Re-Thinking Human Space Exploration Gordon R. Woodcock Associate Fellow, AIAA Huntsville, Alabama ABSTRACT

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1 AIAA SPACE 2009 Conference & Exposition September 2009, Pasadena, California AIAA Re-Thinking Human Space Exploration Gordon R. Woodcock Associate Fellow, AIAA Huntsville, Alabama ABSTRACT A call for an end to human space exploration by a prestigious publication (The Economist) is a wake-up call to advocates of human space flight that the program is mired in stagnation by lack of new technology and has no clear purpose. Popular support for human space flight was high during Apollo and surged again with Gerard O Neill s proposals for space colonization in the 1970s. It has waned greatly in the last couple of decades. Human space flight should be redirected towards bringing the inner solar system into our economic sphere [John Marburger s words in quotes]. Great reductions in operating costs are required and can be achieved through development of reusable space transportation, steps toward settlement via longer and longer tours of duty, e.g. on the Moon, and vigorous development of in-space resources for consumables and construction, leading to near-self-sufficiency. In this way, analysis indicates that lunar products could become economically beneficial here on Earth as well as for space projects. What we learn about self-sufficiency on the Moon could be applied at Mars and elsewhere. Recommendations for redirection are: (i) reduce near-term transportation investment cost by replacing the proposed Ares rockets with a combination of uprated EELVs and a Shuttle-C; (ii) utilize ISS to support assembly of lunar missions; (iii) initiate return to the Moon with the Orion and a version of Altair best suited to the transportation architecture; (iv) evolve re-usable inspace transportation from LEO to the Moon, including use of lunar oxygen... payoff is about the same as reusable launch and investment is less; (v) invest significantly in lunar resource utilization; and (vi) begin a program to develop a practical reusable launch vehicle with very low loss probability per flight and very short turnaround time... demonstrate critical technologies by flight demonstrations before proceeding. It s projected that these steps lead to a long-term program that supports itself through economic self-sufficiency, without huge near-term funding peaks, and with potential to eventually grow to realization of O Neill s visions of a great human civilization in the inner solar system. I. Evolution of Rationales The plaque on the Lunar Module that carried Armstrong and Aldrin to the surface of the Moon 40 years ago says in part, We came in peace for the benefit of all mankind. In 1969 the benefit was wonder, awe and inspiration for people on Earth witnessing this marvelous achievement, and a sense of optimism that the impossible is not impossible. 40 years later, benefit needs to be tangible. Current reasons cited by NASA for return to the Moon are not tangible benefits. Copyright 2009 by Gordon R. Woodcock. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 1

2 In January 2009, a short editorial in the Economist magazine 1, said in essence that nations of the world should quit human space flight because it is expensive and dangerous and doesn t accomplish anything useful. This article went on to say that robots today are capable of accomplishing everything we need from space exploration and science at far less cost and risk. In space travel, as in politics, domestic policy should usually trump grandiose foreign adventures. Moreover, cash is short and space travel costly. Luckily, technology means that man can explore both the moon and Mars more fully without going there himself. Robots are better They can also be made sterile which humans cannot.... The Economist Another way to say it is that we have severe problems here on Earth: Economic distress; depletion of fossil energy resources; global warming, pollution and destruction of environments, all reasons to not use fossil energy sources even if they were not running out; and others. If very expensive human space exploration missions don t contribute to solving these urgent problems, why waste the money and the human resources? Unless we change something, we should not. The Economist editorial is an Emperor Has No Clothes story. No practical reason is apparent for NASA s human return to the Moon fifty years after Apollo, and none for humans to Mars. The reasons now offered by NASA for return to the Moon, analyzed, really say we re going for a lark. Reasons offered for humans to Mars are even more obtuse than those for returning to the Moon. That s where change has to start. Space advocates remember the excitement of the Apollo era. Some now even say to bypass the Moon for Mars, apparently to increase the excitement. But Apollo had definite and strong reasons; it was an integral part of the Cold War. Going to the Moon had the highest national priority, to demonstrate that the U.S. was a more capable space power than any other nation on Earth. At the same time, young people were highly motivated by progress in space development and the notion that their future could lie in space. Not in space engineering, but literally in space as astronauts, workers or settlers. Space prowess was seen as the premier indicator of scientific and technological leadership on the world stage. None of these conditions is true today. Today, in the 21 st Century, the magic is gone. NASA is working to perform what can only be called a repeat of Apollo, which if successful will reach the Moon at least fifty years after Armstrong s and Aldrin s landing, and it is far from clear that NASA will be able to pull it off. Dr. Hermann Koelle sums up the present problem succinctly 2 : Current technology... will not suffice in the future if space travel is extended into space beyond low Earth orbit... The current situation can be summarized by one word: Stagnation! A most interesting phenomenon began in 1974, while the enthusiasm from the Apollo years still lingered. Dr. Gerard O Neill published an article on space colonies in a scientific news journal, Physics Today 3. This article, based on a class design project, said that all the scientific 2

