Spacecraft east-west radiator assembly

A heat transfer assembly can include an equipment panel having an east end and a west end. East and west radiator panels are coupled to the east and west ends, respectively, of the equipment panel. The assembly also includes a plurality of flexible heat pipes each having a first rigid tube thermally coupled to the east radiator panel, a second rigid tube coupled to the equipment panel, a third rigid tube thermally coupled to the west radiator panel, a first flexible tube sealingly coupled between the first and second rigid tubes, and a second flexible tube sealingly coupled between the second and third rigid tubes. The equipment panel is configured to retain one or more equipment modules in thermal contact with the second rigid tube of at least one of the plurality of flexible heat pipes.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

Not applicable.

BACKGROUND

The present invention generally relates to heat-transfer systems and, in particular, to a spacecraft radiator assembly with flexible heat pipes.

2. Description of the Related Art

Spacecraft in a geosynchronous earth orbit (GEO) typically operate such that one side continuously faces toward the ground as the satellite orbits the Earth. Such a satellite will have a north-south axis that, while in orbit, is approximately parallel to the north-south rotational axis of the Earth and an east-west axis that is perpendicular to the north-south axis. As the satellite orbits the Earth, the east and west sides of the spacecraft will alternately face toward the Sun and, twelve hours later, face away from the Sun toward deep space.

As GEO spacecraft are frequently used for communication and observation, the designers must accommodate complex communications payloads with large number of components and high thermal dissipation requirements. For example, a direct-broadcast or broadband spot-beam communications spacecraft may require dissipation of 14 kW or more of heat from the payload electronics. As is well known to those of skill in the art, “fixed” north and south radiator panels provide the most mass-efficient and cost-efficient heat rejection capability, and therefore their area is generally maximized within the constraints imposed by the launch vehicle fairing. However, it is often the case that additional heat rejection capability is required beyond what can be provided by such north and south radiator panels.

One conventional approach to providing additional heat rejection capability is the addition of east and west radiator panels, as shown in the exploded view inFIG. 1of a conventional spacecraft. Because east and west radiator panels receive direct sun exposure during each orbit, they are less effective than north and south radiator panels and therefore operate at higher average temperatures for an equivalent thermal load. This generally limits the use of east and west radiator panels to equipment such as output multiplexers (OMUXs) that can operate at higher temperatures. In addition, east and west radiator panels tend to undergo large diurnal temperature fluctuations, as the individual panels alternately face the Sun and deep space, and equipment that is thermally coupled to conventional east and west radiator panels may require significant heater power to limit the temperature fluctuations to an acceptable range.

Another drawback of conventional radiator panels is that, once the radiator panel is installed, it becomes difficult to access equipment inside the spacecraft including the equipment that is mounted on the radiator panels themselves. This increases the cost and time required for remove-and-replace operations that may be necessary during integration and test of a conventional spacecraft.

SUMMARY

The present invention generally relates to heat-transfer systems and, in particular, to a spacecraft radiator assembly with flexible heat pipes.

It is desirable to provide an east-west heat transfer assembly (EWHTA) having east and west radiator panels that reduce the average temperature as well as the temperature fluctuations seen with conventional panels. In addition, it is advantageous to provide the ability to mount equipment to be cooled by the east and west radiator panels in a location that is separate from the panels themselves, taking advantage of what is generally wasted volume within the body of the spacecraft. It is also beneficial to provide easier access to internal equipment during spacecraft integration and test while maintaining all thermal system connections.

In certain aspects of the present disclosure, a heat transfer assembly for a spacecraft is disclosed. The assembly includes an equipment panel having an east end and a west end, an east radiator panel coupled to the east end of the equipment panel, and a west radiator panel coupled to the west end of the equipment panel. The assembly also includes a plurality of flexible heat pipes each having a first rigid tube thermally coupled to the east radiator panel, a second rigid tube coupled to the equipment panel, a third rigid tube thermally coupled to the west radiator panel, a first flexible tube sealingly coupled between the first and second rigid tubes, and a second flexible tube sealingly coupled between the second and third rigid tubes. The equipment panel is configured to retain one or more equipment modules in thermal contact with the second rigid tube of at least one of the plurality of flexible heat pipes.

