1
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
FORMATION FLIGHT CONTROL DEVICE, OBSERVATION SATELLITE,
GROUND STATION, FORMATION FLIGHT SYSTEM, SAND OBSERVATION
SYSTEM, FORMATION FLIGHT CONTROL METHOD, AND PROGRAM;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
Title of Invention
FORMATION FLIGHT CONTROL DEVICE, OBSERVATION SATELLITE,
GROUND STATION, FORMATION FLIGHT SYSTEM, SAND OBSERVATION
SYSTEM, FORMATION FLIGHT CONTROL METHOD, 5 AND PROGRAM
Technical Field
[0001] The present disclosure relates to a formation flight control device, an
observation satellite, a ground station, a formation flight system, a sand observation
10 system, a formation flight control method, and a program.
Background Art
[0002] Example means for observing a wide area of the ground surface of a
celestial body and imaging the area includes a synthetic-aperture radar (SAR) that is
mounted on, for example, an aircraft or an artificial satellite and generates an observation
15 image of the ground surface through microwave communication. An increase in the
resolution of a SAR reduces the received power per pixel, thus lowering the
signal-to-noise ratio (SNR) of observation images. Although the SNR may be improved
by increasing the transmission power, a machine depending on the power generated by a
solar battery, such as an artificial satellite, cannot easily have greatly increased
20 transmission power.
[0003] Patent Literature 1 describes a technique with which synthetic-aperture
radars mounted on multiple artificial satellites observe one target from different angles of
incidence, and the resultant frequency spectra are synthesized to equivalently widen the
transmission frequency band for raising the resolution of observation images in
25 proportion to the increased bandwidth.
Citation List
Patent Literature
3
[0004] Patent Literature 1: Unexamined Japanese Patent Application Publication
No. 2000-235074
Summary of Invention
Technical Problem
[0005] The technique in Patent Literature 1 for virtually widening 5 a frequency band
can increase resolution without reducing the received power per pixel. However, the
signal-to-noise ratio of observation images is difficult to improve.
[0006] In response to the above issue, an objective of the present disclosure is to
improve the signal-to-noise ratio of observation images.
10 Solution to Problem
[0007] To achieve the above objective, a formation flight control device according
to an aspect of the present disclosure is a device for generating and outputting orbit
control information for controlling observation satellites in an observation satellite group
orbiting a celestial body and sequentially observing a ground surface of the celestial body
15 with an observation interval. The formation flight control device includes orbit
information acquisition means, orbit control information generation means, and orbit
control information. The orbit information acquisition means acquires orbit information
indicating an observation time of a preceding observation satellite of which an
observation order precedes by one, and an orbit of the preceding observation satellite at
20 the observation time. The orbit control information generation means generates, based
on the orbit information, the orbit control information indicating an orbit and a phase
allowing flying, after the observation interval, vertically above an intersection point
between the ground surface and a straight line connecting a center of the celestial body
and the preceding observation satellite at the observation time. The orbit control
25 information output means outputs the orbit control information.
Advantageous Effects of Invention
[0008] The formation flight control device according to the above aspect of the
4
present disclosure generates and outputs the orbit control information indicating an orbit
and a phase allowing flying, after the observation interval, vertically above an
intersection point between the ground surface and a straight line connecting a center of
the celestial body and the preceding observation satellite at the observation time. Thus,
the formation flight control device according to the present disclosure 5 enables all the
observation satellites in the observation satellite group to observe the same observation
region at the same observation angle and improves the signal-to-noise ratio of the
observation image.
Brief Description of Drawings
10 [0009] FIG. 1 is a block diagram of a formation flight system according to
Embodiment 1 of the present disclosure;
FIG. 2 is a diagram describing the orbits of multiple observation satellites in an
observation satellite group;
FIG. 3 is a diagram showing an observation satellite observing a celestial body
15 with a synthetic-aperture radar;
FIG. 4 is a diagram showing the observation geometry of observation satellites;
FIG. 5 is a functional block diagram of an observation satellite;
FIG. 6 is a diagram describing parameters included in orbital elements;
FIG. 7 is a hardware block diagram of a formation flight control device;
20 FIG. 8 is a flowchart of an orbit control information generation process;
FIG. 9 is a diagram describing the orbits of multiple observation satellites in an
observation satellite group according to Embodiment 2 of the present disclosure;
FIG. 10 is a block diagram of a formation flight system according to Embodiment
3 of the present disclosure;
25 FIG. 11 is a functional block diagram of a ground station;
FIG. 12 is a functional block diagram of an observation satellite;
FIG. 13 is a diagram describing a scheme of communication between observation
5
satellites and between the observation satellites and a ground station according to
Embodiment 4 of the present disclosure;
FIG. 14 is a diagram describing another scheme of communication between the
observation satellites and between the observation satellites and the ground station;
FIG. 15 is a block diagram of a sand observation system according 5 to Embodiment
5 of the present disclosure;
FIG. 16 is a block diagram of a sand observation system according to Embodiment
6 of the present disclosure;
FIG. 17 is a functional block diagram of a 3D terrain estimator;
10 FIG. 18 is a diagram showing a composite image and a real terrain;
FIG. 19 is a schematic diagram showing a model in which a terrain estimator has
recognized a cone;
FIG. 20 is a diagram showing a composite image and a real terrain; and
FIG. 21 is a schematic diagram showing a model in which a terrain estimator has
15 recognized a cone.
Description of Embodiments
[0010] Embodiments of the present disclosure will now be described in detail with
reference to the drawings.
[0011] Embodiment 1
20 As shown in FIG. 1, a formation flight system 1 according to Embodiment 1 of the
present disclosure includes an observation satellite group 200G of N (which is a natural
number of at least two) observation satellites 200-1, 200-2, 200-3, ..., and 200-N each
having a synthetic-aperture radar, and a ground station 100 that communicates with the
observation satellite group 200G. The N observation satellites 200-1, 200-2, 200-3, ...,
25 and 200-N may be referred to as the observation satellites 200 without distinguishing the
individual observation satellites. The ground station 100 and the observation satellite
group 200G are connected to allow wireless communication in accordance with a satellite
6
communication protocol, and adjacent observation satellites 200 in the observation
satellite group 200G are also connected in the same manner.
[0012] The ground station 100 communicates with the observation satellites 200
included in the observation satellite group 200G. In the present embodiment, the
ground station 100 transmits observation instruction information for 5 observation to the
observation satellite 200-1 in the observation satellite group 200G, and receives, from the
observation satellite 200-N, observation information indicating observations and
sequentially updated and transferred by the observation satellites 200 in the observation
satellite group 200G. The observation instruction information and the observation
10 information will be described later.
[0013] The observation satellite group 200G includes the N adjacent observation
satellites 200 arranged in the order of the observation satellites 200-1, 200-2, 200-3, ...,
and 200-N and flying in different orbits with a fixed space between adjacent satellites.
Each observation satellite 200 includes a formation flight control device 210 that
15 generates orbit control information based on observation information acquired from the
preceding observation satellite denoted by 200F.
[0014] As shown in FIG. 2, the observation satellites 200 are artificial satellites for
observing the ground surface state of a celestial body 5 that is an observation target while
orbiting the celestial body 5. The observation satellites 200-1, 200-2, 200-3, ..., and
20 200-N fly sequentially in different orbits with a fixed space between adjacent satellites.
