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Abstract High-power small satellites will play an important role in reducing the cost of space missions. High power levels are required to satisfy high bandwidth communication needs, as well as to accommodate other critical systems such as propulsion and high-power electronics. One of the current high-power limitations is the need to overcome the thermal challenges associated with high thermal loads. While substantial work has been done in the development of deployable solar arrays, relatively little attention has been given to small satellite deployable radiators. Previous deployable small satellite radiators rely on a mechanical hinge to conduct heat from spacecraft to radiator. However, this presents a thermal choke point and limits heat flow. Thus, a deployable radiator design concept is currently being explored as a thermal solution for high powered electronics in CubeSats. This Additively Manufactured Deployable Radiator Oscillating Heat Pipes (AMDROHP) design concept combines the function of a deployable radiator with high performance Oscillating Heat Pipes in this compact thermal solution. In this project, significant efforts have gone into developing the mechanical, deployable aspect of this design while maximizing its thermal performance, and this joint development has been discussed in previous publication. This initial design was additively manufactured and thermally tested at the Jet Propulsion Laboratory. The results of the thermal testing of the initial AMDROHP design are discussed and presented in this work. The device is tested across a range of heat inputs under “micro-gravity” and “gravity-assisted” orientations for the working fluids R134a and Ammonia. The performance and behavior of the AMDROHP device are characterized by transient temperature measurement data under these different conditions. The results were interpreted to determine the feasibility of the design. Although AMDROHP did operate under “gravity-assisted” orientation, it did not start-up under “micro-gravity” orientation. Furthermore, the range of operation under “gravity-assisted” orientation was less than expected. Based on these results, possible design changes have been identified to improve AMDROHP performance under space-like conditions. These changes include creating a shorter adiabatic length by decreasing the path length of the helical joint, as well as increasing the inner channel diameter. These changes will allow for better thermal performance and to better avoid any imperfections in the additive manufacturing process to cause negative effects on OHP operation. In this study, experimental testing provided actionable information about the initial design of AMDROHP to lead to design improvements. These design improvements will be implemented in the next design iteration of AMDROHP.
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Passively actuated, triangular radiator fin array
Thermal control is a challenge for spacecraft as they must maintain internal components within operating limits despite significant fluctuations in external and internal thermal loads. Satellites often rely on dynamic thermal control to manage internal temperatures depending on the thermal environment. However, many of these systems are actively managed, relying on the satellite’s internal electronics to control the radiator’s behavior. The problem of thermal control is compounded for small satellites, such as CubeSats, which have high power dissipation per unit surface area, stringent size/weight restrictions, and reduced thermal mass. Passive thermal control is particularly attractive for such small systems, potentially offering increased reliability and simplicity. Attempts at passive, dynamic thermal control of spacecraft radiators have been demonstrated in the literature using louvers actuated by bimetallic coils and radiators deployed by shape memory alloys. In this work, we propose a dynamic thermal control method for CubeSats by using bimetallic coils to passively deploy an array of four triangular radiator fins that, when folded, comprise the external face of a CubeSat. This approach differs from previous approaches as it uses mass efficient, triangular radiative fins as well as bimetallic coils to passively actuate the panels, as opposed to shape memory alloys. The advantages of this design include reduced complexity, cost, volume, and weight when compared to traditional deployable radiators in addition to increased redundancy by using an array of panels. An experimental demonstration of the proposed design is presented indicating the ability to passively deploy a single radiator fin using custom bimetallic coils at a rate of approximately 3.9° of angular rotation per 1 °C with minimal hysteresis. A preliminary model of our design indicates the possibility to achieve a turndown ratio of greater than 7:1. Experimental and numerical prediction results are presented as a motivation for exploration of the proposed design in ongoing work.
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- Award ID(s):
- 1749395
- PAR ID:
- 10229718
- Date Published:
- Journal Name:
- NASA Thermal and Fluid Analysis Workshop, August 18-20, 2020
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract As small spacecraft technologies develop, thermal management devices need to meet the growing demands of high-powered electronics. Currently being developed to meet this demand in CubeSats is the Additively Manufactured Deployable Radiator Oscillating Heat Pipes (AMDROHP). AMDROHP seeks to implement the high thermal conductivity and two-phase technology of Oscillating Heat Pipes into a unique deployable radiator design for a 3U CubeSat, taking advantage of additive manufacturing capabilities. While much consideration has been put into designing the AMDROHP on its own as a heat exchanger, there is also the need for it to be evaluated thermally at a system-level with the rest of the CubeSat while in orbit. In this study, thermal orbital spacecraft simulations, through the Thermal Desktop software, were performed to analyze how AMDROHP thermally integrates and interacts with the rest of the CubeSat and evaluate the survivability of temperature-sensitive components on the spacecraft. The simulations in this study included an 11th-orbit beta angle sweep for a tumbling orientation of the spacecraft in Low Earth Orbit (LEO). These simulations were performed with two AMDROHP devices in the CubeSat bus, each under a direct 25W heat input and performing with a thermal conductance of 6 W/K, which corresponds to the projected performance of the AMDROHP device while in operation. In this paper, the Thermal Desktop model of the AMDROHP CubeSat includes all major physical components, connections, heat loads, and thermal and optical materials. Then, steps are taken to improve the computational speed of the model. Furthermore, the means of addressing the modeling of the complex two-phase behavior of the OHP is outlined. Then, a number of test cases considering various operating conditions were simulated. From these simulations, orbital temperatures of sensitive components, primarily electronics, were collected and analyzed to find the minimum and maximum operating temperatures across all potential orbits. These temperatures were then evaluated to determine the component’s survivability in a worst-case scenario in orbit. From the results, it was found that, with the projected conductance of AMDROHP, all components operate under safe temperature conditions for any beta angle while in Low Earth Orbit. The evaporator is consistently the hottest component of the spacecraft and electronics boards all maintain survivable temperatures and are not at risk of over or underheating, even at worst case temperatures for all orbits tested. Based on the results and analysis of this conceptual study, it is suggested that AMDROHP will perform as an effective management device for small satellites.more » « less
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