JPH0441957B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an earth scanning system using a spin satellite operating in a geostationary orbit.

[Conventional technology]

The following three methods have been used to scan the Earth from a satellite operating in a geostationary orbit through a minute instantaneous viewing angle.

The first method is GOES (USA) or GMS
This is a scanning method used in a meteorological satellite called (Japan).As shown in Fig.
, and the plane mirror 21 is connected to the spin axis 2 of the geostationary satellite.
The incident light 24 that has passed through a sunshade (not shown) is guided in the direction of the spin axis 22 by a plane mirror 21, and transmitted through a telescope section 25 to a detector (not shown). ,
It is configured to detect the state of the earth scanning area by the rotating plane scanning mirror 21. In this case, as the scanning plane mirror 21 rotates, the trajectory in the line-of-sight direction will draw a part of a great circle on the celestial sphere if the spin of the satellite is stopped, and if combined with the spin, the trajectory in the line of sight direction will be the same as that of the scanning plane mirror 21. is becoming possible. In FIG. 5, 22a indicates a spin vector, and 23a indicates a scanning unit rotation vector.

The second method is METEOSAT (European Space Agency)
As shown in FIG. 6, the rotating scanning unit 26 includes a primary reflecting mirror 27, a secondary reflecting mirror 28, which is a part of the objective side of the optical system. It consists of a telescope that integrates a prism 29, and the 20
It is configured to rotate in degrees. The incident light 24 is condensed and guided in the direction of the spin axis 22. Note that 30a indicates a scanning unit rotation vector.

The third method is the method used by a satellite called INSAT (USA).In the case of this satellite, the satellite itself is stable on three axes and does not spin, so the scanning unit does not spin. The rotation corresponds to the satellite's spin, and it also rotates about 10 degrees around an axis perpendicular to the spin rotation.

Also in these second and third scanning methods,
If we stop the spin of the satellite or its corresponding rotation, as the scanning unit rotates, its trajectory on the celestial sphere in the line of sight will all trace a part of a great circle.

[Problem that the invention seeks to solve]

By the way, a common problem with the above-mentioned current scanning methods is that the rotary scanning unit must be accurately held at each of the finely divided angular positions within a limited rotational angle range, and that it must be held sequentially at each of the angular positions. One example is the difficulty of stepping.

For example, in the case of GMS, an angle range of 10 degrees is divided into 2500 steps and the step operation is performed, so extremely fine angle reading accuracy is required. This caused an abnormality in the angle holding of the scanning plane mirror and an abnormality in the step. Additionally, since the rotation angle range of the scanning plane mirror is narrow at 10 degrees, the solid lubricant in the bearings wears unevenly, causing an abnormality in which the range of movement becomes narrower than the predetermined angular range of 10 degrees.

The occurrence of these abnormal conditions causes the GOES and GMS series observation satellites to reach the end of their lifespans in orbit. Various efforts have been made to prevent these abnormalities from occurring, but
No satisfactory method has yet been demonstrated in orbit.

The present invention was made in order to solve the above-mentioned problems in the conventional earth scanning method from a geostationary satellite, and it significantly reduces the angle reading accuracy while maintaining the scanning density, and also eliminates the occurrence of solid lubricant deviation. The purpose is to provide an earth scanning method using a spin satellite in a geostationary orbit.

[Means and actions for solving problems]

In order to solve the above-mentioned problems, the present invention provides a scanning unit that performs line scanning by sweeping the geostationary satellite through a minute instantaneous viewing angle from the geostationary satellite spinning around an axis perpendicular to the orbital plane in a geostationary orbit. In the method of scanning the earth by performing step transitions of the scanning line, the scanning unit is arranged so as to be rotatable around one axis, and the locus of the line of sight by the scanning unit when rotated around the axis is the same as the line of sight along the generatrix. It is constructed to draw a part of a conical surface.