More specifically, the observation satellites 200-1, 200-2, 200-3, ..., and 200-N move in
polar orbits PO-1, PO-2, PO-3, ..., and PO-N that cross the axis of rotation AR and pass
above or through the vicinity of the north pole and the south pole of the celestial body 5.
The N polar orbits PO-1, PO-2, PO-3, ..., and PO-N may be referred to as the polar orbits
25 PO without distinguishing the individual polar orbits. An observation satellite 200 to be
described will be referred to as a target observation satellite 200S. The observation
satellite 200 that is followed by the target observation satellite 200S in a flying order and
7
an observation order will be referred to as a preceding observation satellite 200F. The
observation satellite 200 that follows the target observation satellite 200S in a flying order
and an observation order will be referred to as a succeeding observation satellite 200B.
For example, in FIG. 2, when the observation satellite 200-2 is the target observation
satellite 200S, the observation satellite 200-1 is the preceding observation 5 satellite 200F,
and the observation satellite 200-3 is the succeeding observation satellite 200B.
[0015] As shown in FIG. 3, each observation satellite 200 having a
synthetic-aperture radar observes the ground surface state of the celestial body 5 by
emitting a microwave obliquely downward to the ground surface of the celestial body 5 at
10 an angle of incidence θ0 and receiving a wave reflected from the radio wave irradiation
region irradiated with the microwave, denoted by RD. The celestial body 5 is
specifically a satellite or a planet such as the Earth, Mars, or the Moon. The direction
from the center of the celestial body 5 to the center of the radio wave irradiation region
RD is indicated by a vertical direction DV, and the direction of the incident microwave
15 emitted from the observation satellite 200 is denoted by DI. The angle between the
vertical direction DV and the direction DI is the angle of incidence θ0.
[0016] The observation geometry in the present embodiment will now be described
with reference to FIG. 4. For example, as shown in FIG. 4, the observation satellite
200-1 moves in the polar orbit PO-1 around the celestial body 5, and the observation
20 satellite 200-2 moves in the polar orbit PO-2 around the celestial body 5. At the
observation time of the observation satellite 200-1, a straight line SL1 connecting the
observation satellite 200-1 and the center of the celestial body 5 intersects the ground
surface at an observation ground surface point PG. The observation ground surface
point PG moves with the rotation of the celestial body 5. The observation satellite
25 200-2 undergoes orbit control performed by the formation flight control device 210 and
an orbit controller 230 included in the observation satellite 200-2 to cause a straight line
SL2 connecting the succeeding observation satellite 200-2 and the center of the celestial
8
body 5 to intersect the ground surface at the observation ground surface point PG when
an observation interval elapses from the observation time of the observation satellite
200-1 preceding the observation satellite 200-2. The time when the observation interval
elapses from the observation time of the preceding observation satellite 200F may be
simply referred to as the time after the observation 5 interval.
[0017] The functional components of the observation satellite 200 will now be
described. As shown in FIG. 5, the observation satellite 200 includes an orbit
information acquirer 211, an orbit control information generator 212, and an orbit control
information outputter 213 that are included in the formation flight control device 210, a
10 receiver 220, the orbit controller 230, a posture controller 240, an observer 250, an
observation image analyzer 260, and a transmitter 270.
[0018] The orbit information acquirer 211 acquires, based on the observation
information acquired from the preceding observation satellite 200F through the receiver
220, observation region information, observation angle information, observation interval
15 information, observation time information indicating the observation time of the
preceding observation satellite 200F, and orbit information about the preceding
observation satellite 200F at the observation time of the preceding observation satellite
200F, and feeds the acquired information to the orbit control information generator 212.
The orbit information acquirer 211 is an example of orbit information acquisition means
20 in an aspect of the present disclosure.
[0019] The orbit control information generator 212 uses the various information
items acquired from the orbit information acquirer 211 to generate orbit control
information indicating the orbit and the phase in which the target observation satellite
200S flies, when the observation interval elapses from the observation time of the
25 preceding observation satellite 200F, vertically above the intersection point between the
ground surface of the celestial body 5 and the straight line connecting the center of the
celestial body 5 and the preceding observation satellite 200F at the observation time of
9
the preceding observation satellite 200F. The orbit control information generator 212
feeds the generated orbit control information to the orbit control information outputter
213. The orbit control information generator 212 is an example of orbit control
information generation means in an aspect of the present disclosure.
[0020] The orbit control information outputter 213 outputs 5 the orbit control
information acquired from the orbit control information generator 212 to the orbit
controller 230. The orbit control information outputter 213 is an example of orbit
control information output means in an aspect of the present disclosure.
[0021] The receiver 220 may be implemented by a receiving antenna that receives a
10 radio signal and a reception circuit that performs a reception process such as
analog-digital conversion, demodulation, or decoding on the received radio signal. The
receiver 220 receives the observation instruction information transmitted from the ground
station 100 or the observation information transmitted from the preceding observation
satellite 200F, and subjects the received observation instruction information and
15 observation information to the reception process before outputting the information.
When receiving observation instruction information transmitted from the ground station
100, that is, observation instruction information to be transmitted to the observation
satellite 200-1 of which a flying order and an observation order are the earliest, the
receiver 220 feeds the observation instruction information to the components other than
20 the formation flight control device 210. The receiver 220 is an example of reception
means in an aspect of the present disclosure.
[0022] The observation instruction information includes, for example, observation
region information, observation angle information, and observation interval information.
The observation region information indicates an observation region that is an observation
25 target. Based on the observation region information, each observation satellite 200 uses
the synthetic-aperture radar to emit a microwave to the observation region. The
observation angle information indicates an observation angle to the observation region.
10
The observation angle is specifically the angle of the microwave incident on the
observation region. The observation satellite 200 uses the synthetic-aperture radar to
emit the microwave to the observation region at the angle of incidence indicated by the
observation angle information. The observation interval information indicates intervals
of time at which the observation satellites 200 observe the observation 5 region. More
specifically, the observation interval information indicates the time from when the
preceding observation satellite 200F observes the observation region to when the target
observation satellite 200S observes the same observation region.
[0023] The observation information includes the above observation instruction
10 information, the observation time of each observation satellite 200, the orbit information
about the observation satellite 200 at the observation time, and a composite image. The
orbit information is expressed by, for example, orbital elements indicating the orbit and
the movement of the observation satellite 200. The orbital elements include parameters
such as a semi-major axis (a), an eccentricity (e), an orbital inclination (i), the right
15 ascension of the ascending node Ω, an argument of periapsis ω, and a time of periapsis
passage T.
[0024] As shown in FIG. 6, with the observation satellite 200 in an orbit O that is
elliptical, the semi-major axis, a, is half of the major axis of the orbit O. The
eccentricity, e, is a parameter that defines the absolute shape of the orbit O and a measure
20 of the flattening of the orbit O. The orbit O becomes more circular with decreasing
eccentricity, e, and more elliptical with increasing eccentricity. The eccentricity, e, is
defined by e = √(1 − (b/a)2), where b denotes the semi-minor axis, or half of the minor
axis of the orbit O.
