<title>Sensor fusion for Space Station experiments</title>

Abstract

Sensor Fusion for Space Station ExperimentsRalph R. ReinholdThe Boeing CompanyP0 Box 240002, MIS JR-ilHuntsville AL 35801ABSTRACTMaterials processing and protein crystal growth in microgravity are often given as a raison d'etre for the International SpaceStation. Consequently Boeing has demonstrated an interest in developing an automated protein crystal growth experiment.Sensor fusion and intelligent process control can maximize product quality. Boeing IR&D addressed this issue. Boeing selectedtheir automated Protein Crystal Growth Screening Facility (PCGSF) as a candidate experiment to test the value added presentedby sensor fusion. A study reveals that several PCGSF parameters are sensible. PCGSF initially used static laser scattering todetect aggregation, color imagery to measure size and shape of the protein crystals as they grow and crossed polarizers tomeasure birefringence and discriminate between crystals and other aggregates. Parameters were chosen for sensor fusiondemonstration that are compatible with initial sensors and that have minimal impact on the initial design. The polanmetrymeasurement capability is expanded. The color camera is modified by moving the infrared (IR) blocking filter from the CCD toa filter wheel in the light path allowing near JR spectrometry using band pass filters. A block disk allows imagery of laserscattering from the growth solution. If the sample solution has single crystal aggregates in it then the growth is monitored.Certain aspects of the imagery are processed to provide crystal quality information. The data from the multiple modality imagesare converted into descriptors of crystal quality using fuzzy logic. Fuzzy logic is used to fuse these descriptors into a commondescriptor of crystal goodness.'1. Th[TRODUCTIONThe sensor fusion related activities supported materials processing and protein crystal growth experiments for the Space Station.Our objective was to use multiple sensors synergistically to arrive at new and more useful parameters. We intended to show thatsensor fusion increased the ability to separate good crystals from bad crystals during the growth process. Sensor fusion was to beinstalled in the automated Protein Crystal Growth Screening Facility (PCGSF).We found sensors applicable to protein crystal growth, identified the hardware needed for those sensors and the software toperform the fusion. Protein crystals are grown to analyze the molecular structure with x-ray diffraction. We documented crystaldefects that affect the quality of x-ray diffraction and how sensors may help identify the defects. We produced a script of thesoftware procedures to perform the sensor fusion. We began writing the computer programs to perform signal analysis on theraw data and to fuse this data into a single measurement25. We planned to prove the applications of multisensor fusion with atest and demonstration. The completion ofthe project was interrupted by my reassignment.The use of the Space Station for experiments such as protein crystal growth and others is at the core of reasons for building thespace station. Experiments are performed in microgravity either to remove the effect gravity has on the resultant or to study theeffect gravity has on the process. In many processes, a microgravity based experiment results in a product superior to anyproduced on earth. We want to have the highest quality from these processes.2. PROTEiN CRYSTAL GROWTH2.1 Identification of sensorsThe PCGSF rapidly finds the few good crystals out oftens to hundreds of poor crystals. Then, it manipulates the temperature toenhance the growth ofthose good crystals. In this specific design protein crystals grow in batches using polycarbonate cells.Certain parameters of the crystal growth environment are monitored optically. The proposed sensing system distinguishescrystals from precipitates, detects and evaluates flaws in crystals and detects the onset of nucleation.Although fast growth is important, crystals are being grown in space to attain the highest possible quality. That is achieved ifthere is a method to test any deviation from goodness in the crystal at the earliest possible moment in the growth process andThe Boeing Company, 1994