Expedition 55 Flight Engineer Drew Feustel works inside the Japanese Kibo laboratory module with tiny internal satellites.

Expedition 55 Flight Engineer Drew Feustel works inside the Japanese Kibo laboratory module with tiny internal satellites known as SPHERES, or Synchronized Position Hold, Engage, Reorient, Experimental Satellites. Feustel was operating the SPHERES for the Smoothing-Based Relative Navigation (SmoothNav) experiment which is developing an algorithm to obtain the most probable estimate of the relative positions and velocities between all spacecraft using all available sensor information, including past measurements.