Project Orion studied a propulsion idea that put the energy source outside the vehicle. Repeated nuclear pulses behind a pusher plate would transfer momentum to the spacecraft, with shock absorbers between the plate and the rest of the vehicle.

That is very different from heating propellant inside a reactor. It was also very different from today’s Orion crew capsule, which shares the name but not the propulsion concept.

The archival paper follows the concept and its engineering difficulties. It does not document an operational nuclear-pulse spacecraft. Treat impressive performance estimates as estimates attached to a proposed system.

NERVA was a joint NASA and Atomic Energy Commission program to develop a nuclear rocket. Its reactor would heat propellant, which could then expand through a nozzle to produce thrust.

The program considered applications including long-range missions and upper stages. Hardware was tested on the ground, but funding declined in the late 1960s. The program ended in 1973 before an engine flight test.

The distinction matters: this was more than a drawing, but it never became a flown engine. Explore the engine model above to trace the conceptual route from propellant supply through the heated core to the nozzle.

Inspect the engine model ↑

A rover on Venus has to survive a surface hot enough to defeat ordinary electronics. Zephyr explored another unusual requirement: moving across the ground using a sail.

The NASA Innovative Advanced Concepts study examined a wind-driven vehicle and electronics able to work in extreme heat. The sail is for travel across the surface, not for flight through the atmosphere.

This is an example of mission design shaped by its environment. The hostile atmosphere becomes part of the proposed mobility system. The final report is a feasibility study, not a record of a rover operating on Venus.