In certain aspects of the present disclosure, a spacecraft is disclosed that has a core structure, an east-west equipment panel having an east end and a west end, an east radiator panel rotatably coupled to the east end of the equipment panel, and a west radiator panel rotatably coupled to the west end of the equipment panel. The spacecraft also has a plurality of flexible heat pipes each comprising a first rigid tube thermally coupled to the east radiator panel, a second rigid tube coupled to the equipment panel, a third rigid tube thermally coupled to the west radiator panel, a first flexible tube sealingly coupled between the first and second rigid tubes; and a second flexible tube sealingly coupled between the second and third rigid tubes. The spacecraft also has one or more equipment modules thermally coupled to the second rigid tube of at least one of the plurality of flexible heat pipes.

In certain aspects of the present disclosure, a method of controlling the temperature of an equipment module on a spacecraft is disclosed. The method includes the step of thermally coupling the equipment module to a flexible heat pipe that comprises a first rigid tube thermally coupled to an east radiator panel disposed on an external east surface of the spacecraft, a second rigid tube thermally coupled to a west radiator panel disposed on an external west surface of the spacecraft, and a third rigid tube coupled to the first and second rigid tubes by first and second flexible tubes, respectively, wherein the equipment module is thermally coupled to the third rigid tube.

DETAILED DESCRIPTION

The present invention generally relates to heat-transfer systems and, in particular, to a spacecraft radiator assembly with flexible heat pipes.

The following description discloses embodiments of an east-west heat-transfer assembly that is particularly adapted for use on a GEO spacecraft. In certain embodiments, however, the same concepts and construction may be effectively used on other types of spacecraft as well as other applications where radiator panels provide a source of cooling.

FIG. 1is an exploded view of a spacecraft10equipped with conventional east and west radiator panels30A and30B. The “north”, “south,” “east,” and “west” directions are defined as indicated by the arrows. The spacecraft10has a core structure11that, in this example, takes the form of a central cylinder12with a rectangular “Earth deck”14attached to an end that continuously faces toward the ground and a second deck16attached to the other end of the cylinder12. A north radiator panel22A is attached to a north equipment panel20A and then to the north side of the core structure11, and a south radiator panel22B is attached to a south equipment panel20B and then to the south side of the core structure11. Structural panels18are attached to the east and west sides of the core structure11and fixed east and west radiator panels30A,30B are respectively attached to east and west equipment panels32A,32B and then attached, in this example, to the structural panels18. Communication reflectors19A,19B, and19C are deployably attached to the deck16such that each reflector established a line of communication toward the Earth. Other spacecraft components and subsystems, such as solar power arrays, have been omitted for clarity.

FIG. 2depicts an exemplary EWHTA100according to certain aspects of the present disclosure. The “north”, “south,” “east,” and “west” directions are defined inFIG. 2as indicated by the arrows to indicate the operational orientation of the EWHTA100when installed in a GEO spacecraft (not shown inFIG. 2). The EWHTA100includes an equipment panel115and, in this example, two east radiator panels130A,130B that may also be referred to as the north-east radiator panel130A and south-west radiator panel130B. In certain embodiments, the north and south directions, i.e. a north-south axis, may be arbitrarily rotated in a plane that is perpendicular to an east-west axis without departing from the scope of this disclosure. The EWHTA100also includes two west radiator panels120A,120B. A plurality of flexible heat pipes140run from one of the east radiator panels130A,130B across the equipment panel115to one of the west radiator panels120A,120B. The routing of the flexible heat pipes140is discussed in greater detail with respect toFIG. 3. The construction of the flexible heat pipes140is discussed in greater detail with respect toFIG. 4. Also shown inFIG. 2are two north-south panels110A,110B that, in certain embodiments, are thermally coupled to the equipment panel115such that heat absorbed by the north-south panels110A,110B, for example from equipment modules thermally coupled to the north-south panels110A,110B, may be conducted to the equipment panel115and then rejected to one of the east or west radiator panels.

FIG. 3is a wire-frame view of another embodiment101of an EWHTA according to certain aspects of the present disclosure. In this view, the two east radiator panels130A,130B are shown only in outline so as to reveal the routing of the flexible heat pipes140. The dashed-line box labeled “3B” is shown in enlarged form inFIG. 6.

