System and method to remove heat from a power amplifier

In one aspect a satellite comprises a body, a solid state power amplifier, a heat acquisition and transfer device positioned proximate at least one heat generating element on the solid state power amplifier, and a heat rejection device in thermal communication with the heat acquisition and transfer device to reject heat acquired from the solid state power amplifier. Other aspects may be described.

RELATED APPLICATIONS

FIELD OF THE DISCLOSURE

The subject matter described herein relates to a system and method to remove heat from a power amplifier and more particularly to a thermal radiating solid state power amplifiers which may be suitable for satellite applications.

BACKGROUND

Some aerospace systems have thermal management issues that are particular to the operating environment in which the systems operate. For example, satellites operate in an environment that has a wide range of environmental heat loads and in which the temperature between a side that is shielded from the sun and a side that is exposed to the sun may differ by hundreds of degrees Celsius. Electrical systems and attendant thermal management systems must accommodate these large variations in temperatures.

Accordingly, apparatus and methods for thermal management may find utility, e.g., in aerospace environments such as satellites.

SUMMARY

In one aspect, a system comprises a solid state power amplifier, a heat acquisition and transfer device positioned proximate at least one heat generating element on the solid state power amplifier, and a heat rejection device in thermal communication with the heat acquisition and transfer device to reject heat acquired from the solid state power amplifier.

In another aspect, a satellite comprises a body, a solid state power amplifier, a heat acquisition and transfer device positioned proximate at least one heat generating element on the solid state power amplifier, and a heat rejection device in thermal communication with the heat acquisition and transfer device to reject heat acquired from the solid state power amplifier.

In another aspect, a method to manage heat comprises transferring heat from at least one heat generating element on the solid state power amplifier to a heat acquisition and transfer device, transferring heat from the heat acquisition and transfer device to a heat rejection device, and rejecting the heat directly into space.

The features, functions and advantages discussed herein can be achieved independently in various embodiments described herein or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth to provide a thorough understanding of various embodiments. However, it will be understood by those skilled in the art that the various embodiments may be practiced without the specific details. In other instances, well-known methods, procedures, components, and circuits have not been illustrated or described in detail so as not to obscure the particular embodiments.

Geosynchronous satellites may be characterized as having multiple sides. By convention the forward side of a satellite refers to the side of a satellite which faces Earth and the aft side of a satellite refers to the side of the satellite which faces away from Earth. The remaining sides are referred to by cardinal orientation: north/south and east/west, assigned in accordance with their positions on a map. Thus, when facing the forward side of a satellite, the north side is the side which abuts the top of the forward side, while the south side is the side which abuts the bottom of the forward side. Similarly, when facing the forward side, the west side is the side which abuts the left side of the forward side and the east side is the side which abuts the right side of the forward side.

Briefly, in some examples the subject matter described herein addresses thermal management for electronic systems on space systems such as satellites by providing a system and method to remove heat from heat generating devices such as power amplifier assemblies which incorporates a heat acquisition device, which may be a convective device that is single phase or two phase (either a boiler or an evaporator) or a solid conductor. The heat acquisition device may be a single or two phase microchannel cooling circuit incorporated into the substrate of the power amplifier. The microchannel cooling circuit may be designed such that cooling fluid flows in close proximity to the power amplifier. More preferably, the microchannel cooling circuit may be designed such that cooling fluid flows in close proximity localized heat generating elements which may result in localized heat generating element areas during operation. The microchannel cooling circuit may include an evaporator portion proximate the power amplifier and a condenser portion removed from the amplifier. The condenser may be positioned on a radiating fin which, in turn, may be positioned on an east/west face of the satellite such that the condenser can radiate heat extracted from the power amplifier into the ambient environment of space.

