The SSS Centerprice was a ship that the Sirians left in our Solar system. It only came back to earth if one human activate the transmitter in Luxor. It makes a brokelanding in the Sierra de Chiapas because a Croteam Crate Bus crashed into it.
The SSS Centerprice was left on Titan by Sirians in order for humans to explore the galaxy, when the time is right, and when Chaad Sheen was inactive. Sam used it to travel to Sirius, but before leaving Earth, it was hit by a Crate Bus, therefore being destroyed, although, its main computers were still active, according to NETRICSA.
In The First Encounter, it firstly appears in Luxor by activating the Transmitter. Then it floats over The Great Pyramid and is used to assist killing Ugh-Zan III with its laser cannon. Afterwards, in The Second Encounter, it crashlanded in the Sierra de Chiapas. It was not seen after then.
The SSS Centerprice's laser cannon can kill some beings, and magnetize other ones, for example, it can kill Ugh-Zan III but it can magnetize Sam onboard
The SSS Centerprice looks like a high-tech U.F.O. mothership, with a lot of flashing lights and of course, a giant laser beam. It is based off classic alien motherships.