It can be seen that, in this embodiment, the flexible heat pipe140A runs from the north-west radiator panel120A across the equipment panel115and onto the north-east radiator panel130A and the flexible heat pipe140B runs from the south-west radiator panel120B across the equipment panel115and onto the south-east radiator panel130B. In certain embodiments, the flexible heat pipe140A may be coupled to the south-east radiator panel130B in place of north-east radiator panel130A. In certain embodiments, the flexible heat pipe140B may be coupled to the north-east radiator panel130A in place of south-east radiator panel130B. In certain embodiments, a plurality of flexible heat pipes140run in parallel from one of the west radiator panels120A,120B to one of the east radiator panels130A,130B. The EWHTA101also includes formed heat pipes150mounted on the equipment panel115. These formed heat pipes serve to couple the various flexible heat pipes140so as to, for example, minimize variations in temperature across the equipment panel115. The configuration and function of these formed heat pipes150are discussed in greater detail with respect toFIG. 6.

When a spacecraft that includes an EWHTA101or similar, the east and west directions of the spacecraft will point at the Sun once per orbit. At one point in the orbit, the west radiator panels120A,120B are directly exposed to the Sun, which has an effective surface temperature of approximately 5800 K (10,000° F.), and the east radiator panels130A,130B will be partially exposed to deep space, which has an average temperature of approximately 3 K (−454° F.). The west radiator panels120A,120B will absorb radiated energy from the Sun and their temperature will increase, while the east radiator panels130A,130B will reject heat to deep space and their temperature will decrease. With reference to a conventional spacecraft10ofFIG. 1, equipment modules on the west equipment panel32B that are thermally coupled to only the west radiator panel30B will be significantly heated by heat transfer from the west radiator panel30B as the temperature of the west radiator panel30B exceeds the current temperature of those equipment modules. Equipment modules mounted on the east or west equipment panels32A,32B must therefore be able to survive high operational temperatures driven by this absorption of heat from the Sun as there is not alternate source of cooling to offset the heating by the Sun. On the east side of the example spacecraft10, equipment modules on the east equipment panel32A, being thermally coupled to only the east radiator panel30A will be significantly cooled by heat transfer to the west radiator panel30A as the temperature of the east radiator panel30A drops toward the temperature of deep space. It is possible to minimize the reduction in the operational temperature of the equipment on the equipment panel30A while being cooled by deep space by attaching heaters (not shown inFIG. 1of2) to either the equipment modules or the equipment panel30A. The use of such heaters, however, places an additional load on the power system of the spacecraft10. Even with the heaters, the temperature range between the minimum temperature seen by the equipment modules when their radiator panel is facing toward deep space and the maximum temperature seen when their radiator panel is facing toward the Sun can be quite large and affect, for example, the reliability and performance of the equipment module.

In contrast, a spacecraft with an EWHTA100will expose equipment modules coupled to east and west radiators120A,120B,130A,130B to a smaller temperature range, compared to equipment modules coupled to conventional east and west radiators30A,30B on the spacecraft10. In the example where the west side of the spacecraft is facing toward the Sun, the west radiator panels120A,120B heat up due to absorption of heat from the Sun. This absorbed heat, however, is transferred all the way to the east radiation panels130A,130B by the flexible heat pipes140. This direct transfer of heat from the heated west radiator panels120A,120B to the cooled east radiation panels130A,130B reduces the maximum temperature seen by the west radiator panels120A,120B and simultaneously increases the minimum temperature seen by the east radiation panels130A,130B while in this orientation to the Sun. The equipment modules that are thermally coupled to the equipment panel115will, therefore, see a smaller range of temperatures as the position of the Sun, relative to the spacecraft, moves between the west side and the east side. In addition, the use of heaters to maintain the temperature of the equipment modules above a minimum operational temperature will be reduced, if not eliminated, as the transferred heat from the hot radiation panels, in this example west radiator panels120A,120B, to the cold radiation panels, in this example west radiator panels130A,130B, will increase the minimum temperature seen by the radiation panels and, therefore, the minimum temperature seen by the equipment modules even in the absence of heaters.

A series of thermal simulations were performed for equipment modules mounted on a conventional east radiator panel30A, such as shown inFIG. 1and the same equipment modules mounted on an EWHTA100. The simulations determined the maximum and minimum temperatures seen by the equipment modules and the amount of additional heater power required to limit the temperature swing of the equipment modules to less than 30° C. (86° F.). Simulations were run for the following cases:

Table 1 lists the predicted minimum and maximum temperatures and the heater power required to maintain the temperature of the equipment modules within the allowable temperature swing. Predicted values that exceed the limits are shown in boldface. In will be apparent that the conventional system allows the maximum temperature of the equipment modules to exceed the maximum limit while still requiring significant heater power during the portion of the orbit while the associated radiator panel30A,30B is facing deep space. In contrast, the system of the present disclosure requires only a relatively small amount of heater power and only during the vernal equinox conditions.