By scanning with the scanning section in this way, the rotation angle of the scanning section corresponding to the vertical scanning angle range can be increased, making it possible to significantly reduce angle reading accuracy while maintaining scanning density. becomes. Furthermore, since the rotation angle of the scanning section can be increased, there are no race parts in the bearing that do not come into contact with the balls, which prevents the solid lubricant from being unevenly distributed, resulting in a longer service life.

〔Example〕

Examples will be described below. FIG. 1 is a diagram showing an example of a configuration in which the earth scanning method according to the present invention is applied to a GMS. In the figure, 1 is a plane mirror constituting a rotating scanning section, and the rotation axis 2 of the plane mirror 1 is
is arranged at an angle of about 45 degrees with the spin axis 3 of the satellite, and the plane mirror 1 is fixed to the rotation axis 2.
The rotation axis 2 of the scanning plane mirror 1 and the plane mirror surface vector 4 are arranged so as to form an angle of 5 degrees or more. Note that 5 indicates a telescope section, 2a indicates a scanning section rotation vector, and 3a indicates a spin vector.

By rotating the scanning plane mirror 1 arranged in this manner about its rotation axis 2, the locus of the line of sight caused by the scanning plane mirror draws a conical surface with this as the generating line.

Next, we will explain how the conventional problems can be solved by rotating the scanning plane mirror so that the locus of the line of sight drawn by the scanning plane mirror describes a conical surface. This will be explained based on an example.

In Figure 1, viewing direction vector A → scanning unit rotation vector: B → telescope optical axis vector; C → scanning mirror surface vector: D → rotation angle reference vector: E → rotation angle: θ Angle between the rotation axis and the scanning mirror surface vector :δ, and given B→, C→, E→, θ, and δ, 〓B→・D→=cosδ D/→×B/→/sinδ・E→=cosθ holds, so From this, the scanning mirror vector D→ can be determined. Note that the rotation angle reference vector E→ is a unit vector in the D→×B→ direction when the rotation angle θ is zero.

Next, using this obtained scanning mirror vector D→, the line-of-sight direction vector A→ can be obtained from 〓A→・D→=C→・D→ C→×D→=D→×A→ .

Here, as a specific example, the scanning unit rotation vector (rotation axis direction) makes an angle of 45.63 degrees with the spin vector, and the surface vector of the scanning plane mirror (with the back side of the scanning mirror being positive) makes an angle of 9.89 degrees with the scanning unit rotation axis. When configured to form a degree angle, B → = (-sin45.63°, 0, cos45.63°) C → = (0,0, -1) E → = (cos45.63°, 0, sin45.63°) δ=9.89°. Therefore, when the plane mirror rotation angle θ is changed every 10 degrees and the locus of movement in the line of sight direction as the scanning plane mirror 1 rotates is determined, it becomes an ellipse as shown by the circles in FIG. The interval between the ○ and marks corresponds to the rotation angle of the plane mirror of 10 degrees.

The fact that the locus in the viewing direction by the plane mirror 1 is oval is that the surface vector of the scanning plane mirror 1 traces a circular locus when it rotates around the rotation axis 2; 1
Due to the properties of the mirror, the trajectory of the incident light such that the light reflected by the mirror is directed in the direction of the optical axis of the telescope 5 does not change its orientation from the surface vector of the scanning plane mirror 1, but in the vertical direction, the angle of incidence is added to the angle of reflection. This can be understood from the fact that as a result, the angle doubles.

The vertical angle range required when actually scanning the earth is ±10 degrees, so in the specific example shown in Figure 2, it is sufficient to use the range connecting A, B, and C, and this range is marked with ○. As can be seen from the number of intervals (6 intervals), this corresponds to a rotation angle of 60 degrees of the scanning plane mirror 1. Compared to conventional methods where a 10 degree range was scanned in 2500 steps, in this specific example, a 60 degree rotation angle range only needs to be scanned in 2500 steps, which greatly reduces the precision of angle reading. Ru.

In addition, since the plane mirror 1 is rotated over an angular range of 60 degrees in this way, there are no race parts in the bearing where the balls do not come into contact, and the solid lubricant wears out evenly, eliminating the occurrence of unevenness.

