%T Long-Term Microparticle Flux Variability Indicated by Comparison of
Interplanetary Dust Experiment (IDE) Timed Impacts for LDEF's First
Year in Orbit with Impact Data for the Entire 5.77-Year Orbital
Lifetime
%A C. G. Simon
%A J. D. Mulholland
%A J. P. Oliver
%A W. J. Cooke
%A P. C. Kassel
%B 69 Months in Space - Second LDEF Post-Retrieval Symposium
%R NASA CP-3194, Part 2
%D April, 1993
%P 693-704
%E Arlene S. Levine
%I Langley Research Center Hampton, VA 23681-0001
%U http://setas-www.larc.nasa.gov/ldef/IDE/REFERENC/CGSLD2FL/CGSLD2FL.HTM
%X The electronic sensors of the 
<A HREF="http://setas-www.larc.nasa.gov/ldef/IDE/INFO/A0201.HTM">Interplanetary
Dust Experiment (IDE)</A> recorded precise impact times and approximate directions for
submicron to ~100-micron size particles on all six primary sides of
the spacecraft for the first 346 days of the 
<A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">LDEF</A> orbital mission.
Previously-reported analyses of the timed impact data have established
their spatio-temporal features, including the demonstration that a
preponderance of the particles in this regime are orbital debris and
that a large fraction of the debris particles are encountered in
megameter-size clouds.  Short-term fluxes within such clouds can rise
several orders of magnitude above the long-term average.  These
unexpectedly large short-term variations in debris flux raise the
question of how representative an indication of the multi-year average
flux is given by the nearly one year of timed data.  One of the goals
of the IDE was to conduct an optical survey of impact sites on
detectors that remained active during the entire 
<A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">LDEF</A> mission, to
obtain full-mission fluxes.<P>
We present here the comparisons and contrasts among the new 
<A HREF="http://setas-www.larc.nasa.gov/ldef/IDE/SIMS/OPTICAL/INDEX.HTM">IDE
optical survey impact data</A>, the 
<A HREF="http://setas-www.larc.nasa.gov/ldef/IDE/IDE/DATA/IMPACTS.HTM">IDE 
first-year timed impact data</A>, and impact data from other 
<A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">LDEF</A> 
micrometeoroid and debris experiments.
The following observations are reported.<P>
<OL>
<LI> The 5.77 year long-term integrated microparticle impact fluxes
recorded by <A 
HREF="http://setas-www.larc.nasa.gov/ldef/IDE/INFO/A0201.HTM">IDE</A> detectors matched the
 integrated impact fluxes measured by other 
<A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">LDEF</A> investigators for the
same period.
<LI> IDE integrated microparticle impact fluxes varied by factors from
0.5 to 8.3 for LDEF days 1-346,
 347-2106 and 1-2106 (5.77 years) on rows 3 (trailing edge, or West),
6 (South side), 12 (North side),   and the Earth and Space ends.
<LI> IDE integrated microparticle impact fluxes varied less than 3% for
<A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">LDEF</A> 
days 1-346, 347-2106 and      1-2106 (5.77 years) on row 9
(leading edge, or East).
</OL><P>
These results give further evidence of the accuracy and internal
consistency of the recorded IDE impact data.  This leads to the
further conclusion that the utility of long-term flux ratios for
impacts on various sides of a stabilized satellite in low Earth orbit
(LEO) is extremely limited.  These observations, and their
consequences, highlight the need for continuous, real time monitoring
of the 
<A HREF="http://setas-www.larc.nasa.gov/ldef/IDE/IDE/PLOTS/_IDEPLOT.HTM">dynamic 
microparticle environment in LEO</A>.<P>