WO1991009325A1

WO1991009325A1 - Device to make possible the bringing nearer and bringing together of two objects, particularly two space vehicles

Info

Publication number: WO1991009325A1
Application number: PCT/SE1990/000816
Authority: WO
Inventors: Anders BOSTRÖM
Original assignee: Saab Space Aktiebolag
Priority date: 1989-12-15
Filing date: 1990-12-10
Publication date: 1991-06-27
Also published as: SE8904235D0

Abstract

A device which makes possible the bringing nearer and bringing together of two objects, particularly space vehicles, is described. The object is to determine their relative distance, azimuth angle, elevation angle and relative attitude angles, i.e. heading, roll and pitch angles. The device comprises a transmitter (2) located on one object, for emitting optical radiation, and a receiver (4) for receiving this radiation to the extent it is reflected by a reflector on the second object. The reflector comprises a number of reflector elements (6) with a first, rather limited extension across the incoming radiation. The device is primarily characterized in that the reflector comprises a spherical convex mirror (7) with a second rather great extension across the incoming radiation.

Description

DEVICE TO MAKE POSSIBLE THE BRINGING NEARER AND BRINGING TOGETHER OF TWO OBJECTS. PARTICULARLY TWO SPACE VEHICLES

The present invention relates to a device to make possible the bringing nearer and bringing together of a first and a second object, preferably two space vehicles, i.e. deter¬ mining their relative distance, azimuth angle, elevation and relative attitude angles, i.e. heading, roll and pitch angles, the first object being provided with a transmitter for emitting radiation about a first axis within the optic wavelength range, such as laser light, and a receiver for receiving said radiation to the extent it is reflected by a reflector on the second object, preferably in the same direction as that of the emitted radiation, the receiver comprising a camera with radiation sensitive detector ele¬ ments arranged two-dimensionally in the focal plane of the camera (CCD-camera) arranged in dependence on the received radiation to emit corresponding electric signals, said re¬ flector comprising a number of reflector elements with a first, rather limited extension across the incoming radia¬ tion, preferably in the form of prisms for reflecting incoming radiation in the same direction as the incoming radiation, irrespective of what direction.

Such devices are earlier known, particularly for so-called rendez-vous and docking, i.e. bringing nearer and bringing together two space vehicles . In such procedures it is necessary to determine accurately the relative distance of the space vehicles and their positions, as described above. In devices of the kind mentioned in the introduc¬ tion a number of prisms have been used as reflectors, which reflect incoming radiation in the same direction as the reflectors, irrespective of what direction. These prisms, being at least three, have been located in a first plane, and one additional prism located on a bar, ex¬ tending from said first plane of the particular space ve¬ hicle, i.e. in the direction of the second space vehicle. By such an arrangement it has been possible to determine the distance and the mutual positions of the vehicles.

Such devices have, however, certain drawbacks . The exten¬ ding bar makes it impossible to use the device on short distances. Also, position determination is not as good on short distances .

The object of the present invention is to achieve a device of the kind mentioned in the introduction that does not possess the drawbacks inherent in said known devices, and which is simple and admits accurate position determination even on rather short distances between the objects.

Such a device is primarily characterized in that the re¬ flectors comprise a spherical convex mirror, with a second rather great extension across the incoming radiation.

In a preferred embodiment of the device according to the invention, said reflector elements are placed about the outer limitation of the spherical mirror.

The arrangement that the spherical mirror shall have a rather great extension across the incoming radiation com- pared with the extension of the reflector elements across the incoming radiation is explained by the fact that the spherical mirror will mainly act as a reflecting prism on the distance of the radius of curvature behind the mirror. In order that the accuracy of the position determinations shall be good, this radius of curvature may not be too small. On the other hand, the required extension across the incoming radiation decreases with decreasing radius of curvature.

In order to make possible the distance determination be- tween the two objects when the mutual distance is so small that the first axis cannot be reflected by the reflector elements and be received by the receiver within its field of view, it is suitable to provide the transmitter with at least two radiation sources, arranged at a distance from said first axis .