3 knowledge needed to move humanity into space colonies in very large numbers already existed and needed only to be put into engineering practice. It received coverage in the popular press and attracted an enthusiastic following immediately. It was what people wanted to hear. Space was not just for a very small number of carefully selected government astronauts, it was the new frontier, the new Westward Movement. Anyone could aspire to live and work in space. NASA and the space industry paid little attention and more or less snickered about the whole idea. While O Neill was naïve about the practical technological developments needed, the enormous cost and effort required, and the apparent lack of an economic reason for space colonies, he struck a responsive chord in people s thinking about idealistic futures, and offered a path for humanity more optimistic than Limits to Growth, published by the Club of Rome. Now imagine a situation where there is a human settlement on the Moon, or for that matter, on Mars. Largely self-sufficient, they produce their own air, water, food, and shelter. They also produce stuff that is marketable, either to Earth societies directly or to space uses that provide benefits to Earth societies. They sell to Earth societies and Earth societies sell to them. Trade. This is clearly useful and economically beneficial. John Marburger said it succinctly: It s about bringing the inner solar system into our economic sphere. 4 A vision of a real potential future or a pipe dream? I try to answer that question in this paper. II. Setting Targets Most, if not all, modern scenarios for lunar and Mars missions involve crews from four to eight people. The original von Braun mission design for Mars exploration, published in 1953, had a crew of 70 people. The Lewis and Clark expedition had about 40 people. One can infer that the crew numbers for modern scenarios are based not on how many people ought to be on such an expedition, but on the fact that proposed mission architectures are so incredibly expensive that more than a very small crew will strain credulity about funding. However, if we want economic benefits it is very hard to imagine that we won t need sizable numbers of people working in space. As soon as we mention economics, the cost/price of benefits is the dominant requirement rather than a result of whatever architecture design tickles our fancy. A recent study of potentially beneficial lunar-produced goods focused on high-value projects 5. Production of platinum-group metals (PGMs) was typical. Initial production was set at 10 t. per year, which is about 10% of the current world market. A crude estimate of operating personnel arrived at a figure of 5 to 10 full-time people for maintenance and operations, assuming equipment was mainly automated and robotic. The market value of 10 t. per year is on the order of $350 million at today s price in today s dollars. A moderate fraction can be allocated to labor costs on the Moon. The affordable range in this example is no more than low $10 s million per person-year, a factor about 50 below estimated cost associated with the Constellation architecture. Other examples examined indicated similar cost targets. The target is not well-defined but definitely far below Constellation costs. Koelle projects similar figures for large operations 6, with 3

4 hundreds of people on the Moon. Before we conclude it s hopeless, recognize that we are in the position of marveling at the flying prowess of a World War I airplane and trying to estimate the cost of a transatlantic ticket on a modern jetliner, for which we have little idea of the design or technology. Analytical studies over past decades have looked at the issue of costs for sizable numbers (dozens to thousands) of people on the Moon 7, and reached five conclusions: Major reductions in space transportation cost are necessary, realizable only through longlife reusable systems. Even with that, frequent transporting of people back and forth is unaffordable, therefore long tours of duty at least several years are needed. If people are going to stay several years, they must be allowed to travel with immediate family, who must also be contributors to the enterprise, i.e. workers. Transporting food is unaffordable; therefore we must have bioregenerative life support systems with food production. The carbon and nitrogen portion of biomass inventory probably must initially come from Earth and be recycled; these substances are available on the Moon in parts per million but may not be a practical byproduct of industrial operations. Hydrogen and oxygen are available. Transporting infrastructure (habitats, utilities, industrial equipment) is unaffordable for more than a dozen or so people; most infrastructure must be made on the Moon. Space settlement, therefore, is not an option; it is an imperative if we want humans beyond low Earth orbit to do anything of benefit to our civilization on Earth. As a settlement moves toward self-sufficiency, it becomes economically self-sufficient and there is no further financial burden on people or governments on Earth. III. A Lunar Settlement Approach The question is, How can we make great reductions in cost per productive person hour on the Moon? I outlined solutions in the paragraphs above. But what is the quantitative potential for reduction? The target is far below current estimated costs for the Constellation architecture. An alternate launch architecture also using the Constellation spacecraft, such as presented in Ref.8, would reduce R&D cost by 10 to 20 billion over the very expensive very heavy lift solution currently planned by NASA, but if based on expendable launch vehicles, would probably exhibit about the same recurring cost. There is no magic carpet that will solve the cost problem in one jump. What we can hope for is an evolution that takes sensible technology steps and ultimately reaches the goal. What follows is an illustrative scenario to illustrate how major cost reductions could be realized. It is not a plan or a roadmap. A plan or roadmap needs to be adaptive so that technology advancements can be capitalized on as they occur. For example, the re-usable lunar transporter described in the following paragraphs needs lunar oxygen, about 20 to 25 t. per year in the 4