[0025] The orbital inclination, i, is the angle formed by the equatorial plane of the
25 celestial body 5 and the orbital plane. The right ascension of the ascending node Ω is
the longitude of the ascending node where the orbit O crosses the equatorial plane of the
celestial body 5 from south to north, and a measure of rotation of the ascending node in
11
the rotational direction of the celestial body 5 from a reference position represented by
the vernal point. The argument of periapsis ω is, as viewed from the center of gravity of
the celestial body 5, the angle formed by the ascending node and the periapsis, or the
position at which the orbit O is nearest the center of gravity of the celestial body 5, and
measured in the rotational direction of the celestial body 5 from the 5 ascending node.
The time of periapsis passage T is the time when the celestial body 5 passes through the
periapsis.
[0026] The composite image is produced by sequentially subjecting observation
images acquired by the observation satellites 200 included in the observation satellite
10 group 200G to pixel integration.
[0027] The orbit controller 230 controls the orbit of the observation satellite 200
based on the observation instruction information received from the receiver 220 or the
orbit control information received from the orbit control information outputter 213 in the
formation flight control device 210. For example, the orbit controller 230 controls the
15 orbit of the target observation satellite 200S by causing the thrusters to inject a propellant
for thrust production in accordance with the orbit control information. Upon completion
of the orbit control for the target observation satellite 200S, the orbit controller 230
outputs an orbit control completion signal for indicating the completion to the observer
250. The orbit controller 230 is an example of orbit control means in an aspect of the
20 present disclosure.
[0028] The posture controller 240 controls the posture of the observation satellite
200 based on the observation instruction information or the observation information
acquired through the receiver 220. More specifically, the posture controller 240
calculates the relative posture of the preceding observation satellite 200F to the celestial
25 body 5 at the observation time of the preceding observation satellite 200F based on (the
observation time information about the preceding observation satellite 200F extracted
from) the observation information acquired from the preceding observation satellite 200F.
12
The posture controller 240 then controls the reaction wheel, the control moment
gyroscope (CMG), and the thrusters to control the posture of the target observation
satellite 200S, allowing the target observation satellite 200S to have the same relative
posture as the calculated relative posture after the observation interval. Upon
completion of the posture control for the target observation satellite 5 200S, the posture
controller 240 outputs a posture control completion signal for indicating the completion
to the observer 250. The posture controller 240 is an example of posture control means
in an aspect of the present disclosure.
[0029] The observer 250 is implemented by, for example, a synthetic-aperture radar
10 and observes an observation region on the celestial body 5. After the observer 250
receives the orbit control completion signal from the orbit controller 230 and the posture
control completion signal from the posture controller 240, and when the observation
interval elapses from the observation time of the preceding observation satellite 200F, the
observer 250 emits a microwave to a target region and receives the resultant reflected
15 wave to generate an observation image representing the state of the observation region.
The observer 250 outputs the generated observation image to the observation image
analyzer 260. The observer 250 is an example of observation means in an aspect of the
present disclosure.
[0030] The observation image analyzer 260 integrates the pixels of the composite
20 image generated by the preceding observation satellite 200F and included in the
observation information acquired from the preceding observation satellite 200F and the
observation image generated by the observer 250 to generate a new composite image.
The observation image analyzer 260 outputs the generated composite image to the
transmitter 270. The observation image analyzer 260 is an example of observation
25 image analysis means in an aspect of the present disclosure.
[0031] The transmitter 270 may be implemented by a reception circuit and a
transmitting antenna that transmits a radio signal. The reception circuit performs a
13
transmission process such as encoding, modulation, or digital-analog conversion on the
composite image received from the observation image analyzer 260, the observation time
of the target observation satellite 200S, the orbit information about the target observation
satellite 200S at the observation time, and the observation instruction information
received from the receiver 220. The transmitter 270 subjects the composite 5 image, the
observation time, the orbit information, and the observation instruction information to the
transmission process before transmitting the resultant information to the ground station
100 or the succeeding observation satellite 200B as observation information. The
transmitter 270 is an example of transmission means in an aspect of the present
10 disclosure.
[0032] The hardware configuration of the formation flight control device 210 will
now be described. As shown in FIG. 7, the formation flight control device 210 includes,
as its physical units, a processor 214, a read-only memory (ROM) 215, a random-access
memory (RAM) 216, an auxiliary storage device 217, an input device 218, and an output
15 device 219. The units are electrically connected with one another with a bus line BL.
[0033] The processor 214 is an arithmetic unit such as a central processing unit
(CPU). The processor 214 reads a program and data from the ROM 215 or the auxiliary
storage device 217 onto the RAM 216 and executes the program and data to implement
various functions of the formation flight control device 210.
20 [0034] The ROM 215 is a non-volatile memory for storing programs to be executed
by the processor 214 and data used in the program execution. For example, the ROM
215 stores programs and data associated with an orbit control information generation
process described later.
[0035] The RAM 216 is a volatile memory for temporarily holding a program and
25 data read from the ROM 215 and the auxiliary storage device 217, and serves as a work
area for the processor 214.
[0036] The auxiliary storage device 217 is a non-volatile storage device such as a
14
hard disk drive (HDD) or a solid state drive (SSD) that allows overwriting of stored
content. For example, the auxiliary storage device 217 stores programs to be executed
by the processor 214, data used in the program execution, and data generated from the
program execution.
[0037] The input device 218 is an input interface that allows various 5 information
items to be input from the outside to the formation flight control device 210. For
example, the observation information received by the receiver 220 is input.
[0038] The output device 219 is an output interface that allows various information
items to be output from the formation flight control device 210. For example, the orbit
10 control information is output to the orbit controller 230.
[0039] The orbit information acquirer 211 shown in FIG. 5 is implemented by, for
example, the processor 214, the ROM 215, the RAM 216, and the input device 218.
The orbit control information generator 212 is implemented by, for example, the
processor 214, the ROM 215, and the RAM 216. The orbit control information
15 outputter 213 is implemented by, for example, the output device 219.
[0040] The orbit control information generation process performed by the orbit
control information generator 212 in the formation flight control device 210 will now be
described with reference to the flowchart shown in FIG. 8. The orbit control
information generation process uses the observation information from the preceding
20 observation satellite 200F to generate orbit control information that allows the
observation region observed by the preceding observation satellite 200F to be observed at
the same observation angle. When receiving the observation information on the
preceding observation satellite 200F from the receiver 220, the orbit control information
generator 212 starts the orbit control information generation process.
25 [0041] After starting the orbit control information generation process, the orbit
control information generator 212 first acquires the observation interval information, the
observation time information about the preceding observation satellite 200F, and the orbit
15
information about the preceding observation satellite 200F at the observation time based
on the observation information on the preceding observation satellite 200F acquired
through the input device 218 (step S101).
[0042] The orbit control information generator 212 then calculates the orientation
of the celestial body 5 relative to the preceding observation satellite 5 200F at the
observation time of the preceding observation satellite 200F (step S102). For example,
the orbit control information generator 212 may indicate the orientation of the celestial
body 5 at the observation time of the preceding observation satellite 200F based on a
fixed coordinate system such as the horizontal coordinate system or the equatorial
10 coordinate system. When the celestial body 5 to be observed is the Earth, the
orientation of the celestial body 5 can be expressed in terms of longitude and latitude.
