Engineering topics

Gullahorn, G. E.

Publications and source records attributed to Gullahorn, G. E..

7 records

NASA NTRS1986

Analytical investigation of the dynamics of tethered constellations in Earth orbit, phase 2

The g-tuning maneuvers of a 3-mass, vertical tethered system are considered. In particular, the case of reaching a zero-g acceleration level on board the middle mass from a non-zero initial condition is analyzed. A control law that provides a satisfactory transient response is derived. The constellation dynamics in the case of the middle mass travelling from one tether tip to the other is also investigated. Instabilities that take place at the end of the maneuver are analyzed and accommodated by devising suitable damping algorithms.

Lorenzini, E. C.↗

NASA NTRS1986

Analytical investigation of the dynamics of tethered constellations in Earth orbit, phase 2

The development of a two dimensional analytical model that describes the dynamics of an n-mass vertical tethered system is reported. Two different approaches are described: in the first one the control quantities are the independent variables while in the second one the Cartesian coordinates of each mass expressed in the orbiting reference frame are the independent variables. The latter model was used in the 3-mass version to simulate the dynamics of the tethered system in applications involving the displacement of the middle mass along the tether. In particular, issues related to reproducing predetermined acceleration profiles and g-tuning are reported.

Lorenzini, E.↗

NASA NTRS1985

Analytical investigation of the dynamics of tethered constellations in Earth orbit (phase 2)

The deployment maneuver of three axis vertical constellations with elastic tethers is analyzed. The deployment strategy devised previously was improved. Dampers were added to the system. Effective algorithms for damping out the fundamental vibrational modes of the system were implemented. Simulations of a complete deployment and a subsequent station keeping phase of a three mass constellation is shown.

Lorenzini, E.↗

NASA NTRS1985

Investigation of dynamic noise affecting geodynamics information in a tethered subsatellite

Work performed as part of an investigation of noise affecting instrumentation in a tethered subsatellite, was studied. The following specific topics were addressed during the reporting period: a method for stabilizing the subsatellite against the rotational effects of atmospheric perturbation was developed; a variety of analytic studies of tether dynamics aimed at elucidating dynamic noise processes were performed; a novel mechanism for coupling longitudinal and latitudinal oscillations of the tether was discovered, and random vibration analysis for modeling the tethered subsatellite under atmospheric perturbation were studied.

Gullahorn, G. E.↗

NASA NTRS1985

Gravity gradiometry from the Tethered Satellite System

Measurement of the gradient of the gravitational acceleration from a satellite platform is likely to provide the next improvement in knowledge of the earth's gravity field after the upcoming Geopotential Research Mission (GRM). Observations from the subsatellite of a Tethered Satellite System (TSS) would increase sensitivity and resolution due to the low altitude possible. However, the TSS is a dynamically 'noisy' system and would be perturbed by atmospheric drag fluctuations. The dynamic noise is being modeled in order to evaluate the feasibility of TSS gradiometry and to design methods of abating the error caused by this noise. The demonstration flights of the TSS will provide an opportunity to directly observe the dynamical environment and refine modeling techniques.

Gullahorn, G. E.↗

NASA NTRS1985

Investigation of dynamic noise affecting geodynamics information in a tethered subsatellite

Measurement of the gradient of the gravitational acceleration from a satellite platform is likely to provide the next improvement in knowledge of the Earth's gravity field after the upcoming Geopotential Research Mission. Observations from the subsatellite of a tethered satellite system (TSS) would increase sensitivity and resolution due to the low altitude possible. However, the TSS is a dynamically noisy system and would be perturbed by atmospheric drag fluctuations. The dynamic noise is being modeled in order to evaluate the feasibility of TSS gradiometry and to design methods of abating the error caused by this noise. The demonstration flights of the TSS are to provide an opportunity to directly observe the dynamical environment and refine modeling techniques. Random vibration analysis as a technique for modeling the TSS under atmospheric perturbation was studied.

Gullahorn, G. E.↗

NASA NTRS1984

Investigation of dynamic noise affecting geodynamics information in a tethered subsatellite

The effects of a tethered satellite system's internal dynamics on the subsatellite were calculated including both overall motions (libration and attitude oscillations) and internal tether oscillations. The SKYHOOK tether simulation program was modified to operate with atmospheric density variations and to output quantities of interest. Techniques and software for analyzing the results were developed including noise spectral analysis. A program was begun for computing a stable configuration of a tether system subject to air drag. These configurations will be of use as initial conditions for SKYHOOK and, through linearized analysis, directly for stability and dynamical studies. A case study in which the subsatellite traverses an atmospheric density enhancement confirmed some theoretical calculations, and pointed out some aspects of the interaction with the tether system dynamics.

Gullahorn, G. E.↗