Been trying to identify a book I read in the late early 90s for quite a few years now, It was a children's/ young adult sci-fi story.
Plots Summary/Details: A boy (teenager possibly) had accidentally stowed away on a spacecraft [named Orion, this may have been part of the title and was certainly the cover illustration] which had a experimental faster then light drive, called shifts or something similar, and had landed up on a distant planet; the ship returned automatically without him.
The spaceship creator and some other kids (his nephews?) then had to return there to retrieve him. the ship creator watched a video of a drone/robot vehicle from the ship leaving and being destroyed by alien, but keeps it from every one else for some reason
There were a race of 'dolphin like' aliens, who were slaves to a race 'horse like aliens' on said planet which the protagonists freed while trying to save the missing boy, before returning home, after having had their ship modified by the aliens.
(I may have misremembered parts of the plot, as it was a long time ago.)
Timeframe of Publication I read it in the early or mid 90s, so no later than then, I suspect it may have been earlier so more likely 1980s or even late 70s