This design task paper focuses on determining the science experiments that

Transcription

1 Topic: Science Experiments, D8 Names: Mike Graham, Nikki Thorton, Taite Merriman Date: February 29, 2000 Summary This design task paper focuses on determining the science experiments that should form the payload of the HEDS-UP lander. The investigation focuses on past successes and failures of Martian missions as well as new and novel ideas proposed by the scientific community. Special attention is given to the discovery of experiments that can be made with little or no additional space on the robot required (such as the Pathfinder wheel abrasion experiment and the microprobes on the failed Mars Polar Lander). Finally, understanding the quite natural attention focused on questions concerning life on Mars, part of the report deals with finding the simplest, cheapest and best ways to approach this very complex issue. Introduction In the quest for knowledge about our solar system, robots and rockets may perform the vital work of getting from point A to point B but it is the scientific payload contained with these devices that expands our understanding. In this light, the choice of scientific instrumentation for a mission is of paramount importance. In order to best choose the experiments that should be present on our model we will take a variety of approaches. We will begin by asking two simple questions: What do we want to know about Mars? and What tools do we have available to us to help us learn more? It then becomes necessary to evaluate past Mars missions in order to ascertain what type of work has been done in the past and which kinds of experiments have returned the most useful results. Finally, by looking at both the questions that still need to be answered and the

2 lessons learned from past missions, some initial recommendations for a scientific payload will be made. What Do We Want to Learn? There are many questions about the Martian surface that either remain unanswered or have been given incomplete and often unsatisfactory answers. Some of these, such as atmospheric analysis (i.e. wind speed and direction and dust storm detection and measurement) can be carried out with very simple instruments requiring a minimum of system resources to run. Such experiments have often already been carried out on previous missions, but there remains good reason for attaching them to future missions as well. Large amounts of atmospheric data are required before such data can be of any real long-term use. If, for example, we want to be able to predict the formation of damaging dust storms that could endanger future missions, we would need a large body of knowledge from which to make our forecasts. Other simple experiments, such as the measurement of seismic activity, have also been carried out on previous missions (such as the seismometer used on Viking 2), but, with the advances in technology and scientific understanding of the past 25 years, far more accurate and telling measurements could be made. Some of these simple measurements could be made cheaply with commercially available instruments. Of course, many outside the scientific community are more interested in finding the answers to larger questions such as the existence of life on Mars or the feasibility of human exploration of the planet. While many experiments designed to find answers to these questions could easily become bulky and costly, some relatively simple instruments

3 could be implemented that would go a long way to suggesting possible answers. We believe our mission should focus on these simpler and cheaper experiments. Detection of Life On Mars Baby Steps The detection of life on Mars, for example, was the subject of a complicated and expensive series of experiments on the Viking landers. While those experiments seemed to return decidedly negative results, many have come to question both the methods of experimentation and the location of the mission. We would propose first a search for water content in the Martian soil not just at the surface, but below with microlanders similar to those outfitted on the failed Mars Polar Lander mission. These probes will be discussed in somewhat greater detail in a later section. It would also be beneficial to measure the prevalence of possibly harmful radiation, such as X and gamma rays and Alpha and Beta particles, both at and beneath the Martian surface. The Feasibility of Human Exploration Simple Experiments As to the possibility of human exploration of the Red Planet, several simple feasibility experiments could be carried out on even a lightly outfitted rover. One proposal to be dealt with in greater detail later is the BioTox instrument, which was designed at the University of Colorado to test the toxicity of Martian soil to living cells. Most plans for manned missions to Mars require in-situ resource utilization (ISRU). One useful experiment could involve testing the feasibility of one the planned ISRU schemes. This experiment could take place on a small scale, producing just enough propellant to verify that the specified reactions actually would take place on Mars.

