Showing papers in "Journal of Spacecraft and Rockets in 1994"
TL;DR: In this article, Mill et al. discuss the effects of environmental pollution on the environment and propose an approach to mitigate the environmental impact of greenhouse gas emissions in the air and water.
Abstract: John D. Mill* Environmental Research Institute of Michigan, Arlington, Virginia 22209 Robert R. O'Neil* and Stephan Price* U.S. Air Force Phillips Laboratory, HanscomAFB, Massachusetts 01731 Gerald J. Romick and O. Manuel Uy Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723 E. M. Gaposchkin** Massachusetts Institute of Technology, Lexington, Massachusetts 02173 Glenn C. Light The Aerospace Corporation, Los Angeles, California 90009-2970 W. Walding Moore Jr.** U.S. Army Space and Strategic Defense Command, Huntsville, Alabama 35807-3801 Thomas L. Murdock General Research Corporation, Danvers, Massachusetts 01923 and A. T. Stair Jr. Visidyne, Burlington, Massachusetts 01803
217 citations
TL;DR: In this paper, a box-wing satellite form was investigated that models the satellite as a combination of flat plates arranged in a box shape with a connected solar array, and the non-conservative forces acting on each of the eight surfaces were computed independently, yielding vector accelerations which are summed to compute the total aggregate effect on the satellite center-of-mass.
Abstract: Geodetic satellites such as GEOSAT, SPOT, ERS-1, and TOPEX/Poseidon require accurate orbital computations to support the scientific data they collect. Until recently, gravity field mismodeling was the major source of error in precise orbit definition. However, albedo and infrared re-radiation, and spacecraft thermal imbalances produce in combination no more than a 6-cm radial root-mean-square (RMS) error over a 10-day period. This requires the development of nonconservative force models that take the satellite's complex geometry, attitude, and surface properties into account. For TOPEX/Poseidon, a 'box-wing' satellite form was investigated that models the satellite as a combination of flat plates arranged in a box shape with a connected solar array. The nonconservative forces acting on each of the eight surfaces are computed independently, yielding vector accelerations which are summed to compute the total aggregate effect on the satellite center-of-mass. In order to test the validity of this concept, 'micro-models' based on finite element analysis of TOPEX/Poseidon were used to generate acceleration histories in a wide variety of orbit orientations. These profiles are then compared to the box-wing model. The results of these simulations and their implication on the ability to precisely model the TOPEX/Poseidon orbit are discussed.
123 citations
TL;DR: In this article, an aluminized-po lyimide Kapton multilayer insulation sample was used to study low Earth orbit atomic-oxygen undercutting, which is a potential threat to vulnerable spacecraft materials which have atomicoxygen protective coatings.
Abstract: Atomic-oxygen undercutting is a potential threat to vulnerable spacecraft materials which have atomicoxygen protective coatings. Such undercutting is due to the atomic-oxygen attack of oxidizable materials at microscopic defects in the protective coatings. These defects occur during fabrication and handling, or from micrometeoroid and debris bombardment in space. An aluminized-po lyimide Kapton multilayer insulation sample that was located on the leading edge of the Long Duration Exposure Facility has been used to study low Earth orbit atomic-oxygen undercutting. Cracks in the aluminized coating located around vent holes provided excellent defect sites for the evaluation of atomic-oxygen undercutting. The experimentally observed undercut profiles were compared to predictions from Monte Carlo models for normal incident space ram atomic-oxygen attack. The shape of the undercut profile was found to vary with crack width, which is proportional to the number of oxygen atoms entering the crack. The resulting profiles of atomic-oxygen undercutting which occurred on the aluminized-Kapton sample indicated wide undercut cavities in spite of the fixed ram orientation. Potential causes of the observed undercutting are presented. Implications of the undercutting profiles relevant to Space Station Freedom are also discussed.
95 citations
TL;DR: A multiblock, laminar heating analysis for the shuttle orbiter at three trajectory points ranging from Mach 24.3 to Mach 12.86 on reentry is described in this article.
