SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  AF071-294 (AirForce)
Title:  Advanced Spacecraft Thermal Management Technologies
Research & Technical Areas:  Space Platforms

  Objective:  Develop and validate advanced thermal control technologies for space vehicle applications ranging from nanosats to very large, high-power satellites.
  Description:  Thermal management is quickly becoming a limiting factor for future military satellite systems. Because of the high cost per pound for launch, the focus of satellite component technology development has been to increase performance while decreasing mass and size. As a result, the power density of most spacecraft has significantly increased. In addition, there are new missions that the DoD would like to perform that are limited by the thermal performance of the system. For these reasons, the Air Force is actively pursuing critical advances in satellite thermal management. There are three specific technology challenges that are of interest: 1. Reconfigurable Thermal Networks: Currently, the design, integration, and testing of the thermal control system (TCS) requires years to complete and is a leading contributor to satellite development time. Because of the long design lifetime and the rapid evolution of technology, satellites are obsolete before they are even launched. As a result, the Air Force is interested in technologies that will significantly reduce design time by taking advantages of advances in microelectronics, adaptive control theory, responsivonics (responsive avionics for spacecraft) and other fields. The goal is a reconfigurable TCS that can be tailored on the fly to the needs of the satellite, the mission, and the space environment. In addition to the reconfigurable TCS, we are interested in new insulation technologies. The current state-of-the-art is Multi-Layer Insulation (MLI), which is fragile, requires hours of touch labor and is both difficult to design and quantify in performance. To that end, we are interested in advanced or reconfigurable insulation technologies that eliminate the disadvantages of MLI. 2. Advanced High-Power Deployable Radiators: With advances in solar cell technology and the miniaturization of electronics, new high-power nano- and small satellite concepts have insufficient radiator area. Therefore, high-power deployable radiator concepts that provide efficiencies on the order of 5 kg/kW are of interest. Concepts under consideration include deployable radiators with very high thermal conductivity and compaction ratios. 3. High Conductance Thermally Stable Panels and Structures: Finally, future high-power communication, processors, solid-state laser, and other components are expected to have very high heat rates. For these applications, panels with a thermal conductivity on the order of 100 W/cm2 are needed. Also, thermal stability will be important for these components because of their requirements for high precision and to alleviate thermal stresses. In addition to high-power components, thermal stability is important for large optical and radio frequency (RF) systems. For these systems, degradation caused by thermal deformation is a significant contributor to the degradation of optical and RF signal quality. As the size of optical and RF apertures continues to increase, eliminating thermal deformation becomes critical to achieve the full performance of the system. Technologies are needed to improve the thermal stability of these systems from one end of the structure to the other to within fractions of the wavelength of interest. Achieving these challenges will enable a wide range of missions critical to the warfighter.

  PHASE I: Develop conceptual designs of the hardware based on preliminary analysis. Perform sufficient hardware development and testing to verify system requirements can be met. Proof-of-concept experiments shall be conducted to indicate the practicality of the design in meeting requirements and objectives.
  
  PHASE II: Demonstrate the technology identified in Phase I. Tasks shall include, but are not limited to, a detailed demonstration of key technical parameters that can be accomplished and a detailed performance analysis of the technology. A subscale demo is acceptable, but a full-scale demo is encouraged. Also, model validation testing, a detailed evaluation report, and recommendations are required.

  DUAL USE COMMERCIALIZATION: Military application: Advanced thermal management technologies are applicable to all military spacecraft. Decreasing system mass while increasing component performance is critical for virtually all missions. Commercial application: Potential commercial applications for reconfigurable thermal management include aircraft, automobile, microelectronic applications, or any sector where high power densities are required.

  References:  1. Gilmore, David G., Spacecraft Thermal Control Handbook Volume I: Fundamental Technologies, 2nd Ed, The Aerospace Press, El Segundo, CA, 2002. 2. Lee, Douglas E., “Space Reform,” Air and Space Power Journal, Summer 2004. 3. Bauman, Jane and Suraj Rawal, “Viability of Loop Heat Pipe for Space Solar Power Applications,” AIAA Paper 2001-3078, 35th AIAA Thermophysics Conference, Anaheim, CA, June 2001. 4. Chubb, Donald L., and K. Allan White III, “Liquid Sheet Radiator” 22nd Thermophysics Conference, Paper No. AIAA-1987-1525, Honolulu, Hi, 8 -10 June 1987. 5. V Feig, J., “Radiator Concepts for High Power Systems in Space,” AIAA-84-0055, January 1984.

