Grand Tour program

The Grand Tour is a NASA program that would have sent two groups of robotic probes to all the planets of the outer Solar System.

The concept of the Grand Tour began in 1964, when Gary Flandro of the Jet Propulsion Laboratory (JPL) noted that an alignment of Jupiter, Saturn, Uranus, and Neptune that would occur in the late 1970s would enable a single spacecraft to visit all of the outer planets by using gravity assists.

[2]: 256  These probes, called Thermoelectric Outer Planets Spacecraft (TOPS), were being designed at JPL and featured an operational life of over ten years.

Congressional pressure, combined with internal competition from the recently approved Space Shuttle program, led to the decision to cancel the project in December 1971.

[5] The probes would be built by JPL, with the intention that they would last long enough to complete the original Grand Tour of the four giant planets, but be advertised as missions to only Jupiter and Saturn to reduce estimated total project costs.

The second was designated JSX: it would be launched on a trajectory that would preserve the option of a Grand Tour, while serving as backup for the first probe.

If JST was unsuccessful, JSX could be diverted to perform the Titan flyby itself, which would eliminate the possibility of a Grand Tour.