Showing papers in "Journal of Spacecraft and Rockets in 1990"

New interplanetary proton fluence model

Abstract: A new predictive engineering model for the interplanetary fluence of protons with above 10 MeV and above 30 MeV is described. The data set used is a combination of observations made from the earth's surface and from above the atmosphere between 1956 and 1963 and observations made from spacecraft in the vicinity of earth between 1963 and 1985. The data cover a time period three times as long as the period used in earlier models. With the use of this data set the distinction between 'ordinary proton events' and 'anomalously large events' made in earlier work disappears. This permitted the use of statistical analysis methods developed for 'ordinary events' on the entire data set. The greater than 10 MeV fluences at 1 AU calculated with the new model are about twice those expected on the basis of models now in use. At energies above 30 MeV, the old and new models agree. In contrast to earlier models, the results do not depend critically on the fluence from any one event and are independent of sunspot number. Mission probability curves derived from the fluence distribution are presented.

Accurate Navier-Stokes results for the hypersonic flow over a spherical nosetip

Abstract: The unsteady, thin-layer Navier-Stokes equations for a perfect gas are solved with a linearized block, alternating direction implicit finite-difference solution procedure. Solution errors due to numerical dissipation added to the governing equations are evaluated. Errors in the numerical predictions on three-differe nt grids are determined where Richardson extrapolation is used to estimate the exact solution. Accurate computational results are tabulated for the hypersonic laminar flow over a spherical body, which can be used as a benchmark test case. Predictions obtained from the code are in good agreement with inviscid numerical results and experimental data.

Code calibration program in support of the Aeroassist Flight Experiment

Abstract: The code calibration program for the Langley Aerothermodynamic Upwind Relaxation Algorithm to be used as support for the Aeroassist Flight Experiment (AFE) is discussed. Comparisons between experimental data and numerical simulations are made which focus on perfect-gas tests involving a scale model of the AFE. Aspects of the thermochemical nonequilibrium model are called into question by the results of ground tests performed in a ballistic range and in a shock tunnel.

Psychological, psychiatric, and interpersonal aspects of long-duration space missions.

Abstract: America's future in space calls for manned missions that are of long duration and increasing complexity. Under these conditions, psychological and interpersonal stressors will take on added importance in affecting the safely of the crew and the outcome of the mission. Through an analysis of reports from manned American and Soviet space missions and Earth-bound simulations, several psychological, psychiatric, and interpersonal issues can be identified that could affect the success of the space station and other long-duration space ventures. Psychological issues include sleep problems, alteration in time sense, demographic effects, career motivation, transcendent experiences, homesickness, and alteration in perceptual sensitivities. Psychiatric issues include anxiety, depression, and psychosis, psychosomatic symptoms, emotional problems related to the stage of the mission, and postflight personality changes. Interpersonal issues include interpersonal tension, decreased cohesiveness over time, need for privacy, and task vs emotional leadership. Steps can be taken to minimize the impact of these issues, both before and during the mission.

Small submerged vortex generators for turbulent flow separation control

Abstract: The performance of low-profile submerged vortex generators for controlling moderate two-dimensional turbulent flow separation has been investigated experimentally. Surface static pressure measurements, as well as surface oil flow visualizations, have been used to explore the effect of these vortex generators on separation and reattachment locations and downstream pressure recovery. Drag measurements have also been used to evaluate the device (or parasitic) drag of these vortex generators. All of the vortex generators investigated have been shown to reduce the reattachment distance and increase pressure recovery. A small submerged (Wheeler-type) vortex generator with a device height of only 10% of the boundary-layer thickness is shown to perform as well as a conventional vane-type vortex generator with a device height (and device drag) an order-of-magnitude higher.

Vacuum ultraviolet radiation/atomic oxygen synergism in materials reactivity

Abstract: Experimental results are presented which indicate that low fluxes of vacuum UV (VUV) radiation exert a pronounced influence on the atomic oxygen reactivity of such fluorocarbon and fluorocarbon spacecraft materials as the FEP Teflon and PCTFE that are under consideration for the Space Station Freedom. With simultaneous exposure to VUV fluxes comparable to those experienced in LEO, the reactivity of these materials becomes comparable to that of Kapton; VUV radiation has also been shown to increase the reactivity of Kapton with thermal-energy oxygen atoms.