Keywords:  thermal management, reconfigurable, deployable radiator, thermal stability, multi-layer insulation, MLI, thermal networks, thermal control, high conductivity, thermal stability

Questions and Answers:
Q: For Category 1 - Reconfigurable Thermal Networks, the topic states, "The goal is a reconfigurable TCS that can be tailored on the fly to the needs of the satellite, the mission, and the space environment." The terminology "on the fly" could be construed to mean you want to be able to reconfigure the thermal network while the spacecraft is in orbit, which is obviously attractive, but did you mean that to be a requirement in the proposals?
A: "On the fly" on orbit is not a requirement but a long term goal.
Q: For Category 1 - Reconfigurable Thermal Networks, the topic states, "The goal is a reconfigurable TCS that can be tailored on the fly to the needs of the satellite, the mission, and the space environment." The terminology "on the fly" could be construed to mean you want to be able to reconfigure the thermal network while the spacecraft is in orbit, which is obviously attractive, but did you mean that to be a requirement in the proposals?
A: "On the fly" on orbit is not a requirement but a long term goal.
Q: 1. Advanced High-Power Deployable Radiators: What power range, and what operating temperature range is of interest for the deployable radiators?

2. Also, what is the expected lifetime for the satellites?
A: 1. For nano to small satellites (<400 kg), the power range of interested is 250 to 2000 W. For larger satellites, the power ranges are on the order of tens to 100kW. As for the temperature range, these are standard non-cryogenic radiator panels.

2. For the small satellites, lifetimes are < 1 year. For the larger satellites, lifetime requirements are 5 to 15 years.
Q: The topic states:
"...High Conductance Thermally Stable Panels and Structures: Finally, future high-power communication, processors, solid-state laser, and other components are expected to have very high heat rates. For these applications, panels with a thermal conductivity on the order of 100 W/cm2 are needed...."
I question the value 100 W/cm2 for thermal conductivity.
For conductivity a number such as 2 Watts/cm/cm2/deg Kelvin is considered very good.
If you are referring to energy dissipation at the surface of a panel, and thus a Flux rate, then 100 W/cm2 is very high. The solar loading at satellite orbit is 0.13 W/cm2. The UL-1709 standard (used by the Navy) for kerosene fires is a surface flux loading of 20 W/cm2 and that is considered very difficult to survive.
An aluminum panel 1 cm thick absorbing 100 W/cm2 flux will completely melt in 34 seconds. A stainless steel panel 1 cm thick will completely melt in under 122 seconds. Therefore, could you restate the environment that this panel is supposed to survive with a low to zero coefficient of thermal expansion?
Thank you
A: There is a disconnect between the term "thermal conductivity" and the units, which are obviously a heat flux measurement. When writing the topic, I was trying to quantify the thermal dissipation requirements for the panel for which heat flux is more important. Originally, I was interested in increasing the effective thermal conductivity of the panel. However, after further thought, I didn't want to limit the approach to simply solid conduction. Other forms of heat transfer are just as applicable including forced convection and two-phase flow. The disconnect came from different drafts. The focus should be on the 100 W/cm^2 and not the term "thermal conductivity".

As for the magnitude, there are a number of high heat flux components that the AF would like to incorporate into satellites including high power processors, RF amplifiers, and solid state lasers for communication and signal processing. For these applications thermal stability is important especially at the very high heat rates for these components. Their heat rates can be from 100 to 1000 W/cm^2. It is important to note that the entire panel will not receive the full heat flux, there simply is not enough power on a satellite to produce that much power at the panel level. Instead there will be a discrete number of components: 5, 10, 15.... What is important is the fact that these components have high heat fluxes and the higher the thermal dissipation of the panel the longer the components can be operated before reaching their maximum temperature and must be shut off.

Finally, the concept must also address how to remove the heat from the panel and transfer it to an external location such as a radiator surface. It is true that at these heat rates the aluminum would quickly melt. However, theoretically, I could maintain the temperature of the panel at 273K if I had a large enough radiator panel dissipating the heat of the system.
Q: Under Category 1: Reconfigurable Thermal Networks, the topic states, "As a result, the Air Force is interested in technologies that will significantly reduce design time by taking advantages of advances in microelectronics, adaptive control theory, responsivonics (responsive avionics for spacecraft) and other fields." Would you please clarify this - do you want proposals that utilize these innovative technologies (advanced microelectronics, adaptive control theory, responsivonics and similar) to rapidly reconfigure thermal networks? Or are these examples of technologies being developed for reconfigurable electronic networks and you not necessarily to be applied to reconfigurable thermal networks in the proposal?
A: These are examples utilized for reconfigurable electronics and could have application to thermal control. They are NOT required elements for a proposal. They are possible technologies that could be leveraged for responsive thermal, but by no means are they the only ones. There is a wide variety of potential technologies and all concepts are welcome.
Q: 1. Are your interfacial conductance targets (component-to-structure level) 10W/m2-C to 700W/m2-C?

2. What are the form-factors (footprint) (component and structure)?

3. Must a component-level variable conductance proposal also address structure and panel-to-panel thermal management?
A: 1. For variable conductance architectures, the goal is a low conductance around 10 W/m^2-C with a threshold at 200 W/m^2-C and an objective at 700 W/m^2-C. However, there are other technologies that are applicable to reconfigurable thermal networks than just variable conductance schemes. For those concepts, other values are appropriate. I'm trying to keep the design space as wide as possible, which is why no metrics were provided.

