ALBERT

Description: The CCDs on the Chandra X ray Observatory are sensitive to radiation damage particularly from low-energy protons scattering off the telescope's mirrors onto the focal plane. In its highly elliptical orbit, Chandra passes through a spatially and temporally varying radiation environment, ranging from the radiation belts to the solar wind. Translating thc Advanced CCD Imaging Spectrometer (ACIS) out of the focal position during radiation-belt passages has prevented loss of scientific utility and eventually functionality. However, carefully managing the radiation damage during the remainder of the orbit, without unnecessarily sacrificing observing time, is essential to optimizing the scientific value of this exceptional observatory throughout its planned 10-year mission. In working toward this optimization, the Chandra team developed aid applied radiation-management strategies. These strategies include autonomous instrument safing triggered by the on-board radiation monitor, as well as monitoring, alerts, and intervention based upon real-time space-environment data from NOAA and NASA spacecraft. Furthermore, because Chandra often spends much of its orbit out of the solar wind (in the Earth's outer magnetosphere and magnetosheath), the team developed the Chandra Radiation Model to describe the complete low-energy-proton environment. Management of the radiation damage has thus far succeeded in limiting degradation of the charge-transfer inefficiency (CTI) to less than 4.4*10^-6 and 1.4*10^-6 per year for the front-illuminated and back-illuminated CCDs, respectively.

Description: Internal charging is a risk to spacecraft in energetic electron environments. DICTAT, NU MIT computational codes are the most widely used engineering tools for evaluating internal charging of insulator materials exposed to these environments. Engineering tools are designed for rapid evaluation of ESD threats, but there is a need for more physics based models for investigating the science of materials interactions with energetic electron environments. Current tools are limited by the physics included in the models and ease of user implementation .... additional development work is needed to improve models.

Description: CRMFLX (Chandra Radiation Model of ion FluX) is an environmental risk mitigation tool for use as a decision aid in planning the operations times for Chandra's Advanced CCD Imaging Spectrometer (ACIS) detector. The accurate prediction of the proton flux environment with energies of 100 - 200 keV is needed in order to protect the ACIS detector against proton degradation. Unfortunately, protons of this energy are abundant in the region of space Chandra must operate, and the on-board Electron, Proton, and Helium Instrument (EPHIN) does not measure proton flux levels of the required energy range. In addition to the concerns arising from the radiation belts, substorm injections of plasma from the magnetotail may increase the protons flux by orders of magnitude in this energy range. The Earth's magnetosphere is a dynamic entity, with the size and location of the magnetopause driven by the highly variable solar wind parameters (number density, velocity, and magnetic field components). Operational times for the telescope must be made weeks in advance, decisions which are complicated by the variability of the environment. CRMFLX is an engineering model developed to address these problems and provides proton flux and fluence statistics for the terrestrial outer magnetosphere, magnetosheath, and solar wind for use in scheduling ACIS operations. CRMFLX implements a number of standard models to predict the bow shock, magnetopause, and plasma sheet boundaries based on the sampling of historical solar wind data sets. Measurements from the GEOTAIL and POLAR spacecraft are used to create the proton flux database. This paper describes the recently released CRMFLX v2 implementation that includes an algorithm that propagates flux from an observation location to other regions of the magnetosphere based on convective ExB and VB-curvature particle drift motions in electric and magnetic fields. This technique has the advantage of more completely filling out the database and makes maximum use of limited data obtained during high Kp periods or in areas of the magnetosphere with poor satellite coverage.

Description: Developing reliable space systems for lunar exploration and infrastructure for extended duration operations on the lunar surface requires analysis and mitigation of potential system vulnerabilities to radiation effects on materials and systems. This paper reviews the characteristics of space radiation environments relevant to lunar programs including the trans-Earth and trans-lunar injection trajectories through the Earth's radiation belts, solar wind surface dose environments, energetic solar particle events, and galactic cosmic rays and discusses the radiation design environments being developed for lunar program requirements to assure that systems operate successfully in the space environment.

Description: The Genesis spacecraft launched on 8 August 2001 sampled solar wind environments at L1 from 2001 to 2004. After the Science Capsule door was opened, numerous foils and samples were exposed to the various solar wind environments during periods including slow solar wind from the streamer belts, fast solar wind flows from coronal holes, and coronal mass ejections. The Survey and Examination of Eroded Returned Surfaces (SEERS) program led by NASA's Space Environments and Effects program had initiated access for the space materials community to the remaining Science Capsule hardware after the science samples had been removed for evaluation of materials exposure to the space environment. This presentation will describe the process used to generate a reference radiation Genesis Radiation Environment developed for the SEERS program for use by the materials science community in their analyses of the Genesis hardware.

