Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “PLANETARY GRAVITATION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3

Magnetour: Surfing Planetary Systems on Electromagnetic and Multi-Body Gravity Fields

In this NIAC Phase One study, we propose a new mission concept, named Magnetour, to facilitate the exploration of outer planet systems and address both power and propulsion challenges. Our approach would enable a single spacecraft to orbit and travel between multiple moons of an outer planet, with no propellant required. Our approach would enable a single spacecraft to orbit and travel between multiple moons of an outer planet, with no propellant nor onboard power source required. To achieve this free-lunch _Grand Tour', we exploit the unexplored combination of magnetic and multi-body gravitational fields of planetary systems, with a unique focus on using a bare tether for power and propulsion. The main objective of the study is to develop this conceptually novel mission architecture, explore its design space, and investigate its feasibility and applicability to enhance the exploration of planetary systems within a 10-year timeframe. Propellantless propulsion technology offers enormous potential to transform the way NASA conducts outer planet missions. We hope to demonstrate that our free-lunch tour concept can replace heavy, costly, traditional chemical-based missions and can open up a new variety of trajectories around outer planets. Leveraging the powerful magnetic and multi-body gravity fields of planetary systems to travel freely among planetary moons would allow for long-term missions and provide unique scientific capabilities and flagship-class science for a fraction of the mass and cost of traditional concepts. New mission design techniques are needed to fully exploit the potential of this new concept.This final report contains the results and findings of the Phase One study, and is organized as follows. First, an overview of the Magnetour mission concept is presented. Then, the research methodology adopted for this Phase One study is described, followed by a brief outline of the main findings and their correspondence with the original Phase One task plan. Next, an overview of the environment of outer planets is provided, including magnetosphere, radiation belt and planetary moons. Then performance of electrodynamic tethers is assessed, as well as other electromagnetic systems. A method to exploit multi-body dynamics is given next. These analyses allow us to carry out a Jovian mission design to gain insight in the benefits of Magnetour. In addition, a spacecraft configuration is presented that fully incorporates the tether in the design. Finally technology roadmap considerations are discussed.

Gravity Fields↗

MAGNETOUR: Surfing Planetary Systems on Electromagnetic and Multi-Body Gravity Fields

A comprehensive visit of the complex outer planet systems is a central goal in space science. However, orbiting multiple moons of the same planet would be extremely prohibitive using traditional propulsion and power technologies. In this paper, a new mission concept, named Magnetour, is presented to facilitate the exploration of outer planet systems and address both power and propulsion challenges. This approach would enable a single spacecraft to orbit and travel between multiple moons of an outer planet, without significant propellant or onboard power source. To achieve this free-lunch ‘Grand Tour’, Magnetour exploits the unexplored combination of magnetic and multi-body gravitational fields of planetary systems, with a unique focus on using a bare electrodynamic tether for power and propulsion. Preliminary results indicate that the Magnetour concept is sound and is potentially highly promising at Jupiter.

Lantoine, Gregory↗

Long-time predictions in nonlinear dynamics

It is known that nonintegrable dynamical systems do not allow precise predictions concerning their behavior for arbitrary long times. The available series solutions are not uniformly convergent according to Poincare's theorem and numerical integrations lose their meaningfulness after the elapse of arbitrary long times. Two approaches are the use of existing global integrals and statistical methods. This paper presents a generalized method along the first approach. As examples long-time predictions in the classical gravitational satellite and planetary problems are treated.

Szebehely, V.↗

Contributions to the Earth's Obliquity Rate, Precession, and Nutation

The precession and nutation of the Earth's equator arise from solar, lunar, and planetary torques on the oblate Earth. The mean lunar orbit plane is nearly coincident with the ecliptic plane. A small tilt out of the ecliptic is caused by planetary perturbations and the Earth's gravitational harmonic J(sub 2). These planetary perturbations on the lunar orbit result in torques on the oblate Earth which contribute to precession, obliquity rate, and nutation while the J(sub 2) perturbations contribute to precession and nutation. Small additional contributions to the secular rates arise from tidal effects and planetary torques on the Earth's bulge. The total correction to the obliquity rate is -0.024 sec/century, it is an observable motion in space (the much larger conventional obliquity rate is wholly from the motion of the ecliptic, not the equator), and it is not present in the IAU-adopted expressions for the orientation of the Earth's equator. The effects have generally been allowed for in past nutation theories and some precession theories. For the planetary effect, the contributions to the 18.6 yr nutation are -0.03 mas (milliarcseconds) for the in-phase Delta(psi) plus out-of-phase contributions of 0.14 mas in Delta(psi) and -0.03 mas in Delta(sub epsilon). The latter terms demonstrate that out-of-phase contributions can arise by means other than dissipation. The sum of the contributions to the precession rate is considered and the inferred value of the moment of inertia combination (C-A)/C, which is used to scale the coefficients in the nutation series, is evaluated. Using an updated value for the precession rate, the rigid body (C-A)/C =0.003 273 763 4 which, in combination with a satellite-derived J(sub 2), gives a normalized polar moment of inertia C/MR(exp 2) = 0.330 700 7. The planetary contributions to the precession and obliquity rates are not constant for long times causing accelerations in both quantities. Acceleration in precession also arises from tides and changing J(sub 2) Contributions from the improved theory, masses, ecliptic motion, and measured values of the precession rate and obliquity are combined to give expressions (polynomials in time) for precession, obliquity, and Greenwich Mean Sidereal Time.