[0043] The orbit control information generator 212 then calculates the position
taken by an observation ground surface point PG at the observation time of the preceding
observation satellite 200F (step S103). The orbit control information generator 212
15 determines the observation ground surface point PG as the intersection point between the
ground surface and the straight line SL1 connecting the center of the celestial body 5 and
the preceding observation satellite 200F at the observation time of the preceding
observation satellite 200F, and calculates the position of the observation ground surface
point PG (see FIG. 3).
20 [0044] The orbit control information generator 212 then calculates the position of
the observation ground surface point PG after the observation interval (step S104). The
orbit control information generator 212 determines the observation ground surface point
PG as the intersection point between the ground surface and the straight line SL2
connecting the center of the celestial body 5 and the target observation satellite 200S after
25 the observation interval, and calculates the position of the observation ground surface
point PG (see FIG. 4).
[0045] The orbit control information generator 212 then calculates the target orbit
16
and the transfer orbit of the target observation satellite 200S (step S105). The target
orbit of the target observation satellite 200S is an orbit in which, after the observation
interval, the target observation satellite 200S passes vertically above the observation
ground surface point PG calculated in step S104. Calculating the target orbit involves a
degree of freedom in the altitude of the target observation satellite 200S 5 vertically above
the observation ground surface point PG. The altitude of the target observation satellite
200S in the target orbit may be, for example, the altitude at which the target observation
satellite 200S is currently flying, the altitude at which the preceding observation satellite
200F passes vertically above the observation ground surface point PG, or the altitude
10 input from an external device such as the ground station 100. The velocity vector in the
target orbit may be the relative velocity vector of the preceding observation satellite 200F
passing vertically above the observation ground surface point PG, relative to the celestial
body 5.
[0046] The orbit control information generator 212 then calculates the transfer orbit
15 of the target observation satellite 200S from the current orbit to the target orbit. For
example, the orbit control information generator 212 uses particle swarm optimization
(PSO), an optimization technique for searching developed based on swarm behavior of
animals, to calculate the transfer orbit that minimizes the amount of propellant used..
[0047] After performing the processing in step S105, the orbit control information
20 generator 212 generates orbit control information indicating the target orbit and the
transfer orbit, feeds the generated orbit control information to the orbit control
information outputter 213 (step S106), and ends the orbit control information generation
process.
[0048] As described above, the formation flight control device 210 according to the
25 present embodiment calculates the position of the observation ground surface point PG at
the observation time of the preceding observation satellite 200F and the position of the
observation ground surface point PG after the observation interval, and generates the
17
orbit control information indicating the target orbit and the transfer orbit that allow the
target observation satellite 200S after the observation interval to pass vertically above the
observation ground surface point PG after the observation interval. The orbit of the
target observation satellite 200S is controlled based on the generated orbit control
information. This orbit control enables all the observation satellites 5 200 in the
observation satellite group 200G to observe the same observation region at the same
observation angle. The observation images acquired by the observation satellites 200
are sequentially subjected to pixel integration to generate a composite image, enabling the
observation image to have an improved signal-to-noise ratio.
10 [0049] Embodiment 2
In Embodiment 1, as described above, the observation satellites 200 included in the
observation satellite group 200G fly in the polar orbits PO that pass above or through in
the vicinity of the north pole and the south pole of the celestial body 5. However, polar
regions of the celestial body 5 may not be observed in some actual operations. In
15 Embodiment 2, observation satellites 200 move in non-polar orbits passing off the polar
regions of the celestial body 5. To avoid redundancy, the differences from Embodiment
1 will now be mainly described.
[0050] In the present embodiment, as shown in FIG. 9, the observation satellites
200-1, 200-2, ..., and 200-N move in non-polar orbits NPO-1, NPO-2, ..., and NPO-N
20 that do not cross the axis of rotation AR of the celestial body 5 or do not pass above or
through the vicinity of the north pole and the south pole.
[0051] Thus, the formation flight system 1 according to Embodiment 2 also enables
all the observation satellites 200 included in the observation satellite group 200G to
observe the same observation region at the same observation angle and improves the
25 signal-to-noise ratio of the composite image produced by sequentially subjecting
observation images acquired by the observation satellites 200 to pixel integration. The
formation flight system 1 according to the present embodiment is specifically effective
18
for an observation target that is a low-latitude region.
[0052] Embodiment 3
In Embodiments 1 and 2, as described above, the ground station 100 transmits
observation instruction information to the observation satellite 200-1 of which a flying
order and an observation order are the earliest in the observation satellite 5 group 200G,
and receives, from the observation satellite 200-N of which a flying order and an
observation order are the latest, observation information sequentially updated and
transferred by the observation satellites 200 in the observation satellite group 200G. In
Embodiment 3, however, each of the observation satellites 200 in the observation satellite
10 group 200G communicates with the ground station 100. The differences from
Embodiments 1 and 2 will now be mainly described.
[0053] As shown in FIG. 10, the formation flight system 1 according to
Embodiment 3 includes the ground station 100 that communicates with each of the
observation satellites 200 in the observation satellite group 200G, and the observation
15 satellite group 200G of the N observation satellites 200-1, 200-2, 200-3, ..., and 200-N
that observe an observation region indicated based on observation instruction information
received from the ground station 100 and transmit observation information including an
observation image to the ground station 100.
[0054] In the formation flight system 1 according to Embodiment 3, unlike
20 Embodiments 1 and 2, the ground station 100 includes a formation flight control device
110, whereas each of the observation satellites 200 in the observation satellite group
200G includes no formation flight control device 210, as shown in FIG. 11.
[0055] As shown in FIG. 11, the ground station 100 according to Embodiment 3
includes, as its functional units, an orbit information acquirer 111, an orbit control
25 information generator 112, and an orbit control information outputter 113 that are
included in the formation flight control device 110, a ground transmitter 120, a ground
receiver 130, an observation image storage 140, and an observation image analyzer 150.
19
[0056] The orbit information acquirer 111 acquires, from an external source,
observation region information, observation angle information, observation interval
information, observation time information indicating the observation time of the
preceding observation satellite 200F, and orbit information about the preceding
observation satellite 200F at the observation time of the preceding observation 5 satellite
200F, and feeds the acquired information to the orbit control information generator 112.
[0057] The orbit control information generator 112 uses the various information
items acquired from the orbit information acquirer 111 to generate orbit control
information indicating the orbit and the phase in which, after the observation interval, the
10 target observation satellite 200S flies vertically above the intersection point between the
ground surface of the celestial body 5 and the straight line connecting the center of the
celestial body 5 and the preceding observation satellite 200F at the observation time of
the preceding observation satellite 200F. The orbit control information generator 112
feeds the generated orbit control information to the orbit control information outputter
15 113 together with the various information items acquired from the orbit information
acquirer 111.
[0058] The orbit control information outputter 213 outputs various information
items including the orbit control information acquired from the orbit control information
generator 212 to the ground transmitter 120.
20 [0059] The ground transmitter 120 transmits the orbit control information received
from the orbit control information outputter 213, and the observation region information,
the observation angle information, and the observation interval information acquired by
the orbit information acquirer 111 to each observation satellite 200 as observation
instruction information. The ground transmitter 120 is an example of ground
25 transmission means in an aspect of the present disclosure.
