GB2145895A

GB2145895A - Satellite attitude sensor

Info

Publication number: GB2145895A
Application number: GB08420274A
Authority: GB
Inventors: Gunter Gambke; Naoyuki Natori
Original assignee: Messerschmitt Bolkow Blohm AG; Mitsubishi Electric Corp
Current assignee: Airbus Defence and Space GmbH; Mitsubishi Electric Corp
Priority date: 1983-08-17
Filing date: 1984-08-09
Publication date: 1985-04-03
Also published as: GB8420274D0; JPS6047800A; DE3329670A1; FR2550858A1

Abstract

A zero-seeking optical sensor for an earth satellite reproduces two opposite edges of the earth on a receiver 7. The radiation incident within the respective fields of vision 8a and 8b or 12a and 12b on the receiver 7 are measured, and any displacement of the satellite from a reference attitude can be determined from the difference in radiation energies. In order to be able to determine the attitude of the satellite at different heights, the optical position sensor 6 has mirrors 11 which vary the fields of vision from 8a, 8b to 12a, 12b so that opposite edges of the earth are always observed. <IMAGE>

Description

SPECIFICATION Optical position sensor for a satellite This invention relates to an optical position sensor for a satellite which with the aid of an optical system and of a receiver picks up optical radiation from a body in space, for instance the earth, within a specific directed field of vision and with the aid of an evaluation circuit by reason of the received radiation energy in comparison with a reference energy determines the displacement of the satellite out of the line of vision.

An optical position sensor of this kind, carried by a satellite, serves to determine the position of the satellite relative to another body in space. The present invention will be described with reference to an infra-red radiation detector which is used when determining the position of the satellite relative to the earth.

A conventional position sensor of the kind in question can be designated as a so-called static sensor. The functional principle thereof may be explained with reference to Fig. 1 of the accompanying drawings. In Fig. 1, designated by the numeral 1 is the earth. Designated by numerals 2a and 2b are the optical fields of vision of two infra-red radiation detectors of the static type for determining the roll position of a satellite. Designated by numerals 3a and 3b are the optical fields of vision of the sensors for determining the pitch position.

Designated by numeral 4 is an edge of the earth which is within the field of vision of the infra-red radiation detector and which is detected by this, and designated y numeral 5 is an earth satellite.

The detector operates as follows: The infrared radiation detector is aligned by its optical axis at the earth 1. The detector has two pairs of optical systems, and each in turn embraces two optical fields, namely the fields of vision 2a and 2b for detecting the roll position and the fields of vision 3a and 3b for detecting the pitch position. These fields of vision are so aligned that the edge 4 of the earth can be observed with them.

With reference to the roll position of the satellite, the energies received within the two fields of vision 2a or 2b respectively from the earth are proportional to the areas A and B on the earth which lie within the associated fields of vision. The difference AW between the energies received for the associated fields of vision and emanating from the earth can be expressed by the following formula: AWa(A-B) (1) In accordance with this formula the energy difference is directly proportional to the difference of the respective areas A and B lying in the fields of vision. If the roll position of the satellite changes, then also the areas of the earth lying within the fields of vision also change and thus also the difference AW between the amounts of energy which are detected within the fields of vision 2a and 2b.

It is assumed that when the roll position of the satellite is determined the difference between the amounts of energy within the two fields of vision 2a and 2b can be considered as a contant which is indicate.d by AWo. If the satellite moves out of the associated reference roll position, a different difference AWl is detected, and the angle of drift i\S, associated therewith, of the angle of roll AWl can be expressed. For this the following formula applies; lSSaW = (AWl -l\WO) (2) The change of the angle of roll is proportional to the energy W, i.e. proportional to the difference between AWl and AWO.

The pitch position of the satellite can be detected in a similar way.

Accordingly a conventional position sensor having a radiation detector is based on the simple principle that the amounts of the energies incident within the two fields of vision are compared with one another.

As explained above, the optical fields of vision are, at the start, always so orientated that the edge of the earth is observed. If, however, the trajectory height of the satellite changes, then the described position sensor cannot be operated in the predetermined way.

If, accordingly, the trajectory height of the satellite is too high, both fields of vision are directed merely at cosmic space. If, on the other hand, the trajectory height of the satel lite is too low, then the two fields of vision merely encounter the surface of the earth.

In both cases no edge of the earth can be observed and accordingly also no change in position can be detected. Upon a change in the trajectory height, in these two situations, the amount IXW1 indicated in Formula 2 is equal to 0. A position sensor of the described static kind is, therefore, not suitable for a satellite which is used for various trajectory heights unless the optical system is every time designed anew for satellites with different trajectory heights. For this reason an optical position sensor of this kinds is not suitable for use at different trajectory heights.

The problem underlying the invention is to improve an optical sensor of the kind in question in such a way that it can be used for satellites on different trajectory heights without the construction having to be modified in a complicated manner.

This problem is solved, in accordance with the invention, in that the optical system of the position sensor has additional optical elements for varying the line of vision.