Williams, James G.↗

Definition phase of Grand Tour missions/radio science investigations study for outer planets missions

Scientific instrumentation for satellite communication and radio tracking systems in the outer planet exploration mission is discussed. Mission planning considers observations of planetary and satellite-masses, -atmospheres, -magnetic fields, -surfaces, -gravitational fields, solar wind composition, planetary radio emissions, and tests of general relativity in time delay and ray bending experiments.

Tyler, G. L.↗

Cometary dynamics

Modern theories of cometary dynamics are described. Attention is given to Oort's hypothesis that the Solar System is surrounded by a spherically symmetrical cloud of about 10 to the 11th to 10 to the 12th comets extending out to interstellar distances. Dynamical modelling and statistical analyses of cometary motion have confirmed the ability of the Oort hypothesis to explain the observed distribution of energies for the long-period cometary orbits. Some of the sources cometary motion perturbations are discussed, including: random passing stars; interstellar clouds; and the galactic gravitational field. Perturbations in cometary motion in the planetary region are attributed to the gravitational fields of the major planets and nongravitational forces resulting from jetting of volatiles on the surfaces of cometary nuclei. Observational evidence for the existence of a massive inner Oort cloud extending from just beyond the orbit of Neptune to 10,000 AU is presented.

Weissman, P. R.↗

Interior structure of Uranus

Key measurements are discussed which are diagnostic of Uranus' interior structure and evolutionary history, and reviews their present status. Typical interior models have chondritic cores, but have the bulk of their mass in an envelope consisting of ice component, principally H2O. The total amount of free H2 in the planet cannot exceed approximately 1 to 2 earth masses. Measurements of the gravitational moments of Uranus are beginning to be accurate enough to constrain models, but are limited in utility by uncertainty in the rotation period. Discussed is evidence that the outermost planetary layers have a gravitationally significant quantity of denser material (ice component?) in addition to H2 and He. The He/H ratio and the deuterium abundance in the atmosphere may be diagnostic of the planet's previous evolutionary history. It is argued that the planet's interior is likely to now be at a temperature approximately 10(3) deg K. Uranus' interior with Neptune's in a number of ways, considering heat flow, degree of internal differentiation, and possible magnetic field.

Hubbard, W. B.↗

Formation of spectral lines in planetary atmospheres. I - Theory for cloudy atmospheres: Application to Venus.

The theory of the formation of spectral lines in a cloudy planetary atmosphere is studied in detail. It is shown that models based upon homogeneous, isotropically scattering atmospheres cannot be used to reproduce observed spectroscopic features of phase effect and the shape of spectral lines for weak and strong bands. The theory must, therefore, be developed using an inhomogeneous (gravitational) model of a planetary atmosphere, accurately incorporating all the physical processes of radiative transfer. Such a model of the lower Venus atmosphere, consistent with our present knowledge, is constructed. The results discussed in this article demonstrate the effects of the parameters that describe the atmospheric model on the spectroscopic features of spectral line profile and phase effect, at visible and near infrared wavelengths. This information enables us to develop a comprehensive theory of line formation in a Venus atmosphere.

Hunt, G. E.↗

Realistic gravitational focusing of meteoroid streams

A meteor shower can be modeled, to first order, as a parallel stream of particles encountering the Earth. Gravity bends the trajectories of these particles inward, producing an increase in flux both near the planet and along the anti-radiant line. This effect is known as gravitational focusing, and the interception of a portion of meteoroid trajectories by the Earth or another massive body is known as planetary shielding. For a perfectly parallel meteoroid stream, gravitational focusing produces a flux singularity along the anti-radiant line, near which intense enhancements in flux occur. In reality, meteoroids will exhibit some dispersion in their motion that removes this singularity. We present a modified analytic treatment of gravitational focusing and planetary shielding that takes this dispersion into account and discuss its ramifications for several problems in meteor astronomy.

Althea Valkyrie Moorhead↗

Was core formation violent enough to homogenize the early mantle?

The dynamics of iron, its thermal state and its phase in the accreting Earth probably played a major role in the Earth's early thermal evolution. Plausible impact thermal histories make it possible that pure iron was molten in the accreting Earth after it was about 10% grown. Hence, iron eutectic alloys (FeS, FeO) certainly were. Additionally, the initial temperature of the core is an important constraint on the secular cooling of the early Earth and on the strength of the early geodynamo. Whether iron is solid or molten would influence geochemical equilibria in the upper and lower mantle; the mode of core formation, by spherical or near-spherical blobs, stalk-like instabilities, or something more catastrophic would influence the partitioning of siderophiles between silicate and iron phases. Early descent of iron (during accretion) favors partitioning according to low-pressure phase equilibria, whereas late descent favors higher pressure. The later core formation occurs, the greater the heat pulse, due to the strong dependence of gravitational potential energy on planetary radius. The heat may homogenize the mantle if core formation is global; otherwise, heterogeneity of iron differentiation may leave some of the pre-archean mantle unaffected. The larger the chunks of proto-core (and hence smaller surface/volume ratios) the greater the heterogeneity.

