ALBERT

Description: The Systems Improved Numerical Fluids Analysis Code, SINFAC, consists of additional routines added to the April 1983 revision of SINDA, a general thermal analyzer program. The purpose of the additional routines is to allow for the modeling of active heat transfer loops. The modeler can simulate the steady-state and pseudo-transient operations of 16 different heat transfer loop components including radiators, evaporators, condensers, mechanical pumps, reservoirs and many types of valves and fittings. In addition, the program contains a property analysis routine that can be used to compute the thermodynamic properties of 20 different refrigerants. SINFAC can simulate the response to transient boundary conditions. SINFAC was first developed as a method for computing the steady-state performance of two phase systems. It was then modified using CNFRWD, SINDA's explicit time-integration scheme, to accommodate transient thermal models. However, SINFAC cannot simulate pressure drops due to time-dependent fluid acceleration, transient boil-out, or transient fill-up, except in the accumulator. SINFAC also requires the user to be familiar with SINDA. The solution procedure used by SINFAC is similar to that which an engineer would use to solve a system manually. The solution to a system requires the determination of all of the outlet conditions of each component such as the flow rate, pressure, and enthalpy. To obtain these values, the user first estimates the inlet conditions to the first component of the system, then computes the outlet conditions from the data supplied by the manufacturer of the first component. The user then estimates the temperature at the outlet of the third component and computes the corresponding flow resistance of the second component. With the flow resistance of the second component, the user computes the conditions down stream, namely the inlet conditions of the third. The computations follow for the rest of the system, back to the first component. On the first pass, the user finds that the calculated outlet conditions of the last component do not match the estimated inlet conditions of the first. The user then modifies the estimated inlet conditions of the first component in an attempt to match the calculated values. The user estimated values are called State Variables. The differences between the user estimated values and calculated values are called the Error Variables. The procedure systematically changes the State Variables until all of the Error Variables are less than the user-specified iteration limits. The solution procedure is referred to as SCX. It consists of two phases, the Systems phase and the Controller phase. The X is to imply experimental. SCX computes each next set of State Variables in two phases. In the first phase, SCX fixes the controller positions and modifies the other State Variables by the Newton-Raphson method. This first phase is the Systems phase. Once the Newton-Raphson method has solved the problem for the fixed controller positions, SCX next calculates new controller positions based on Newton's method while treating each sensor-controller pair independently but allowing all to change in one iteration. This phase is the Controller phase. SINFAC is available by license for a period of ten (10) years to approved licensees. The licenced program product includes the source code for the additional routines to SINDA, the SINDA object code, command procedures, sample data and supporting documentation. Additional documentation may be purchased at the price below. SINFAC was created for use on a DEC VAX under VMS. Source code is written in FORTRAN 77, requires 180k of memory, and should be fully transportable. The program was developed in 1988.

Description: It is pointed out that active thermal control systems can theoretically provide a more isothermal spacecraft at less power and weight than required by conventional passive systems. The present paper is concerned with a study of the advantages, with respect to weight and power savings, which can be achieved by using active thermal control systems in future NASA spacecraft. In the study, a prototype NASA spacecraft, based on the Upper Atmosphere Research Satellite (UARS), is considered. In order to represent thermal requirements of future spacecraft, the UARS requirements were modified for the prototype, which was called AEOS (advanced earth-orbiting spacecraft). Five types of active thermal-control systems were considered. The results which can be obtained with the different thermal-control systems are compared.

Description: A strategy was investigated by which thermal designers for spacecraft could devise an optimal thermal control system to maintain the required temperatures, temperature differences, changes in temperature, and changes in temperature differences for specified equipment and elements of the spacecraft's structure. Thermal control is to be maintained by the coating pattern chosen for the external surfaces and heaters chosen to supplement the coatings. The approach is to minimize the thermal control power, thereby minimizing the weight of the thermal control system. Because there are so many complex computations involved in determining the optimal coating design a computerized approach was contemplated. An optimization strategy including all the elements considered by the thermal designer for use in the early stages of design, where impact on the mission is greatest, and a plan for implementing the strategy were successfully developed. How the optimization process may be used to optimize the design of the Space Telescope as a test case is demonstrated.

Description: The purpose of this paper is to present a modeling technique that has proven successful in simulating pumped, two-phase cooling systems. The technique uses the standard SINDA thermal-analysis program and thereby extends the capabilities of SINDA to complex, active spacecraft thermal-control systems. This paper provides sufficient detail that a current SINDA user will be able to apply the technique by reference to this paper alone.

Description: The FWDBCK time step, which is usually chosen intuitively to achieve adequate accuracy at reasonable computational costs, can in fact lead to large errors. NASA observed such errors in solving cryogenic problems on the COBE spacecraft, but a similar error is also demonstrated for a single node radiating to space. An algorithm has been developed for selecting the time step during the course of the simulation. The error incurred when the time derivative is replaced by the FWDBCK time difference can be estimated from the Taylor-Series expression for the temperature. The algorithm selects the time step to keep this error small. The efficacy of the method is demonstrated on the COBE and single-node problems.

Description: A pumped, two-phase heat-transport system is being developed for possible use for temperature control of scientific instruments on future NASA missions. As compared to a single-phase system, this two-phase system can maintain tighter temperature control with less pumping power. A laboratory model of the system has been built and tested. The measured heat transfer coefficients were approximately the same as in heat pipes, 220 Btu/hr-sq ft-F, as compared to 25 Btu/hr-sq ft-F for single-phase liquid flow. Heat shearing between experiments has been demonstrated wherein vapor generated in the cold plate of an active experiment was condensed in a cold, unheated experiment. System stability has been observed. However, additional development is needed. The use of non-azeotropic mixtures of coolants appears especially promising as a simple way to determine exit quality and thus control the flow rates to prevent dryout.

Description: Computer optimization of spacecraft optical coatings for temperature control, using finite element analysis and matrix inversion

Description: Heat balance equations for optimizing optical coating patterns for spacecraft temperature control system

Description: Optimization for selection of optical coating patterns of external surfaces of spacecraft for temperature control

Description: Systems Improved Numerical Fluids Analysis Code, SINFAC, consists of additional routines added to April, 1983, version of SINDA. Additional routines provide for mathematical modeling of active heat-transfer loops. Simulates steady-state and pseudo-transient operations of 16 different components of heat-transfer loops, including radiators, evaporators, condensers, mechanical pumps, reservoirs, and many types of valves and fittings. Program contains property-analysis routine used to compute thermodynamic properties of 20 different refrigerants. Source code written in FORTRAN 77.