Remote activation mechanism for equipment hold down and release

Details Remote activation mechanism for equipment hold down and release Remote activation mechanism for equipment hold down and release

2002-01-08

2004-07-06

Jackson, Stephen W. (Department: 2836)

Electricity: electrical systems and devices

Control circuits for electromagnetic devices

For relays or solenoids

C361S194000, C361S206000

Reexamination Certificate

active

06760211

ABSTRACT:

The present invention refers to a remote activation mechanism for equipment hold down and release, specially applicable to the release of systems and equipment requiring a firm structural hold down, such as deployable antennas, solar panels, deployable radiators, as well as ejectable equipment (such as covers) of space vehicles, oceanographic equipment, aeronautics, military equipment, etc.
There are units or appendages needing remote release activation. A clear example, although not the only one, is the release of satellite appendages that require generally to be firmly joined to the satellite structure to survive the launch loads, while they require to be in a different configuration to be operative, decoupled, far away from the satellite main structure, or disconnected from the satellite structure. Appendages such as antennas, solar arrays, thermal radiators, experiments, ejectable protection covers etc., need to be released and deployed or ejected once the vehicle is in orbit.
Up to now, the problem of the release of such equipment has been solved using pyrotechnic release systems, such as cable/bar cutters, pushers and releasable appendage separation nuts. Those systems are based on the activation of a cutting, pushing, or separation mechanical system, using the pressure of the gases produced when a small explosive charge is detonated. Those actuators have been used extensively due to its compactness, simplicity and reliability. Nevertheless, those systems have the following inconveniences:
a) They can produce uncontrolled residue, such as metallic particles, polluting gases, etc. that in many cases cannot be afforded due to the type of systems the satellite contains, such as optical equipment, precision mechanisms, electronic equipment, etc.
b) They produce very high accelerations at high frequencies, which shock the main structure, transmitting this excitation to all the equipment located at the surroundings. Those accelerations at high frequencies are the main characteristic of explosive actuators, being extremely dangerous for the integrity of delicate equipment such as radio frequency and electronic equipment.
Those accelerations have two main causes. The first one is the explosion itself; the second is the sudden energy deformation liberation originated by the necessary preload of the hold down system. It is necessary to add that the achieved acceleration level is hardly attained by analysis due to the complexity of the model definition to represent the real event, and due to the uncertainty in the definition of the parameters involved in its simulation. Due to that, expensive tests on model representing the reality should be necessary.
c) Pyrotechnic systems are not reusable. They demand the complete substitution of the actuator to be able to maintain the system at the same operative level than before, as well as a new re-connection of the electric connectors necessary to provide the initiator activation current. That makes that in a satellite qualification test campaign to be performed before being launched and before being operated in orbit, could need of great quantity of pyrotechnic devices.
d) Pyrotechnic systems have an intrinsic risk during their manipulation, storage, or operation, being necessary to take care of potential electrostatic discharges and of potential electromagnetic interference that could activate those systems.
e) Pyrotechnic systems have not the capacity of being proven functionally before being used to achieve a confidence in their operation, being necessary the use of statistical data or test by lot on randomly selected units. Therefore, the pyrotechnic device that will be used in orbit could not be used on ground for test purposes, being impossible to perform a direct verification of the unit. Additionally, the connectors providing electric current to the pyrotechnic initiators should be disconnected and re-connected in each operation, meaning a significant increase of failure risk in that electrical connection.
f) The pyrotechnic systems are based on the detonation of an explosive material. This detonating material is usually provided with a limited life due to the degradation of the stability of explosive chemical composition with time.
An alternative to pyrotechnic systems, used in some cases, is the use of motorised hold down and release mechanisms. Those mechanisms are usually complex and heavy, suffering of lack of compactness, high cost, high sensibility to the environmental conditions, and low reliability.
The current tendency in the satellite construction is towards smaller vehicles with more sensitive instrumentation. The combination of highly sensitive equipment, in smaller and slighter structures in combination with hold down release mechanisms makes necessary the development of non explosive release actuators for not endangering the survival of the mission.
These inconveniences have given way to non-explosive hold down release mechanisms, based on three different concepts:
a) Mechanisms with a fusible wire, based on providing the sufficient heating energy to a wire that maintains the mechanism preload up to fuse it (or at least weaken it up to rupture). The rupture or fusion of that wire makes as a trigger that activates the mechanism that performs the release. Once the wire breaks or fuses and the mechanism is operated, the system should be rearmed and the initiator containing the fused or broken wire should be substituted to have the device ready for a new operation.
b) Mechanisms with paraffin actuators, based in the paraffin increase of volume when it fuses (15% approximately). This increase of volume is controlled as to push a stem that can activate the release. These mechanisms are voluminous, complex, expensive and very slow in their performance, being able to present problems of leakage or molecular contamination in vacuum environment.
c) Mechanism with shape memory alloy piece, based in the use of the significant contraction or expansion of shape memory alloys when the piece reaches its transition temperature, activating directly the release, by breaking the joining bolt or by changing the geometry of the element maintaining the joint sufficiently as to release the fastener or the retainer.
Pieces manufactured with shape memory alloys, being processed in a suitable way and under certain circumstances, have the property of being able to change their form cyclically with their temperature, being able to reach a deformation of 4%.
Those mechanisms can be activated, or using direct application of heat on the shape memory alloy piece up to reaching its transformation temperature, or applying a direct electric current through this piece in order to heat it up to reaching their transformation temperature. They are based on the rupture of the fastener or retainer, being very compact. But they have the inconvenience that they can originate particles of the fractured piece that could endanger the operation of delicate equipment. Additionally, they should be substituted completely for a new use, making impossible their direct verification before operation.
Those mechanisms, based on the geometry change of the element maintaining the joint as to release the fastener or the retainer, are voluminous and heavy, having lack of compactness. They are usually used in very specialised applications that usually are not extendable to other uses.
All them highly reduce the high accelerations at high frequencies that characterises to pyrotechnic devices as they do not need any explosion, and release activation is not so sudden but more progressive than in the case of pyrotechnic devices. Nevertheless, they already have the above described inconveniences.
The objective of the present invention is to solve the problems of pyrotechnic devices and the inconveniences of the existing non-explosive actuators, by means of an actuator that fulfils the following characteristics.
a) Non pyrotechnic device (no explosion).
b) High load carrying capability, with easy preloading operation.
c) Non causing high acceleration during operation (progressive r

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