maintain workforce morale by providing enjoyable fresh foods.)

The range of output products and the rate of diversification of products will depend on the economics of construction in space vs. lift from Earth. To sustain rapid exponential growth, an increasing share of the total must be built in space. For example, if 5% of the output products' mass must still be obtained from Earth when 600,000 tons per year is being processed, about 100 flights per year of a Shuttle-derived freight rocket will be

decade, to a point where the entire market for new generator capacity worldwide apparently might be provided by space-built satellite power. That Study found the market 25 years from now $200-400 billion per year. It found exponential growth essential for beating interest costs, and ran into the biggest uncertainty over what fraction of the products assembled in space must be hauled from Earth. As both studies in the past two years have concluded, effort must go into designing fabricated products optimized for construction from lunar

F-4

R&D COST ESTIMATES

export labor. The latter two have been ignored in this simplified treatment. The time-line appears rather insensitive to those numbers until the first plateau; after that, the actual growth rate depends on them more.

The takeoff point in space manufacturing will reflect our cultural values. It might be defined in one way as the point at which the rate of valuegeneration exceeds the rate of investment, the latter including development, construction, transport, and interest charges.

R&D cost estimation is a notoriously uncertain business. Given the transport economies just outlined, R&D costs may dominate the total in

vestment required to reach the takeoff point. R&D costs have ranged from as little as $6 million per ton in 1960 dollars for a throwaway rocket whose engines had already been developed, the Saturn V, to over $200 million per ton for the Apollo Command Module.

To estimate R&D costs for space manufacturing, it seems best to use a modern example: Shuttle R&D totals $6.3 billion. " Of that total, I take two-thirds as devoted to the Orbiter, a complex but reusable 68-ton vehicle. Orbiter R&D costs approximately $62 million per ton. The relatively simple external tank and one SRB total 76 tons, and cost $28 million per ton for R&D.

The components of the space-manufacturing program just described have been analyzed for cost on that basis, as summarized in F-4. Mass-driver structures were estimated on the basis of individual non-equivalent sections every 5% in bucket

velocity. The crew-transport module for 60 people was taken as a Shuttle payload of 11 tons dry mass, and the workforce habitat module was assigned a mass of 12 tons. To compare this primitive approach with the more detailed estimates made during the 1977 study, all mass-driver R&D in F-4 costs $2.4 billion. Several months later different persons obtained a figure of $3.3 billion, which includes construction of several mass-driver tugs and an extensive program of unmanned observations by lunar polar orbiter and exploration by roving lander. No sensible person would conclude from that a figure of $2.7 billion 20%. Other estimates, equally defensible, were higher and lower by factors of two.

F-4 shows a range of cost estimates for some items for which there are data from previous studies of orbital transfer vehicles, space stations, a lunar base, and a Shuttle-derived lift vehicle. All estimates are necessarily rough and do not consider overall integration, government infrastructure, and commonality with other applications, but they do serve to show that the investments fall in a reasonable range.

Both studies reveal clearly that reaching the economic takeoff point does not require large monolithic habitats ("space colonies"). Furthermore, colonies could not be developed like aerospace hardware, for R&D cost reasons. When the time comes to build such structures, they will have to be designed and constructed like ships or like buildings rather than like jet aircraft. Spacefarms, like monolithic habitats, do not appear to be essential in reaching the takeoff point.

The 1976 Ames Study concluded that over the range of 1 to 30 kg/sec in throughput, chemical extraction and fabrication plant mass and power should be proportional to throughput. For minimizing R&D costs, therefore, it seems best to design such plants for moderate size (1 kg/sec or 30,000 ton/yr) and then to parallel identical units.

It is reassuring to find that most of the necessary early R&D steps have potential benefit to all largescale high-orbital activity, whether or not using lunar materials.

To indicate the uncertainty of R&D cost estimation, in a recent NASA Johnson Space Center study a large, fully reusable Class IV launch vehicle was assigned an R&D cost of $6 million per ton-a factor of ten below the figure used in this article, and one-seventh of the average for the Shuttle. " Until far more detailed work is done, it seems premature to argue which, if any, of these estimates is near the truth. I use the higher figures mainly to be on the safe side.

