%T Continued investigation of LDEF's Structural Frame and Thermal Blankets by the Meteoroid & Debris Special Investigation Group
%A Thomas H. See
%A Kimberly S. Mack
%A Jack L. Warren
%A Michael E. Zolensky
%A Herbert A. Zook
%B 69 Months in Space - Second LDEF Post-Retrieval Symposium
%R NASA CP-3194, Part 2
%D April, 1993
%P 313-324
%E Arlene S. Levine
%I Langley Research Center Hampton, VA 23681-0001
%U http://setas-www.larc.nasa.gov/setas/PUBS/LDEF/cp3194-93-p313.ps.Z
%X Since the return of the 
<A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">Long Duration 
Exposure Facility (LDEF)</A> in January, 1990, the 
<A HREF="http://www-sn.jsc.nasa.gov/curator/seh/ldef/m&d_fact.htm">Meteoroid 
and Debris Special Investigation Group (M&D SIG)</A> has been examining 
<A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">LDEF</A> 
hardware (i.e., experiment trays and structural components) in an effort to define the low-Earth 
orbit (LEO) particulate environment as witnessed by the spacecraft during its 5.7 year stay in 
orbit.  Last year we reported (ref. 1) on the frequency of larger features as determined from data 
acquired by the 
<A HREF="http://www-sn.jsc.nasa.gov/curator/seh/ldef/sig_mem.htm">M&D 
SIG's Analysis Team (A-Team)</A> during 
<A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">LDEF</A> deintegration.  At that time 
the 
<A HREF="http://www-sn.jsc.nasa.gov/curator/seh/ldef/sig_mem.htm">A-Team</A> examined 
every square millimeter of the spacecraft locating and documenting the 
presence of all impact craters >=500 micrometers in diameter and all 
penetration holes >=300 micrometers in diameter 
(ref. 2).  Over the past year 
<A HREF="http://www-sn.jsc.nasa.gov/curator/seh/ldef/m&d_fact.htm">M&D 
SIG</A> members and 
<A HREF="http://www.jsc.nasa.gov/jsc/JSC_contractors.html">Lockheed 
Engineering & Sciences Co.</A> 
personnel at the <A HREF="http://www.jsc.nasa.gov/">Johnson Space Center 
(JSC) in Houston, Texas</A> have been examining selected 
<A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">LDEF</A> 
structural frame components (i.e., intercostals) in much greater detail in order to augment 
this large-particle data with that from smaller particles.<P>
In all, <A HREF="http://setas-www.larc.nasa.gov/setas/ldef.html">LDEF</A> exposed ~130 m2 of 
surface area to the LEO particulate environment, ~15.4 m2 
of which was occupied by structural frame components of the spacecraft.  This report focuses on 
the <A HREF="http://www-sn.jsc.nasa.gov/curator/seh/ldef/plots.htm">data</A> acquired by detailed examination of
<A HREF="http://www-sn.jsc.nasa.gov/curator/seh/ldef/plots.htm">LDEF 
intercostals</A>, 68 of which are now in 
<A HREF="http://www-sn.jsc.nasa.gov/curator/seh/seh.htm">possession</A> of the <A HREF="http://www-sn.jsc.nasa.gov/curator/seh/ldef/m&d_fact.htm">M&D SIG</A> 
at <A HREF="http://www.jsc.nasa.gov/">JSC</A> (Figure 1).  In addition, limited data will be presented for 
several small sections from A0178 thermal control blankets that were examined/counted prior to 
being shipped to Principal Investigators (PI's) for scientific study.  As was the case in Ref. 1, the 
<A HREF="http://www-sn.jsc.nasa.gov/curator/seh/ldef/plots.htm">data</A> presented here are limited to measurements of crater and penetration-hole diameters and 
their frequency of occurrence which permits, yet also constrains, more model-dependent, 
interpretative efforts.  Such efforts will focus on the conversion of crater and penetration-hole 
sizes to projectile diameters (and masses), on absolute particle fluxes, and on the distribution of 
particle-encounter velocities.  These are all complex issues (refs. 3, 4, 5, 6, 7, 8) that presently 
cannot be pursued without making various assumptions which relate, in part, to crater-scaling 
relationships, and to assumed trajectories of natural and man-made particle populations in LEO 
that control the initial impact conditions.