Among the frontiers of astronomy are the polarization measurements of x- and γ-rays, emitted from phenomena such as γ-ray bursts, pulsars, and active galactic nuclei. Our payload utilizes a 4x4 pixel CdTe array developed to characterize background radiation in the 20-1000 keV energy range. SSGX features both the CACTμS detection unit (previously launched from Italy in 2002) and an innovative electronic data collection system designed by ARC students. DAISI samples detector analog voltages, supplies required voltages, monitors system operation, regulates electronics temperature, responds to remote communication, and continuously records acquired data as well as system status to permanent storage. Preparing for integration, the SSGX is contained within a (31 x 26 x 30) cm3 volume, has a mass of 9.99 kg, utilizes a maximum current draw of 1.497 A, and communicates at an effective data rate of 70.4 bps. This relatively modest experiment is crucial for developing reliable calibration data for future instrumentation. Further, this project provisions international collaboration between ARC undergraduates and research partners in Portugal and Italy. Our goal is thus to obtain, for the first time, a fine measurement of all background components capable of deteriorating a γ-ray polarimeter response in space.
Overview and Background
Previous Flight Experience
Our Stratospheric Spectropolarimeter Gamma-X (SSGX) payload is based on the detection capacities of the Compact Array of Cadmium Telluride Micro Spectrometers (CACTμS), . During a twelve-hour balloon flight, launched from Sicily, Italy, in 2002, the CACTμS instrument collected data exclusively for single events’ background. We now propose to explore the implementation of coincidence logic for double and multiple events. Double events (two hits within different pixels, the first interaction being a Compton) are essential in determining Compton photons' new direction and therefore the polarization direction.
The CACTμS instrument includes the primary detector housing (CdTe detectors) with associated front-end electronics (voltage supplies, temperature sensors, Charge Sensitive Preamps/CSPs
With respect to other former CACTμS’ electronics subsystems, our new SSGX payload represents a major upgrading with substantial downsizing in both weight and dimensions of the service electronics. The image below shows the large dimensions of CACTμS’ subsystems that included the analog front end electronics (AFEE) box, the Pulse Code Modulation Unit (PCM), the scientific Data Handling System (DHS) with Analogue to Digital Conversion (ADC) and digital control electronics, and the Telecommand/Telemetry unit. These would easily occupy all of the space allotted for the four large payloads as accommodated by HASP.
LaSpace and HASP project information:
Simulation Files for MEGAlib:
Lesson Plan and Activity
Payload Subsystem DAISI
DAISI (Data Acquisition/Integrated Storage Interface) is an electronics platform developed by the American River College Physics & Astronomy Club, designed to collect sensor data from multiple sources, monitor and regulate system functionality, and record collected data to an SD card. The primary data collected consists of analog voltage levels from the array of eight CdTe strips for the purpose of recording x-ray and γ-ray events. Additional data collected includes system voltage levels, detector and electronics temperatures, and system status such as error states. This data is also saved in real time to an SD card for post-flight evaluation, and instantaneous readings of all data may also be queried utilizing an RS-232 interface. The RS-232 interface is further capable of receiving commands to override and adjust automatic functionality. Finally, through monitoring of the electronics temperature, onboard logic can respond by activating resistive heating elements for purposes of thermal regulation, ensuring that all components remain within appropriate thermal tolerances.
High Altitude Ballon
Currently preparing for payload integration/ flight anticipated date September 2018, also seeking additional flight opportunities.