Solar Thermal Propulsion and a Gravity Well Dive Could Take a Spaceship Outside Sol

Solar Thermal Propulsion and a Gravity Well Dive Could Take a Spaceship Outside Sol 6 photos
Rhea Scorpius Heating Thermal CapacitorRhea Scorpius Heating Thermal CapacitorRhea Scorpius Heating Thermal CapacitorRhea Scorpius Heating Thermal CapacitorDemonstration Rocket for Agile Cislunar Operations (DRACO)
As you're reading this, NASA's records read some 250 spacecraft sent into space, carrying with them either humans or our hopes for some revolutionary discovery. None of them have actually left our solar system, with only one being close to doing so, 46 years after it departed our planet.
It's Voyager 1 I'm talking about, a spacecraft launched in 1977, and currently the one that's farthest out from home: almost 15 million miles (2.4 million km). It took the spacecraft almost five decades to reach that spot, located 160 astronomical units from Earth.

The real wonders of space probably lie in the interstellar space. According to some scientists, that starts about 550 astronomical units away from our planet. At a speed of just three astronomical units per year, it would take Voyager a very, very long time to reach it.

The above makes it obvious that if we are to ever leave the confines of our own solar system faster, new technologies and methods have to be devised. We know of no one working on a warp drive yet, but some people are trying to use nature and the properties of the Universe, combined with technology, to allow spacecraft to escape Sol.

One idea involves a spacecraft powered by solar thermal propulsion and something called an Oberth maneuver. Named after physicist Hermann Oberth, one of the promoters of early rocket technology during the Second World War, it's a technique that calls for a spacecraft to essentially drop into the gravity well of a nearby celestial body.

By letting itself go this way, the ship should gain speed, and if that is backed by impressive propulsion technology, higher escape velocity could in theory reached a lot easier. Technically, any celestial body in our solar system could be used for this, but given how the larger the body the larger the well, our Sun comes out as a prime target for such a maneuver.

During last year's NASA Innovative Advanced Concepts (NIAC) program grants, a researcher from the Los Alamos National Lab, Jason Benkoski, proposed something called a "combined heat shield and solar thermal propulsion system for an Oberth maneuver" – and no, there's no acronym for that.

Such a means of propulsion and a solar Oberth maneuver should allow spacecraft to exit the solar system at higher velocities, thus reaching their targets in the Kuiper Belt (located between 30 and 55 AU beyond the orbit of Neptune), or even interstellar space, much faster.

One major hurdle with such a move is the Sun's heat, as the spacecraft would need to get pretty close for it to work. That's why the team behind the idea is looking into heat shield/heat exchanger technology. Furthermore, prototypes of solar thermal propulsion tech, made with special materials capable of withstanding high temperatures (2,800 degrees Kelvin/2,500 Celsius), have already been built and tested, making people confident the idea has some merit.

The same heat though raises concerns about how the spacecraft could store fuel in cryogenic state in such conditions. That's why, as part of the NIAC grant, Benkoski suggested a study into alternate propellants and how much of them it would take to allow maximum escape velocity for a fully loaded spacecraft.

We're told the fuels currently being researched are hydrogen, lithium hydride, lithium, methane, ammonia, and even water.

We're not given any info on the current state of the research, but we do know what the people working on it are aiming for: a spacecraft leaving the solar system at a speed of at least ten astronomical units.

On a realistic note, it's unlikely we’ll see anything significant being announced on this front sometime soon, but there is some reassurance in the fact people have begun looking beyond our immediate neighborhood.
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Editor's note: Gallery shows the Rhea Scorpius Heating Thermal Capacitor.

About the author: Daniel Patrascu
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Daniel loves writing (or so he claims), and he uses this skill to offer readers a "behind the scenes" look at the automotive industry. He also enjoys talking about space exploration and robots, because in his view the only way forward for humanity is away from this planet, in metal bodies.
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