KEYWORDS: Sensors, Aerospace engineering, Calibration, Electrons, Particles, Data processing, Ions, Data modeling, Space operations, Space operations, Telescopes, Space telescopes, Data conversion
The space weather instruments (Space Environment In-Situ Suite – SEISS) on the soon to be launched, NOAA GOES-R series spacecraft offer significant space weather measurement performance advances over the previous GOES N-P series instruments. The specifications require that the instruments ensure proper operation under the most stressful high flux conditions corresponding to the largest solar particle event expected during the program, while maintaining high sensitivity at low flux levels. Since the performance of remote sensing instruments is sensitive to local space weather conditions, the SEISS data will be of be of use to a broad community of users. The SEISS suite comprises five individual sensors and a data processing unit: Magnetospheric Particle Sensor-Low (0.03–30 keV electrons and ions), Magnetospheric Particle Sensor-High (0.05–4 MeV electrons, 0.08–12 MeV protons), two Solar And Galactic Proton Sensors (1 to >500 MeV protons), and the Energetic Heavy ion Sensor (10-200 MeV for H, H to Fe with single element resolution). We present comparisons between the enhanced GOES-R instruments and the current GOES space weather measurement capabilities. We provide an overview of the sensor configurations and performance. Results of extensive sensor modeling with GEANT, FLUKA and SIMION are compared with calibration data measured over nearly the entire energy range of the instruments. Combination of the calibration results and model are used to calculate the geometric factors of the various energy channels. The calibrated geometric factors and typical and extreme space weather environments are used to calculate the expected on-orbit performance.
The Teledyne microdosimeter is a novel miniature dosimeter that has become recently available to satellite
manufacturers and programs to provide awareness of the total radiation dose received by the satellite and its associated
subsystems. A characterization of the response of the dosimeter to protons of energies from 30 - 200 MeV as a function
of angle, energy and dose rate is presented in this paper. In addition, the response of the dosimeter to a simulated Solar
proton event with several different levels of shielding has been measured. These results show that the dosimeter
response is relatively uniform over a wide range of conditions for protons. Monte Carlo modeling of the dosimeter for
isotropic particle fluxes (both electrons and protons) has also been accomplished. It is shown that a simplified model is
appropriate in determining the response of the dosimeter when using it to design low cost, simple instruments for space
weather and situational awareness applications.
KEYWORDS: Electrons, Sensors, Particles, Space telescopes, Calibration, Telescopes, Space operations, Data modeling, Digital breast tomosynthesis, Collimators
The CEASE instrument was designed to measure energetic electrons and protons in the space environment. It consists
of two dosimeter detectors, a particle telescope and a Single Event Effect rate detector. CEASE was designed to be an
engineering instrument providing real-time warnings of space weather hazards to the spacecraft operators. The Air
Force Research Laboratory has flown CEASE instruments on two long term missions and is using the data as a part of its
radiation belt model research. A third CEASE instrument will be flown on the Air Force Research Laboratory DSX
mission. The method and results of the calibration of the particle telescope sensor on CEASE will be presented. An
extensive program of telescope response simulation calculations has also been carried out using both simple analytical
models and the Monte Carlo particle interaction codes, MCNPX and Integrated TIGER Series. Comparison of
calculated telescope results to the measured calibration data will be presented.
This paper describes the power
of leveraging radiation modeling software to quickly construct direct
simulation Monte-Carlo models. The radiation modeling code, GEANT,
provides not only the framework to develop models with complicated geometries,
but it gives one control over particle kinematics and propagation.
An obvious added benefit to this
approach is that the same model used for contamination analysis can also
be used to perform radiation studies. Results of a simple model are
presented followed by a discussion of the full potential of this
approach.
The Midcourse Space Experiment (MSX) spacecraft has now been in orbit for over 8 years. The Total Pressure Sensor (TPS) has continually made measurements of the ambient and spacecraft induced environment since launch on April 24, 1996. The environment surrounding the satellite continues to be very dynamic. The magnitude of the solar induced pressure peaks has not decayed with time as would be expected. Even sole consideration of measured pressure versus duration of solar illumination does not illustrate long term decay. The TPS has continued to measure pressure variations of more than 2 orders of magnitude as the sun illuminates the blankets surrounding the instrument. The multi-layer thermal blankets appear to represent a large virtual source of water. The measured pressure is highly dependent upon the solar angle and the shadowing of surfaces by other structures. We will focus our attention on the results from an identical set of experiments conducted each year in July.
