Protective housing for space applications

Abstract: A structure and a method for housing equipment pieces in space vehicles in which the pieces of equipment are suspended to the inside of a sealable container, said container (1) is then closed and filled by a light-weight loose material and a nonfreezing thermally conducting liquid under pressure.

Description: The present invention relates to a structure for housing equipment pieces in space vehicles such as telecommunication satellites. The invention further relates to a method for housing equipment pieces in space vehicles such as telecommunication satellites. The inside of telecommunication satellites and similar space vehicles is susbstantially occupied, besides fuel tanks, by a variety of electronic boxes, i.e. enclosed and sealed cases housing electronic devices and circuits, that are to be secured to the satellite frame and electrically connected to each other and to external devices. Such electronic boxes, collectively known as payload, include for example batteries, signal transponders, data handling equipment, converters and so on. Within the spacecraft structure each box has a fixed location determined by a number of constraints, such as size, thermal dissipation, center of gravity, rigidity, EMC immunity. The boxes are linked to one another by a variety of electric wiring or harness. Presently known arrangements for housing and securing such electronic boxes to the inside of a satellite or similar vehicle have the drawback of subjecting the equipment to amplification load coming from dynamic coupling environment. More particularly, a dynamic coupling is said to exist when a source of force (or acceleration) applies to the satellite a given force or acceleration (input force), and the equipment is subjected to a force or acceleration (output force) that is larger than that of the source. A relatively high level of force (or acceleration) applied to the payload requires the use of special and complex structures for mounting the payload that increases the overall mass of the satellite. A method for providing an easily removable shock absorbing encapsulant for filling the voids between a housing and the electronic circuit assemblies arranged therein is disclosed in US 4,118,816. According to this document the filling material is made of pellets of silicone rubber. Other methods for protecting electronic components and circuits inside an electronic equipment are disclosed in JP 02 213199 and IBM Tech. Disclosure Bulletin (McGregor J E) - Vol2, no.5, Feb 1960 page 18 XP002071529. JP 02 213199 discloses a method for filling a molding agent in an electronic apparatus. According to JP 02 213199 an electronic apparatus comprising a series of electronic components is arranged on a support board housed in a case which is filled with a molding agent. For facilitating filling, the case is provided with an air vent opening placed above the opening of the apparatus for filling up the molding agent. McGregor refers to a liquid-tight container for housing electronic components. According to the teaching of this document, the electronic components are rigidly supported in the container by means of nylon spheres with a high modulus of rigidity. In addition, a cooling liquid is circulated within the vacancies between said spheres by means of an external pump. It is the object of the present invention to overcome the above drawbacks and more precisely to prevent dynamic coupling between the two mechanical environments made up by the container housing the equipment and the equipment items. This object is achieved through a structure as defined in claim 1; a method as claimed in claim 7 and a space vehicle as defined in claim 13. The invention will now be disclosed in detail with particular reference to the attached drawings illustrating a non limiting preferred embodiment of the invention, in which: Fig. 1 is a schematic cross section view of a structure according to the invention; Fig. 1A is an enlarged view of a detail of Fig. 1; and Fig. 2 is a more detailed view of a main container in its integration phase. With reference to the drawings, the structure of the invention comprises a main container 1 and a cover 2 adapted to sealingly close the container through conventional means that are not illustrated in the drawings. The main container 1 has a generally cylindrical shape, but also a cubic box could be chosen, and the cover 2 is provided with a filling port 3 and a relief valve 4. A number of equipment pieces 10A, 10B, ..., 10N are mechanically suspended within the container 1 through wires or a set of hoisting devices 5 so that the location of each item is not fixed. Then the container is hermetically closed by applying the cover and a filler is introduced into the container through the filling port 3 so as to fill the voids (vacancies) and pressurize it of some millibars in respect of the external atmospheric pressure. Thus each individual item of the equipment can move but only within a very small portion of the main container. Preferably the filler has elastic plus mechanical absorption properties so that when the container is subjected to an acceleration, the items inside the container are accelerated of an amount lower than that of the source of acceleration, i.e. there is no amplification factor. The filler comprises a light-weight loose material and a nonfreezing thermally conducting liquid. The light-weight (or low density) loose material can be formed for example by balls of a polymeric material such as preferably polystyrene or polyurethane, or other shock absorbing polymeric materials such as polyisocianurate, cellular glass, styrofoam, perlite and phenolic-based products, mineral wool, dichloro-fluoro-ethane based products, elastomers, synthetic rubber, polyethylene-based products, cellulose-made products, polyamide-based products. The polymeric balls are mixed with a nonfreezing conducting liquid such as water or mineral oil, with anti-freezing mixture. After suspending the items and completing the functional tests, the main container is filled with polystyrene balls so that the equipment items can stand up without falling when loosing the hoisting devices. Afterwards the main container is closed and through the filling port other polystyrene is admitted to slightly pressurize the container by specific Fluid Ground Support Equipment (FGSE) so to eliminate vacancies inside the container 1. Finally watery matter or in general a thermally conductive not freezing liquid is admitted into the container, always through the filling port 3, to fill the air gaps left among the balls so that at last only liquid and polystyrene is found around the equipment items. Of course the equipment items and the connectors are water-tight. The filler, that is a very light density material, wraps the equipment items located inside the main container 1 in a tridimensional configuration. This very compact configuration strongly reduces the envelope sizes of the overall layout. Since the liquid is thermally conductive it can dissipate power with n*4π*r 2 equivalent radiative surface, where n is the number of balls of radius r enclosed in the main container. This constitutes more than 1,000 times of radiation surface than in any other ever built satellite. When using a structure according to the invention, the force acting on the payload due to the acceleration applied by a launcher generates onto the spacecraft (S/C) main box (primary structure) a quasi-static load of 3-4 g along any directions and the single equipment item should not be subjected to an acceleration higher than that. This low level of acceleration allows to greatly simplify the equipment structure thus reducing the mass by a significant amount. Moreover, the arrangement leaves free room around the equipment items with an easier handling for operational checks. The small size of the overall layout and the equipment suspension permit to have less stringent specification as far as the S/C center of gravity is concerned. This important parameter can in fact be modified to best satisfy the launcher specifications up to the final integration process where equipment accommodation inside the main container can still be changed following mass balance results. Equipment integration can begin without primary structure availability, so integration and preliminary functional tests take place immediately after procurement. Dummies can be used when the equipments are not available yet, so to already find final solutions for harness requirements. Although the invention has been disclosed with reference to preferred and non-limiting embodiments, the same is not to be meant as limited to the illustrated examples but extends to include all the modifications and changes within the scope of the appended claims.

