An Analysis of the Precursor Measurements of Mars Needed to Reduce the Risk of the First Human Mission to Mars
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The specific objectives in the area of Biohazard / Planetary Protection were to:
3.1.2 Risks The most significant risk identified by the Biohazard Focus Team is that associated with the possibility of transporting a replicating life form to Earth, where it is found to have a negative effect on some aspect of the Earth’s ecosystem (Risk #3 in Table 1). This is known in the planetary protection discipline as “back contamination”. By definition, risks are a combination of probability and consequences. In the case of the back contamination risk, most scientists would agree that the probability of a negative consequence is very low (but as summarized by the Space Studies Board, 1997, “non-zero”), but the consequences could potentially be very large. A related, relatively low risk derives from martian life forms released in the surface habitat. Such life forms could pose a health hazard to the crew on Mars. Since the astronauts who visit the martian surface are assumed to be coming back to Earth (and in this sense are an extension of the Earth’s biosphere), the risk of their infection by martian organisms is included within this risk. A second risk identified by the Biohazard Focus Team is that associated with Planetary Protection “forward contamination” – the risk of terrestrial life transported to Mars. One concern focuses on local or widespread contamination of the martian surface, leading to possible false positive indications of life on Mars (Risk #8 in Table 1). A related risk, with lower consequences, concerns round-trip terrestrial life forms returned to Earth upon completion of the human mission. This could also lead to false positive indications of life on Mars. 3.1.3 Investigations to Address Risk #3 – Martian Life Transported to Earth Does martian life exist? First of all, a consensus finding of the MHP SSG is that it is not realistic to assume that a returning human mission that has visited the martian surface will have no uncontained martian material associated with it. This would mean no dust on the outside of the spacecraft, in the air filters, in the airlocks, on the outside of sample containment vessels, or anywhere!! Finding an engineering solution to this would be too complex (and the complexity would add a different kind of risk) and too expensive. Thus, the precursor information of most value is whether the dust and other martian particulates that would be present in or on a returning spacecraft (other than deliberately collected samples, which can be held in sealed containers) have life forms associated with them, and if so, whether that life is hazardous. Fortunately, answering this question does not require proof that extant life is absent everywhere on Mars. That (and its inverse question, is life present, and if so where) are very large questions that lie at the heart of the Mars Exploration Program (MEPAG’s Goal I), and it may take many missions over an extended period of time to answer. There could well be environmental niches (e.g. the deep subsurface) that are occupied by life, but for which there is no transport mechanism to the human landing site. KEY BIOHAZARD QUESTIONS: The Biohazard Focus Team concluded that the following two questions need to be answered in the negative in order for the mission to be judged free, to within acceptable risk standards, of biohazards:
In situ vs. sample return investigationsThe only quantitative data to date are derived from the Viking lander life detection [Horowitz, 1986 and references therein] and gas chromatograph – mass spectrometer experiments [Biemann et al., 1977]. These results are generally interpreted to indicate that replicating microbial life is rare or absent in the surface soil at two widely separated locations on Mars, and further that these soils do not contain organic compounds at abundances above a detection limit of 1 ppb. The accepted explanations for these results encompass the high levels of solar ultraviolet radiation and the apparent oxidizing conditions encountered in the surface soil [Klein et al., 1992]. However, the Viking results do not address the possibility of martian life at concentrations below detection limits in the soil, nor the possibility of more abundant life in other locations on or below the surface. The Viking experience illustrates the striking challenge facing any attempt to discover martian life via in situ analysis—a definitive positive result could be obtained (if the experiment was designed correctly), but it will be impossible to obtain a definitive negative result, since there would always be questions about whether we used the right life detection test. We need definitive negative answers to the Key Biohazard Questions listed above. In the planning (approximately 2000-2002) for the receipt of contained martian samples returned by a hypothetical round-trip robotic mission, a major and well-designed effort was put into defining the tests that would allow professionals who are responsible for protecting public safety to make a consensus decision about whether or not the samples are safe with respect to