In accordance herewith, by use of appropri ate optical elements, more specially mirrors, the possibility is afforded of varying the field of vision of the optical position sensor in accordance with the respective trajectory height of the satellite. If the satellite is used in the case of a trajectory height different from that originally planned or intended for the basic position sensor, all that is necessary is that these optical elements have to be adjusted anew, so that in each case the edge of the earth is detected by the optical position sensor at the new trajectory height. A position sensor in accordance with the invention can, therefore, be adapted simply to the respective instance of use.

The invention will be described further, by way of example with reference to Figs. 2 and 3 of the accompanying drawings, in which: Figure 2 is a schematic representation of an optical position sensor in accordance with the invention suitable for an earth satellite having different trajectory heights; and Figure 3 is a schematic general view of the further elements used in the position sensor.

In Fig. 2 designated by the reference numeral 6 is an optical position sensor having an infra-red radiation receiver. The radiation receiver with its optical system is designated by the numeral 7. Designated by the numerals 8a and 8b are, in turn, the two fields of vision of the position sensor in the case of a specific trajectory height above the earth 9.

The edge of the earth lies within the fields of vision 8a and 8b. Designated by the numerals 1 2a and 1 2b are the fields of vision of the optical position sensor in the case of a different trajectory height above the earth which is designated here by the numeral 10. The edge of the earth again lies within the fields of vision 12aand 12b.

The adjustment of the fields of vision, as a function of the respective trajectory height of the satellite, is ensured by two mirrors by which the respective radiation within a field of vision is deflected onto the receiver 7 of the position sensor.

The functional principle of the optical position sensor will be described in conjunction with the position regulation about one axis only. The positional regulation for the other axes is effected similarly.

The infra-red radiation receiver 6 of the optical position sensor has the optical system 7 with the fields of vision 8a and 8b, with which the edge of the earth 9 is detected, in order thus, as described above, to calculte the position of the satellite. If, for example, the trajectory height of the satellite is raised, then as from a specific height the edges of the earth are no longer detected. This applies, for instance, for the second trajectory height, shown in Fig. 2, relative to the earth now designated by the numeral 10. The two fields of vision of the position sensor would, in this case, detect merely the radiation from space.

In order again to detect the edges of the earth, the mirrors are adjusted, so that again the radiation emitted from the edges of the earth falls into the optical system of the position sensor. The fields of vision of the position sensor, newly adjusted in this way, are designated by the numerals 1 2a and 1 2b.

Shown in Fig. 3 is an overall perspective view for the optical position sensor. Designated again by the numeral 7 is the optical system and designated by the numeral 11 are the mirrors. Furthermore, a processor circuit 13, a motor adjusting drive 14 for the mirrors as well as a stepping motor 1 5 are provided.

If infra-red energy from the earth is incident in the direction of the optical position sensor, this radiation is so deflected at the mirror that it falls into the optical system. This optical system consists, for example, of an objective and an infra-red receiver. By appropriate design of the optical system, for example with the aid of a so-called chopper disc, a single infra-red receiver can be used to detect the infra-red radiation from both fields of vision.

The incident energy is converted into a voltage which is then fed to the processor circuit 1 3. In this the difference between the respective energies is converted, in accordance with the above-indicated principle, into a position error AE.

The mirrors 11 can be controlled in their angular positions by the motor adjusting drive 14 and the stepping motor 15, in order to adjust the fields of vision of the optical system in such a way that in each case the edge of the earth is picked up. The setting angle Af of the mirrors 11 is adjusted for example by a control signal which is sent out from a control station on earth, or by a signal which is derived in the satellite itself, as a function of the change in the trajectory height.

If the satellite changes its trajectory height only slightly, the mirrors can be adjusted mechanically without the motor adjusting drive 14 and the stepping motor 1 5 being used. Depending on the preset trajectory height of the satellite, the mirrors are fixed at a fixed angle. As mentioned above, it is likewise possible to adjust the mirrors constantly during the flight of the satellite, for example when the satellite follows a more or less severely eccentric trajectory. With a position sensor in accordance with the invention accordingly satellites can be used in different trajectory heights without the construction of the position sensor having to be carried.

Merely the setting angle of the mirrors has to be changed, which is dependent upon the respective trajectory height.

Claims

1. An optical position sensor for a satellite which with the aid of an optical system and of a receiver picks up optical radiation from a body in space, for instance the earth, within a specific directed field of vision and with the aid of an evaluation circuit by reason of the received radiation energy in comparison with a reference energy determines the displacement of the satellite out of the line of vision, characterised in that the optical system of the position sensor has additional optical elements for varying the line of vision.

2. A position sensor as claimed in claim 1, characterised in that the additional optical elements are adjustable mirrors.

3. A position sensor as claimed in claim 2, characterised in that an adjusting motor is connected to the mirrors.

4. An optical position sensor for a satellite substantially as hereinbefore described with reference to and as illustrated in Figs. 2 and 3 of the accompanying drawings.