Bob E. Wood

Cryogenic quartz crystal microbalance-characterization and calibration for Midcourse Space Experiment (MSX) program

This paper presents the results of an investigation of the operational characteristics of two cryogenically cooled quartz crystal microbalances (CQCM) which are flight units for the Midcourse Space Experiment (MSX) program. The units were operated at temperatures that ranged from 15 K up to 300 K. During the course of this investigation, the CQCMs were temperature cycled over this range for 5 complete warmup/cooldown cycles using warmup rates of 2.5 K/min and 1.0 K/min. There was concern over stop/start operations on orbit wherein the CQCM power could be turned off for some time. The CQCMs were cycled in this manner to determine the return frequency variations after power restoration. A three week drift test at 15 K was carried out to determine the drift in CQCM frequency with time. Temperature effects of the heat sink attached to the CQCM base were also determined by varying this temperature. Finally, films of nitrogen, oxygen, carbon dioxide, and water were deposited at the 15 K base temperature, and a thermogravimetric analysis was done for each of the gases condensed, both for individual gases and for gas mixtures. The results of these analyses will be used to interpret on-orbit analysis of contaminants that are condensed during operation of the SPIRIT III telescope on the MSX satellite.

Quartz crystal microbalance (QCM) flight measurements of contamination on the MSX satellite

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

Effects of cryocontaminants on cryogenic superpolished mirror and superpolished quartz crystal microbalance

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.

Long-term observations of the particle environment surrounding the MSX spacecraft

Many systems contain cryogenic optical systems that operate at temperatures where gases such as nitrogen, oxygen, carbon dioxide, and water will condense. This study presents experimental results of the effects of these gases condensed on highly polished (superpolished) mirror surfaces cooled to temperatures as low as 15 K under vacuum conditions. Using these gases as contaminants, the bidirectional reflectance distribution function was obtained at a wavelength of 0.6328 micron for various contaminant film thicknesses up to 8 microns. Most of the data were obtained using as the mirror surface the superpolished sense crystal of a previously developed quartz crystal microbalance (SPQCM). The SPQCM allowed the mass of the actual contaminant layer to be measured directly.

Measurement of long-term outgassing from the materials used on the MSX spacecraft

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.

Optical effects of condensates on cryogenic mirrors for the Midcourse Space Experiment (MSX)

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 sensors primary goal was to monitor the early mission (less than one week) ambient pressure surrounding the spacecrafts 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.

Update of the midcourse space experiment (MSX) satellite measurements of contaminant films using QCMs

The effect of condensates on optical surfaces is a continuing concern for space-based optical systems such as the Midcourse Space Experiment. Many such systems contain cryogenic optical surfaces that operate on low temperatures where gases such as nitrogen, oxygen, carbon dioxide, and water will condense. This study presents the effects of these gases on mirror surfaces at temperatures as low as 15 K under high vacuum conditions. The bidirectional reflectance distribution function was determined for these condensates in various film thicknesses up to 8 mm. Optical scatter, thickness, and density measurements were obtained simultaneously with the superpolished quartz crystal microbalance (SPQCM). Correlations between thin film deposition, as determined by the SPQCM, and the expected increase in optical scatter are shown. These correlations are important in determining launch decisions in cases where various degrees of condensation may have occurred on cryogenic optical systems during ground processing.

Satellite contamination and materials outgassing effects databases

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

QCM flight measurements of contaminant films and their effect on midcourse space experiment (MSX) satellite optics

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.

Updated Version of the NASA SEE Program Spacecraft Contamination and Materials Outgassing Effect s Knowledgebase

This paper describes a program for consolidating data from quartz crystal microbalances (QCMs) that will enable one to rapidly locate previous measurements on specific materials and data from past space flight experiments. When complete, the databases will contain information on materials outgassing obtained using the ASTM-E-1559 standard, and flight observations of mass accumulations. Once established, these databases will be available to the entire community and will provide a valuable source of material outgassing information. The data should be useful to those working in the Contamination area for mission design and materials specification. Data are being accumulated from both national and international sources. The space flight database will include data from past NASA missions, as well as DOD [including the BMDO-sponsored Mid-course Space Experiment (MSX) program], Canadian Space Agency, European Space Agency, Russian MIR space station, and eventually, the International Space Station. A website is being generated which will be the vehicle for storing the data that are accumulated. Once completed, the databases will be managed by the NASA/Space and Environmental Effects (SEE) Program Office at the Marshall Space Flight Center in Huntsville, Alabama.