A document discusses an approach to insulating propulsion lines for spacecraft. In spacecraft that have propulsion lines that are located externally with open bus architecture, the lines are typically insulated by Multi Layer Insulation (MLI) blankets. MLI on propulsion lines tends to have large and somewhat random variances in its heat loss properties (effective emittance) from one location to the next, which makes it an un-robust approach to control propulsion line temperatures. The approach described here consists of a “clamshell” design in which the inner surface of the shell is coated with low-emissivity aluminized Kapton tape, and the outer surface is covered with black tape. This clamshell completely encloses the propulsion line. The line itself is covered with its heater, which in turn, is covered completely with black tape.
This approach would be low in heater power needs because even though the outer surface of the prop line (and its heater) is covered with black tape as well as the outer surface of the clamshell, the inner surface of the clamshell is covered with low-emissivity aluminized Kapton tape. Hence, the heat loss from the line will be small and comparable to the MLI based one.
In terms of contamination changing the radiative properties of surfaces, since the clamshell’s inner surface is always protected during handling and is only installed after all the work on the prop line has been completed, the controlling surface, which is the clamshell’s inner surface, is always in pristine condition.
This proposed design allows for a much more deterministic and predictable design using a very simple and implementable approach for thermal control. It also uses low heater power and is robust to handling and contamination during and after implementation.
This work was done by Pradeep Bhandari of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47441
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Robust Thermal Control of Propulsion Lines for Space Missions
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Overview
The document titled "Robust Thermal Control of Propulsion Lines for Space Missions" from NASA's Jet Propulsion Laboratory discusses the challenges and solutions related to maintaining the temperature of propulsion lines in spacecraft. These lines, which transport propellants like hydrazine, are critical for the performance of thrusters and engines. The temperature of these lines must be carefully controlled within a narrow range of +15°C to +50°C to prevent issues such as freezing of the propellant or overheating before it enters the thrusters.
The document outlines the factors affecting the temperature of propulsion lines, including heat loss characteristics of Multi Layer Insulation (MLI), the local thermal environment, mechanical support heat loss, and the effectiveness of heaters. Due to the poor thermal conduction along the axial direction of the lines, temperature variations can occur even over short distances, complicating the thermal control process. Typically, a single temperature sensor is used to control multiple heater patches along a section of the line, which can lead to challenges in maintaining uniform temperatures.
To address these issues, the document proposes a novel "clamshell" design for thermal control. This design features an inner surface coated with low emissivity aluminized Kapton tape and an outer surface covered with black tape, effectively enclosing the propulsion line. This approach aims to enhance thermal insulation and minimize heat loss, thereby improving the overall thermal management of the propulsion lines.
The report emphasizes the importance of robust thermal control systems in ensuring the reliability and efficiency of spacecraft propulsion systems. It highlights the need for innovative solutions to overcome the limitations of traditional methods, such as MLI and mechanical thermostats, which may lack flexibility and responsiveness in dynamic space environments.
Overall, the document serves as a technical support package that not only details the challenges faced in thermal control of propulsion lines but also presents a promising design solution that could significantly improve the thermal management of spacecraft systems. This research is part of NASA's broader efforts to advance aerospace technology and enhance the performance of space missions.
