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NASA Technical Reports Server (NTRS) 19990110322: In-Situ Resource Utilization for Economical Space Missions PDF

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ln-Situ Resource Utilization for Economical Space Missions Summmary of research report required by subject grant NAG-l-1825 submitted by: Kumar Ramohalli, Space Engineering Research Center University of Arizona, Tucson. Arizona 85722-3308 INTRODUCTION Abstract This paper presents some recent developments in Cost, perceived or real, continues to the technologies of ISRU with the specific intention of cost reductions in space missions. Recognizing be a major deterrent in the timely that a certain level of teclmology maturation is execution of space missions. Despite nc_-ssary before the mission designers will rosy promises by managers, and seriously consider any technology, the hypothesis is made that the overall cost-index is inversely valiant efforts by engineers, the cost proportional to file TRL. Also recognizing that the of the first step itself (space access) cost is directly proportional to the mass at launch. the cost-index is identified as the ratio of the launch continues to be around $10,000/kg to mass to the TRL. Whether this cost-index is the LEO, and much higher for planetary true measure of the overall mission cost is arguable; targets. Smaller, cheaper, faster, however, the relative costs of comparable technologies can be readily assessed by applying better approaches to spacecraft (the. identical rules of such an evaluation. As one payload) have introduced significant example of this approach, Mars Sample Return economy, compared to previous (MSR) is studied, and nine competing teclmologies axe evaluated for the key Mars Ascent Velficle missions; however, when more (MAX/). It is found that the technology of ox'ygen ambitious missions are considered, production tkrough the dissociation of atmospheric the state-of-the-an costs continue to carbon dioxide can be a key technology. In addition to reporting upon this technology briefly, one be high. innovative application that significantly enhances the science capabilities of a rover [s discussed. Three facets of this cost issue are important. First, improvements are necessary in the launch system. The t_nd towards RLV's from the ELV's is encouraging. A program on hybrids 33has been making advances in lower costs through simpler propellants. Second, the advances in micro-technologies 34 will help us achieve greater science returns ."or a given mass. Third, an entirely new best available components by approach to space missions, themselves. This FoM can be, in fact specifically utilizing local resources should be, different for different instead of relying upon earth- missions. For example, in a simple transported resources, has been earth-observation mission, the number studied for a number of years My, but of bits of data received per kg of not executed in any space missions so launch mass could be one definition; far. In addition to the understandable on the other hand, in a sample return reluctance to try something "untested mission, the mass of sample returned and new", in the place of "tried and to earth divided by the mass of the proven" components, on high-profile initial craft leaving the earth, may be a missions which are constantly under better definition. While these are only media scrutiny, it is only fair to the initial steps towards an acceptable acknowledge that these ISRU FoM, the overall costs and risk must technologies have not yet advanced to be introduced for a fuller reflection of acceptable TRL's, at least in the the true picture. The numerical values judgment of the mission planners; the of the component performance are burden of the proof-of concept of constantly changing, especially in ISRU is on the engineers. ISRU, and the best estimates (1997) Additionally, there is need for a are used in this paper. rational, quantitative methodology for evaluating the overall economics of The specific example of Mars Sample ISRU, just as it is the case for any Return (MSR) is studied in the component of a spacecraft. What had context of a simple (direct) ascent been an "innate feel" and "experience which is taken to require 6km/s driven evaluations" were given a (incremental velocity, or, delta v). formal structure through the Figure- While other maneuvers are possible of-Merit concept, first proposed 9 in such as throttling, multistaging, or, 1989. The overall mission was combinations thereof, for the divided into five major components: purposes of this comparative study, (1) the trajectory/orbital mechanics, the simple approach illustrates the (2) transportation/propulsion, (3) C3I, point. (4) power/support components, and (5) ISRU. These five components THEBACKGROUND were studied in detail for any mission; however, the heart of the