4 Other simple experiments could use the robot itself to test various new techniques for navigation and communications. These tests could be as simple as finding the maximum range of a communications technique or measuring signal strength at various points in the landing area. Even these simple readings can help determine key coefficients such as conductivity and permeability for the Martian surface. These coefficients are necessary for designing the most effective communications strategies for future missions. BioTox Looking at Potential Hazards One of the more interesting experiments to be proposed in the past several years is the BioTox experiment from the University of Colorado. This instrument carries freezedried bioluminescent bacteria (Vibrio fisheri) to the Martian surface. There, the bacteria are brought out of stasis and are then exposed to the soil from the planet. The reactions of these bacteria to adverse conditions have been thoroughly measured and quantified. Therefore the inhibition of light production corresponds to an inhibition of metabolism. Mars Pathfinder On July 4, 1997, the Mars Pathfinder along with the microrover Sojourner landed on the surface of Mars. This was one of NASA s first Discovery class missions. Several scientific instruments were included on the Pathfinder and Sojourner, including the Imager for Mars Pathfinder, the Alpha Proton X-Ray Spectrometer, and the Atmospheric Structure Instrument/Meteorology Package. These instruments allowed for scientific experiments resulting in data of Mars geology, surface morphology,

5 geochemistry of soil and rock, the magnetic properties of soil and dust, atmospheric properties, Sojourner wheel abrasion, and material adherence properties. Figure 1 Mars Pathfinder and Sojourner Alpha Proton X-Ray Spectrometer The Alpha Proton X-Ray Spectrometer gathers information regarding the elemental composition of soil and rocks. This is achieved by interacting the matter with alpha particles of a known energy. Three interactions occur from this process, which include the scattering of alpha particles, nuclear reactions with certain light elements, and excitation of the atomic structure from the alpha particles. The energy spectra of the reflected alpha particles are then observed and the elemental compound is determined from this information. Most major elements, except hydrogen, can be determined in this manner. This process provides great insight into the structure and composition of the rocks and soils found on the surface.

6 Results from the spectrometer proved to be informative beyond the scientists expectations. Prior to observing the data gathered from the Pathfinder mission, it was believed that the volcanic geology of Mars consisted mostly of basalts (a hard, black volcanic rock consisting of less than 53 percent silica). But on the other hand, the rocks analyzed by Pathfinder were not found to be basalt. It is now believed that the primary composition of the surface rocks is andesites (a black to gray volcanic rock composed of 53 to 63 percent silica). Figure 2 shows the analysis of the data collected by Pathfinder. The red squares represent meteorites found on Earth classified as being from Mars, while the blue stars are rocks found of the surface. Figure 2 Analysis of Volcanic Rock By using the data collected from the Alpha Proton X-Ray Spectrometer, much could be learned about the surface of Mars and the availability of the elements for in sutu

7 purposes of future missions. The continued exploration of the composition of the soil and surface rocks will continue to bring new insights into the understanding of Mars. Wheel Abrasion Experiment The effects of Mars rocky surface on the mechanical components, such as the wheels, of a rover were not well known before the experiments performed by Pathfinder and Sojourner. The Wheel Abrasion Experiment (WAE) was conducted to learn more about the wear and tear produced when a rover would travel on the surface. WAE used thin strips of metal consisting of aluminum, nickel and platinum, which were between 200 and 1000 angstroms thick. These strips were placed on black anodized aluminum strips on only one of the Sojourner wheels. Changes in reflectivity of the metal pieces of film are analyzed as the wheel traverses by a photovoltaic sensor. This data provides information about the abrasions created when the wheel contacts the surface and the texture of the soil, allowing future designers to better understand the effects of the Martian surface. Materials Adherence Experiment The most logical power source for a Martian vehicle such as the Sojourner is solar power. Solar power allows the unit to run entirely from power converted from sunlight, thus no batteries that will only run for some pre-determined amount of time. A picture of solar rays is

