NASA thermal control technologies for robotic spacecraft
This presentation summarizes the current efforts at NASA/Goddard and NASA/JPL to develop new thermal control technology for future robotic NASA missions.
robotic↗
Engineering topics
Swanson, T. D.
Publications and source records attributed to Swanson, T. D..
MEMS Louvers for Thermal Control
Mechanical louvers have frequently been used for spacecraft and instrument thermal control purposes. These devices typically consist of parallel or radial vanes, which can be opened or closed to vary the effective emissivity of the underlying surface. This project demonstrates the feasibility of using Micro-Electromechanical Systems (MEMS) technology to miniaturize louvers for such purposes. This concept offers the possibility of substituting the smaller, lighter weight, more rugged, and less costly MEMS devices for such mechanical louvers. In effect, a smart skin that self adjusts in response to environmental influences could be developed composed of arrays of thousands of miniaturized louvers. Several orders of magnitude size, weight, and volume decreases are potentially achieved using micro-electromechanical techniques. The use of this technology offers substantial benefits in spacecraft/instrument design, integration and testing, and flight operations. It will be particularly beneficial for the emerging smaller spacecraft and instruments of the future. In addition, this MEMS thermal louver technology can form the basis for related spacecraft instrument applications. The specific goal of this effort was to develop a preliminary MEMS device capable of modulating the effective emissivity of radiators on spacecraft. The concept pursued uses hinged panels, or louvers, in a manner such that heat emitted from the radiators is a function of louver angle. An electrostatic comb drive or other such actuator can control the louver position. The initial design calls for the louvers to be gold coated while the underlying surface is of high emissivity. Since, the base MEMS material, silicon, is transparent in the InfraRed (IR) spectrum, the device has a minimum emissivity when closed and a maximum emissivity when open. An initial set of polysilicon louver devices was designed at the Johns Hopkins Applied Physics Laboratory in conjunction with the Thermal Engineering Branch at NASA's Goddard Space Flight Center.
Champion, J. L.↗
The bubbly-slug transition in a boiling two-phase flow under microgravity
A theory is presented to describe, in reduced gravity flow boiling, the transition from bubbly two-phase flow to slug flow. It is shown that characteristics of the bubbly flow and the transition were controlled by the mechanism of vapor bubble growth dynamics. By considering in nucleate boiling, behavior of vapor bubbles at departure from a heated surface a condition required for transition was determined. Although required, this condition alone could not ensure coalescence of bubbles to cause the transition to slug two-phase flow. The condition leading to coalescence, therefore, was obtained by examining oscillations of vapor bubbles following their departure from the heated surface. The predicted transition conditions were compared with the prediction and test data reported for adiabatic reduced gravity two-phase flow, and good qualitative agreement was found.
Kiper, Ali M.↗
Prediction of heat transfer to a thin liquid film in plane and radially spreading flows
The energy equation is incorporated in the solution algorithm of Rahman et al. (1990) to compute the heat transfer to a thin film in the presence or absence of gravity. For a plane flow under zero gravity, it is found that, for both isothermal and uniformly heated walls, the heat transfer coefficient gradually decreases downstream, with Nu-asterisk (the Nusselt number in terms of film height) remaining approximately constant except for regions very close to the entrance. In the case of radial flow under zero gravity, Nu-asterisk is found to decrease monotonically when the plane is uniformly heated. Two different flow regimes are identified in the presence of gravity for both plane and radial flows. The results of the study may be applicable to the design of space-based cooling systems.
Rahman, M. M.↗
Transient analysis of a capillary pumped loop heat pipe
A bench-top Capillary Pumped Loop (CPL) test system has been developed and tested to investigate the transient mode operation of this system by applying a step power input to the evaporators. Tests were conducted at several power input and evaporator inlet subcooling combinations. In addition, a lumped-heat-capacity model of the CPL test system has been presented which is used for predicting qualitatively the transient operation characteristics. Good agreement has been obtained between the predicted and the measured temperature variations. A simple evaporator inlet subcooler model has also been developed to study effects of inlet subcooling on the steady-state evaporator wall temperature. Results were compared with the test data collected.
Kiper, A. M.↗
Lunar radiators with specular reflectors
A unique radiator, suitable for use in relatively hot thermal environments such as the moon, has been devised and analyzed. The radiator uses a parabolic specular reflector to deflect the solar rays and to shield the radiator from the hot lunar soil. It can provide sink temperatures on the order of 147 K and effective emittances approximately equal to the emittance of the surface of the radiator. Similar performance can be obtained on sun-oriented spacecraft that have a limited view of space.