5 beginning with two to three lunar trips per year. It appears in the scenario before a re-usable launch vehicle because the savings are similar and the development time and cost probably less. Non-recurring costs for scenario elements, such as the lunar transporter, an RLV, and lunar surface infrastructure were not included in the analysis. Amortization of non-recurring costs requires a specific end-to-end timeline, and I chose not to speculate on one. Amortization was used to project annual costs for evolution stages within the scenario, because it is appropriate for a particular asset such as a habitation module, or a re-usable transporter. In these cases the amortization period can be based on the asset operating life, or in the case of a long-lived asset, a reasonable writeoff period. RLV costs were taken from reference 9 which included amortization of R&D and fleet investment. A. Evolution of the Scenario: The reference and starting case is like the Constellation spacecraft system, with a small lunar habitat able to support four people, but with a launch architecture that substantially reduces launch system development cost. Expendable launch is priced at the estimated cost per kg for the Delta IV H. (Shuttle-C would be very similar in cost per kg.) The evolution steps follow an approximate order of payoff leverage and are as follows: 1. Replacement of the Constellation spacecraft with the re-usable lunar transporter; showing the effect of making the in-space segment re-usable. Six people, six month tour. Lunar oxygen production begins, since it is needed to support the re-usable transporter. This transporter could initially be used in a cargo mode to obtain flight experience and reduce risk. 2. I also did a case where lunar resources (ISRU) for structural manufacturing, probably using lunar steel, is introduced early, before introduction of an RLV. Percentages of systems made on the Moon are consistent with lunar manufacture of basic structure but not of sophisticated parts. This may be important to demonstrate the potential for lunar manufacture of a major part of the infrastructure. This case was for 12 people for 1 year tour, with lunar food growth. 3. Introduction of an RLV, initially priced at $4000/kg and incrementally reduced, but never below $3000/kg. Because of evolution toward self-sufficiency, launch rates for any stage never exceed ~ 100 per year. 12 people, 1 year tour. Lunar food growth, with equipment built on Earth. For convenience in counting launches for scenario analysis the RLV was assumed to have the same payload as a Delta IV H, probably smaller than optimal. 4. Beginning of lunar infrastructure production if it occurs after introduction of an RLV. 30% of food growth modules and 20% of habitation systems, by mass, produced on the Moon. 24 people, 2 year tour 5. Increased reliance on lunar infrastructure production; 50% of food growth modules and 40% of habitation systems. 48 people, 4 year tour 6. Further increase in lunar infrastructure production; 90% of food growth systems and 80% of habitation systems. Modest decrease in housekeeping resupply assuming increased reliance on lunar production. 300 people, 20 year tour. At this point it is a proto-settlement. 5

6 This is a partial scenario; no mention is made, and none considered, as to what the people produce that s useful to create economic value. This scenario is only a study to illustrate how technology could be leveraged to generate dramatic cost reductions in supporting people on the Moon. It is presumed the people have useful employment, otherwise the base/settlement could not grow. It is presumed that these activities pay for themselves and increasingly bear the costs estimated here. B. Scenario Result: Results of the scenario analysis are presented in the chart and table immediately below. Also see the appendix for cost analysis details. The little code at the top of each bar is number of people/ tour of duty/ % of food growth system made on the Moon (dash mean no food growth system)/ % of habitation system made on the Moon. $1,800 Cost per person/year in millions $1,600 $1,400 $1,200 $1,000 $800 $600 $400 Habitation Systems Resupply Food Growth System Passenger Transport $200 $0 Constellation Re-usable LEO-lunar Re-usable LEO-lunar Early ISRU RLV RLV RLV RLV Note that early introduction of lunar manufacturing has significant leverage. The quantities are at a pilot-plant level, order of one to three tons per month. Manufacturing processes beyond making steel are making plate and simple sections, shaping the plate, machining and welding. This step may be desirable before introduction of an RLV. A fifty-to-one reduction by the end of the scenario is not achieved; the factor is about 40. Habitation systems are almost half the total in the right-hand bar (see table for values). Nonetheless, it is clear that dramatic cost reductions are possible through evolutionary technology advancements. 6