The invention will now be described in more detail, with reference to the accompanying drawings, in which:

Figure 1 shows schematically a longitudinal section through a transmitter/receiver (on a first object, not shown) , a reflector (on a second object, not shown) ;

Figure 2 shows a view towards the markings II-II in Figure 1; while

Figure 3 shows schematically a longitudinal section, as in Figure 1, of the corresponding details, the transmitter being provided with two additional radiation sources.

In figure 1, a transmitter/receiver is designated by 1. It comprises a radiation source 2, in this case a laser diode, a semi-opaque mirror 3 set at an angle of 45° in front of the radiation source and at the same angle in front of a receiver 4 in the form of a CCD-camera, i.e. a camera with radiation-sensitive detector elements arranged two-dimensionally in the focal plane of the camera. In a known manner, these detector elements emit electric sig¬ nals in dependence on the received radiation. The direc¬ tion of the incoming rays can thus be determined with a resolution that depends on the optics of the camera and the area of extension of the detector elements. With the aid of the semi-opaque mirror 3 the reflected rays can be received and detected in exactly the same direction as the direction in which they are emitted, i.e. about a first axis, denominated by 5 in the figure. Transmitters/recei¬ vers are assumed to be provided on a first object, in this case a small space vehicle. On the second object, in this case a bigger space vehicle, a reflector is provided. It comprises four reflector ele¬ ments 6 in the form of prisms that reflect the received radiation in the same direction as it is received in a narrow lobe. At distances of the here relevant size the lobe width is of no importance. The reflector elements 6 are, as is evident from figure 2, located about the outer edge of a spherical mirror 7, which has its centre of curvature in a point C and its focus in a point F. This spherical mirror 7 acts here with respect to the direction to the mirror image of the radiation source that appears, as a prism of the kind just mentioned, on the distance from the mirror to its centre of curvature behind the mirror.

In a way known per se the mutual distance and relative at¬ titude positions in azimuth, elevation and relative atti¬ tude angles, i.e. heading, roll and pitch angles, of the two objects, in this case the two space vehicles, can be determined through the three-dimensionally arranged re- flection points which are defined by the position of the centre of curvature of the four reflector elements 6 and of the mirror 7. Three reflector elements 6 would be suf¬ ficient, however. In the shown example the reflector ele¬ ments are symmetrically located about the spherical mir- ror, as only roll angles in the range of ±5° have to be taken into account. For large roll angles the reflector elements would need to be located unsymmetrically in order to admit a uniform determination of the roll angle.

For small mutual distances between said two objects, two additional radiation sources 8 are used with advantage, located at a distance from the first axis 5. With the aid of the mirrors reflected by the spherical mirror 7 from said radiation sources, the distance can in a known way be determined through signal processing of the signals recei¬ ved from the receiver, i.e. the CCD-camera.

Claims

1. A device to make possible the bringing nearer and bringing together of a first and a second object, preferably two space vehicles, i.e. determining their relative distance, azimuth angle, elevation angle and relative attitude angles, heading, roll and pitch angles, the first object being provided with a trans¬ mitter (2) for emitting radiation about a first axis (5) within the optical wavelength range, such as la¬ ser light, and a receiver (4) for receiving said ra- diation to the extent it is reflected by a reflector on the second object, preferably in the same direc¬ tion as the emitted radiation, the receiver (4) com¬ prising a camera with radiation-sensitive detector elements arranged two-dimensionally in the focal plane of the camera (CCD-camera) arranged in depen¬ dence on the received radiation to emit the corre¬ sponding electric signals, said reflector comprising a number of reflector elements (6) with a first rather limited extension across the incoming radia- tion, preferably in the form of prisms for reflecting the incoming radiation in the same direction as the incoming radiation irrespective of its direction, characterized in that the reflector comprises a spherical convex mirror (7) with a second, rather great extension across the incoming radiation.

2. A device according to claim 1, characterized in that said reflector elements (6) are located about the outer limit of the spherical mirror (7) .

3. A device according to claim 1 or 2, characteri- z e d in that the transmitter (2) is provided with at least two radiation sources (8) arranged at a dis¬ tance from said first axis (5) , to make it possible to determine the distance between the two objects at distances so small that radiation about the first axis cannot be reflected in the reflector element (6) or be received by the receiver (4) within its field of view.