DEPARTURE
A FIELD GUIDE TO VOYAGER & PIONEER
Ten chapters on the four machines that used the outer planets as stepping stones out of the Solar System — and the two messages they carry for whoever finds them. Scroll to begin the mission.
BEGIN — CHAPTER 01 →Only four machines have ever done this
Orbiting the Sun takes one speed. Escaping Earth takes more. Escaping the Sun's gravity entirely — leaving on a trajectory that never comes back — takes the third cosmic velocity, and no spacecraft launches with that much fuel to spare. Every probe that has managed it borrowed the rest of the speed from the planets themselves.
Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2 are on permanent solar-escape trajectories today. A fifth, New Horizons, joined them in 2006. Compare how fast each one is now moving away from the Sun.
FIG. 1.1 — HELIOCENTRIC SPEED, ILLUSTRATIVE (KM/S). BARS SCALED TO 20 KM/S.
Stealing momentum from a planet
A planet in orbit is itself moving fast. Swing a spacecraft close behind it, in the direction of its travel, and the planet's gravity bends the flight path while the planet's own motion adds to the spacecraft's speed — like a ball bouncing off the front of a moving train. The planet loses an immeasurably small amount of orbital energy in return.
Drag the approach angle below to see the outbound trajectory — and its speed change — respond.
FIG. 2.1 — THE GRAND TOUR: A 176-YEAR ALIGNMENT
In the late 1970s, Jupiter, Saturn, Uranus, and Neptune lined up in a configuration that let a single spacecraft use each planet's gravity to reach the next — a free ride that would not recur for 176 years. Voyager 2 is the only spacecraft ever to take it.
The first to leave the inner Solar System
Pioneer 10 launched March 2, 1972, the first spacecraft to cross the asteroid belt and the first to reach Jupiter. Pioneer 11 followed in April 1973, flying past Jupiter in 1974 and becoming the first spacecraft ever to reach Saturn in 1979. Simple, spin-stabilised, and built years before Voyager, they proved the outer Solar System was survivable.
FIG. 3.1 — SCHEMATIC (NOT TO SCALE). SELECT A COMPONENT.
Built to work alone for fifty years
Voyager 2 launched August 20, 1977; Voyager 1 followed on September 5, on a faster path that overtook its twin. Both carry three radioisotope generators, no repair option, and a command computer running at roughly 8,000 instructions per second — a fraction of a modern watch. Select a component.
What was expected, and what was found
Messages with almost no chance of arriving
Both Pioneers carry a small engraved plaque; both Voyagers carry a gold-plated phonograph record. Neither was expected to ever be found. Both were made anyway.
Turning the camera back around
In February 1990, already well past Neptune's orbit and with its planetary mission complete, Voyager 1 turned its camera back toward the Sun on request and took a final family portrait of the Solar System. In one frame, Earth appears as a single pixel, caught in a scattered ray of sunlight — a world reduced, at that distance, to less than nothing.
Where the Sun's influence ends
The Sun blows a bubble of charged particles — the heliosphere — far past the planets. There is no visible wall at its edge; scientists identify the crossing from a sudden jump in plasma density and a drop in solar-wind speed to zero. Step through the boundary layers.
Two still speaking, two gone silent
Figures below are illustrative, approximate, and current to mid-2026 — treat exact distances as a snapshot, not a live feed.
What we chose to say about ourselves
At its current speed, Voyager 1 will not have a close encounter with another star system for roughly 40,000 years. Whatever it carries will still be legible long after everyone who built it is gone.