Use of atmospheric braking during Mars missions

Abstract: The use of a high-lift, winged atmospheric entry-glide vehicle by an early Mars manned mission lasting 14-16 months allows the effective use of atmospheric braking to decelerate upon arrival at Mars. Following nearly-constant deceleration, the vehicle skips out of the atmosphere into a low planetary orbit. The maximum atmospheric heating rate thus generated is of the order of 100 W/sq cm at the stagnation point for a fully catalytic surface; the corresponding equilibrium wall temperature was 2150 K. The vehicle envisioned could be radiatively cooled to an entry speed of over 8 km/sec.

Adaptive structures - An overview

Abstract: Introduction A DAPTIVE structures is defined in this paper as a structural system whose geometric and inherent structural characteristics can be changed beneficially to meet mission requirements either through remote commands and/or automatically in response to external stimulations. A similar definition has been used by the Institute of Space and Astronautical Science (ISAS) in Japan. The author believes the concepts related to adaptive structures will make possible future NASA missions such as the large deployable reflector (LDR) and optical interferometer as shown in Figs. 1 and 2. The requirements for these missions that drive the need for adaptive structures can be generalized as micron-level precision for 20 m structures that must operate for 20 to 30 years. The number of organizations working in areas related to adaptive structures has increased dramatically, and several Centers for research have been established; examples are the Center for Space Engineering Research focused on controlled structures technology at Massachusetts Institute of Technology and the Smart Materials and Structures Laboratory at Virginia Polytechnic Institute and State University. Other organizations, such as the Jet Propulsion Laboratory and ISAS, have emphasized adaptive structures in their structures research program. The number of meetings and sessions at technical meetings related to this area has increased; as an example, three sessions on adaptive structures were presented at the 30th Structures, Structural Dynamics, and Materials (SDM) Conference in Mobile, AL, in March 1989; sessions are being developed for the American Society of Mechanical Engineers (ASME) Winter Annual Meeting in Dec. 1989, and plans are under way to establish a joint U.S./Japan meeting on adaptive structures in 1990. This paper will summarize briefly the activities in adaptive structures; however, a large number of references are included. The author would appreciate input on inadvertent omissions of key contributions. Only information available to the author from the open literature and the abstracts submitted to the 30th SDM Conference were used. The objective is not to provide an inclusive list of references and contributors but to use references and examples available to the author to convey the intended information. Adaptive structures is a multidisciplinary activity that includes materials, actuators, sensors, controls, composites, structures, concepts, and dynamics; the emphasis is on the end deliverable hardware system, a structure that meets the mission performance requirements.

Threshold voltage for arcing on negatively biased solar arrays

Abstract: The arcing that has been found to occur when negatively biased high-voltage solar arrays in LEO lie at a critical voltage with respect to the plasma environment is presently proposed to be due to a breakdown of gas emitted under electron bombardment from the solar cells' cover-glass. The elements of the model for this phenomenon include an electron current flow from the interconnect to a neighboring cover-glass, which desorbs neutral molecules under the electron bombardment. The neutral molecules form a gas over the interconnect, and this gas breaks down when the voltage over the interconnect is sufficiently high. Specific scaling predictions are made on the basis of the geometric structure and gas in question.

