MIDORI II (ADEOS-II)

MIDORI II, formally designated ADEOS-II (Advanced Earth Observing Satellite II), is a Japanese Earth observation satellite built to continue and expand on a remote-sensing program begun in the mid-1990s. Catalogued by NORAD under ID 27597 and carrying the international designator 2002-056A, the spacecraft was launched on 13 December 2002 and placed into a near-circular sun-synchronous orbit approximately 800 kilometres above Earth. Although its operational life proved shorter than planned, it represented one of the most ambitious Earth observation endeavors undertaken by Japan's space program at the time, and it remains catalogued as still in orbit.

Mission and Purpose

ADEOS-II was conceived as the follow-on to Japan's first Advanced Earth Observing Satellite, a mission flown in 1996 that itself ended prematurely due to power system problems. The successor was designed to pick up where that earlier effort left off, providing comprehensive, long-term observations of Earth's environment — particularly the oceans, atmosphere, and land surface — with an emphasis on understanding large-scale climate dynamics and the global water and energy cycles.

The satellite carried a suite of instruments intended to monitor sea-surface winds, ocean color, vegetation cover, and atmospheric composition, among other parameters. These measurements were relevant not only to climate science but also to practical applications such as fisheries management, agricultural monitoring, and disaster preparedness. Because understanding Earth's environment requires a globally coordinated effort, the mission was undertaken as a collaboration: Japan's National Space Development Agency (NASDA) led the project, with contributions from NASA and the French space agency CNES, each of which provided scientific instruments for the payload.

The broader ambition of the mission was to build a long-term, continuous dataset of Earth observations that could be compared against data from previous satellites and used to track environmental change over time. In this sense, ADEOS-II was as much about scientific continuity as it was about any single measurement — researchers needed reliable, repeated observations over years and decades to detect meaningful trends in climate variables.

Tragically, the satellite's operational phase was cut short. In October 2003, less than a year after launch, the spacecraft's solar panels failed catastrophically, leaving the satellite without the power needed to operate its instruments or maintain communications. The mission effectively ended at that point, with the satellite falling silent well before the multi-year data record its designers had envisioned could be established.

Orbit and Tracking

MIDORI II occupies a sun-synchronous orbit (SSO), a type of near-polar orbit engineered so that the satellite's orbital plane precesses at a rate that keeps it roughly aligned with the direction of the Sun throughout the year. This means the satellite passes over any given point on Earth at approximately the same local solar time on each successive orbit — a property that is extremely valuable for Earth observation, because consistent illumination conditions make it much easier to compare images and measurements taken on different days or different seasons.

The spacecraft's current tracked orbital parameters reflect a nearly circular trajectory: the apogee stands at 800 km and the perigee at 797 km, giving a nearly negligible eccentricity. This near-perfect circularity is characteristic of well-maintained observation orbits and ensures that the satellite maintains a consistent altitude and ground-track geometry over its operational area. The orbital inclination is 98.8°, which is slightly retrograde relative to Earth's rotation — a defining feature of sun-synchronous orbits, which must be tilted slightly past 90° to achieve the necessary nodal precession.

With an orbital period of 100.7 minutes, the satellite completes roughly 14 full circuits of the globe per day. Over successive orbits, the ground track shifts westward slightly with each pass, allowing the satellite to build up near-complete global coverage over a period of several days. This repeat-coverage geometry was essential to the satellite's Earth observation mission, enabling systematic mapping of large regions rather than opportunistic snapshots.

Although the mission ended in 2003 when power was lost, the physical spacecraft continues to orbit. At an altitude of approximately 800 km, atmospheric drag is extremely low, and uncontrolled objects at this height can remain in orbit for very long periods without decaying. The satellite is tracked by ground-based surveillance networks and remains listed in the catalog as an intact, orbiting payload object.

Design and Operator

MIDORI II was designed and manufactured by Mitsubishi Electric, one of Japan's leading aerospace contractors, under contract to NASDA. At launch, the spacecraft had a mass of 3,680 kg, making it a large, sophisticated platform by the standards of Earth observation satellites. This mass reflected both the substantial bus structure required to support a multi-instrument payload and the large solar arrays needed to power the instruments and spacecraft systems.

The satellite was operated by the National Space Development Agency of Japan, the government body responsible at the time for Japan's civilian space activities. NASDA was later merged with other Japanese space organizations to form JAXA (Japan Aerospace Exploration Agency) in 2003, meaning that the final months of MIDORI II's operational life coincided with the transition to the successor agency.

The spacecraft's design drew on experience gained from the first ADEOS mission, with engineers working to address power system vulnerabilities that had cut that earlier satellite's life short. Despite these efforts, the solar array failure that ended MIDORI II's mission in October 2003 echoed the fate of its predecessor in an unfortunate pattern. The failure mode — loss of solar panel integrity — highlighted the challenges of building large, deployable power structures capable of surviving the thermal cycling, radiation, and micrometeorite environment of low Earth orbit over extended periods.

Because the mission ended prematurely, certain catalog fields for MIDORI II — including specific details about mission objectives as recorded in the tracking database — are listed as unknown, reflecting the incomplete operational record left behind by the early termination.

Legacy and Current Status

Despite its short operational life, MIDORI II made meaningful contributions to Earth science during the roughly ten months it functioned. The instruments aboard the satellite gathered data on ocean surface conditions, atmospheric water vapor, and vegetation dynamics that were used in peer-reviewed research and contributed to the international scientific community's understanding of environmental processes. Even a partial dataset, when of high quality and well-characterized, can be scientifically valuable — particularly when it overlaps with measurements from other satellites, enabling cross-calibration and validation studies.

The satellite also reinforced important lessons for the spacecraft engineering community about solar array reliability and the risks of complex deployed structures in the space environment. The back-to-back failures of ADEOS-I and ADEOS-II prompted serious examination of design practices and contributed to more conservative and robust approaches in subsequent Japanese and international Earth observation programs.

The lineage of Earth observation that ADEOS-II represented continued in other programs. Japan went on to develop further Earth-observing platforms, and the international partnerships pioneered by NASDA with NASA and CNES helped establish models for collaborative space science that remain influential today. In this sense, MIDORI II's significance extends beyond the data it collected: it was part of the institutional and technical learning process that shaped modern Earth observation infrastructure.

As of the most recent tracking data, the satellite's orbital shell — at roughly 800 km altitude with an inclination of 98.8° — remains populated by the spacecraft's physical remains. The object continues to be catalogued and tracked as part of the broader space situational awareness effort. No reentry date has been determined, and the object is expected to remain in orbit for the foreseeable future, gradually subject to the very slow orbital decay that affects all low Earth orbit objects over time.

Observability

At approximately 800 km altitude with a relatively high inclination of 98.8°, MIDORI II has a wide observational footprint and can, in principle, pass over most inhabited latitudes at various times throughout the day. However, as a non-operational satellite that no longer carries active orientation control, its orientation in space is unknown, and the amount of sunlight it reflects at any given moment is unpredictable. Large spacecraft components — particularly the remains of its substantial solar arrays — can produce visible glints under the right geometry, but no reliable brightness predictions are available for this object. Observers interested in attempting a visual sighting should consult the live orbital data available on this page for current pass predictions, bearing in mind that visibility will be highly variable and is not guaranteed.