the possibility of biohazards [Rummel et al., 2002]. The advantage of investigations based on sample return is that the full power of analytic instrumentation that exists on Earth can be brought to bear, complex sample preparation procedures can be carried out, tests involving mechanical difficulty and/or live organisms can be attempted, detailed systems of positive and negative control standards can be established, and early unanticipated results can be followed up with a revised analysis plan. The outcome of these discussions was that a first draft large (but defined) list of tests was constructed. By definition, a sample that passes those tests can be interpreted to be safe. This is exactly the same outcome needed for the Key Biohazard Questions listed above—we need a definitive negative answer. For this reason, the Biohazard Focus Team has concluded that investigations based on sample return will be required to achieve answers with sufficient confidence to at least Question Qa. Moreover, since Qa involves a global transport mechanism, a sample from anywhere on Mars that the wind blows would be sufficient to answer the question. An issue for Question Qb is one of sampling significance. It will not be possible to know exactly where a human EVA might plan to go, and to pre-sample everywhere along that path. Fortunately, employing the concept of geologically based environments, it is possible to define larger entities within which a sample can be assumed to be representative. These environments include, as a minimum, the surface soil and the atmosphere. The human crews could also come in contact with subsurface material at depths below the (UV-irradiated, oxidizing) surface layer or in rock or ice-rich materials not sampled by Viking [Space Studies Board, 2002a]. In addition, Mars has different geological terrains, and future missions may define zones with different biological potentials. The complete definition of these environments is not necessary at this time, and can be deferred to future workers who will have more complete information. However, the Biohazard Focus Team has concluded that as long as we have a definitive negative answer to Question Qa (by means of sample return), it may be possible to design screening investigations to answer Question Qb by in situ means. Measurements could include:
If martian life is found, is it hazardous? If martian life is found in any sample, that life must be assumed hazardous until proven otherwise [Space Studies Board, 1997; 2002b]. Hazard determination is complex, and involves the understanding of possible hazard to Earth’s biosphere, crew health, and potential spacecraft and habitat equipment and materials. These determinations may require extensive experiments, which would be carried out in laboratories on Earth. This assessment must, at a minimum, satisfy the recommendations of “A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth” [Rummel et al., 2002]. 3.1.4 Investigations to Address Risk #8 – Terrestrial Life Transported to Mars Can terrestrial life survive and reproduce on the martian surface? Important questions for a human mission involve the survival and reproduction of terrestrial microorganisms on the martian surface. A key corollary is to determine the rate of destruction of organic material by the martian surface environment. Many details of these questions can, and should, be addressed in terrestrial simulation laboratories, rather than by deliberately placing terrestrial organisms on the martian surface. Can terrestrial life, or its remains, be dispersed on Mars ? This question addresses a wide variety of dispersal mechanisms, many of which are being investigated in the existing Mars science program and in recommendations for other Focus Groups. For instance, it will be important to determine the mechanisms and rates of martian surface aeolian processes which disburse organic contaminants. It will also be important to determine the mechanisms of transport of surface organic contaminants into the martian subsurface, and in particular, into a martian aquifer. A parallel study, currently being addressed by the Mars Technology Program Planetary Protection effort, seeks to determine the adhesion characteristics of organic contaminants on landed mission elements, and the conditions and rates under which these contaminants are transferred to the martian environment. FINDING: PROPOSED INVESTIGATION AND MEASUREMENTS1C. Determine if each martian site to be visited by humans is free, to within acceptable risk standards, of biohazards which may have adverse effects on humans and other terrestrial species. Sampling into the subsurface for this investigation must extend to the maximum depth to which the human mission may come into contact with uncontained martian material. Measurements:
