Corona discharge events when operating NASA Johnson Space Center's (JSC's) Chamber B could render damage upon test subjects, facility equipment, or test articles within the chamber. Curves have been established that relate the voltages, pressures, and electric gaps that describe the conditions where corona discharge is likely to occur. Applying safety factors, JSC has specified ranges for voltages and pressures that are well outside of where corona discharge is likely. Normal operation of the chamber calls for turning off, or reducing, voltage supplied inside the chamber when the pressure is within this defined corona discharge range. The defined pressure range is 5 X 10 -4 Torr to 50 Torr. While within this range voltage inside the chamber is to be reduced to, or below, 80 Vac or 140 Vdc. Recently an unexpected corona discharge event occurred when it was believed the chamber was at full vacuum. One of the manlocks was also depressurized, having been previously equalized to the main chamber via an equalization (EQ) valve and having its door to the chamber open. After the manlock-to-chamber door was open, the EQ valve was commanded closed. After operations were complete the manlock-to-chamber door was closed. The manlock was then repressurized, at which time a corona discharge event occurred within the main chamber. Investigation showed that the EQ valve, which was believed to be closed, was actually open. Thus, when the manlock was repressurized, atmospheric air was introduced into the main chamber, causing its pressure to rise to within corona discharge range while the test article heater cage was powered with 208 Vac. This paper will discuss in more detail the events leading up to the corona discharge event, and the hardware mitigation steps taken to prevent a corona discharge event from reoccurring. Hardware mitigation improvements include heater cage terminal wiring design features and electrical interlock controls to reduce the 208-Vac operating voltage while in corona discharge range.
The history and development of a ground-based space simulation facility and its current capabilities.
Korea Aerospace Research Institute completed construction of a large test facility to verify the performance of spacecraft electric thrusters in February 2024. The test facility's horizontal vacuum chamber with a diameter of 3.8 meters and a cylinder length of 10 meters features cryogenic disks maintained below 50 K for effective and efficient exhaust of propellants, such as xenon and krypton. For thruster ignition tests at low temperature, a removable thermal shroud (1 meter in diameter by 1 meter long) that can be cooled to -70 °C was installed. In addition, to minimize impact on the thruster by sputtered particles, which would be ejected when discharged heavy ions collide with the chamber inner wall, graphite sheets were applied to the inner area of the chamber within the thruster plume angle. Prior to use, vacuum levels were measured in response to changing flow rates of xenon gas to verify the propellant pumping performance of the test facility. An electric thruster ignition experiment was then performed to confirm the performance of the test facility.
Effective pharmacy compounding practices require controlled environments to ensure the safety of compounded sterile preparations. United States Pharmacopeia General Chapter <797> (USP <797>) provides guidelines to minimize microbial contamination and endotoxins. Factors influencing microbial control include temperature, air change rates, relative humidity (RH), and personnel. Our organization observed increased colony-forming unit growth during humid months, despite maintaining RH below 60%. We hypothesized further RH adjustments may reduce out-of-limit (OOL) results. This study assessed RH's impact on microbial growth in sterile environments. We sought to identify optimal humidity levels to reduce environmental monitoring (EM) OOL incidences and to improve microbial control. We analyzed EM data from 11 compounding cleanrooms during a 15-month period (January 2022 through March 2023). Air and surface samples were collected per USP <797> procedures. Temperature was maintained within 18–20 °C. The study aimed to identify a specific RH cutpoint threshold to reduce OOL results significantly. A total of 732 data points was analyzed using statistical software. The analysis found a significant correlation between RH and OOL results. Among 732 data points, highly pathogenic microorganism OOL results accounted for 48 (6.6%), action level OOL results accounted for 10 (1.4%), and both result types for 3 (0.4%) data points. The odds ratio (OR) for OOL results at RH levels ≥50% was 5.993, with a 95% confidence interval (3.375, 10.642), and a p-value of < .001. At RH levels <50%, the OR was 0.167, indicating an 83.3% reduction in OOL results. We determined an optimal upper limit RH threshold of 50%. Our data further indicate higher OOL recovery during humid months (i.e., months with elevated RH). Targeting RH of 50% improves microbial control in sterile environments. This study confirms reducing RH below the USP <797> threshold of 60% can improve microbial control.
