Variable Heat Rejection Device

Abstract

A heat rejection system that employs temperature sensitive shape memory materials to control the heat rejection capacity of a vehicle to maintain a safe vehicle temperature. The technology provides for a wide range of heat rejection rates by actuation of the orientation or position of a heat rejection panel which impacts effective properties of the heat rejection system in response to temperature. When employed as a radiator for crewed spacecraft thermal control this permits the use of higher freezing point, non-toxic thermal working fluids in single-loop thermal control systems for crewed vehicles in space and other extraterrestrial environments.

Claims

1. A thermal energy radiator system, relating to a variable heat rejection, that controls the heat rejection capacity at least in part through articulation or shape change of a thermal energy radiator comprising: a) at least one thermal energy radiator structured and arranged to radiate thermal energy generated by at least one thermal energy source of at least one spacecraft into an external environment; b) at least one thermal energy transport system structured and arranged to collect heat from at least one thermal energy source and transport said collected heat to said thermal energy radiator; c) wherein said thermal energy transport system may transport heat through any typical means of heat transport including, but not limited to, thermal fluid flow and thermal conduction; d) wherein said thermal energy radiator contains a facesheet structure which articulates or changes shape in response to the temperature of said thermal energy radiator, thermal energy transport system, or thermal environment; e) wherein said thermal energy radiator articulation or shape change behavior comprises: at least one shape which has a high heat rejection capacity; and at least one shape which has a low heat rejection capacity, wherein the shape taken by the thermal energy radiator depends on temperature; f) wherein said thermal energy radiator articulation or shape change behavior further comprises the selective obscuring and exposing, in whole or part, of thermal energy radiator surfaces to affect effective view factor; and g) wherein said thermal energy radiator articulation or shape change behavior further comprises the selective obscuring and exposing, in whole or part, of high and low emissivity surfaces to affect effective emissivity.

2. The thermal energy radiator according to claim 1 wherein said thermal energy radiator articulation or shape change behavior further comprises: a) a shape or configuration that causes a reduced heat rejection in response to temperatures below at least one transition temperature; b) a shape or configuration that causes an increased heat rejection in response to temperatures above at least one transition temperature; c) wherein said articulation or shape change occurs due to temperature sensitive shape memory inherent to the material of at least one component of said thermal energy radiator; d) wherein said articulation or shape change can occur without active control or the addition of any power other than the thermal power provided by the energy transport system or the thermal environment; e) wherein said articulation or shape change to decrease heat rejection may occur multiple times, or continuously, as many times as temperature cycles from above to below the transition temperature of the change while in service; and f) wherein said articulation or shape change to increase heat rejection may occur multiple times, or continuously, as many times as temperature cycles from below to above the transition temperature of the change while in service.

3. The heat rejection system according to claim 1 wherein said thermal energy radiator articulation or shape change behavior further comprises: a) the selective obscuring of thermal energy radiator surfaces when in a shape or configuration corresponding to reduced heat rejection; b) the selective exposing of thermal energy radiator surfaces when in a shape of configuration corresponding to increased heat rejection; c) wherein said thermal energy radiator surfaces may be obscured or exposed in whole or in part; d) wherein the effective view factor or area of thermal energy heat rejection to the sink temperature is lower when in a shape or configuration corresponding to reduced heat rejection; and e) wherein the effective view factor or area of thermal energy heat rejection to the sink temperature is higher when in a shape or configuration corresponding to increased heat rejection.

4. The thermal energy radiator according to claim 1 wherein said thermal energy radiator articulation or shape change behavior further comprises: a) the selective obscuring of thermal energy radiator surfaces having a high emissivity and exposing of surfaces having a low emissivity when in a shape or configuration corresponding to reduced heat rejection; b) the selective exposing of thermal energy radiator surfaces having a high emissivity and obscuring of surfaces having a low emissivity when in a shape or configuration corresponding to increased heat rejection; c) wherein said surfaces may be coated, covered, or otherwise treated to achieve the desired emissivity; d) wherein said surfaces may be obscured or exposed in whole or in part; e) wherein the effective emissivity of thermal energy heat rejection to the sink temperature is lower when in a shape or configuration corresponding to reduced heat rejection; and f) wherein the effective emissivity of thermal energy heat rejection to the sink temperature is higher when in a shape of configuration corresponding to increased heat rejection.