2. Form factors are difficult to address. These systems will be relegated to ESPA and smallish satellites (<400kg). Ideally, the system should be capable of dealing with a wide array of form factors from small to large components (all components used traditionally on spacecraft). The more form factors that can be dealt with the better.
Also, solutions don't have to simply be at the component level. They can also be at the panel, subsystem, or whole satellite level.

3. No, but how it would fit into a thermal control system should be briefly discussed.
Q: 1. Advanced High-Power Deployable Radiators: What power range, and what operating temperature range is of interest for the deployable radiators?

2. Also, what is the expected lifetime for the satellites?
A: 1. For nano to small satellites (<400 kg), the power range of interested is 250 to 2000 W. For larger satellites, the power ranges are on the order of tens to 100kW. As for the temperature range, these are standard non-cryogenic radiator panels.

2. For the small satellites, lifetimes are < 1 year. For the larger satellites, lifetime requirements are 5 to 15 years.
Q: The topic states:
"...High Conductance Thermally Stable Panels and Structures: Finally, future high-power communication, processors, solid-state laser, and other components are expected to have very high heat rates. For these applications, panels with a thermal conductivity on the order of 100 W/cm2 are needed...."
I question the value 100 W/cm2 for thermal conductivity.
For conductivity a number such as 2 Watts/cm/cm2/deg Kelvin is considered very good.
If you are referring to energy dissipation at the surface of a panel, and thus a Flux rate, then 100 W/cm2 is very high. The solar loading at satellite orbit is 0.13 W/cm2. The UL-1709 standard (used by the Navy) for kerosene fires is a surface flux loading of 20 W/cm2 and that is considered very difficult to survive.
An aluminum panel 1 cm thick absorbing 100 W/cm2 flux will completely melt in 34 seconds. A stainless steel panel 1 cm thick will completely melt in under 122 seconds. Therefore, could you restate the environment that this panel is supposed to survive with a low to zero coefficient of thermal expansion?
Thank you
A: There is a disconnect between the term "thermal conductivity" and the units, which are obviously a heat flux measurement. When writing the topic, I was trying to quantify the thermal dissipation requirements for the panel for which heat flux is more important. Originally, I was interested in increasing the effective thermal conductivity of the panel. However, after further thought, I didn't want to limit the approach to simply solid conduction. Other forms of heat transfer are just as applicable including forced convection and two-phase flow. The disconnect came from different drafts. The focus should be on the 100 W/cm^2 and not the term "thermal conductivity".

As for the magnitude, there are a number of high heat flux components that the AF would like to incorporate into satellites including high power processors, RF amplifiers, and solid state lasers for communication and signal processing. For these applications thermal stability is important especially at the very high heat rates for these components. Their heat rates can be from 100 to 1000 W/cm^2. It is important to note that the entire panel will not receive the full heat flux, there simply is not enough power on a satellite to produce that much power at the panel level. Instead there will be a discrete number of components: 5, 10, 15.... What is important is the fact that these components have high heat fluxes and the higher the thermal dissipation of the panel the longer the components can be operated before reaching their maximum temperature and must be shut off.

Finally, the concept must also address how to remove the heat from the panel and transfer it to an external location such as a radiator surface. It is true that at these heat rates the aluminum would quickly melt. However, theoretically, I could maintain the temperature of the panel at 273K if I had a large enough radiator panel dissipating the heat of the system.
Q: Under Category 1: Reconfigurable Thermal Networks, the topic states, "As a result, the Air Force is interested in technologies that will significantly reduce design time by taking advantages of advances in microelectronics, adaptive control theory, responsivonics (responsive avionics for spacecraft) and other fields." Would you please clarify this - do you want proposals that utilize these innovative technologies (advanced microelectronics, adaptive control theory, responsivonics and similar) to rapidly reconfigure thermal networks? Or are these examples of technologies being developed for reconfigurable electronic networks and you not necessarily to be applied to reconfigurable thermal networks in the proposal?
A: These are examples utilized for reconfigurable electronics and could have application to thermal control. They are NOT required elements for a proposal. They are possible technologies that could be leveraged for responsive thermal, but by no means are they the only ones. There is a wide variety of potential technologies and all concepts are welcome.
Q: 1. Are your interfacial conductance targets (component-to-structure level) 10W/m2-C to 700W/m2-C?

2. What are the form-factors (footprint) (component and structure)?

3. Must a component-level variable conductance proposal also address structure and panel-to-panel thermal management?
A: 1. For variable conductance architectures, the goal is a low conductance around 10 W/m^2-C with a threshold at 200 W/m^2-C and an objective at 700 W/m^2-C. However, there are other technologies that are applicable to reconfigurable thermal networks than just variable conductance schemes. For those concepts, other values are appropriate. I'm trying to keep the design space as wide as possible, which is why no metrics were provided.

2. Form factors are difficult to address. These systems will be relegated to ESPA and smallish satellites (<400kg). Ideally, the system should be capable of dealing with a wide array of form factors from small to large components (all components used traditionally on spacecraft). The more form factors that can be dealt with the better.
Also, solutions don't have to simply be at the component level. They can also be at the panel, subsystem, or whole satellite level.

3. No, but how it would fit into a thermal control system should be briefly discussed.

Record: of