The required R&D investment falls naturally into three blocks:

1. All items necessary to reach the first plateau, at which point the base would begin putting 30,000 tons per year of lunar materials into space. That first block would cost $3400 million, or $700 million per year spread over five years-a sum and rate well within governmental R&D funding patterns, being far less than the annual Department of Energy budget for nuclear-power R&D, and well under peak funding for Shuttle development.

2. SDLV development plus intermediate-level ($400 million per year) research on processing and fabrication. This would cost $700 million per year for two years-also within government precedents.

3. A remaining $14 billion for processing and fabrication development falls intermediate in scale between Shuttle and Apollo R&D. The processingdesign group at the 1977 study rather strongly believed that estimate far too high. If that figure is high, it is likely to be compensated for by errors in the other direction made on other items.

In brief, the gradual, step-by-step approach to space manufacturing comes within the general range of NASA funding, at least until processing and fabrication plants must be developed. If a decision on R&D funding of the third block were delayed until then, at that point prospective investors would know that the major questions of lunar-materials transfer, of low-cost interorbital transport, and of the long-term health of workers in

space had been answered. If the requirement then existed for large tonnages of manufactured products in geosynchronous orbit, funding for additional R&D would be easier to justify than it would likely have been earlier.

A total of $14 billion in R&D funding spread over several years comes within the ability of the private sector. In 1990, for example, the electric utilities will have to be investing in new generator capacity at a rate of more than $20 billion per year. Even in 1977 the life-insurance companies, major financiers for the utilities, disposed of some $45 billion in investment cash flow.

In a stepwise approach, the items requiring relatively large R&D expenditures can be deferred. to a late stage in the program, when the most unusual and therefore high-technical-risk items have been proven, and when profits from manufacturing are in sight.

On the Advisory Panel of our Task Group on Large Space Structures formed by the Universities Space Research Association, we have several senior executives of major utilities and life-insurance companies. The Advisory Panel has discussed R&D funding of a space-manufacturing program at some length. They feel private sources of capital unlikely to appear on a significant scale, that is, on the scale of tens of billions, until technical risks have fallen to the level of hydroelectric power. They agree that demonstrations of lunar-materials transport, of satellite power transmission, and of the processing of lunar materials to pure elements in space would constitute adequate reduction of risks. After that, our financial friends assure us, there should be no difficulty in obtaining ample private funding for a rapid buildup if the economic estimates show clearly that space-manufactured satellite power will undersell that from coal and the atom.

Given the breakthrough in transport economy described here, the pacing item in the development of space manufacturing appears to be the start of processing R&D.

Many development scenarios are possible, and I provide one (F-5) as illustration. It delays the peak of the third block of R&D funding until the twoyear period for emplacing the lunar-materials transport system, and is consistent with F-3. A still more cautious scenario would insert an additional decision delay until starting the transport of lunar materials, and would make the third block of R&D funding a more highly peaked three-year effort.

F-3 and F-5, combined with a hardware cost assessment of $1100/kg, a 10% interest rate in constant dollars (17% discounting), and an assigned value of $60/kg for fabricated export products made in space, allow calculation of the takeoff point as six years after the start of lift. I

assume that the equipment to be located in space will cost on Earth eighteen times as much per kilogram as the value per kilogram in geosynchronous orbit of the products fabricated in space. The first is based on the cost of military aircraft, while the second is based on satellite power stations of 83,000 tons mass," figured as worth $500/kw at the busbar on Earth. For the time line of F-6, the total program up to takeoff would cost $24 billion, exclusive of interest. After "takeoff," debt retirement and earnings would accelerate rapidly.

The 1977 Study considered many points not brought up in my simplified argument: workforce selection and training costs, salary costs, crewexchange times and resulting transport loads, and an overall higher estimate of R&D costs. It reached quite similar conclusions on times and buildup rates, but gave a total investment up to the takeoff point of more like $50-60 billion-about the cost of an Apollo project in today's dollars. Both efforts constitute simply first cuts toward a generally promising approach. Better answers, or still more efficient scenarios, will have to await longer-term or continuous studies using the well-known but expensive techniques of critical-path analysis and cost/benefit theory embodied in large, thorough, flexible computer programs.