Abstract: A multiblock, laminar heating analysis for the shuttle orbiter at three trajectory points ranging from Mach 24.3 to Mach 12.86 on reentry is described. The analysis is performed using the Langley Aerothermodynamic Upwind Relaxation Algorithm with a seven species chemical nonequilibrium model. A finite-catalytic-wall model appropriate for shuttle tiles at a radiative equilibrium wall temperature is applied. Computed heating levels are generally in good agreement with the flight data, although a few rather large discrepancies remain unexplained. The multiblock relaxation strategy partitions the flowfield into manageable blocks requiring a fraction of the computational resources (time and memory) required by a full domain approach. In fact, the computational cost for a solution at even a single trajectory point would be prohibitively expensive at the given resolution without the multiblock approach. Converged blocks are reassembled to enable a fully coupled converged solution over the entire vehicle, starting from a nearly converged initial condition.
81 citations
TL;DR: In this paper, an axisymmetric analog for three-dimensional boundary layers and a generalized body-fitted coordinate system are used to calculate heating rates on 3D vehicles at angle of attack.
Abstract: An approximate method for calculating heating rates on three-dimensional vehicles at angle of attack is presented. The method is based on the axisymmetric analog for three-dimensional boundary layers and uses a generalized body-fitted coordinate system. Edge conditions for the boundary-layer solution are obtained from an inviscid flowfield solution, and because of the coordinate system used, the method is applicable to any blunt body geometry for which an inviscid flowfield solution can be obtained. The method is validated by comparing with experimental heating data and with thin-layer Navier-Stokes calculations on the shuttle orbiter at both wind-tunnel and flight conditions and with thin-layer Navier-Stokes calculations on the HL-20 at wind-tunnel conditions.
73 citations
TL;DR: In this paper, an experimental investigation of the near-wake flowfield downstream of a conical boattailed afterbody in supersonic flow is presented, where flow visualization, mean static pressure measurements, and three-component laser Doppler velocimeter data have been obtained throughout the near wake of the body.
Abstract: An experimental investigation of the near-wake flowfield downstream of a conical boattailed afterbody in supersonic flow is presented. The afterbody investigated is typical of those for conventional boattailed missiles and projectiles in unpowered flight. Flow visualization, mean static pressure measurements, and three-component laser Doppler velocimeter data have been obtained throughout the near wake of the body. The effects of afterbody boattailing on the physics of the near-wake flow are determined by comparing the present data with similar data obtained on a cylindrical afterbody. Results indicate that a net afterbody drag reduction of 21 % is achieved with the current boattailed afterbody for a freestream Mach number of 2.46. The shear-layer growth rate, and therefore mass entrainment from the recirculation region behind the base, is shown to be significantly reduced by afterbody boattailing due to the reduction in turbulence levels throughout the near wake as compared to the cylindrical afterbody.
58 citations
TL;DR: In this article, the authors used CFL3D, an implicit upwind-biased finite-volume algorithm developed at NASA Langley, to calculate the 3D Navier-Stokes equations of the Mach 6 viscous optimized waverider.
Abstract: The performance of a Mach 6 viscous optimized waverider was calculated using the 3-D Navier-Stokes equations. The Mach 6 viscous optimized waverider was generated using MAXWARP, a code developed at the University of Maryland. The computations were performed using CFL3D, an implicit upwind-biased finite-volume algorithm developed at NASA Langley. Results show that good agreement was found between the calculated performance by MAXWARP and results from the Mach 6 Navier-Stokes computation. Furthermore, off-design performance of the Mach 6 optimized waverider was computed at Mach 4 and 8. The performance at these Mach numbers compared well with the performance of the viscous optimized waveriders specifically designed for these Mach numbers. Finally, contours of different flow parameters in the cross-flow plane were examined for the three calculations. The results indicate that the flow gradients are relatively small within the captured flow, and the variation itself is well behaved; thus, making the waverider configuration a promising choice for an engine/airframe design, especially for cruise-type applications.
57 citations
TL;DR: In this paper, an analysis of the longitudinal aerodynamics of the shuttle orbiter in the hypersonic flight regime is made through the use of computational fluid dynamics, with particular attention given to establishing the cause of the "pitching moment anomaly," which occurred on the orbiter's first flight, and to computing the aerodynamic of a complete orbiter configuration at flight conditions.
