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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 more pelling。
Until a national debate on this topic has transpired； until we have a better idea of the rationale and the cost/benefit ratio of human missions to Mars； what should we do？ My suggestion is that we pursue research and development projects that can be justified on their own merits or by their relevance to other goals； but that can also contribute to human missions to Mars should we later decide to go。 Such an agenda would include：
·U。S。 astronauts on the Russian space station Mir for joint flights of gradually increasing duration； aiming at one to two years； the Mars flight time。
·Configuration of the international space station so its principal function is to study the long…term effects of the space environment on humans。
·Early implementation of a rotating or tethered 〃artificial gravity〃 module on the international space station； for other animals and then for humans。
·Enhanced studies of the Sun； including a distributed set of robot probes in orbit about the Sun； to monitor solar activity and give the earliest possible warning to astronauts of hazardous 〃solar flares〃—mass ejections of electrons and protons from the Sun's corona。
·U。S。/Russian and multilateral development of Energiya and Proton rocket technology for the U。S。 and international space programs。 Although the United States is unlikely to depend primarily on a Soviet booster； Energiya has roughly the lift of the Saturn V that sent the Apollo astronauts to the Moon。 The United States let the Saturn V assembly line die； and it cannot readily be resuscitated。 Proton is the most reliable large booster now in service。 Russia is eager to sell this technology for hard currency。
·Joint projects with NASDA （the Japanese space agency） and Tokyo University； the European Space Agency； and the Russian Space Agency； along with Canada and other nations。 In most cases these should be equal partnerships； not the United States insisting on calling the shots。 For the robotic exploration of Mars； such programs are already under way。 For human flight； the chief such activity is clearly the international space station。 Eventually； we might muster joint simulated planetary missions in low Earth orbit。 One of the principal objectives of these programs should be to build a tradition of cooperative technical excellence。
·Technological development—using state…of…the…art robotics and artificial intelligence—of rovers； balloons； and aircraft for the exploration of Mars； and implementation of the first international return sample mission。 Robotic spacecraft that can return samples from Mars can be tested on near…Earth asteroids and the Moon。 Samples returned from carefully selected regions of the Moon can have their ages determined and contribute in a fundamental way to our understanding of the early history of the Earth。
·Further development of technologies to manufacture fuel and oxidizer out of Martian materials。 In one estimate； based on a prototype instrument designed by Robert Zubrin and colleagues