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AIM End of Prime Mission Review CDE: Cosmic Dust Experiment November 17, 2009 PowerPoint Presentation
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AIM End of Prime Mission Review CDE: Cosmic Dust Experiment November 17, 2009

AIM End of Prime Mission Review CDE: Cosmic Dust Experiment November 17, 2009

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AIM End of Prime Mission Review CDE: Cosmic Dust Experiment November 17, 2009

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  1. AIM End of Prime Mission ReviewCDE: Cosmic Dust ExperimentNovember 17, 2009 Mihály Horányi LASP, Univ. of Coloradohoranyi@colorado.edu Andrew Poppe LASP, Univ. of Colorado poppe@lasp.colorado.edu Mark LanktonLASP, Univ. of Colorado lankton@lasp.colorado.edu

  2. Agenda • Instrument Overview and Science Objectives • Pre-flight Testing • On-orbit Performance • Science Results • Data Products • Lessons Learned • Conclusions

  3. Instrument Overview and Science Objectives

  4. Scientific Motivation • Polar Mesospheric Cloud (PMC) growth is controlled by several factors • Temperature, water vapor, condensation nuclei concentration • The Cosmic Dust Experiment (CDE) aims to measure the influx and variability of cosmic dust and correlate measurements with PMC activity indices

  5. AIM Level 1 Requirements: CDE CDE: *CDE instrument is not included in the minimum mission

  6. Instrument Description • CDE is an in-situ dust impact detector • 12 polyvinylidene fluoride (PVDF) detectors register charge upon dust impacts • 2 reference detectors protected from dust impacts for background noise • Approximately zenith pointing • CDE has a total area of 0.11 m2, a one second time resolutionand was designed to detect submicron sized particles. • Development is identical to the New Horizons - Student Dust Counter

  7. PVDF Film Al/Ni Contacts Measurement Principle • Depolarization induced current • Magnitude of integrated current calibrated to mass of particle

  8. Instrument Calibration • Calibration was performed in two steps: • Level 1: Electronics (DN to charge) • Performed at LASP • Level 2: PVDF Detectors (Charge to mass, assuming velocity) • Detectors calibrated using dust accelerator in Heidelberg, Germany (MPI-K) • SDC calibration (2003) • CDE calibration (2006) • SDC and CDE datasets combined due to similarity of detectors

  9. DN-to-charge calibration Empirically derived pre-flight Dependent on channel, e-box temperature, PVDF temperature Level 1 Calibration: DN to Charge

  10. Charge-to-mass calibration curve Analysis from James et al., Nuc. Inst. Meth, in review Empirically derived from calibration with dust accelerator at MPI-K Level 2 Calibration: Charge to Mass

  11. Pre-flight Testing

  12. Pre-flight Testing • PVDF Thermal Life-cycle Test • Instrument & Spacecraft Thermal Vacuum Tests  • Instrument EMI/EMC Testing  • Instrument Vibration Testing  • Software Testing 

  13. PVDF Thermal Testing • PVDF detector run through representative life cycle of thermal cycling • +/- 75 °C temperature ramps, 10,000 cycles • Performed at Glenn Research Center • Testing Results • PVDF detectors passed the minimum test requirements with no degradation or damage found • Testing chamber failed after ~6000 cycles, however, test declared a success

  14. On-orbit Performance

  15. CDE collected two years of data in the prime mission Data were much noisier than anticipated Data for first nine months (June 07 - Feb 08), while noisy, are analyzable and algorithms have been developed to identify and reduce the noise Data after first safehold (Feb 08) are significantly noisier and we are unable to analyze this data Performance Overview

  16. On-orbit Performance • During flight, some anomalies arose : • Increased noise levels on all channels • Anomalous STIM calibration results • Repeated watchdog resets • Detector failure *No science impact

  17. CDE Raw Data - Channel 1 Analyzable Unable to analyze

  18. CDE has ability to perform internal electronic calibrations to monitor any degradation On-orbit tests showed anomalous results Anomalous STIM Calibration • No definitive explanation for STIM behavior • Impact on science: unable to resolve hits with radii • r > 2 m • STIM calibrations are performed monthly and performance is tracked • No change to date

