How these connect

The alignment is only an opportunity if a spacecraft can be handed from one planet to the next without carrying the fuel to do it.

The frame was taken by Voyager 1's narrow-angle camera on 14 February 1990, on the last day the cameras were used.

The Jet Propulsion Laboratory manages the network for NASA and allocates its time across every deep-space mission.

The dated launch of the spacecraft it committed to flight.

Sagan chaired the committee that selected the images, music, greetings and sounds within a few months in 1977.

A copy is mounted on the side of the spacecraft, unconnected to any instrument or to the power system.

An identical copy is carried by Voyager 2, so two exist beyond the heliopause on divergent trajectories.

The observation was made because Sagan argued for it over several years against the accurate objection that it would return no science.

Sagan worked on the mission's imaging science and chaired the Golden Record committee.

Stone was Voyager project scientist from 1972 until 2022 and set the evidential bar for declaring an interstellar crossing.

The project scientist role covered both spacecraft as a single mission.

Titan is Saturn's largest moon and the only moon in the solar system with a substantial atmosphere.

The late-1970s planetary configuration is what made a multi-planet mission affordable, and the launch date was fixed by it rather than by programme readiness.

Identical spacecraft launched sixteen days apart onto different trajectories, which is what makes the differences between their measurements interpretable as differences in the medium rather than in the instruments.

Every operational decision since the last encounter has been governed by a power budget falling about four watts a year that cannot be repaired or replenished.

The geometry required for a close Titan pass deflected Voyager 1 north out of the ecliptic plane, permanently removing every remaining planet from its reach.

The Deep Space Network is the only facility on Earth able to detect a signal of this weakness or to command the spacecraft.

Neither spacecraft carried propellant for trajectory changes of this magnitude; the energy to reach Saturn came from Jupiter.

JPL built both spacecraft and has flown them continuously since 1977.

Voyager 1 was launched from Launch Complex 41 at Cape Canaveral on 5 September 1977.

Closest approach 5 March 1979, the first of the mission's gravity assists.

Closest approach 12 November 1980, the last planet Voyager 1 visited.

The Titan flyby was the reason Voyager 1's Saturn encounter was shaped as it was.

All long-range communication passes through the 3.7-metre dish, which must remain pointed at Earth for the link to close at all.

With the plasma science instrument dead since 1980, the plasma wave subsystem is Voyager 1's only route to a density measurement.

The Centaur high-energy upper stage was the only vehicle element available in 1977 capable of injecting a spacecraft of this mass directly towards Jupiter.

Voyager 2's slower trajectory existed specifically to preserve the alignment's Uranus and Neptune options, which no later launch could recover.

The same decline forced the March 2025 instrument shutdown and would have forced another before the end of 2026 had the July 2026 manoeuvre not deferred it.

Four planets were reached with four successive assists, each one setting up the geometry for the next.

The same flight team commands both spacecraft from Pasadena.

Voyager 2 was launched from the same pad sixteen days earlier, on 20 August 1977.

Closest approach 9 July 1979, four months after its twin.

Closest approach 25 August 1981, shaped for onward travel to Uranus rather than for Titan.

Both spacecraft flew on the same launch vehicle configuration.