Effectiveness of Passive Devices for Axisymmetric Base Drag Reduction at Mach 2

Abstract: Experiments have been made to assess the effectiveness of passive devices for reducing base and total afterbody drag at Mach 2 The devices examined include primarily base cavities and ventilated cavities Results show that ventilated cavities offer significant base-drag reduction and net-drag reduction of engineering value A correlation of base- and net-drag reduction for ventilated cavities has been suggested Typical effects of these devices on boat-tailed and flared bases have also been assessed ^DB -pb D h L M #00 t Nomenclature = forebody (max) cross-sectional area, 490625 mm2 = total area of ventilation = total afterbody drag coefficient, net-drag force/to^ A) = base-drag coefficient = base-pressure coefficient = forebody (max) diam, 25 mm = cavity depth = afterbody length = freestream Mach number = freestream dynamic pressure = cavity lip thickness

Need for Control of Numerical Accuracy

Abstract: The need for the control of numerical accuracy in computational fluid dynamics (CFD) code solutions is reviewed in the light of current journal practice and experience with implementation of an editorial policy on the same subject published by the Journal of Fluids Engineering. Various actual objections to that policy are listed and responses are given. The general successes and particular difficulties experienced in the implementation of the policy are noted. The broader question of code verification, validation, and certification is considered. It is suggested that professional societies such as the AIAA and American Society of Mechanical Engineers may ultimately become involved in the task of certification of commercially available CFD codes.

Hypersonic viscous shock-layer solutions over long slender bodies. I - High Reynolds number flows

Abstract: Numerical solutions from the time-steady viscous shock-layer (VSL) equations are presented for the hypersonic laminar and turbulent flow of a perfect gas over long slender bodies. These results are obtained from a spatial-marching, implicit, finite-difference technique, which includes coupling of the normal momentum and continuity equations and use of the Vigneron pressure condition in the subsonic nose region. Detailed comparisons have been made with other predictions and experimental data to assess the accuracy of the present numerical technique, especially for slender-body flows. The comparisons have been shown to yield accurate results. Two widely used algebraic turbulence models, namely the Cebeci-Smith (CS) and the Baldwin-Lomax (BL) models, have been analyzed with the present technique for application to long, slender bodies. The BL model has been modified in the present work for pressure-gradient effects and applied successfully at hypersonic flow conditions. Both of these models have been shown to result in similar heating predictions for the attached flows analyzed here.

Psychosocial effects of adjustment in Antarctica - Lessons for long-duration spaceflight

Abstract: This paper examines the utility of remote, isolated Antarctic research stations as analogs for long-duration spaceflights from the perspective of psychosocial processes of adaptation and adjustment. Certain features of the physical and man-made environments found in Antarctica are similar to those that will be encountered in outer space. In both settings, men and women are likely to experience a number of physiological and psychological changes in response to the extreme environmental conditions and the prolonged' isolation and confinement. Biomedical research in Antarctica provides an opportunity to study the causes of these changes and to develop strategies for reducing the risks to health and well-being before they pose a serious threat to crew safety and mission success. A number of lessons for long-duration spaceflight are examined, including screening and selection of personnel; training programs designed to facilitate individual adjustment and group adaptation and minimize group conflict; identification of optimal leadership characteristics for small, isolated groups; an understanding of social dynamics and group "microcultures" necessary for the organization and management of small but heterogeneous groups; organization of work activities; facility design; and support infrastructure.

Solar photon thrustor

Abstract: A space vehicle that uses a solar sail for propulsion can be significantly improved in performance by separating the function of collecting the solar photons from the function of reflecting the solar photons. In the Solar Photon Thrustor concept, the collector is a large reflecting surface similar in size and mass per unit area to that of a standard flat solar sail. The collector always faces the sun so as to present the maximum area for collection of sunlight. The collector is also designed to be a light concentrator. The concentrated sunlight is sent to a reflecting surface of much smaller mass, which redirects the light at the proper angle to provide the desired direction of net force. Since the collector surface is always facing the sun no matter what the desired direction of thrust, the Solar Photon Thrustor always operates in a maximum solar light power collection mode.

