The Aceton Assimilator was a free floating space mine used during Earth's Middle Ages by the Menthar civilisation during their war with the Promallians.
The Assimilator consisted of a power generator which drained energy from any nearby power source, and an emitter which converted the energy into deadly radiation.
The Menthars hid several hundred thousand aceton assimilators in the floating remains of Orelious IX, creating an instant booby trap. The Promellian battle cruiser Cleponji encountered this booby trap following the destruction of Orelious, where it eventually succumbed to the assimilators.
Over a millennium later, the Federation starship USS Enterprise-D, following the discovery of the Cleponji, also fell prey to the effects of the assimilators. They were able to out-maneuver the devices by utilizing the ship's thrusters to navigate out of the field. Following their escape, the Enterprise destroyed the trap field as well as the Cleponji to prevent anyone else from becoming trapped in the future. 
- Okuda, Michael and Denise. The Star Trek Encyclopedia Third Edition. Pocket Books. 1999.