[0060] The ground receiver 130 receives observation information transmitted from
the observation satellite 200 when the observation instruction information is transmitted
20
from the ground transmitter 120. The observation information includes an observation
image acquired by the observation satellite 200 that has received the observation
instruction information. The ground receiver 130 feeds the observation information
received from the observation satellite 200 to the observation image storage 140.
[0061] The observation image storage 140 stores the observation 5 image included in
the observation information acquired from the ground receiver 130, and feeds the
observation image to the observation image analyzer 150.
[0062] The observation image analyzer 150 sequentially subjects observation
images of the same observation region acquired from the observation image storage 140
10 to pixel integration to generate a composite image.
[0063] As shown in FIG. 12, each observation satellite 200 according to
Embodiment 3 includes, as its functional units, a receiver 220, an orbit controller 230, a
posture controller 240, an observer 250, and a transmitter 270.
[0064] The receiver 220 receives observation instruction information transmitted
15 from the ground station 100 and feeds the received observation instruction information to
each component.
[0065] The orbit controller 230 controls the orbit of the target observation satellite
200S by, for example, causing the thrusters to inject a propellant for thrust production
based on the orbit control information included in the observation instruction information
20 acquired from the receiver 220. Upon completion of the orbit control for the target
observation satellite 200S, the orbit controller 230 outputs an orbit control completion
signal to the observer 250.
[0066] The posture controller 240 calculates the relative posture of the preceding
observation satellite 200F to the celestial body 5 at the observation time of the preceding
25 observation satellite 200F based on the observation instruction information. The posture
controller 240 then controls the posture of the target observation satellite 200S, allowing
the target observation satellite 200S to have the same relative posture as the calculated
21
relative posture after the observation interval. Upon completion of the posture control
for the target observation satellite 200S, the posture controller 240 outputs a posture
control completion signal to the observer 250.
[0067] After the observer 250 receives the orbit control completion signal from the
orbit controller 230 and the posture control completion signal from the 5 posture controller
240, and after the observation interval, the observer 250 emits a microwave to an
observation region on the celestial body 5 and receives the resultant reflected wave to
generate an observation image representing the state of the observation region. The
observer 250 outputs the generated observation image to the transmitter 270.
10 [0068] The transmitter 270 may be implemented by a reception circuit and a
transmitting antenna that transmits a radio signal. The reception circuit performs a
transmission process such as encoding, modulation, or digital-analog conversion on the
observation image received from the observer 250 and the observation instruction
information received from the receiver 220. The transmitter 270 subjects the
15 observation image and the observation instruction information to the transmission process
before transmitting the resultant information to the ground station 100 as observation
information.
[0069] As described above, in the formation flight system 1 according to
Embodiment 3, unlike Embodiments 1 and 2, the ground station 100 includes the
20 formation flight control device 110 and transmits observation instruction information
including orbit control information to each of the observation satellites 200. The ground
station 100 receives observation information transmitted from the observation satellite
200 in response to the observation instruction information, and sequentially subjects the
observation images included in the observation information to pixel integration to
25 generate a composite image. Thus, the formation flight system 1 according to
Embodiment 3 also enables all the observation satellites 200 included in the observation
satellite group 200G to observe the same observation region at the same observation
22
angle, and thus improves the signal-to-noise ratio of the composite image produced by
sequentially subjecting observation images acquired by the ground station 100 to pixel
integration.
[0070] Embodiment 4
In Embodiments 1 to 3, observation instruction information 5 and observation
information are communicated directly between the ground station 100 and the
observation satellites 200 or between the observation satellites 200. However, the
information may be communicated through a relay.
[0071] As shown in FIG. 13, a formation flight system 1 according to Embodiment
10 4 includes a geostationary relay satellite 300 that revolves around the celestial body 5 in
the period in which the celestial body 5 rotates on its axis, and relays data
communications between a ground station 100 and observation satellites 200 or between
the observation satellites 200. The formation flight system 1 according to Embodiment
4 allows observation information to be communicated through the geostationary relay
15 satellite 300 for, for example, satellites that are too far away from each other to
communicate, like the observation satellite 200-1 and the observation satellite 200-2
shown in FIG. 13.
[0072] As shown in FIG. 14, the observation satellite 200-1 and the observation
satellite 200-2 may communicate data to each other via one or more ground stations 100
20 installed on the celestial body 5.
[0073] The formation flight system 1 according to Embodiment 4 also enables all
the observation satellites 200 included in the observation satellite group 200G to observe
the same observation region at the same observation angle, and thus improves the
signal-to-noise ratio of the composite image produced by sequentially subjecting
25 observation images to pixel integration.
[0074] Embodiment 5
The formation flight system 1 according to Embodiments 1 to 4 may be used in a
23
sand observation system that observes the state of sand over a ground surface of the
celestial body 5.
[0075] As shown in FIG. 15, a sand observation system 2 according to
Embodiment 5 includes the formation flight system 1 according to Embodiments 1 to 4, a
change detector 410, a ground-surface information storage 420, and an 5 output interface
430.
[0076] The ground-surface information storage 420 may store ground-surface
information including, for example, an observation image of the ground surface and
numerical data associated with a position on the ground surface. The ground-surface
10 information storage 420 is an example of ground-surface information storage means in an
aspect of the present disclosure. In the present embodiment described below, the
ground-surface information is a composite image produced by the formation flight
system 1.
[0077] The formation flight system 1 feeds, to the change detector 410, a composite
15 image subjected to pixel integration with the method according to any of Embodiments 1
to 4. The change detector 410 extracts, from the ground-surface information storage
420, a previous composite image produced by observing the same region as the
composite image acquired from the formation flight system 1. The change detector 410
compares the composite image acquired from the formation flight system 1 with the
20 composite image extracted from the ground-surface information storage 420 to detect the
difference, and feeds the change to the output interface 430. The composite image
acquired from the formation flight system 1 is stored into the ground-surface information
storage 420. The change detector 410 is an example of change detection means in an
aspect of the present disclosure.
25 [0078] The sand observation system 2 according to Embodiment 5 also enables all
the observation satellites 200 included in the observation satellite group 200G to observe
the same observation region at the same observation angle, and thus improves the
24
signal-to-noise ratio of the composite image produced by sequentially subjecting
observation images to pixel integration.
[0079] Embodiment 6
A sand observation system 2 for estimating the shape of a sandhill on the celestial
body 5 will now be described. As shown in FIG. 16, the sand observation 5 system 2
according to Embodiment 6 includes the formation flight system 1 according to
Embodiments 1 to 4, an input interface 510, a composite image storage 520, an image
referrer 530, a 3D terrain estimator 540, a soil information determiner 550, a soil
information storage 560, and an output interface 570.
10 [0080] Estimation target information specifying a sandhill to be estimated is
acquired through the input interface 510. A sandhill may be specified using any method
through the input interface 510. A method of specifying a sandhill may be, for example,
a way of displaying a map and specifying a figure or a rectangle including the figure on
the map as a target region, or a way of specifying a target region by longitude and latitude.
15 The input interface 510 feeds the estimation target information indicating a target region
to the image referrer 530 and the soil information determiner 550.
