If Jason Benkoski Right, the path to interstellar space begins in a shipping container tucked away behind a laboratory in Maryland. The set-up looks like something out of a low-budget sci-fi movie: one wall of the container is lined with thousands of LEDs, an unfathomable wire mesh runs down the center, and a thick black curtain partially obscures the device. This is the solar simulator from the Applied Physics Laboratory at Johns Hopkins University, a tool that can shine with the intensity of 20 suns. On Thursday afternoon, Benkoski mounted a small black and white tile over the trellis and pulled a dark curtain around the facility before exiting the shipping container. Then he hit the light switch.
Once the solar simulator was hot, Benkoski started pumping liquid helium through a small built-in tube that snaked through the slab. The helium absorbed heat from the LEDs as it coiled into the channel and expanded until it was finally released through a small nozzle. It may not sound like much, but Benkoski and his team have just demonstrated solar thermal propulsion, a previously theoretical type of rocket motor powered by heat from the sun. They believe this could be the key to interstellar exploration.
“It’s very easy for someone to dismiss the idea and say, ‘On the back of an envelope it looks great, but if you actually build it you will never get those theoretical numbers.’ says Benkoski, a scientist in the applied physics lab and team leader working on a solar thermal propulsion system. “What this shows is that solar thermal propulsion is not just a fantasy. It might actually work.
Only two spacecraft, Voyager 1 and Voyager 2, have left our solar system. But that was a science bonus after completing their main mission of exploring Jupiter and Saturn. None of the spaceships were equipped with the right instruments to study the boundary between our star’s planetary stronghold and the rest of the universe. In addition, the Voyager twins are slow. Traveling at 30,000 miles an hour, it took them nearly half a century to escape the influence of the sun.
But the data they sent back from the edge is enticing. This showed that much of what physicists predicted about the environment on the outskirts of the solar system was wrong. Unsurprisingly, a large group of astrophysicists, cosmologists and planetologists are calling for a dedicated interstellar probe to explore this new frontier.
In 2019, NASA called on the Applied Physics Laboratory to study the concepts for a dedicated interstellar mission. At the end of next year, the team will submit their research to the Decennial Heliophysical Survey of the National Academies of Science, Engineering and Medicine, which determines the scientific priorities related to the sun for the next 10 years. APL researchers working on the Interstellar probe program study all aspects of the mission, from cost estimates to instrumentation. But simply figuring out how to get to interstellar space in a reasonable amount of time is by far the most important and important piece of the puzzle.
The edge of the solar system – called the heliopause – is extremely far away. By the time a spacecraft reaches Pluto, it’s only a third of the way to interstellar space. And the APL team is studying a probe that would go three times farther than the edge of the solar system, traveling 50 billion miles, in about half the time it took for the Voyager spacecraft just to reach the edge. To successfully complete this type of mission, they will need a probe unlike anything that has ever been built. “We want to create a spaceship that will go faster, further and get closer to the sun like anything that has been done before,” says Benkoski. “It’s like the hardest thing you can do.”