new concept There is need for a quantitative and is the recognition that the effective rational methodology for estimating combination of these components is the overall (mission) effect of far more important than achieving the choosing various subsystems that comprise the spacecraft.9 (Ideally, the tube, which has the advantage of one would like to extend the choices cooler ends for easy seals, and the beyond the spacecraft subsystems, preferred material has been and include the other details such as "ceramic" polycrystalline zirconia the orbital mechanics and the doped with vacancy promoters. This communication network). With a system has been studied by a number description of the components, it is of companies, notably, Westinghouse, desirable to predict the outcome, of Ceramatec, and United Technologies. which life-cycle costs and the While continuing to pursue other reliability (probability of success) higher-tech options, the University of appear to be very important currently Arizona, NASA Space Engineering (1996-97). The Technology Research Center (SERC) built and Readiness Levels (TRL) of various delivered a four-cell, lower TRL components play a role in the mission system to NASA LeRC for outcome; generally, lower TRL's demonstration purposes 5. First used lead to greater costs that must be at LeRC in the summer of 1992, with invested to bring the component to a a few simple modifications, the unit sufficiently high TRL to be has worked reliably since. In fact, flightworthy. On the other hand, it is LeRC has operated this unit at several possible to use a lower TRL locations in the USA during the AIAA component, and accept the penalty. annual propulsion meetings. At the This penalty is usually in the form of end of a typical 30 minute heavier mass, or superfluous sub- presentation, it has operated a CO-O2 components. The heavier mass (at rocket to confirm that the fuel- launch) can be translated into cost. oxidizer produced can indeed develop However, it is not clear that the lower thrust in a rocket motor. The higher- TRL components are any less reliable tech options that the UA SERC has than the higher TRL ones. A simple pursued since that time have been example may help illustrate the point. most promising, shown higher In the field of ISRU for low-cost efficiency and a much higher specific Mars missions, the production of production rate, but have simply not oxygen and a fuel has been pursued been as reliable; they have failed at for a long time. The teclmology of various levels. The main point is that solid oxide electrolysis of the lower TRL "kluge" unit, although atmospheric carbon dioxide is ahnost heavy and power-hungry, has 100 years old (Walther Nernst, U.S. operated more reliably than the higher Patent #623,811, dated April 25, TRL traits. 1899). For a long time, the preferred geometrical configuration has been The complexity of the system can be launch) will, or will not, meet its cost expected to lead to lower reliability. goals. In the current interpretation, Again using the above example, the the risk is clearly the probability that lower TRL ceramic tube unit is very the mission will fail to meet its simple, while the higher TRL units are goal(s). In addition, some of the more complex. authors have restricted their methodology to the launch vehicles, THE BASIC HYPOTHESES and some to small satellites only. Thus, the current work, although a The basic hypotheses used in this simple first step, is different from the paper are: available studies. the overall mission cost is inversely The TRL and complexity numbers proportional to the TRL, and (indices) are arrived at using the the probability of mission failure is NASA ITP document (1991), where directly proportional to the the TRL definitions leave very little complexity. room for interpretation. In the area of previous missions, the Voyager It is understood that the TRL and (MJS77) was chosen for comparisons. complexity are independent of each Here, the TRL of components that other. This highly simplified were selected (1977) were discerned approach has the advantage that the through a detailed telephone usual cost index, namely the mass at conversation with Bud Schurmeier. launch can be divided by the TRL to The objective of this exercise was to arrive at a relative cost index for show that the current approach can be competing technologies; similarly, the verified for its intrinsic merit through complexity number is divided by the its "predictions" of a past successful TRL to arrive at a relative (probability mission. of) failure index for missions using competing technologies. The approach uses a simple spreadsheet to interlink the various Relevant work by others in the field calculations. are available in references 18-24. It is important to clearly tmderstand a The example is Mars Sample Return. fundamental point of difference: Recent studies