Abstract: An analysis of the longitudinal aerodynamics of the shuttle orbiter in the hypersonic flight regime is made through the use of computational fluid dynamics. Particular attention is given to establishing the cause of the 'pitching moment anomaly,' which occurred on the orbiter's first flight, and to computing the aerodynamics of a complete orbiter configuration at flight conditions. Data from ground-based facilities as well as orbiter flight data are used to validate the computed results. Analysis shows that the pitching moment anomaly is a real-gas chemistry effect that was not simulated in ground-based facilities, which used air as a test gas. Computed flight aerodynamics for the orbiter are within 5% of the measured flight values and trim bodyflap deflections are predicted to within 10%.
52 citations
TL;DR: In this paper, a model has been developed to examine, on a local scale, the reactions of rocket exhaust from solid rocket motors with stratospheric ozone at two different altitudes, and it has been found that afterburning chemistry of reactive exhaust products can cause local but transient (on the order of several minutes) loss of ozone.
Abstract: A model has been developed to examine, on a local scale, the reactions of rocket exhaust from solid rocket motors with stratospheric ozone. The effects were examined at two different altitudes. Results of the modeling study indicate that afterburning chemistry of reactive exhaust products can cause local but transient (on the order of several minutes) loss of ozone. The modeling study included potential heterogeneous reactions at aluminum oxide surfaces. Results indicate that these potential heterogeneous reactions do not have a major impact on the local plume chemistry. Homogeneous reactions appear to be of more consequence during the early dispersion of the plume. It has also been found that the rate of plume dispersion has a very significant effect on local ozone loss.
51 citations
TL;DR: In this paper, the high-altitude/high-Knudsen number aerodynamics of the Shuttle Orbiter were computed from Low-Earth Orbit down to 100 km using three-dimensional direct simulation Monte Carlo and free molecule codes.
Abstract: The high-altitude/high-Knudsen number aerodynamics of the Shuttle Orbiter are computed from Low-Earth Orbit down to 100 km using three-dimensional direct simulation Monte Carlo and free molecule codes. Results are compared with Blanchard's latest Shuttle aerodynamic model, which is based on in-flight accelerometer measurements, and bridging formula models. Good comparison is observed, except for the normal force and pitching moment coefficients. The present results were obtained for a generic Shuttle geometry configuration corresponding to a zero deflection for all control surfaces.
50 citations
TL;DR: The National Space Science Data Center (NSSDC) trapped radiation models calculate the integral and differential electron and proton flux for given values of particle energy E, drift shell parameter L, and magnetic field strength normalized to the equatorial/minimum value on the field line B/BQ for either solar maximum or solar minimum conditions as discussed by the authors.
Abstract: The National Space Science Data Center (NSSDC) trapped radiation models calculate the integral and differential electron and proton flux for given values of particle energy E, drift shell parameter L, and magnetic field strength normalized to the equatorial/minimum value on the field line B/BQ for either solar maximum or solar minimum conditions. The most recent versions of the series of models, which have been developed and continuously improved over several decades by Vette and co-workers at NSSDC, are AE-8 for electrons and AP-8 for protons. The paper provides a brief history of the modeling efforts at NSSDC and discusses some of the problems encountered when applying the models at low altitudes. Recommendations are made and discussed about the correct use of the trapped particle models in conjunction with geomagnetic field models. Specifically, the importance of using the correct dipole moment and the correct #0 value (i.e., obtained by field line tracing) is illustrated.
TL;DR: Results showed that in unit gravity, the bioreactor would simulate primary microgravity trajectories of particles and migration time, however, by rotating theBioreactor under the influence of gravity produces a significant component of particle motion and associated shear stress not found in microgravity environment.
Abstract: A mathematical model was recently developed to characterize cell-medium interactions within a Couette-flow bioreactor. To test the efficiency of the model, numerical simulations and space-flight experiments have been conducted. In this study, the momentum equations for the steady-state fluid flow is solved first followed by the equations for the motion of a particle. Results showed that in unit gravity, the bioreactor would simulate primary microgravity trajectories of particles and migration time. However, by rotating the bioreactor under the influence of gravity produces a significant component of particle motion and associated shear stress not found in microgravity environment. In addition, the total force per unit of cross-sectional area on a particle in microgravity is significantly smaller than the calculated value in unit gravity. 17 refs.