Claims: A structure for housing electronic equipment pieces (10) in a space vehicle, the structure comprising: a sealable main container (1,2); means (5) for mechanically suspending said pieces (10) of equipment to the interior of said container (1,2), said pieces of equipment being free to move within a portion of said main container; means (3) for injecting a filler under pressure inside said sealable main container (1,2); a filler having elastic plus mechanical absorption properties, said filler wrapping each piece of equipment located inside said main container and absorbing the inertial load exercised by said pieces of equipment when an acceleration force is applied to said main container. A structure as claimed in claim 1, characterized in that said electronic equipment pieces (10) are enclosed and sealed cases housing electronic devices and circuits. A structure as claimed in claim 2, characterized in that said filler comprises a light-weight loose material and a nonfreezing thermally conducting liquid under pressure. A structure as claimed in claim 3, characterized in that said light-weight loose material comprises balls (6) of a shock absorbing polymeric material. A structure as claimed in any one of the preceding claims, characterized in that said sealable container (1,2) comprises a box-like container (1) and a cover (2) carrying a filling port (3) and a relief valve (4), that can be sealingly fitted to said box-like container (1). A structure as claimed in any one of the preceding claims, characterized in that said means (5) for suspending said pieces (10) of equipment comprises wires or a set of hoisting devices (5). A method for housing electronic equipment pieces (10) in space vehicles, the method comprising the steps of: providing a sealable main container (1,2); suspending said pieces of equipment to the interior of said container so as to leave said pieces of equipment free to move within a portion of said main container (1,2); closing said container and filling the remaining inner space thereof with a filler having elastic plus mechanical absorption properties, said filler wrapping each piece of equipment located inside said main container and absorbing the inertial load exercised by said pieces of equipment when an acceleration force is applied to said main container. A method as claimed in claim 7, characterized in that said filler comprises a light-weight loose material and a non freezing thermally conducting liquid under pressure. A method as claimed in claim 8 characterized in that said light-weight loose material comprises balls (6) of a shock absorbing polymeric material. A method as claimed in claim 9, characterized in that said polymeric material is selected from the group consisting of: polystyrene, polyurethane, polyisocianurate, cellular glass, styrofoam, perlite and phenolic-based products, mineral wool, dichloro-fluoro-ethane based products, elastomers, synthetic rubber, polyethylene-based products, cellulose-made products, polyamide-based products. A method as claimed in claim 8, characterized in that said nonfreezing thermally conducting liquid is selected from the group consisting of: a mixture of water or mineral oil, or water based liquids, or oilbased liquids, and anti-freezing liquids. A method as claimed in claims 8 to 11, characterized in that said filling step comprises: admitting an amount of said light-weight loose material into said container; filling the container with said thermally conducting liquid. A space vehicle incorporating a payload consisting in a plurality of electronic equipment pieces electrically connected to each other, said equipment pieces (10) being suspended inside a sealable main container (1,2) so as to leave said pieces of equipment free to move within a portion of said main container (1,2), said main container being provided with means (3) for injecting a filler therein under pressure, said container (1,2) being filled with a filler having elastic plus mechanical absorption properties wrapping each piece (10) of equipment located inside said main container (1,2) and absorbing the inertial load exercised by said pieces of equipment when an acceleration force is applied to said main container.

Inventors: NEGESAT DI BOER FABRIZIO, BODINI, AMEDEO, Negesat Di Boer Fabrizio &amp; C. SNC
Applicants: NEGESAT DI BOER FABRIZIO & C S, NEGESAT DI BOER FABRIZIO & C. SNC
Application year: 1998
Main classification: H05K5
IPC codes: H05K5, B64G1, H05K7