"Neutron Star" is an English language science fiction short story by American writer Larry Niven.
He has the Puppeteers construct what he dubs the Skydiver to his precise specifications, supposedly to ensure he survives to return with the relevant data.
As the mysterious pull exceeds one Earth gravity, Shaeffer accelerates the Skydiver to compensate for the unknown X-force until he is in free fall (though the accelerometer registers 1.2 gees).
Shaeffer programs the autopilot in a thrust pattern that allows him to reach the center of mass of the ship in effective free fall, though he nearly fails to do so.
After returning to We Made It, Shaeffer is hospitalized (he has received a sunburn by starlight blue-shifted into the ultraviolet) for observation at the Puppeteer's insistence.
While explaining tidal forces to the Puppeteer, Schaeffer realizes the alien had no knowledge of tides, something that would be elementary for a sentient species living on a world with a moon.
"Neutron Star" won the Hugo Award for Best Short Story and ranked #30 in the LOCUS Magazine Readers Poll, All-time Best Novellette.