In some examples the power amplifier may comprise Gallium-Nitride (GaN). The use of GaN materials may enable the amplifier to operate at higher temperatures including localized heat generating element temperatures of over 200 deg C. This allows for satellite designs in which heat may be rejected from a satellite side that is exposed to normal solar thermal loads. For example, satellites in a geosynchronous orbit generally receive more solar exposure on east/west sides than on north/south sides. The use of GaN power amplifiers renders it feasible to reject heat from an East/West side of a satellite. In further examples, the use of a GaN may allow for the power amplifier to be placed in locations on the satellite that generally receive more solar exposure such as the east/west sides of a geosynchronous orbiting satellite. Locating high power devices in locations where there is higher solar exposure may enable more optimized and efficient spacecraft design, for example less material required to transport the cooling fluid from a power amplifier to the radiator.

Additional features and examples will be explained below with reference toFIGS. 1-5.

FIG. 1illustrates an exemplary environment100in which embodiments of a thermal radiating solid state power amplifier can be implemented. The environment100includes a space system, such as a satellite102, mobile ground-based or airborne receiver(s)106, and a ground station108. For example, the satellite102may be implemented as a communication platform or a positioning satellite.

Satellites such as satellite102may be characterized as having multiple sides. By convention the forward side130of a satellite102refers to the side of a satellite102which faces Earth and the aft side132of a satellite102refers to the side of the satellite102which faces away from Earth. The remaining sides are referred to by cardinal orientation: north/south and east/west, assigned in accordance with their positions on a map. Thus, when facing the forward side130of a satellite102, the north side138is the side which abuts the top of the forward side130, while the south side140is the side which abuts the bottom of the forward side130. Similarly, when facing the forward side130, the west side134is the side which abuts the left side of the forward side130and the east side136is the side which abuts the right side of the forward side130. One skilled in the art will recognize that the satellite102need not be precisely in the shape of a rectangular prism as depicted inFIG. 1.

FIG. 2is a schematic, cross-sectional block diagram of a thermal radiating power amplifier assembly, according to aspects. Referring toFIG. 2, in some examples, the assembly comprises a substrate210comprising a fluid filled microchannel cooling circuit250, a solid state power amplifier230mounted on the substrate210, and a first heat rejection device270coupled to the microchannel cooling circuit250.

In greater detail, in some examples a power amplifier assembly may be formed as a semiconductor stack205. The substrate210may be formed from a conventional semiconductor substrate material, e.g., Silicon Carbide (SiC) or the like. An amplifier layer230comprising Gallium Nitride (GaN) may be disposed on the substrate210. From a heat management perspective, the intersection of dissimilar materials in the substrate210and the amplifier layer230defines a thermal boundary layer220. A contact layer240may be disposed on the amplifier layer230. In some examples the contact layer240may comprise Aluminum Gallium Nitride (AlGaN).

In the example depicted inFIG. 2, a microchannel cooling circuit250extends through portions of the substrate210. In some examples the amplifier assembly205is formed on a die, the microchannel cooling circuit250comprises a plurality of microchannels250which extend proximate one or more heat generating elements on the die. The microchannel cooling circuit250may be filled with a thermal fluid, e.g., a refrigerant or organic fluid such as an alcohol. In addition, the working fluid may be a single phase, liquid, or two phase, a mixture of liquid and vapor.

In some examples the microchannel cooling circuit250comprises one or more evaporators or boilers252in the substrate210. The specific location of the evaporator(s) or boiler252is not critical. Locating the evaporator(s) relatively higher in the substrate (i.e., closer to the GaN amplifier230) reduces resistance in the solid components. In some embodiments the condenser260is embedded in a thermal two dimension or three dimension radiator270.

FIGS. 3A-3Bare schematic illustrations of physical components of a system which may include a thermal radiating power amplifier, according to aspects. Referring toFIGS. 3A-3B, in some examples a solid state power amplifier assembly205may be coupled to a condenser260that is mounted on a radiator270. The radiator270depicted inFIGS. 3A-3Bmay be substantially T-shaped and comprises a first panel272to which the solid state power amplifier assembly205is mounted and a second panel274extending from the first panel272.

