The Solar Occultation for Ice Experiment (SOFIE) instrument is one of three science instruments for the Aeronomy of
Ice in the Mesosphere (AIM) mission. SOFIE is used to measure solar attenuation by mesospheric ice aerosols during
each observatory sunrise and sunset using an 8-channel (16-detector) differential absorption radiometer. It directly
views the sun and compares the near UV to the mid-IR spectral response during exo-atmospheric and endo-atmospheric
measurements. Deposition of molecular films can degrade the reflectance and transmittance of SOFIE's optics. During
on-orbit performance, it may be possible for the extended solar exposure to promote photochemical deposition and
darkening effects in the UV. This paper will review the methods used to derive and verify contamination control
budgets for particulate and molecular contamination during the fabrication and testing of the SOFIE instrument.
Reported results include the molecular surface cleanliness throughout integration and test as well as outgassing
measurements using internal and external quartz crystal microbalances. This information provides important baseline
data for future correlation of instrument outgassing and potential photo-deposited contamination effects should they
occur during on-orbit solar exposure
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.
The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument is a 10-channel earth limb-viewing sensor that measures atmospheric emissions in the spectral range of 1.27 μm to 16.9 μm. SABER is part of NASA's Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) mission, which was successfully launched in December 2001. Uncommon among limb-viewing sensors, SABER employs an on-axis telescope design with reimaging optics to allow for an intermediate field stop and a Lyot stop. Additional stray light protection is achieved by an innovative inner Lyot stop, which is placed conjugate to the secondary obscuration and support structure. Presented in this paper is the off-axis response of SABER as measured in the Terrestrial Black Hole off-axis scatter facility at the Space Dynamics Laboratory. The measurement was made at visible wavelengths; thus, the response is only representative of SABER's short wavelength channels. The measurement validated the stray light design and complemented the APART software model, which predicts that mirror scatter is the dominant stray light mechanism at short wavelengths. In addition, estimates of the mirror bi-directional reflectance distribution function (BRDF) were made. The off-axis response measurement indicates that SABER is an exceptional stray light suppression telescope.
Semi-volatile residues on aerospace hardware can be analyzed using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). This method can be correlated with quantitative Mil-STD 1246 NVR measurements while simultaneously providing qualitative identification of a large variety of compounds. Its high sensitivity supports the direct sampling of small areas of critical surfaces. This method involves transferring the contaminant film to a small solvent-saturated wipe, followed by extraction of the wipe, then concentration of the solvent extract and subsequent spectroscopic analysis using an FT-IR with a diffuse reflectance accessory. A library of standard curves for different classes of typical aerospace contaminants has been established. Quantitative analysis has been proven successful over orders of magnitude and detection limits exceeding 0.1 ug/cm2 are routinely achieved. Several practical applications have been performed using this analytical method and detailed discussion of analysis techniques is presented. The discussion will include: instrumentation setup, selection and preparation of sample collection materials, sample extract preparation, preparation of standard calibration curves and spectral interpretation.
The SABER instrument (Sounding of the Atmosphere using Broadband Emission Spectroscopy) is a cryogenic infrared sensor on the TIMED spacecraft with stringent molecular and particulate contamination control requirements. The sensor measures infrared emissions from atmospheric constituents in the earth limb at altitudes ranging from 60 to 180 km using radiatively-cooled 240 K optics and a mechanically-refrigerated 75 K detector. The stray light performance requirements necessitate nearly pristine foreoptics. The cold detector in a warm sensor presents challenges in controlling the cryodeposition of water and other condensable vapors. Accordingly, SABER incorporates several unique design features and test strategies to control and measure the particulate and molecular contamination environment. These include internal witness mirrors, dedicated purge/depressurization manifolds, labyrinths, cold stops, and validated procedures for bakeout, cooldown, and warmup. The pre-launch and on-orbit contamination control performance for the SABER telescope will be reviewed.
Molecular surface contaminants can cause degradation of optical systems, especially if the contaminants exhibit strong absorption bands in the region of interest. Different strategies for estimation of spectral degradation responses due to uniform films for various types of systems are reviewed. One tool for calculating the effects of contaminant film thickness on signal degradation in the mid IR region is the simulation program CALCRT. The CALCRT database will be reviewed to correlate spectral n and k values associated with specific classes of organic functional groups. Various schemes are also investigated to estimate the spectral degradation in the UV-Vis region. Experimental measurements of reflectance changes in the IR to UV-Vis regions due to specific contaminants will be compared. Approaches for estimating changes in thermal emissivity and solar absorptivity will also be discussed.
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 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.
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.
This review paper focuses on measurement techniques and facilities for the study of the contamination and space environment effects on optical and thermal radiative surfaces. Laboratory measurements are reviewed and illustrate how cryogenic and relatively warm surfaces can be affected by contaminants, vacuum, and UV. The laboratory data are used to illustrate the important parameters that require consideration when trying to determine these types of effects on future satellite missions. Optical properties of thin contaminants films, BRDF measurements on cryogenic films, quartz crystal microbalance (QCM) measurements, and UV effects on silicone/hydrocarbon films are presented and discussed relative to their applications to satellite systems. The laboratory data are complemented with flight data from the Midcourse Space Experiment (MSX) satellite. Laboratory results were used to interpret MSX spacecraft flight data. The MSX demonstration and validation satellite program was funded by the Ballistic Missile Defense Organization. MSX had UV, visible, and infrared instruments including the Spirit 3 cryogenic telescope and had several contamination instruments for measuring pressure, gas species, water and particulate concentrations, and condensable gas species. Some of the data collected from the flight QCMs are presented.
