Derek W. Hengeveld

Review of Modern Spacecraft Thermal Control Technologies

Originally created and developed for space applications, several commercial terrestrial technologies still permeate our society today. Examples include solar cells, Global Positioning Systems, and less expensive methods of carbon nanotube manufacture. Given a long and successful history of spinoffs, there might exist opportunities for the transfer of modern spacecraft thermal control technologies to terrestrial HVAC&R applications. First, this paper presents a broad overview of spacecraft thermal control. Next, a review of several modern spacecraft thermal control subsystem technologies is provided, each including an assessment of their potential use for terrestrial applications.

Optimal Placement of Electronic Components to Minimize Heat Flux Nonuniformities

Development of electronic devices and systems with increased capability and good reliability will require improved thermal management techniques. Technology improvements such as embedded heat pipes, integrated pumped fluid loops, and integrated high conductivity thermal spreaders such as annealed pyrolytic graphite provide advances that can enable more powerful devices in ever-decreasing package sizes. Although technology innovations provide one solution path, an alternative method that has not received much attention is simply optimized component placement. The present approach provides a fast method for determining optimized component placement that approaches a uniform distribution of heat flux. The result is improved thermal performance of electronic systems. A tool was developed which can optimally place any number of components within a rectangular domain. Optimized results were obtained for 18 uniform and 11 non-uniform components within 20 s and 7 s, respectively, using a 2.5GHz Core™ Duo processor. The approach presented in this paper is especially useful in situations where limited or no thermophysical and environmental conditions are readily available for the problem at hand and can be utilized in a variety of industries including microelectronics and satellite development.

Hot- and Cold-Case Orbits for Robust Thermal Control

Realizing cheaper, more flexible alternatives to traditional satellites requires robust design approaches. Robust satellite subsystems are designed to meet a broad range of mission requirements; consequently, they drastically reduce nonrecurring engineering costs and greatly diminish design, development, assembly, integration, and test schedules. Robust thermal control subsystems must be capable of handling a broad range of thermal environments, thus reducing design and development costs but can be susceptible to overdesign. Therefore, improved design methodologiesareneededtomaintaintheiradvantageswhileminimizingexcessivedesign.Asa firststep,designhotandcold-case orbits shouldbe examined. Theprimarygoal of the study described in thispaper wasto identify single hot- and cold-case design orbits that work well in the design of robust thermal control subsystems over a wide range of satellite surface properties and likely operating environments. A general approach was developed to identify worst-case orbits that employ a combination of statistical and historical data such that statistically insignificant orbits are disregarded. Using this method, individual hot- and cold-case design orbits were found at beta angle/ inclinationcombinationsof72 deg =52 degand0 deg =28 deg,respectively.Theuseofthesedesignorbitsworkswell for a wide range of different satellite surface properties.

Thermal control subsystem requirements and challenges for a responsive satellite bus

The traditional approach to satellite design is a customized and highly optimized satellite bus. The primary design driver is to minimize mass but often at the expense of schedule and non-recurring engineering costs. The result after years of development is a high performance system with minimal flexibility. Consequently, there is a need for responsive, small satellites that are able to accommodate different missions, changing threats, and emerging technologies for which the traditional development approach is unable to satisfy. Instead, systems must be modular and/or robust. One of the subsystems that will be challenging for the development of modular and/or robust architectures is the thermal control subsystem (TCS). To design a traditional TCS, virtually every aspect of the mission, the satellite, and the components must be known before an intense design program can be completed. However, the mission, payload, components, and requirements are largely unknown before mission initiation. To provide a baseline for the TCS design and to help bound the problem for the development of robust thermal systems, the range of external and internal heat loads for small satellites were evaluated. From this analysis, the realistic worst design cases were identified along with other requirements for robust thermal control systems. Finally, the paper will discuss the merits of various thermal architectures and the challenges associated with achieving the requirements for robust thermal control for responsive satellite buses.

Determination of Operationally Responsive Space (ORS) Hot and Cold Case Design Orbits

Operationally Responsive Space (ORS) concepts emphasize satellites that are faster, cheaper and good enough. Applying this notion to ORS thermal control subsystems (TCS) allows for more relaxed design methodologies. That is, ORS TCS should be robust enough to be able to handle most but not all situations. Consequentially, a new approach to identifying worst case orbits employing a combination of statistical and historical data was sought for these specific types of missions. In effect, orbits that have little potential of being utilized for ORS missions were disregarded. Design hot and cold case orbital parameters for four satellite surface types utilizing an approach more suitable for ORS were found. A hot and cold case design orbit was found at Beta Angle/inclination combinations of 72°/52° and 0°/28°, respectively.