Vehicle Charging Effects During Electron Beam Emission from the CHARGE-2 Experiment

Abstract: The CHARGE-2 sounding rocket payload has measured the transient and steady-state charging of a spacecraft in LEO during the emission of a low-power electron beam The electron beam successfully escaped the emitting spacecraft above 240 km, rather than being degraded by the spacecraft's potentials These potentials were limited to about half of the 1-kV beam accelerating potential at all latitudes, suggesting that the electron beam was able to escape at altitudes down to 160 km Electrons created from beam-plasma interactions become increasingly important in the return current below 240 km, and increased with decreasing altitude

Measurement of in-flight base pressure on an artillery-fired projectile

Abstract: T HE in-flight base pressure has been measured on conventionally fired artillery projectiles No previous successful effort for such measurements and projectiles is apparent A passively actuated base-sealing mechanism provided protection to the sensitive base-pressure instrumentation prior to gun muzzle exit and was released after exit to allow base-pressure sensing in flight Comparisons are made of flight measurements with base-pressure data from wind-tunnel testing

Computational requirements for hypersonic flight performance estimates

Abstract: The computational requirements for hypersonic flight performance estimates are discussed and a procedure for fulfilling these requirements is presented. In order to effectively use computational fluid dynamics in design, especially for estimating performance quantities, consideration should be given to the credibility of CFD, design sensitivities, test uncertainties, risk assessment, and consistency in determination. It is found that a design-specific computational technology developed with programmatic research can be used in the design of hypervelocity vehicles.

Conversion of omnidirectional proton fluxes into a pitch angle distribution

Abstract: The long-term radiation exposures anticipated for astronauts aboard oriented space stations entail consideration of spacecraft mass distribution and the direction of high-energy proton flux. A scheme has been developed for deriving pitch-angle distributions of energetic protons from the omnidirectional fluxes contained in the AP-8 MIN magnetospheric radiation model. A functional form is also presented for expressing the proton pitch-angle distributions at a given energy and L coordinate, as a function of only three parameters.

Three-dimensional upwind parabolized Navier-Stokes code for real gas flows

Abstract: A real gas, upwind, parabolized Navier-Stokes (PNS) code has been developed to compute the three-dimensional hypersonic flow of equilibrium air around various body shapes. The new code is an extension of the upwind (perfect gas) PNS code of Lawrence et al. (1986). The upwind algorithm is based on Roe's (1981) flux-difference splitting scheme which has been modified to account for real gas effects using the nearly exact approach of Vinokur and Liu (1988). Simplified curve fits are employed to obtain the thermodynamic and transport properties of equilibrium air. The new code has been validated by computing the M-infinity = 25 laminar flow of air over cones at various angles of attack. The results of these computations are compared with the results from a conventional centrally-differenced, real gas PNS code and the previous axisymmetric, upwind, real gas code. The agreement is excellent in all cases.

Crack growth behavior in a composite propellant with strain gradients. II

Abstract: The crack growth behavior in a highly filled composite propellant with strain gradients was studied through the use of centrally cracked, wedge-shaped sheet specimen. The specimens were tested under a constant strain rate condition at room temperature. Two crack lengths were considered. The experimental data were analyzed to calculate the instantaneous stress intensity factor K} and the associated instantaneous crack growth rate da/dl. In the data analysis, four data processing methods—the secant method, the modified secant method, the spline fitting method, and the total polynomial method—were considered. The effect of the data processing method and the time interval for crack length measurement on the accuracy of the calculated crack growth rate was investigated. In addition, the effect of the initial crack length, the nonuniform gross strain field, and the data processing method on the crack growth behavior was also investigated, and the functional relationship between the stress intensity factor and the crack growth rate was determined.

Experimental study of plasma contactor phenomena

Abstract: Results illustrating variations in plasma properties near hollow cathode plasma contactors (for use with electrodynamic tethers and in other charge control applications) are presented. Emphasis is placed on describing results obtained when the plasma contactor is collecting electrons from a simulated ionospheric plasma. Two important results include 1) the observation of a double layer located between the plasma generated by the contactor and the simulated ionospheric plasma and 2) enhanced effectiveness of the electron collection process when the ionization rate within the plasma adjacent to the contactor is increased.

