A solar-powered rocket might be our ticket to interstellar space


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A solar powered rocket might be our ticket to interstellar space

If Jason Pinkowski is right, the path to interstellar space begins in a shipping container tucked behind an elevated bay for the lab in Maryland. The setup feels like something out of a low-budget science fiction movie: one of the container walls are lined with thousands of LEDs, a mysterious metal trellis running down the center, and a thick black curtain partially obscures the device. This is the solar simulator for the Johns Hopkins University Applied Physics Laboratory, and it’s an instrument that can fluoresce with an intensity of 20 suns. On a Thursday afternoon, Benkoski installed a small black and white tile on the trellis and pulled a dark curtain around the setting before exiting the shipping container. Then he hit the light switch.

Once the solar simulator got hot, Benkoski began pumping liquid helium through a small, compact tube twisting across the plate. The helium absorbed the heat from the LEDs as it passed through the channel and expanded until it was finally released through a small nozzle. It might not sound like much, but Pinkowski and his team have just demonstrated solar thermal propulsion, a previously theoretical type of rocket engines powered by the sun’s heat. They think it could be the key to interstellar exploration.

“It’s really easy for someone to turn down the idea and say, ‘On the back of an envelope, it looks cool, but if you actually build it, you never get those theoretical numbers,’ ” says Pinkowski, a material scientist at the Applied Physics Lab and the team leader on System “Solar thermal propulsion. What this shows is that solar thermal propulsion is not just a fantasy. It can actually work.”

It has only two spacecraft, Voyager 1 and Voyager 2 He left our solar system. But this was a scientific reward after they had completed their main mission to explore Jupiter and Saturn. Neither spacecraft has been equipped with the appropriate tools to study the boundaries between the fiefdom of our star planet and the rest of the universe. Plus, the Voyager twins are two slow. Clumping at 30,000 mph, it took nearly half a century to escape the influence of the sun.

But the data they sent from the edge is confusing. Showed it Much of what physicists expected about the environment at the edge of the Solar System was wrong. Unsurprisingly, a large group of astrophysicists, cosmologists and planetary scientists are calling for an interstellar probe dedicated to exploring these new frontiers.

In 2019, NASA chose the Applied Physics Laboratory Study concepts for an ad hoc interstellar mission. At the end of next year, the team will present its research to the National Academies of Sciences, Engineering and Medicine for the Decodal Solar Physics Survey, which identifies the science priorities for the sun for the next 10 years. APL researchers are working on The interstellar probe The program examines all aspects of the job, from cost estimates to hardware. But just knowing how to reach interstellar space in any reasonable amount of time is by far the biggest and most important piece of the puzzle.

Don’t stop at the solar area

The edge of the solar system – called the heliosphere – is very far away. By the time the spacecraft reaches Pluto, it is only one-third of the way to interstellar space. The APL team is studying a probe that would go three times farther from the edge of the solar system, on a journey of 50 billion miles, in about half the time it took the Voyager spacecraft to reach the edge. To accomplish this kind of task, they would need a probe unlike anything they had ever been built. “We want to create a spacecraft that travels faster and farther and closer to the sun than anything has done before,” says Pinkowski. “It’s like the hardest thing you could do.”

In mid-November, Interstellar Probe researchers met online for a One week conference To share updates as the study enters its final year. At the conference, teams from APL and NASA shared the results of their work on solar thermal propulsion, which they believe is the fastest way to get a probe into interstellar space. The idea is to run a rocket engine with heat from the sun rather than combustion. According to Benkoski’s calculations, this engine would be three times more efficient than the best conventional chemical engines available today. “From a physics standpoint, it’s hard for me to imagine anything that will beat solar thermal propulsion in terms of efficiency,” says Pinkowski. “But can you prevent it from exploding?”

Unlike the conventional engine mounted on the rear end of the missile, the solar thermal engine researchers are studying will be integrated with the spacecraft’s armor. The hard flat cover is made of black carbon foam with one side covered with white reflective material. Externally, it will look very similar to Heat shield on the Parker solar probe. The crucial difference is the twisted pipeline that is hidden just below the surface. If the interstellar probe passes close to the Sun and pushes hydrogen into the blood vessels of the shield, the hydrogen will expand and explode from a nozzle at the end of the tube. The heat shield will generate thrust.