7 These cost figures include very significant amounts of amortization. For example, the cost of building and transporting a habitation module is incurred before it is used. Therefore, that investment cost should be written off over the period of use of the module. Excel has a function to calculate this; the function needs total cost, cost of money (i.e. interest or return), and writeoff period. For interest rate, I used a commercial-like scenario. Businesses typically seek a 15% return on equity, typically pay about 7% for debt financing, and typically use a roughly 50/50 split between debt and equity. This works out to an averaged return rate of 11%. I used writeoff periods of 5 years for transportation vehicles and 10 years for lunar facilities. The RLV cost was taken from reference 9 and not calculated in this paper; it included amortization. Constell -ation Reusable LEO- Lunar Reusable LEO- Lunar, Early ISRU RLV RLV RLV RLV Descriptor Code 4/0.5/-/0 6/0.5/-/0 12/1/30/20 12/1/0/0 24/2/30/ 20 48/4/50/ /20/ 90/80 Passenger Transport $1,149 $ $ $ $75.78 $34.96 $6.61 Food Growth System 0 0 $53.06 $40.55 $29.59 $22.80 $9.10 Resupply $270 $253 $62 $27 $18.43 $13.33 $8.30 Habitation Systems $ $ $ $59.33 $45.15 $32.96 $14.76 Totals $1, $1, $ $ $ $ $38.77 Annual in millions $6,269 $6,322 $7,325 $3,503 $4,055 $4,994 $11,631 The financial scenario reflects a reasonable estimate of actual costs including cost of money. A realistic funding scenario would be enormously more complex, and probably result in somewhat lower costs, but trying to construct a realistic scenario at the present state of knowledge is futile. The projected annual cost does not exceed about 6 billion per year until the proto-settlement period. The re-usable lunar transporter enables a 50% increase in number of people on the Moon without increase in annual cost. Significant savings occur as soon as reusable launch is introduced and lunar food growth begins. The reduced cost in the mid-period of the chart is somewhat intentional because developing the technology for near lunar self-sufficiency will require a lot of research and development expenditure not included in these numbers. Also not included are mission costs. Missions are the activities, industrial and perhaps scientific, that accomplish the purposes of people living and working on the Moon. Missions would be funded by their beneficiaries. From today s perspective we can only make rough projections of such possible activities, as noted later. 7

8 $14,000 $12,000 Annual Cost in Millions to Support Humans on the Moon $10,000 $8,000 $6,000 $4,000 $2,000 $0 Constellation Re-usable LEOlunalunar Re-usable LEO- Early ISRU RLV RLV RLV RLV C. Transportation Cost: Re-usable Earth Orbit to Moon Transporter In reference 5 I outlined a tourist transportation system for carrying tourists to the Moon and back with a target price of $20 million or less per person, on the premise that people would pay as much to go to the Moon as they have to visit ISS. It was adopted as a centerpiece of these scenarios. In the reference I assumed high traffic rates to reflect a mature tourist industry. In the present scenarios the traffic rates are much lower, and transportation costs are considerably more than $20 million per person. The technical solution: Relies on reusable launch to reduce launch cost; assumes overall market is sufficient to support a reusable system. Features the reusable lunar transportation system pictured here, derived from the Constellation lunar lander concept(now called Altair), but without the ascent stage. It is refueled on the Moon for direct departure to Earth and has an aeroshell for aerocapture in low Earth orbit. Uses a propellant depot in low lunar orbit or L1 to refuel the vehicle on the way to the Moon. (Calculations were based on low lunar orbit.) Oxygen Tanks ( 6 total) Passenger Cabin Hydrogen Tank 2 - RL-10A-4 class engines 8

9 It could use electric propulsion cargo transport to replenish the propellant depot, if electric propulsion systems are cost-competitive. The lunar vehicle general arrangement was depicted above. It is enclosed in a large aeroshell open on the leeward side. (The crew/passengers need to be able to see out.) A mission profile summary (SI units) appears here. The first occurrence of load propellant means load before launch, but also means load in low Earth orbit for subsequent trips. The vehicle makes Lunar Passenger Transport Profile Event Delta V Mass Ratio Propellant Hardware Mass Remaining Lander/Ascent Empty w/payload Load Propellant TLI MCC & ACS LOI Rend/Berth Refuel LOX Refuel LH Separate PDI ACS LS Arr Drop Surface Payload Refuel LOX TEI MCC& ACS Aero/Post-aero Stage Inerts Crew Cab Including Crew Aerobrake LOX Capacity LH2 Capacity Loaded at Launch Loaded in LO LH2 left after descent Loaded on LS LH2 capacity LH2 Used for descent LH2 Avail for ascent LOX for ascent Ascent load rendezvous with a propellant depot upon arrival in low lunar orbit and receives enough propellant for the descent, plus extra hydrogen for the ascent from the Moon. (This profile assumes only oxygen propellant production on the Moon.) After descent and landing, the passengers disembark and any surface payload is offloaded. Oxygen produced on the Moon is loaded for the ascent. Passengers re-embark and the vehicle lifts off for a direct insertion to a trans-earth trajectory. A partial lunar orbit may be used for phasing but there is no rendezvous in lunar orbit on the return trip. Upon arrival at Earth, the vehicle does an aerocapture into low Earth orbit. Passengers transfer to a space station or a waiting launch vehicle for return to Earth. The next mission begins with reloading propellant, passengers and payload for the next trip. 9