We present a summary of the particle environment surrounding the Midcourse Space Experiment (MSX) satellite after 32 months on orbit, including two discrete particle releases produced by micrometeoroid or debris impact. We report on the characteristics of that environment, including particle occurrence rates, velocities, size distributions and trends in the environment. To our knowledge, the long term particle contamination observations that we have made on MSX are the first of their kind. The particle occurrence rate decreased steadily during the first year on orbit, but then remained at a constant level after 32 months on orbit. Our estimate of the total number of particles on the spacecraft surfaces at launch. We conclude that environmental effects such as UV, radiation, thermal cycling, and micrometeoroid impacts are a significant and continuing source of particles on orbit.
The Midcourse Space Experiment (MSX) spacecraft was specifically designed and processed to minimize contamination. This spacecraft represents a best case scenario of spacecraft induced environment. The contamination instrument suite consisted of 10 sensors for monitoring the gaseous and particulate environment. The Total Pressure Sensor (TPS) has continuously measured the ambient local pressure surrounding MSX since its launch on April 24, 1996. The sensor's primary goal was to monitor the early mission (less than one week) ambient pressure surrounding the spacecraft's optical telescopes and to indicate when environmental conditions were acceptable for opening the protective covers. However, the instrument has illustrated that it is quite robust and has successfully measured the long-term decay of the pressure environment. The primary constituent of the atmosphere is water outgassed from the thermal blankets of the spacecraft. The water-induced environment was expected to rapidly decay over the first few months to levels more closely approaching the natural environment. The data generally shows decay toward this level, however, the pressure is quite variable with time and can be influenced by discrete illumination and spacecraft orbital events. Several experiments conducted yearly indicate that the thermal blankets retain significant quantities of water. The local pressure due to water vapor is shown to increase by a factor of 100 from direct solar illumination. Moreover, the multi-layer construction of the blankets causes them to form a deep reservoir that continues to be a source of water vapor 3+ years into the mission. We will present pressure data from several experiments, each separated by one orbital year, that exhibit these water vapor induced pressure busts. The decay and longevity of these bursts will also be discussed.
Outgassing experiments in space were conducted during the critical period in the cryogen lifetime of the large infrared telescope called Spatial Infrared Imager and Telescope (SPIRIT III) on the Midcourse Space Experiment (MSX) spacecraft. This was the period when the solid hydrogen in the dewar was being depleted and the optical components were warming up to evaporate previously condensed volatile materials. The volatile condensable materials were collected on the cryogenically cooled surfaces during the 4 months of prelaunch testing and the 10 months in orbit. The contamination instruments on board the spacecraft were used to monitor the outgassing of these materials. Besides contamination monitoring, it was also desired to control the heating or warm-up process without contaminating the still functioning UV and visible sensors. After considering several scenarios via thermal modeling, it was decided to conduct the warm-up period into two phases, with the first phase intended to approach but not exceed the sublimation point of ice on the primary mirror. Solar radiation was used to heat the SPIRIT III baffle and parts of the +Y face of the spacecraft while the contamination instruments were monitored the outgassing event. Ice redistribution from the baffle to the much colder primary mirror, as well as external pressure bursts and slight film depositions on quartz crystal microbalances were observed. The second phase of warm-up experiments again used solar heating to drive the telescope optics through the 150 K range for final sublimation of any ice remaining as well as condensed hydrocarbons from the cold primary mirror. The results of these end-of-cryo experiments are discussed in terms of the measured film deposits on the cryogenic quartz crystal microbalance and the pressures from the total pressure sensor.
The Midcourse Space Experiment (MSX) satellite was launched on April 24, 1996. This paper provides an update of the quartz crystal microbalance (QCM) data accumulated over these last four years in space. The MSX is the only known experiment that has provided continuous contamination monitoring for such an extended length of time. The five QCMs on board the satellite have provided on-orbit data that have been invaluable in characterizing contamination levels around the spacecraft and inside the cryogenic Spatial Infrared Imaging Telescope (SPIRIT 3). One of the QCMs, the cryogenic QCM (CQCM), located internal to SPIRIT 3, was mounted adjacent to the primary mirror and provided contamination accretion measurements during the 10-month lifetime of SPIRIT 3. Real- time monitoring of contaminant mass deposition on the primary mirror was provided by this CQCM which was cooled to the same temperature as the mirror - approximately 20K. Thermogravimetric analyses (TGAs) on the CQCM provided insight into the amount and species of contaminants condensed on the SPIRIT 3 primary mirror during various spacecraft activities. The four temperature-controlled QCMs (TQCMs) were mounted on external surfaces of the spacecraft for monitoring spacecraft contamination deposition. The TQCMs operated at approximately -50$DEGC and were positioned strategically to monitor the silicone and organic contaminant flux arriving at specific locations. Updated time histories of contaminant thickness deposition for each of the QCMs are presented. Gradual contaminant thickness increase was observed during the first year in space. During the second year, the QCM frequencies (contaminant film thickness) began to decrease, with the time of onset depending on QCM location. Possible explanationsfor this interesting behavior are discussed.