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.
This paper discusses the pressure spike phenomenon measured by the Total Pressure Sensor (TPS) on the Midcourse
Space Experiment (MSX) spacecraft as it passes through aurora! regions. The TPS is an inverted magnetron, cold cathode
gauge that has a range of 10'° to i0 Ton and is sampled at a 1 Hertz rate. The operation of the instrument depends uponthe
conversion of neutral molecules to ions and the measurement of the resultant current. The TPS has monitored large (>10 fold
increase) pressure transients in the auroral regions of the Earth, which have very short temporal width (< 3 seconds). It is
shown experimentally that the injection of electrons into the TPS orifice results in a higher apparent pressure measurement,
presumably due to an increase in the ion formation rate. An equivalent positive ion flux, however, does not noticeably effect
the TPS pressure measurement. It is therefore believed that the on-orbit transients seen by the MSX TPS are consistent with
an increased flux of electrons from the auroral regions into the entrance aperture of the gauge. This paper describes ground
experiments to quantify the phenomenon with a flight spare TPS and correlates these results to the measurements made onboard
the MSX spacecraft.
The midcourse space experiment (MSX) satellite was launched into a 903 Km, 99.4-deg orbit April 24, 1996. It carries imaging spectrometers and radiometers that operate in the UV, visible, and infrared spectral ranges. In addition, it carries several contamination measuring instruments that are being used to characterize the contamination environment on, in, and around the satellite. Five are quartz crystal microbalances (QCMs), four of which are temperature- controlled (TQCMs). They are located on various external surfaces of the spacecraft and are operating at minus 40 degrees Celsius to minus 50 degrees Celsius to measure the condensation of silicone and organic molecules. One is a cryogenic quartz crystal microbalance (CQCM) which is located adjacent to the SPIRIT III infrared cryogenic telescope primary mirror. Its temperature followed the mirror which cooled from 28 to 20 K during the first week of operation. All QCMs recorded deposition in the 10 - 20 ng/cm$2)-day (1-2 angstrom/day) range. Thermo-gravimetric analyses on the QCMs provided insight into the amount and species of contaminants condensed. Data from the QCMs and other instruments in the contamination experiment (CE) suite played an important role in determining when it was safe to open covers on some of the optical instruments.
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 total pressure sensor (TPS) is one of ten contamination sensors aboard the midcourse space experiment (MSX) satellite. The TPS measures both the natural and spacecraft induced pressure environments. This paper presents a first look at the TPS data from the early operations phase of the MSX mission. Flight data are show to be in good agreement with the external contamination model predictions for MSX. TPS fluctuations are shown to be consistent with the venting characteristics of the Spirit III cryogenic cover. Data are presented which characterize and confirm the tumbling nature of the receding Spirit III cover upon its release. Finally, flight data over an orbital period are shown to conform to a bimodal pressure profile.
The 10.6 (mu) bi-directional reflectance distribution function (BRDF) of the SPIRIT III primary mirror was measured after each major phase of sensor development and testing. The compiled BRDF history provides useful insights with respect to the cleanliness levels that may be reasonably expected for a cryogenic infrared sensor of this size and complexity. The use of nitrogen blow-off was demonstrated as an effective, low-risk option for `touching-up' critical infrared optics. The BRDF measured before integration with the MSX spacecraft was consistent with the scatter that would be produced by a surface cleanliness of near Level 100. Follow-on BRDF measurements will not be possible, since the SPIRIT III sensor will remain cold and under vacuum throughout spacecraft processing. An internal cryogenic quartz crystal microbalance has been used to monitor molecular redistribution processes that may occur when internal temperatures change during cryogen refills of other cryo-vacuum operations. The CQCM data is easily understood, and will provide a valuable diagnostic during pre-launch processing of the SPIRIT III cryostat.
Chemglaze Z306 flat black polyurethane paint on Chemglaze 9922 epoxy primer is the most predominantly used optically black coating on the MSX spacecraft. All MSX surfaces painted with Chemglaze Z306/9922 were baked at 90 - 100 degree(s)C under high vacuum to reduce the potential outgassing during ground operations and on-orbit. Analytical measurements have been performed to verify the bakeout efficiency, identify the outgassing products, and assist in quantitative predictions of on-orbit outgassing rates and their effects. The bakeout of the SPIRIT III telescope main baffle was monitored using a quartz crystal microbalance (QCM) and residual gas analyzers. The apparent outgassing rates of organic species decreased significantly during the bakeout. Gas chromatography/mass spectrometry (GC/MS) and FTIR analyses of cold trap samples collected at intervals during the bakeout were conducted in order to identify the outgassing species. The outgassing products at 100 degree(s)C of individual samples of G-10 fiberglass epoxy and Chemglaze Z306/9922 were analyzed using GC/MS to determine the source of the various species observed during the bakeout of the baffle. These analyses provide baseline data which will assist in the interpretation of contamination measurements (QCM, witness mirror film accumulations, and residual gas analyses) to be performed during SPIRIT III sensor integration and test.
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