3.1.5 Measurements to be made in Earth Laboratories The Biohazard Focus Group identified and prioritized measurements to be made in Earth laboratories to address the highest risks. The clear priority will be assays made on samples collected on Mars and brought to Earth by robotic missions. Representative samples of the atmosphere, dust, near-surface soil, deep soil, rock and ice must be tested for evidence of martian life [Space Studies Board, 1997]. That life, if found, must be fully characterized, and its potential for biological hazard must be determined. Current recommendations for measurements to test for evidence of life and biological hazard are contained in of “A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth” [Rummel et al., 2002]. Other measurements, important to forward Planetary Protection, should be conducted in simulated Mars environments. Terrestrial microorganisms should be tested for evidence of survival and genetic adaptation under simulated martian conditions [Schuerger et al., 2003]. Finally, the potential for forward contamination by robotic and human missions must be understood. Microbial assays should be undertaken to fully characterize the microbial populations of spacecraft assembly cleanrooms and to fully characterize the microbial populations shed by humans [Venkateswaran et al., 2002]. 3.1.6 Measurements to be made at Mars The biohazard and planetary protection risks to a human mission depend strongly on whether, and when, evidence of martian life is found. Measurements by precursor missions can reduce uncertainty and, to an extent, risk in either case. FINDING: PROPOSED INVESTIGATION AND MEASUREMENTS 4. Determine the processes by which terrestrial microbial life, or its remains, is dispersed and/or destroyed on Mars (including within ISRU-related water deposits), the rates and scale of these processes, and the potential impact on future scientific investigations. Measurements:
Before martian life is found Chemical and isotopic indications of possible martian life can be measured in the martian atmosphere, dust, near-surface soil, deep soil, rock and ice at any landing site, to determine if such indications are widespread or localized. Such measurements were initially attempted by the Viking gas chromatograph - mass spectrometers [Biemann et al., 1977], and improved measurements should be possible using the instruments on the Mars Science Laboratory. The remote sensing suite on Mars Express is already producing maps of minerals, including clays and hydrates, that are often found in terrestrial localities affected by hydrocarbons. The 2005 Mars Reconnaissance Orbiter, with extremely high resolution and hyperspectral imaging, may permit confident identification of altered minerals and fossil hot springs. Evidence for the products of metabolism can also be measured in the atmosphere, dust, near-surface soil, deep soil, rock and ice at any landing site to determine if metabolizing organisms are widespread or localized. Such measurements were initially attempted by the Viking life detection experiments. None of the spacecraft currently at Mars, nor those planned for the next decade, has the capability to improve on these measurements. Flight experiments to measure the metabolism of unknown martian organisms do not appear to be justified until those organisms are shown to exist in returned samples. These measurements are assumed to be within the purview of a future Mars Science Program. If martian life is found In the event that in situ investigations or a sample return mission provides evidence for martian life, subsequent investigations can be targeted to the characteristics of that life. Prior to a human mission it would be imperative to test for evidence of the discovered martian life and possible biohazards via robotic spacecraft in the specific environments to be encountered by human crews.
3.2.1 Introduction The martian atmosphere is the origin of many possible hazards to both humans and equipment. The unknown thermodynamic properties of the bulk gas fluid, including unexpected turbulence in the near-surface boundary layer [Zurek et al., 1992], represent risks during vehicle entry, descent and landing (EDL). Major dust storms may also affect EDL and adversely affect a human explorer’s ability to perform extravehicular activities (EVAs). More recent laboratory [Eden and Vonnegut, 1973] and terrestrial desert studies [Renno et al., 2004] indicate that triboelectric effects within dust storms can give rise to large electric fields which might prove hazardous to both explorers and equipment. The Atmosphere Focus Team collected such hazards and assessed the likelihood and consequences of their risks. The results are included in this section. The scope considered by the Atmosphere Focus Team includes all atmospheric risks to the success of a human mission from the ground level to the ionosphere. Discussions included variations in atmospheric parameters that affect flight and surface activities, electrical effects of the atmosphere, photochemistry, dust storms, communication and other topics.
Table 2 indicates the primary risks anticipated to human explorers. The Atmosphere Focus Team was in unanimous agreement that the primary atmospheric risks lies in the EDL and TAO periods, when vehicles are susceptible to turbulent wind forces and atmospheric density anomalies that can alter planned trajectories. Other high rated risks include dust storm electricity generation/discharge and surface operations during dust storms; these are included primarily because so little information currently exists regarding the phenomena, making great uncertainty in any assessment and mitigation plan.