8 shown to the left, taken of the Sojourner before being deported to the Martian surface. The only problem with utilizing solar powered equipment on the surface of Mars is the dust settling from the atmosphere. The Mars atmosphere is full of dust, and there are frequent turbulent dust storms, which would eventually cause dust to settle on the solar cells. The Materials Adherence Experiment (MAE) was performed to analyze the amount of dust settling on the unit, and the attenuating effects this dust had on the solar cells. NASA s MAE discovered that the atmospheric dust could cause between 0.5% (little dust activity) and 55% (dust storm activity) degradation in the performance of the cells during a thirty day period. This degradation occurs due to a layer of dust forming on the rover, blocking out a portion of the sunlight needed to produce the solar energy. Figure 4, below, displays the amount of dust measured by the MAE equipment over 25 solar days. Figure 3 Dust Coverage over 25 Sols

9 As can be seen, a noticeable amount of dust that could cause potential problems collects on the rover, with very little amounts of the dust being removed by natural causes (i.e., wind). The settling of the dust will eventually cause major problems, including diminishing the effectiveness of the solar power cells to near zero. The data provides insight into the harmful effects of dust and the cons of using solar powered arrays as the primary source for energy. Because of the potential hazard, dust removal techniques will need to be developed and tested on future missions to insure the optimal performance of the solar arrays. Viking Missions Lessons Learned Perhaps the most useful design ideas can be gleaned from the scientific experiments used on past missions to the Martian surface. Several of the experiments carried out on the Viking missions, including measurements of seismic and biologic activity, dealt with questions still very much in both the public and scientific consciousness today. Of late the topic of possible life on Mars has again advanced to the forefront of scientific thought. The recent discovery of possible fossilized microorganisms in a Martian meteorite found in Antarctica combined with the realization that life on Earth can exist in even the most seemingly inhospitable environs has caused scientists to reevaluate their proclamation that Mars is a dead planet. To that effect, we will examine the design, mission and results of the Unified Mars Life Detection System.

10 The life detection instrumentation on the Viking lander actually consisted of four separate experiments; each designed to independently search for signs of biologic activity similar to the signs of terrestrial biologic activity. The Gas Chromatograph-Mass Spectrometer (GCMS) was designed to heat pulverized Martian soil to a temperature of 500 degrees Celsius in an effort to detect organic materials using a Mass Spectrometer. The other experiments to be used in conjunction with the GCMS included the pyrolytic release experiment, which would require the addition of radioactive carbon dioxide, carbon monoxide and a small amount of water vapor in order to detect resting metabolism of organisms on the Martian surface. The labeled release experiment was to add a dilute solution of carbon 14 organic matter to soil samples again to detect any metabolism that might indicate life. The final experiment came to be known as the Chicken Soup test because it added a large amount of water and organic material to the sample. Analyzing the results of the biology experiments, however, proved exceedingly difficult. Three of the experiments (all but the GCMS) returned what initially appeared to be positive, if puzzling, results. One possible explanation for the results was biologic activity, but other causes were possible, too. The Viking scientists believed that the GCMS would be one possible tool for finding the proper interpretation of the other three experiments. When the GCMS experiment was finally run, the soil sample released a large amount of water, but probably no organic molecules. It was believed that if the results of the other three experiments were the result of life, than there would be organic compounds present in the

11 same soil sample. In this sense, the GCMS served as a court of appeals in overturning the possible conclusions of the rest of the instrument package. How Does This Apply? Of course, the results of the experiments carried out on the Viking missions sated the curiosity of many for a time. But many whose hopes for life on Mars have been recently bolstered by advances in microbiology and discoveries of possible fossilized remains have begun to raise questions about the effectiveness of the Viking experiment package. The question then becomes what can be done in future missions to make up for the shortfalls of the Viking experiments? While few argue that the results returned from the Viking probes were incorrectly interpreted, some have begun to question the completeness of the search methods. With the recent understanding of the feasibility of life in such inhospitable locales as Colorado hot springs and subterranean vents, scientists better understand the processes required for life to survive in harsh climates such as the Martian surface. Another possibility for the failure of the Viking missions to detect any sign of life is the location of the landing site. Current data suggests that if may be more likely for life to exist upon Mars near some region of increased geologic activity. There, microorganisms might find the energy, elements and liquid water that they are postulated to require. Future missions in search of life, therefore, should be concerned with search for these essentials and not necessarily the organisms themselves.