In some examples the radiator270may be formed from a suitably rigid material such that the radiator270may function as a structural load path for the condenser260. For example, the radiator may be formed from an aluminum alloy, carbon fiber composite, or other high thermally conductive materials capable of operating at high temperatures. Inclusion of the second panel274reduces peak thermal environmental loads and diurnal temperature variations.

Further, the T-shaped radiator270provides the ability to dissipate heat in two different planes. This feature may find particular utility when the radiator270is positioned on either a west side134of a satellite102or on an east side136of a satellite102. In use, when the satellite is oriented such that radiation from the sun is incident on the first panel272at an approximately normal angle of incidence there is substantially no radiation incident on the second panel274. Accordingly, heat in the thermal fluid circulating in condenser260may be dissipated when the fluid flows through the second of the condenser260on the second panel274. Conversely, when the satellite is oriented such that radiation from the sun is incident on the second panel274at an approximately normal angle of incidence there is substantially no radiation incident on the first panel272. Accordingly, heat in the thermal fluid circulating in condenser260may be dissipated when the fluid flows through the second of the condenser260on the first panel272. Moreover, often shapes that distribute the radiative view over a wider solid angle may be implemented. Any convex shape will improve upon a flat, normal radiator

FIG. 4Ais a schematic diagram of a system400incorporating a thermal radiating power amplifier, according to aspects. Referring toFIG. 4A, in some embodiments the system400comprises a plurality of power amplifiers230in thermal communication with evaporators252in the manner described above with reference toFIGS. 2-3. A fluid circuit410provides a fluid communication path between the evaporators252and condenser260. Thermal fluid may be driven through the circuit410by a pump420, which may be implemented as a conventional positive displacement pump, an electrohydrodynamic (EHD) pump, or the like.

In other examples a system such as the system depicted inFIG. 4Amay rely on a loop heat pipe (LHP) to pump fluid through the fluid circuit410.FIG. 4Bdepicts a system400in which pump420is replaced with a loop heat pipe440comprising a base plate442, an evaporator444, and a condenser446.

While the examples depicted inFIGS. 2, 3A-3B, and 4A-4Ban evaporator and a condenser, one skilled in the art will recognize that other examples may use different heat transfer mechanisms. By way of example, in other examples a solid heat conductor may be used to conduct heat generated by amplifier230to a heat pipe capable of transporting heat at high temperatures and thence to a thermal radiator270. A loop heat pipe or capillary pumped loop may be used to passively pump fluid through the system. The loop heat pipe or capillary pumped loop may be driven by evaporation of heat flow from the heat generating element of the power amplifier to be cooler or it may be driven by parasitic heat loads from cooler spots on the power amplifier and condensed before flowing into the heat acquisition device.

Another example of a heat acquisition and transport technology is an oscillating heat pipe (also known as a pulsating heat pipe) that functions via stochastic, pulsating flow of an ebullient mixture through a serpentine flow path that is driven by heat fluxes through local sections of the wall of the heat pipe envelope. Such an oscillating heat pipe design may be combined with other heat transport technologies described here and may be located near the heat generating element or nearer the radiator or may transport heat from the heat generating element all the way to the radiator. Further, the system may be protected from cold thermal environments by a combination of radiative and conductive insulation, adjustments to pumping rates, and by valving.

FIG. 5is a flowchart illustrating operations in a method500to operate a thermal radiating solid state power amplifier according to aspects. Referring toFIG. 5, at operation510heat is transferred from one or more heat generating elements on a power amplifier230to a heat acquisition and transfer device. For example in the embodiment depicted inFIG. 2, a thermal fluid is pumped through the microchannel cooling circuit250to transfer heat from the power amplifier230to the fluid in the microchannel cooling circuit. At operation515the heat is transferred to a heat rejection device. For example in the embodiment depicted inFIG. 2the thermal fluid extracts heat from the power amplifier assembly205in the evaporators252and transfers the heat to the condenser(s)260on radiator(s)270, where the heat is radiated (operation520) into space.