10 A depot in low lunar orbit introduces Earth-orbit-to-Moon launch window constraints, assuming departure from ISS. There is no constraint on return trips. The constraint is being able to reach the desired lunar orbit. Launch windows occur about once a month to any particular lunar orbit. Launch windows from ISS to the Earth-Moon L1 libration point occur about every 10 days. The oxygen load for lunar landing could be produced on the Moon but would need to be delivered to the depot on a separate mission since this vehicle does not stop in lunar orbit on the return trip. One could analyze a number of variations on this profile, but here I only sought a rough estimate of personnel transport cost. Note that to carry out this mission profile, between 11 and 12 t. of propellant must be delivered to lunar orbit for the depot; up to 18 t. are required for a cargo mission, because the lunar descent mass is greater. This same vehicle can deliver 8.7 t. to the depot in two trips without refueling in lunar orbit, using a propulsive-recovery booster stage to reduce delta V for the lunar vehicle. The booster stage is the same design but does not need an aerobrake. The crew cab is not used for cargo operations. Alternatively, a separate vehicle or an electric propulsion system could be used. If this vehicle is used, about 6 t. of propellant must be delivered to LEO for each t. delivered to LLO. If electric propulsion were used, the ratio would be about 1 to 1 but each delivery trip would take about six months. Also note, of course, that lunar oxygen could be delivered to the depot at less recurring cost than from LEO. For this analysis I did not estimate these options and used the 6:1 ratio. Recent data from lunar orbiter missions indicate the amount of water on the Moon may be considerably greater than previously thought. If this is borne out, making hydrogen on the Moon may be a consideration, and a reusable lunar transporter would provide even greater cost savings. For cargo delivery, the lunar transporter can be expended on the lunar surface or returned to LEO. The payload limitation is the ability to reach lunar orbit for refueling, and that limit results in a cargo capability about 10 t. This limitation can be removed by using a similar stage as a recoverable booster, as also proposed for propellant delivery to lunar orbit. In that case, the payload capability is about 25.7 t. returned to Earth and about 27 t. if the transporter remains on the lunar surface and is not re-used. The insensitivity to the return trip is due to replenishing LOX while on the Moon. D. Transportation Cost: Reusable Launch Launch prices for existing launch vehicles are proprietary, negotiated with the customer for each contract for one or more launches, and can vary significantly depending on integration and other services purchased with the vehicle. For Delta IV H, I used a nominal cost of $250 million based on the notion that each purchase would be for several launches. At 26 t. to ISS that equates to $9600/kg. For an RLV at modest rates ~ per year, I used $4000/kg, based on Reference 9; most launches will be propellant for lunar transportation. For the higher traffic portions of the scenario, RLV cost was discounted somewhat, but never below $3000/kg. (The RLV was used 10

11 only in conjunction with the reusable lunar transporter.) The RLV payload was taken as 26 t. to simplify counting launches. A larger vehicle is probably beneficial. The RLV was represented only in terms of cost per kg to ISS. E. Resupply and Food Growth A typical food allowance is about 1 kg per person per day (fresh and frozen food, not freezedried). These are presumably hard-working people and they won t eat like sparrows. This needs to be about doubled to allow for packaging and wastage, and about doubled again to account for the pressurized logistics module in which it would be transported to the Moon. So the gross cargo requirement is about 4 to 5 kg/person-day; I used 5. To this was added 2.75 kg/person-day to cover resupply for the food growth system and the habitation systems. For the very mature cases, resupply was reduced by a factor to recognize maturity of the systems and operations. The alternative to food resupply is local food growth. On the Moon, this requires a pressurized module. Sunlight can be piped in, but during the lunar night artificial lighting is needed. For controlled-environment agriculture, 10 to 20 square meters per person is required. I assumed an ISS-size module, with three levels and average shelf width of 3 m, 10 meters long, for a total of 90 square meters to feed five people, with one equivalent person full time to maintain agriculture operations. I assumed an outfitted module mass 15 t. (An ISS module is somewhat more, but has a lot more outfitting.) Artificial light was assumed to be 300 W (of light) per square meter of crop (90 sq. m total for 27 kw), 10 hours out of 24 during the lunar night, using 50% efficient LED lights. The energy requirement is 54 kw, fourteen 10 hour periods for a total of about 8,000 kwh. A regenerative fuel-cell system at 1000 Wh/kg, mass about 8 t., lunar day charging power about 16 kw, is adequate for the lighting. I generalized these figures to 3 t. per person fed for the food growth module and another 1.6 t. for its power system. If module pressure vessel and secondary structure were fabricated on the Moon from lunar steel (available in the regolith at typical concentration of 1%, as asteroidal nickel-iron), items supplied from Earth would include hatch mechanisms, cabling, lighting, electronics for internal environment monitoring, and active thermal control components. The module wall serves as radiator. Also, fuel cell reactant pressure vessels could be overwrapped with lunar glass. Lunar glass may turn out to be much stronger than terrestrial glass because terrestrial glass is weakened by water content. The reference fuel cell system was assumed to use liquefied reactants to reduce shipping mass, but gas storage, while heavier, is much more efficient and less costly. A reasonable estimate for lunar content is to replace up to 80% of the transportation mass. (The lunar content would be heavier than the 20% it replaces.) F. Habitats Habitats are a complex subject. Many competing ideas exist, including inflatable structures, and use of lunar lava tubes which may or may not exist. Here I kept it simple. A 6-meter diameter module, 10 to 12 meters long, provides enough space for a two-level 120 sq. m (1200+ sq. ft) 11

