NASA-ISRO Synthetic Aperture Radar (NISAR)

Background

NISAR is a joint mission between NASA and the Indian Space Research Organisation (ISRO). NISAR, or the NASA-ISRO Synthetic Aperture Radar, is an Earth observation mission that uses L-band and S-band synthetic aperture radars (SAR) to perform high-resolution, all-weather, and day-and-night imaging of Earth's surface to monitor and analyze environmental changes. NISAR observes the Earth's land and ice-covered surfaces every 12 days on ascending and descending passes, providing a global view of changes over time.

Problem

NISAR required both (1) developing a detailed design for the mission, and (2) executing the mission in operations. CLASP was used in both of these efforts.

In formulation, various aspects of the NISAR mission were informed through analysis including sizing of the onboard solid state recorder. Sizing the onboard solid state recorder was difficult as the recorder needed to be modelled at a high fidelity to account for its file-based data storage, data priority policy, and downlink policy. This level of fidelity was needed due to the variable cadence and high volume of data collected by NISAR on a regular basis (tens of Tb per day).

In operations, observation schedules and downlink schedules need to be created that balance:

1. 1. The science goals of the mission
2. 2. Operational constraints of the radars
3. 3. Geometric constraints needed for SAR interferometry
4. 4. Downlink capability of ground station networks

Downlinks need to be scheduled for communication with both the Near Space Network (NSN) and the ISRO Telemetry Tracking and Command Network (ISTRAC).

In addition to meeting the above scheduling constraints, the NISAR mission planning tools were designed to be operations-facing such that they support features such as:

• - Modifying existing science campaigns to reflect changing science priorities
• - Using explainable scheduling algorithms that inform the science team as to why coverage may not have been achieved in certain locations to the given constraints
• - Providing bounds on the runtime of the schedulers so that they can be quickly used during operations

Technology

1. 1. Observation Scheduling (CLASP): For science observation scheduling, we use the Coverage-aware Large Scale Activity Scheduler/Planner (CLASP) to schedule observations for over 50 science campaigns. CLASP uses an iterative greedy scheduling algorithm to schedule observations of target areas. CLASP enables encoding complex campaign prioritization schemes to determine the areas observed and the instrument modes used to observe those areas.
2. 2. Data Volume Modeling (SSR Model): Within CLASP, we implemented a high-resolution model of the onboard solid state recorder. Given an observation schedule and downlink schedule, the model identifies cases where the onboard storage would overflow. The model simulates:
   1.     a. A discrete file-based data storage policy of the SSR, where files are retained onboard in full until downlinked in their entirety
   2.     b. A file prioritization policy
   3.     c. Downlinking of files to specific or both ground station networks (NSN and ISTRAC)

Impact

NISAR mission planning tools, in particular CLASP, have been an essential part of the entire mission lifecycle, from helping design the NISAR mission by performing tradeoff studies to scheduling observations and downlinks during operations.

As of March 31st, 2026, within the first three months of usage after launch, the NISAR mission planning tools (including CLASP) have been used to take over 120,000 observations across over 50 different science campaigns.

Status

Since 2009, NISAR mission planning tools have been used to inform the mission design. These tools were later augmented to be used during operations in addition to mission design.

The NISAR satellite was launched July 30th, 2025.

By December 2025, NISAR commissioning was completed and NISAR transitioned to its primary science mission. From this point onwards, NISAR mission planning tools, including CLASP, have been used to schedule observations and downlinks.

Publications

Team

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

- Joshua Doubleday
- Ian Roundhill
- Tom Moline
- Christopher Wells
- Gavin Brisebois
- Caleb Wagner