not be lost to analyses. For example, capture cells made of "getter" materials 

 have been discussed wherein the meteoroid vaporizes enough getter material to 

 trap reactive elements. The specific needs in the passive collection area are to 

 develop efficient materials or devices that trap meteoroids or their debris with- 

 out causing significant chemical or physical alteration or contamination with 

 collector or spacecraft materials. Some of this development can be done on the 

 ground using particles accelerated to high velocity with light gas guns, plasma 

 drag accelerators, or electrostatic accelerators. The ultimate tests must be made 

 in Earth orbit with real meteoroids. Extensive development will require frequent 

 exposure opportunities. 



The detection technology needs to be adapted to the particular problem of 

 accurately measuring orbital parameters of micrometer- to millimeter-sized par- 

 ticles. The required accuracy of the velocity vector is about a few percent. 

 Plasma pulse detectors were used for TOF and impact-angle measurements on 

 Pioneers 8 and 9 and the LEAM (lunar ejecta and meteorites) instrument placed 

 on the lunar surface by Apollo 17 astronauts. Improvements in the plasma area 

 would be to simplify the technique so that large areas could be instrumented at 

 minimal cost. Another position-sensitive technique that is being actively studied 

 involves piezoelectric sensors that use arrival times in a detector array to pin- 

 point the exact impact location. A final technique uses a polarized PVDF plastic 

 film that generates electric pulses when it is perforated. This material needs no 

 electrical bias. The impact point is measured by signal-delay times. It appears 

 that there are several detector technologies that are suitable for orbital param- 

 eter measurement and the major task is probably to develop a workable system 

 combined with the collection capability. 



4.5 Opportunities 



In the near term, collection experiments can use collection areas approxi- 

 mately a meter squared and exposure times of months. Much larger areas and 

 exposure times would be desirable to collect very large or very rare particles. 



Near-term exposure and recovery opportunities include recoverable satellites 

 such as LDEF and EURECA. A first-rate collection and trajectory measurement 

 experiment of several square meters' area could be included on an Explorer-class 

 mission, with subsequent sample recovery and return to Earth. This could be a 

 dedicated mission or an add-on to a multiinstrumented spacecraft. A timely 

 completion of such a mission would be of considerable value in planning larger 

 and more complex collectors for the Space Station. The Shuttle itself does not 

 have sufficient exposure times to be useful except for simple tests involving a 

 few impacts. A 2-m 2 collector exposed for a year would provide an excellent 

 opportunity to collect a significant number of 0.01- to 0.1 -mm particles. A 

 100-m 2 collector on Space Station would provide the unique opportunity to 

 collect millimeter-sized particles. Because the reason for having a large area is 



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