Cooperman, S. A.↗

Accumulation of solid bodies in the solar nebula

Research on the accumulation of solid bodies in the solar nebula is discussed. Studies of the earliest stage of accumulation of solid bodies in the solar system, which occured in the presence of the gaseous component of the solar nebula, are discussed. The combined effects of gas drag and gravitational perturbations of a planetary embryo on the orbital evolution of planetesimals, the effects of resonant trapping on planetesimals, and planetary mass accretion are discussed.

Weidenschilling, S. J.↗

Solar system exploration

Two fundamental goals lie at the heart of U.S. solar system exploration efforts: first, to characterize the evolution of the solar system; second, to understand the processes which produced life. Progress in planetary science is traced from Newton's definition of the principles of gravitation through a variety of NASA planetary probes in orbit, on other planets and traveling beyond the solar system. It is noted that most of the planetary data collected by space probes are always eventually applied to improving the understanding of the earth, moon, Venus and Mars, the planets of greatest interest to humans. Significant data gathered by the Mariner, Viking, Apollo, Pioneer, and Voyager spacecraft are summarized, along with the required mission support capabilities and mission profiles. Proposed and planned future missions to Jupiter, Saturn, Titan, the asteroids and for a comet rendzvous are described.

Briggs, Geoffrey A.↗

Mars Aeronomy Observer: Report of the Science Working Team

The Mars Aeronomy Observer (MAO) is a candidate follow-on mission to Mars Observer (MO) in the Planetary Observer Program. The four Mariner and two Viking spacecraft sent to Mars between 1965 and 1976 have provided a wealth of information concerning Martian planetology. The Mars Observer, to be launched in 1990, will build on their results by further examining the elemental and mineralogical composition of the surface, the strength and multipolar composition of the planetary magnetic field, the gravitational field and topography, and the circulation of the lower atmosphere. The Mars Aeronomy Observer is intended to address the last major aspects of Martian environment which have yet to be investigated: the upper atmosphere, the ionsphere, and the solar wind interaction region.

Hunten, Donald M.↗

Numerical simulation of satellite-ring interactions - Resonances and satellite-ring torques

The Krook kinetic equation for planetary rings is numerically solved in two spatial dimensions and in time, with (1) interparticle collisions and (2) satellite-forcing, but (3) without self-gravity, for the case of a flattened planetary ring that undergoes gravitational perturbation by a nearby satellite. It is noted that the amplitude of wakes is limited by purely kinematic effects, even in the absence of collisions. Attention is given to the results of a simulation of an inner Lindblad-resonance location, as the distribution approaches steady state; these simulations do not show an increase in velocity dispersion in the resonance zone, obviating a net torque.

Brophy, Thomas G.↗

GMM-1: A 50 degree and order gravitational field model for Mars

Knowledge of the gravitational field, in combination with surface topography, provides one of the principal means of inferring the internal structure of a planetary body. The highest resolution gravitational field for Mars published thus far was derived from Doppler tracking data from the Mariner 9 and Viking 1 and 2 spacecraft and is complete to degree and order 18 corresponding to a half wavelength resolution of approximately 600 km. This field, which is characterized by a spatial resolution that is slightly better than that of the highest resolution (16x16) topographic model, has been utilized extensively in analyses of the state of stress and isostatic compensation of the Martian lithosphere. However, the resolution and quality of current gravity and topographic fields are such that the origin and evolution of even the major physiographic features on Mars, such as the hemispheric dichotomy and Tharsis rise, are not well understood. We have re-analyzed the Viking and Mariner data sets and have derived a new gravitational field, which we designated GMM-1 (Goddard Mars Model-1). This model is complete to spherical harmonic degree and order 50 with a corresponding (half wavelength) spatial resolution of 200-300 km where the data permit. In contrast to previous models, GMM-1 was solved to as high degree and order as necessary to nearly exhaust the attenuated gravitational signal contained in the tracking data.

Smith, D. E.↗

Dust evolution from comets and asteroids: Their velocities at Earth orbit intersection

In this study on the evolution of dust particles from comets and asteroids, the effects of accurate many-body planetary motion on the gravitational perturbations of the dust grains are computed. In a computer simulation, dust grains of radius 10, 30, and 100 micron were released at perihelion passage from each of 36 different celestial bodies: 16 main asteroids, 15 short period comets with perihelion greater than 1 AU, and 5 short period comets with perihelion less than 1 AU. It is found that when dust grains evolve to intersection with the earth's orbit, they nearly always retain orbital characteristics indicative of their origins. Grains from main belt asteroids differ significantly in orbital characteristics, especially orbital eccentricity, from grains that evolve from comets.

Jackson, A. A.↗