Pioneer H

In 1971, a formal mission study was proposed for a spacecraft to be launched to Jupiter in 1974, where it would use the gas giant as a gravitational slingshot to travel outside the ecliptic.

TRW assembled the spare components into a new spacecraft, but NASA management did not approve the mission proposal, and it was never launched.

[2] While described in official Smithsonian records as a "replica", the spacecraft was considered fully functional by Pioneer mission planners (though its RTGs were never installed).

Mark Wolverton quotes James Van Allen in The Depths of Space:[3] We mounted an intensive campaign to launch the flight-worthy spare spacecraft and its instrument complement on a low-cost, out-of-ecliptic mission via a high-inclination flyby of Jupiter.

However, our case fell on deaf ears at NASA headquarters, and the spare spacecraft now hangs in the main gallery of the National Air and Space Museum, at 1 AU and zero ecliptic latitude.