Australian news, and some related international items

American public opinion ignored as NASA prioritises colonising Mars, over research to save the climate

63 percent according to a 2018 Pew Research Center survey—believe that NASA should prioritize monitoring Earth’s climate system. Only a minority—18 percent—said that NASA should prioritize sending humans to Mars.

Is using nuclear materials for space travel dangerous, genius, or a little of both? bulletin of the Atomic Scientists , Bulletin of the Atomic Scientists, By Susan D’Agostino | July 28, 2021 

The 1977 Soviet satellite Kosmos 954 was supposed to monitor ocean traffic using radar—a technology that works best at short distances. For this reason, the craft traveled in Earth’s low orbit, where solar panels alone could not provide consistent power. And so, the satellite was equipped with a small, efficient, yet powerful nuclear reactor fueled by approximately 50 kg of weapons-grade uranium 235. Within weeks of its launch, Kosmos 954 veered from its path like a drunkard on a walk. The Soviets tried to eject its radioactive core into a higher orbit by way of a safety system designed for that purpose. But the safety system failed. In January 1978, Kosmos 954 burst into the Western Canada skyline, scattering radioactive dust and debris over a nearly 400-mile path. The cleanup and recovery process, which took nearly eight months and started in the subarctic winter, found that virtually all of the satellite fragments were radioactive, including one that was “sufficient to kill a person or number of persons remaining in contact with that part for a few hours.”

Now that the United States has set a goal of a human mission to Mars by 2039, the words “nuclear” and “space” are again popping up together in newspaper headlines. Nuclear propulsion systems for space exploration—should they materialize—are expected to offer significant advantages, including the possibility of sending spacecraft farther, in less time, and more efficiently than traditional chemical propulsion systems. But extreme physical conditions on the launchpad, in space, and during reentry raise questions about risk-mitigation measures, especially when nuclear materials are present. 

Why not travel to Mars on a chemically propelled spacecraft? Spaceships that use chemical propellants benefit from tremendous thrust to get the job done. However, they also need to carry fuel and oxidizer to power that incredible upward or forward movement………..

Even if a spacecraft were able to refuel with a chemical propellant in space or magically carry enough chemical propellant for the journey to Mars, the long transit time would present a hazard to the crew……..

In theory, nuclear propulsion for space travel will offer two significant advantages over chemical propulsion. First, since nuclear systems are much more efficient, the amount of fuel required for the journey to Mars is practical. Second, without a need to traverse the shortest path, the flight could take off from Earth and Mars anytime—without delay. The latter would reduce the length of the roundtrip journey and the crew’s exposure to radiation.

Still, attaching what amounts to a nuclear reactor to a human-occupied spaceship is not without risks.

Is the idea of sending nuclear materials into space new? The idea of sending nuclear materials into outer space is not new. And unlike Kosmos 954, many instances have been successful. Since 1961, NASA has powered more than 25 space missions with nuclear materials. The only other practical power option—solar power—is often unavailable in dark, dusty, far-off corners of the solar system.

Likewise, the Atomic Energy Commission launched a nuclear-thermal rocket propulsion research and development program in 1955. …….funding and interest in the programs dried up in the 1970s……

What new plans does the United States have for sending nuclear materials to space? The National Academies’ report released earlier this year recommended that NASA “commit within the year to conducting an extensive and objective assessment of the merits and challenges of using different types of space nuclear propulsion systems and to making significant technology investments this decade.” The report offers a roadmap for developing two different kinds of propulsion systems—nuclear electric and nuclear thermal—for human missions to Mars.

nuclear electric propulsion system bears some resemblance to a terrestrial power plant. That is, first a fission reactor generates power for electric thrusters. That power positively charges the ions in the gas propellant, after which electric, magnetic, or electrostatic fields accelerate the ions. The accelerated ions are then pushed out through a thruster, which propels the spacecraft.

Alternatively, in a nuclear thermal propulsion system, the reactor operates more as a heat exchanger in which a fuel such as liquid hydrogen is first heated to very high temperatures—up to 4,600 degrees Fahrenheit—that is then exhausted through a rocket nozzle to produce thrust.

“For nuclear thermal propulsion, the challenge is: temperature, temperature, temperature,” Anthony Calomino, a materials and structure research engineer at NASA’s Langley Research Center, said. “There are not many materials that can survive those kinds of temperatures.” ………..

While nuclear electric propulsion systems do not require extreme temperatures, they face a different hurdle. Nuclear electric systems have six subsystems, including a reactor, shield, power conversion, heat rejection, power management and distribution, and electric propulsion systems. The operating power of all of these subsystems will need to be scaled up by orders of magnitude—and in such a way that they continue to work together—before they are ready for space……………..

Why is the United States planning to send humans to Mars anyway? Some argue that the scientific value of a human-crewed Mars mission could be captured by robots at a much lower cost and risk. Others think that humans, whose role in terrestrial climate change is apparent, should first rehabilitate Earth before colonizing other planets. Still others worry that human microbes could contaminate the Red Planet.

Indeed, a majority of Americans—63 percent according to a 2018 Pew Research Center survey—believe that NASA should prioritize monitoring Earth’s climate system. Only a minority—18 percent—said that NASA should prioritize sending humans to Mars…………….

July 29, 2021 - Posted by | Uncategorized

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