Table 2 also lists the current state of knowledge for the top-level atmospheric risks. It is noted that in Investigation (1), (2), and (3), the information set is not complete enough (or non-existent in some cases) to initiate an educated hazard assessment and mitigation plan. 3.2.4 Desired Future State of Knowledge Table 2 lists the recommended state of the investigations being considered by the Atmosphere Focus Team. Note that in most cases, there is a distinct mismatch between the requirements to understand a hazard as represented in the recommended state of knowledge and the current knowledge base. Table 2. Current and Recommended Knowledge for Atmospheric Investigations
3.2.5 Investigations, Measurements, and Priorities to Reduce Risk(s) and/or Costs3.2.5.1 Investigations and Measurements The green-colored insets identify the Atmosphere Focus Team’s top-rated investigations and associated measurements. The three primary investigations outlined include (as numbered from composite list in Executive Summary):
The Atmosphere Focus Team recognizes that meteorological effects of dust storms are included in both Investigation 1B and 7. While it is tempting to merge these two investigations, the dust storm risk to human explorers during EDL is considered much greater (inflated, highly turbulent atmosphere) than the dust storm risk to humans already on the ground (limited visibility). Hence, dust storm ground-level effects have been separated from those of EDL. 3.2.5.2 Risk Mitigation and Reduction The Atmosphere Focus Team identified five major categories of risk to a human exploration to Mars (Table 2), and a description of the category and mitigation strategy is presented. 1.Wind shear, turbulence, and density anomalies that may create uncompensatable trajectory offsets during EDL and TAO (Risk #2 in Table 1). Unexpected fluid variations are a concern, primarily in two regions: between 30-60 km and 0-20 km. The region between 30-60 km is a critical region for aerocapture, where the dynamic pressures of an incoming body are the greatest, and maximum acceleration occurs. A density miscalculation in this region can lead to both an offset in anticipated landing location and/or higher than expected descent velocities. Given a direct entry scenario for a human mission, accurate densities in this region are critical to the safety of the crew. The region between 0-20 km contains the highly variable planetary boundary layer. During daytime, the surface heats the lower atmosphere (with cooler air above) creating a naturally unstable situation [Zurek et al., 1992]. These instabilities can manifest themselves as convective systems with both turbulence and shear wind flows. Unforeseen increases in topographically-driven winds (e.g., katabatic winds) can also create unexpected shears. As a result, the incoming vehicle (now moving relatively slowly for precision landing) may experience oscillations, a change in orientation, and/or large wind drift offsets. During the MER/Spirit EDL, lower-than-modeled middle atmosphere densities and unexpected oscillations near parachute deployment occurred that nearly exceeded safe ranges. To mitigate this situation, the Atmosphere Focus Team suggests a strategy parallel to the study of terrestrial weather, where forecasts are derived based upon advanced modeling, but using timely measurements to both set the initial conditions and in validation. The primary objective is to improve and enhance the martian global circulation models (GCMs) and mesoscale models, so that forecasting can occur to derive the mean state and variability in atmospheric conditions for EDL. First, in situ meteorological V, T, and during EDL and at the surface (lander package) should be a standard measurement obtained on every future landed mission. This recommendation extends to the upcoming MSL opportunity. Regarding EDL measurements, the number of profiles obtained between the present and a 2030 human mission would greatly improve the data set already available [Seiff and Kirk, 1977; Magalhaes et al., 1999] for model validation/initiation (by over a factor of 2). Regarding surface/near-surface measurements, long-term measurements are critical in setting accurate model initial conditions of the surface heat energy driver responsible for lower/middle atmosphere instabilities. Landed packages can also remotely sense the structure and turbulence in the boundary layer above [Smith et al., 2004], thereby linking this surface heat energy to its associated boundary layer turbulence. Second, to obtain complete coverage in space and time, an orbital remote-sensing weather station is recommended to obtain vertical profiles of V, T, and around the globe with high temporal and spatial resolution, particularly emphasizing heights between 0-20 km and 30-60 km. Orbital remote sensing techniques to derive the atmospheric state at ground and regions from the ground to 20 km are evolving. Remote sensing of winds in the boundary layer will require a separate development effort. Landed remote sensing tools exist to measure thermal activity [Smith et al., 2004] but a development effort is required to obtain independent wind measurements. These measurements are recommended to make the forecasting tools (the circulation models) as accurate as possible. Consequently, a parallel effort is recommended for advancing the model capabilities, including GCM improvement in resolution and in the incorporation of modeling to greater heights (preferable surface to > 100 km). Mesoscale models require improvement in realistic boundary conditions that match the measurements and integrate into larger GCMs. Implicitly incorporated into these recommendations is the collection of atmospheric state and variability during unstable dust storms. Such storms give rise to lower/middle atmosphere temperature increases that inflate the atmosphere (even measured above 100 km altitude) and are a source of instability-related fluid waves and turbulence. Numerical models need to predict the turbulence within and in the vicinity of more violent, unstable dust storms. During any actual human EDL in 2030, the Atmosphere Focus Team suggests bringing all available assets to bear, with an orbital platform providing the most timely density and wind profiles, along with numerical models which fill in coverage and identify potentially unstable atmospheric situations based on the recent remote-sensed profiles in the landing site region. Finally, in analogy to launch preparation from Earth, the Atmosphere Focus Team suggests a pre-descent “weather sounding probe” be deployed just prior to human entry, this sent along the identical path anticipated for the human-containing vehicle to determine regions of high variability along the descent path. For the return trip, pre-ascent weather probes can be sent from ground upward to derive high altitude meteorological conditions before launch from Mars. The Atmosphere Focus Team recognizes that the recommended measurement and modeling efforts must be initiated at the earliest opportunity in order to incorporate the full range of expected atmospheric variations into the EDL system design and testing. Requirements for EDL design have to be formulated much earlier than the actual 2030 human mission, thus supporting measurements in 1B should be obtained prior to design initiation. This requires that the orbital meteorological asset be robustly built in order to remain at Mars from the pre-EDL FINDING: PROPOSED INVESTIGATION AND MEASUREMENTS 1B. Determine the atmospheric fluid variations from ground to >90 km that affect EDL and TAO including both ambient conditions and dust storms. Measurements:
Particular emphasis on measurements between 0-20 km to quantify boundary layer wind and turbulence and 30-60 km where vehicle dynamic pressure is large.
