On Aug. 18, engineers and flight control specialists at NASA will fire small rockets aboard the Cassini space probe in order to bring it to within 723 miles of Earth, and thereby eventually to propel it further out into the solar system. The probe will be traveling at 42,300 mph. It is not supposed to inadvertently enter Earth's atmosphere, burn up on re-entry, and release 15 or 20 pounds of lethal plutonium 238 dust. This dust should not, in turn, cause tens of thousands of humans, randomly chosen by fate, to contract lung cancer and die lingering, hacking, excruciating deaths over the next 50 years.

When this doesn't happen (NASA rates the chance of such an "event" at less than 1 in 1.2 million), fans of space exploration will say "I told you so" to anti-nuclear protesters. The protesters will, in turn, continue to advise all who will listen that the sky is more likely to fall than not. Next time...

And people are listening to them.

"We have 60 affiliate groups world-wide," says Bruce Gagnon, who helps coordinate the Global Network Against Weapons and Nuclear Power in Space from his home in Gainesville. "They make up literally millions of people."

People are listening because nuclear power is linked in myriad ways both to human sickness and to the comic doom of high-level waste disposal. And people are listening because of the gut feeling -- not to mention empirical evidence -- that "peaceful" nuclear applications like Cassini's plutonium-fueled radioisotope thermal electric generators (RTGs, in NASA parlance) are inseparable from the vast catalog of U.S. military dreams for space. Still others are listening because they're worried that, 30 years after the first moon landing, as jowly generals and space travelers celebrate the End of Limits, the anti-nukers might be winning.

"This is not a routine nuclear dispute," wrote M. Jack Ohanian in a recent Op-Ed piece for the Tampa Tribune. "If such mischief is allowed to influence public policy-making on radiation applications, the results will be far-reaching and devastating: Exploration of the solar system will be stalled, testing of new power systems for use in space will be stopped, and industrial and military uses of radioisotopes in satellite systems will be stifled. Congressional action could determine not only the immediate fate of RTGs, but also an advanced radioisotope power system for future missions in NASA's outer-planets project."

Ohanian is interim dean of engineering at the University of Florida, where he has served as professor of nuclear and radiological engineering since 1963. A past president of the American Nuclear Society, Ohanian has watched with alarm as Gagnon's rag-tag band of nuns, peaceniks, professors and scientists have doggedly dragged the issue of space nuclear power -- and military power -- into the public arena. "I object to tying really good space missions to the Air Force mission," Ohanian says. "Cassini and these have nothing to do with the military objectives ... they're barking up the wrong tree."

But Ohanian's commentary subtlely ratifies what the anti-nukers have been saying for more than a decade: This fight isn't about one mission or one 72-pound box of plutonium. It's not about the 27 nuclear-powered missions that NASA has already flown, or even those still in the works. This is about the future of space exploration, the future of war, and the future of the planet itself. It's about whether outer space will be a realm of peace and reason, or the U.S. Air Force will be allowed to turn the sky into a deadly garrison in the service of commerce.

NASA's success with Cassini, which was launched on Oct. 13, 1997, promises not only a quantum leap in mankind's data about Saturn, its ring system and satellites (data that may or may not be adequately analyzed; see Too much to take in). The nuclear battery in Cassini has been developed and refined at the expense of solar alternatives, in order to keep folks like Ohanian busy -- and working on ever more ambitious nuclear space projects.

In the near future, the U.S. Space Command will require megawatt and even gigawatt power sources in compact packages for use in anti-satellite weapons and potentially even space-to-ground weapons systems, according to military projections. For that, nuclear power is the only solution. And to keep nuclear power an option, a vast infrastructure of laboratories and scientists must be kept on budget and on alert. NASA is a key part of that infrastructure.

"If NASA decides to send people to Mars with a nuclear rocket, we want to make sure that the rocket is as safe as possible, and perhaps to improve the performance," says John Cole, a manager in the Advanced Space Transportation Project office at NASA's Marshall Space Flight Center in Huntsville, Ala.

Cole's words are published in a report on the advanced propulsion research conference held at Marshall this past April. The nuclear rocket of which he writes would be a new design being developed at the University of Florida, presumably with Ohanian's knowledge.

Asked what sort of research his department is doing, Ohanian talks about "new fuel concepts -- and simpler, more safe reactors," medical applications, robots to handle nuclear waste and land-mine detectors. Nothing about space. Asked directly about NASA's nuclear propulsion experiments at Huntsville, Ohanian demurs.

"The only time I see that is for these very long-range missions," Ohanian says. "I don't see that for the near-Earth sort of things. People still work on those deep-space applications." The professor then hints at the question's sensitive nature. Can't be too careful who you talk to about these things.

"Years ago, there was this nutty idea that we're going to have nuclear airplanes," Ohanian continues. "Well, it's not going to be done. Having this would cause a very bad public-relations reaction -- against our peaceful nuclear efforts."

