Long Duration Exposure Facility
(LDEF) Archive System

NASA Langley Research Center
Hampton, Virginia

Impact Damage of LDEF Surfaces

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Almost every type of spacecraft surface or material that was in use in the 1980's, or conceived for potential use in the foreseeable future was exposed to the low-Earth orbit environment on LDEF. Therefore, examinations of the impact-induced damage to such surfaces/materials can provide extremely valuable information for spacecraft designers. One of the most significant results from the inspection of impact sites on LDEF is the fact that much of the total damage resulted from the synergistic effects of several environmental factors of LEO space, and not just hypervelocity impacts by meteoroid or debris particles.

Impact damage can degrade the performance of exposed spacecraft materials and, in some cases, destroy a spacecraft's ability to perform or complete its mission (e.g., larger particles can penetrate through protective walls). With a relative impact velocity of 10 km/s, a piece of aluminum debris which is ~0.7 mm in diameter can penetrate through a typical 2.5 mm thick aluminum satellite wall. During its 5.75 year exposure, LDEF saw one (1) impact of this size per 7 m2 of exposed surface area in the RAM direction. In addition to this, LDEF experienced ~1 impact/m2, on ram-exposed surfaces, which could have penetrated a typical 1.5 mm thick aluminum electronics box. While these impacts can be extremely damaging to internal components, electronics, batteries, motors, and mechanisms, they are relatively rare. Smaller impacts, which can degrade mission performance or cause mission denial, are much more common with tens of thousands, if not millions of such impacts/m2 of exposed surface area occurring throughout a satellite's lifetime.

Impact damage is typically described in terms of crater or penetration-hole diameters, with only an occasional reference being made to spall zones. This is primarily due to the fact that other damage mechanisms are not well understood, nor are they currently included in most analytical equations.

Currently, most satellite structures are constructed from metal, with the majority being aluminum. However, a few satellites utilized composite materials such as graphite-epoxy and carbon-carbon in their construction, with more expected to do so in the future, since such materials offer considerable weight savings, and thus, launch costs. Because LDEF was designed to withstand multiple launches, retrievals, and landing loads, its structure was made from atypically heavy (for satellites) aluminum I-beams. A few experiment structures (e.g., electronics boxes) on LDEF possessed aluminum wall thicknesses on the order of 2-2.5 mm, while other experiments exposed samples of graphite-epoxy composites. As a result, LDEF-flown materials provide examples of typical impact cratering and penetration behavior of various spacecraft materials.

During the deintegration of LDEF at the Kennedy Space Center, the Meteoroid&Debris Special Investigation Group (M&D SIG) documented and photographed more than 4,000 visible impact features on all LDEF surfaces during their nearly four month inspections. These documented features ranged in size from ~0.3 mm to ~5 mm. Since the spring of 1990, experiment Principle Investigators and the M&D SIG have documented more than 15,000 smaller impact features. The M&D database which contains information (e.g., diameter, location, target material, etc.) on the vast majority of these features can currently be accessed via Telnet, and soon will be accessible via a searchable WWW interface.

The following images are intended to provide examples of the types of damage that can occur to space-exposed surfaces as a result of impacts by meteoroids and debris particles in the LEO environment. Larger versions of each image, along with a brief description can be seen by clicking on the thumbnail image.


Additional LDEF Impact Feature Photographs
(Higher Resolution)
Page 1 | Page 2

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