5. The thermal energy radiator according to claim 1 wherein said thermal energy radiator comprises: a) at least one shape memory structure which exhibits two- or more shape memory states; b) at least one shape memory structure which in a cold memory state has a shape roughly enabling the low heat rejection shape of the thermal energy radiator; c) at least one shape memory structure which in a hot memory state has a shape roughly enabling the high heat rejection shape of the thermal energy radiator; d) wherein the shape memory structure provides a force which acts upon the radiator structure at low temperature to cause the low heat rejection shape; and e) wherein the shape memory structure provides a force which acts upon the radiator structure at high temperature to cause the high heat rejection shape.

6. The thermal energy radiator according to claim 1 wherein said thermal energy radiator forms a shape which comprises: a) a rough approximation of at least one flat shape with high heat rejection surface facing a cold heat sink above at least one transition temperature; and b) a closed or partially closed flat shape with high heat rejection surface not facing a cold heat sink below at least one transition temperature.

7. The thermal energy radiator according to claim 2 wherein said thermal energy radiator may be actively controlled as needed by heating the shape memory material component of said thermal energy radiator.

8. A heat rejection system wherein an array comprises at least one articulating or shape changing thermal energy radiator according to claim 1 such that: a) each member of the array may be arranged in series in the energy transport system; b) each member of the array may be arranged in parallel in the energy transport system; c) wherein said array is composed of any combination of the above arrangements; and d) wherein each thermal energy radiator of said array responds to temperature local to its place in the array.

9. The heat rejection system according to claim 8 wherein a fluid loop consisting of at least one thermal fluid which is capable of transporting heat transports heat from at least one source to each array member of said heat rejection system according to its place in said array of thermal energy radiators.

10. The heat rejection system according to claim 8 wherein a thermal radiation shield is located to cover gaps present in the cold shape at each end of a series arrangement of at least one thermal energy radiator such that the view of the thermal energy radiator's active surface to the external environment is blocked.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 and FIG. 2 shows a diagrammatic cross sectional view illustrating a cold or low heat rejection state (FIG. 1) and a warm or high heat rejection state (FIG. 2) of a thermal energy radiator according to a preferred embodiment of the present invention

[0020] FIG. 3. shows a diagrammatic view illustrating a thermal fluid heat transport system having at least one heat rejection system according to the preferred embodiment of FIG. 1 and FIG. 2.

[0021] FIG. 4. shows a diagrammatic view illustrating behavior of a heat rejection system containing an array of the thermal energy radiators according to the preferred embodiment of FIG. 3.

[0022] FIG. 5. Shows a diagrammatic view illustrating the shape memory structure which actuates the thermal energy radiator according to the preferred embodiment of FIG. 1 and FIG. 2.

DETAILED DESCRIPTION OF THE BEST MODES AND PREFERRED EMBODIMENTS OF THE INVENTION

[0023] FIG. 1 and FIG. 2 show a diagrammatic cross sectional view illustrating a cold or low heat rejection state and a warm or high heat rejection state, respectively, of thermal energy radiator system 100 at least one of which comprises a key and enabling element of a heat rejection system 300 (see FIG. 3) according to a preferred embodiment of the present invention. A spacecraft, satellite or other extraterrestrial vehicle 110 (shown in part only and to rough scale) preferably includes an environment 310 for crew 320, heat generating hardware and systems 330, or both, and at least one thermal energy radiator system 100. Heat is preferably collected from heat sources within the vehicle 110 and transported to a heat rejection system 300 by means of a thermal control system 310.

[0024] Extraterrestrial environment 120 comprises a range of temperatures and other conditions that are uninhabitable by humans and inhospitable to electronics, avionics and hardware, and thus requires the use of a thermal control system 310 to maintain a vehicle environment 310 hospitable to the intended mission and function of the vehicle 110. In the case of a crewed vehicle 110 the vehicle environment 310 must be human-life supporting, and preferably comprises an enclosed space with artificially-controlled atmospheric conditions hospitable to human life. Any exchange between vehicle environment 310 and the external environment 120 is preferably controlled to maintain these conditions.

