Every time we think we’ve got concepts like “gravity” and “orbit” figured out, something comes along that forces us to take a second look, then a third, and so on. We know we need (a lot of) energy to reach space, but once we’re there, we can cover impressive distances almost for free, courtesy of the Planetary Superhighway or Interplanetary Transport Network. What’s the trick?
The famous science fiction writer Robert Heinlein said if you can place a spaceship in orbit, you’re halfway to anywhere. It’s no easy task: Earth demands 8 kilometers per second to achieve a minimal orbit, and more than 11 if we want to escape it… not to mention that we have to go riding giant bombs.
But once we leave our home behind with sheer brute force, the possibility opens up to cover enormous distances by obeying the rules of a complex efficiency game. It would be fabulous to spend extra energy and get there faster, however, we would be forced to carry that energy with us (somehow). What’s the alternative? The Interplanetary Transport Network, the Planetary Superhighway.
Getting to Know the Planetary Superhighway
Although its essence dates back to the 1890s and the investigations of Henri Poincaré, the system was conceived by software engineer Martin Lo of the Jet Propulsion Laboratory for the design of the flight plan of the Genesis mission, whose objective was to collect solar wind particles. Most missions are prepared by exploiting the effects of gravity on the spacecraft when it approaches a planet or moon (called “gravitational assist” or “slingshot”), but the Superhighway includes an additional factor: the effect of the Sun on planets, or of planets on their close moons.
Each planet and moon has five Lagrange points, where the gravity of two bodies is in balance. As the planets and their moons orbit the Sun, these Lagrange points approach, and in some cases overlap. Following a precise flight plan, a spacecraft could wait at one of these points until falling under the influence of a planet, wait again, and hop orbits to another planet. The Superhighway concept merely connects all these points, and in theory, an explorer could go from Mercury to Pluto and back, consuming minimal amounts of fuel.
Everywhere... with a Lot of Patience
The article on the Planetary Superhighway published by Shane Ross is full of fabulous details, but there is one comparison that stands out above the rest: The Genesis mission traveled more than 30 million kilometers using only 5% of its mass as fuel. A car’s full tank also represents (approximately) 5% of its total mass, and with that, it can barely cover about 500 kilometers under optimal conditions.
The Superhighway is under constant change, and the necessary calculations are certainly complex, but these low-energy paths demonstrate that the direct route is not always the best for a mission. What is its weak point? Slowness. Traveling from Earth to Mars using this method would take about ten thousand years…
Sources: NASA, Phys.org, ResearchGate