430,000 miles per hour

It is simple in theory but extremely difficult in practice. The Solar Thermal Rocket is only effective if it can perform the Oberth maneuver, an orbital mechanical penetration that turns the Sun into a giant slingshot. The sun’s gravity acts as a force multiplier that greatly increases the spacecraft’s speed if a spacecraft launches its engines as it orbits the star. The closer the spacecraft is to the sun during the Oberth maneuver, the faster it will go. In designing the APL mission, the interstellar probe would pass only a million miles away The sore surface of the sun.

To put this into perspective, by the time NASA’s Parker Solar Probe comes close to its closest in 2025, it will be 4 million miles from the surface of the Sun and lock it up at Approximately 430,000 miles per hour. That’s about twice the speed the interstellar probe aims to reach, and the Parker Solar Probe built its velocity with the help of gravity from the Sun and Venus over a period of seven years. The interstellar probe would have to accelerate from about 30,000 mph to about 200,000 mph in one shot around the sun, which means approaching the star. Very close.

Dean Sheikh, a materials technologist at NASA’s Jet Propulsion Laboratory who presented a case study of a solar thermal missile during the recent conference, says approaching a thermonuclear explosion the size of the sun creates all kinds of physical challenges. For the APL mission, the probe would spend about 2.5 hours in temperatures around 4,500 degrees Fahrenheit as it completed the Oberth maneuver. It’s more than hot enough to melt through the Parker Solar Probe’s thermal shield, so a Sheikh team at NASA found new materials that could be covered on the outside to reflect the thermal energy. Combined with the cooling effect of hydrogen flowing through the channels in the heat shield, these coatings will keep the interstellar probe cool as it is propelled by the sun. “You want to maximize the amount of energy you take back,” the sheikh says. “Even small differences in material reflection start to heat up your spacecraft enormously.”

“We don’t have many options”

Still, a bigger problem is how to deal with the flow of hot hydrogen through the channels. At extremely high temperatures, hydrogen eats directly through the carbon-based core of the heat shield, meaning the inner channels must be covered with a stronger material. The team has identified some materials that can do the job, but there isn’t a lot of data on their performance, especially extreme temperatures. “There aren’t many materials that can meet these demands,” the sheikh says. “In some ways, that’s a good thing, because we just have to look at this material. But it’s also bad because we don’t have a lot of options.”

The sheikh says the big finding from his research is that there are a lot of tests that need to be done on heat shielding materials before sending a solar thermal missile around the sun. But it is not a deal breaker. In fact, amazing advances in materials science are finally making the idea seem actionable more than 60 years after its inception First to conceive By engineers in the United States Air Force. “I thought I came up with this great idea independently, but people talked about it in 1956,” says Pinkowski. “Additive manufacturing is a key component of that, and we couldn’t do that 20 years ago. Now I can 3D print the metals in the lab.”

Even if Pinkowski was not the first to come up with the idea of ​​solar thermal propulsion, he believes he was the first to demonstrate an engine prototype. During his experiments with oriented tiles in a shipping container, Benkoski and his team showed that it is possible to generate thrust by using sunlight to heat the gas as it passes through channels embedded in a heat shield. These experiences had several limitations. They did not use the same materials or fuel that would be used in an actual mission, and the tests occurred at temperatures much lower than what an interstellar probe would test. But the important thing, says Pinkowski, is that data from low-temperature experiments match models that predict how the interstellar probe will perform its actual mission once the modifications are made to the various materials. We did it on a system that would never fly. Now the second step is to start replacing each of these components with the things you would put on a real spacecraft for the Oberth maneuver, ”says Pinkowski.

And a long way to go

The concept still has a long way to go before it is ready for use on a mission – and with only a year left in studying the interstellar probe, there isn’t enough time to launch a small satellite to conduct experiments in low Earth orbit. But by the time Benkoski and his APL colleagues present their report next year, they will have produced a wealth of data that lay the groundwork for tests in space. There is no guarantee that the National Academies will choose the interstellar probe concept as their top priority for the next decade. But when we’re ready to leave the sun behind, there’s a good chance we will have to use it to shore up our way out of the door.

This story originally appeared wired.com.


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