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The problem of how to power spaceships for long journeys into space could have just been solved by an astronomer at Columbia University in New York, David Kipping. His idea: To power spaceships up to the size of whole planets, you can harness the extreme gravitational forces of black holes with a “halo drive,” a boomerang of photons shot from a laser. No more running out of fuel, it’s easy “light sailing” so long as you stay within the interstellar highways near optimal black holes, taking full advantage of a gravitational assist.
Kipping noted on Twitter that a major inspiration was the Dyson Slingshot, an idea from the 1960s by physicist Freeman Dyson. Dyson, now 95, believes that space travel could be powered by gravitational slingshots created near massive planets or black holes, something that has proven true when NASA sent the Voyager and Galileo spacecraft to Jupiter. The unmanned ships were able to accelerate without propellant thanks to Jupiter’s size and orbital speed around the sun of 13.1 kilometers per second.
— Bryan Kelly (@BryanKeIIy) March 4, 2019
However, the problem with flying spaceships nearing black holes is extreme: too close and they are destroyed. Kipping’s new idea is to avoid sending the ship and instead send out photons via a laser which get trapped in a circular orbit, returning safely to the ship. Then the ship can harness the amped-up energized photons with solar sails or other means, pushing even the largest of spacecraft along at relativistic speeds without the need for any other source of fuel.
“If we can’t build engines with the power levels that we need, maybe we could borrow it from the universe. Maybe we could steal it from a star, more specifically, a dead star,” said Kipping.
The astronomer says that black holes that move in orbit around another object or another black hole would be the best ones to target. That way, halo drives could harness even higher levels of energy.
— Paul Gilster (@centauri_dreams) March 5, 2019
As a fascinating side-note, if Kipping’s idea holds true then that points to the possibility that extraterrestrials may also target these black-hole “binary systems” to power their spacecraft. So locating these systems would be the perfect spot to look for evidence of interstellar highways.
Kipping described what the maneuver might look like for an astronaut approaching such systems.
“You monitor the orbiting black holes closely and at just the right moment, you fire your laser straight down at one of the black holes. More specifically, you fire it at the black hole moving towards you,” said Kipping.
If the laser beam missed the event horizon or center, then the beam would be bent around the black hole and continue traveling back to the spaceship. The light becomes “blueshifted,” taking on more kinetic energy but traveling at the same speed of light.
“Because you expended no fuel in the act of accelerating, you can essentially accelerate any mass object you want so long as the mass of that object is much lower than that of the black hole. So yes, that means in principle you could accelerate a planet-sized spacecraft to relativistic speed for free.”
To help narrow down the field of 10 billion binary black-hole systems in the Milky Way alone, astronomers could look for the few perfect trajectories created by binary black-hole systems that can act both as accelerators and decelerators for traveling spaceships.
Although it’s amazing to think that we may have already envisioned a means of free interstellar transportation, there is, of course, the initial fuel cost of traveling to the binary black-hole system, to begin with. Perhaps the halo drive will give future astronauts the incentive they need to carry out such an ambitious mission.
See Kipping discuss the Halo Drive below:
Featured images: Screenshots via YouTube