Engineering topics
Publications and source records attributed to Orr, L. H..
Orbital Lifetime Program (OL) analyzes long-term motion of Earthorbiting spacecraft at altitudes of up to 2,500 km. Models perturbations to orbit caused by solar-radiation pressure, atmospheric drag, and gravitational effects of Sun, Moon, and oblate Earth. Used to predict orbital lifetime and decay rate of satellites. OL written in FORTRAN 77.
A FORTRAN program used by Langley Research Center for analyzing orbital lifetimes of spacecraft is described. Calculations can, at the user's option, take into account perturbations in the orbit due to atmospheric drag, solar radiation pressure, and gravitation effects of the Sun, the Moon, and Earth oblateness. Instructions are provided for access and use of the program, and several sample cases are included with detailed descriptions of their associated input and output.
The Reference Space Station design under consideration by NASA will contain several articular components, notably solar arrays and radiators. A technique to model articulation for use in determining Space Station controllability is described. The technique involves treating each articular component as a rigid free body, subject to the constraint of being attached to the Space Station proper. Because of the relatively large areas associated with some of the articular components, the resulting aerodynamics and solar radiation pressure induced forces and torques are shown to be significant. The effects of articulation on Space Station controllability as compared to the non-articulated rigid-body model are demonstrated. Plots of control forces and torques required to maintain orbital altitude and vehicle attitude are presented.