Children's book 50s or 60s, in which time travel gives accidental space travel to moons of either Jupiter or Saturn as the time machine is fixed at a point in space, and the movement of the solar system over time 'moves' the earth away from it. It is a sealed machine with oxygen, so this is not fatal.
The author's name would begin with a letter between G and Q based on where in the library it was shelved (which I can remember). I read it around 44 years ago. It was a hardback.
It may have starred two children and a professor who built the machine.
I read it around 1974 from Garston Library, Liverpool.
It is not a conflation of the suggested Heinlein books, both of which I also read as a child, but later.
Following more research, it's more like (but I don't think it is) a cross between Danny Dunn and the Anti-Gravity Paint and Danny Dunn, Time Traveler. I still think it's a real separate single book by a different author than the Danny Dunn series whose authors have names beginning A, & W, but in tone it would have been more like the Danny Dunn than Heinlein.