Time travel pod

The 31st century time travel pod was a small craft, first encountered by Enterprise NX-01 in 2152.
The craft was approximately six meters long, but was much bigger on the inside than on the outside.

Pods commissioned during the 31st century were powered by a temporal displacement drive. They also could absorb electromagnetic radiation, allowing them to remain undetected by the sensor technology of the 22nd century.
They were, additionally, equipped with organic circuitry. Their power or propulsion systems were not visible or detectable from the outside.

One such pod traveled back to the 22nd century, where it apparently suffered some sort of critical disaster.
The pod was heavily damaged, and its sole occupant was long dead by the time it was discovered by Enterprise in 2152.
The damaged pod was also emitting temporal radiation, which affected individuals too close to the pod, making close study a risk.

Unfortunately, both the Suliban Cabal and Tholian Assembly also learned of this pod's existence and sent vessels to retrieve it.
Their plans where thwarted when Enterprise's crew used a temporal beacon, assembled using technology left behind by a temporal agent, to send a signal to the future.
Within seconds of the beacon being activated, the pod, the dead pilot, and the beacon itself all vanished, possibly having been retrieved by operatives from the future.

The fate of the pod, and nature of the disaster that killed its pilot, remain a mystery.