While conceding nothing in the ongoing safety debate, nuclear and military planners have long understood the public-relations danger associated with their work. The nuclear fraternity developed a special discretion that envelopes and extends well beyond official security ratings and classifications. The "don't ask, don't tell" culture both deflects and fuels what insiders regard as the paranoia of anti-nuke activists.

But the paranoia cuts both ways. Ohanian's article warns of a bill in Congress that would ban nukes in space. There is no such bill.

"My impression was, he was trying to create panic," says Gagnon, without irony. He adds that he would welcome such a bill.

There are, however, several international treaties prohibiting offensive weapons in space as well as the commercialization of extraterrestrial bodies, and much of the discussion in space and military circles centers on contravening these rules.

On April 28 and 29 at Cape Canaveral Air Force Station, officials unveiled their latest plans for military dominance in space, called "Vision for 2025." Gagnon was there but could not get a copy of the new report -- probably because the previous version, "Vision for 2020," is now posted on the web at the Global Network site, and has been made exhibit A in the battle against weapons in space (www.spacecom.af.mil/usspace/LRP/cover.htm).

Still, Gagnon posted a report of the conference quoting Air Force Col. Tom Clark that certain "policies and treaties" impede proper U.S. military domination of the universe. "Some treaties may need to be renegotiated," Clark reportedly told the crowd. "We should not ignore the potential for combat in space." During the question-and-answer period, Clark, responding to Gagnon's written question about the status of anti-satellite weapons testing and deployment, said deployment would be ready around 2008 but that this issue was "politically sensitive." According to Gagnon, Clark went on to say that ultimately the U.S. would "need an event to drive the public to support ASAT deployment. But it will happen. We are now talking, planning, doing research and development. Someone will attack one of our systems."

Clark's logic is compelling, drawn from classic studies of power dynamics and resource allocation. It's the kind of thing they drill into the young recruits at West Point and Andover and Langley: There are always enemies.

Gagnon worries that Clark or someone in his command will himself engineer an attack on a U.S. corporate satellite, similar to the Gulf of Tonkin episode that touched off the United States' escalation in Vietnam, or the sinking of the USS Maine. Clark and his people are determined to grow their command.

"The bottom line is that every credible vision for economic prosperity and military effectiveness by 2020 depends on space-based capabilities," says the plan for "Vision for 2020," published in 1998 by the U.S. Space Command. And the reasoning is compelling, if one assumes a need for unchecked technology and weaponry as a prerequisite for security and general happiness.

The basic vision goes like this:

Many companies will launch ever more sophisticated, ever more expensive satellites to both keep an eye on the ground and serve the exploding communications networks sprouting up. Think of pocket-sized phones with call-anywhere capability, Internet access, digital television-level bandwidth. The military and all important corporations will depend on these networks of satellites both for information gathering and communications capabilities. "So [the military] must leverage advancements in other sectors through active global partnerships with civil, commercial, and international space programs," reads "Vision for 2020."

Of course, they'll have to protect it.

"Competitors" will notice this dependence on space, and calculate it as a vulnerability unless the satellites are well-protected. Competitors will become "aggressors," targeting U.S. space assets while erecting their own networks -- all of them fortified. Bottom line: "Our citizens won't accept that their military was unprepared to protect our troops from an enemy's free use of space."

Like joint military-police exercises in "urban warfare," planning such as this happens in plain sight with no accompanying debate about the underlying assumptions or priorities. News reports, when they mention the nuclear aspect of the Cassini mission, discuss the carbon cladding on this RTG, and NASA's recent efforts to create more efficient nuclear batteries for the eight to 12 additional missions it plans for this technology. They consider only the million-to-one chance of a re-entry failure. They ignore the recent talk of reopening nuclear factories to feed NASA's needs. They ignore reports that workers in the plants where Cassini's nuclear batteries were produced have experienced a dizzying array of serious illnesses and mysterious deaths. They ignore the expanding private space budgets as NASA's own budget shrinks. They make no examination of the nation's overall space policy, which is somehow assumed to be the same as it was during the days of Apollo: a world of heroes and wonder set before the iron backdrop of realpolitik.

"Yeah," concedes Ohanian, "there probably should be some debate."

Gagnon, who cut his teeth in the late 1980s battling the nuclear-equipped Galileo space probe, has been trying to spark this debate for 10 years. "What this whole thing is about -- [and the] Mars [mission] will be the epitome of this -- is the aerospace industry sees this as a wonderful way to get its hands on everybody's pocketbook," Gagnon says.

And so he and kindred spirits chain themselves to fences and ride cramped paddy wagons to jail, and sometimes the media shows up and takes a picture, and sometimes not. The insiders notice and the epithets still fly, but less often now. NASA press releases speak of safer nuclear batteries. NASA spokesman deny the Global Network has anything to do with this.

"They're beginning to recognize that, 'We're gonna have to deal with these people, they're getting stronger, they're not going to go away,'" says Gagnon. "We've been popping up all over the world, literally, at events."

Let the debate begin.