[0025] Heat rejection system 300 preferably functions to regulate the temperatures of maimed spacecraft 110, by transporting heat to at least one thermal energy radiator 100 which preferably emits heat into the external environment 120. Manned spacecraft 110 preferably comprises multiple subsystems each of which are heat sources and are temperature sensitive. Heat must be transported away from such subsystems to maintain temperatures within operating ranges. Likewise, human-life supporting environment 310 preferably utilizes temperature regulation to maintain a comfortable environment. Primarily, heat rejection system 300 preferably transports heat away from at least one heat source as shown in FIG. 3, to at least one thermal energy radiator 100 to be radiated into external environment 120.

[0026] When manned spacecraft 110 operates with all subsystems running at full capacity, the heat load rejected preferably is at maximum capacity of the heat rejection system 300. Should a spacecraft continuously need to operate only at or near this maximum heat load, a heat rejection system 300 for the spacecraft only need be designed to transport a narrow range of heat and operate continuously at that level of heat transportation. However, when a spacecraft operates in multiple configurations, having differing subsystems operating simultaneously, the heat load may be anywhere from maximum (all subsystems running) to a minimum (all or nearly all subsystems in standby generating nearly no heat). Manned spacecraft 110 is preferably utilized with such a widely varying heat load, preferably over the course of an operational run, alternately preferable over the course of multiple operational runs.

[0027] Further, the thermal environment 120 to which the thermal energy radiator emits heat varies. When vehicle 110 orbits a planet the thermal environment 120 cycles as a function of orbital period where periods of warm temperature occur in view of the sun and periods of cold temperature occur in the shadow of the planet. Vehicle 110 in transit to a distant planet, satellite, or other celestial body experiences long periods of extreme cold preceded and followed by a much warmer cyclic orbital thermal environment 120. Vehicle 110 which further explores other celestial bodies can experience a wide range of thermal environment 120 depending on the size of the body, the presence of atmosphere, and relative orientation on the body with respect to the sun, and the rotating period of the body. When a thermal energy radiator 100 emits heat to a warm thermal environment 120 its capacity to emit heat is less than when the same radiator emits heat to a cold thermal environment 120. As with heat load, should a spacecraft 110 operate in a constant thermal environment 120 a heat rejection system 300 need be designed only to reject a narrow range of heat. Where spacecraft 110 rejects heat to a varying thermal environment 120 it must be designed to reject the maximum heat load at the warmest environment temperature (the hot condition), and to reject the minimum heat load at the coldest environment temperature, (the cold condition). Manned spacecraft 110 is preferably utilized with such a widely varying thermal environment, preferably over the course of an operational run, alternately preferable over the course of multiple operational runs.

[0028] Upon reading the teachings of this specification, those skilled in the art will now appreciate that, under appropriate circumstances, considering such issues as cost, future technologies, etc., other applications of heat rejection systems, such as, for example, non-terrestrial planetary colonies and terrestrial applications for which convection may be similarly augmented, and etc., may suffice.

[0029] The dangers in operating a radiator system at widely varying heat loads and thermal environments, without a variable heat load capacity, present themselves in the two extremes of operation. If a radiator system is designed for high heat loads in the warmest environment, when it then operates at low heat loads and cold environments, it transports too much heat and the subsystems of the spacecraft become too cold resulting in condensation or extreme thermal contraction and subsystem failures. Further, if this high heat load radiator system operates at too low of a temperature the thermal fluid within the radiator may freeze causing radiator failure and heat transport problems which compound when the heat load rises again.

[0030] If a radiator system is designed for lower heat loads in the coldest environment, when it operates at high heat loads, it is not capable of transporting enough heat and the subsystems of the spacecraft become overheated and fail. Likewise, personnel in either extreme condition of operation will experience life-threatening, mental, and other problems.