Particle occurrence rates, velocities, size distributions, and trends in the environment have been measured above the Midcourse Space Experiment satellite using optical sensors. Results from the spacecraft's first year on orbit are presented. Particles were detected during relatively quiescent times and as a result of distinct particle release events. On 11 November 1996, we observed a discrete particle release even that is not attributable to spacecraft activity. We hypothesize that this event was caused by an impact by either orbital debris or a micrometeoroid. We present the particle size and velocity distributions from that event and compare them to the quiescent distributions and to previous model predictions.
The Total Pressure Sensor (TPS) on-board the Midcourse Space Experiment (MSX) Spacecraft has continuously measured the ambient local pressure since launch of MSX on April 24, 1996. The primary goals of the sensor are: 1) to monitor the ambient pressure surrounding the spacecraft's optical telescopes and to indicate when environmental conditions are acceptable for opening the protective covers, and 2) to monitor the long-term decay of the species outgassed from the spacecraft. The water-induced environment was expected to rapidly decay over the first few months to elves more closely approaching the natural environment. The data generally shows decay toward this level, however, the pressure is quite variable with time and can be influenced by discrete illumination and spacecraft orbital events. Several experiments, conducted approximately one year into the mission, indicate that the thermal blankets retain significant quantities of water. The local pressure due to water vapor is shown to increase by a factor of 100 from direct solar illumination of the blankets. Moreover, the multi-layer construction of the blankets causes them to form a deep reservoir, which continues to be a source of water vapor several tens of months into the mission. Additionally, the TPS has monitored numerous events in which the measured ambient pressure on the optics deck has exceeded 10-9 Torr. Several of these events did not include solar illumination of the blankets. These events indicate that sources other than the MLI blankets are the cause for certain high-pressure transients. Finally, these events are not limited to the early mission, outgassing phase of the program. They have been witnessed over a year into the mission. The results documented herein indicate that special consideration must be given in the design of optical sensors to account for long term outgassing of a spacecraft.
Many contamination lessons have been learned since the Midcourse Space Experiment satellite was launched on April 24, 1996. FOremost is the inclusion of spacecraft design and thermal engineers with the contamination team early in the program, which resulted in the placement of vents away from the optical sensors, the separation into clean and 'dirty' sections, the exclusion of thrusters, the use of non- perforated silver/Teflon on the optical sensor axis, and the outgassing procedures instituted for all subsystem suppliers. The use of contamination instruments as monitors during integration and testing enabled correct technical decision to be made during several contamination incidents. In space, the contamination monitoring instruments supported programmatic decisions during the early mission planning. During the warm-up of the cryogenic telescope, it was learned that a small gap between the multilayer insulation and the internal baffles contributed to mass redistribution of water vapor. Consequently, it was also learned that a careful warming procedure may potentially be used to clean space-based cryogenic mirrors of condensed water vapor. Particles brought from the ground can be released by mechanical motions such as door openings as well as by thermal shock induced by the Sun during umbra exit. Solar- induced water evaporation from multilayer insulation can dominate the gaseous environment over the spacecraft's lifetime of several years.
The MSX Contamination Experiment team was responsible for establishing design and operational guidelines and the contamination control plan for the Midcourse Space Experiment (MSX), as well as for tracking hardware cleanliness prior to launch. The approaches taken and the results are described.
The Midcourse Space Experiment (MSX) is a Ballistic Missile Defense Organization (BMDO) demonstration and validation
satellite program that has both defense and civilian applications. MSX has UV, visible, and infrared instruments including
the SPIRIT 3 cryogenic telescope. It also has several contamination measuring instruments for measuring pressure, gas
species, water and particulate concentrations and condensable gas species. A cryogenic quartz crystal microbalance (CQCM)
and four temperature controlled microbalances (TQCMs) are part of this suite of contamination measuring instruments. This
paper describes some of the flight QCM data obtained and analyzed to date. The CQCM is located internal to the SPIRIT 3
cryogenic telescope and is mounted adjacent to the primary mirror. Real-time monitoring of contaminant mass deposition on
the primary mirror is provided by the CQCM which is cooled to the same temperature as the mirror -20 K. The four
TQCMs are mounted on the outside of the spacecraft and monitor contaminant deposition on the external surfaces. The
TQCMs operate at -50°C and are positioned strategically to monitor the silicone and organic contaminant flux arriving at
the UV and visible instruments, or coming from specific contaminant sources such as the solar panels. During the first week
of flight operation, all QCMs recorded deposition in the 10-20 ng/cm2-day (1-2 A/day) range. These TQCM deposition rates
have continuously decreased, and after 270 days mission elapsed time (MET), the rates have fallen to values between 0 and
0. 15 A/day depending on TQCM location. Thermogravimetric analyses (TGAs) on the CQCM and TQCMs have provided
valuable insight into the amount and species of contaminants condensed.
