as a child I experienced many of the same things as the boy in "Flight of the Navigator"

The thing I remember the most was the "Green CRT" screen TV that appeared to me in church one day where the plans to actually building a "Flying saucer" were on the screen. In the center of the Time-Space ship was a perfectly spherical Crystal (likely man made or UFO made) that was about 3 feet in diameter which powers the ship and is located in the center of the ship. Then the ship runs off the magnetic fields of the sun and the Earth like the Ark of the Covenant. However, it is a different technology than we use now because it's all free and there to use and you couldn't be charged for it. So, they had to really work hard to find ways to charge people for electricity because it doesn't even need to be generated at all the way the Ark of the Covenant and UFO Time-Space vehicles work. So, in a time space vehicle your power source is literally the sun and the planets of the system you are in.

That's why you need a mothership for travel between Solar systems because you don't have proximity to solar and Planetary power sources. Also, this way there doesn't have to be ANY technology in any time you travel to because you are never going to "run out of gas" because whether there is technology at that time or not on a planet or anywhere in the solar system doesn't matter because your power source is always the sun and the planets and nothing else (within the solar system).