Opacity, visible, depth 0.2-10, dtau = 0.1, once every 10 min design period through the actual implementation of EDL and/or the possibility of sending successive integrated remote-sensing meteorological systems on successive orbiters. 2. Dust storm electrification may cause arcing, affecting TAO (Risk #6 in Table 1). Based on laboratory studies and terrestrial desert tests, there is a growing body of evidence that dust devils and storms may develop dipole-like electric field structures similar in nature to terrestrial thunderstorms [Farrell et al., 2004]. Further, the field strengths may approach the local breakdown field strength of the martian atmosphere, leading to discharges [Melnik and Parrot, 1998]. A hazard during the vulnerable human return launch from Mars would be a lightning strike to the ascending vehicle. Apollo 12 suffered a lightning strike at launch, upsetting the navigation and electrical system. During human occupation of Mars, dust storm discharges and induced electrostatic effects may also force human explorers to seek shelter, reducing EVA time, habitat maintenance, etc. Mitigation strategies include avoidance of aeolian dust clouds both at launch and during human EVA periods. However, to date, there are no measurements of martian atmospheric electricity to evaluate the consequences of the proposed risk. The Atmosphere Focus Team suggests placing an atmospheric electricity (DC and AC E-fields, conductivity) package on at least one future landed missions to a FINDING: PROPOSED INVESTIGATION AND MEASUREMENTS (cont.)
Note particular emphasis on measurements between 0-20 km to quantify boundary layer wind and turbulence and 30-60 km where vehicle dynamic pressure is large.
Note: We have not reached agreement on the minimum number of atmospheric measurements described above, but it would be prudent to instrument all Mars atmospheric flight missions to extract required vehicle design and environment information. Our current understanding of the atmosphere comes primarily from orbital measurements, a small number of surface meteorology stations and a few entry profiles. Each landed mission to Mars has the potential to gather data which will significantly improve our models of the martian atmosphere and its variability. It is thus desired that each opportunity be used to its fullest potential to gather atmospheric data. Reconstructing atmospheric dynamics from tracking data is useful but insufficient. Properly instrumenting entry vehicles is required. ssess the risk. 3. During crew occupation and EVA, dust storms may affect visibility, restrict departure times, limit EVAs, and hamper regular habitat maintenance (Risk #9 in Table 1). Operations in a major dust storm can be stalled due to obscured visibility and adhering dust. On Mars, global dust storms can last for 3 months [Zurek et al., 1992], with possible crew internment for long periods (especially if there is a passage of high opacity core regions). Mitigation strategies include designing low maintenance habitats and EVA systems and/or avoiding human occupation at times when storms are expected. The ability to predict the large seasonal storms has greatly improved with MGS/TES, but regional and local storms appear quasi-random [Cantor, 2003]. To assess the risk, lander meteorological packages (like those suggested in point 1 above) should also have the capability to assess dust density/opacity. A remote-sensing orbital weather station (like that described in point 1 above) would have the capability to monitor dust storm frequency, size, occurrence and thermodynamic characteristics over a long baseline, and act to alert surface-stationed astronauts of impending storm activity. 4 FINDING: PROPOSED INVESTIGATION AND MEASUREMENTS 3. Derive the basic measurements of atmospheric electricity that affects TAO and human occupation. Measurements:
. Photochemical reactions in the atmosphere may create chemically-reactive gases that lead to corrosive or toxic environments (Risk #14 in Table 1). Landed missions have yet to fail because of a corrosive/reactive agent, but certain locations and seasons may favor the increased production of reactive chemicals [Delory et al., 2005; Atreya et al., 2005]. A mitigation strategy is to avoid occupation and EVA during chemically active periods and/or active locations. Special non-reactive coverings may have to be designed for EVA suites and habitats. Mass spectrometers placed at various locations on the surface can monitor the presence of reactive chemicals that are produced beyond trace levels. Orbital platforms are not considered effective since measured columnar densities may not indicate concentration levels at the surface. 