Particles generated from spacecraft surfaces will interfere with the remote sensing of emissions from objects in space, the earth, and its upper atmosphere. We have previously reviewed the sources, sizes, and composition of particles observed in local spacecraft environments and presented predictions of the optical signatures these particles would generate and presented predictions of the signatures of these nearfield particles as detected by spacecraft optical systems. Particles leaving spacecraft surfaces will be accelerated by atmospheric drag (and magnetic forces if charged). Velocities and accelerations relative to the spacecraft x,y,z, coordinate system allow the particle to move through the optical sensors' field-of-view after they leave the spacecraft surfaces. The particle's trajectory during the optical system integration time gives rise to a particle track in the detected image. Particles can be remotely detected across the UV-IR spectral region by their thermal emission, scattered sunlight, and earthshine. The spectral-bandpass-integrated signatures of these particles (dependent upon size and composition) is then mapped back onto the UV, visible, and IR sensor systems. At distances less than kilometers, these particles are out of focus for telescoped imaging systems. The image produced is blurred over several pixels. We present here data on the optical signatures observed after the mechanical doors covering the MSX primary optical sensors are removed. This data represents the first observations by these sensors on-orbit, and must be treated as preliminary until a more careful review and calibration is completed. Within these constraints, we have analyzed the data to derive preliminarily positions and trajectories.
The krypton radiometer (KR) is one of a suite of instruments that monitor the gaseous and particulate contamination environments of the midcourse space experiment (MSX) spacecraft. The krypton radiometer measures the local water density in a volume of space approximately 50 cm from the spacecraft near its +X/+Y/+Z corner. The instrument comprises an array of krypton VUV lines source lamps that dissociate water and a near UV radiometer that detects the chemiluminescence from the OH dissociation products. Ground calibrations indicate that the instrument has sufficient sensitivity to detect water densities as low as 1.5 multiplied by 107 molecules cm-3. Water is the primary outgassing species during the early part of a spaceflight. Water deposition is also a particular concern to cryogenic sensors, such as the spatial infrared imaging telescope III (SPIRIT III) on this spacecraft. As the mission progresses, we will correlate the KR measurements of the water density with measurements by the neutral mass spectrometer, total pressure sensor and cryogenic quartz crystal microbalance. Using the MSX external contamination model we will create a complete description of the MSX water environment including outgassing, return flux and deposition, and effects.
The xenon flashlamp is one of a suite of instruments that monitor the particulate and gaseous contamination environments of the midcourse space experiment (MSX) spacecraft. The near-field particulate measurement comprises the high intensity xenon flashlamp that illuminates a volume of space in the field of view of the UVISI wide field of view visible imager (UVISI IVW). Radiation scattered by illuminated contaminant particles is imaged by the IVW. The intensity of the radiation is related to a particle's size and composition. The particle's track yields information about its velocity and trajectory. From ground calibration data we estimate a sensitivity to detect particles smaller than 1 micrometer and to determine cross-field velocities from 1 mm/sec to 50 m/sec. The visible radiation measurement of the particulate environment provided by the xenon flashlamp and UVISI IVW is complemented by multiband IR, UV, and visible measurements by other MSX sensors. The early mission data from this experiment will quantify the relationship between ground contamination control measures, the on-orbit contamination environment, and the performance history of on-orbit sensors.
We have designed, fabricated, and tested two flashlamp-based instruments that will characterize the particulate and water vapor contamination environments aboard the Midcourse Space Experiment (MSX) spacecraft: the Xenon Flashlamp and the Krypton Radiometer. These instruments will operate as part of suite of instruments to monitor the MSX contamination environment over its five-year mission. The Xenon Flashlamp illuminates particles in the field of view of the UVISI Wide Field of View Visible Imager, which in turn measures the scattered radiation. The particle measurement can detect particles smaller than 1 micrometers and can measure cross-field particle velocities from 0.5 cm/sec to 50 m/sec. The Krypton Radiometer measures the local water vapor density. VUV radiation from an array of RF-excited krypton lamps photodissociates H2O in the fields of view of a filtered radiometer and one of the UVISI Spectrographic Imagers. The radiometer and the spectrograph simultaneously measure the intensity of the resulting OH chemiluminescence. The H2O density is proportional to that intensity. The spectrograph will provide a positive identification of the radiating species. Instrument descriptions as well as ground test and simulation data are presented.
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