INSAT-3D

INSAT-3D is an Indian geostationary satellite operated by the Indian Space Research Organisation (ISRO) that serves meteorological observation, data relay, and satellite-aided search and rescue functions over the Indian subcontinent and surrounding regions. Launched in July 2013 aboard an Ariane 5 ECA rocket from the Guiana Space Centre in French Guiana, the spacecraft represents a significant step forward in India's indigenous weather satellite capabilities. It is catalogued by the United States Space Force under NORAD ID 39216 and carries the international designator 2013-038B, indicating it was the second tracked object released from the 38th launch of 2013.

Mission and Purpose

The primary role of INSAT-3D is to provide continuous meteorological imaging of the Earth's surface and atmosphere, supporting weather forecasting, climate monitoring, and disaster warning services across South Asia and the broader Indian Ocean region. Satellites of this type collect data across multiple spectral bands, enabling forecasters to track cloud systems, sea surface temperatures, vegetation health, and atmospheric water vapor in near-real time. This capability is particularly valuable for a country like India, which faces recurring high-impact weather events including tropical cyclones forming over the Bay of Bengal and the Arabian Sea, seasonal monsoon variability, and flooding episodes that can affect hundreds of millions of people.

Beyond weather imaging, INSAT-3D is equipped to function as a data relay platform. This means it can receive transmissions from unattended ground-based instruments — such as automatic weather stations, river-gauge sensors, and ocean buoys — and forward that data to processing centers, greatly extending the geographic reach of India's environmental monitoring network without the need for dedicated terrestrial communications links to each individual sensor.

The satellite also carries a search and rescue transponder, making it part of the international COSPAS-SARSAT network. In this role, it can pick up distress signals from emergency beacons activated by aircraft, maritime vessels, or individuals in remote terrain and relay those alerts to ground stations, where they are forwarded to rescue coordination authorities. This capability has practical life-saving consequences across the vast Indian Ocean region, where maritime and aviation incidents can occur far from land-based detection infrastructure.

INSAT-3D incorporates several notable onboard technology features. Among these are a star sensor for precise attitude determination, and a micro-stepping Solar Array Drive Assembly — a mechanism that positions the solar panels to face the sun while deliberately minimizing vibrations transmitted to the spacecraft body. This is important for a meteorological satellite because even slight mechanical disturbances can degrade the resolution and geometric accuracy of images. The satellite also includes a Bus Management Unit that handles overall platform control functions as well as telemetry and telecommand processing. Image motion compensation and mirror motion compensation systems are incorporated to further improve the quality of meteorological imagery, and the satellite is designed to perform bi-annual rotation maneuvers to optimize sensor performance over time.

Orbit and Tracking

INSAT-3D occupies a geostationary orbit, meaning it travels at an altitude and speed that keeps it effectively stationary relative to a fixed point on Earth's surface. This characteristic is fundamental to its mission: a weather imaging satellite must stare continuously at the same geographic area to track the evolution of weather systems over time, something only a geostationary orbit makes possible.

According to current tracking data, the satellite has an apogee of 35,799 km and a perigee of 35,791 km, indicating an orbit that is very nearly circular, as is expected for an operational geostationary spacecraft. The orbital period is 1,436.1 minutes — almost exactly one sidereal day — which is what enables the satellite to maintain its fixed apparent position over the equator. The inclination of the orbital plane is 1.9°, a slight deviation from a true equatorial orbit. Perfectly geostationary satellites maintain zero inclination, but over time perturbations from the Moon's and Sun's gravity cause inclination to drift. The small inclination figure observed for INSAT-3D means it traces a very small figure-eight pattern, known as an analemma, over its nominal sub-satellite point as seen from the ground. This is characteristic of operational geostationary satellites that are being actively maintained through station-keeping maneuvers, though the precise extent of ongoing station-keeping activities is not detailed in publicly available catalog data.

INSAT-3D was assigned NORAD catalog number 39216 and is tracked continuously by the United States Space Surveillance Network. It remains in orbit as of the most recently available data, with no reentry or decay event on record.

Design and Operator

INSAT-3D was developed by the Indian Space Research Organisation, the primary space agency of India, which operates under the Department of Space and reports to the Government of India. ISRO has managed the INSAT series of multipurpose geostationary satellites since the 1980s, using them to serve telecommunications, meteorology, and broadcasting needs across the country. The 3D designation places the satellite within a later generation of the INSAT-3 subseries, which also includes other platforms with specialized remote sensing and communications roles.

The spacecraft's manufacturer is not recorded in the publicly available satellite catalog data. The satellite's mass is similarly not listed in the catalog entry used here and is therefore not stated. INSAT-3D was delivered to orbit by an Ariane 5 ECA launch vehicle, one of the most capable heavy-lift rockets available at the time, operated by Arianespace from the Guiana Space Centre in Kourou, French Guiana. The use of a European commercial launch vehicle for this Indian government satellite reflects a common practice among space agencies of contracting launch services internationally when domestic vehicles do not yet provide the required lift capacity to geostationary transfer orbit at the mass required.

The launch took place on July 24, 2013 (in Universal Coordinated Time terms, with local Eastern Daylight Time placing the event on the evening of that date). Following launch, the satellite would have undergone an apogee kick and a series of orbit-raising maneuvers to transfer from the geostationary transfer orbit in which it was initially placed to its operational geostationary slot.

Significance and Current Status

INSAT-3D marked an advancement in India's self-reliant approach to operational meteorology from space. By developing the satellite domestically through ISRO, India gained greater control over the design, capability, and scheduling of its weather observation infrastructure rather than depending entirely on foreign spacecraft or data-sharing agreements. The improvements incorporated into INSAT-3D — particularly the vibration-reduction mechanisms and image compensation systems — addressed lessons from earlier Indian meteorological satellites and allowed the platform to deliver higher-quality data products to the India Meteorological Department and other users.

The satellite's search and rescue capability places India as a contributing member of the global COSPAS-SARSAT system, reinforcing regional coordination in maritime and aviation emergency response across the Indian Ocean, a waterway of immense commercial and humanitarian importance.

INSAT-3D remains in orbit and has been supplemented over the years by subsequent satellites in India's geostationary weather constellation, including INSAT-3DR, which was launched in 2016 and carries a broadly similar payload suite. The operation of multiple satellites in this role provides redundancy and allows for broader or more frequent coverage of the region. The specific current operational status of INSAT-3D — whether it continues to return science data, has been placed in a storage mode, or has been retired from primary operations — is not confirmed in the catalog data available here.

How to Spot It

As a geostationary satellite, INSAT-3D is not realistically observable with the naked eye under normal circumstances, and it is not a target typically tracked for visual observing purposes. Geostationary objects sit at an altitude of approximately 35,800 km, which is roughly 100 times higher than low Earth orbit satellites such as the International Space Station. At that distance, even a large spacecraft reflects only an extremely faint amount of sunlight. Dedicated amateur astronomers equipped with motorized telescopes can, under suitable conditions, observe geostationary satellites as faint stationary points of light against a moving star field, but this requires significant equipment and technique.

Because its inclination is only 1.9° and its orbit is nearly perfectly circular, INSAT-3D remains essentially fixed over a single longitude on the equator as seen from the ground. Observers at fixed locations in India or the broader Indian Ocean region can therefore point a sufficiently powerful optical instrument at the satellite's known sky position and observe it without the satellite drifting significantly. For most users of this tracking page, however, the satellite's orbital data is of primary relevance for understanding its ground coverage and communications geometry rather than for planning visual observations.