This invention relates to deployable antennae in general and to shape memory deployable dish antenna in particular.
Parabolic dish antennae are desirable for space communications as they offer high so-called antenna ‘gain’ (concentration and beam width of the signal energy) and through it, extend a satellite's effective communications range. For a given electromagnetic wavelength, the larger the diameter of a dish antenna, the higher its ‘gain’.
Rigid permanent dish antennae due to their size and geometry are impractical for smaller satellites, such as ‘mini’-, ‘micro’- and ‘nano’-types of satellites presently gaining wider usage. Present deployable dish antennae have been largely unfeasible as well, due to their size, shape, weight and their deployment mechanism complexity and mechanical interface requirements.
At present, deployable reflector dish antennae used in satellites generally fall into two groups. One group comprises dish antenna assemblies with several petal-shaped rigid elements forming a paraboloid reflector when unfolded. Because these elements are rigid, they are often stowed as a stack, to be opened and deployed rotationally.
The other group includes antenna reflectors which comprise a set of supports to which a flexible reflective membrane is attached. The supporting structures, such as radial ribs, are relatively rigid and are customarily stowed as an elongated bundle folded along its longitudinal axis. Some membrane support structures when deployed take a form of complex three-dimensional lattices which unfurl/unfold in space and support the attached reflective membrane in the required paraboloid shape.
A wide variety of the dish antenna deployment mechanisms exist or have been proposed. They include mechanical gearing assemblies, cables and tensioners and some limited shape memory actuators. Majority of them are mechanically quite complex and sometimes fail to fully deploy the antennae.
The present deployable dish assemblies are also awkward to store since they have to be located and oriented in very limited and specific ways to conform to the available envelopes aboard the launch vehicles while still be a part of a satellite.
Also because of the necessity to conform to the launch vehicle's configuration and the overall satellite physical envelope, the location selection of the antenna on a satellite itself is complicated, subject to numerous constraints and trade-offs.
Additionally, the sometimes off-axis placement of the antenna deployment mechanism adversely affects the center of gravity and rotational moments of a satellite and introduces complications for its in-flight positioning and maneuvering.
The addition of the deployment mechanisms and their rigid mechanical interfaces with the antennae themselves add to the assemblies' bulk, weight and complexity, the latter leading to their reduced overall reliability.
Thus, it is the objective of instant invention to provide a compact deployable dish antenna assembly which prior to deployment would be stowable in a variety of locations and at various attitudes on a satellite.
Another objective is to provide an antenna whose deployment would be reliable.
Another objective is to provide an antenna with high volumetric packing efficiency.
Yet another objective is to provide an antenna which would not require separate mechanical deployment mechanism.
Another objective is to provide an antenna which would be lightweight.
Yet another objective is to provide an antenna which would be compatible with deep space environment.
Another objective is to provide an antenna whose deployment would be energy efficient.
In accordance with the present invention, shape memory based deployable reflective dish antenna is described and its several embodiments are presented.
The shape memory antenna dish is formed into its desired deployed shape during manufacturing and subsequent ‘training’ where it is mechanically restrained in the deployed geometry while being heated at—or above the phase—or glass transition temperature of the shape memory material and is allowed to cool off. Thereafter, mechanical restraints are removed at which point the dish remains in its deployed configuration. The dish then is highly radially folded/corrugated to provide for efficient storage.
The shape memory dish antenna remains in its packaged configuration until deployment. At deployment it is heated to—or above the phase—or glass transition temperature of the shape memory material, and returns to their original ‘as-trained’ shape.
In addition to the dish itself, several shape memory antenna feeds are also presented, some with telescopic waveguide elements extended by several types of shape memory actuators and some having an extendable shape memory waveguides formed from corrugated tubular shape memory preforms. These feeds can be used interchangeably with the antenna dish.
Some antenna embodiments presented, in addition, include deployable sub-reflectors positioned above the main reflector and facing the feeds, and some use small patch antennas instead of the feeds and sub-reflectors.
Articles made with shape memory materials, their fabrication, ‘training’ and usage are known in their respective arts.
