by I.A. Crawford
The Case for Mars
The well-worn arguments against sending people to Mars have been reiterated by Sleep (1997), who asserts that this would be "the most dangerous, costly, inefficient and counter-productive method yet devised for exploring the Red Planet", and that machines could do it all much better. I certainly agree that the robotic exploration of Mars to date has been a tremendous success, and that the collection, early in the next century, of a few kilograms of Mars rock by a robotic sample return mission will be of tremendous scientific importance. However, a momentšs reflection will show that a proper exploration of Mars will require a lot more than this.
The ultimate aim of planetary science must be to understand the other planets to the same extent that we understand the Earth, and even that is far from complete. Mars has a surface area approximately equal to the land area of Earth, and by all accounts it has had a highly complicated geological, climatological, and, possibly, biological history. To reach anything like an adequate understanding of Mars will require, as a minimum, the analysis of tonnes (possibly thousands of tonnes) of rocks collected from all over the planet; it will require magnetic, gravity and seismic surveys; and it will require boreholes, probably kilometres deep, drilled in selected regions. The idea that this could be achieved with half a dozen robot landers is frankly ridiculous.
Consider the most important scientific question which needs to be addressed on Mars: did life evolve when, some 3.5 to 4 billion years ago, liquid water flowed on its surface and conditions were similar to those that prevailed on Earth when life evolved here? Recent work on the origin of life (e.g. de Duve 1995) is close to predicting that life ought to have evolved on Mars at that time. It is hugely important for our understanding of the origin of life, and indeed for the whole science of biology, to ascertain whether or not it did so, and, if it did, how similar Martian lifeforms were to terrestrial ones. An answer to this question will require procedures similar to those used to find the oldest microfossils on Earth (e.g. Schopf 1993): it will be necessary to conduct a detailed search for Martian sedimentary rocks of the appropriate age, to determine their geological and palaeo-environmental context, and to painstakingly sift through them with microscopes. It is very difficult to see how such a programme could be conducted satisfactorily with robots alone.
Space Infrastructure
The main point I want to make is that science stands to benefit greatly from exploiting the technology, and especially the infrastructure, developed to support a human space flight capability. By infrastructure I mean all the background capabilities (for example, launchers, spaceports, space stations, interplanetary transports, lunar and planetary outposts) which purely scientific budgets could never afford to develop, but which nevertheless act to facilitate scientific research which would not otherwise take place. We have seen how this worked in the case of Apollo, and how the ISS will provide infrastructural support for a wide range of scientific investigations.
The in-orbit repair of the Hubble Space Telescope (HST) in 1993 provides a good example of the usefulness of a human space flight infrastructure. Sleep (1997) has rather disparagingly asserted that this was only to correct a fault of NASAšs own making, but this misses the point entirely: without that human intervention in space we would still be stuck with the uncorrected telescope, and astronomy would be greatly impoverished as a consequence. Moreover, the first HST refurbishment mission (STS 61) didnšt just install the corrective optics (COSTAR), it also replaced the solar panels, installed new gyros, repaired the GHRS, and installed WF/PC2. A subsequent astronaut-tended upgrade last year (STS 82) installed two new instruments (STIS and NICMOS), and two further deliveries of new instruments are planned. Thus the HST experience clearly illustrates the scientific advantages of being able to call upon the capabilities of a human space flight infrastructure when the need arises (something already foreseen by Spitzer 1974).
Future potential
Considerable as these advantages have been, however, they pale into insignificance compared to those potentially available in the future. We have already outlined the likely scientific benefits of human outposts on the Moon and Mars, and alluded to the possibilities for building large astronomical instruments in space. Other possibilities include the development, and in-space construction, of interplanetary vehicles capable of taking human crews to both near-Earth and Main Belt asteroids, and to the Galilean satellites of Jupiter. In the case of the asteroids, the primary motivation for human exploration is likely to be economic rather than scientific (e.g. Lewis et al. 1993), but it seems clear that our knowledge of these objects, and thus of the early history of the solar system, would be greatly increased as a consequence. As regards the Galilean satellites, the arguments for human exploration closely follow those already advanced for the Moon and Mars. Consider Europa, for example, a world almost as large as our Moon and which is of biological interest owing to the likely presence of an ocean of liquid water below its icy crust. How much of the history, structure and environment of this important object will it be possible to piece together from robotic missions alone?