Spacecraft must be tested in acoustic environments by means of reverberant chamber tests (i.e., reverberant field acoustic noise [RFAN] tests) or direct field acoustic noise (DFAN) tests, where many speakers surround the test object. These tests require acoustic control software and matching hardware to drive the speakers with a controlled noise spectrum. Suppliers of such systems and test facilities are sometimes challenged with acoustic standing waves that create hotspots with higher-than-specified sound pressure levels that could damage the device under test (DUT) by exciting structural resonances. As a safety measure to protect the DUT, a response-limiting method (i.e., notching) is applied where critical frequencies in the acoustic spectrum are attenuated to keep the structural response levels limited. This paper will present a detailed overview of a study that analyzes the effects, benefits, and risks of utilizing mechanically coupled notching in both linear and nonlinear responses from mechanically decoupled acoustic environments. Furthermore, notching on structural response channels can invalidate a test with respect to the specified octave test spectrum. A modified true octave band control method is used, which allows attenuation of narrowband frequencies while still meeting the general specification. The general applicability is discussed with respect to a “test like you fly” acoustic testing condition.
Aerosol photometers are widely used to leak test high-efficiency particulate air (HEPA) filters in cleanrooms, containment laboratories and associated devices, and other clean environments, relying on the principle that the photometric response is linearly proportional to the mass concentration of a polydisperse aerosol at a fixed particle size distribution (PSD). Although not characterized in practice, the PSD of the challenge and calibration aerosols is highly likely to vary among job sites and the makes and models of photometers employed, respectively. The disagreement between practice and theory naturally raises the question—does valid filter leak testing depend on the PSD of the challenge and calibration aerosols? To answer the question, we measured the leakage rates of the same set of leaks on a HEPA filter with 1) two challenge aerosols of distinct PSDs (i.e., count median diameters [CMDs] of 202 nm and 229 nm, respectively) using one photometer, and 2) two photometers calibrated with aerosols of distinct PSDs (i.e., CMDs of 212 nm and 175 nm, respectively). By comparing the leakage rates (from 0.0x% to 1.x%) under each condition, it was found that the measurements were not statistically different when varying the challenge aerosols or the calibration aerosols. To understand the independence of valid leakage testing on the PSD of either the challenge or the calibration aerosols, we experimentally confirmed that leaks on HEPA filters did not alter the aerosol PSD from upstream to downstream. As filter leaks are defined as defects on a filter that allow airflow to bypass the filter, it is expected that they do not present any particle capture mechanisms. Yet it is the identical aerosol PSD upstream and downstream of a leak that enables any linear photometer to read the same and valid leakage rate for the leak, irrespective of the compositions of the challenge and calibration aerosols. These theoretical and experimental findings validate several industry practices. First, a properly calibrated photometer performs valid filter leak testing even though the challenge aerosols, although not characterized, are bound to vary from site to site. Second, two photometers, properly calibrated with aerosols of distinct PSDs, yield identical leakage results for the same filter leak. Finally, the two-point (the two extremes of the intended measurement range) calibration is the preferred practice for photometers due to the strict requirement and challenge of achieving consistent aerosol PSD throughout the measurement range in a multipoint calibration, as done in other instruments.