TL;DR: An experimental and theoretical investigation of an expanding plasma generated by an arc produced by biasing a conductor underneath a thin layer of anodized aluminum 160-V negative of a laboratory plasma that can produce large peak arc currents by discharging large surface areas is presented in this article.
Abstract: An experimental and theoretical investigation of an expanding plasma generated by an arc produced by biasing a conductor underneath a thin layer of anodized aluminum 160-V negative of a laboratory plasma that can produce large peak arc currents by discharging large surface areas is presented. A simple theory shows that the time scales and observed current magnitudes are consistent with the expansion of a discharge-generated plasma. The implication for large spacecraft in low Earth orbit, such as Space Station Freedom (SSF) which can store large amounts of charge, is that arcs with the same amount of energy similar to those observed in the laboratory may occur. The energy in these arcs degrade the surface of the anodized aluminum thermal control coatings by producing large pits in the surface. These pits tend to increase the temperature of the spacecraft, and the material from the pits can become an additional source of contamination . The rise time and intensity of theses arc could produce significant EMI. To prevent the occurrence of these undesirable effects, SSF will utilize a plasma contactor that will control the structure to ambient plasma potentials.
TL;DR: In this paper, the authors present an application of the direct simulation Monte Carlo method (DSMC) to the complete expansion process of a real thruster: from the stagnation chamber of the thruster, to the far-field expansion of the plume.
Abstract: Computational results are presented for the flow through a helium microthruster. This device is to be used for fine adjustments in attitude control for a proposed space experiment. The mass-flow rates used by the thruster are very low giving Knudsen numbers at the nozzle throat between 0.01 and 1 based on the stagnation conditions and the nozzle throat diameter. These conditions indicate that low-density effects will dominate the fluid mechanics. Therefore, the flows are computed with a particle simulation scheme [the direct simulation Monte Carlo method (DSMC)]. This study presents an application of the DSMC technique to the complete expansion process of a real thruster: from the stagnation chamber of the thruster, to the far-field expansion of the plume. The numerical approach is evaluated by comparison with existing experimental data taken in the expansion plume. The computational results are employed to assess the effect of varying the mass-flow rate on the terminal state of the gas. In addition, the effect of including the background chamber pressure measured in the experimental vacuum facility is investigated and found to be significant.
TL;DR: In this paper, a new criterion for the definition of an aerodynamically sharp shape is proposed based on this work, and the analysis that resulted in the new sharp and blunt shape criteria for aerodynamics.
Abstract: Computational fluid dynamics studies at supersonic and hypersonic speeds have resulted in an improved understanding of the meaning of aerodynamically, as opposed to geometrically, sharp and blunt shapes. An analytic investigation using Newtonian theory was conducted to support the computational results. Based on this work, a new criterion for the definition of an aerodynamically sharp shape is proposed. Defining the power-law shape to be the relevant gauge function, one can classify bodies with it > 2/3 as aerodynamical ly sharp, even though the initial body slope dr/djc is 90 deg. The paper describes the analysis that resulted in the new sharp and blunt shape criteria for aerodynamics. Nomenclature A = constant in power-law body equation defining fineness ratio Cp = pressure coefficient / = fineness ratio for the Sears-Haack body, Eq. (9) / = length of the body in definition of von Karman ogive and Sears-Haack body n = exponent in power-law body definition, Eq. (1) R = longitudinal radius of curvature, Eq. (2) R (0) = longitudinal curvature at x = 0, the leading-edge radius RK_O = longitudinal radius of curvature for a von Karman ogive RS-H = longitudinal radius of curvature for a Sears-Haack body r =body radius at a given x location TK-O =body radius for a von Karman ogive rs-H =body radius for the Sears-Haack body S = cross-sectional area SK-O =cross-sectional area of the von Karman ogive s =arc length along the surface from the leading edge, x = 0 V - volume of Sears-Haack body x = axial distance from leading edge £ ^transformed independent variable for the Sears-Haack body, Eq. (7) 0 =body slope angle, tan"1 (dr/dx)
TL;DR: In this paper, a second-order high-resolution scheme for solving the new Lagrangian Euler equations is employed to accurately resolve the complicated shock patterns and associated slip lines and their interactions.
