Heather Rodriguez (ESCG/Jacobs Sverdrup), Mark Mulrooney (ESCG/MEI Technologies), Edwin Barker (NASA Johnson Space Center)
Keywords: Optical properties
Abstract:
Multi-layer insulation (MLI) is a material used on rocket bodies and satellites primarily for thermal insulation. MLI is comprised of a variety of materials, layer numbers, and dimensions to satisfy specific design requirements. Typically, it is a sandwich of outward facing copper-colored Kapton layers with inward facing aluminized backing. The inner layers consist of alternating DACRON or Nomex netting and aluminized Mylar. From an orbital mechanics perspective, if this material becomes separated from a spacecraft or rocket body, its orbit will vary greatly in eccentricity due to both its high area-to-mass ratio (A/m) and its susceptibility to solar radiation pressure perturbations. Recently, a debris population was found with high A/m which could be MLI.
Laboratory photometric measurements of one intact piece and three different layers of MLI are presented in an effort to ascertain the characteristics of MLI light curves and aid in identifying the source of the new population. For this paper, the layers used will be consistent with the aforementioned common MLI. Using a robotic arm, the piece was rotated from 0-360 degrees in 10? increments along the object s longest axis. Laboratory photometric data was recorded with a CCD camera and a 300 W Xenon arc light source selected to approximate the solar spectrum. The measurements were taken in white light and using various filters (Johnson Blue (B), Visible (V), and Bessell Red (R)), all taken at an 18 degree (light-object-camera) phase angle selected to closely match typical GEO observations which follow the anti-solar point. As expected, the MLI pieces exhibited characteristics similar to a bimodal magnitude plot of a flat plate, but with photometric features dependent upon the layer composition. To minimize highlight saturation (and consequent loss of intensity information), exposure times were selected empirically based on layer type and filter.
In addition to photometric laboratory measurements, laboratory spectral measurements were acquired for each MLI sample. Spectral data will be combined to match the wavelength region of photometric data to establish a fiduciary reference for the photometric measurements. Not only will this help validate the color photometry, but it will also assist interpretation and analysis of telescopic data. As an example, copper-colored Kapton shows a strong absorption feature near 4800 angstroms. If the observed debris is MLI and the outer layer of copper coloring of Kapton is present, evidence of this material should be seen spectroscopically by the specific absorption feature as well as photometrically (eg. by using R-B (red-blue) light curves).
Using laboratory photometric and spectroscopic measurements an optical property database is provided for a representative high A/m object. These results should directly aid the accurate interpretation of telescopically acquired optical orbital debris photometry of both high A/m targets as well as satellites and spacecraft that incorporate MLI.
Date of Conference: September 12-15, 2007
Track: Poster