5. Atmospheric conditions on Mars, at times, may lead to communication losses and navigation anomalies (Risk #16 in Table 1). Ionospheric variations/scintillations can disrupt RF propagation [Safaeinili et al., 2003] and electrical activity (discharges) in dust storms [Renno et al., 2003] can be a source of RF interference. Strategies are already applied to mitigate ionospheric disruption by transmitting at frequencies well above the peak ionospheric plasma frequency. Mitigation strategies in electric dust storms may also be the application of judicious choice in frequency selection to avoid noisy, contaminated frequency bands. However, fundamental information of dust storms RF emission is suggested to make this choice. An atmospheric electricity package with AC E-field sensing capability (like that suggested in point 2) is capable of deriving the intrinsic RF emission within a dust storm. 3.2.6 Impact on MEPAG Goal IV and Changes in CriticalityThe primary atmosphere-related investigations, those of understanding the fluid properties of the atmosphere and atmospheric electricity, remain high priorities in both original and latest version of the MEPAG goals. The criticality of both has increased slightly, with fluid variations being considered the highest priority in the overall Goal IV investigations (Investigation 1B). One reasons for the change of criticality was the difficult EDLs experienced by the robotic MERs, which punctuated the need for timely and accurate measurements of the atmospheric state at descent.
T FINDING: PROPOSED INVESTIGATION AND MEASUREMENTS 7. Determine the meteorological properties of dust storms at ground level that affect human occupation and EVA. Measurements:
he Atmosphere Focus Team recommends research and technology investments in remote sensing meteorological tools, particularly methods for (1) orbital remote-sensing of atmospheric winds at all altitudes independently of temperature/density-derived methods, (2) orbital remote-sense of the surface and near surface (0-20 km) V, T, and , especially in the turbulent boundary layer, and (3) landed remote sensing of vertical V and T profiles up to 5 km. The Atmosphere Focus Team also recommends further development of GCM and mesoscale codes, including improvements in resolution and spatial coverage (particularly height).
3.3.1 Introduction Apollo astronauts learned first hand how problems with dust impact lunar surface missions [NASA, 1969a; 1969b; 1971a; 1971b; 1972; 1973]. After three days, lunar dust contamination on EVA suit bearings led to such great difficulty in movement that another EVA would not have been possible. Dust clinging to EVA suits was transported into the Lunar Module [Connors, 1994]. During the return trip to Earth, when micro gravity was reestablished, the dust became airborne and floated through the cabin. Crews inhaled the dust and it irritated their eyes [Kennedy and Harris, 1992]. Some mechanical systems aboard the spacecraft were damaged due to dust contamination. Study results obtained by robotic martian missions indicate that martian surface soil may be oxidative and reactive [Zent and McKay, 1994]. Exposures to the reactive martian dust may pose an even greater concern to crew health and integrity of the mechanical systems. As NASA embarks on planetary surface missions to support its Exploration Vision, the effects of these extraterrestrial dusts must be well understood and systems must be designed to operate reliably and protect the crew in the dusty environments of the Moon and Mars [National Research Council, 2002]. The Dust/Soil Focus Team evaluated potential hazards to human support surface systems caused by the presence of martian dust and developed recommended investigations and measurements by MHP missions to mitigate the risks. Impacts on MEPAG Goal IV In order to provide guidance to Mars Human Precursor mission designers to gather information needed to bring our understanding of martian dust, soil and toxicology to the recommended state of knowledge, the Dust/Soil Focus Team recommends modifying Goal IV. Investigation 2, “Chemical and toxicological properties”, should be expanded to include specific measurements. In addition, dust and soil should be broken out of investigation 5, “engineering properties of the martian surface, and characterize topography, and other environment characteristics and measurements.” Specific recommendations are provided in the Precursor Investigations topic in this section. 3.3.2 Risks and Priorities The Dust/Soil Focus Team identified four major hazardous conditions associated with martian dust; adhesion and accumulation, inhalation and ingestion, dust storms and biology (Table 1). The Dust/Soil Focus Team then developed risk statements, consequence, likelihood and context [Murphy et al., 1996]. (Dust storm risks were addressed by the Atmosphere Focus Team and Biohazard risks were addressed by the Biohazard Focus Team). The Dust/Soil Focus Team identified numerous risks that were subsets of higher level risks. The higher level risks are shown below. The lower level risks are labeled “subset risks”. 