Abstract: A computational analysis of the two-dimensional supersonic inviscid flowfield in a second-throat ejector-diffuser (STED) system is presented. A second-order high-resolution scheme for solving the new Lagrangian Euler equations is employed to accurately resolve the complicated shock patterns and associated slip lines and their interactions. A parametric study covering a variety of Xst and Ost is implemented to investigate their effects on the flow structure in STED as well as its performance. Results suggest that the averaged Mach number along the entrance plane of the second throat is a suitable criterion for the justification of the performance of STED. With this criterion, an optimal design insuring the largest pressure recovery can be achieved.
TL;DR: Current and future research areas of interest are described and an indication of computer resources and code enhancements needed to continue the progress in projectile computational aerodynamics is provided.
Abstract: The ability to predict the complete set of aerodynamic performance parameters for projectile configurations is the goal of the computational aerodynamicists at the U.S. Army Research Laboratory. To achieve this goal, predictive capabilities that use Navier-Stokes computational techniques have been developed and applied to an extensive number of projectile configurations. A summary of code validation efforts and applications for both spin-stabilized and fin-stabilized projectile configurations are described. Significant progress in the predictive capability for projectile aerodynamics has been achieved through the availability of substantial supercomputer resources and modern computational techniques. Current and future research areas of interest are described and provide an indication of computer resources and code enhancements needed to continue the progress in projectile computational aerodynamics. 44 refs.
TL;DR: The National Oceanic and Atmospheric Administration's National Geophysical Data Center maintains a data base of anomalous spacecraft behavior attributed to environmental interactions as discussed by the authors, and the data base and its capabilities are described.
Abstract: The National Oceanic and Atmospheric Administration's National Geophysical Data Center maintains a data base of anomalous spacecraft behavior attributed to environmental interactions. This paper introduces the data base and its capabilities. Examples from the data base are presented, and their environmentally related trends are illustrated. The active sun during 1989 provided valuable lessons in the interaction between the space environment and space borne technology. The effects of that activity are summarized.
TL;DR: In this paper, the effect of surface tension on rotating fluids, applicable to a partially filled full-scale Gravity Probe-B Spacecraft Dewar tank with and without installing baffle boards, is studied/Results of slosh-wave excitation along the liquid-vapor interface induced by gravity-gradient acceleration are examined.
Abstract: The dynamical behavior of fluids affected by an asymmetric gravity-gradient acceleration is studied. The effect of surface tension on rotating fluids, applicable to a partially filled full-scale Gravity Probe-B Spacecraft Dewar tank with and without installing baffle boards, is studied/Results of slosh-wave excitation along the liquid-vapor interface induced by gravity-gradient acceleration are examined. These results indicate that the gravity-gradient acceleration is equivalent to the combined effect of a twisting force and torsional moment acting on the spacecraft. The results are clearly seen from the eccentric contour of a bubble revolving around the axis of a Dewar in a horizontal r-9 plane. As the viscous force across the liquid-solid interface greatly contributes to the damping of slosh-wave excitation, installing baffles in the rotating Dewar is expected to dampen these waves. Results show that the damping effect provided by a baffle reduces the amplitude of slosh-wave excitation and lowers the degree of asymmetry in the liquid-vapor distribution. Computation of bubble (helium vapor) mass-center fluctuations also verifies that rotating a Dewar with baffles installed produces less fluctuation than without the baffles.
TL;DR: In this article, the thermal performance and ablation characteristics of the newly developed lightweight ceramic ablators (LCAs) in a supersonic, high-enthalpy convective environment were presented.