Space radiation dose estimates on the surface of Mars

Abstract: The Langley cosmic ray transport code and the Langley nucleon transport code (BRYNTRN) are used to quantify the transport and attenuation of galactic cosmic rays (GCR) and solar proton flares through the Martian atmosphere Surface doses are estimated using both a low density and a high density carbon dioxide model of the atmosphere which, in the vertical direction, provides a total of 16 g/sq cm and 22 g/sq cm of protection, respectively At the Mars surface during the solar minimum cycle, a blood-forming organ (BFO) dose equivalent of 105 to 12 rem/yr due to galactic cosmic ray transport and attenuation is calculated Estimates of the BFO dose equivalents which would have been incurred from the three large solar flare events of August 1972, November 1960, and February 1956 are also calculated at the surface Results indicate surface BFO dose equivalents of approximately 2 to 5, 5 to 7, and 8 to 10 rem per event, respectively Doses are also estimated at altitudes up to 12 km above the Martian surface where the atmosphere will provide less total protection

Exterior spacecraft subsystem protective shielding analysis and design

Abstract: All spacecraft are susceptible to impacts by meteoroids and pieces of orbiting space debris An effective mechanism is developed to protect external spacecraft subsystems against damage by ricochet particles formed during such impacts Equations and design procedures for protective shield panels are developed based on observed ricochet phenomena and calculated ricochet particle sizes and speeds It is found that the diameter of the most damaging ricochet debris particle can be as large as 40 percent of the original project tile diameter, and can travel at speeds between 24 and 36 percent of the original projectile impact velocity Panel dimensions are shown to be strongly dependent on their inclination to the impact velocity vector and on their distribution around a spacecraft module It is concluded that obliquity effects of high-speed impacts must be considered in the design of any structure exposed to the meteoroid and space debris environment

Theory of plasma contactors in ground-based experiments and low earth orbit

Abstract: An examination of several models of electron collection by plasma contactors leads to a definition of the range of validity and applicability for each model. It is noted that most present ground-based experiments are of limited relevance to space applications of plasma contactors, since they operate in a regime where the magnetic field and effective collisions are at most only marginally important. An exception is the experiment of Stenzel and Urrutia (1986), which examined a plasma whose electron Larmor radius was small by comparison to the scale of the potential, and in which the anomalous transport of electrons across the magnetic field was important. The enhanced electron current was not continuous in time, but occurred in periodic bursts as the instabilities periodically emerged, saturated, and decayed.

Response of a Liquid Column to Counterdirectional Excitation

Abstract: A finite cylindrical liquid column consisting of incompressible and frictionless liquid subjected to a counterdirectional axial harmonic excitation is modeled. The liquid system is assumed to be in a zero-gravity environment and held together by surface tension, which acts as the restoring force. The response of the system has been determined for a free surface elevation and velocity distribution. In addition, transient behavior was treated and damping introduced in the resonance terms. It was found that the first resonance response is sharply tuned and could easily be missed by a sweeping experiment. The investigation was performed for the design of the German D-2 Spacelab-mission "LICORE."

Organization, Selection, and Training of Crews for Extended Spaceflight: Findings from Analogs and Implications

Abstract: Ample research evidence from space analogs points to the crucial role that teamwork plays in the performance of small groups in isolation and confinement. This paper surveys findings about the impacts of group behavior and social interaction on crew morale, coordination, and productivity. Implications for the organization, selection, and training of crews for extended spaceflight are discussed.

Lateral Oscillations of Sting-Mounted Models at High Alpha

Abstract: It is shown that in a static test of a model of a high-performance aircraft or missile, lateral oscillations can occur, resulting in static, time-average measurements of the asymmetric loads that are close to zero. In contrast, the loads needed for analysis of full-scale aircraft or missile maneuvers are the instantaneous asymmetric loads, which because of the coupling between vehicle motion and flow separation will approach their maximum magnitude. Results applicable to full-scale free flight could be obtained by use of an apparatus such as the rotary rig, which permits coning and/or spinning motions of the model, provided that the measurements are corrected for support and wall interference effects. Until such capability is in hand, the best approach appears to be to use the asymmetric load extremes, e.g., such as determined in a static test where the model has been rolled through the full 360-deg range.