  19. Laboratory Investigations

  20. Lab Investigations • Laboratory investigations were undertaken in order to help explain the presence of large amounts of noise in the Northern Hemisphere • While a DC pyroelectric current would not pass through the pulse shaper, an increased RMS noise on the pyroelectric current could register as false hits • Constructed a lab setup to measure the output current and resulting hits under flight-like conditions

  21. Lab Investigations • Data was taken from a PVDF channel during multiple cycles of the CDE flight thermal environment • One example “orbit” shown here

  22. Lab Investigations • The PVDF current vs. temperature rate-of-change for one “orbit” • Note hysteresis and sudden spikes in current

  23. Lab Investigations • Comparison of lab and flight data • Spatial distribution using dT/dt as index • Charge distribution

  24. Lab Investigations • Conclusions: • The temperature profile of the CDE PVDF detectors causes a significant pyroelectric current. • This pyroelectric current yields numerous false hits with spatial and charge distributions similar to that seen on CDE in the Northern Hemisphere • Investigation still continuing on pyroelectric RMS noise

  25. Science Results

  26. CDE Reduction Outline • The main steps in CDE Noise Reduction: • Remove 1st Order Coincident • Temporally Coincident (hits within ±1 second) • Spatially Coincident (hits within ±0.25º latitude) • Identify noise patterns in the data • Remove 2nd Order Coincident • Hits that “belong” to a distinct noise pattern in the data, yet weren’t coincident • Calculate average fluxes, dust influx variability, other measures of dust influx

  27. Northern Hemisphere (masked out completely for data analysis) Various Lines CDE Initial Data Includes all data - both coincident and unique

  28. CDE Line Identification Identification of a line on Channel 8, using 1st order coincident data Code requires initial latitude and start/stop time for each line - manual input Calculate SZA for each point on line and use for comparison

  29. CDE Candidate Hits Data post-1st order removal Residual Lines Residual lines are removed by comparing these data to identified and catalogued lines

  30. CDE Dust Impacts • For each channel, determine a cutoff, cutoff, and only hits with total > cutoff, are considered dust impacts • Dust impact data then used to calculate: • Total dust influx ( 1.5 < r < 8 m ) • Comparison to previous models • Cumulative mass influx • Latitudinal variability • North / South pole variability • Temporal variability

  31. CDE Total Cumulative Flux Cumulative flux for CDE (r > 1.5 m) agrees well with other measurements

  32. CDE Science Results Detectors show high degree of variability, perhaps due to some inconsistency in the noise reduction algorithms.

  33. Data Products

  34. Data Products • CDE has released two levels of science products: • Level 1: Charge • Amount of charge generated by PVDF upon particles impact • Level 2: Mass • Calculated mass of impacting particle • All data available on Hampton Univ. AIM website • Currently at final version, V5 • Data available from June 1, 2007 to June 1, 2009 • No use statistics to date, although, most likely very little usage of CDE data

  35. Lessons Learned

  36. Lessons Learned • Characterize and understand the basic physical behavior of PVDF under flight-like conditions • Such testing would have revealed some of the anomalies seen in flight • Would have allowed for mitigation strategies

  37. Lessons Learned • Understand the behavior of the circuitry under flight-like conditions, specifically the detector temperature ramp rates • An improved analog detection and filtering scheme would improve the quality and reliability of the data • CDE simply integrates the signal current regardless of its waveform • Noise events and dust impacts have different waveforms that could have been exploited to support an onboard noise reduction scheme • Develop ability to filter noise events from science based on their waveforms

  38. Conclusions

  39. Conclusions The CDE experiment has not resolved the open issues about the variability of cosmic dust into the atmosphere. The CDE noise reduction scheme has to be further scrutinized to identify the large channel-to-channel variability of the measured dust fluxes. The data collected before the first AIM safehold event is of high value and every effort has to be made to make it available to the scientific community. The CDE design of the PVDF detector system is not suitable to make measurements in a rapidly changing thermal environment. While PVDF sensors remain an attractive choice due to their large surface-to-mass ratio and low cost, new signal processing algorithms are needed to reduce their susceptibility to noise. A method to identify multiple signals from a single sensor needs to be developed to enable coincidence requirements for the identification of true dust events. Improvements in the thermal stability and vibration/mechanical isolation of PVDF-based detectors could dramatically improve the performance of a CDE-type instrument.