12 apartment, adequate for 4 people. Mass would likely be less than 30 t., similar to the launch mass for the lunar transporter. These payloads are well below the size for a Shuttle-C and within the capability of a reasonably sized RLV. I estimated the module cost as $400 million. As for the food growth module, most could be built on the Moon. Eventually, over 90% could be lunar-fabricated and manufacturing improvements would further reduce the cost. What s offered here is not a plan. A plan is not possible, because mission specifics that far in the future can only be projected, not planned. It is an analytical demonstration of potential economic feasibility, and outlines a general approach to realizing the opportunity, over time, for bringing the inner solar system into our economic sphere. IV. Evolution into the Future A. Lunar Manufactured Products: Glass and Steel The first structural materials developed on the Moon will probably be sintered and cast basalt and regolith, metals, glass fibers and ceramic (glass-glass) composites. The latter are expected to be high-performance in view of the high strength of glasses in the absence of water, and could be used for space vehicle structures as well as perhaps heat shields. One benefit of launching fabricated hardware from the Moon, in addition to the low delta V requirements, is that a fairing is not needed (no atmosphere) and large ungainly objects could be launched intact, as long as they are able to survive the roughly 1/2 g acceleration for a lunar launch. Calculating the mass payoff ratio for delivery to GEO from the Moon versus delivery from Earth, including expected need to deliver hydrogen to GEO for the lunar-geo round trip transporter, gives a value about 3, a substantial advantage. The cost payoff ratio is much more difficult to estimate, but appears to be about 2. Affordability of people on the Moon in such a scenario is consistent with a role of managing and maintaining highly automated production equipment. The lunar workforce needed to support this specific activity ranges from about 10 to support construction of communications platforms and other specialized spacecraft, to hundreds to support construction of very large systems such as solar power satellites. B. Lunar Manufactured Products: Oxygen Another potential early export is lunar oxygen. This is likely to start with lunar oxygen supply to lunar missions (mainly reusable landers) but could grow. In 2004, then-president Bush said in a speech on the Vision for Space Exploration 10, Spacecraft assembled and provisioned on the Moon could escape its far lower gravity using far less energy, and thus, far less cost. It probably doesn t make sense to launch Mars spacecraft from the Moon but there is a way to have your cake and eat it too, at least for missions that go beyond the Moon. For example, the usual proposals for humans-to-mars architectures involve essentially all expendable hardware and a lot of it, including heavy-lift launchers and a habitat system for the transits from Earth to Mars and return that has most of the functionality of the ISS. In my view, we might go to Mars 12

13 one time that way, but as happened with Apollo after a few missions, been there, done that sets in and human lunar (or Mars) activity is terminated due to the high cost. Lunar oxygen, and Mars propellant enable a fully reusable Earth-Mars human transportation system with a fraction of the cost of the usual architecture, as illustrated in the graph here. The payoff gets even better if hydrogen can also be produced on the Moon. Billions of Dollars Conventional Hardware Cost Earth Launch Cost Elliptic Orbit Expendable Lander Elliptic Orbit Reusable Lander The Earth-Mars vehicle serves as its own propellant depot. It is assembled in LEO and loaded with propellant. It is sized to depart to Mars from a highly elliptic orbit, which, delta V-wise, is about halfway to Mars and back (for a conjunction mission profile). The propellant loaded in LEO serves to propel the vehicle to the elliptic orbit with a C3 about -3, which keeps apogee far enough from lunar orbit that lunar perturbations are very small. It is then refueled with oxygen from the Moon and hydrogen from Earth. The crew of 8 boards (using a lunar crew vehicle to get to the elliptic orbit) and the vehicle performs trans-mars injection (TMI). Approaching Mars, the lander separates to do its own aerocapture; the two vehicles are similar in size, making design of a mated aerocapture configuration problematical. After both vehicles aerocapture into elliptic Mars orbit, they rendezvous, the crew boards the lander and performs the surface mission. After the surface mission the crew ascends and the interplanetary vehicle performs trans-earth injection (TEI). (The crew ascent vehicle is abandoned in Mars orbit.) No staging occurs; the aerobrake is retained for use at Earth. The total propulsive delta V for the interplanetary vehicle, TMI, TEI and the minor maneuvers, is about 3 km/s which is feasible for a single cryogenic stage. Shortly before Earth arrival the crew boards its entry vehicle for entry, descent and landing on Earth. The interplanetary vehicle performs aerocapture at Earth to another elliptic orbit, positioned for the next Mars opportunity; thus nothing is expended except the Mars lander and the crew ascent vehicle. At such a time as both hydrogen and oxygen can be produced on Mars, the Mars lander can also become reusable. A cost comparison is shown above. Conventional means launched from a circular low Earth orbit. The use of an elliptic orbit and using the vehicle as its own propellant depot is a good idea whether lunar propellant is used or not. (The vehicle doesn t care where it gets its propellant.) It is the same size and reusable either way. Each subsequent Mars opportunity will need different elliptic Earth and Mars parking orbits, so permanent depots at either planet are problematical. 13

