grains and organic materials can be collected in relatively unmodified form. 

 Strong, low-velocity particles can be captured intact. The fragile particles that 

 may be characteristic of comets will probably fragment during collection, but 

 even for the most fragile materials it is expected that individual solid compo- 

 nents will be recovered without major modification. The passive technique is 

 relatively well developed and could be used at the present time. 



Totally nondestructive collection is theoretically possible using electrostatic 

 or magnetic fields to decelerate micrometer-sized meteoroids from cosmic 

 velocities. Figure 4-1 shows a conceptual design of an electrostatic collector. 

 Particles are charged with an electron beam and then decelerated by electro- 

 static fields that retard the particle motion. This is essentially the inverse of elec- 

 trostatic dust accelerators used in the laboratory to calibrate micrometeoroid 

 impact sensors such as those used on the flybys of comet Halley. In the labora- 

 tory, micrometer and submicrometer particles are highly charged and then accel- 

 erated with a potential of a few million volts to attain velocities as high as 

 50 km/sec. 



Feasibility studies are currently under way to determine whether the electro- 

 static technique can be used for practical and efficient collection in space. 

 Although there have been conceptual studies, there is no laboratory experience 

 with actual capture of hypervelocity particles. The active capture approach has 

 many attractions, but there are formidable problems that must be solved before 

 a significant number of particles in the nanogram to microgram range can be 

 collected. 



4.4 Technology Needs 



Only a few meteoroids have been collected in space and, although orbital 

 measurements have been made for particles, they were not made for collected 

 material. Presently there is a considerable amount of activity in the collection 

 and detection fields. An impressive set of particle impact detectors flew on the 

 comet Halley probes, Giotto and Vega, and are planned for the Jupiter probe, 

 Galileo. Particle collection experiments involving capture cells and cratering into 

 solids are carried on LDEF and the Soviet space station. The technology of 

 hypervelocity capture of small meteoroids is also under development for possible 

 use on a comet-sample-return mission using a flyby spacecraft on an Earth-return 

 trajectory. This mission is part of the Solar System Exploration Committee 

 (SSEC) core program. There is progress being made in the collection and the 

 detection of particles, and it is timely to combine the technologies to produce a 

 device that collects particles and measures their orbital parameters. The major 

 technology needs are to refine the collection techniques and to adapt detection 

 methods so that precise speeds and impact directions can be measured. 



The capture techniques need to be refined so that some intact particles can 

 be collected, and volatile elements such as carbon, nitrogen, and hydrogen will 



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