[0031] A radiator system is typically static in form, which is to say that once placed into service, or deployed, the radiator system is a rigid structure having a set area, a set view factor, and a set surface emissivity. These properties describe the heat rejection capacity of a thermal energy radiator system as defined by the Stefan-Boltzmann relationship which is known as Q=εσFA(T.sup.4−T.sub.env.sup.4) where Q is the heat rejection, ε is the emissivity of a surface, F is the view factor between objects, A is the area of the emitting surface, T is the temperature of that surface, T.sub.env is the temperature of the environment, and σ is a constant. The static nature of the radiator system has generally led to approaches to the problem of variable heat load and variable environment which vary the temperature or emissivity of the surface. Examples of temperature approaches include fluid choice, where a working fluid having a very low pour point and wide operating range is used, regenerative heat exchangers, which cool the fluid entering the radiator using fluid exiting the radiator, and a stagnating fluid, where the thermal working fluid is made to stall in portions of the radiator system reducing the heat transported to those portions of the radiator. Examples of emissivity approaches include electrochromic materials, which change emissivity upon the application of a voltage. Other approaches have added hardware to the radiator which obscure the surface thus changing view factor which include louvers and micro louvers.

[0032] The cold and hot shapes described in FIG. 1 and FIG. 2, respectively, of the thermal energy radiator 100 correspond in heat rejection function to the extreme cases described above, which serves to demonstrate the variable heat rejection capability of the preferred embodiment of the present invention. The thermal energy radiator 100 comprises at least one facesheet 130, at least one heat transport loop 140, and a thermal connection between these elements 150. The facesheet further comprises a conductive structure 160 and a supporting structure 170 which may be separate as shown or combined in a multi-functional structure. The element 560 described in FIG. 5 comprising the interface between the thermal energy radiator 100 of the heat transport loop 140 in the preferred implementation contains a shape memory structure which exhibits the behavior of two-way shape memory which actuates the position of the facesheet 130.

[0033] Two-way shape memory is a behavior of certain metal alloys, polymers, and other classes of materials whereby the material is trained to recover one of at least two shapes in the presence of stimuli. The preferred stimulus is temperature such that one shape may occur below at least one transition temperature of the shape memory material and another shape of the material is recovered when its temperature rises above at least one transition temperature. This particular behavior is referred to as two-way shape memory and is the preferred behavior of the shape memory structure 560. Upon reading the teachings of this specification, those skilled in the art will now appreciate that, under appropriate circumstances, considering such issues as cost, future applications, application parameters, etc., other shape memory behaviors, such as, for example, one-way shape memory or multiple-shape memory, may suffice.

[0034] Several shape memory alloys exhibit behavior according to the preferred stimulus. The temperature at which these shape memory alloys transition is in part a function of the alloying composition so that a shape memory structure composed of such an alloy may be tailored to the operating constraints of the spacecraft 110. The preferred shape memory material is a Nickel-Titanium based metal alloy with transition temperatures in the vicinity of 0 C. Upon reading the teachings of this specification, those skilled in the art will now appreciate that, under appropriate circumstances, considering such issues as thermal working fluid, operating temperature, future applications, application parameters, etc., other shape memory materials, such as, for example Copper and ferrous based shape memory materials or shape memory polymers, etc., and other transition temperature ranges, may suffice.

[0035] The facesheet structure 130 preferably is a multi-functional sheet having adequate form and thermally conductive behavior to meet the function of the conductive structure 160 and support structure 170. The facesheet structure 130, including at least one such structure 132 which may be in conjunction with a mirrored second such structure 133 as shown in the preferred embodiment, is actuated by the shape memory structure 560 to take a position that corresponds generally with the cold shape of the thermal energy radiator 100 shown in FIG. 1 or the hot shape of the thermal energy radiator 100 shown in FIG. 2. The conductive structure 160 transports heat conductively from the heat transport loop 140 to the active surface 190 of the thermal energy radiator facesheet 130. It also serves thus to communicate local temperature of the thermal energy radiator facesheet 130 to the shape memory structure 560. The multi-functional conductive structure 160 and supporting structure 170 preferably comprises a high conductivity carbon fiber composite material for the combined high stiffness, high thermal conductivity, and weight efficiency. Upon reading the teachings of this specification, those skilled in the art will now appreciate that, under appropriate circumstances, considering such issues as cost, future applications, available materials, etc., other materials, for example glass fiber composites, or laminations with graphite, etc., may suffice.