14 V. Recommendations for the Near Term (1) Reduce the investment cost required to return to the Moon by using a combination of uprated EELVs (Delta IV and Atlas V) and a Shuttle-C for the launch systems. For ISS access, use the Orion with either an EELV uprated if necessary, or the Ares I, whichever is least costly and gives earliest operational capability. (2) Utilize the ISS to support assembly of lunar missions from the smaller payloads that result from (1). (3) Initiate return to the Moon with the Orion spacecraft and whatever version of Altair best suits the transportation architecture. (4) Evolve re-usable in-space transportation from LEO to the Moon, including use of lunar oxygen propellant and later, propellant depots in lunar orbit or at a libration point. This can be done in modest steps. The payoff per trip is somewhat less than developing a reusable launch vehicle but the investment cost is a lot less. (5) Invest significantly in lunar resource utilization, especially production of propellant oxygen and engineering materials such as sintered or cast regolith masonry, steel, and ceramic composites. Experiments with these technologies should be a part of early lunar surface activities; this can and should begin with robotic missions. (6) Begin a program to develop a practical reusable launch vehicle with very low loss probability per flight and turnaround time from landing to next launch less than a week. Demonstrate all the critical technologies by flight demonstrations (which can be subscale and need not reach orbit) before proceeding with a full-scale development program. VI. A Long-Term Look Once a stable proto-settlement exists on the Moon, people with enough wherewithal (more or less tens of millions of dollars) may wish to emigrate there at their own expense. This would presumably benefit the settlement because it would add to the labor force at less cost than if they did not pay their own way. However, to the extent analysts have thought about economics at all, we have always looked at settlements as something like company towns where each person serves a particular mission assignment. Understanding the evolution of settlements with volunteer settlers needs more thorough economics analysis. The cost estimate earlier for transportation to Mars brings Mars possibly within reach of very well-heeled (hundreds of millions of dollars) settlers. Future technologies will undoubtedly further reduce the cost of Mars transportation; for example, re-usable semi-cycler mission profiles for personnel transportation appear even less costly than the profile described above. 14

15 The feasible carrying capacity of the Moon and Mars, i.e. the number of inhabitants these planets can support, is probably much less than that of Earth. Continued growth in numbers of our species (which, of course, not everyone thinks desirable) would require improving the efficiency of use of resources. O Neill recognized that in the 1970s, which was one of the motivations for his free-floating fabricated space habitats. Resources of the inner SS are enough to support hundreds of times Earth s population in such solar-powered habitats. For example, consider atmosphere mass and volume per person. A conventional habitable spacecraft such as ISS provides about 100 m 3 atmosphere per person. An O Neill habitat provides about 10,000 m 3 per person. But Earth s total atmosphere is roughly 10,000 times that, taken as volume at sea level pressure. The structural material for an O Neill habitat would be mostly steel. There are more efficient materials but they are not as plentiful or as durable. There are apparently enough nickel-iron asteroids in the main belt to supply steel for enormous numbers of habitats. Atmosphere to fill them, specifically nitrogen, may be the limiting factor (oxygen can be extracted from rocks). Icy cometary objects or outer planet atmospheres are potential sources. One problem is the amount of productive effort required to turn these resources into the necessary fabricated ecosystems. An O Neill habitat represents roughly a thousand times more manufactured hardware per person than that of modern industrial societies. (A lunar or Mars settlement represents at most a few times.) The solution is probably highly automated and robotic manufacturing from raw materials through finished product. Lunar and Mars settlements have the same need to a lesser degree. VII. Conclusion Space settlement need not be a distant-future pipe dream. Reshaping our human exploration program to produce tangible benefits for all mankind offers a sound foundation for human exploration and settlement, and an orderly path to bringing the inner solar system into our economic sphere. VIII. References 1. Mars Rising?, The Economist, January 24, 2009, p Koelle, Dr. H. H., Assessing the First Hundred Years of Space Flight Development, discussions. 3. O Neill, Dr. Gerard K., The Colonization of Space, Physics Today, September, Marburger, John, (Director, Office of Science and Technology Policy, Executive Office of the President), 44th Goddard Memorial Symposium, Greenbelt, Maryland, Keynote Address, March, Woodcock, Gordon, Architectures and Evolutions to Enable Lunar Development, presented at AIAA Space Koelle, Dr. H. H., A Space Travel Scenario of the 21st Century, Working Paper, an update of the 5th COSMIC study of the International Astronautical Federation, 50th IAF Congress, Amsterdam, October

