suggested as possible approaches for this type of collection, but they are only in 

 early stages of development. 



An example of an impact collection technique is the capture cell in which a 

 particle penetrates a thin film and enters an enclosed volume where vapor and 

 debris are trapped. For capture cells the information that is obtained for a par- 

 ticle is bulk elemental and isotopic composition, as well as some limited data on 

 shape and density from the shape and size of the penetration hole. The compart- 

 mentalization of capture cells allows the collection of discrete particles over a 

 wide size range. A major advantage of capture cells is that all condensable mate- 

 rials are trapped in the cell for later analysis. Other destructive collection 

 schemes involve direct cratering into either a solid or a porous material. For 

 impacts at moderate velocity into some metals, the efficiency of retention of 

 meteoroid residue as material lining the crater bottom can be appreciable. This 

 technique has the advantage that the sample is highly concentrated and is not 

 diluted with collection material, as is the case with capture cells. Disadvantages 

 are that volatile materials are lost preferentially and at the higher velocities all 

 the projectile is vaporized. The shock-loading of the impacting particle can be 

 considerably decreased by using a low-density substrate material. This can be a 

 foam, a stack of thin foils, or a suspension of particles or fibers. If the velocity 

 is not extreme, particles can be collected intact with this approach in the sense 

 that some original phase and structural information is preserved. It is unlikely 

 that fragile particles can be captured in pristine condition, but it is likely that 

 particles or components of particles that are strong mineral grains can be decel- 

 erated without melting or severe heating. Recent work with impacts recovered 

 from Solar Max have demonstrated that some fragments of fragile particles can 

 be captured in unmelted form. 



There are two generic approaches to "nondestructive capture" of hyper- 

 velocity particles: passive capture and active capture. The passive approach uses 

 input into suitable low-density, inert capture media to absorb kinetic energy in a 

 manner that minimizes alteration of the particle. Active collection utilizes force 

 fields to decelerate particles. 



The success of passive intact capture of hypervelocity particles rests on the 

 ability to absorb the maximum amount of particle kinetic energy by a passive 

 capturing medium while maintaining the energy removal rate below the 

 threshold that will cause particle damage. Examples of possible passive capture 

 media are low-density polymeric foams, suspended micrograins, gas, void-metal 

 composites, felts, and aerogels. Considerable laboratory success has been realized 

 from the use of low-density polymeric foams to capture comet analog silicate 

 grains in an organic binder at speeds up to 6 km/sec. Laboratory tests with pure 

 aluminum projectiles have demonstrated recovery of 60% of the projectile mass 

 at speeds of 7.9 km/sec. 



A considerable body of laboratory data suggests that the passive capture tech- 

 niques can be used to collect meteoroids in space. It is likely that both mineral 



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