have shown that the "risk", as used by many of the Mars Ascent Vehicle (MAV) is the authors, seems to be the program most critical component of the overall risk. That is, an evaluation of mission. For this reason, this initial whether the program (leading to the study considers variations in the MAV propulsion options. The comparisons of competing incremental velocity for the Mars technologies. In other words, what is ascent (returning towards earth) is presented is a "living" spreadsheet calculated to be 6 km/s. If different where different input data can be trajectory plans are used, the number incorporated. could change, but will not alter the main message of this report. A THE RESULTS consistent structural factor is used from the literature. (In the case of The results are presented in tabular hydrogen storage, extensive literature and graphical form. It is interesting to search, and contacts with experts in note that the hybrid rocket emerges as the field, led us to the number used, the clear winner in terms of lower namely, two kg of inert mass for cost and overall merit. The relative every kg of hydrogen stored; in fact, ranking, or the merits of one system there appears to be no known case of over the other, are secondary to the successful storage of liquid hydrogen main conclusion: the current approach in space for longer than a few provides the first step in a rational months.) The nine options encompass evaluation of competing technologies the usual technology options for in space missions. The probability of propulsion. These vary from the failure, as used here, is merely a reed-and-tested LOX-Hydrogen relative index of the competing system at a TRL of 9,..to...the systems. Thus, a number equal to or interesting possibility of a simple greater than 1 (one) should not be hybrid rocket at a much lower TRL. (mis)interpreted to mean certainty of Also included are the traditional failure. It merely states the fact that a storage mono and bipropellant high number means a higher systems. One recent contender has probability of failure, or inherent risk been the glow discharge system compared to a lower number system. pioneered at ODU for the production of a fuel (CO) and the oxygen from Future work should pursue the further atmospheric carbon dioxide. refinement of the approach and should specifically examine the immediate Admittedly, some interpretation and and future missions of importance. technical judgment are involved in the These could include all of the Mars complexity numbers. However, it is Surveyor missions, and the aerobot emphasized that changes in these missions. numbers will not affect the mainstream theme of this report which The inherent shnplicity and flexibility is showing a methodology for rational of the current approach have much to offer in comparison with more incentive for embarking upon an sophisticated cost/risk models. entirely new class of reliable, low- cost, high-return science missions of SUMMARY the near-term future explorations. This preliminary work, aimed at REFERENCES relating the emerging ISRU approach to. the overall economics of space 1. Clark AC, "Electromagnetic missions, has shown promise in Launching as a Major Contribution to identifying a Figure-of-Merit that can Space Flight," J British Interplanetary be an index of the overall Society vol 19, pp 261-267, effectiveness. The aim, at this stage, November 1950. 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Proceedings of The Second Lunar Analytical Laboratory Workshop 34. Lustgarten, K, "The New (LAL-II), Dijon, France, A. Deepak Millennium: Spacecraft the Size of Publishing, Hampton, Virginia, pp Toaster Ovens and Payloads the Size 78-98, 1997. of Sugar Cubes," Final Frontier, pp 22-25, May/June 1997. 29. Lewis, J, and Lewis, R, Space Resources, Columbia University 35. Marcozzi, M, and Ramohalli, Press, New York; 1987. KNR, "A Multiple Rover Concept with ISRU, presented at the 1997 30. Lewis, JS, Rain of Iron and Ice, International Conference on Mobile the very real threat of comet and Planetary Robots and Rover asteroid bombardment, Addison Roundup, Santa Monica, January 29, Wesley, Reading, Mass, 1996. 1997. 31. Lewis, JS, Mining the Sky: Untold riches from the asteroids, ACKNOWZEDGME:VTS comets and planets, Addison-Wesley, Reading, Mass, 1996. This work was supported by NASA through tile grant NAGW-1332, and the authors thank Drs_ Murray Hirschbein, Gordon JohtLston, and Carl Pilcher for 32. Qi, J, "Geometric Effects in guidance and support. Student support was pro,ided by the University of Arizona attd the authors thank Dr. Hybrid Rocket Fuel Burning Rate," Michael A. Cnsanovich, VP Research, for this help. presented at Third Pacific Intemational Conference on > T -x-- >_ © C/] > >_ N °_ _J ,,j ,,j ,.... >_ _ >_ >_ ,.- ;>, ,i j C, ,J_ ,- >, _ I... ,_ 0 I

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