Unmanned spacecraft are spacecraft without people ("man") on board, used for unmanned spaceflight. Unmanned spacecraft may have varying levels of autonomy from human input, they may be remote controlled, remote guided or even autonomous ("robotic"). Many habitable spacecraft also have varying levels of robotic features. For example the space stations Salyut 7 and Mir, and the ISS module Zarya were capable of unmanned remote guided station keeping, and docking maneuvers with both resupply craft and new modules. The most common unmanned spacecraft categories are robotic spacecraft, unmanned resupply spacecraft, space probes and space observatories. Not every unmanned spacecraft is a robotic spacecraft, for example a reflector ball is a non-robotic unmanned spacecraft.