KEYWORDS: Sensors, Contamination, Photonic integrated circuits, Crystals, Temperature metrology, Analog electronics, Data modeling, Quartz, Space telescopes, Space operations
Currently, no accurate models or recent data exist for modeling contamination from spacecraft thrusters to meet the stringent requirements of the International Space Station (ISS). Few flight measurements of contaminant deposition from spacecraft thrusters have been made, and no measurements have been made for angles away from the plume centerline. The Plume Impingement Contamination-II (PIC-II)1 experiment is planned to provide such measurements using quartz crystal microbalances placed into the plume of a Shuttle Orbiter RCS thruster. To this end, the Johns Hopkins University Applied Physics Laboratory (APL) has supported NASA in the development of the PIC-II experiment Flight Electronics Unit known as the Remote Arm TQCM System (RATS), which will measure the contamination in the Shuttle Obiter RCS thruster. The development was based on an ongoing effort between the APL and QCM Research to develop an inexpensive, miniature TQCM controller based on a legacy of QCM controllers developed at the APL. PIC-II will provide substantial improvements over previous systems, including higher resolution, greater flexibility, intensive housekeeping, and in-situ operational control. Details of the experiment hardware and measurement technique are given. The importance of the experiment to the ISS and the general plume contamination community is 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.
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.
Quartz crystal microbalances (QCM) have been used for over twenty years as contamination monitors in space satellites to measure film deposition on sensitive surfaces such optical mirrors, thermal radiators and solar arrays. However, it is only recently that miniature quartz crystal microbalances were used as particle monitors after the QCMs were coated with low outgassing grease to trap and measure the mass of particles impinging on the quartz surfaces. Results of these experiments utilizing 'sticky' QCMs are described for a series of wind- tunnel missile tests.
A particle monitor based on the near forward scattering of light from an AlGaAs laser diode was modified for space flight and proved to be robust and reliable during an actual space launch. Near-field particles could result in large extraneous signals from the IR, visible and UV telescopes on board a spacecraft because of their proximity to the sensors. It is therefore desirable to build a particle monitor to go with optical sensors in order to correlate various particulate events with spacecraft operations, so that their effects on the sensors can be corrected. This device, along with the power supply, associated analog and digital electronics, and mechanical mounting will be described. Particulate measurements during ground testing will be presented.
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