[0036] Shape memory structure 560 has at least one trained memory of the shape that corresponds generally with the cold shape of the thermal energy radiator 100 shown in FIG. 1 and at least one other trained memory of the shape that corresponds generally with the hot shape of the thermal energy radiator 100 shown in FIG. 2. Shape memory structure 560 preferably comprises concentric tubes composed of shape memory elements with at least one tube 520 providing a path for heat transport fluid to pass to the facesheet 130 and at least one tube 530 which provides a path, preferably in the annulus between 520 and 530, for heat transport fluid to return from the facesheet 130. An insulating structure 510, preferably located within the inner most tube 520 and insulating said tube from the high temperature of the entering fluid 540. Thus insulated, both inner tube 520 and outer tube 530 actuate upon the temperature of the exiting fluid 550. Upon reading the teachings of the specifications, those skilled in the art will now appreciate that, under appropriate circumstances, considering such issues as cost, future applications, available materials, etc., other configurations of the shape memory structure, for example reverse direction of flow, having flexible material rather than shape memory elements composing at least one tube, having concentric cross sections that are not circular, having eccentric, off center, or other relative positioning, etc., may suffice

[0037] This coupling preferably comprises shape memory structure 560 coupled to facesheet structure 130 such that force is transferred between the structures. When the temperature of fluid exiting the facesheet 130 is below at least one transition temperature of the shape memory structure 560, the shape memory structure 560 reverts to a cold memory shape resulting in the cold shape of the thermal energy radiator 100 shown in FIG. 1. When the temperature of the facesheet 130 rises above at least one transition temperature of the shape memory structure 560, the shape memory structure 560 forcibly recovers to its hot shape, resulting in the hot shape of the thermal energy radiator 100 shown in FIG. 2. Upon reading the teachings of this specification, those skilled in the art will now appreciate that, under appropriate circumstances, considering such issues as cost, future applications, available materials, etc., orientations and positions other than illustrated may be employed to the same or greater effect, such as, for example, a single panel without a mirror which actuates 180 degrees for the same effect, etc., may suffice.

[0038] The thermal energy radiator 100 further presents surfaces of differing thermal emissivity. The active surface 190 of the thermal energy radiator facesheet 130 is preferably coated or treated for a high emissivity. The active surface 190 treatment preferably comprises a silver-Teflon material, AZ93 white paint, or a treatment having significantly similar high emissivity and low solar absorptivity properties. The inactive surface 180 is preferably coated or treated for a low emissivity. The inactive surface 180 treatment preferably comprises at least one layer of aluminized mylar, where multiple layers are separated by a small gap to minimize heat transport through this side. Upon reading the teaching of this specification, those skilled in the art will now appreciate that, under appropriate circumstances, considering such issues as cost, future applications, available materials, etc., other treatments may be applied for similar effect, such as, for example, various colors of space rated paint, silvered film, multi-layer insulation, etc., may suffice.

[0039] The combination of temperature sensitive shape change and the obscuring and exposing of active 190 and inactive 180 surfaces affords a large change in effective emissivity and a change in effective view factor from the cold shape of thermal energy radiator 100 of FIG. 1 to the hot shape of the thermal energy radiator 100 of FIG. 2. This behavior results in a very low heat rejection capacity for the cold shape appropriate for low heat loads in extreme cold environments 150, and a very high heat rejection capacity for the hot shape appropriate for high heat loads in warm thermal environments 150.

[0040] FIG. 3 shows a diagrammatic view illustrating thermal control system 310 according to a preferred embodiment of the present invention which consists of a heat rejection system 300, a previously described thermally controlled environment 310 having heat sources, and a heat transport system 340 which transports heat from vehicle heat sources 320 and 330 to the heat rejection system 300. The heat transport system 310 preferably consists of at least one single-loop thermal fluid loop 380 consisting of a thermal fluid capable of transporting heat, preferably a non-toxic fluid such as propylene glycol, and may include a pump 350 and a bypass mixing valve 360 which controls flow to maintain a setpoint temperature at 370. Upon reading the teaching of this specification, however, those skilled in the art will now appreciate that the variable shape behavior of the thermal energy radiator facesheet 130 does not require a fluid loop 340 to achieve the described behavior; other thermal transport systems may be employed, such as conductive heat transport coupled directly to a heat source, thermoelectric heat transport, etc., may suffice.

