Engineering topics

Shahid-Saless, Bahman

Publications and source records attributed to Shahid-Saless, Bahman.

9 records

NASA NTRS1994

Relativistic effects on the motion of asteroids and comets

We study the effects arising from relativistic perturbations on the motion of asteroids and comets and show that for a number of such objects, inclusion of relativistic contributions in the equations of motion gives rise to significant improvements in the orbital solutions. Furthermore we argue that ignoring relativistic corrections to the equations of motion, while using masses derived from relativistic ephemerides yields incorrect solutions corresponding to an inconsistent, non-Newtonian, nonrelativistic model.

Shahid-Saless, Bahman↗

NASA NTRS1993

Curvature-Squared Cosmology In The First-Order Formalism

Paper presents theoretical study of some of general-relativistic ramifications of gravitational-field energy density proportional to R - alpha R(exp 2) (where R is local scalar curvature of space-time and alpha is a constant).

Shahid-Saless, Bahman↗

NASA NTRS1992

Local gravitomagnetic perturbations of the lunar orbit

Using the metric in the local inertial frame of the Earth, we calculate relativistic effects on the lunar orbit with the synodic month period. It is shown that such perturbations arise entirely from the gravitomagnetic components of the local metric which exist because of the relative motion of the sun with respect to the Earth. In the case of general relativity, the net perturbation has an amplitude of 3 cm for the lunar range.

Shahid-Saless, Bahman↗

NASA NTRS1992

Local Gravitomagnetism

In quasi-inertial reference frame, geodetic precession is gravitomagnetic phenomenon. Report presents theoretical analysis of gravitomagnetism as perceived by observer in quasi-inertial reference frame near spinning body. Study addresses manifestations of gravitomagnetism in this reference frame, with emphasis on two measurable phenomena: precession of gyroscope in orbit about Earth, and perturbation of trajectory of satellite in orbit around Earth.

Shahid-Saless, Bahman↗

NASA NTRS1991

A picosecond accuracy relativistic VLBI model via Fermi normal coordinates

Fermi normal coordinates are used to construct transformations relating solar system barycentric coordinates to local inertial geocentric coordinates. Relativistic corrections to terrestrial VLBI measurements are calculated, and this formalism is developed to include corrections needed for picosecond accuracy. A calculation of photon time delay which includes effects arising from the motion of gravitational sources is given.

Shahid-Saless, Bahman↗

NASA NTRS1991

Palatini variation of curvature-squared action and gravitational collapse

It is shown that Palatini variation of a class of gravitational actions based on a quadratic generalization of the Einstein-Hilbert action results in a metric-incompatible theory of gravity but one that satisfies Birkhoff's theorem. The usual fourth-order field equations are replaced by two second-order equations. Application of the field equations to a model of freely falling dust are discussed.

Shahid-Saless, Bahman↗

NASA NTRS1990

Curvature-squared cosmology in the first-order formalism

Variation of the R + alpha-R-squared action with respect to independent metric and connection fields is shown to be equivalent to the metric-compatible fourth-order gravity coupled to a vector defined as a function of the trace of the energy-momentum tensor. The field equations are second order. The Friedmann cosmology based on this model is studied and it is shown to include nonsingular solutions at t = 0.

Shahid-Saless, Bahman↗

NASA NTRS1990

Local gravitomagnetism

In a simple two-body system, the gravitomagnetic components of the metric in the local quasi-inertial frame of one of the bodies is calculated. The local geometry in this frame which is freely falling along the geodesic but is directionally fixed with respect to distant stars is primarily defined by the gravitomagnetic components of the local metric. This metric serves to track down the various contributions from the local and distant source and thus provides further insight to the nature of gravitomagnetism. As a result it is shown that in the quasi-inertial frame geodetic precession is a gravitomagnetic phenomenon. Furthermore a connection between local gravitomagnetic effects and Einstein's principle of equivalence is established.

Shahid-Saless, Bahman↗

NASA NTRS1989

Geodetic precession or dragging of inertial frames

In General Relativity, the Principle of General Covariance allows one to describe phenomena by means of any convenient choice of coordinate system. Here, it is shown that the geodetic precession of a gyroscope orbiting a spherically symmetric, nonrotating mass can be recast as a Lense-Thirring frame-dragging effect, in an appropriately chosen coordinate frame whose origin falls freely along with the gyroscope and whose spatial coordinate axes point in fixed directions.

Ashby, Neil↗