6.5-meter Diameter Large Thermal Vacuum Chamber is a versatile space simulation facility designed and configured to conduct a variety of thermal vacuum qualification tests on satellite payloads. Completed in 2018, the facility layout has been designed to streamline and to simplify test preparation and testing activities. The chamber has a cylindrical configuration and is housed inside a 22-m (72-ft) x 45-m (148-ft) large cleanroom (ISO Class 8) with a usable volume of approximately 200 m 3 (6.5-m diameter x 7.5-m length chamber) or 7056 cu. ft (21-ft diameter x 25-ft length chamber). The system can reach approximately a 5 x 10 -6 mbar vacuum level within 8 hours and has the capability to attain temperature extremes from 100 K to 433 K on its thermal shrouds. The thermal system can handle an approximately 100-kW heat load with 10 K homogeneity at 173 K on the thermal shrouds with a cluster of thermal conditioning units. The facility has 256 dedicated T-type thermocouple channels for temperature monitoring of the payload and systems, such as residual gas analyzers, quartz crystal microbalances, and atmospheric gas analyzers for chamber cleanliness monitoring. The facility also has unique features, such as a precise payload positioning system, a thermal cycling box, a flexi shroud for optimizing the internal chamber test volume, a four-rail system for GSE (i.e., ground support equipment), internal and external work platforms, a fresh air recirculation system, a closed-circuit television monitoring system, and so forth. The facility is equipped with significant liquid nitrogen storage (approximately 400,000 L [105,700 gal.]) and a distribution system (i.e., approximately 2200 m [7200 ft] of vacuum-jacketed super-insulated lines). The complete system is realized with a state-of-the-art control and data acquisition system, and has built-in hot redundancies for critical hardware. It uses a PC-PLC-SCADA-based electrical, instrumentation, control, and monitoring system (i.e., a personal-computer-based, programmable-logic-controller-and-supervisory-control-and-data-acquisition-supported EICMS) for control (operational interface and process monitoring) and elaborate data acquisition. Its unique system configuration is amenable to future augmentations, as well. This paper provides a complete overview of the facility and presents system configuration details, design considerations, realization aspects, and acceptance test results.
This paper will give an overview of a contamination event that happened in the Laboratory for Atmospheric and Space Physics’ largest thermal vacuum chamber, and the methods of cleaning the chamber.
Limited regulatory guidance is available for bioburden levels on product-contact surfaces in nonsterile manufacturing environments. Cleaning procedures that address both product residues and microbial contamination ensure effective contamination control.
With one multi-variable acceleration model family, which is commonly used in real world practice, the distributional stress condition and distributional usage are converted to single-valued equivalent stress condition and single-valued equivalent usage, respectively. The derived single-valued equivalent stress condition is exact solution without approximation. The algorithm with approximation for single-valued equivalent stress condition in more general situations is also discussed. The equivalent usage is derived independently from the stress. These results significantly simplify the reliability analysis of the products subject to the random loading conditions with multiple stress types. The applications in reliability validation test and reliability prediction are discussed.
Mission engineering and reliability engineering are systems engineering disciplines used throughout product development and sustainment of a system. This paper highlights the commonalities and differences between the two disciplines of mission and reliability engineering. Mission engineering generally lacks standardization and precision of analysis due to less guidance documentation, uncertainty, and data limitations. Reliability analysis can improve the results of mission engineering analysis and thus, should be embedded within mission engineering. A recommendation is to include reliability as a component of the system Measures of Success (MOSs), Measures of Effectiveness (MOEs), and Measures of Performance (MOPs). Additional recommendations are centered around how reliability is represented in a mission engineering architecture and determining a logical approach to improve mission engineering decision capability and outcomes. Conclusions focus on an integrated approach to measuring system and mission effectiveness throughout system design and sustainment.
Abstract In today's global environment, accelerated life testing (ALT) is becoming a competitive advantage when time spent from the conceptual stage to final product development needs to be minimized. Using ALT techniques for semiconductors and structural applications has substantial challenges when defining the thermal fatigue life-stress relationship to represent actual field performance. Helpful strategies to address such common problems using ALT are presented for faster ALT planning. Test examples from the refrigeration industry are used for this demonstration. The tests and analyses performed effectively increased the degree of reliability improvement and reduced the total number of test hours, resulting in a shorter design cycle.
Maintaining and improving cleanroom manufacturing operations are required to ensure quality products. In today's world, there are many challenges facing cleanrooms and controlled environments and their support areas. Proper cleaning and sanitization of all cleanrooms and controlled environments are key to maintaining these facilities at the level for which they were designed.
The development of cleanroom standards began in the United States Air Force and has grown into a global industry with the founding of ISO Technical Committee 209, Cleanrooms and associated controlled environments. The Institute of Environmental Sciences and Technology has played a vital role from the beginning.