Abstract: This paper presents the thermal performance and ablation characteristics of the newly developed lightweight ceramic ablators (LCAs) in a supersonic, high-enthalpy convective environment. Lightweight ceramic ablators were recently conceived and developed at NASA Ames using low-density ceramic or carbon fibrous matrices as substrates for main structural support and organic resins as fillers. These LCAs were successfully produced with densities ranging from approximately 0.224 to 1.282 g/cu cm. Several infiltrants with different char yields were used to study the effect on surface recession. Tests were conducted in the NASA Ames arc-jet facilities. Material thermal performance was evaluated at cold-wall heat fluxes from 113.5 to 1634 W/sq cm, and stagnation pressures of 0.018 to 0.331 atm. Conventional ablators such as SLA-561, Avcoat 5026-39HC, MA-25S, and balsa wood were tested at the same heat fluxes for direct comparison. Surface temperature was measured using optical pyrometers, and the recession rates were obtained from the high-speed films. In-depth temperature data were obtained to determine the thermal penetration depths and conductivity. Preliminary results indicated that most LCAs performed comparably to or better than conventional ablators. At low flux levels (less than 454 W/sq cm), the addition of silicon carbide and polymethyl methacrylate significantly improved the ablationmore » performance of silica substrates. The carbon-based LCAs were the most mass-efficient at high flux levels (greater than 454 W/sq cm). 16 refs.« less
TL;DR: In this paper, a low-speed wind-tunnel investigation was conducted to examine the aerodynamic characteristics of a one-thirdscale model of a canard-controlled missile at high angles of attack using force and moment measurements.
Abstract: A low-speed wind-tunnel investigation was conducted to examine the aerodynamic characteristics of a one-thirdscale model of a canard-controlled missile at high angles of attack using force and moment measurements. The data were taken at a nominal Mach number of 0.2 for angles of attack up to 50 deg at three different canard deflection settings. The test runs were limited to 0and 45-deg missile roll angles (symmetric configurations) and two sets of tails (aft fins), one with the full area including the roll damping tabs (rollerons) and the other without the rollerons. The data indicate that the rollerons act as an effective fin area at low speeds and high angles of attack, and make the missile more stable. The test data were also used to validate the aerodynamic characteristics of the missile as predicted by the Missile Datcom program. The agreement between the Datcom predictions and the test data is fairly good, with the latter indicating a slightly higher static stability.
TL;DR: In this article, large-angle blunt cones, with various corner radii, were tested in dissociated air, COi, and COi-Ar gas mixtures at angles of attack from 0 to 20 deg.
Abstract: Large-angle blunt cones, with various corner radii, were tested in dissociated air, COi, and COi-Ar gas mixtures. These experiments were conducted at angles of attack from 0 to 20 deg. Heating distribution data and bow shock-wave geometry were obtained during exposure of the cones to the three gases. The data can be used to partially validate two-dimensional (2-D) axisymmetric and three-dimensional Navier-Stokes solutions of the heating distribution over a 140-deg blunt cone in a simulated Martian atmosphere. The predicted heating distribution over the cones and estimated bow shock standoff distances using a 2-D axisymmetric Navier-Stokes code were compared with test data taken at zero angle of attack.
TL;DR: In this paper, the applicability of the basic concept of waveriding at high altitudes, and the extent to which the large viscous forces degrade the aerodynamic performance of high-altitude/high-Knudsen-number waveriders are discussed.
Abstract: The present paper addresses the applicability of the basic concept of waveriding at high altitudes, and the extent to which the large viscous forces degrade the aerodynamic performance of waveriders. The waverider under consideration was designed using a continuum flow methodology. It is shown that the lift-to-drag ratio of high-altitude/high-Knudsen-number waveriders can be expected to be significantly lower than their low altitude/low Knudsen number counterparts. The aerodynamic performance of a representative waverider which was optimized for a 90-km, Mach-25 application is studied for altitudes ranging from 97 km to 145 km and incidence angles of 0 to 30 deg. Typical values of the lift-to-drag ratio were computed to be in the range of 0 to 0.3. Friction forces are mostly responsible for this poor performance. Friction forces account for more than 93 percent of the drag and significantly reduce lift.
TL;DR: In this paper, an experimental technique is developed and used to simulate the response of aluminum debris shields for impacts up to 18 km/s, where the impactor and bumper are surrogates that have the same dimensions as the originals, but are composed of a material whose specific energies of melting and vaporization are much lower than those of aluminum.
