atavachron
Star Trek: The Original Series
Episode: TOS 078 - All Our Yesterdays
Sarepeidon technology which allows one-way time travel of the user's choice by way of pre-selected destinations within the planet's own history, programmed and archived for use on circular disks.
Return was prohibited due to changes that had to be made with this system to the user's cell structure to allow survival in other time periods.
When the Sarpeidon sun, Beta Niobe, went nova in 2270, the entire planetary population traveled back to various times via the atavachron to escape death.