Abstract For implementing force limiting during a shaker vibration test it is often necessary to add adaptive fixturing above the force transducers as an interface to the test article mount points. Since the measured force contribution due to this added mass influences the force-limited input notching, the standard recommended practice is to limit adaptive fixturing mass to 10% of the total mass above the force transducers to minimize the notching error. However, it is sometimes difficult to design interface fixturing that can meet that mass-limiting criterion while maintaining the requisite rigidity to avoid dynamic influence of the fixturing. This paper develops a quantification of the notching error due to adaptive fixturing mass, along with nominal force sensitivity and mass measurement error, and recommends approaches for reducing or otherwise evaluating the effect of this error to aid in fixturing design that may exceed the 10% mass criterion.
ISO/TC 209 released its first Technical Report in 2023 to help clarify information regarding airborne particle counting provided in Parts 1 and 2 of ISO 14644. It also intends to dispel observed issues of misuse and misunderstanding of key sections of these standards with regard to airborne particle sampling.
The current set of tools taught and deployed by the Six Sigma Black Belts and professionals primarily focus on Statistical Process Control (SPC), Process Capability, correlation, multiple regression etc. However, reliability has gained and is gaining increasing importance in business priorities. The conventional Six Sigma Approach can therefore be strengthened by adding a set of reliability engineering tools to improve its effectiveness. We can call this Reliability Focused Six Sigma or RFSS. In this unique RFSS approach, the conventional Six Sigma tools can be augmented with reliability tools such as life data analysis, warranty data analysis, Robust Design, Shainin Tools: Paired Comparison, Component Search, Reliability Testing, Tolerance Stack-up Analysis etc.
Abstract ISO TC 209 has developed a series of standards for cleanrooms and associated controlled environments. To date, 19 ISO 14644 and 14698 standards have been published. With respect to particles, the focus has been on airborne particles up to 5 micrometers. In many applications, larger particles--even visible particles--need to be controlled. ISO 14644-17 ‘Particle deposition rate applications’ provides guidance on the control of macroparticles. Background information with a personal view is given. The new standard offers control tools for many industries.
It is my privilege to recognize all the thousands of experienced people who, during the past 60 years, developed the technical documents, trained new generations of specialists, and provided the best solutions for environmentally-controlled facilities and processes. Future generations, worldwide, will benefit as the requirements for revised standards are defined to meet the challenges. In my long career in the fields of ultra-clean spaces, ultra-pure water, chemicals and gasses required in laboratory and process applications, I can appreciate the partnerships that have been successful for their missions. The Institute of Environmental Sciences and Technology (IEST) will continue to be the leader. Thank you IEST and all those that volunteered to keep the clean room standards updated with technology.
Abstract Our team has developed and tested a solid-state solar simulating lamp for use with space simulation vacuum chambers. Unlike traditional lamps, our system uses solid-state light-emitting diodes (LEDs) to generate the light. The emission wavelengths of the LEDs can be selected and controlled so that their combined output better approximates the profile of the solar spectrum. Though our system can accommodate visual or infrared LEDs, we focused our efforts on generating ultraviolet (UV) light in the 265-400 nanometer (nm) range. Compared to deuterium lamps, the LEDs are advantageous because they can be selected and controlled such that the output profile of the lamp better approximates the irradiance of the sun. Deuterium lamps are most intense at 200 nm with their intensity decreasing by more than 90% as the spectrum approaches 400 nm. Light from the sun is of relatively low intensity in the 200-250 nm range, but its intensity increases by more than 2000% from 250 nm to 400 nm. The modular design of our lamp (Figure 1) allows it to individually control the current to each of 80 strings of LEDs, totaling to 904 individual UV LEDs in a compact, circular pattern designed to shine through an 11.5-inch-diameter chamber window. The light from each LED is collimated using a 6-millimeter-diameter silica ball lens, and the array has a combined nominal optical power output of 90 watts (W). Because UV LEDs are relatively inefficient, creating the 90W of optical power requires 1800W of electrical power. The waste heat from the LEDs is managed by a liquid-cooled plate and external chiller.