16 7. Woodcock, Gordon, Logistics support of Lunar Bases, IAA , presented at the 37th IAC, Innsbruck, Austria, Wingo, Dennis, and Woodcock, Gordon, Lunar Development Architecture Approaches Adaptable to International Cooperation, presented at AIAA Space Woodcock, Gordon, Re-usable Launch Revisited: Low Cost Potentials?, presented at AIAA Space President George W. Bush, speech at NASA Headquarters, A Renewed Spirit of Discovery January 14,

17 IX Appendix: Cost Estimate Tables PASSENGER TRAVEL Number of people supported People per trip Stay Time Number of pasenger trips Taxi propellant to LEO per passenger trip Propellant to lunar orbit per trip Propellant to lunar orbit total Lunar Cargo Taxi Propellant to LO per trip LEO/LO propellant ratio Propellant to LEO LEO launches for propellant LEO launches to service lunar taxi LEO launches for passengers Total LEO launches RLV Rate Factor RLV rate slope 90% 90% 90% 90% 90% 90% Exponent RLV Cost Factor Total RLV Cost (Delta IV H 1st & 2nd col.) $3,750 $3,750 $1,560 $1,404 $1,264 $1,547 Lunar Taxi Passenger Trips Lunar Taxi Propellant Trips Lunar Taxi Operations

18 Taxi life Taxi trips per year (per taxi) Personnel Taxis operating Propellant Taxis operating Taxi fleet Investment Amortization -$ $ $ $ $ $ Taxi ops cost per lunar passenger trip Taxi ops cost per lunar cargo trip Total Ops Cost Total annual cost $4,165 $4,165 $1,975 $1,819 $1,678 $1,984 Transportation cost per person supported $ $ $ $75.78 $34.96 $6.61 FOOD GROWTH MODULES Mass of crop module per person fed Mass of (lighting) power module per fed Percent made on Moon 0 30% 0 30% 50% 90% Crop module cargo requirement Power Module cargo requirement Total Cargo Cargo capability per trip Cargo trips Propellant to Lunar Orbit per cargo trip Propellant to lunar orbit

19 Lunar Cargo Taxi Propellant to LO per trip LEO/LO propellant ratio Propellant to LEO LEO launches for propellant LEO launches for cargo RLV Rate Factor RLV Cost Factor Total RLV Cost $1,350 $2,475 $1,591 $1,936 $2,687 $3,176 Amortization N/A -$ $ $ $ $ Lunar Cargo Taxi Propellant to LO per trip Lunar Taxi Propellant Trips Lunar Taxi Operations Delivery Period Taxis operating Additional taxi fleet investment Additional investment Amortization -$ $ $ $ $ $ Taxi ops cost per lunar cargo trip Total Ops Cost Food Growth Module Est Cost per Food Growth Power Unit cost per N/A N/A Food Growth Modules Food Growth Power Modules

20 Production factor Cost of Modules $0 $500 $500 $810 $1,458 $6,897 Amortization $0 -$135 -$135 -$219 -$394 -$1,866 Total Amortization Cost $211 $637 $487 $710 $1,094 $2,730 Per person $35.25 $53.06 $40.55 $29.59 $22.80 $9.10 Cargo to Moon transport cost ($m/t.) $72.42 $61.95 $27.36 $22.95 $22.13 $20.66 Resupply Factor Resupply without food growth (t./yr) Resupply with food growth $6.02 $12.05 $12.05 $19.27 $28.91 $ Resupply per person result $ $62.18 $27.46 $18.43 $13.33 $8.30 HAB MODULES Mass per person accommodated Utilities module mass per person accomm Percent made on Moon 0 25% 0 25% 40% 80% Total Cargo mass Cargo capability per trip Cargo trips Propellant to Lunar Orbit per cargo trip Propellant to lunar orbit Lunar Cargo Taxi Propellant to LO per trip LEO/LO propellant ratio Propellant to LEO LEO launches for propellant LEO launches for cargo

21 RLV Rate Factor RLV Cost Factor Total RLV Cost $3,825 $4,950 $2,621 $3,432 $4,967 $9,980 Amortization -$ $ $ $ $ $1, Lunar Cargo Taxi Propellant to LO per trip Lunar Taxi Propellant Trips Lunar Taxi Operations Delivery Period Taxis operating Additional taxi fleet investment Additional investment Amortization -$ $ $ $ $ $ Taxi ops cost per lunar cargo trip Total Ops Cost Habitation Module Est Cost per Utilities Unit cost per Habitation Modules Utilities Modules Production Factor Cost of Modules $810 $972 $972 $1,750 $3,149 $14,600 Amortization -$ $ $ $ $ $2, Total Cost $889 $1,107 $712 $1,084 $1,582 $4,428 Per person $ $92.29 $59.33 $45.15 $32.96 $14.76 Grand Total Per Person (All Tables) $1, $ $ $ $90.72 $