FIG. 4is a top view of an exemplary flexible heat pipe140according to certain aspects of the present disclosure. The flexible heat pipe140comprises a first rigid tube141A, a second rigid tube141C, a third rigid tube141E, a first flexible tube141B sealingly coupled between the first and second rigid tubes141A,141C, and a second flexible tube141D sealingly coupled between the second and third rigid tubes141C,141E. The first and third rigid tubes141A,141E are each closed at an outboard end. The assembly of tubes141A-141E form a sealed interior volume (not visible inFIG. 4) that contains a heat transfer fluid. In certain embodiments, the flexible heat pipe contains a wick (not visible inFIG. 4) that creates a gas-phase passage and a liquid-phase passage within the interior volume that facilitates the transfer of the liquid-phase heat transfer fluid from the colder portion(s) of the flexible heat pipe140to the hotter portion(s) of the flexible heat pipe140. In certain embodiments, the first and second flexible tubes141B,141D are configured such that the adjacent rigid portions141A and141C and141E can be rotated with respect to each other over a range of angles without disconnection of the various elements of the flexible heat pipe140. In certain embodiments, the rigid tube141A can be moved over a range of angles with respect to rigid tube141C. In certain embodiments, rigid tube141A can be oriented at any angle between 0°, i.e. extending straight out from, and 90° with respect to rigid tube141C. In certain embodiments, the rigid tube141A can be moved over a range of −90° to +90° with respect to rigid tube141C.

FIG. 5is a perspective view of an exemplary spacecraft200with a EWHTA100according to certain aspects of the present disclosure. The east radiator panels130A,130B have been removed to expose the inner elements of the spacecraft200. It will be apparent that the central cylinder220has been vertically split, compared to the central cylinder12ofFIG. 1, by the introduction of the equipment panel115that extends from the Earth deck14downward through the split mid-deck210.

FIG. 6is a cutaway top view of the spacecraft200ofFIG. 5according to certain aspects of the present disclosure. The view is taken just below the Earth deck14and faces downward, with certain elements removed for clarity. The middeck210is visible in the middle, with the north and south equipment panels20A,20B and north and south radiator panels22A,22B positioned at the top and bottom, in the orientation of this view. Various pieces of equipment60are mounted to the north and south equipment panels20A,20B.

An EWHTA100is visible in the middle of the spacecraft200, with the equipment panel115passing left-to-right in this view across the middle of the middeck210. The north-west radiator panel120B is shown in an “open” position, with the closed position122shown in dashed line. A flexible heat pipe141is shown with the rigid tube141A embedded within the open radiator panel122, and with the closed position143of the same rigid tube141A shown in dashed line. Representative equipment modules50A and50B are shown mounted to the equipment panel115and thermally coupled to the rigid tube141C of the flexible heat pipe100, which is shown as embedded within the panel115. Embedding the rigid pipe141C within the equipment panel115may provide greater flexibility in positioning equipment on the panel, as well as the potential to mount equipment to both sides of the equipment panel115with equal thermal performance. In certain embodiments, the rigid portions of heat pipe141may be mounted to an inner or outer surface of one or more of the radiators120B,130B or to one of the surfaces of the equipment panel115. Mounting the heat pipe on the surface may provide a benefit in manufacture or assembly of the radiators120B,130B or equipment panel115. As an example, the rigid tube141E is shown as mounted on the inner surface of radiator130B, for example by bolting and thermally bonding with brackets (not shown inFIG. 6). Other means of thermally coupling the various portions of heat pipe141to the respective radiators and panels will be apparent to those of skill in the art. The mounting of equipment modules50A and50B is discussed in greater detail with respect toFIG. 7. It will be apparent how the flexible tube141B, positioned proximate to the hinge of the radiator panel122, enables the radiator panel122to be opened without requiring prior removal of equipment or the flexible heat pipe141, thus simplifying the process of gaining access to the equipment within the spacecraft200.

FIG. 7is an enlarged side view of a portion of equipment panel115of the EWHTA100ofFIG. 5according to certain aspects of the present disclosure. The rigid tubes141C are shown for multiple flexible heat pipes141, wherein the nomenclature of “141C-x” indicates individual flexible heat pipes141. The arrows at the left and right section-lines indicate which radiator panel each line is connected to. For example, the first flexible heat pipe141, identified as “141C-1” is thermally coupled to north-west radiator panel120A on the left and to north-east radiator panel130A on the right. The flexible heat pipes141are arranged in pairs, for example flexible heat pipes141C-1and141C-2, which are respectively coupled to the northern and southern of the east and west radiator panels.

