Engineering topics

Wells, Eugene M.

Publications and source records attributed to Wells, Eugene M..

4 records

NASA NTRS1996

Performance Evaluation of the Gravity Probe B Design

This report documents the simulation of the Lockheed Martin designed Gravity Probe B (GPB) spacecraft developed tool by bd Systems Inc using the TREETOPS simulation. This study quantifies the effects of flexibility and liquid helium slosh on GPB spacecraft control performance. The TREETOPS simulation tool permits the simulation of flexible structures given that a flexible body model of the structure is available. For purposes of this study, a flexible model of the GPB spacecraft was obtained from Lockheed Martin. To model the liquid helium slosh effects, computational fluid dynamics (CFD) results' were obtained, and used to develop a dynamic model of the slosh effects. The flexible body and slosh effects were incorporated separately into the TREETOPS simulation, which places the vehicle in a 650 km circular polar orbit and subjects the spacecraft to realistic environmental disturbances and sensor error quantities. In all of the analysis conducted in this study the spacecraft is pointed at an inertially fixed guide star (GS) and is rotating at a constant rate about this line of sight.

Francis, Ronnie↗

NASA NTRS1996

Performance Evaluation Gravity Probe B Design

This final report documents the work done to develop a 6 degree-of-freedom simulation of the Lockheed Martin Gravity Probe B (GPB) Spacecraft. This simulation includes the effects of vehicle flexibility and propellant slosh. The simulation was used to investigate the control performance of the spacecraft when subjected to realistic on orbit disturbances.

Francis, Ronnie↗

NASA NTRS1990

Navigation systems requirement analysis for the Aeroassist Flight Experiment (AFE)

Navigation requirements for Aeroassist Flight Experiment (AFE) spacecraft passing through the earth's atmosphere have been studied using a 6-DOF dynamics model, an Inertial Measurement Unit model, a baseline AFE aeropass flight guidance logic, and a baseline AFE aeropass control model. The goal of this study is to determine, in a statistical sense, how much flight path angle error can be tolerated at Entry Interface (EI) and still have acceptable delta-V requirements at exit to position the AFE spacecraft for recovery. Assuming there is fuel available to produce 370 ft/sec of delta-V at atmospheric exit, a 3-sigma standard deviation in flight path angle error of 0.04 degree at EI would result in a 98 percent probability of mission success. In addition to the required delta-V at exit, other aeropass parameters such as maximum aeroheating rate, fuel consumption, and the science requirements affecting mission success are also investigated.

Huang, K. H.↗

NASA NTRS1990

A numerical algorithm to propagate navigation error covariance matrices associated with generalized strapdown inertial measurement units

The design and operation of a Strapdown Navigation Analysis Program (SNAP) developed to perform covariance analysis on spacecraft inertial-measurement-unit (IMU) navigation errors are described and demonstrated. Consideration is given to the IMU modeling subroutine (with user-specified sensor characteristics), the data input procedures, state updates and the simulation of instrument failures, the determination of the nominal trajectory, the mapping-matrix and Monte Carlo covariance-matrix propagation methods, and aided-navigation simulation. Numerical results are presented in tables for sample applications involving (1) the Galileo/IUS spacecraft from its deployment from the Space Shuttle to a point 10 to the 8th ft from the center of the earth and (2) the TDRS-C/IUS spacecraft from Space Shuttle liftoff to a point about 2 h before IUS deployment. SNAP is shown to give reliable results for both cases, with good general agreement between the mapping-matrix and Monte Carlo predictions.

Weir, Kent A.↗