GB2266634A

GB2266634A - Solar sensor for satellite attitude determination

Info

Publication number: GB2266634A
Application number: GB9308671A
Authority: GB
Inventors: Erich Weichs
Original assignee: Deutsche Aerospace AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1992-04-29
Filing date: 1993-04-27
Publication date: 1993-11-03
Anticipated expiration: 2013-04-27
Also published as: GB2266634B; JPH0626857A; FR2690738A1; GB9308671D0; FR2690738B1; DE4214136C2; JP2644961B2; ITMI930805A0; ITMI930805A1; IT1272470B; DE4214136A1

Abstract

The angle of incidence of sunlight onto a sensor is used for satellite attitude determination. The point of impact of sunlight entering through an aperture onto a single detector strip comprising a number of individual sensors is used to determine the angle of incidence. The aperture is in the form of a right angle or another predetermined angle, whereby the one angle of incidence is determined from the irradiated detectors of one half of the detector strip and the other angle of incidence is determined from the irradiated detectors of the other half of the detector strip. These are scanned simultaneously at the outlet of an electronic readout system, whereby the angles are calculated in an electronic analyzer. <IMAGE>

Description

a SOLAR SENSOR FOR z-AXES FOR SATELLITE ATTITUDE DETERMINATION This invention relates to a solar sensor for zaxes for satellite attitude determination, in which the point of impact of sunlight entering through an aperture on a detector strip comprising a number of individual sensors is used to determine its angle of incidence.

Solar sensors for z-axes for satellite attitude determination are know per se. The principles of a satellite attitude determination system, wherein the relative position of the sun to the coordinate system of the satellite, amongst other things, is proposed for this purpose, are known from the publication "Spacecraft Attitude Determination and Control" by James R. Wertz, published by D. Reidel Publishing Company, 1985. The diagram shown in Figure 1 depicts such an attitude determination system using solar sensors in simplified form. In this figure the "S" represents the vector of the sun, a the angle of the sun vector projection onto the xz-plane to the z-axis and (3 the angle of the sun vector projection on the yzplane to the z-axis.Hence, two solar sensors arranged at an angle of 90" to one another must be used for these angles a and p for attitude determination according to the prior art.

In known solar sensors of the applicant the point at which sunlight entering through an aperture hits a detector strip with 2048 detectors arranged in a row is used to determine the angle of incidence. In order to measure the two angles a and ss, two sensors or sensor heads arranged at 90" are required - as already indicated - and in conjunction with these two detector strips are needed with the appropriate read-out electronics in addition to an electronics pack for the attitude control system.

The object of the present invention is to provide a solar sensor of the aforementioned type, by means of which angles a and ss can be determined with only one sensor and one detector strip.

This object is achieved in accordance with the invention in that a screen having light entry means in the form of a right angle or another specific angle is arranged at a specific distance above an image plane in which the detector strip lies and the angle of incidence of sunlight from the irradiated detectors of one half of the detector strip and the angle of incidence from the irradiated detectors of the other half of the detector strip are scanned simultaneously at the outlet of an electronic read-out system and calculated in a connected electronic analyzer.

An embodiment of the invention in explained in the following description, and this explanation is supplemented by the figures in the drawing, in which: Figure 1 is a diagram illustrating the attitude determination system using a solar sensor according to the prior art; and Figure 2 is a schematic perspective view of the structure of an example of a solar sensor for simultaneous determination of angles a and ss.

The invention envisages that angles a and ss may be determined with only one sensor and one detector strip by means of appropriate shaping of the light entry aperture and appropriate arrangement of the detector strip, whereby the previously existing measurement principle may be retained. Hence, the local position or point of impact of light entering through an aperture "S" onto a surface arranged at a distance "a" therefrom is used to determine the angle of incidence.

As previously, light-sensitive detectors arranged in a row at a defined space from one another to form a strip are used to determine the position of impact of the light. There is a wide variety of such arrangements available differing according to number of detectors and mode of operation. To find the irradiated detectors, read-outs of the voltages of all the detectors are taken periodically. This read-out process occurs serially, i.e. voltages of detectors 1 to n, which are proportional to the incidence of light at the corresponding detector, are arranged in time sequence at the outlet point of the electronic read-out of the detector strip.

Such detector strips are either based on photodiodes or on CCDs (charge coupled devices). The present embodiment has a detector strip comprising 4000 individual detectors. The radiation status of each individually numbered detector is scanned at the outlet point of the electronic read-out. An electronic analyzer connected at the outlet then calculates the angle or angles of incidence of the light from the number of irradiated detectors.

As shown in Figure 2, the entry aperture S of the screen is in the form of a right angle. For optimisation, other angles may also be used. When the incidence of light is exactly perpendicular - i.e. the vector of the sun is then perpendicular to the sensor surface (a = 0 , ss = 0 ) - the aperture images irradiate the detectors with the numbers 1000 and 3000.

If the solar rays now hit at a different angle, then this results in a movement of the aperture image in the image plane. In the relevant measurement range - i.e.

in the range of movement of point E of the aperture image on the image plane - the angle of incidence a may be determined from the directly irradiated detector(s) in the range of numbers from 1 to 2000 and the angle of incidence ss from the directly irradiated detectors in the range of numbers from 2001 to 4000. The maximum final values of the measurable angles as well as the angles at the central position - in which detectors 1000 and 3000 are irradiated - result from the geometry of the entry aperture and its disposition relative to the image plane (distance apart, lateral shift) and these factors are structurally adjustable. It is advantageous if the detector strip and its support means are arranged in a common housing together with the electronic read-out system and the electronic analyzer and associated cabling.

Claims

1. A solar sensor for z-axes for satellite attitude determination, in which the point of impact of sunlight entering through an aperture on a detector strip comprising a number of individual sensors is used to determine its angle of incidence, characterised in that a screen having light entry means in the form of a right angle or another specific angle is arranged at a specific distance above an image plane in which the detector strip lies and the angle of incidence of sunlight from the irradiated detectors of one half of the detector strip and the angle of incidence from the irradiated detectors of the other half of the detector strip are scanned simultaneously at the outlet of an electronic read-out system and calculated in a connected electronic analyzer.

2. A solar sensor according to Claim 1 wherein the maximum final value of the measurable angles as well as the angles at the central position (sun vertical to the light entry means) are determined from the geometry of the light entry means, the distance of the light entry means from the image plane and the lateral shift of the light entry means in relation to the image plane.

3. A solar sensor according to Claim 2 wherein the distance of the light entry means from the image plane and its lateral shift in relation to the image plane are adjustable.

4. A solar sensor according to any preceding claim wherein the detector strip and support means therefor are arranged in a common housing together with the electronic read-out system, the electronic analyzer and associated cabling.

5. A solar sensor for z-axes for satellite attitude determination substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.