The Petrov Ramjet

Last week, NASA astronomers announced the discovery of the planet Kepler 425b, a new candidate for Earth 2.0. So far, NASA’s Kepler Space Telescope has found 4,696 such possible home worlds. Unfortunately, Kepler 425b is 1,400 light-years away from Earth. So how could we ever reach such a planet, even one within 50 or 100 light-years of Earth?

Bussard ramjet
Artist’s rendering of a Bussard ramjet (NASA)

In 1960, physicist Robert W. Bussard proposed a design for long-range spacecraft propulsion designated the Bussard ramjet. His prototype called for a fusion rocket that collected hydrogen in large electromagnetic arrays. The rocket’s speed would then force the hydrogen through progressively tighter magnetic fields to create a nuclear fusion reaction. Bussard’s design inspired the Petrov ramjet, one of the many hypothetical technologies I adapted for my novel Our Dried Voices:

“After decades of exploratory dead ends, Seashell funded scientists announced in 2092 that they had discovered an Earth-like planet approximately sixteen light-years from Earth. This planet, later named Pearl, was believed to be rocky, about half the size of Earth, and potentially bearing surface water. It orbited a dim red star comparable to the Earth’s sun, called Falder 347, with a mean orbital radius of 56 million kilometers. The only problem, assuming Pearl was capable of sustaining life, was how to get there. In 2101, Seashell scientists built a satellite, Pearl I, to attempt a voyage to that distant world. The satellite was powered by a modified version of the Bussard ramjet prototype, renamed the Petrov ramjet after its designer, the Russian aeronautical engineer Dr. Ilya Petrov.

“The Petrov ramjet was driven by a fusion rocket capable of propelling the satellite at 70% light speed. The massive quantity of fuel necessary for this sustained fusion reaction could not be carried on board the satellite but instead was gathered in the form of hydrogen gas from the interstellar medium by a series of electromagnetic fields, 50 kilometers in diameter. These magnetic fields collected and compressed the hydrogen to generate a thermonuclear fusion reaction, then directed the energy of that reaction opposite to the intended direction of travel to produce the forward acceleration of the ramjet.

“However, when collected while the ramjet traveled against the stellar winds, these hydrogen ions created a significant drag force equal to the mass of ions collected per second multiplied by the velocity of the ions as propelled by the winds, estimated to be about 500,000 meters per second. Seashell scientists decided Pearl I could not travel in a straight line, but instead would have to maneuver like a sailboat, tacking back and forth to either reduce drag force or maximize the effect of tailwinds. By traveling straight ahead at its maximum velocity of 70% light speed, Pearl I could have reached its destination in just under twenty-three years. Yet given the problem of stellar winds, the satellite would require an onboard navigational system to direct the craft in relation to wind patterns. Accounting for these course adjustments, Seashell estimated it might take up to 60 years to reach Pearl.”