THERMAL PROTECTION FOR SPACECRAFT ENTERING AT ESCAPE VELOCITY
Thermal protection for spacecraft entering at escape velocity
REENTRY↗
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Results for “ESCAPE VELOCITY”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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CALCULATION OF FLOW FIELDS ABOUT BLUNT BODIES OF REVOLUTION TRAVELING AT ESCAPE VELOCITY
The method of Gravalos for calculating the inviscid flow about blunt supersonic bodies has been applied to the case of a hemisphere-cylinder at escape velocity. Numerical results are presented for the flow variables throughout the shock layer, both near the nose and downstream along the cylinder. The results are compared with data from six flow fields at lower velocities in order to illustrate the effects peculiar to escape-velocity re-entry. The body pressures and shock shapes computed by this method agree well with available experimental data at Mach numbers from 3 to 10, and are correlated fairly well by cylindrical blast-wave parameters.
Body of revolution↗
Meteorite impact ejecta - Dependence of mass and energy lost on planetary escape velocity
The amounts of material and energy which escape a planet in a meteorite impact event is calculated as functions of impact and escape velocities. Results are obtained from the computed flow induced by the impact of iron and gabbroic anorthosite spheres onto a half-space of anorthosite at impact velocities of 5 to 45 km/sec. The impact-induced flows were determined by a numerical method using the mass, momentum, and energy conservation relations in finite-difference approximation, within an Eulerian computational grid. The impact velocities at which ejecta losses equal meteorite mass gains are found to be approximately 20, 35, and 45 km/sec for anorthosite objects and approximately 25, 35, and 40 km/sec for iron objects striking anorthosite surfaces for the gravity fields of the moon, Mercury and Mars.
Okeefe, J. D.↗
CALCULATION OF FLOW FIELDS ABOUT BLUNT BODIES OF REVOLUTION TRAVELING AT ESCAPE VELOCITY
Inviscid supersonic flow around a hemisphere- cylinder at escape velocity is analyzed throughout the shock layer, with reference to reentry aerodynamics
REENTRY PHYSICS↗
An experimental study of molecular surface interactions at velocities up to and exceeding space probe escape velocities Final report
Momentum accomodation coefficients obtained from low velocity molecule-surface interactions, for space probe drag calculations
ACCOMMODATION COEFFICIENT↗
Spaceflight Hazards of Escape-Velocity-Domain Impact Ejecta in the CR3BP
As a consequence of planned/proposed human lunar activity, the long-term effects of lunar debris and ejecta resulting from large-body (> 1000 kg) impacts on the lunar surface is investigated. The Escape-Velocity-Domain (EVD) ejecta behavior is characterized in terms of destination, duration in lunar orbit, and total displaced mass. Likewise, the amount of mass sent into geosynchronous orbit is also characterized and assessed as a function of impact location in terms of Sun-Earth-Moon angle, lunar latitude and longitude, and impact angle. Finally, a threat analysis is performed on critical assets in Earth and Lunar orbit such as the I.S.S., geosynchronous satellites, prospective lunar base, and the Deep Space Gateway now under construction.
