IAC-04-IAA.3.8.1.02 SOLAR SYSTEM EXPLORATION: A VISION FOR THE NEXT HUNDRED YEARS R. L. McNutt, Jr. Johns Hopkins University Applied Physics Laboratory Laurel, Maryland, USA [email protected] ABSTRACT The current challenge of space travel is multi-tiered. It includes continuing the robotic assay of the solar system while pressing the human frontier beyond cislunar space, with Mars as an ob- vious destination. The primary challenge is propulsion. For human voyages beyond Mars (and perhaps to Mars), the refinement of nuclear fission as a power source and propulsive means will likely set the limits to optimal deep space propulsion for the foreseeable future. Costs, driven largely by access to space, continue to stall significant advances for both manned and unmanned missions. While there continues to be a hope that commercialization will lead to lower launch costs, the needed technology, initial capital investments, and markets have con- tinued to fail to materialize. Hence, initial development in deep space will likely remain govern- ment sponsored and driven by scientific goals linked to national prestige and perceived security issues. Against this backdrop, we consider linkage of scientific goals, current efforts, expecta- tions, current technical capabilities, and requirements for the detailed exploration of the solar system and consolidation of off-Earth outposts. Over the next century, distances of 50 AU could be reached by human crews but only if resources are brought to bear by international consortia. INTRODUCTION years hence, if that much3, usually – and rightly – that policy goals and technologies "Where there is no vision the people perish.” will change so radically on longer time scales – Proverbs, 29:181 that further extrapolation must be relegated to the realm of science fiction – or fantasy. There is a great deal of new interest in However, as we have now entered the sec- space and space travel with the recent (Feb. ond century of aeronautics, we have a base- 2004) publication of the Aldridge Commis- line to look back on. We can look at what sion Report2, efforts on developing current people thought might happen in the previous space tourism, and the ongoing series of hundred years, what really did happen – and missions to provide scientific exploration why, and, perhaps more to the point, what it (notably of Mercury, Mars, Saturn, and cost. Pluto). NASA undergoes a “road mapping” Especially following the technical gains in activity on three-year centers that feed into rocketry and atomic power brought about by the overall Agency Strategic Plans, and this the second world war, there was a great deal type of planning has been extended in the of speculation of what we could, and would, recent work of the Aldridge Commission. do in space. Historically, space exploration Nonetheless, these exercises typically has always been aligned with an outward project only into a “far future” of typically 20 look. In the beginning, the vision was of 1 manned flights to earth orbit and beyond. formance required of the Crew Exploration While that outlook gave way to robotic Vehicle (CEV) if it is to be up to that task. probes always going to a destination first, it has always, at least to the majority of people, Key Mission Elements been with the idea that eventually humans would follow. For any mission there are four key ele- ments: the case for going, the means to go, The Art of Prediction an agreement to go by all stakeholders, and a source of funds sufficient to finance the Future predictions can, and many times, expedition. are misleading. An example is the prediction The reason for going for the Apollo mis- from the early days of the automobile that it sions was the geopolitical situation while the would be soon supplanted by personal air- reason for going for robotic missions has planes for local travel, a scenario yet to be been a combination of supporting Apollo borne out. At the same time, such predic- goals (early on), science mixed with geopoli- tions, if grounded in limits imposed by phys- tics (the U.S. and Soviet Union were both ics and chemistry and for which there is a sending missions to the Moon, Venus, and technology path, can work out. Usually, the Mars early on), and science with some level implementation is not as easy as originally of lingering international competition (Mars thought because the Devil always is in the Express and Mars Global Surveyor) and in- details. An example is Von Braun’s 6400- ternational cooperation (Cassini/Huygens). metric ton ferry vehicles for carrying 39.4 The means for going, space technology, metric tons to a 102-km orbit for building has a long history6 but significantly grew from Mars transfer vehicles4, 5. The propellants for the V-2 work of World War II and later inter- three stages were nitric acid and hydrazine. continental ballistic missile (ICBM) develop- The Space Shuttle is a single vehicle with ment programs during the Cold War. The detachable solid rocket boosters (using solid end of that