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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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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Approximations of distant retrograde orbits for mission design

Distant retrograde orbits (DROs) are stable periodic orbit solutions of the equations of motion in the circular restricted three body problem. Since no closed form expressions for DROs are known, we present methods for approximating a family of planar DROs for an arbitrary, fixed mass ratio. Furthermore we give methods for computing the first and second derivatives of the position and velocity with respect to the variables that parameterize the family. The approximation and derivative methods described allow a mission designer to target specific DROs or a range of DROs with no regard to phasing in contrast to the more limited case of targeting a six-state only.

Distant Retrograde Orbits (DRO)↗
NASA NTRS1977

Dynamic model for an instrument pointing system

The instrument pointing system concept discussed in the present paper was developed for Spacelab missions. The system is mounted on soft shockmounts to minimize Shuttle disturbances (such as man motion, thruster firings, etc.) and to reduce the effect of large center of mass offsets between the instrument and the pointing system gimbal axes. The instrument pointing system is soft mounted to the Spacelab pallet located in the Orbiter payload bay. The nonlinear model, incorporating the dynamic equations of motion, the controller equations and the definition of sensor dynamics and gimbal bearing friction, is given, along with a system of linearized equations of motion of the Space Shuttle Orbiter and instrument pointing system (linearized model).

Howell, J. T.↗
NASA NTRS2006

A Dynamical Systems Approach to the Design of the Science Orbit Around Europa

The science orbit for a future mission to Europa requires low eccentricity, low altitude, and high inclination. However, high inclination orbits around planetary satellites are unstable due to third-body perturbations. Without control, the orbiter impacts Europa after few weeks. To minimize control, a tour over the stable-unstable, averaged manifolds of unstable frozen orbits has been suggested. We proceed with the unaveraged equations and study the manifolds of unstable orbits that are periodic in a rotating frame attached to Europa. Massive numerical computation helps in understanding the unstable dynamics close to Europa, and, thus, in selecting long lifetime high inclination orbits. A final test of a selected set of initial conditions on a high fidelity, ephemeris model, validate the results.

Europa↗
NASA NTRS1990

A close-up view of Triton

Triton, the only large moon in the solar system with a retrograde motion, is investigated. The moon rotates about Neptune every 5.88 days and its annual cycle lasts 165 years. The orbit of Triton is 355,000 km from Neptune and it is inclined 23 deg relative to Neptune's equator. The precession of its orbital plane causes complications in its seasonal progression. Triton has a radius of 1353 km and a density of 2.07 gm/cu cm. Triton is believed to have a core of rock surrounded by water ice and a surface veneer of methane and nitrogen ice. The bright haze in its atmosphere could be small grains of particulates. Triton's surface features suggest that the moon should have remained molten until about 1 billion years ago. In order to explain the active geyser-like plumes observed near the subsolar latitude of about 50 deg south, various mechanisms are suggested including explosive escape of nitrogen gas, surface winds, and buoyancy of warmer gas. Voyager 2, which left Neptune and Triton in August 1989 and is now moving out of the solar system, is expected to provide the first glimpses of interstellar material.

Tsurutani, Bruce T.↗
NASA NTRS1975

Lunar and solar perturbations on the orbit of a geosynchronous satellite

The luni-solar effects cause a large amplitude, long-period perturbation of the orbital plane. Canonical differential equations associated with this motion contain a singular point, and are expanded about this point to third order. A solution is given that is valid for long times and is not restricted to small inclinations. Higher order terms are investigated. Expressions are given for the inclination (I) and node as a function of time. Comparisons with a numerically integrated solution show a disagreement in inclination of only .03 deg after 11 years.