3.3.3 Primary Risks Dust Adherence and Accumulation Failure Due to Abrasion and Accumulation (Risk #4 in Table 1): Risk Statement: If abrasion and adhesion properties of martian dust are not understood, systems may not be properly designed. If critical mechanical systems fail due to abrasion and adhesion of dust accumulated on systems, loss of science, injury or loss of crew member(s) may result. Consequences: 3-5, loss of science, severe injury or loss of crew. Likelihood: 5, surface life support systems do not yet exist to handle abrasion and adhesion of dust in martian environments. Context: Abrasive properties of dust accumulating on surfaces and penetrating systems could lead to failure of air generation and delivery, carbon dioxide removal, fire detection (causing false alarms) and suppression, EVA suits, rovers, windows, visors, and optics. If critical life support systems completely fail, rescue or mission termination is not feasible due to the laws of orbital mechanics. Subset Risks:
Failure of Electrical Systems (Risk #4 in Table 1): Risk Statement: If electrostatic properties of martian dust are not understood systems may not be properly designed. If critical electrical life-safety systems fail due to dust accumulation on systems, injury or loss of crew member(s), or loss of science would result. Consequences: 3-5, loss of science, severe injury or loss of crew. Likelihood: 5, surface life support systems do not yet exist to handle electrical effects of the dust in martian environments. Context: Electrical properties of dust accumulating on surfaces and penetrating systems could lead to failure of air generation and delivery of electronics, carbon dioxide removal, fire detection and suppression, EVA suits, rovers, windows, visors, optics, and power generation systems. The martian regolith may be so insulating that a common electrical ground would not be established among structures, vehicles and astronauts, resulting in electrical discharge when they come into contact, causing injury to astronauts or failure of electronic systems. If critical life support systems completely fail, rescue or mission termination is not feasible due to the laws of orbital mechanics. (Probable mitigation solution for electrical grounding risk already exists. On Pathfinder, all ground wires are connected to a common buss and ground through the atmosphere via corona discharge). Subset Risks
System Failure Due to Corrosive Effects of Dust (Risk #4 in Table 1): Risk Statement: If corrosive properties of martian dust in the presence of water or other reactive chemicals are not understood systems may not be properly designed. If critical life-safety systems fail due to corrosive effects of dust accumulated on systems, injury or loss of crew member(s) may result. Consequences: 4-5, severe injury or loss of crew. Likelihood: 5, corrosion control in life support systems does not yet exist to function in martian dusty environments. Context: Corrosive properties of dust accumulating on surfaces and penetrating systems could lead to failure of air generation and delivery, carbon dioxide removal, fire detection and suppression, EVA suits, rovers, windows, visors, optics, and power generation systems. Materials selection is dependent on the corrosive properties of martian dust. Because condensation, frost, EVA activities such as drilling and humidity in the habitat environment may contribute to oxidation, this risk applies to both interior and exterior surfaces. Subset Risks:
Dust Inhalation and Ingestion Dust Toxicity to Crew (Risk #5 in Table 1): Risk Statement: If the crew inhales or ingests dust, adverse health effects may result. Consequences: 2-5, mild illness to loss of crew Likelihood: 5, Dust in the human environment resulting from human interactions of the martian surface may be inevitable, and dust mitigation strategies for the human habitation modules are currently not developed. Context: Dust transported into the habitat via leakage or EVA suits may decrease effectiveness of air, water and food management systems and lead to inhalation and ingestion of dust particles. The properties of soils, which can produce medical impact to humans on planetary surfaces, include both physical and chemical reactions with skin, eyes and mucous membranes. Sub micron particles could lead to effects similar to black lung disease. Peroxide is chemically reactive. Martian dust may also contain toxic materials and trace contaminants. Very small particles, especially in low gravity, stay in the atmosphere longer and increase chances of inhalation. Electrostatically charged particles adhere to tissue and create bronchial