7. The technology they had in the 70's was similar to a modern day that could fit in our pocket. (space science; The Farthest: Voyager in Space Viewing Guide)

Key Fob.

Explanation:

On the 5th of September, 1977, the National Aeronautics and Space Administration (NASA) launched a spacecraft known as "Voyager 1" to study and explore the outer planets of the solar system.

Additionally, two voyager spacecraft were built for the above mentioned study and exploration exercise; Voyager 1 and Voyager 2. Voyager 2 was actually the first spacecraft while Voyager 1 was launched sixteen (16) days after and was faster.

According to Rich Terrile, the technology they had in the 70's was similar to a modern day Key Fob that could fit in our pocket because the processing power of the computer chip found in a Key Fob was comparable to the much larger voyager probe (Voyager 1 and Voyager 2) of the 70's, that was tagged an artificial brain.

This ultimately implies that, the computer chip found in a car Key Fob is more powerful and sophisticated than the Voyager probe, even though the Key Fob is smaller but having the same amount of memory.

force required to detach it is given by

charges are taken to be fundamental charge

now we have

so above is the minimum distance at which it will detach

3. dark matter

empty space could also be a simple vacuum