12 Microprobes and the European Space Agency The European Space Agency s Beagle 2 lander will carry a series of instruments designed to search for criteria of past life on the Martian surface. The lander will look for water, carbonate materials and organic residues while measuring the complexity of and organic materials found on the surface. These indirect tests for life on the planet, either past or present, are more in agreement with current budgetary constraints. One similar effort from NASA involved a pair of microprobes attached to the failed Mars Polar Lander. These Above: Beagle 2 probes were to have been released high above the planet and allowed to crash into the surface thus allowing the collection of samples two meters below the Martian surface. The purpose of these probes was to search for evolved water, a necessity for life, but we believe these probes could be well adapted to several different uses. Summary and Recommendations In the final analysis, the instrumentation the robot carries will be determined by a combination of factors including usefulness, cost and size. In terms of the sheer amount of useful data returned, we must recommend the Alpha Proton X-Ray Spectrometer (APXR) carried on the Pathfinder mission. We would also suggest that the lander be equipped with (hopefully commercially available) meteorological equipment at least an anemometer for measurements of storm severity. The microprobes designed for the Polar Lander would provide additional data without putting any strain on the robot itself, so we find them well worth consideration. We would also like to see an instrument to measure the amounts of harmful radiation (x-rays and gamma rays) that reach the Martian

13 surface as this experiment would further our understanding of the harsh conditions any life would have to survive. The BioTox experiment would also be a simple, yet telling test of the ability of Mars to support life as we know it. Finally, and perhaps most importantly, we would like to include experiments more closely tied to practical concerns. These experiments (such as dust removal from solar panels) would not necessarily tell us much about Mars itself, but they would make it much easier for us to study it in more detail on future missions. Here we will need the help of the rest of the design teams. As teams come across new and untried ideas (especially in the fields of navigation and communication), we can see if they could be integrated with our design in order to ascertain their feasibility. Works Cited Literature: [1] Brown, F. S., Adelson, H. E., et al. Biology Instruments for the Viking Mars Mission. Review of Scientific Instruments vol. 49 (1978): p [2] Ezell, E. C., Ezell, L. N., On Mars: Exploration of the Red Planet Washington: NASA History Series, [3] Henry, Robert M., Greene, George C. Anemometers for Mars. Technical Paper - Society of Manufacturing Engineers Flow, Its Measure and Control in Science and Industry. vol. 1 (1974): p [4] Landis, Geoffrey A., Jenkins, Phillip P. Dust on Mars: Materials Adherence Experiment Results from Mars Pathfinder. Conference Record of the IEEE Photovoltaic Specialists Conference vol. 1 (1997): p

14 [5] Martin, Joseph P., Johnson, Richard D. Mars Life Detection System. Journal of the Astronautical Sciences vol. 23 (1975): p [6] Morgenthaler, George W. BioTox: A Biologically-based Soil Toxicity Instrument Space vol. 1 (1998): p 22-28/ [7] Owen, T. Composition of the Martian Atmosphere. Advances in Space Research vol. 2 ( 1982): p [8] Siebert, M.W., Keith, Th.G., Jr., Ferguson, D.C. «Mars Pathfinder Wheel Abrasion Experiment - Ground and Flight Results. Lubrication Engineering vol. 54 (1998): p Web Pages: [1] European Space Agency. Beagle 2: A Lander for Mars. February 15, February 25, [2] Exobiology Program Office. An Exobiological Strategy for Mars Exploration. Last modified August 19, February 14, < [3] Landis, Geoffrey A. and Jenkins, Phillip. DUST ON MARS: Materials Adherence Experiment Results From Mars Pathfinder February 14, < >. [4] Landis, Geoffrey A. Mars Dust Removal Technology February 14, < [5] Landis, Geoffrey A. Solar Cell Selection for Mars February 14, < [6] Mars Surveyor Program: 98 Lander and Orbiter Missions Science Experiments. Washington, D.C: Office of Space Science, NASA, 1995.