[0081] The formation flight system 1 stores a composite image subjected to pixel
integration with the method according to any of Embodiments 1 to 4 into the composite
image storage 520. The image referrer 530 extracts, from the composite image storage
20 520, a composite image including the estimation target region indicated by the estimation
target information acquired through the input interface 510, and feeds the extracted
composite image to the 3D terrain estimator 540. The composite image is assumed to
include radio wave emission direction information indicating the direction in which a
radio wave such as a microwave is emitted, or the observation direction of each
25 observation satellite 200 including a synthetic-aperture radar. The composite image
storage 520 is an example of composite image storage means in an aspect of the present
disclosure. The image referrer 530 is an example of image reference means in an aspect
25
of the present disclosure.
[0082] The soil information determiner 550 extracts, from soil information stored in
the soil information storage 560, soil information about the estimation target sandhill
indicated by the estimation target information fed from the input interface 510, and feeds
the extracted soil information to the 3D terrain estimator 540. The 5 soil information
storage 560 may prestore overall soil information over the celestial body 5 or acquire soil
information as appropriate through the Internet. Example soil information indicates that
the soil of a sandhill is sand or gravel.
[0083] The 3D terrain estimator 540 uses the composite image, the radio wave
10 incident direction information, and the soil information to generate 3D terrain estimation
information indicating the estimation results of the estimation target 3D terrain acquired
by processing the composite image, and feeds the generated information to the output
interface 570. The 3D terrain estimator 540 is an example of 3D terrain estimation
means in an aspect of the present disclosure.
15 [0084] As shown in FIG. 17, the 3D terrain estimator 540 includes, for example, a
terrain determiner 541, a hill height estimator 542, and a terrain estimator 543.
[0085] Based on the light and shade indicated by pixel values in the composite
image acquired from the image referrer 530 and the radio wave emission direction
information included in the composite image, the terrain determiner 541 determines that
20 the light and shade in the composite image are caused by a conical hill. The terrain
determiner 541 locally holds a 3D terrain model formed of, for example, a plane, a cone,
and a light emission direction, and automatically represents the composite image acquired
from the image referrer 530 as the 3D terrain model. The terrain determiner 541 may
model the shape of a hill not only as a cone but also as a quadrangular pyramid to more
25 precisely determine the shape that causes the light and shade in the composite image.
The radio wave emission direction information that can be generated automatically from
the composite image may not be included in the composite image.
26
[0086] When determining that light and shade in the composite image are caused
by a hill, the terrain determiner 541 calculates a cone radius R based on the size of the
conical area forming the light and shade, and feeds the calculated value to the hill height
estimator 542. The hill height estimator 542 calculates a cone height H based on the
cone radius R acquired from the terrain determiner 541 and the 5 angle of repose θR
depending on the soil type indicated by the soil information about the estimation target,
and feeds the calculated value to the terrain estimator 543. The angle of repose θR is the
maximum angle formed by the horizontal plane and the slope of a sandhill at which the
sandhill can be maintained without slumping, and depends on, for example, the grain size
10 and the grain shape. The terrain determiner 541 further feeds coordinate information
including the cone radius R and the coordinates of the bottom center of the cone to the
terrain estimator 543.
[0087] The terrain estimator 543 estimates the conical terrain based on the various
information items acquired from the terrain determiner 541 and the cone height H and the
15 cone radius R acquired from the hill height estimator 542. The terrain estimator 543
thus generates 3D terrain estimation information modeling the hill area determined by the
terrain determiner 541, as a cone located on a plane, and feeds the generated information
to the output interface 570.
[0088] FIG. 18 shows a composite image fed to the terrain determiner 541 and an
20 image of a real terrain. In this example, the relationship between the angle of incidence
θ0 and the angle of repose θR is expressed by θR < θ0.
[0089] In this case, the foreshortening effect occurs to cause the displayed hill to be
nearer the observation satellite 200 than the true plane position, and the radar shadow
effect occurs to shade the slope opposite to the microwave emitter. The upper part of
25 FIG. 18 is the composite image, and the lower part of FIG. 18 is a cross-sectional view of
the real terrain showing a section SC corresponding to section X1-X2 in the composite
image. The composite image in the upper part is divided into a bright part PB, an
27
intermediate part PI, and a dark part PD represented by three gradations of brightness.
The terrain determiner 541 determines the intermediate part PI as a plane, and determines,
based on the radio wave emission direction and the bright part PB shaped as a fan, an
area including the fan-shaped bright part PB as a cone. The dark part PD is a radar
shadow, or an area hidden from the emission radar, and the ground surface 5 of the area is
unobservable. In the section SC of the lower part, the area is unmeasurable. The top
of the bright part PB, or the highest part, is displaced toward the radio wave emitter due
to the foreshortening effect. However, in a plan view, the positional information about
the direction vertical to the radio wave emission direction is unchanged. The hill height
10 estimator 542 thus measures the maximum width of the fan-shaped bright part PB, or the
radio wave irradiation region, as a cone diameter D, and determines half of the value as
the cone radius R. The terrain determiner 541 also assumes that the apex of the cone is
positioned on the segment denoted by Y1-Y2 with the maximum width of the fan-shaped
bright part PB in the direction vertical to the radio wave emission direction.
15 [0090] FIG. 19 is a schematic diagram showing a model in which the terrain
estimator 543 has recognized a cone. The schematic diagram shows the relationship
between the cone radius R, the angle of repose θR, and the cone height H. The lower
part of FIG. 19 shows a section SC including the apex of the cone. The hill height
estimator 542 calculates the cone height H from the equation, H = R × tanθR, and feeds
20 the calculated value to the terrain estimator 543.
[0091] The bright part PB is modified into a fan shape having the radius R with the
vertex positioned on line X1-X2 in the upper part of FIG. 19. The foreshortening is
corrected in this manner. Similarly, a dark part PDa is modified into a fan shape having
the radius R with the vertex positioned on line X1-X2. A dark part PDc is recognized as
25 a part of the dark part PD belonging to the intermediate part PI, and represented as an
area different in brightness from the dark part PDa. A dark part PDb is the border
between the dark part PDa and the dark part PDc, and the arc of the circular sector of the
28
bright part PB and the dark part PDb form a circle having the radius R. In this manner,
terrain information is acquired about a radar shadow that cannot be measured by the
existing technique.
[0092] FIG. 20 is a diagram showing a composite image acquired by the terrain
determiner 541 and a real terrain. In this example, the relationship between 5 the angle of
incidence θ0 and the angle of repose θR is expressed by θR > θ0.
[0093] In this case, the layover effect occurs in the observation image to reverse the
upper area and the lower area, causing a whiteout. The upper part of FIG. 20 is the
composite image, and the lower part of FIG. 20 is a cross-sectional view of the real
10 terrain showing a section SC corresponding to section X1-X2 in the composite image.
[0094] The terrain determiner 541 determines the intermediate part PI as a plane,
and determines, based on the radio wave emission direction and the crescent bright part
PB, an area including the crescent bright part PB as a cone. The bright part PB is a
layover area, or an area causing a whiteout image because a high area is nearer the
15 observation satellite 200 than the plane, and the ground surface of the area is
unobservable. The bright part PB has a top PT denoted by a white circle, or the highest
part, displaced toward the radio wave emitter due to the layover effect.
