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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Failure modes of reduced-order orbit determination filters and their remedies

Ways in which failure can occur in reduced-order, orbit determination filter, error covariance calculations are discussed. In the context of this article, reduced-order filters denote nonoptimal filters which include fixed levels of uncertainty in some parameters of the measurement models or in the spacecraft dynamical model which are not explicitly estimated in the filter equations. Failure is defined as an increase in the orbit determination covariance with the addition of data or as an unreasonable growth in the covariance with time, i.e., nonasymptotic behavior of the covariance. Some simple, known cases of failure are discussed along with their traditional remedies. In addition, more modern remedies are discussed which are currently under development at the Jet Propulsion Laboratory. The article first describes the known problems of reduced-order filters when they are employed for orbit determination, and their traditional remedies. Then, having defined these, the relevancy and desirability of the more modern remedies are made apparent.

Scheeres, D. J.↗
NASA NTRS1975

Thirteenth-order orbital resonance on a Diademe 2 fragment

A strong thirteenth-order resonance has been observed in an analysis which is based on U.S. Navy tracking data regarding the slowly decaying orbit of a Diademe 2 fragment. The exact commensurability for the orbit occurred in late 1973. The major changes due to the resonance were over by late 1974. Approaches for a significant improvement of thirteenth-order geopotential terms are discussed.

Wagner, C. A.↗
NASA NTRS1975

Adiabatic invariants and phase equilibria for first-order orbital resonances

In the planar circular restricted three-body problem, the evolution of near-commensurable orbits is studied under change in the mass ratio, mu. The evolution involves preservation of two adiabatic invariants. Transition from circulation to libration may occur; such transitions are of two types. Type I transition occurs when the evolutionary track in phase space passes through near-zero eccentricity; as in the ordinary case (no transition), pre- and post-evolutionary states are linked by solution of a two-point boundary-value problem. Type II transition occurs when the evolutionary track encounters an unstable phase equilibrium or periodic orbit. There is then a discontinuous change in one adiabatic invariant, and pre- and post-evolutionary states are linked by solution of a three-point boundary-value problem. No evolutionary track can encounter a stable phase equilibrium, but the class of all stable phase equilibria is mapped into itself under mu change.

Heppenheimer, T. A.↗
NASA NTRS1991

Feasibility analysis of cislunar flight using the Shuttle Orbiter

A first order orbital mechanics analysis was conducted to examine the possibility of utilizing the Space Shuttle Orbiter to perform payload delivery missions to lunar orbit. In the analysis, the earth orbit of departure was constrained to be that of Space Station Freedom. Furthermore, no enhancements of the Orbiter's thermal protection system were assumed. Therefore, earth orbit insertion maneuvers were constrained to be all propulsive. Only minimal constraints were placed on the lunar orbits and no consideration was given to possible landing sites for lunar surface payloads. The various phases and maneuvers of the mission are discussed for both a conventional (Apollo type) and an unconventional mission profile. The velocity impulses needed, and the propellant masses required are presented for all of the mission maneuvers. Maximum payload capabilities were determined for both of the mission profiles examined. In addition, other issues relating to the feasibility of such lunar shuttle missions are discussed. The results of the analysis indicate that the Shuttle Orbiter would be a poor vehicle for payload delivery missions to lunar orbit.

Haynes, Davy A.↗
NASA NTRS1979

Present obliquity oscillations of Mars - Fourth-order accuracy in orbital e and I

A long period analysis of solar system orbital evolution, correct to fourth order in orbital eccentricities and inclinations (Bretagnon, 1974), and an improved value of the planet's moment of inertia (Reasenberg, 1977) have been incorporated in a recalculation of the obliquity oscillations of Mars. A linearized solution predicts a maximum oscillation amplitude of 13.6 deg centered on a long-term average value of 24.4 deg. A numerical integration of the obliquity for the past 10,000,000 years is also presented. Epochs of minimal oscillation like the present occur at intervals of the order of 4 m.y.

Ward, W. R.↗
NASA NTRS1975

Gravitational Harmonics from Shallow Resonant Orbits

Five gravitational constraints were derived for the GEOS 2 orbit (order 13, to 30th degree) whose principal resonant period is 6 days. The constraints explain the sinusoidal variation with argument of perigee of a lumped harmonic found from 41 6-day arcs of optical and laser data. The condition equations, derived from elementary perturbation theory are shown to account for almost all of the resonant information in the tracking data.

Wagner, C. A.↗
NASA NTRS1974

Magnetopause rotational forms

Magnetic field data from the Goddard Space Flight Center magnetometer experiment on board Ogo 5 are analyzed by the minimum-variance technique for two magnetopause crossings, believed to provide the best evidence presently available of magnetopause rotational discontinuities. Approximate agreement with predictions from MHD and first-order orbit theory is found, but available low-energy electron data suggest the presence of significant non-MHD effects. The paper also illustrates an improved method for data interval selection, a new magnetopause hodogram representation, and the utility of data simulation.

Sonnerup, B. U. O.↗
NASA NTRS1974

Note on the symmetry of perturbed Hartree-Fock and X-alpha wavefunctions

An objection to the effect that the first-order orbitals describing the perturbation of Hartree-Fock or X-alpha closed shell atoms by a multipole electric field may not have the required symmetry properties is acknowledged and answered. It is shown that the assumption of the expected symmetry is a self-consistent one.

Eaves, J. O.↗
NASA NTRS1979

Gradient and curvature drifts in magnetic fields with arbitrary spatial variation

It is shown that, for a magnetic field of arbitrary spatial variation, a nearly isotropic distribution of charged particles drifts with a velocity given by the usual first-order orbit theory drifts averaged over pitch angle. It is assumed that the near-isotropy brought about by scattering, but conclusions concerning drift are insensitive to the details of the scattering process. It is found that this drift velocity is correct even for arbitrarily large ratios of particle gyroradius to magnetic spatial scale, although this velocity must, like all drift effects, be viewed on a scale larger than a gyroradius. Hence for many astrophysical applications, such as cosmic rays, where anisotropies are small, the usual drift velocities provide a valid approximation to convective motions even if the magnetic field scales are very small.

Isenberg, P. A.↗