Good scifi shows always have good(ish) science behind them, Lost in Space isn't one of them.
Growing up with this show I could never get over the bad science that destroyed any enjoyment of the show.
The Jupiter 2's computer cannot compensate for the additional weight of an extra person yet the much smaller robot displays computing power far greater than any supercomputer (full automation, voice recognition, ability to identify danger before a human, etc).
The Jupiter 2 is travelling to Alpha Centuri, the closest star to our sun when it goes off course. Each episode has them land on a planet, presumably between Earth and Alpha Centuri, which has its own star, its own individual life form (no ecosystems seem to be neccessary) and a breathable atmosphere.
Half of scifi is the fiction element but good scifi keeps the fiction within the realms of possibility.