Characteristically, the top PT moves to the plane outside the conical area on the screen.
However, in a plan view, the positional information about the direction vertical to the
20 radio wave emission direction is unchanged. The hill height estimator 542 thus
determines the maximum width of the crescent bright part PB, or the radio wave
irradiation region, as a cone diameter D, and half of the value as the cone radius R. In
other cases, the hill height estimator 542 measures the diameter of the dark part PD and
determines half of the value as the cone radius R. The terrain determiner 541 assumes
25 that the apex of the cone is positioned on line Y1-Y2 with the maximum width of the
crescent bright part PB in the direction vertical to the radio wave emission direction. In
other cases, the terrain determiner 541 assumes the center of the circular dark part PD as
29
the apex of the cone.
[0095] FIG. 21 is a schematic diagram showing a model in which the terrain
estimator 543 has recognized a cone. The schematic diagram shows the relationship
between the cone radius R, the angle of repose θR, and the cone height H. The lower
part of FIG. 21 shows a section SC including the apex of the cone. 5 The hill height
estimator 542 calculates the cone height H from the equation, H = R × tanθR, and feeds
the calculated value to the terrain estimator 543.
[0096] The bright part PB is modified into a fan shape having the radius R with the
vertex positioned on line X1-X2 in the upper part of FIG. 21. The layover is corrected
10 in this manner. Similarly, the dark part PD is modified into a fan shape having the
radius R with the vertex on line X1-X2 in the figure. After the correction, the terrain
estimator 543 generates 3D terrain estimation information.
[0097] In an example, the above functions may be used to determine the amount of
excavated soil at a soil excavation site. The sand observation system 2 may compare the
15 3D terrain estimation information generated based on the composite image acquired
before the excavation with the 3D terrain estimation information generated based on the
composite image acquired after the excavation, and determine the difference as the
amount of excavated soil. The sand observation system 2 that has known the
components and the specific gravity of soil to be excavated may also estimate the weight
20 of excavated soil.
[0098] As described above, the sand observation system 2 according to
Embodiment 6 includes the formation flight system 1 according to Embodiments 1 to 4,
and enables all the observation satellites 200 included in the observation satellite group
200G to observe the same observation region at the same observation angle, and thus
25 improves the signal-to-noise ratio of the composite image produced by sequentially
subjecting observation images to pixel integration. Additionally, when characteristic
effects occur in an observation image due to the radio wave emission direction, the sand
30
observation system 2 allows the 3D terrain estimator 540 to generate terrain estimation
information close to the real terrain.
[0099] The present disclosure is not limited to the above embodiments, and may be
altered and modified variously without departing from the spirit and scope of the present
5 disclosure.
[0100] In the above embodiments, each observation satellite 200 uses a
synthetic-aperture radar to observe the ground surface of the celestial body 5 to be
observed. However, the observation satellite 200 may observe the ground surface of the
celestial body 5 using a high-resolution optical sensor included in place of or together
10 with the synthetic-aperture radar.
[0101] In the above embodiments, the program for the orbit control information
generation process performed by the orbit control information generator 212 in the
formation flight control device 210 is, for example, prestored in the ROM 215.
However, the present disclosure is not limited to the example. The operation programs
15 for the above various processes may be implemented in a general-purpose computer, a
framework, or a workstation known in the art to function as a device corresponding to the
formation flight control device 210 according to the above embodiments.
[0102] The programs may be provided in any manner and for example, distributed
on non-transitory computer-readable recording media (flexible disks, compact disc or
20 CD-ROMs, or digital versatile disc or DVD-ROMs). In other cases, the programs may
be stored in a storage on a network such as the Internet and allowed to be downloaded.
[0103] The above processing may be shared and performed by an operating system
(OS) and an application program or executed by the OS and the application program in
cooperation with each other. In either case, the application program may be stored in a
25 non-transitory recording medium or a storage. The program may be superimposed on a
carrier wave to be distributed through a network. For example, the program may be
posted on a bulletin board system (BBS) on a network and distributed through the
31
network. The above processing may be designed to be performed by executing the
program in the same manner as other application programs under the control of the OS.
[0104] The foregoing describes some example embodiments for explanatory
purposes. Although the foregoing discussion has presented specific embodiments,
persons skilled in the art will recognize that changes may be made 5 in form and detail
without departing from the broader spirit and scope of the invention. Accordingly, the
specification and drawings are to be regarded in an illustrative rather than a restrictive
sense. This detailed description, therefore, is not to be taken in a limiting sense, and the
scope of the invention is defined only by the included claims, along with the full range of
10 equivalents to which such claims are entitled.
Reference Signs List
[0105]
1 Formation flight system
2 Sand observation system
15 5 Celestial body
100 Ground station
110 Formation flight control device
111 Orbit information acquirer
112 Orbit control information generator
20 113 Orbit control information outputter
120 Ground transmitter
130 Ground receiver
140 Observation image storage
150 Observation image analyzer
25 200, 200-1, 200-2, 200-3, 200-N Observation satellite
200B Succeeding observation satellite
200F Preceding observation satellite
32
200S Target observation satellite
200G Observation satellite group
210 Formation flight control device
211 Orbit information acquirer
212 Orbit control information 5 generator
213 Orbit control information outputter
214 Processor
215 ROM
216 RAM
10 217 Auxiliary storage device
218 Input device
219 Output device
220 Receiver
230 Orbit controller
15 240 Posture controller
250 Observer
260 Observation image analyzer
270 Transmitter
300 Geostationary relay satellite
20 410 Change detector
420 Ground-surface information storage
430 Output interface
510 Input interface
520 Composite image storage
25 530 Image referrer
540 3D terrain estimator
541 Terrain determiner
33
542 Hill height estimator
543 Terrain estimator
550 Soil information determiner
560 Soil information storage
570 5 Output interface
a Semi-major axis
b Semi-minor axis
i Orbital inclination
Ω Right ascension of ascending node
10 ω Argument of periapsis
θ0 Angle of incidence
θR Angle of repose
AR Axis of rotation
BL Bus line
15 DI Incident direction
D Cone diameter
DV Vertical direction
H Height of cone
NPO-1, NPO-2, NPO-N Non-polar orbit
20 O Orbit
PO-1, PO-2, PO-3, PO-N Polar orbit
PG Observation ground surface point
PB Bright part
PI Intermediate part
25 PD, PDa, PDb, PDc Dark part
PT Top
R Cone radius
34
RD Radio wave irradiation region
SC Section of terrain
SL1, SL2 Straight line
35
We Claim :
1. A formation flight control device for generating and outputting orbit control
information for controlling observation satellites in an observation satellite group orbiting
a celestial body and sequentially observing a ground surface of the celestial body with an
observation interval, the formation flight control 5 device comprising:
orbit information acquisition means for acquiring orbit information indicating an
observation time of a preceding observation satellite of which an observation order
precedes by one, and an orbit of the preceding observation satellite at the observation
time;
10 orbit control information generation means for generating, based on the orbit
information, the orbit control information indicating an orbit and a phase allowing flying,
after the observation interval, vertically above an intersection point between the ground
surface and a straight line connecting a center of the celestial body and the preceding
observation satellite at the observation time; and
15 orbit control information output means for outputting the orbit control information.