In the more distant future, we should keep in mind the enormous scientific opportunities that would result from the ability to construct fast (v > 0.1c) interstellar space probes (Crawford 1990). However, it is important to understand that the construction of even an unmanned interstellar probe will entail large-scale engineering work in space (see Mallove and Matloff 1989, and Crawford 1990 for reviews), and will only be possible once the necessary infrastructure has been developed.
Wider motives for human space flight
I have argued above that science has been, and will continue to be, a major beneficiary of human space flight, and that the vociferous opposition to it from some quarters of the scientific community is badly misplaced. It seems to me that most of this opposition, from Richard Woolley onwards, stems from two implicit, but erroneous, assumptions: first, that the primary motives for sending people into space are, or at least ought to be, scientific; and second, that the high cost of human space flight is taken from existing scientific budgets.
In fact, ambitious human space projects are undertaken for a variety of reasons, most of which are sociopolitical in nature rather than scientific. In the case of Apollo these arose from the perceived imperatives of the Cold War, and are now thankfully behind us. However, compelling social and political arguments in support of human space flight remain. These range from the economic (where major space initiatives act as high technology 'public works' projects, having a significant multiplier effect on the economy as a whole; e.g. Bezdek and Wendling 1992), to the geopolitical (especially the encouragement of co-operation between former Cold War adversaries). In the future, powerful sociopolitical reasons for human space flight are likely to include the demands of the world economy for extraterrestrial raw materials, and the continuing need for high-profile international projects as aids in building a stable geopolitical environment here on Earth (Crawford 1995). Quite frankly, these arguments are sufficiently strong to justify a major human space programme even in the absence of any scientific benefits whatsoever.
As the complex motivations for human space flight are not primarily scientific, it follows that they are not, and indeed cannot be, financed primarily from scientific budgets. Consider the US space programme: NASA currently has an annual budget of approximately $14 billion (which, to put things in perspective, is only about 5% of the US military budget). However, this should not be perceived as a science budget per se, because NASA is not primarily a science agency (US Congress 1958). There are those in the scientific community who seem to believe that if only NASA was not operating the Space Shuttle, or contributing to the ISS, then the whole $14 billion would be available for space science. However, as we have seen, the former activities are motivated primarily by politically worthwhile, but generally non-scientific, policy objectives of the US government; if the money was not spent on manned space flight it would more likely be spent on military hardware, welfare payments, or tax cuts than on science.
It is true that there is currently a grey area where the manned and unmanned budgets sometimes have to compete for funds within NASA, and that there has been a history of cost overruns in the former decreasing provision for the latter (Van Allen 1986). However, while this is certainly unfortunate, it is really an argument for reform of the way NASAšs budget is allocated by the US Congress rather than for the abandonment of a human space flight capability. Pursuing the latter course would only marginally increase the funds available for space science in the short term, but would prevent the long-term development of a space infrastructure from which science stands to gain so much.
Science education
Nor should we overlook the stimulus to scientific and technical education provided by high-profile human space activities. This extends well beyond stimulating young people to embark on careers in science and engineering, important though that is, but also leads to an increased scientific awareness throughout society. Sagan (1994) put it eloquently: "Exploratory space flight puts scientific ideas, scientific thinking, and scientific vocabulary in the public eye. It elevates the general level of intellectual inquiry." The whole scientific enterprise has the greatest possible interest in encouraging this process.
Conclusion
While recognizing that many of the driving forces behind human space flight are social and political, rather than narrowly scientific, it seems clear that science has been, and will continue to be, a major beneficiary of having people in space. What, after all, is the alternative? We can either stay at home, sending a few robot spacecraft to our neighbouring planets, and continuing to gaze at the more distant universe across light years of empty space, or we can get ourselves out among the planets and, eventually, the stars. In which alternative future would we learn the most about this universe and our place within it?
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