IRS-P5 (CARTOSAT-1)

IRS-P5, better known as Cartosat-1, is an Earth observation satellite developed and launched by the Indian Space Research Organisation (ISRO). Catalogued under NORAD ID 28649 and carrying the international designator 2005-017A, the spacecraft was placed into a Sun-synchronous orbit on 4 May 2005 and remains operational in that orbit today. It represents a significant milestone in India's civil remote sensing program, being the first satellite in the Cartosat series and the eleventh member of the broader Indian Remote Sensing Satellite (IRS) family. Its primary purpose is high-resolution stereoscopic imaging of the Earth's surface, with an emphasis on cartographic and mapping applications across the Indian subcontinent and beyond.

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Mission and Purpose

Cartosat-1 was designed with a specific and well-defined mandate: to provide precise, large-scale cartographic data suitable for topographic mapping, infrastructure planning, and land-use assessment. Unlike earlier IRS satellites that were primarily oriented toward multispectral resource monitoring, Cartosat-1 introduced stereoscopic imaging capability to India's Earth observation fleet. Stereoscopy — the acquisition of paired images of the same ground area from slightly different viewing angles — allows analysts to derive accurate three-dimensional surface models. These elevation models are foundational to tasks such as contour mapping, road and railway planning, watershed delineation, and urban development surveys.

The satellite carries two panchromatic cameras oriented at different angles along the spacecraft's flight path, one looking slightly forward and the other slightly aft. This arrangement means that as the satellite passes over a target area, both cameras capture the scene within a short time of each other, producing the stereo pair needed for elevation extraction. The resulting data have been applied extensively in producing and updating the national topographic map series of India, as well as in international mapping projects.

Operational oversight of the satellite's data services is provided in conjunction with the National Technical Research Organisation (NTRO), reflecting the satellite's importance not only to civilian cartographic agencies but also to national-level geospatial intelligence requirements. Data products derived from Cartosat-1 imagery have been distributed to a wide range of users, including national and state government agencies, academic institutions, and international partners through ISRO's data dissemination frameworks.

The mission also contributed to disaster management and response efforts. Detailed elevation models and high-resolution imagery from Cartosat-1 have assisted in flood plain mapping, coastal zone monitoring, and post-disaster damage assessment. Although the satellite's catalog entry does not specify a current mission status in the tracking database, the spacecraft has demonstrated well beyond its original design expectations in terms of operational longevity.

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Orbit and Tracking

Cartosat-1 occupies a Sun-synchronous orbit (SSO), a specialized near-polar orbital regime in which the satellite's orbital plane precesses at a rate that keeps it synchronized with the apparent motion of the Sun. This configuration ensures that the satellite passes over any given location at roughly the same local solar time on each revisit. Consistent solar illumination angles are critically important for imaging satellites because they make it possible to compare images taken on different dates without the confounding variable of dramatically different shadow lengths or lighting geometries.

The spacecraft's current tracked orbital parameters place its apogee at 601 km and its perigee at 597 km above Earth's surface, describing a nearly circular orbit with very little eccentricity. This tight apogee-perigee spread — a difference of only 4 km — is characteristic of a well-maintained, operationally refined orbit for an Earth observation platform, where consistency of ground resolution and swath geometry is important.

The orbit has an inclination of 97.5°, which is the slightly retrograde tilt required to achieve Sun-synchronous precession at this altitude. At this inclination, the satellite's ground track covers all latitudes between roughly 97.5° north and south of the equator — in practical terms, providing global coverage including polar and high-latitude regions, though imaging missions typically focus on mid-latitude and tropical zones. The orbital period is approximately 96.5 minutes, meaning the satellite completes just under fifteen full orbits of the Earth every day, building up a repeating ground-track pattern that enables systematic global coverage over a cycle of days.

The satellite is tracked continuously by the global network of radar and optical sensors that feed into the US Space Surveillance Network and affiliated international systems. Its NORAD catalog number, 28649, is the unique numerical identifier used to distinguish this object from all other tracked artificial Earth satellites and debris. Real-time and predictive tracking data, including precise pass times over specific geographic locations, are available through this catalog and are updated routinely as new observations refine the orbital elements.

