KEYWORDS: Ions, Signal to noise ratio, Spectroscopy, Molecules, Data processing, Contamination, Signal detection, Interference (communication), Adsorption, Mars
The ExoMars 2020 MOMA (Mars Organic Molecule Analyzer) Gas Chromatograph Mass Spectrometer instrument is a key component of the Pasteur life detection payload on the ExoMars 2020 rover mission. As such it is subject to Planetary Protection requirements which include being sufficiently contamination controlled to preclude false positive or false negative results due to contamination. Detailed evaluation of the interaction instrument background and the other performance attributes of the Gas Chromatograph Mass Spectrometer during testing under Mars like conditions of temperature and pressure was carried out. This was the first test of the fully integrated test of the Gas Chromatograph Mass Spectrometer. The data from the testing was evaluated in four different modes of data analysis commonly used for processing gas chromatograph mass spectrometer data. This analysis showed that the instrument was capable of meeting its detection limit requirements. The analysis of the data also showed that the probability of false positives and false negatives within the specified instrument performance capabilities was minimal as evaluated at this time.
The ExoMars 2020 Rover is a life detection mission, and is classified as Planetary Protection (PP) Mission Category IVb, the first IVb mission since the Viking missions. Mars Organic Molecule Analyzer – Mass Spectrometer (MOMA-MS) is a life detection instrument for the rover. To meet the stringent bioburden requirement of 0.03 spore/m2, the MS is subjected to Dry Heat Microbial Reduction (DHMR) to decrease the bioburden from a measured 88 spores/m2 to 0.009 spores/m2. After DHMR, exposure of the sample path must be kept to an absolute minimum and requires aseptic operations. Aseptic operations include determining the safe exposure time based on the surface area of exposure and particle fallout expected in the aseptic ISO class 5 workspace, preparing an aseptic ISO class 5 workspace, and using sterile garments and tools. During the exposure activity the environment is monitored with active and passive fallout for bioburden and real time airborne particle counts. Sterile tools are handled by a two person team so the operator touches only the tool and not the exterior surfaces of the sterilization pouch, and a sterile operating field is established as a safe place to organize tools or parts during the aseptic operations. In cases where aseptic operations are not feasible, localized DHMR is used after exposure. Any breach in the PP cleanliness can necessitate repeating instrument level DHMR, which not only has significant cost and schedule implications, but also is a risk to hardware that is not rated for repeated long exposures to high temperatures.
A revision of a theoretical mechanism proposed last year based upon the known chemical and physical interactions of laser radiation, fused silica, aromatic molecules and environmental factors will be presented, as relates to other proposed mechanisms. This paper specifically addresses the interaction of toluene with 1064nm laser radiation as related to the formation of benzyl radical, and to free radical photochemistry of toluene. This will address specifically, the effects of oxygen and water in the system, the effects of hydroxyl radical in the system, the interpretation of the XPS spectra of laser damaged silica in the presence and absence of aromatic hydrocarbons and the relationship of these points to the photochemistry of silica.
The art of flight quality solid-state laser development is still relatively young, and much is still unknown regarding the
best procedures, components, and packaging required for achieving the maximum possible lifetime and reliability when
deployed in the harsh space environment. One of the most important issues is the limited and unstable supply of quality,
high power diode arrays with significant technological heritage and market lifetime. Since Spectra Diode Labs
Inc. ended their involvement in the pulsed array business in the late 1990's, there has been a flurry of activity from other
manufacturers, but little effort focused on flight quality production. This forces NASA, inevitably, to examine the use of
commercial parts to enable space flight laser designs.
System-level issues such as power cycling, operational derating, duty cycle, and contamination risks to other laser
components are some of the more significant unknown, if unquantifiable, parameters that directly effect transmitter
reliability. Designs and processes can be formulated for the system and the components (including thorough modeling)
to mitigate risk based on the known failures modes as well as lessons learned that GSFC has collected over the past ten
years of space flight operation of lasers.
In addition, knowledge of the potential failure modes related to the system and the components themselves can allow the
qualification testing to be done in an efficient yet, effective manner. Careful test plan development coupled with physics
of failure knowledge will enable cost effect qualification of commercial technology. Presented here will be lessons
learned from space flight experience, brief synopsis of known potential failure modes, mitigation techniques, and options
for testing from the system level to the component level.
Detailed surface chemical analysis of laser induced damage to a Nd:YAG total internal reflection (TIR) slab, in conjunction with knowledge of optical behaviors can provide the identification of not only the damage that occurred, but how it was initiated. Careful evaluation of surface analytical results can provide a great deal more information. Laser damage occurring in high quality optical components at laser intensities well below expected damage thresholds are anomalous. Detailed chemical surface analysis combined with fundamental knowledge of optics provided not only identification of the precipitating mechanism but, identification of issues in optical component manufacture and complex chemical reactions within the affected region. Laser-contaminant, contaminant-contaminant, and contaminant-optic reactions were detected.
