Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
1999-10-01
2001-06-05
Poon, Peter M. (Department: 3643)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
C244S164000
Reexamination Certificate
active
06241192
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to an earth observation system for observing the earth by operating a plurality of observation satellites. More particularly, the present invention is concerned with an earth observation system for operating the observation satellites ordinarily in a steady observation operation mode for observing globally the earth over the whole surface thereof while operating the satellites in a high-frequency observation operation mode for observing a given or particular district or local area on the earth with an increased observation frequency when occasion requires. Furthermore, the invention concerns a structure of the observation satellite, a sensor system for earth observation, an observation satellite operating ground system, and a data receiving system for the earth observation system. Moreover, the present invention also relates to an earth observation method and a program for allowing the observation method to be executed with the aid of a computer.
In the conventional earth observation system known heretofore, a single observation satellite is operated on and along a predetermined sun-synchronized quasi-recurrent orbit, wherein the number of days of a recurring period of the orbit, i.e., the number of days taken for the observation satellite to be able to observe again a same spot on the earth, is constant. The frequency of observation for a single given spot on the earth is in a range of once per several days to once per several weeks.
Thus, with the conventional earth observation system in which one observation satellite is operated on and along the predetermined orbit, it is certainly possible to observe globally and substantially uniformly the earth over the whole surface thereof. However, realization of the recursive observation of a given area or district on the earth will take a time interval as long as several days or several weeks. Thus, with the conventional observation satellite, it is impossible to effectuate a high-frequency observation of a given or particular district on the earth by maneuvering the satellite in a high-frequency observation operation mode which is of course favorable for observing a phenomenon, event or the like such as, for example, disaster occurring at a given or particular district on the earth.
Furthermore, even with the observation satellite equipped with an orbit control facility, correction of the orbit is possible only in conjunction with either the sun-synchronized quasi-recurrent orbit or the sun-synchronized recurrent orbit. To say in another way, any approaches or attempts for operating the satellite through combination of the sun-synchronized quasi-recurrent orbit and the sun-synchronized recurrent orbit have not yet been reported.
SUMMARY OF THE INVENTION
In the light of the state of the art described above, it is an object of the present invention to provide an earth observation system which makes it possible to operate the observation satellite selectively not only on and along the recurrent orbit but also on the quasi-recurrent orbit through orbit transfer, for thereby allowing the observation satellite to be operated in a steady observation operation mode for observing globally and substantially uniformly the earth over the whole surface thereof or in a high-frequency observation operation mode for observing concentratively a given or particular district with an enhanced observation frequency as occasion requires, in contrast to the conventional earth observation system where only one predetermined operation orbit is made available for each satellite.
In view of the above and other objects which will become apparent as the description proceeds, the earth observation system taught by the present invention includes a plurality of observation satellites each imparted with an orbit transfer facility, wherein in a steady observation operation mode, the observation satellites are operated on the quasi-recurrent orbits, respectively, while when a high-frequency observation operation mode in which observation for a given or particular district on the earth is performed at an increased frequency becomes necessary as occasion requires, appropriate ones of the observation satellites are transferred to the recurrent orbits for operation of the satellites on these recurrent orbits, respectively. Further, the present invention teaches that in the steady observation operation mode, the observation satellites are operated on and along sun-synchronized quasi-recurrent orbits (described in detail later on) while in the high-frequency observation operation mode for observation of a particular district or area on the earth, the observation satellites are operated on and along sun-synchronized recurrent orbits (also described in detail later on), by realizing the transfer of the satellites between the two types of orbits mentioned above through maneuver incurring less energy consumption.
Thus, according to a general aspect of the present invention, there is provided an earth observation system which includes a plurality of observation satellites each equipped with an orbit transfer facility, and an observation satellite operating ground system for performing control for maintaining orbits for the observation satellites, respectively, or for changing or transferring the orbits for the observation satellites, wherein in a steady observation operation mode, the observation satellites are operated on a plurality of quasi-recurrent orbits, respectively, for performing observation of the earth, while when a high-frequency observation operation mode where observation for a particular district on the earth is carried out at an increased frequency is required, appropriate ones of the observation satellites are transferred to recurrent orbits so that the particular district can be observed with the transferred observation satellites at an increased frequency, and wherein when the high-frequency observation operation mode becomes no more necessary, the satellites transferred to the recurrent orbits are again transferred back to the original quasi-recurrent orbits, respectively.
In a mode for carrying out the invention, it is preferred that in the steady observation operation mode of the earth observation system described above, the plurality of observation satellites are constellated for operation on a plurality of sun-synchronized quasi-recurrent orbits, respectively, which have a same altitude and a same inclination and which differ from one another in respect to the right ascension of ascending node, while in the high-frequency observation operation mode, the given observation satellites are transferred, respectively, to a plurality of sun-synchronized recurrent orbits each having a nominal altitude of 561 km and a nominal inclination of 97.6 degrees or alternatively to a plurality of sun-synchronized recurrent orbits each having a nominal altitude of 888.3 km and a nominal inclination of 98.9 degrees, to thereby operate all of the observation satellites transferred to the sun-synchronized recurrent orbits with such constellation that the particular district on the earth can be observed with all of the orbit-transferred observation satellites.
In another mode for carrying out the invention, it is preferred that in the earth observation system described above, each of the observation satellites is equipped with an earth observation sensor, wherein with regard to the operational orbits of the observation satellites in the steady observation operation mode, values of altitude and inclination of the operational orbits are, respectively, in proximity to values of altitude and inclination of the observation orbits in the high-frequency observation operation mode for observing a particular district on the earth, and wherein the observation sensor has an appropriate swath width so that global observation of the earth over the whole surface thereof can be carried out in the steady observation operation mode within a number of days of a recurring period or within a number of revolutions in a recurri
Hamano Nobuo
Kondo Hideji
Matsumura Hiroshi
Hitachi , Ltd.
Jakel Kevin
Poon Peter M.
Sofer & Haroun LLP
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