The prior art for deployable antennae is extensive, since these antennae have been a key piece of communications equipment for satellites from the dawn of space exploration. Deployable antennae with shape memory elements are relatively new, however.
For example, U.S. Pat. No. 7,710,348 to Taylor et al. teaches a deployable antenna reflector which utilizes a shape memory element to open conventional rigid ribs supporting a flexible reflector.
U.S. Pat. Nos. 8,259,033 and 9,281,569, both to Taylor et al. teach a deployable antenna reflector with longitudinal and circumferential shape memory stiffeners supporting a reflective elastic material.
U.S. Pat. No. 10,170,843 to Thomson et al. teaches mechanically actuated foldable support conventional ribs for antenna reflector and a pleated foldable reflector itself.
None of the prior art above suggests or teaches a deployable shape memory solid reflector created from a folded/corrugated preform.
None teaches deployable shape memory antenna feeds or sub-reflector supports, or using patch antennas in conjunction with parabolic reflectors.
In contrast to the prior art mentioned hereinabove, the instant invention describes shape memory dish antenna which offers the following advantages.
High Volumetric Storage Efficiency
The reflector of the instant antenna system is tightly folded and merely requires application of heat for its deployment. Without any mechanical deployment apparatus, the resulting assembly offers a very dense package. The required heaters can be very compact as well, or the reflector can be heated directly with electric current.
In addition, the very shapes of the deployable reflector can be optimized for both storage and for deployment. Thus, greater design latitudes exist to optimize packaging, interface with the satellite, and deployment of the antenna.
Light Weight
Due to the absence of the relatively heavy mechanical deployment drives and their associated interfaces, the weight of instant antenna system is greatly reduced. The required heaters can be very thin and lightweight and in some applications the actuating heat can be generated by passing electric current directly through the reflector and feeds themselves. A completely passive heating and subsequent antenna deployment can be achieved by exposing the antenna system elements to sunlight by appropriately maneuvering the satellite. In the vacuum of space, solar heating can be considerable.
Simplified Construction
The instant antenna system comprises a very limited number of parts. There are basically no separate ‘actuators’ per se, other than heaters, with the system elements deploying themselves upon application of heat, by utilizing elastic energy stored at the time of packaging. The deployment heaters of instant invention are much smaller and less complicated than mechanical actuators of the present deployable antennas.
Improved Reliability
With thermal actuation of instant invention replacing present electro-mechanical actuators the instant antenna system is much more reliable, since the only moving parts are the very support elements themselves. With timed heater activation specific deployment sequences are possible to minimize the risk of malfunction or interference.
Easier Redundancy Implementation
Since it is much easier to provide redundancy to an electrically heated deployment system than to a mechanical actuator(s)-based one, the shape memory based antenna systems can have enhanced redundancy of its deployment apparatus.
Heating and Deployment by Sunlight
As mentioned above, since heating of satellite components by solar radiation in space can be considerable, the instant antenna system elements can be exposed to sunlight instead of heaters for deployment. This also can be used as a backup procedure in case of a heater failure. To facilitate sunlight heating the system elements can have radiation-absorptive coating(s).
High Stored Energy
The shape memory materials used for the support elements store considerable elastic energy at the time of packaging and can generate considerable forces during deployment to overcome potential adhesions, friction and snags.
Relaxed Requirements for Placement/Orientation on Satellite or Launch Vehicle.
Due to the compact size of the antenna system its location on a satellite is not as constrained as for the present deployable antennas. This simplifies the design of a satellite itself and/or its operations. In addition, the instant antenna system can be more easily located to minimize its effect on the location of the satellite's center of gravity, which will also simplify satellite operations.
In the foregoing description like components are labeled by the like numerals.
Deployable antenna system 2 is depicted in an exploded view on
A preferably convex secondary reflector 60 is connected to coiled extendable supports 44 made with shape memory material mounted on ring 46 which in turn is connected to the upper face of feed 123. Supports 44 are heated for deployment by a tubular upper heater 51.