Molecular contamination in laser systems presents a significant risk to laser operation. The principle reason for molecular contamination being a significant risk is the lack of knowledge concerning the interactions of the contaminants, optics, laser radiation, and intra-laser environment. A long term instrumented vacuum operation test was carried out to investigate the potential contamination effects in a laser. The test provided information concerning the behavior of the laser operation of a two wavelength 532 and 1064nm q-switched Nd:YAG, the behavior of the residual contamination and residual gases in the vacuum environment. The interactions of the contaminants and the residual gases in the system in the presence of laser radiation are discussed.
The theoretical treatment of laser-induced damage to optical materials has in the past been largely based upon phenomenological observations, empirical treatments and the non-linear effective medium approximation. In some instances such as intrinsic damage thresholds, these approaches show merit. In many other cases, such as those related to contamination, laser optical damage, specific treatment of both matter and energy is required. The base assumptions of some of the more common theories of laser material interactions are discussed and their effects upon the predicted behavior identified. While this paper does not provide a quantitative solution to the issue of laser damage thresholds, it provides physically sound descriptions of interactions and points the way to potential solutions.
NASA is striving to develop a scientific understanding of the universe, the Earth-Sun System and the Earth's response to natural or human-induced changes. Space lasers are vital tools for NASA's missions to advance our understanding of space research and improving our prediction capability for climate, and natural hazards. Unfortunately, several past spaceflight missions that utilized lasers proved to be short-lived and unreliable. In this paper, we are shedding more light on the contamination issue in the absence of gravity. We performed a set of relevant experiments on liquids and subsequently correlated the results to the spaceflight laser environment. We found that in the absence of gravity the contamination plays a major role in spaceflight laser failures. We also proposed a methodology using the adsorption mechanism to be adopted in future spaceflight lasers to minimize the presence of contaminants in the laser compartment.
Space Lasers are vital tools for NASA's space missions and military applications. Although, lasers are highly reliable on the ground, several past space laser missions proved to be short-lived and unreliable. In this communication, we are shedding more light on the contamination and radiation issues, which are the most common causes for optical damages and laser failures in space. At first, we will present results based on the study of liquids and subsequently correlate these results to the particulates of the laser system environment. We present a model explaining how the laser beam traps contaminants against the optical surfaces and cause optical damages and the role of gravity in the process. We also report the results of the second harmonic generation efficiency for nonlinear optical crystals irradiated with high-energy beams of protons. In addition, we are proposing to employ the technique of adsorption to minimize the presence of adsorbing molecules present in the laser compartment.
In high intensity laser systems, molecular contamination represents a risk to the optics. In most situations, molecular contamination is somewhat of a wild card. It is known that it is not required that the contaminant be condensible to initiate damage within a laser system. It is also known that in many cases materials that pass ASTM E-595, are known to precipitate laser optic damage. What has not been known is why. Methods have been developed for the identification, and potential quantitation of trace material emissions that initiate laser optic damage.
A series of laser optics damaged in the presence of molecular contaminants were analyzed. The properties of the base fused silica was determined to undergo changes with lifetimes of greater than two months. The magnitude of the changes is significantly greater than predicted as the maximum limit for this type of change. The changes in the fused silica provide significant insight into the behavior of silica in high intensity laser optical systems.
Many of the investigations of contamination related laser damage to date have been largely phenomenological. These papers can provide some direction in the quest for determining and maintaining adequate laser cleanliness levels. Purely optical analyses of laser contamination effects likewise provide direction. Neither the phenomenological nor the purely classical optical methods provide a solid basis for the determination of a safe or acceptable contamination level. This is borne out by the present state of the art. Investigation of the purely physical, optical, or chemical properties of the contamination is insufficient and incomplete. It is necessary to look at the combined physical, chemical and optical properties of the laser system, which includes the contamination. Determination of some key properties of the laser/contaminant system and their interactions has been carried out and the results are promising.
Laser and instrument systems used for space flight have extreme requirements for cleanliness. Many of these systems specify or require cleanliness target values approaching one monolayer of non-volatile residue (NVR) or even less in some cases. This opens up a completely new series of challenges that are added to the challenges facing contamination control and contamination analysis personnel. As the amount of molecular contamination on a surface approaches zero, the behavior of the contaminant changes. These behavioral changes require knowledge of the surfaces and the contamination beyond whether bulk material is soluble in the solvent. As the thickness of the contamination drops below a few monolayers, the bulk properties become nearly irrelevant. Knowledge of the interactions of the contaminant with the surface becomes critical. This includes both the equilibrium and kinetics of the surface adsorption. The paper will address the fundamental physical, procedural, philosophical, and technical aspects of cleaning surfaces to the monolayer level.
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