The dashed-line boxes50A and50B indicate where the representative electronics modules50A and50B shown inFIG. 5are mounted. Electronics module50A is mounted over, and thermally coupled to, the flexible heat pipes141C-1,141C-2,141C-3, and141C-4. If the equipment module50A is considered to be at a uniform temperature across its base, then the equipment module50A will transfer heat to each of the four flexible heat pipes141C-1,141C-2,141C-3, and141C-4. This provides redundancy in the event that performance of one of the flexible heat pipes141is degraded, for example by loss of the heat transfer fluid in that flexible heat pipe141. Equipment module50B is coupled to only two flexible heat pipes141C-1and141C-2. In certain embodiments, the equipment modules50A and50B are attached to the support structure of equipment panel115and simply held in thermal contact with the rigid tubes141C of the various flexible heat pipes. In certain embodiments, the equipment modules50A and50B may be attached directly to the rigid tubes141C of one or more of the flexible heat pipes141. In certain embodiments, additional thermal coupling elements, for example shaped copper straps or thermal grease, may be provided to improve the thermal coupling of the equipment modules50A,50B to the respective rigid tubes141C.

In certain embodiments, formed heat pipes150thermally couple one of each pair of flexible heat pipes141to one of the adjacent pairs. In this embodiment, a first portion of a formed heat pipe150-2is thermally coupled to the flexible heat pipe141C-2of one pair and a second portion of the formed heat pipe150-2is coupled to flexible heat pipe141C-3of an adjacent pair, with a short vertical portion joining the first and second portions. This provides additional redundancy across the plurality of flexible heat pipes141, in the event that one of the flexible heat pipes141fails, and also serves to distribute heat across the EWHTA100more evenly. For example, if the equipment module50B was dissipating a large amount of heat, the flexible heat pipes141C-1and141C-2would be running hotter than the adjacent heat pipes141C-3and141C-4. The formed heat pipe150-2will transfer some of the heat from flexible heat pipe141C-2to flexible heat pipe141C-3, thereby assisting is transferring this heat to the radiator panels120A,120B,130A,130B.

The disclosed examples of an east-west heat transfer assembly illustrate exemplary configurations wherein heat from spacecraft equipment modules are rejected through east-facing and west-facing radiator panels without subjecting the equipment modules to the temperature extremes or large temperature swings seen with conventional designs. With one of the east and west radiator panels always facing toward deep space, the heat received by the Sun-facing radiator panel is transferred to the other radiator panel and rejected to deep space rather than being transferred into the equipment modules. This provides the additional benefit of reducing or eliminating the need for heater power to maintain the equipment modules within a certain temperature range. While the disclosed configurations include pairs of radiator panels on each of the east and west sides of the spacecraft, it will be apparent to those of skill in the art that the number, size, and location of the radiator panels can be varied without departing from the scope of this disclosure. In addition, the same principles and designs can be applied to the north-facing and south-facing radiator panels of a GEO spacecraft or to a non-orbiting spacecraft to provide easy access to the interior of the spacecraft without prior removal or disassembly of the thermal control system.

This application includes description that is provided to enable a person of ordinary skill in the art to practice the various aspects described herein. While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. It is understood that the specific order or hierarchy of steps or blocks in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps or blocks in the processes may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language claims.

Headings and subheadings, if any, are used for convenience only and do not limit the invention.

Reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Use of the articles “a” and “an” is to be interpreted as equivalent to the phrase “at least one.” Unless specifically stated otherwise, the terms “a set” and “some” refer to one or more.

Although the relationships among various components are described herein and/or are illustrated as being orthogonal or perpendicular, those components can be arranged in other configurations in some embodiments. For example, the angles formed between the referenced components can be greater or less than 90 degrees in some embodiments.

Although various components are illustrated as being flat and/or straight, those components can have other configurations, such as curved or tapered for example, in some embodiments.

A phrase such as an “aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase such as an aspect may refer to one or more aspects and vice versa. A phrase such as an “embodiment” does not imply that such embodiment is essential to the subject technology or that such embodiment applies to all configurations of the subject technology. A disclosure relating to an embodiment may apply to all embodiments, or one or more embodiments. A phrase such as an embodiment may refer to one or more embodiments and vice versa.