The requirements on space mission duration have continued to increase and tribology is the key technology for extending life of space mechanisms. This paper describes adhesion experiment, which is the most fundamental wear mechanism in vacuum, and lubrication technology focused on fluid lubricants (oil or grease). It is also shown that two oil-lubricated space mechanisms, a reaction wheel and a strain wave gearing, operate with a small quantity of lubricant. Basic study using a laboratory friction tester showed that the lubrication lifetime with a small quantity of fluid lubricants under high vacuum become short when the lubricant quantity is small. This is possibly due to the insufficient resupply of the lubricant from the surrounding due to the viscosity increase. The occurrence of oxidative polymerization under high vacuum catalyzed by a nascent surface is suggested.