deposits. Possible toxicity (acute pulmonary distress and systemic effects) caused by nanoparticles, if present in the martian atmosphere, should be considered as an added risk. Since the site specific lung deposition of inhaled medical aerosol particles depends, among other factors, upon the aerodynamic size and electrostatic charge distributions and the gravitational forces, respiratory drug delivery may be compromised due to reduced and zero gravity conditions. Subset Risk: Inhalation or ingestion of the dust may cause irritation or disease that can compromise an astronaut’s health and their ability to carry out mission objectives. Transport of these species to the humid atmosphere of the habitation module may cause the generation of additional toxic and corrosive species. Risk Mitigation and Reduction Risk mitigation would entail designing robust systems to function reliably in Mars’ dusty environment. Obtaining recommended measurements is the first step in mitigating the risks. Developing simulated martian dust is the next step. (Simulants are discussed further in Section 3.3.6). These simulants would be used in simulated martian environment laboratories to validated granular materials models and computer simulations and for testing promising technologies and flight hardware to ensure flight systems perform reliably in the martian environment. Mission planners may select a landing site that has lower dust content on the surface to reduce the amount of dust affecting surface systems, thereby mitigating the risk. 3.3.4 Current State of Knowledge Martian dust physical properties, such as particle size distribution, particle hardness, particle shape, clod size, clod hardness, particle density, friction angle, cohesion, adhesion, dielectric characteristics, magnetic effects, elemental composition, and reactivity have been modeled based on observations from surface rovers and orbital spacecraft [Matijevic, 1997]. Models indicate particle size is .1 to 2000 m, particle hardness is 1 to 7 on Moh’s hardness scale, dust particles are tabular, angular and rounded, particle density is 2.6 to 3.0 g/cm3, friction angle is 18o to 40 o, dielectric characteristics are K’ = 1.9d, cohesion is 0 to 20 kPa, and adhesion is 0.9 to 79 Pa [Greeley and Haberle, 1991; Shorthill, 1976]. Observations indicate the dust is magnetic [Hviid et al., 1997]. Direct measurements detected Si, Al, Fe, Mg, Ca, Ti, S, Cl and Br in the soil [Rieder et al., 1997]. The soil, probably slightly acidic, is generally oxidized but may be reactive. 3.3.5 Desired Future State of Knowledge To reduce risk for the first human Mars mission, Earth-based laboratory and computer simulations and toxicological studies need to be performed to ensure that human systems operate properly and crew health is protected. Physical property parameters predicted by models should be verified in situ by direct measurement to ensure that Earth-based simulations and studies are valid. In order to design human systems that would properly function in the dusty martian environment specific knowledge should be obtained to provide simulation and study designers with detailed chemical and physical properties of martian dust and sand to understand adhesive, electrostatic, and abrasive properties [NRC, 2002]. These properties include shape and size distribution, mineralogy, electrical and thermal conductivity, triboelectric and photoemission properties, chemistry of relevance to predicting corrosion effects, polarity and magnitude of charge on individual dust particles and concentration of free atmospheric ions with positive and negative polarities. To protect the crew from potential hazards of martian dust, reactive, corrosive and irritant properties need to be understood [NRC, 2002]. To obtain the needed information requires assays for chemicals with known toxic effect on humans, e.g., oxidizing species such as CrVI; characterization of soluble ion distributions; understanding of reactions that occur upon humidification and released volatiles; knowledge of shapes of martian dust grains sufficient to assess their possible impact on human soft tissue (especially eyes and lungs), and determination of toxic response in animals should be performed. 3.3.6 Investigations, Measurements, and Priorities to Reduce Risk(s) and/or Cost The Dust/Soil Focus Team evaluated each risk and recommended investigations that would be needed to provide data to mitigate the risk. It also prioritized measurements based on the probability and consequence of risks, evaluating if investigations must be performed in situ or if the mitigation could be performed on Earth using existing data to create simulated martian environments or computer software, and considering cost of performing in-situ measurement versus the value of the data that would be obtained. |