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Design and Operator

Cartosat-1 was designed, built, and launched entirely by the Indian Space Research Organisation, headquartered in Bengaluru, India. ISRO developed the satellite under its IRS program, which has been the backbone of India's operational remote sensing capability since the late 1980s. The IRS constellation has grown substantially over the decades and encompasses satellites optimized for a range of applications, from agricultural monitoring and ocean color observation to high-resolution land imaging. Cartosat-1, as the eleventh IRS satellite, represented a natural progression toward finer spatial resolution and three-dimensional data products.

The spacecraft's launch mass was approximately 1,560 kg, reflecting a mid-sized Earth observation platform. It was launched aboard one of ISRO's Polar Satellite Launch Vehicles (PSLV), the workhorse rocket that has orbited the majority of India's remote sensing spacecraft. The PSLV's reliability and precision in deploying payloads into Sun-synchronous orbits made it the natural choice for Cartosat-1.

In terms of its physical configuration, Cartosat-1 follows the general architecture typical of IRS-series satellites, incorporating a three-axis stabilized platform that keeps the imaging cameras pointed consistently at the Earth's surface. Solar panels provide electrical power, and the onboard systems manage thermal regulation, attitude control, and data handling. The dual-camera stereo imaging system is the central payload, and the data are transmitted to ground stations where they are processed into standard cartographic products.

It should be noted that specific figures for the spacecraft's mass as currently recorded in the satellite catalog for this object are listed as unknown; the commonly cited launch mass figure of approximately 1,560 kg is drawn from ISRO program documentation rather than from the verified tracking catalog entry.

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Significance and Legacy

Cartosat-1 occupies a historically important position in India's space program. As the inaugural member of the Cartosat series, it established the design heritage and operational philosophy that subsequent Cartosat satellites have built upon. The series has since expanded to include satellites with substantially higher resolutions and more advanced imaging geometries, but Cartosat-1 provided the foundation — both technically and institutionally — for that growth.

Beyond its domestic contributions, the satellite helped demonstrate to the international remote sensing community that ISRO was capable of producing operationally robust, high-quality imaging spacecraft. The cartographic products derived from its imagery met internationally recognized accuracy standards for topographic mapping, lending credibility to India's position as a provider of geospatial data products on the world market.

The satellite's longevity in orbit is itself notable. Having launched in May 2005 and remaining in orbit as of the time of this writing, the spacecraft has far exceeded the service life typical of satellites of its generation. Whether it continues to return usable scientific or operational data is not confirmed in the publicly available tracking catalog, which lists its mission status as unknown. Nevertheless, the structural and orbital persistence of the spacecraft is a testament to the engineering standards applied during its construction.

The Cartosat program Cartosat-1 initiated has continued with multiple follow-on missions, progressively refining stereo imaging capabilities, improving ground resolution, and expanding the range of applications. This lineage traces directly back to the design decisions and operational lessons accumulated during Cartosat-1's active years.

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How to Spot It

Cartosat-1 orbits at an altitude between 597 and 601 km with an inclination of 97.5° and an orbital period of 96.5 minutes, which means it passes over most inhabited latitudes multiple times per day. However, like most Earth observation satellites of its size and design, it is not among the brightest objects visible to the naked eye. Its visibility on any given pass depends on a combination of factors: the satellite must be in sunlight while the observer on the ground is in twilight or darkness, and the geometry of the pass — specifically how high above the horizon it rises — determines how long it is potentially visible and how bright it appears.

Passes that carry Cartosat-1 high overhead (near zenith) and occur during the first hour or two after local sunset, or before local sunrise, offer the best prospects for naked-eye observation under dark sky conditions. The satellite will appear as a steadily moving point of light with no blinking, traversing the sky in a roughly south-to-north or north-to-south direction consistent with its polar orbit. Using the real-time tracking tools available on this site with NORAD ID 28649 will provide precise pass predictions for any location on Earth, including rise and set times, maximum elevation, and apparent brightness estimates.