Corrugated feed 123 made with shape memory material with lumen 124 is coaxially positioned at the center of reflector 100 and is surrounded by a tubular lower heater 52 which heats feed 123 for its extension and deployment.
Bottom heaters 55a, 55b and 55c controllably heat dish 100 for its transition into deployed configuration 100a.
Referring to
An alternative antenna system embodiment 4 is illustrated on
Feed assemblies 40 and 42 can be deployed independently of dish 100 by actions of heaters 51 and 52.
An alternative antenna system embodiment 6 is illustrated on
Upon application of heat supplied by heater 51 (not shown) supports 156 extend and assume their deployed shape 156a shown on
An alternative antenna system embodiment 8 is shown on
Antenna system 8 is close in construction to embodiment 4, with the difference being the supports for secondary reflector 60 and an extendable feed assembly variant 47. Feed assembly 47 is almost identical to feed assembly 40 with the difference being the absence of supports 44. Its activation by heater 52 (not shown) through the action of coil 48 transitioning to its deployed configuration 48a, and its subsequent deployed configuration 47a are also similar to those of feed assembly 40.
Referring to
As shown on
The transition of antenna system 8 to its fully deployed configuration 8b is complete when dish 100 is in its deployed configuration 100a by cooperative action of bottom heaters 55a, 55b and 55c (not shown), feed assembly 47 in its deployed configuration 47a and supports 160 in their fully deployed configurations 160b.
In system deployed configuration 8b secondary reflector 60 is positioned to face deployed dish 100a and lumen 43 of feed 47.
On
Dish 100 is then deployed by action of bottom heaters 55a, 55b and 55c (not shown) and assumes its deployed configuration 100a, causing supports 160 to assume their final deployed configuration 160b which positions patch antenna 61 at the focal point of deployed dish 100a, thus completing deployment of antenna system in its fully deployed configuration 9b. Not shown on these figures is a radio-frequency cable which would normally connect patch antenna 61 to a transceiver on a satellite. Such a cable would be routed from a transceiver to patch 61 along one of supports 160b.
Since patch antenna 61 can both emit and receive electromagnetic radiation by itself, a dedicated feed is not required in the system.
Deployable antenna system 10 is depicted on
Referring to
The shape memory materials used in the instant antenna system construction may include shape memory alloys (‘SMAs’) or shape memory polymers (‘SMPs’).
Shape memory alloys comprise numerous alloys such as AgCd, AuCd, cobalt-, copper-, iron-, nickel- and titanium-based, with most well-known and used being Cu—Al—Ni and Ni—Ti alloys (the latter known as ‘nitinols’).
Shape memory polymers comprise linear block polymers such as polyurethanes, polyurethanes with ionic or mesogenic components made by prepolymer method, block copolymer of polyethylene terephthalate (PET) and polyethyleneoxide (PEO), block copolymers containing polystyrene and poly(1,4-butadiene), and an ABA triblock copolymer made from poly(2-methyl-2-oxazoline) and polytetrahydrofuran.
Also, cross-linked PEO-PET block copolymers and PEEK can be used as shape memory elements of instant invention.
Some of these SMPs can be made to contain carbon which makes them electrically conductive. This conductivity can be advantageous for their direct heating with electrical current and the reflectance of the antenna dish made from them.
Operation
The controlled deployment sequences of antenna system elements ensure reliable deployment of the antenna, its achieving desired paraboloid configuration 100a and proper deployment and positioning of the feed, secondary reflector 60 or patch antenna 61.
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Other Embodiments
On
Voltage sources 210a, 210b and 210c can be combined into a single source attached in the center and outer edge of dish 100, if it is determined that a reliable deployment can be achieved with simultaneous heating of all parts of dish 100.
When dish 100 is directly heated electrically, in all antenna embodiments heaters 55a, 55b and 55c are not required.
Likewise, direct electrical heating can be used for feed and supports deployment, obviating the need for heaters 51, 52 and heater assembly 54.
A number of heat pipe technologies are well known in their respective art, and are widely used for heat transfer applications in satellites. Flat heat pipes in particular are also well known in the art.
