Freitag, 11. März 2016 - 08:00 Uhr
During the Cold War, the Soviet Union had over 30 fission powered satellites, like this Rorsat. SMITHSONIAN/DIA
YOU DO NOT want to go to Mars. At least, not with today’s engines powering the trip. A chemically propelled voyage would take 18 months, one way. During which time any combination of boredom, radiation poisoning, and cancer will likely kill you. Suppose you make it? Congratulations on being the first Martian to die of old age, because a return trip from the Red Planet is currently impossible without using wishful logistics like fuel harvesting.
The Russians think they can do better. Last week, their national nuclear corporation Rosatom announced it is building a nuclear engine that will reach Mars in a month and a half—with fuel to burn for the trip home. Russia might not achieve its goal of launching a prototype by 2025. But that has more to do with the country’s financial situation (not great) than the technical challenges of a nuclear engine.
Soviet scientists actually solved many of those challenges by 1967, when they started launching fission-powered satellites. Americans had their own program, called SNAP-10A, which launched in in 1965. Ah, the Cold War.
Both countries prematurely quashed their nuclear thermal propulsion programs (Though the Soviets’ lasted into the 1980s). “Prematurely” because those fission systems were made for relatively lightweight orbital satellites—not high-thrust, interplanetary vessels fattened with life support for human riders. Nonetheless, “A nuclear contraption should not be too far off, not too complicated,” says Nikolai Sokov, senior fellow at the James Martin Center for Nonproliferation Studies in Monterey, CA. “The really expensive thing will be designing a ship around these things.”
Nuclear thermal is but one flavor of nuclear propulsion. Rosatom did not respond to questions about their system’s specs, but its announcement hints at some sort of thermal fission. Which is to say, the engine would generate heat by splitting atoms and use that heat to burn hydrogen or some other chemical. Burning stuff goes one direction, spaceship goes the other.
The principle isn’t too far from chemical propulsion. The fastest chemical rockets produce thrust by igniting one type of chemical (the oxidizer) to burn another (the propellant), creating thrust. Chemical or otherwise, rocket scientists rate propulsion methods based on a metric called Specific Impulse, “Which means, if I have a pound of fuel, for how many seconds will that pound of fuel create a pound of thrust,” says Robert Kennedy, a systems engineer for Tetra Tech in Oak Ridge, TN, and former congressional fellow for the US House of Representatives’s space subcommittee. For instance, one pound of the chemical mixture powering the Space Launch System—NASA’s in utero rocket for the agency’s planned mission to Mars—produces about 269 seconds of thrust in a vacuum.
But the outcomes of those two methods are radically different, because chemical rocketry has a catch-22. The faster or farther you want to go, the more fuel you need to pack. The more fuel you pack, the heavier your rocket. And the heavier your rocket, the more fuel you need to bring…
Eventually, the equation balancing thrust to weight plateaus, which is why a year and a half is around the lower time limit for sending a chemically propelled, crewed mission to Mars. (Until Elon Musk’s spiritual descendants build asteroid-mined interplanetary fuel stations.) And that’s not even considering the incredible cost of launching fuel—about $3,000 a pound. Expensive, but the politics surrounding nuclear make it a harder sell in America, so NASA is stuck with the Space Launch System (and its thirsty fuel tanks) for now.
The engines the Soviets and Americans were developing during the Space Race, on the other hand, had at least double a chemical rocket’s specific impulse. Modern versions could likely do even better. Which means spaceships would be able to carry a lot more fuel, and therefore fire their thrusters for a longer portion of the trip to Mars (bonus: artificial gravity!). Even better, a thermal fission spaceship would have enough fuel to decelerate, go into Martian orbit, and even return to Earth.
Calling for a fission mission to Mars is great for inspiring space dreamers, but Russia’s planned engine could have practical, near-term applications. Satellites need to fire their thrusters every so often to stay in their ideal orbits (Also, to keep from crashing to Earth). Sokov thinks the main rationale for developing a nuclear thermal engine would be to allow for more of these orbital corrections, significantly increasing a satellite’s working lifespan. Fission power would also give probes more maneuverability. “One civilian application is to collect all the space junk,” says Sokov. “You are free to think of other, perhaps not as innocent applications.”
Russia may have the will to go nuclear, but it probably lacks the means. Rosatom has budgeted roughly 15 billion rubles on the project, which began in 2010 and is scheduled to have a launch-ready vehicle by 2025. That’s about $700 million: eyebrow-raisingly cheap for a 15-year long space project. For reference, just the rocket part of NASA’s Space Launch System is projected to cost nearly $10 billion.
And those 15 billion rubles don’t include the cost of launch, which could be why Rosatom made its 6-weeks-to-Mars announcement last week. “Going public can serve a number of purposes, including getting funding, increasing visibility, things like that from politicians, readers, and others who would like this visionary thing,” says Sokov. Rosatom plans to have a land-based test reactor by 2018.
If the Russian Federation does succeed, they won’t be stopped by international treaties—which only apply to nuclear weapons. That does not mean the engine would be completely safe, however. Things launched from rockets do not always make it to space, and things in orbit sometimes fall to Earth. In 1978, a nuclear-powered Soviet satellite crashed in northern Canada, spewing radioactive waste over nearly 50,000 square miles. But listen, tovarisch: One does not make omelette without breaking eggs, no?
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