The mass-driver clearly plays a key role in the development of space manufacturing. Without that, or something equivalent to it, the upgrading of the Shuttle, lunar-materials transfer, and low-cost interorbital transport will all be impossible. Recognizing that fact, the propulsion division of NASA's Office of Advanced Science and Technology has recently begun support of massdriver research at a modest level. As a first step, a group of student volunteers, together with Prof. Kolm and myself, built a 2-m-long mass-driver of larger caliber than the Shuttle upper-stage engine. The model was built almost entirely of scrap or surplus materials. The group completed the mass-driver in three months, and demonstrated it at the May 9-12 Princeton/AIAA Conference on Space Manufacturing, at the final briefing of the 1977 Ames Study, and at the California Aerospace Day celebration a few hours before the first Shuttle free flight.

Unfortunately, the uncertainties of changing administrations in Washington have delayed funding for a second, much higher-performance model. Funds assured at the time of writing would not even buy materials for that model, the superconducting bucket of which would reach a speed of 700 mph in 5 m to impart an acceleration of 1000 gs in vacuum. Partly to end these delays, a group of us has formed the Space Studies Institute, a non-profit corporation able to receive tax

deductible subscriptions." Subscriptions from persons of all ages and backgrounds have already begun flowing in, and we will depend on them to construct the second model of the mass-driver. The officers of the Space Studies Institute serve without salary, so funds donated can be applied with close to 100% efficiency.

From a practical viewpoint, the most significant conclusion of the recent work is that the Shuttle, far from being a limited device poorly suited to the tasks now emerging as of greatest economic value, may prove an excellent launch vehicle even for an program ambitious, large-scale of space manufacturing.

References

1. The 1976 NASA-Ames/OAST Summer Study on Space Manufacturing of Non-Terrestrial Materials, published in Dec 1977 by AIAA as Progress in Astronautics and Aeronautics: Space-Based Manufacturing from Nonterrestrial Materials, referred to below as SMNTM, Progress Series Vol. 57, series editor, Martin Summerfield, volume editor, G. K. O'Neill, volume assistant editor, B. O'Leary.

2. Allen, C. W., Astrophysical Quantities, Third Edition, p. 157, Athlone Press, London, 1973.

3. O'Neill, G. K., "The Colonization of Space," Physics Today, Vol. 27, No. 9, Sep 1974, pp. 32-40.

4. Chilton, F., Hibbs, B., Kolm, H., O'Neill, G. K., and Phillips, J., "Electromagnetic Mass-Drivers," in SMNTM.

5. Chilton, F., Hibbs, B., Kolm, H., O'Neill, G. K., and Phillips, J., "Mass-Driver Applications," in SMNTM.

6. O'Neill, G. K., "Mass-Driver as Shuttle Upper Stage," in Proceedings, 1977 Princeton/AIAA Conference on Space Manufacturing, AIAA, 1977.

7. Kolm, H., and O'Neill, G. K., "Mass-Drivers for Lunar Materials Transport and as Reaction Engines," in Proceedings, 1977 IAF Conference on Astronautics, Prague.

8. Space Manufacturing/Space Settlements, the 1977 NASA-Ames Study to be published as single NASA Special Publication containing 16 articles and an introduction, in progress.

9. Kolm, H., et al, "The Magneplane System," Cryogenics, Vol. 15, No. 7, July 1975, pp. 981-995.

10. Phinney, W., Criswell, D., Drexler, E. and Garmirian, J., "Lunar Resources and Their Utilization," in SMNTM.

11. "Initial Technical, Environmental and Economic Evaluation of Space Solar Power Concepts," Vol. 1, summary, JSC-11568, Aug 31, 1976, NASA Johnson Space Center, Houston, Tex.

Reference

12. Thompson, R., "The Space Shuttle System Progress Report," AIAA Preprint No. 77-338. 13. Kolm, H., "Axial Mass-Driver Design," in Proceedings, 1977 Princeton/ AIAA Conference on Space Manufacturing, AIAA, 1977.

14. Space Studies Institute, Box 82, Princeton, N.J. 08540.