Engineering topics

Modest, M. F.

Publications and source records attributed to Modest, M. F..

6 records

NASA NTRS1985

Challenges in the development of the orbiter radiator system

Major technical challenges which were met in the design and development of the Space Shuttle Orbiter Radiator System are discussed. This system rejects up to 30 kW of waste heat from eight individual radiators having a combined surface area of 175 sq m. The radiators, which are deployable, are mounted on the inside of the payload bay doors for protection from aerodynamic heating during ascent and re-entry. While in orbit the payload bay doors are opened to expose the radiators for operation. An R21 coolant loop accumulates waste heat from various components in the Orbiter and delivers the heat to the radiators for rejection to space. Specific challenges included high acoustically induced loads during lift-off, severe radiating area constraints, demanding heat load control requirements, and long life goals. Details of major design and analysis efforts are discussed. The success of the developed hardware in satisfying mission objectives showed how well the design challenge was met.

Williams, J. L.↗

NASA NTRS1980

Solar flux incident on an orbiting surface after reflection from a planet

Algorithms describing the solar radiation impinging on an infinitesimal surface after reflection from a gray and diffuse planet are derived. The following conditions apply: only radiation from the sunny half of the planet is taken into account; the radiation must fall on the top of the orbiting surface, and radiation must come from that part of the planet that can be seen from the orbiting body. A simple approximate formula is presented which displays excellent accuracy for all significant situations, with an error which is always less than 5% of the maximum possible reflected flux. Attention is also given to solar albedo flux on a surface directly facing the planet, the influence of solar position on albedo flux, and to solar albedo flux as a function of the surface-planet tilt angle.

Modest, M. F.↗

NASA NTRS1978

Three-dimensional radiative exchange factors for nongray, nondiffuse surfaces

A computer program using a variation of the Monte Carlo method was developed to predict radiative exchange factors in three-dimensional configurations with curved surfaces. The model allows for arbitrary emission, absorption, and reflection characteristics and for radiation exchange between surfaces as well as external irradiation through openings. It was shown that exchange factors can be determined efficiently by using the normal Monte Carlo method for closed configurations and/or high surface emissivities, while energy partitioning is vastly superior in the case of open configurations and/or low surface emissivities. Comparison with some experiments performed on the Space Shuttle heat rejection system demonstrates the model's accuracy as well as its superiority over a simplified diffuse-surface analysis, which requires similar amounts of computer time.

Modest, M. F.↗

NASA NTRS1977

Determination of three-dimensional radiative exchange factors for the Space Shuttle by Monte Carlo

A program was developed to predict radiative exchange factors in three-dimensional configurations with curved, specularly-reflecting surfaces using the Monte Carlo method. It was shown that this can be done efficiently by using the normal Monte Carlo method for closed configurations and/or high surface emissivities, while Energy Partitioning should be used for open configurations and/or low surface emissivities. Comparison with experiments on the Space Shuttle radiator panels showed that the simple model of gray, diffuse emission is sufficient for the prediction of exchange factors between actual (silver-coated teflon) surfaces. For solar-irradiation exchange factors on the Space Shuttle, on the other hand, spectral and directional variations of surface properties must be taken into account.

Modest, M. F.↗

NASA NTRS1975

Radiative equilibrium in a rectangular enclosure bounded by gray walls

Two-dimensional temperature and heat-flux distributions are calculated for an absorbing-emitting gray medium at radiative equilibrium in a rectangular enclosure. The bounding walls are gray and diffuse with arbitrary surface-temperature distributions, and heat generation may take place inside the medium. As a first approximation, the problem is solved for optically thick systems (differential approximation). These results are subsequently improved by the introduction of a number of geometrical parameters to yield good accuracy for all optical thicknesses. As examples, two cases are discussed in detail: (1) uniform heat generation in a black enclosure, and (2) an enclosure with one gray surface at constant temperature. Comparison with some numerical solutions generated by Hottel's /Hottel and Cohen (1958) and Einstein (1963)/ zonal method shows excellent agreement.

Modest, M. F.↗

NASA NTRS1974

Two-dimensional radiative equilibrium of a gray medium in a plane layer bounded by gray nonisothermal walls

Radiative equilibrium temperature and surface heat flux distributions are calculated for an absorbing-emitting gray medium in an infinite plane layer bounded by gray diffuse walls with arbitrary temperature distributions. Superposition is used to obtain the solution for the differential approximation, which yields good accuracy for the optically thick medium. To also obtain accurate results for optically thin and intermediate regimes, the differential approximation is subsequently improved by a number of geometrical parameters, which are derived from the exact expression for the intensity. As an example, the case of constant temperature at the upper wall and a temperature step at the lower wall without heat generation in the medium is presented. Comparison with other available results shows excellent agreement.

Modest, M. F.↗