Heat pipes advantageously transfer heat from one of their ends to another. As a result, a heat pipe is uniquely suitable for heating the distal end of the heat pipe-based shell 101 first, so it extends before the rest of the shell 101's sections do.
As the distal end of shell 101 heats up and assumes its deployed shape, heat is diffused along the shell and gradually raises the temperature of the middle- and then the proximal sections of shell 101. As a result, shell 101 radially extends to its full deployed size and shape.
In addition, heat pipe technology can be used for feeds 123, 150 and 180. Instead of solid shape memory shells from which these components are constructed, they can be made hollow and operate as heat pipes.
Additionally, feed actuators 41 and 48, supports 44 and 160 can all be made to utilize heat pipe technology as well.
By using heat pipe technology, heating of the shape memory elements can be greatly simplified, since heat can be applied from their proximal ends only and the resulting temperature distribution is fairly uniform from one end of a heat pipe to another.
Thanks to the nature of heat pipes operation, shape memory components' distal sections will be heated first, thus transforming them into their deployed configuration, to be followed by the proximal sections, as is desirable for reliable antenna deployment.
The heat pipes working compound can be water, ammonia or other, the first two being especially chemically compatible with nickel-titanium shape memory alloys which can be utilized for the antenna system.
Other antenna configurations, although not illustrated, are feasible.
Solid dish 100 can be perforated to reduce weight, provided the perforations are smaller than the operational electromagnetic wavelength of the antenna.
Also to save weight, a metallic wire mesh made from a memory shape material can be substituted for a solid sheet for dish 100.
Although shown as circular in its configurations, dish 100 can have an ovoid shape, deploying into an oblong paraboloid. Also, the feeds, secondary reflectors and patch antennae can be positioned at an angle to dish 100 centerline or off-center for off-axis dish operation. Such configurations are well known in the art.
Patch antenna 61 can have a receiver pre-amplifier and/or a transmit power amplifier integrated in it for a combined package held by supports 160b.
As shown on
Although shown as circular, feed lumens 43, 124a and 186a can be oval or rectangular, with different shape proportions. The resulting waveguides of these lumen geometries and their respective performance are well known in the art.
Various heat sources can be used to activate the shape memory elements and deploy the antenna, such as sunlight, chemical heat generators, electric infrared sources, and nuclear sources.
Shape memory components can have thermally absorbing coatings to facilitate their heating and deployment by sunlight.
Bottom heaters 55a, 55b and 55c do not have to be discrete, as single heating element can be sufficient in heating dish 100 for deployment if it is determined that the shape transformation is accomplished successfully. A heater with a radially varying heat output, for example made with a plurality of annular heating sub-elements or with varying radial density of individual heaters or a single element with radially varying resistance is also possible for controlled heating of dish 100.
Electrical contacts used for direct heating of shape memory components by electric current can be made to disengage from the heated components upon deployment.
The electrical contacts can also be made frangible, to also disengage from the components upon their deployment.
The power leads to the heaters on the shape memory components or the components themselves can be made retractable or coiled to retreat after the components' deployment.
Shape memory antenna components can have conductive or resistive film coatings deposited on their surfaces in various patterns to facilitate their controlled heating by electric current applied to these coatings and their resulting controlled deployment.
The feeds do not have to be centered with respect to the primary reflector, and the reflector itself does not have to be circularly symmetric. Rather, off-axis operation is possible, and, indeed, is widely practiced in the art.
Although descriptions provided above contain many specific details, they should not be construed as limiting the scope of the present invention.
Thus, the scope of this invention should be determined from the appended claims and their legal equivalents.
Number | Name | Date | Kind |
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20040085615 | Hill | May 2004 | A1 |
20110298688 | Jalali Mazlouman | Dec 2011 | A1 |
20170201031 | Gelb | Jul 2017 | A1 |
Number | Date | Country |
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101713306 | Oct 2015 | KR |
101868768 | Jan 2018 | KR |
Number | Date | Country | |
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20220013919 A1 | Jan 2022 | US |