Emergency destruction system

For the device used by Predators, see Self-Destruct Device

"And when we throw the switches, how long before the ship blows?"
"Ten minutes."
"No bullshit?"
"If we ain't outta here in ten minutes, we won't need no rocket to fly through space."

―Ripley and Parker, regarding the Nostromo's self destruct (from Alien)

Nostromo Self Destruct — The instructions to the self destruct mechanism aboard the *Nostromo*.

Self destruct systems or emergency destruction systems are present aboard most commercial starships. Initiating the self destruct on a spacecraft disengages its engine coolant system, quickly causing the vessel's power core to overload and explode, destroying the spacecraft entirely.

Aboard the Nostromo

The self destruct system aboard the USCSS Nostromo operated on a ten-minute delay, with an initial five-minute fail-safe window during which the process could be reversed. However, after these five minutes had elapsed, the meltdown of the ship's core was irreversible and could not be stopped. When the ten minutes ended, the ship's core would explode with tremendous force, utterly destroying the spacecraft. In 2122, Warrant Officer Ellen Ripley engaged the self destruct aboard the Nostromo in an attempt to kill the Alien, which had stowed away on board.

Behind the Scenes

In Alien, it is never stated why a commercial towing vehicle such as the Nostromo would need a self destruct mechanism. However, several theories have been proposed by fans in the years since:

In an emergency, it would be better to blow up an out-of-control starship hauling a colossal ore refinery rather than allow it to crash into a populated planet or colony.
Contemporary space rockets include self destruct systems in case they veer off course at launch, and the system on the Nostromo could be of similar purpose (although it seems likely that the Nostromo was built in orbit rather than launched from Earth).
The presence of Colonial Marines in the Alien universe implies there must be a threat or threats that the Marines were established to counter. Therefore, self destruct systems may be designed to prevent valuable equipment and technology from falling into the hands of competitors, pirates or terrorists (a huge starship could be used as a devastating weapon if captured).