[0041] FIG. 4 shows the heat rejection system 300 as comprised of at least one thermal energy radiator 100 arranged as an array in both series and parallel, where any arrangement in series, parallel, or both is preferred, and an array heat transport system 400 which transports heat from the heat transport system 340 to each thermal energy radiator 100 in the array according to the arrangement of the array. The array heat transport system 400 receives thermal fluid from the heat transport system 310 fluid loop 380 at an inlet to the array 410. Thermal fluid then travels from the inlet to the array 410 through the array heat transport system 400 transferring heat from the thermal fluid to at least one thermal energy radiator 100, passing in the process through fluid passages 401 and 402 according the arrangement of thermal energy radiators 100 in the flow path, and exits the array heat transport system 400 to the vehicle heat transport system 380 by way of the array heat transport system outlet 420. Each thermal energy radiator 100 in the heat rejection system 300 responds to temperature local to its position on the array heat transport system 400. As the fluid moves along fluid passage 401 and 402, heat is transported to each thermal energy radiator 100 which rejects that heat to the thermal environment 120, thereby reducing the temperature of the fluid before it moves to the next radiator. This behavior creates a temperature gradient along fluid passages 401 and 402. This gradient, and the quantity of thermal energy radiators in the fluid path, allows for smooth variation of heat rejection system 300 heat rejection capacity.

[0042] For illustration of this smoothing behavior, FIG. 4 is separated into two independent heat load cases, high heat load case 450 to the left of imaginary line 430 and low heat load case 440 to the right of imaginary line 430. In the high heat load case 450 the inlet fluid 410 temperature is high. This high temperature fluid is distributed through fluid passages 401 where the high temperature causes all thermal energy radiators to take the high heat rejection shape. As the high temperature fluid travels along fluid passage 401 and the temperature of the fluid declines as heat is removed from it, it nevertheless does not decline to a temperature below the transition temperature of any of the thermal energy radiators 100 in fluid path 401. In the low heat load case 440 the inlet fluid temperature is lower, but still high enough that all thermal energy radiators 100 in fluid passage 402 at and upstream of 441. At position 442 the local temperature has dropped sufficiently that a portion of the thermal energy radiator 100 at that position has fallen below the transition for that component. This process continues until at position 444 the low fluid temperature has caused the thermal energy radiator 100 to take a low heat rejection shape and thus limit heat rejection.

[0043] This smoothing behavior has the further effect of limiting the lowest fluid temperature returning to the thermal control system 310 at array heat transport system outlet 420 to a value in the vicinity of the lowest common transition temperature of the heat rejection system 300.

[0044] Turn-down of heat rejection system 300 may be increased significantly by placement of radiative shields or covers, whether permanently or temporarily, along the edge of the paired arrangement of thermal energy radiators 100 as illustrated on flow passages 401 and 402. Such a shield, to be effective, would have a low emissivity and would preferably be composed of a multilayer insulation, and would cover all gaps in the cold shape thus blocking a view of the active surface 190 of the thermal energy radiator 100 to the thermal environment 120.

[0045] Further note of the behavior is that it is continuous and passive. The taking of a hot and cold shape by the thermal energy radiator 100 occurs continuously once put into service and until arrested by an external restraint, without external action, as temperature of the radiator varies, as vehicle heat load varies, and as thermal environment 120 varies.

[0046] Although applicant has described applicant's preferred embodiments of this invention, it will be understood that the broadest scope of the invention includes modifications such as diverse shapes, sizes, arrangements, shape memory behaviors, etc. Such scope is limited only by the below claims as read in connection with the above specification. Further, many other advantages of applicant's invention will be apparent to those skilled in the art from the above descriptions and the below claims.