Graf, O. F., Jr.↗
NASA NTRS1977

Quantum mechanical theory of a structured atom-diatom collision system - A + BC/1-Sigma/

The problem of a 2-p state atom colliding with a singlet sigma state diatom, which involves multiple potential surfaces, is investigated. Within a diabatic representation for the electronic degrees of freedom (plus spin-orbit interaction), coupled scattering equations are derived in both space-fixed and body-fixed coordinate systems. Coefficients, analogous to Percival-Seaton coefficients, are obtained. Approximations to the exact equations, including angular momenta decoupling approximations, are discussed for both the space-fixed and body-fixed formalisms.

Devries, P. L.↗
NASA NTRS1980

Images of Jupiter's sulfur ring

Images of the ring of singly ionized sulfur encircling Jupiter, obtained on two successive nights in April 1979, show that the ring characteristics may change dramatically in about 24 hr. On the first night the ring was narrow and confined to the magnetic equator inside Io's orbit. On the second night it was confined symmetrically about the centrifugal symmetry surface and showed considerable radial structure, including a 'fan' extending to Io's orbit. Many of the differences in the ring on the two nights can be explained in terms of differences in sulfur plasma temperature.

Pilcher, C. B.↗
NASA NTRS1984

Cross-tail ion drift in a realistic model magnetotail

By integrating the exact equations of motion, particle orbits have been followed in a good model magnetospheric field consisting of a planetary dipole, forward magnetosphere, and magnetotail current system. Proton energies from 2 eV to 20 keV were used for the full range of equatorial pitch angles and phase. Despite considerable pitch angle scattering in the equatorial plane crossings, it is found, first, that the bounce-averaged cross-tail drift velocity is approximately independent of pitch angle. Second, it is found that, averaged over initial gyrophase, the drift velocity (due to field curvature and gradient) is proportional to proton energy and is given to good approximation by adiabatic approximations, even up to 20 keV, despite the extreme lack of meeting the adiabatic criteria.

Propp, K.↗
NASA NTRS1985

The Mars Observer Mission

The Mars Observer Mission is to be the first in a series of modest-cost inner-planet missions. Launch is planned for the August/September 1990 Mars opportunity with arrival at Mars one year later. The geoscience/climatology objectives are to be met during a mapping mission over the course of one Mars year (687 days). The mapping orbit will be near-polar (93 degree orbital inclination), sun-synchronous (2 PM sunward equator crossing), and near-circular (350 km orbit altitude, 116 minute period). The spacecraft, to be selected in late 1985, will be a modified version of an existing commercial design which, in the mapping orbit, will maintain a nadir orientation. Experiments and instruments will be selected through an Announcement of Opportunity (AO) process with release of the AO in April 1985, and selection in early 1986. A description of current planning for this mission, with emphasis on climatology, is presented here.

Palluconi, F. D.↗
NASA NTRS1993

Approximate optimal guidance for the advanced launch system

A real-time guidance scheme for the problem of maximizing the payload into orbit subject to the equations of motion for a rocket over a spherical, non-rotating earth is presented. An approximate optimal launch guidance law is developed based upon an asymptotic expansion of the Hamilton - Jacobi - Bellman or dynamic programming equation. The expansion is performed in terms of a small parameter, which is used to separate the dynamics of the problem into primary and perturbation dynamics. For the zeroth-order problem the small parameter is set to zero and a closed-form solution to the zeroth-order expansion term of Hamilton - Jacobi - Bellman equation is obtained. Higher-order terms of the expansion include the effects of the neglected perturbation dynamics. These higher-order terms are determined from the solution of first-order linear partial differential equations requiring only the evaluation of quadratures. This technique is preferred as a real-time, on-line guidance scheme to alternative numerical iterative optimization schemes because of the unreliable convergence properties of these iterative guidance schemes and because the quadratures needed for the approximate optimal guidance law can be performed rapidly and by parallel processing. Even if the approximate solution is not nearly optimal, when using this technique the zeroth-order solution always provides a path which satisfies the terminal constraints. Results for two-degree-of-freedom simulations are presented for the simplified problem of flight in the equatorial plane and compared to the guidance scheme generated by the shooting method which is an iterative second-order technique.

Feeley, T. S.↗