reflector. This slow, deliberate sequence ensures the delicate boom and antenna unfold without damage or misalignment, and paves the way for the next phase.

Phase 3: Commissioning

After deployment and until the 90th day from launch, all systems are checked and calibrated. This includes the satellite’s mainframe, radar electronics, and onboard instruments developed by both Isro and JPL.

Phase 4: Science Ops

Once fully operational, Nisar will begin capturing data across both L-band and S-band frequencies. The satellite will observe ground movement, ice sheets, forests and land use — feeding data to researchers worldwide. Regular manoeuvres will keep it in position, and a pre-coordinated observation plan will guide its workload until the end of its mission life.