2. The formation flight control device according to claim 1, wherein the orbit
control information generation means generates the orbit control information about the
observation satellites flying in polar orbits passing through a vicinity of a north pole and a
20 south pole of the celestial body.
3. The formation flight control device according to claim 1, wherein the orbit
control information generation means generates the orbit control information about the
observation satellites flying in non-polar orbits not passing through a vicinity of a north
25 pole and a south pole of the celestial body.
4. An observation satellite comprising:
36
the formation flight control device according to any one of claims 1 to 3;
reception means for receiving observation information indicating an observation
from the preceding observation satellite;
orbit control means for controlling an orbit based on the orbit control information;
posture control means for calculating, based on the observation 5 information, a
relative posture of the preceding observation satellite to the celestial body at the
observation time, and performing control to have a posture identical to the relative
posture of the preceding observation satellite after the observation interval;
observation means for observing, after the observation interval, an observation
10 target on the celestial body, the observation target being observed by the preceding
observation satellite; and
transmission means for transmitting observation information including an
observation by the observation means to a succeeding observation satellite of which an
observation order follows by one.
15
5. The observation satellite according to claim 4, wherein
the observation satellite includes a synthetic-aperture radar, and
the observation means observes the observation target with the synthetic-aperture
radar.
20
6. A ground station for transmitting observation instruction information for
observation to each of a plurality of observation satellites in an observation satellite group
orbiting a celestial body and sequentially observing a ground surface of the celestial body
with an observation interval, the ground station comprising:
25 a formation flight control device to calculate, based on the observation instruction
information transmitted to a preceding observation satellite of which an observation order
precedes by one, orbit information indicating an observation time of the preceding
37
observation satellite, and an orbit of the preceding observation satellite at the observation
time, and to generate orbit control information indicating an orbit and a phase allowing
flying, after the observation interval, vertically above an intersection point between the
ground surface and a straight line connecting a center of the celestial body and the
preceding observation satellite at the observation 5 time; and
ground transmission means for transmitting observation instruction information
including the orbit control information to a succeeding observation satellite of which an
observation order follows by one.
10 7. A formation flight system comprising:
an observation satellite group of a plurality of satellites to orbit a celestial body, to
sequentially observe a ground surface of the celestial body with an observation interval,
and to transmit observation information indicating an observation; and
a ground station to transmit observation instruction information for observation,
15 and to receive the observation information indicating the observation from a satellite of
the plurality of satellites,
wherein the satellite or the ground station includes a formation flight control device
to calculate, based on the observation instruction information transmitted to a preceding
observation satellite of which an observation order precedes by one, orbit information
20 indicating an observation time of the preceding observation satellite, and an orbit of the
preceding observation satellite at the observation time, and to generate orbit control
information indicating an orbit and a phase allowing flying, after the observation interval,
vertically above an intersection point between the ground surface and a straight line
connecting a center of the celestial body and the preceding observation satellite at the
25 observation time.
8. The formation flight system according to claim 7, further comprising:
38
a geostationary relay satellite to relay communication between the plurality of
satellites or between a satellite of the plurality of satellites and the ground station.
9. The formation flight system according to claim 7 or 8, further comprising:
observation image analysis means for generating a composite image 5 by subjecting
observation images acquired by the plurality of satellites to pixel integration.
10. A sand observation system comprising:
a formation flight system including
10 an observation satellite group of a plurality of satellites to orbit a celestial
body, to sequentially observe a ground surface of the celestial body with an observation
interval, and to transmit observation information indicating an observation,
a ground station to transmit observation instruction information for
observation, and to receive the observation information indicating the observation from
15 the satellite, and
a formation flight control device to calculate, based on the observation
instruction information transmitted to a preceding observation satellite of which an
observation order precedes by one, orbit information indicating an observation time of the
preceding observation satellite, and an orbit of the preceding observation satellite at the
20 observation time, and to generate orbit control information indicating an orbit and a phase
allowing flying, after the observation interval, vertically above an intersection point
between the ground surface and a straight line connecting a center of the celestial body
and the preceding observation satellite at the observation time;
ground-surface information storage means for storing ground-surface information
25 about the celestial body;
change detection means for comparing a composite image fed from the formation
flight system and generated by subjecting observation images acquired by the plurality of
39
satellites to pixel integration with ground-surface information stored in the
ground-surface information storage means and about an area identical to an area in the
composite image, and detecting a change; and
an output interface to output a place with the change.
5
11. A sand observation system comprising:
a formation flight system including
an observation satellite group of a plurality of satellites to orbit a celestial
body, to sequentially observe a ground surface of the celestial body with an observation
10 interval, and to transmit observation information indicating an observation,
a ground station to transmit observation instruction information for
observation, and to receive the observation information indicating the observation from
the satellite, and
a formation flight control device to calculate, based on the observation
15 instruction information transmitted to a preceding observation satellite of which an
observation order precedes by one, orbit information indicating an observation time of the
preceding observation satellite, and an orbit of the preceding observation satellite at the
observation time, and to generate orbit control information indicating an orbit and a phase
allowing flying, after the observation interval, vertically above an intersection point
20 between the ground surface and a straight line connecting a center of the celestial body
and the preceding observation satellite at the observation time;
composite image storage means for storing a composite image generated by
subjecting observation images acquired by the plurality of satellites to pixel integration;
an input interface to input estimation target information specifying a sandhill to be
25 estimated;
image reference means for extracting a composite image including the sandhill
from the composite image storage means in accordance with the estimation target
40
information;
three-dimensional terrain estimation means for processing the composite image
extracted by the image reference means to identify the sandhill, and generating
three-dimensional terrain estimation information about the sandhill; and
an output interface to output the three-dimensional terrain estimation 5 information.
12. A formation flight control method for generating and outputting orbit
control information for controlling a plurality of observation satellites in an observation
satellite group orbiting a celestial body and sequentially observing a ground surface of the
10 celestial body with an observation interval, the formation flight control method
comprising:
acquiring orbit information indicating an observation time of a preceding
observation satellite of which an observation order precedes by one in the plurality of
observation satellites in the observation satellite group orbiting the celestial body and
15 sequentially observing the ground surface of the celestial body with the observation
interval, and an orbit of the preceding observation satellite at the observation time; and
generating, based on the orbit information, orbit control information indicating an
orbit and a phase allowing flying, after the observation interval, vertically above an
intersection point between the ground surface and a straight line connecting a center of
20 the celestial body and the preceding observation satellite at the observation time.
13. A program for causing a computer to function as
orbit information acquisition means for acquiring orbit information indicating an
observation time of a preceding observation satellite of which an observation order
25 precedes by one in a plurality of observation satellites in an observation satellite group
orbiting a celestial body and sequentially observing a ground surface of the celestial body
with an observation interval, and an orbit of the preceding observation satellite at the
observation time,
orbit control information generation means for generating, based on the orbit
information, orbit control information indicating an orbit and a phase allowing flying,
after the observation interval, vertically above an intersection point between the ground
surface and a straight line connecting a center of the celestial body 5 and the preceding
observation satellite at the observation time, and
orbit control information output means for outputting the orbit control information.