In Figure 2, the circles indicated by a, b, and c represent the range of incident light passing through the cylindrical part of the satellite when the ratio of the telescope aperture to the satellite diameter is approximately 0.2 in a cylindrical spinning satellite. , which correspond to the cases where the line of sight directions are A, B, and C, respectively. In this case, the sunshield opening shape at the outer circumference of the satellite is approximately enveloped by circles a, b, and c.
The opening has an opening shape as shown by 6 in FIG.

Furthermore, when the scanning plane mirror is rotated as in the present invention, if the line of sight of the plane mirror is configured to draw a conical surface, the field of view outside the range of scanning the earth can be easily blocked by the constituent parts of the satellite. It can be configured as follows. The viewing direction outside the earth scanning range is, for example, the angular position D in FIG. 2, and in the satellite shown in FIG. 3, the portion indicated by 7 constitutes the portion that blocks the viewing field. This shielding portion 7 can be provided with a substantially circular blackbody target for infrared calibration, indicated by d in FIG.

Figure 4 shows the scanning method according to the present invention.
It is a figure showing an example applied to METEOSAT.
In this embodiment, a telescope 8 consisting of a primary reflecting mirror, a secondary reflecting mirror, etc. constituting a rotating scanning section is arranged such that its rotating axis 9 is substantially orthogonal to the spin axis 3; The optical axis 1 of the scanning telescope 8
0 and the scanning rotation axis 9 are configured to form an angle of about 10 degrees or more. Note that 9a is a scanning unit rotation vector.

In this embodiment as well, the scanning telescope 8 is connected to the rotation axis 9
By rotating the scanning telescope 8 around the
The same effects as in the embodiment can be obtained. In this embodiment, the incident light 11 is incident on the secondary reflecting mirror 13 by the primary reflecting mirror 12, and the light from the secondary reflecting mirror 13 is once connected to the rotating shaft 9 by the reflecting mirror or prism 14 attached to the scanning section. guided in the direction of agreement. It is then guided in the required direction by a reflector or prism 15 attached to the body.

〔Effect of the invention〕

As described above based on the embodiments, according to the present invention, when the scanning unit is rotated around its rotation axis, the trajectory of the line of sight by the scanning unit covers a part of the conical surface with the line of sight as the generatrix. Since it is configured to draw, the rotation angle of the scanning section corresponding to the vertical scanning angle range can be set large, and the angle reading accuracy can be significantly reduced while maintaining the scanning density. Furthermore, since the rotation angle of the scanning section can be made large, the solid lubricant in the bearing is prevented from being unevenly distributed, and the life of the bearing can be extended.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing a first embodiment of the earth scanning method according to the present invention, Fig. 2 is a diagram showing a trajectory in the line of sight direction in the first embodiment, and Fig. 3 is a diagram showing the locus of the line of sight in the first embodiment. A diagram showing the appearance of a cylindrical spin satellite,
FIG. 4 is a schematic diagram showing a second embodiment of the present invention, and FIGS. 5 and 6 are schematic diagrams showing a conventional earth scanning method. In the figure, 1 is a scanning plane mirror, 2 is a rotation axis, and 3
is a spin axis, 4 is a plane mirror vector, 5 is a telescope section, 6 is a sunshade, 7 is a shielding section, 8 is a scanning telescope, 9 is a rotation axis, and 10 is a telescope optical axis.

Claims (1)

[Claims] 1 A geostationary satellite spinning around an axis perpendicular to the orbital plane in a geostationary orbit performs line scanning by sweeping the spin of the geostationary satellite through a minute instantaneous viewing angle, and the scanning section moves the scanning line step by step to scan the earth. In the scanning method, the scanning unit is arranged so as to be rotatable around one axis, and the locus of the line of sight of the scanning unit when rotated around the axis draws a part of a conical surface with the line of sight as the generatrix. An earth scanning method characterized by the following configuration.