  40. Backup Slides

  41. Thermal Requirements • CDE Level 3 Requirements (CDE-T-01000) • Tested at both the instrument and the spacecraft level • All Level 3 and GDRD Thermal requirements met • Operates over full temp range & cycle numbers • Passed all performance tests • Highlighted requirements may not have been met in-flight

  42. EMI / EMC Testing • AIM GDRD specifies MIL-STD-461C / 462 • RE02 – 14kHz to 10GHz • CE01 – 30Hz to 15kHz • CE03 – 15kHz to 10GHz • RS03 – 14kHz to 15GHz, 5 V/m modulated by 1kHz • CS01 – 30Hz to 50kHz, 2.8 Vrms sine • CS02 – 50kHz to 400MHz, 2.8 Vrms sine • CS06 – 10us & 0.1uS 78V transients • Testing Results • Radiated – Modulated 30MHz-300MHz RF • Multiple events in the same second on one or more channels • Conducted – 10uS transients, 1.5kHz – 40kHz sine waves • Simultaneous events on multiple channels • No operational anomalies • All susceptibilities are discernible from actual science events • Waiver AIM-038 requested for RS03, CS01, CS06

  43. Vibration Testing • PVDF Panel Results • During the Z-axis random vibration run, one #0-80 fastener backed out from the detector panel. After the run was complete, this fastener was reinstalled, and all #0-80 fasteners were re-checked for proper torque. The Z-axis random vibration was then run again without incident. • After this occurrence, all #0-80 fasteners were staked to prevent loosening. • No visible damage observed during vibration testing. • No frequency shifts noted in sine surveys during testing. • No functional changes observed during vibration testing. • Electronics Box Results • No anomalies observed during vibration testing. • No visible damage observed during vibration testing. • No functional changes observed during vibration testing.

  44. Software Testing • CDE Flight Software tested at NASA Independent Verification and Validation Facility • Only minor changes to code

  45. CDE has ability to watchdog reboot to prevent software from “hanging” Interference from CIPS seen pre-launch yielded prediction of one reset per 6 months Post-launch, CDE began experiencing 1-2 reboots per week FSW patch loaded to CDE to help diagnose the cause and source of the reboots Additional data from patch proved inconclusive, however, watchdogs have stopped (latest in May 09) Theories include: Greater interference from CIPS than in testing Stray grounding EMI/EMC interference No final resolution, however, no impact on science Watchdog Reboots

  46. Channels 9 and 10 have most likely experienced a mechanical failure Sudden degradation of science data (seen below ~AD 460 for Ch9) STIM calibrations show evidence of an electrical short Detector Failure • Several possible explanations, but no definitive answer • Impact on science: • Channels failed after AIM safehold

  47. On-orbit Trending • CDE temperatures remain nominal • 4 on PVDF panel, 2 on analog board, 2 on digital board • CDE voltages remain nominal • +5/-5V, +2.5V (ADC, FPGA, Therm), Flash Volt • CDE commanding remains nominal • All commanding currently out of on-board Autonomy • Daily channel ON/OFF commands • Watchdog monitoring • Monthly STIM calibration

  48. CDE Amplitude Fit Corresponding amplitude fit - determines center and sigma in mass

  49. CDE Sigma Scatterplot Mass sigma, mass, versus latitude sigma, lat, for all candidate hits on channel one Many hits fall within a 2- radius  identification of leftover noise! Can develop a cutoff for each channel that we believe removes most noise from candidate hit population - look at “sigmagram” plots

  50. CDE Sigmagram • For each channel, analyze the flux dependence on the total sigma: • Flux calculated in the standard manner: • # of candidate hits / total measurement time / channel area • Theory predicts specific shape for Flux v. Total Sigma curve: • Two assumptions: • Noise flux obeys exponential relationship to sigma (we assume Gaussian): • Dust hits have no correlation with total sigma  flux is linear drop versus sigma • Fit flux with a sum of the two functions