Wittal, M. M.↗
LOOK AT THE REENTRY PROBLEM
Reentry guidance and control in near-earth orbits and near escape velocity as well as in deep space and at velocities in excess of escape velocity
DEEP SPACE↗
Statistical survey of pitch angle distributions in core (0-50 eV) ions from Dynamics Explorer 1: Outflow in the auroral zone, polar cap, and cusp
Core (0-50 eV) ion pitch angle measurements from the retarding ion mass spectrometer on Dynamics Explorer 1 are examined with respect to magnetic disturbance, invariant latitude, magnetic local time, and altitude for ions H(+), He(+), O(+), M/Z = 2 (D(+) or He(++)), and O(++). Included are outflow events in the auroral zone, polar cap, and cusp, separated into altitude regions below and above 3 R(sub E). In addition to the customary division into beam, conic, and upwelling distributions, the high-latitude observations fall into three categories corresponding to ion bulk speeds that are (1) less than, (2) comparable to, or (3) faster than that of the spacecraft. This separation, along with the altitude partition, serves to identify conditions under which ionospheric source ions are gravita- tionally bound and when they are more energetic and able to escape to the outer magnetosphere. Features of the cleft ion fountain inferred from single event studies are clearly identifiable in the statistical results. In addition, it is found that the dayside pre-noon cleft is a dayside afternoon cleft, or auroral zone, becomes an additional source for increased activity. The auroral oval as a whole appears to be a steady source of escape velocity H(+), a steady source of escape velocity He(+) ions for the dusk sector, and a source of escape velocity heavy ions for dusk local times primarily during increased activity. The polar cap above the auroral zone is a consistent source of low-energy ions, although only the lighter mass particles appear to have sufficient velocity, on average, to escape to higher altitudes. The observations support two concepts for outflow: (1) The cleft ion fountain consists of ionospheric plasma of 1-20 eV energy streaming upward into the magnetosphere where high-latitude convection electric fields cause poleward dispersion. (2) The auroral ion fountain involves field-aligned beams which flow out along auroral latitude field lines; and, in addition, for late afternoon local times, they experience additional acceleration such that the ion energy distribution tends to exceed the detection range of the instrument (greater than 50-60 eV).
Giles, B. L.↗
Accumulation of the Terrestrial Planets
The validity of the two body approximation in calculations of planetary growth is examined. Use of this approximation is essential to practical 3 dimensional simulations of planetary growth. With regard to gravitational perturbations, the changes in semimajor axis, eccentricity, and inclination resulting from close planetesimal encounters (near 1 A.U.) out to 10 Tisserand sphere of influence radii were calculated by two and three dimensional numerical integration. These were compared with the results of treating the encounter as a two body problem, as is customary in Monte Carlo calculations of orbital evolution and in numerical and analytical studies of planetary accumulation. It is found that for values of (V/V sub e) approx. 0.35 (V = relative velocity, V = escape velocity of largest body), the two body approximation fails to describe the outcome of individual encounters. In this low velocity region, the two body gravitational focusing cross section is no longer valid.
Wetherill, G. W.↗
System Engineering a Solar Thermal Propulsion Mission Concept for Rapid Interstellar Medium Access
The interstellar medium (ISM) represents the next frontier in space exploration, with many new discoveries to be made. The challenge, being so far away from Earth, the ISM requires many decades to reach. To advance our knowledge of what exists beyond our Solar System, new approaches for rapid access are required. One such approach is solar thermal propulsion (STP). The approach uses several Venus and Earth gravity assists to fly to Jupiter and use its gravity well to dive towards the Sun. Approaching within 3 solar radii a perihelion burn would be performed, maximizing the spacecraft’s ΔV to achieve high Solar System escape velocities. A unique aspect of the STP mission concept is that the Sun is not only used as a gravity well for an Oberth manoeuvre, but also to heat the fuel to ultra-high-temperatures (>3000 K), enabling a monopropellant burn with high specific impulse (Isp). Prior preliminary studies indicated escape velocities of over 20 astronomical unit (AU)/yr would be possible. An in-depth modelling exercise was undertaken to determine how such a system would perform. The model in this paper showed the current STP design is capable of providing just under 9±1 AU/yr, but there are many technology developments that could increase escape velocity. The technologies vary from items that could be implemented in the near term, like turbo-pumps driven by the hydrogen, to items requiring more extensive development programs like thin coatings which do not erode in superheated hydrogen. After reviewing the STP approach, and comparing it to a solid rocket motor (SRM), it was found that with currently available technology, SRM outperforms STP with an escape velocity of approximately 10-12 AU/yr. However, future advances in heat exchanger lining materials, turbo pumps, and advanced heat exchanger geometries may enable solar thermal propulsion to provide higher escape velocities, providing one of the fastest ways to exit the solar system. Ultimately, if all technology paths could be implemented with minimal side effects, the performance in a best-case scenario could reach up to 16 AU/yr.
