inclination. Most particles probably will not have uniquely determinable parents 

 and will be sporadic. A small fraction of the detected particles will have not yet 

 had their orbits significantly modified and it will be possible to match them with 

 their source body. Because it may be possible to detect large numbers of parti- 

 cles, the total number of particles with identified sources could, in principle, be 

 large. Orbital evolution caused by Poynting-Robertson drag is slowest for the 

 larger particles and so the best collection experiment is one that collects large 

 numbers of relatively large dust particles. The science return from laboratory 

 analysis is also greater for large particles. 



The most straightforward technique for determining the orbital elements of 

 an impacting dust particle is to measure the time of flight (TOF) and path direc- 

 tion of a particle that first penetrates a thin, front film, passes through an open 

 space, and then enters a rear-collection substrate or device. This basic technique 

 for orbit measurement was actually first used on Pioneers 8 and 9 over 15 years 

 ago. The detection of the front-film penetration can be made from the light, 

 shock wave, or ion pulse generated during the impact. The velocity (TOF) and 

 direction measurements can be made solely by electronic methods or by a com- 

 bination of real-time electronic measurement followed by later measurements of 

 the impact sites in the laboratory. The TOF between the front film and substrate 

 must be established electronically at the time of collection and must have a 

 precision of a few percent. The path direction can be determined by position- 

 sensitive detectors similar to those used for two-dimensional ionizing radiation 

 detectors. The acoustic, light, or ion pulse can be detected by a sensor-array grid 

 square. The path direction requires the measurement of the location of the 

 front-film penetration and entry into the rear substrate. A modification of the 

 purely electronic approach is to use coarse position sensors to identify the 

 general region where the impact occurred and to precisely measure the TOF. 

 After return to the laboratory, the penetration hole and rear impact can be 

 located and measured to determine the particle path to great precision. 



Dust collection from Earth orbit is complicated by the high velocity of the 

 incoming particles. Impact velocities range from 4 to over 70 km/sec and the 

 typical impact velocity for 1Chum particles is about 15 km/sec. Even at the 

 minimum velocity, the kinetic energy exceeds the binding energy, and non- 

 destructive collection is by no means a trivial process. The most developed col- 

 lection concepts involve direct impact and collection by totally mechanical 

 processes. Material was collected with some of these techniques on Gemini, 

 Skylab, and Solar Max, and there is considerable expectation that the large 

 number of similar collection experiments on LDEF will also return important 

 data. Although the direct-impact techniques can recover some unmelted mate- 

 rial, in general the collection is destructive and most structural information is 

 lost. True nondestructive collection would require a device that could decelerate 

 incoming particles without causing excessive heating or mechanical stress. Low- 

 pressure gas cells, foams, and electrostatic or electromagnetic devices have been 



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