Large craters on the meteoroid and space debris impact experiment

Examination of 29.37 sq m of thick aluminum plates from the LDEF, which were exposed to the meteoroid and man-made orbital debris environments for 5.8 years, revealed 606 craters that were 0.5 mm in diameter or larger. Most were nearly hemispherical. There was a large variation in the number density of craters around the three axis gravity gradient stabilized spacecraft. A new model of the near-Earth meteoroid environment gives good agreement with the crater fluxes measured on the fourteen faces of the LDEF. The man-made orbital debris model of Kessler, which predicts that 16 pct. of the craters would be caused by man-made debris, is plausible. No chemical analyses of impactor residue that will distinguish between meteoroids and man-made debris is yet available

Laser propulsion option

The use of laser thrusters with exhaust powers in the 25 MW to 250 MW range can reduce the fuel that would be needed to transport the lunar outpost equipment to low-lunar orbit with a chemical OTV by 57000 Kg to 105000 Kg with no significant penalty in trip time. This would save one or two launches of the heavy-load launch vehicle. Nuclear-electric OTVs would take 40 to 120 times as long to get to the moon and would spend 100 to 1700 times as long in the Van Allen radiation belts as OTVs that have laser thrusters

Small craters on the meteoroid and space debris impact experiment

Examination of 9.34 m(exp 2) of thick aluminum plates from the Long Duration Exposure Facility (LDEF) using a 25X microscope revealed 4341 craters that were 0.1 mm in diameter or larger. The largest was 3 mm in diameter. Most were roughly hemispherical with lips that were raised above the original plate surface. The crater diameter measured was the diameter at the top of the raised lips. There was a large variation in the number density of craters around the three-axis gravity-gradient stabilized spacecraft. A model of the near-Earth meteoroid environment is presented which uses a meteoroid size distribution based on the crater size distribution on the space end of the LDEF. An argument is made that nearly all the craters on the space end must have been caused by meteoroids and that very few could have been caused by man-made orbital debris. However, no chemical analysis of impactor residue that will distinguish between meteoroids and man-made debris is yet available. A small area (0.0447 m(exp 2)) of one of the plates on the space end was scanned with a 200X microscope revealing 155 craters between 10 micron and 100 micron in diameter and 3 craters smaller than 10 micron. This data was used to extend the size distribution of meteoroids down to approximately 1 micron. New penetration equations developed by Alan Watts were used to relate crater dimensions to meteoroid size. The equations suggest that meteoroids must have a density near 2.5 g/cm(exp 3) to produce craters of the shape found on the LDEF. The near-Earth meteoroid model suggests that about 80 to 85 percent of the 100 micron to 1 mm diameter craters on the twelve peripheral rows of the LDEF were caused by meteoroids, leaving 15 to 20 percent to be caused by man-made orbital debris

Method and apparatus for determining time, direction, and composition of impacting space particles

A space particle collector for recording the time specific particles are captured, and its direction at the time of capture, utilizes an array of targets, each comprised of an MOS capacitor on a chip charged from an external source and discharged upon impact by a particle through a tab on the chip that serves as a fuse. Any impacting particle creates a crater, but only the first will cause a discharge of the capacitor. A substantial part of the metal film around the first crater is burned off by the discharge current. The time of the impulse which burns the tab, and the identification of the target, is recorded together with data from flight instruments. The metal film is partitioned into pie sections to provide a plurality of targets on each of an array of silicon wafers, thus increasing the total number of identified particles that can be collected. It is thus certain which particles were captured at what specific times

Laser-powered lunar base

The objective was to compare a nuclear reactor-driven Sterling engine lunar base power source to a laser-to-electric converter with orbiting laser power station, each providing 1 MW of electricity to the lunar base. The comparison was made on the basis of total mass required in low-Earth-orbit for each system. This total mass includes transportation mass required to place systems in low-lunar orbit or on the lunar surface. The nuclear reactor with Sterling engines is considered the reference mission for lunar base power and is described first. The details of the laser-to-electric converter and mass are discussed. The next two solar-driven high-power laser concepts, the diode array laser or the iodine laser system, are discussed with associated masses in low-lunar-orbit. Finally, the payoff for laser-power beaming is summarized

Mir Environmental Effects Payload and Returned Mir Solar Panel Cleanliness

The MIR Environmental Effects Payload (MEEP) was attached to the Docking Module of the MIR space station for 18 months during calendar years 1996 and 1997 (March 1996, STS 76 to October 1997, STS 86). A solar panel array with more than 10 years space exposure was removed from the MIR core module in November 1997, and returned to Earth in January, 1998, STS 89. MEEP and the returned solar array are part of the International Space Station (ISS) Risk Mitigation Program. This space flight hardware has been inspected and studied by teams of space environmental effects (SEE) investigators for micrometeoroid and space debris effects, space exposure effects on materials, and electrical performance. This paper reports changes in cleanliness of parts of MEEP and the solar array due to the space exposures. Special attention is given to the extensive water soluble residues deposited on some of the flight hardware surfaces. Directionality of deposition and chemistry of these residues are discussed

Acoustic Emission Signals in Thin Plates Produced by Impact Damage

Acoustic emission (AE) signals created by impact sources in thin aluminum and graphite/epoxy composite plates were analyzed. Two different impact velocity regimes were studied. Low-velocity (less than 0.21 km/s) impacts were created with an airgun firing spherical steel projectiles (4.5 mm diameter). High-velocity (1.8 to 7 km/s) impacts were generated with a two-stage light-gas gun firing small cylindrical nylon projectiles (1.5 mm diameter). Both the impact velocity and impact angle were varied. The impacts did not penetrate the aluminum plates at either low or high velocities. For high-velocity impacts in composites, there were both impacts that fully penetrated the plate as well as impacts that did not. All impacts generated very large amplitude AE signals (1-5 V at the sensor), which propagated as plate (extensional and/or flexural) modes. In the low-velocity impact studies, the signal was dominated by a large flexural mode with only a small extensional mode component detected. As the impact velocity was increased within the low velocity regime, the overall amplitudes of both the extensional and flexural modes increased. In addition, a relative increase in the amplitude of high-frequency components of the flexural mode was also observed. Signals caused by high-velocity impacts that did not penetrate the plate contained both a large extensional and flexural mode component of comparable amplitudes. The signals also contained components of much higher frequency and were easily differentiated from those caused by low-velocity impacts. An interesting phenomenon was observed in that the large flexural mode component, seen in every other case, was absent from the signal when the impact particle fully penetrated through the composite plates

Vacuum/Zero Net-Gravity Application for On-Orbit TPS Tile Repair

The Orbiter Columbia catastrophically failed during reentry February 1, 2003. All space Shuttle flights were suspended, including logistics support for the International Space Station. NASA LaRC s Structures and Materials Competency is performing characterizations of candidate materials for on-orbit repair of orbiter Thermal Protection System (TPS) tiles to support Return-to-Flight activities led by JSC. At least ten materials properties or attributes (adhesion to damage site, thermal protection, char/ash strength, thermal expansion, blistering, flaming, mixing ease, application in vacuum and zero gravity, cure time, shelf or storage life, and short-term outgassing and foaming) of candidate materials are of interest for on-orbit repair. This paper reports application in vacuum and zero net-gravity (for viscous flow repair materials). A description of the test apparatus and preliminary results of several candidate materials are presented. The filling of damage cavities is different for some candidate repair materials in combined vacuum and zero net-gravity than in either vacuum or zero net- gravity alone