Alkalai, Leon↗
Stellar winds driven by Alfven waves
Models of stellar winds were considered in which the dynamic expansion of a corona is driven by Alfven waves propagating outward along radial magnetic field lines. In the presence of Alfven waves, a coronal expansion can exist for a broad range of reference conditions which would, in the absence of waves, lead to static configurations. Wind models in which the acceleration mechanism is due to Alfven waves alone and exhibit lower mass fluxes and higher energies per particle are compared to wind models in which the acceleration is due to thermal processes. For example, winds driven by Alfven waves exhibit streaming velocities at infinity which may vary between the escape velocity at the coronal base and the geometrical mean of the escape velocity and the speed of light. Upper and lower limits were derived for the allowed energy fluxes and mass fluxes associated with these winds.
Belcher, J. W.↗
Collisional growth of planetesimals
Safronov's (1972) demonstration that relative velocities of planetesimals would be comparable to the dominant size bodies' escape velocities, combined with a plausible size distribution that has most mass in the largest bodies, yielded his evolution model with limited growth of the largest planetesimal with respect to its next largest neighbors. A numerical simulation of planetesimal accretion (Greenberg et al., 1978) suggests that at least over one stage of collisional accretion, velocities were much lower than the escape velocity of the largest bodies, because the bulk of the mass still resided in km-scale bodies. The low velocities at this early stage may conceivably have permitted early runaway growth, which, in turn, would have kept the velocities low and permitted continued runaway growth of the largest bodies.
Greenberg, R.↗
AGN Obscuration Through Dusty Infrared Dominated Flows: Radiation-Hydrodynamics Solution for the Wind - 1
We construct a radiation-hydrodynamics model for the obscuring toroidal structure in active galactic nuclei. In this model the obscuration is produced at parsec scale by a dense, dusty wind which is supported by infrared radiation pressure on dust grains. To find the distribution of radiation pressure, we numerically solve the 2D radiation transfer problem in a flux limited diffusion approximation. We iteratively couple the solution with calculations of stationary 1D models for the wind, and obtain the z-component of the velocity. Our results demonstrate that for AGN luminosities greater than 0.1 L(sub edd) external illumination can support a geometrically thick obscuration via outflows driven by infrared radiation pressure. The terminal velocity of marginally Compton-thin models (0.2 < tau(sub T) < 0.6), is comparable to or greater than the escape velocity. In Compton thick models the maximum value of the vertical component of the velocity is lower than the escape velocity, suggesting that a significant part of our torus is in the form of failed wind. The results demonstrate that obscuration via normal or failed infrared-driven winds is a viable option for the AGN torus problem and AGN unification models. Such winds can also provide an important channel for AGN feedback.
Dorodnitsyn, A.↗
Solar wind and micrometeorite effects in the lunar regolith
Using available data from the literature, an outline is formulated for the major physical and chemical effects expected during solar-wind bombardment of the lunar regolith. In agreement with results of Auger and other analyses of the composition of lunar grain surfaces, this outline predicts that solar-wind sputtering will tend to clean exposed grain surfaces by ejecting material at velocities exceeding lunar escape velocity. Results are also discussed which show that Fe is partially reduced in the outer few 10 nm of grain surfaces and that this reduced Fe forms 10-nm-diameter metal spheres throughout the glass during agglutinate formation by micrometeorite impacts. These metal spheres give the agglutinates their distinctive optical and magnetic properties and are partially responsible for the decreasing albedo of the lunar surface with exposure age.
