then can we afford to go to Mars？
If there were 20 percent more discretionary funds in the U。S。 federal budget （or the budgets of the other spacefaring nations）； I probably would not feel so conflicted about advocating sending humans to Mars。 If there were 20 percent less； I don't think the most diehard space enthusiast would be urging such a mission。 Surely there is some point at which the national economy is in such dire straits that sending people to Mats is unconscionable。 The question is where we draw the line。 plainly such a line exists； and every participant in these debates should stipulate where that line should be drawn； what fraction of the gross national product for space is too much。 I'd like the same thing done for 〃defense。〃
Public opinion polls show that many Americans think the NASA budget is about equal to the defense budget。 In fact； the entire NASA budget； including human and robotic missions and aeronautics； is about 5 percent of the U。S。 defense budget。 How much spending for defense actually weakens the country？ And even if NASA were cancelled altogether； would we free up what is needed to solve our national problems？
HUMAN SPACEFLIGHT In general—to say nothing of expeditions to Mars—would be much more readily supportable if； as in the fifteenth…century arguments of Columbus and Henry the Navigator； there were a profit lure。* Some arguments have been advanced。 The high vacuum or low gravity or intense radiation environment of near…Earth space might be utilized； it is said； for mercial benefit。 All such proposals must be challenged by this question： Could parable or better products be manufactured down here on Earth if the development money made available were parable to what is being poured into the space program？ Judging by how little money corporations have been willing to invest in such technology—apart from the entities building the rockets and spacecraft themselves—the prospects； at least at present； seem to be not very high。
* Even then it wasn't easy。 The Portuguese chronicler Gomes Eanes de Zurara reported this assessment by Prince Henry the Navigator： 〃It seemed to the Lord Infante that if he or some other lord did not endeavor to gain that knowledge； no mariners nor merchants would ever dare to attempt it； for it is clear that none of them ever trouble themselves to sail to a place where there is not a sure and certain hope of profit。〃
The notion that rare materials might be available elsewhere is tempered by the fact that freightage is high。 There may； for all we know； be oceans of petroleum on Titan； but transporting it to Earth will be expensive。 Platinum…group metals may be abundant in certain asteroids。 If we could move these asteroids into orbit around the Earth； perhaps we could conveniently mine them。 But at least for the foreseeable future this seems dangerously imprudent； as I describe later in this book。
In his classic science fiction novel The Man Who Sold the Moon； Robert Heinlein imagined the profit motive as the key to space travel。 He hadn't foreseen that the Cold War would sell the Moon。 But he did recognize that an honest profit argument would be difficult to e by。 Heinlein envisioned； therefore； a scam in which the lunar surface was salted with diamonds so later explorers could breathlessly discover them and initiate a diamond rush。 We've since returned samples from the Moon； though； and there is not a hint of mercially interesting diamonds there。
However； Kiyoshi Kuramoto and Takafumi Matsui of the University of Tokyo have studied how the central iron cores of Earth； Venus； and Mars formed； and find that the Martian mantle （between crust and core） should be rich in carbon—richer than that of the Moon or Venus or Earth。 Deeper than 300 kilometers； the pressures should transform carbon into diamond。 We know that Mars has been geologically active over its history。 Material from great depth will occasionally be extruded up to the surface； and not just in the great volcanos。 So there does seem to be a case for diamonds on other worlds—on Mars； lied not the Moon。 In what quantities； of what quality and size； and in which locales we do not yet know。
The return to Earth of a spacecraft stuffed with gorgeous multicarat diamonds would doubtless depress prices （as well as the shareholders of the de Beers and General Electric corporations）。 But because of the ornamental and industrial applications of diamonds； perhaps there is a lower limit below which prices will not go。 Conceivably； the affected industries might find cause to promote the early exploration of Mars。
The idea that Martian diamonds will pay for exploring Mars is at best a very long shot； but it's an example of how rare and valuable substances may be discoverable on other worlds。 It would be foolish； though； to count on such contingencies。 If we seek to justify missions to other worlds； we'll have to find other reasons。
BEYOND DISCUSSIONS OF PROFITS and costs； even reduced costs； we must also describe benefits； if they exist。 Advocates of human missions to Mars must address whether； in the long term； missions up there are likely to mitigate any of the problems down here。 Consider now the standard set of justifications and see if you find them valid； invalid； or indeterminate：
Human missions to Mars would spectacularly improve our knowledge of the planet； including the search for present and past life。 The program is likely to clarify our understanding of the environment of our own planet； as robotic missions have already begun to do。 The history of our civilization shows that the pursuit of basic knowledge is the way the most significant practical advances e about。 Opinion polls suggest that the most popular reason for 〃exploring space〃 is 〃increased knowledge。〃 But are humans in space essential to achieve this goal？ Robotic missions； given high national priority and equipped with improved machine intelligence； seem to me entirely capable of answering； as well as astronauts can； all the questions we need to ask—and at Maybe 10 percent the cost。
It is alleged that 〃spinoff〃 will transpire—huge technological benefits that would otherwise fail to e about—thereby improving our international petitiveness and the domestic economy。 But this is an old argument： Spend 80 billion （in contemporary money） to send Apollo astronauts to the Moon； and we'll throw in a free stickless frying pan。 Plainly； if we're after frying pans； we can invest the money directly and save almost all of that 80 billion。
The argument is specious for other reasons as well； one of which is that DuPont's Teflon technology long antedated Apollo。 The same is true of cardiac pacemakers； ballpoint pens； Velcro； and other purported spinoffs of the Apollo program。 （I once had the opportunity to talk with the inventor of the cardiac pacemaker； who himself nearly had a coronary accident describing the injustice of what he perceived as NASA taking credit for his device。） If there are technologies we urgently need； then spend the money and develop them。 Why go to Mars to do it？
Of course it would be impossible for so much new technology as NASA requires to be developed and not have some spillover into the general economy； some inventions useful down here。 For example； the powdered orange juice substitute Tang was a product of the manned space program； and spinoffs have occurred in cordless tools； implanted cardiac defibrillators； liquid…cooled garments； and digital imaging—to name a few。 But they hardly justify human voyages to Mars or the existence of NASA。
We could see the old spinoff engine wheezing and puffing in the waning days of the Reagan…era Star Wars office。 Hydrogen bomb…driven X…ray lasers on orbiting battle stations will help perfect laser surgery； they told us。 But if we need laser surgery； if it's a high national priority； by all means let's allocate the funds to develop it。 just leave Star Wars out of it。 Spinoff justifications constitute an admission that the program can't stand on its own two feet； cannot be justified by the purpose for which it was originally sold。
Once upon a time it was thought； on the basis of econometric models； that for every dollar invested in NASA many dollars were pum