Costello, Frederick A.↗
Performance testing of a two-phase interface heat exchanger
This paper describes the design and performance testing of a heat exchanger which interfaces separate two-phase ammonia thermal loops. The basic design involves a tube-in-tube concept, with boiling occurring in the inner tube and condensation in the outer tube. Eight such tubes are arranged in parallel. Testing has demonstrated that up to 8.2 kW of heat may be transferred across the heat exchanger when the saturation temperature difference between the systems is 5 C. Performance of the heat exchanger is affected primarily by the mass flow rate of ammonia in the liquid supply loop.
Mccabe, M. E., Jr.↗
Heat transfer to a thin liquid film with a free surface
The numerically computed flow field and heat transfer coefficient are presented for the free surface flow of a thin liquid film in the presence or absence of a gravitational body force. The results of an approximate analysis using the Pohlhausen integral method is also discussed. The flow systems studied here include both plane and radial film flows in the presence or absence of a gravitational body force. The heating conditions include isothermal and uniformly heated surfaces. The transport conditions considered at the free surface are an adiabatic condition and an evaporative free surface maintained at its saturation temperature. The height of the free surface, flow field and heat transfer coefficient, were found to be strongly affected by the gravitational body force. They were also found to depend on the Reynolds number and Froude number of the incoming fluid. In the presence of gravity, a hydraulic jump was found to occur under some flow conditions.
Rahman, M. M.↗
Exploratory study of temperature oscillations related to transient operation of a Capillary Pumped Loop heat pipe
An analytical study has been conducted for better understanding of a peculiar transient behavior which was displayed in testing of a Capillary Pumped Loop (CPL) heat pipe system. During several test runs of this CPL system varying degrees of surface temperature oscillations occurred in the inlet line of the evaporators. Although several theories have been forwarded to explain this observed phenomenon, a satisfactory understanding of causes of these oscillations is still missing. The present investigation derives the conditions which lead to such oscillatory temperature behavior in evaporator inlet section of the mentioned CPL system. Stability characteristics of these temperature oscillations were investigated.
Kiper, A. M.↗
Test results of a pumped two-phase mounting plate with ammonia
The design, fabrication, and testing of full-scale prototype units of a two-phase mounting plate (TPMP), which will be used in a two-phase ammonia-based thermal control system for a large spacecraft, are described. The mounting plate uses an evaporator design in which liquid is mechanically pumped through porous feed tubes within the plate. The prototype TPMPs were tested with ammonia at heat loads over 3000 W (3.2 W/sq cm) and local heat fluxes of up to 4 W/sq cm. Calculated total heat transfer coefficients from these tests were between 0.8 and 1.0 W/sq cm per C. This represents a better than twenty-fold improvement over comparable single-phase heat transfer coefficients. Design diagrams are included.
Swanson, T. D.↗
Design and test of a pumped two-phase mounting plate
The design, fabrication, and testing of the full-scale development unit of a pumped two-phase mounting plate (TPMP) used in advanced two-phase spacecraft thermal control systems are described. The mounting plate is tested with R-11 in the evaporator mode for total heat loads of over 3000 watts and local heat fluxes over 4 W/sq cm, and in the condenser mode with condenser loads from 60 to 400 watts and inlet qualities from 8 to 94 percent. The calculated heat-transfer coefficients are between 0.66 and 1.0 W/sq cm/C and are nearly independent of the flow rate and heat load except at very low heat loads. It is shown that the TPMP can be run with inlet conditions down to 22 C subcooling without any significant gradients in the plate and that it performs well with nonuniform heat fluxes.
Grote, M. G.↗
Study on the application of NASA energy management techniques for control of a terrestrial solar water heating system
This paper addresses the potential for enhanced solar system performance through sophisticated control of the collector loop flow rate. Computer simulations utilizing the TRNSYS solar energy program were performed to study the relative effect on system performance of eight specific control algorithms. Six of these control algorithms are of the proportional type: two are concave exponentials, two are simple linear functions, and two are convex exponentials. These six functions are typical of what might be expected from future, more advanced, controllers. The other two algorithms are of the on/off type and are thus typical of existing control devices. Results of extensive computer simulations utilizing actual weather data indicate that proportional control does not significantly improve system performance. However, it is shown that thermal stratification in the liquid storage tank may significantly improve performance.
Swanson, T. D.↗