Abstract: An experimental technique is developed and used to simulate the response of aluminum debris shields for impacts up to 18 km/s. To simulate an aluminum impact on an aluminum shield, the velocity is reduced by a scale factor, and the impactor and bumper are surrogates that have the same dimensions as the originals, but are composed of a material whose specific energies of melting and vaporization are much lower than those of aluminum. Cadmium is used as the surrogate material, because it has unique properties that satisfy the attendant scaling requirements and because its velocity scale factor is 3.1, thereby allowing tests at actual velocities up to 5.8 km/s to simulate aluminum impacts at velocities up to 18 km/s. Such tests reproduce the initial momentum of an aluminum impactor and the impulse distribution delivered to the rear wall. Cadmium tests, at scaled velocities near 7 km/s, agreed well with aluminum tests near 7 km/s, both in terms of debris cloud geometry and the minimum impactor size for wall perforation. Simulations at higher scaled velocities showed that the minimum diameter for penetration increases with increasing velocities above 10.5 km/s, in sharp contrast to current empirical shield models.
TL;DR: In this paper, the masses in low Earth orbit (LEO) were compared for several propulsion systems: nitrogen tetroxide/monomethyl hydrazine (NTO/MMH), oxygen/methane (O2/CH4), metallized O2/H2/Al propellants, and O2H2Al systems.
Abstract: To provide the transportation of lunar base elements to the moon, large high-energy propulsion systems will be required. Advanced propulsion systems for lunar missions can provide significant launch mass reductions and payload increases. These mass reductions and added payload masses can be translated into significant launch cost savings for the lunar base missions. The masses in low Earth orbit (LEO) were compared for several propulsion systems: nitrogen tetroxide/monomethyl hydrazine (NTO/MMH), oxygen/methane (O2/CH4), oxygen/hydrogen (O2/H2), and metallized O2/H2/Al propellants. Also, the payload mass increases enabled with O2/H2 and O2/H2/Al systems were addressed. In addition, many system design issues involving the engine thrust levels, engine commonality between the transfer vehicle and the excursion vehicle, and the number of launches to place the lunar mission vehicles into LEO will be discussed. Analyses of small lunar missions launched from a single STS-C flight are also presented.
TL;DR: In this paper, the authors investigated the arcing of negatively biased solar arrays in a low-Earth orbit plasma environment and determined that the adhesive used to bind the protective coverglass to the solar cells was a key factor in observed arcing rates.
Abstract: Experimental and theoretical efforts have been conducted to investigate the arcing of negatively biased solar arrays in a low-Earth orbit plasma environment. Experiments were conducted in an ultrahigh vacuum plasma test chamber, where the environment could be controlled carefully. Outgassing of the adhesive used to bind the protective coverglass to the solar cells was determined to be a key factor hi observed arcing rates. These rates could be reduced by greater than a factor of 100 by eliminating or fully outgassing the excess adhesive remaining at the edge of the solar cells. Optical emission from solar cell arcs was observed to correlate linearly with arc current, both temporally and in total intensity. Solar cell arcing rates were also observed to scale linearly with plasma density. The plasma scaling is in good agreement with a theory based on enhanced field electron emission charging of dielectric surfaces, leading to enhanced electric fields at the conductor/adhesive/plasma triple junction. Apparent thresholds for solar cell arcing are reported.
TL;DR: In this article, the authors describe hypersonic interceptor aero-optics performance predictions, including the effect of the mean flowfield and turbulence on the tracking and imaging capability of on-board optical sensors.
Abstract: This paper describes hypersonic interceptor aero-optics performance predictions. It includes code results for three-dimensional shapes and comparisons to initial experiments. It covers the aerothermal, aerodynamic computational codes that are capable of covering the entire flight regime from subsonic to hypersonic flow and includes chemical reactions and turbulence. Heat transfer to the various surfaces is calculated as an input to cooling and ablation processes. The aero-optics codes determine the effect of the mean flowfield and turbulence on the tracking and imaging capability of on-board optical sensors. This paper concentrates on the latter aspects.