Description: No abstract available

Description: A Solar Sail Radiation Environment (SSRE) model has been developed for characterizing the radiation dose and internal charging environments in the solar wind. The SSRE model defines the 0.01 keV to 1 MeV charged particle environment for use in testing the radiation dose vulnerability of candidate solar sail materials and for use in evaluating the internal charging effects in the interplanetary environment. Solar wind and energetic particle instruments aboard the Ulysses spacecraft provide the particle data used to derive the environments for the high inclination 0.5 AU Solar Polar Imager mission and the 1.0 AU L1 solar sail missions. Ulysses is the only spacecraft to sample high latitude solar wind environments far from the ecliptic plane and is therefore uniquely capable of providing the information necessary for defining radiation environments for the Solar Polar Imager spacecraft. Cold plasma moments are used to derive differential flux spectra based on Kappa distribution functions. Energetic particle flux measurements are used to constrain the high energy, non-thermal tails of the distribution functions providing a comprehensive electron, proton, and helium spectra from less than 0.01 keV to a few MeV.

Description: NASA launched the Chandra X-ray Observatory in July 1999. Soon after first light in August 1999, however, degradation in the energy resolution and charge transfer efficiency of the Advanced CCD Imaging Spectrometer (ACIS) x-ray detectors was observed. The source of the degradation was quickly identified as radiation damage in the charge-transfer channel of the front-illuminated CCDs, by weakly penetrating ("soft", 100-500 keV) protons as Chandra passed through the Earth s radiation belts and ring currents. As soft protons were not considered a risk to spacecraft health before launch, the only on-board radiation monitoring system is the Electron, Proton, and Helium Instrument (EPHIN) which was included on Chandra with the primary purpose of monitoring energetic solar particle events. Further damage to the ACIS detector has been successfully mitigated through a combination of careful mission planning, autonomous on-board radiation protection, and manual intervention based upon real-time monitoring of the soft-proton environment. The AE-8 and AP-8 trapped radiation models and Chandra Radiation Models are used to schedule science operations in regions of low proton flux. EPHIN has been used as the primary autonomous in-situ radiation trigger; but, it is not sensitive to the soft protons that damage the front-illuminated CCDs. Monitoring of near-real-time space weather data sources provides critical information on the proton environment outside the Earth's magnetosphere due to solar proton events and other phenomena. The operations team uses data from the Geostationary Operational Environmental Satellites (GOES) to provide near-real-time monitoring of the proton environment; however, these data do not give a representative measure of the soft-proton (less than 1 MeV) flux in Chandra s high elliptical orbit. The only source of relevant measurements of sub-MeV protons is the Electron, Proton, and Alpha Monitor (EPAM) aboard the Advanced Composition Explorer (ACE) satellite at L1, with real-time data provided by NOAA's Space Weather Prediction Center. This presentation will discuss radiation mitigation against proton damage, including models and real-time data sources used to protect the ACIS detector system.

Description: The design estimate for the materials for the International Space Station (ISS) specified in SSP 30512 was a conservative estimate. The environment dose was over estimated. The materials originally qualified for approximately 10-15 years are anticipated to be acceptable for periods of up to 20-30 years based on SSP-30512 or 40-60 years based on 2x SSP-30512. This viewgraph presentation shows charts and graphs that review the altitude, the solar minimum and maximum, and the radiation exposure of other satellite, among other graphics.

Description: Not long after launch of the Chandra X-Ray Observatory, it was discovered that the Advanced CCD Imaging Spectrometer (ACIS) detector was rapidly degrading due to radiation. Analysis by Chandra personnel showed that this degradation was due to 10w energy protons (100 - 200 keV) that scattered down the optical path onto the focal plane. In response to this unexpected problem, the Chandra Team developed a radiation-protection program that has been used to manage the radiation damage to the CCDs. This program consists of multiple approaches - scheduled sating of the ACIS detector from the radiation environment during passage through radiation belts, real-time monitoring of space weather conditions, on-board monitoring of radiation environment levels, and the creation of a radiation environment model for use in computing proton flux and fluence at energies that damage the ACIS detector. This radiation mitigation program has been very successful. The initial precipitous increase in the CCDs' charge transfer inefficiency (CTI) resulting from proton damage has been slowed dramatically, with the front-illuminated CCDS having an increase in CTI of only 2.3% per year, allowing the ASIS detector's expected lifetime to exceed requirements. This paper concentrates on one aspect of the Chandra radiation mitigation program, the creation of the Chandra Radiation Model (CRM). Because of Chandra's highly elliptical orbit, the spacecraft spends most of its time outside of the trapped radiation belts that present the severest risks to the ACIS detector. However, there is still a proton flux environment that must be accounted for in all parts of Chandra's orbit. At the time of Chandra's launch there was no engineering model of the radiation environment that could be used in the outer regions of the spacecraft's orbit, so the CRM was developed to provide the flux environment of 100 - 200 keV protons in the outer magnetosphere, magnetosheath, and solar wind regions of geospace. This presentation describes CRM, its role in Chandra operations, and its prediction of the ACIS CTI increase.