Macroscopic Cutting of Aerogel Collectors for Stardust and Future Sample Return Missions

Introduction: Silica aerogel is an ultra-lowdensity glass foam used in collector tiles for the capture of particles in low Earth orbit [1] and, recently, for the capture of cometary particles by NASA’s Stardust mission [2]. Reliable and reproducible methods for cutting these and future collector tiles from sample return missions are necessary to enable detailed study of the captured material. These methods must permit clean and controlled cutting of the fragile aerogel on a range of size scales. Several approaches for large-scale cutting have been tested in the past (for examples, see [3]); however, previous methods suffer from a) loss of optical clarity which restricts further extraction and analysis of impacted material and b) large loss of aerogel material on either side of the cut (kerf). We report here an ‘ultrasonic macroblade’ cutting technique for generating large-scale cuts in silica aerogel for subdividing silica aerogel collector tiles used in particle capture on sample return missions. This technique is an extension of the ultrasonic diamond microblade cutting method [4,5], and it is complementary to the smaller-scale cutting capabilities previously described [4-6] for removing individual impacts and particulate debris in aerogel volumes with lateral dimensions typically less than a millimeter. Ultrasonic vibrations applied to ‘macroblades’ provide smooth cut surfaces with high optical clarity and almost no material loss. These large-scale cuts can be made relatively quickly over several-centimeter distances so that an entire Stardust collector tile can be cut. Sub-sections can have thicknesses as thin as a millimeter. Macroscopic cutting enables subdivision and storage of tiles; or distribution of portions of aerogel tiles for immediate analysis by in situ techniques (ie. x-ray); or further extraction of individual tracks, isolation of particles and preparation of samples suited for other analysis techniques (ie. TEM, nanoSIMS). In addition to whole tile subdivision, this method can be used to split or “unzip” impact tracks in order to harvest the terminal debris particles as has been done in the past using razor blades [1], but with greatly improved control and precision. This cutting capability has been implemented in the Stardust Laboratory at NASA’s Johnson Space Center as one of a suite of cutting methods to be used in Stardust sample curation. Method and Results: The ‘ultrasonic macroblade’ is a thin, steel, utility-knife-shaped blade driven at ultrasonic frequencies. This macroblade is controlled by a micromanipulator (joy-stick or dial controls) for fine motion control through the aerogel. The ultrasonic oscillations are generated by the piezo-driver of a MicroDissector (Eppendorf) which is mounted on the micromanipulator. Details of the setup are given in [4]. The macroblade itself is produced by laser-cutting 2-cm long steel blades from 100-micron thick, double-edged, high carbon steel razor blades (Electron Microscopy Sciences). Cutting debris is gently filed off to avoid damaging the sharp cutting edge. Some blade tips show warping due to the thermal processing involved, and these are discarded. Figure 1 shows the blade used for this work after epoxy-mounting to a stem to fit the MicroDissector piezo-driver. The effective cutting length after mounting is 1.7 cm; however, longer blades can be produced to generate deeper cuts. The blade width is 2 mm, and the thickness is 100 microns with a 20° cutting angle to the spine of the blade.