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4 The Meteoroid Environment and Its Effects on Spacecraft
Pages 29-39

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From page 29...
... limit represents meteoroids, which are so infrequent as to be negligible as primary impactors on spacecraft. This is also the size at which the meteoroid flux is two orders of magnitude lower than the space debris flux in portions of low Earth orbit (LEO)
From page 30...
... 4 Meteor showers from stream meteoroids are well known, whereas the sporadic meteoroid population is less well understood. Unlike knowledge of orbital debris, knowledge of meteoroids results in part from ground-based observations of the interaction of meteoroids with the atmosphere (used as a detector for this purpose)
From page 31...
... Nevertheless, the Olympus telecommunication satellite suffered an impact, likely from a small Perseid meteoroid at the height of the shower, which ultimately led to the termination of that mission. After the experience of the 1993 Perseid shower and the Olympus impact, the space community became sensitive to the impact damage possibly associated with meteor storms.
From page 32...
... 7 However, there is growing evidence that higher-velocity meteoroid collisions may produce plasma, generation of which in the vicinity of an impact may be more damaging in some cases than the purely mechanical effects. 8 This electrical damage can occur in the form of electrostatic discharges or electromagnetic pulses resulting from the direct ionization of the meteoroid and part of the spacecraft.9 Many ground-based experiments have shown that plasma is generated by hypervelocity impacts.10 With respect to electrical effects, meteoroid velocity is the dominant factor, with the amount of charge generated typically scal ing as mass times velocity to the fourth power.11 At least two spacecraft have suffered electrical anomalies that might potentially have been caused by meteoroid impacts during Perseid meteor shower enhancements, including the Olympus satellite in 1993 (Box 4.2)
From page 33...
... DETECTION AND MONITORING The primary methods for estimating the overall meteoroid flux, velocity, and physical properties of meteoroids include ground-based radar and optical measurements of meteors, in situ impact detections of meteoroids (includ ing detections on returned surfaces) , zodiacal brightness measurements, and IDP studies.
From page 34...
... Note that for many of these techniques the speed of individual particles is not known but is usually assumed to be ~20 km/s based on findings about mean speed from earlier radar and optical meteor measurements. More recently published estimates of meteoroid speed using high-power large-aperture radars (HPLA)
From page 35...
... Another cornerstone of all meteoroid environment models is the meteoroid velocity distribution at Earth. Most models use either the Harvard Radio Meteor Project radar-derived velocity distribution 23 or the distribu A.D.
From page 36...
... If strong changes in the velocity distribution with mass are present in the environment, large errors in assessments of damage may occur, including both mechanical and electrical impact effects. A final major parameter required to interpret meteoroid impact effects is the bulk density of a meteoroid.
From page 37...
... There are two contemporary NASA meteoroid models in use today: NASA SSP 30425, developed in the late 1980s and early 1990s primarily to address the issue of meteoroid damage to the space station, 31 and the NASA Meteoroid Environment Model.32 Both models use as their flux reference the Grün et al. Interplanetary Flux Model (Grün IFM)
From page 38...
... Jones, Annual variation of sporadic radar meteor rates, Monthly Notices of the Royal Astronomical Society 35 367:709-716, 2006, available at http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2966.2005.09974.x/pdf, accessed August 16, 2011. 36 Anderson and Smith, Natural Orbital Environment Guidelines for Use in Aerospace Vehicle Development, 1994.
From page 39...
... Recommendation: The NASA meteoroid and orbital debris programs should establish a baseline effort to evaluate major uncertainties in the Meteoroid Environment Model regarding the meteoroid environ ment in the following areas: (1) meteoroid velocity distributions as a function of mass; (2)


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