Housley, R. M.↗
Ground radar detection of meteoroids in space
A special test to lower the detection threshold for satellite fragments potentially dangerous to spacecraft was carried out by NORAD for NASA, using modified radar software. The Perimeter Acquisition Radar Attack Characterization System, a large, planar face, phased radar, operates at a nominal 430 MHz and produces 120 pulses per second, 45 of which were dedicated to search. In a time period of 8.4 hours of observations over three days, over 6000 objects were detected and tracked of which 37 were determined to have velocities greater than escape velocity. Six of these were larger objects with radar cross sections greater than 0.1 sq m and were probably orbiting satellites. A table gives the flux of both observed groups.
Kessler, D. J.↗
Impact and explosion crater ejecta, fragment size, and velocity
A model was developed for the mass distribution of fragments that are ejected at a given velocity for impact and explosion craters. The model is semi-empirical in nature and is derived from (1) numerical calculations of cratering and the resultant mass versus ejection velocity, (2) observed ejecta blanket particle size distributions, (3) an empirical relationship between maximum ejecta fragment size and crater diameter and an assumption on the functional form for the distribution of fragements ejected at a given velocity. This model implies that for planetary impacts into competent rock, the distribution of fragments ejected at a given velocity are nearly monodisperse, e.g., 20% of the mass of the ejecta at a given velocity contain fragments having a mass less than 0.1 times a mass of the largest fragment moving at that velocity. Using this model, the largest fragment that can be ejected from asteroids, the moon, Mars, and Earth is calculated as a function of crater diameter. In addition, the internal energy of ejecta versus ejecta velocity is found. The internal energy of fragments having velocities exceeding the escape velocity of the moon will exceed the energy required for incipient melting for solid silicates and thus, constrains the maximum ejected solid fragment size.
Okeefe, J. D.↗
Ballistics Model for Particles on a Horizontal Plane in a Vacuum Propelled by a Vertically Impinging Gas Jet
A simple trajectory model has been developed and is presented. The particle trajectory path is estimated by computing the vertical position as a function of the horizontal position using a constant horizontal velocity and a vertical acceleration approximated as a power law. The vertical particle position is then found by solving the differential equation of motion using a double integral of vertical acceleration divided by the square of the horizontal velocity, integrated over the horizontal position. The input parameters are: x(sub 0) and y(sub 0), the initial particle starting point; the derivative of the trajectory at x(sub 0) and y(sub 0), s(sub 0) = s(x(sub 0))= dx(y)/dy conditional expectation y = y((sub 0); and b where bx(sub 0)/y(sub 0) is the final trajectory angle before gravity pulls the particle down. The final parameter v(sub 0) is an approximation to a constant horizontal velocity. This model is time independent, providing vertical position x as a function of horizontal distance y: x(y) = (x(sub 0) + s(sub 0) (y-y(sub 0))) + bx(sub 0) -(s(sub 0)y(sub 0) ((y - y(sub 0)/y(sub 0) - ln((y/y(sub 0)))-((g(y-y(sub 0)(exp 2))/ 2((v(sub 0)(exp 2). The first term on the right in the above equation is due to simple ballistics and a spherically expanding gas so that the trajectory is a straight line intersecting (0,0), which is the point at the center of the gas impingement on the surface. The second term on the right is due to vertical acceleration, which may be positive or negative. The last term on the right is the gravity term, which for a particle with velocities less than escape velocity will eventually bring the particle back to the ground. The parameters b, s(sub 0), and in some cases v(sub 0), are taken from an interpolation of similar parameters determined from a CFD simulation matrix, coupled with complete particle trajectory simulations.
Lane, J. E.↗
Preliminary Results on the Gravitational Slingshot Effect and the Population of Hyperbolic Meteoroids at Earth
Interstellar meteoroids, solid particles arriving from outside our Solar System, are not easily distinguished from local meteoroids. A velocity above the escape velocity of the Sun is often used as an indicator of a possible interstellar origin. We demonstrate that the gravitational slingshot effect, resulting from the passage of local meteoroid near a planet, can produce hyperbolic meteoroids at the Earth s orbit with excess velocities comparable to those expected of interstellar meteoroids.
Wiegert, P. A.↗