geopolitical competition combined propellant) and a throwaway main tank car- with the current lack of deep-space commer- rying liquid oxygen (LOX) and liquid hydro- cial activity and limited Earth-orbital satellite gen (LH2). It is a 2040-metric ton vehicle that markets has led to slower development in can carry 24.4 metric tons to a 204-km orbit. many areas, especially where radiation The Shuttle has better performance but with hardness of electronics is an issue. less cargo because a realistic altitude is Stakeholders include advocates of a mis- higher than Von Braun envisioned. Von sion, non-advocate reviewers (whose job is Braun also envisioned the driving cost for his to see that invested monies are well spent), Mars mission being the $500M for 5,303,850 those who are forwarding funds, and those metric tons of propellant for the ferry ships to who can be impacted positively by success transport propellant and supplies to Earth and negatively by failure. A well thought out orbit (this translates to ~$3.6B FY96$) during strategy includes all stakeholders and pro- the 950 flights by 46 vessels in eight months vides both framework and substance of an (one ferry flight every 10 days, 6 ferries as- agreement to do the mission. sumed to be out of commission at any given Finally, there must be a source of funds time). Given the historical costs of building sufficient and available in the needed time- and operating four Space Shuttles, these are phasing to support the endeavor. Such pro- obviously not the resilient, cost-effective ve- grammatic support has typically come from hicles Von Braun had in mind. However, his the government exclusively for non- calculations may give some insight into some communications satellites. Typically new of the top level requirements of a human missions have significant new technologies mission to Mars that may translate into per- that require implementation (and sometimes 2 DRIVERS Science Questions Mission Science Objectives Distance / Objective Questions Time = Science Measurement Objectives Speed Required Instruments/Crew Instrument/Crew Resources and Data link Requirements Mission and Spacecraft Requirements Operational Data Product lifetime Analysis Product Science Result FIG. 1: Answering solar system science questions is a “system of systems” problem. unanticipated development) and involve the the Earth-moon system will be driven by, next step in a non-routine, non-recurring and/or framed in terms of, science return scenario of exploration. Costing of such en- from various solar system bodies. While be- deavors is tricky at best and requires some ginning with the Moon and Mars, the es- “adequate” level of reserves that can be poused vision in principal reaches throughout drawn upon to support the resolution of un- the solar system. The science objectives are anticipated development problems. At the thus the generic drivers that trace down same time, some members of the through the hardware requirements. Appro- stakeholder community will be pressing to priate analyses should then be capable of keep outlays as low as possible. While such providing results that answer the posed tensions are “obvious”, space missions, as questions. Demonstration of such closure (at with other large engineering endeavors, in- least in principle) is part of the strategy that volve large sums of money that are not easily must be developed up front (Figure 1). The turned off mid-project if the budget is ex- global requirements that drive the mission ceeded. Overruns and missed schedules design, implementing technologies, and es- are, and have been, tolerated on many indi- pecially cost include: (1) how far are we go- vidual programs, because the termination ing, how long can we take, is this a flyby, cost can be too high if sufficient funds have rendezvous, or return mission, i.e. what total already been spent. However, such overages velocity change capability is required, (2) can put a programmatic end to follow-on what are the data link requirements, band- missions. width, coverage continuity, and (3) what is the required operational lifetime – driven by System of Systems both point (1) and reserve requirements – and including hardware, autonomy, sparing Currently, and for much of the foresee- philosophy, and consumables, both for the able future, deep-space missions (defined as mission and for a human crew, if there is non-Earth orbit), and certainly those beyond one. 3 THE PAST Those who seen to think that the Moon is the goal of interplanetary travel should "Those who cannot remember the past are remember that the Solar system contains condemned to repeat it.” – G. Santayana7 eight other planets, at least thirty moons and some thousands of asteroids. The Beginnings total area of the major bodies is about 250 times that of the Earth, though the The conquest of the solar system has four giant planets probably do not pos- been a favorite theme of science fiction writ- sess stable surfaces on which landings ers for well over a hundred years.