Engineering topics
Publications and source records attributed to Culp, Robert D..
The research conducted under NASA Research Grant has been reported periodically throughout the duration of this grant. This research has been coordinated with the work supported by NASA Graduate Student Research Grant awarded to further the graduate doctoral program of Kira Jorgensen. This work will continue through the completion of Kira Jorgensen's Ph.D. program in May, 2000.
This is the final report documenting the results of the polarization testing of near-planar objects with various reflectance properties. The purpose of this investigation was to determine the portion of the reflected signal which is polarized for materials commonly used in space applications. Tests were conducted on several samples, with surface characteristics ranging from highly reflective to relatively dark. The measurements were obtained by suspending the test object in a beam of collimated light. The amount of light falling on the sample was controlled by a circular aperture placed in the light field. The polarized reflectance at various phase angles was then measured. A nonlinear least squares fitting program was used for analysis. For the specular test objects, the reflected signals were measured in one degree increments near the specular point. Otherwise, measurements were taken every five degrees in phase angle. Generally, the more diffuse surfaces had lower polarized reflectances than their more specular counterparts. The reflected signals for the more diffuse surfaces were spread over a larger phase angle range, while the signals from the more specular samples were reflected almost entirely within five degrees of angular deviation from the specular point. The method used to test all the surfaces is presented. The results of this study will be used to support the NASA Orbital Debris Optical Signature Tests. These tests are intended to help better understand the reflectance properties of materials often used in space applications. This data will then be used to improve the capabilities for identification and tracking of space debris.
This report documents the status of the Orbital Debris Radar Calibration Spheres (ODERACS) 2 white spheres optical calibration study. The purpose of this study is to determine the spectral reflectivity and scattering characteristics in the visible wavelength region for the white spheres that were added to the project in the fall, 1994. Laboratory measurements were performed upon these objects and an analysis of the resulting data was conducted. These measurements are performed by illuminating the objects with a collimated beam of light and measuring the reflected light versus the phase angle. The phase angle is defined as the angle between the light source and the sensor, as viewed from the object. By measuring the reflected signal at the various phase angles, one is able to estimate the reflectance properties of the object. The methodology used in taking the measurements and reducing the data are presented. The results of this study will be used to support the calibration of ground-based optical instruments used in support of space debris research. Visible measurements will be made by the GEODDS, NASA and ILADOT telescopes.
Papers from the sixteenth annual American Astronautical Society Rocky Mountain Guidance and Control Conference are presented. The topics covered include the following: advances in guidance, navigation, and control; control system videos; guidance, navigation and control embedded flight control systems; recent experiences; guidance and control storyboard displays; and applications of modern control, featuring the Hubble Space Telescope (HST) performance enhancement study.
When a satellite fragments, a debris cloud is produced which continues to orbit the earth in its place. The fragments do not remain in the same orbit as their parent, however, and the shape of this cloud begins to evolve. Over the course of several years, the cloud changes from an ellipsoid, to a pinched torus in the parent orbital plane, to a full torus in the equatorial plane, after which time it is considered to be part of the background environment. The elapsed time between breakup and background is called the time-to-background (TTB) and is calculated differently by different researchers. This report reviews existing methods employed by programs DEBRIS and SCREEN for determining the TTB, and offers two others for consideration for a community-wide standard. It is concluded that while each method has its merits, the debris community should agree on a specific computational definition for TTB that could be used as an industry-wide standard for comparing results.
The scientific mission of the Earth Observing System (EOS) is modeled to analyze the potential hazard of space debris and its impact on the effectiveness of the program. Specific attention is given to the hazard posed by untrackable debris and the velocities and impact rates of such debris. The NASA Debris Flux Model (DFM) is utilized, and the results are compared to those of the Frag model which predicts the background environment from known parameters and the Screen model for estimating collision probabilities. The probability of damaging impacts is shown to be significant and to increase over time; an EOS spacecraft has a 10 percent chance of being struck by a 1-cm object traveling at 14 km/s. The present analyses demonstrate the need to design the EOS spacecraft for a LEO environment in which collisions with debris are very likely.
The study proposes a space experiment using extended Space Shuttle external tanks to test the impact of orbital debris. The External Tank Calibrated Impact Response test, EXCALIBIR, is a low-cost low-risk, high-payoff approach to investigating the threat to resident space objects posed by untrackable orbital debris, to provide lethality data to the kinetic energy weapons community, and to aid in the testing of space and missile interceptor technology. This experiment is a feasible use of existing assets - the external tank, observation and data collection facilities, launch facilities, and interceptor technology and tests planned for other programs.
Analysis of space debris requires the researcher to have a three-dimensional spatial framework and understanding. By using computers to image and display the space debris volumes, the researcher is provided with an added visual analysis tool. This paper describes volumetric visualization of space debris. Two imaging approaches are used. The first method visualizes the cube faces of the volumetric image. The second method uses a ray-tracing technique to display surfaces within the volume. Three examples of space debris volumes are described.