oreseen 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 pumped into the U。S。 economy。 If this multiplier effect applied more to NASA than to most government agencies； it would provide a potent fiscal and social justification for the space program。 NASA supporters were not shy about appealing to this argument。 But a 1994 Congressional Budget Office study found it to be a delusion。 While NASA spending benefits some production segments of the U。S。 economy—especially the aerospace industry—there is no preferential multiplier effect。 Likewise； while NASA spending certainly creates or maintains jobs and profits； it does so no more efficiently than many other government agencies。
Then there's education； an argument that has proved from time to time very attractive in the White House。 Doctorates in science peaked somewhere around the time of Apollo 11； maybe even with the proper phase lag after the start of the Apollo program。 The cause…and…effect relationship is perhaps undemonstrated； although not implausible。 But so what？ If we're interested in improving education； is going to Mars the best route？ Think of what we could do with 100 billion for teacher training and salaries； school laboratories and libraries； scholarships for disadvantaged students； research facilities； and graduate fellowships。 Is it really true that the best way to promote science education is to go to Mars？
Another argument is that human missions to Mars will occupy the military…industrial plex； diffusing the temptation to use its considerable political muscle to exaggerate external threats and pump up defense funding。 The other side of this particular coin is that by going to Mars we maintain a standby technological capacity that might be important for future military contingencies。 Of course； we might simply ask those guys to do something directly useful for the civilian economy。 But as we saw in the 1970s with Grumman buses and Boeing/Vertol muter trains； the aerospace industry experiences real difficulty in producing petitively for the civilian economy。 Certainly a tank may travel 1；000 miles a year and a bus 1；000 miles a week； so the basic designs must be different。 But on matters of reliability at least； the Defense Department seems to be much less demanding。
Cooperation in space； as I've already mentioned； is being an instrument of international cooperation—for example； in slowing the proliferation of strategic weapons to new nations。 Rockets demissioned because of the end of the Cold War might be gainfully employed in missions to Earth orbit； the Moon； the planets； asteroids； and ets。 But all this can be acplished without human missions to Mars。
Other justifications are offered。 It is argued that the ultimate solution to world energy problems is to strip…mine the Moon； return the solar…wind…implanted helium…3 back to Earth； and use it in fusion reactors。 What fusion reactors？ Even if this were possible； even if it were cost…effective； it is a technology 50 or 100 years away。 Our energy problems need to be solved at a less leisurely pace。
Even stranger is the argument that we have to send human beings into space in order to solve the world population crisis。 But some 250；000 more people are born than die every day—
which means cans that we would have to launch 250；000 people per day into space to maintain world population at its present levels。 This appears to be beyond our present capability。
I RUN THROUGH such a list and try to add up the pros and cons； bearing in mind the other urgent claims on the federal budget。 To me； the argument so far es down to this question： Can the sum of a large number of individually inadequate Justifications add up to an adequate justification？
I don't think any of the items on my list of purported justifications is demonstrably worth 500 billion or even 100 billion； certainly not in the short term。 On the other hand； most of them are worth something； and if I have five items each worth 20 billion； maybe it adds up to 100 billion。 If we can be clever about reducing costs and making true international partnerships； the justifications bee mo