Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
2001-09-17
2004-01-20
Dinh, Tien (Department: 3644)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
C248S584000, C248S581000
Reexamination Certificate
active
06679455
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pointing device for supporting and pointing loads or components in a determined position. More particularly, the invention relates to precision pointing devices for placing in unstable environments that impart vibrations or multiple movements to such systems. In addition, the invention also relates to pointing systems on board space vehicles such as those used in satellites, exploration modules, or space probes.
PRIOR ART
In numerous fields, and in particular in the aerospace, detection, or telecommunications fields, some of the components used need to be pointed or steered with great accuracy. The loads or components concerned are any type of apparatus that needs to be accurately pointed in order to operate. By way of example, such components can be plasma thrusters for correcting the position of a satellite in orbit, transceiver antennas, mirrors, . . . In such applications, the components are associated with a pointing device or mechanism which is designed to support the components and to place them in a determined position. A component and its pointing mechanism once in association form an assembly which implements both the pointing function and the function of the component.
By way of example, when pointing plasma thrusters for correcting satellite orbits or when pointing satellite antennas, the range of values over which the entire component and pointing mechanism assembly can move is of the order of a few degrees. Thus, the reliability of the mechanisms both in terms of strength and in terms of precision determines whether or not the components they support operate properly.
Two problems arise with onboard components, i.e. components which need to be transported to the site at which they are to operate, e.g. those used in satellites that need to be placed in orbit by means of a rocket. Firstly, during transport, the pointing mechanism which supports the component must be capable of holding the component in a safe position while also guaranteeing proper mechanical behavior for protecting the component as far as possible against the significant stresses and vibrations due to accelerations. Secondly, the pointing mechanism must then be capable of becoming operational, i.e. the mechanism must have retained a predetermined orientation or must be capable of being moved so as to point the component into a determined position.
Concerning components that need to operate during transport or in an environment that is highly disturbed (vibration, impact, acceleration, . . . ), the two above-identified problems amount to a single problem. Under such circumstances, the system must be capable of protecting the component as much as possible from the mechanical disturbances generated by its conditions of use while simultaneously ensuring that the component is pointed precisely.
Considering such problems, numerous pointing systems have been devised, however they generally present mechanical structures that are very complicated, thereby significantly increasing the mass and the cost of the assembly to be transported or to be used without genuinely protecting the supported component from shock or vibration during transport or in operation.
Amongst known pointing systems, there are mechanisms making use of cardan mounts or of shafts. Those systems suffer from a major drawback associated with the hinge elements used. Cardan mounts or shafts as used in such systems cannot hold the component stably, and they transfer a large amount of vibration to the component during transport. In order to keep the assembly in a stable position during transport, solutions involving locking the pointing system have been considered. By way of example, they consist in a device of the kind described in “High performance reactionless scan mechanism”, by E. I. William, R. T. Summers, M. A. Ostaszewski, Ball Aerospace, 29th Aerospace Mechanism Symposium, NASA Conference Publication 3293, which device presents a pointing mechanism with cardan mounts that are “locked” via the actuators for launch purposes. Nevertheless, in such a mechanism, the cardan mounts are prevented from moving only via the actuators which leaves the cardan mounts with a certain amount of slack that is sufficient for transmitting undesirable vibration to the load.
Another solution, described in the document “Thruster orientation mechanism”, by S. Mankai, Alcatel Space Industries, 8th European Space Mechanisms and Tribology Symposium, ESA SP-438, consists in a plasma thrust pointing system which comprises two plasma thrusters disposed on a common plate carried by silicone dampers and a two-axis cardan mount fitted with ball bearings. That system is pointed by linear actuators placed on roller screws. The entire mechanical structure of that system is locked by an assembly of holding plates and bolts fitted with apparatus including pyrotechnical cutters for releasing the assembly on its site of operation. That solution is unsatisfactory since shocks due to the pyrotechnical devices are undesirable on sensitive components such as plasma thrusters. In addition, the system is very heavy, having a mass of 17 kilograms (kg) even though the maximum mass required for that type of system in a plasma thrust application for a satellite is no more than 8 kg. Finally, apart from its large mass, that system continues to be highly vibratory.
OBJECT AND BRIEF SUMMARY OF THE INVENTION
The present invention seeks to remedy the above-mentioned drawbacks and to provide a pointing device that is simple and capable, in a single structure, of combining the functions of stabilization and of pointing.
These objects are achieved by means of a pointing device for supporting a load on a support element, the load being supported above the support element by moving link means, wherein the moving link means comprise at least three distinct link arms distributed around the load, each link arm comprising a flexible element having a first end connected to the support element via a first hinge having a single degree of freedom, and a second end connected to the load via a second hinge having a single degree of freedom, and wherein the pointing device further comprises at least one means for transmitting movement disposed between the support element and the load to point the load relative to the support element.
The device of the invention thus makes it possible to connect a load to a support element via backlash-free links, thus giving additional stiffness to the assembly while conserving a certain amount of mobility for pointing.
In a particular aspect of the invention, the load also comprises a fixing bracket connected to the link arms.
In an aspect of the invention, in each link arm, the first hinge has a first pin supporting the first end of the flexible element, the first pin being fixed to the support element by a fixing member, and the second hinge comprises a second pin supporting the second end of the flexible element, the second pin being fixed to the load by a fixing member, the first and second pins of each link arm being parallel to each other and perpendicular to the flexible element when the device is in its initial position.
Thus, by means of these hinges assembled to each of its ends, and because of the flexible element which is connected to said hinges, each link arm retains stiffness necessary for supporting the load while nevertheless remaining movable in various directions so as to allow the supported load to be pointed in a determined direction.
According to a characteristic of the invention, the movement transmission means comprises an actuator formed by a stator element fixed to the support element, the stator element supporting a turntable having a retaining element fixed eccentrically on the turntable and having attached thereto a first ball-and-socket joint disposed at one end of a connecting rod, a second ball-and-socket joint disposed at the opposite end of the connecting rod being attached to a retaining element disposed on the supported load, the first and second ball-and-socket joints provide
Dinh Tien
SNECMA Moteurs
Weingarten Schurgin, Gagnebin & Lebovici LLP
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