In June, just as we were switching over from work on Interplanetary Dust to Stardust Interstellar work there was a failure of the air chiller that handles the air coming into the Cosmic Dust Lab (CDL). Although the interstellar tray was never in danger this failure could in principle have put the interstellar tray at risk. This incident has caused us to reconsider the wisdom of doing scanning and extractions on the entire tray at once. Although we had thought hard about possible failure modes we did not anticipate this one and may not anticipate the next one, which might have less happy consequences. In consultation with the Interstellar Preliminary Examination (ISPE) Science Council and the Stardust Oversight Committee of the Curation and Analysis Planning Team for Extraterrestrial, Materials (CAPTEM), we have decided to do scanning of tiles and extraction of tracks on individual tiles after they have been extracted from the tray rather than before. There is a consensus that this approach will present less overall risk to the collector.
Although the new approach has numerous advantages – improved imaging for scanning, improved extraction speed, immediate extraction of foils, and the ability to do scanning and extractions in parallel – we did not take it before because of concern about loss of trajectory information and loss of aerogel collecting area during extraction. To address these concerns we will place artificial “witness tracks” into each aerogel tile before it is removed from the tray to permanently record the local orientation. We have also done successful extractions of three tiles so far without substantial loss of material. We will carefully monitor future extractions to minimize loss of material. Finally, we have designed and built prototypes of new tile holders that will be used to mount each tile permanently for long-term storage.
The failure of the air chiller on the air handling system for CDL resulted in a substantial delay in restarting work on the IS tray, and thus of scanning and uploading new data for Stardust@home. However, we think that in the end this is good news: the new approach should give a substantial improvement in processing speed, and may provide better selectivity in finding IS dust candidates due to the improvement in imaging.