Barn door tracker

A barn door tracker, also known as a Haig or Scotch mount, is a device used to cancel out the diurnal motion of the Earth for the observation or photography of astronomical objects.

In late 2002 and early 2003, NASA astronaut Don Pettit, part of International Space Station Expedition 6, constructed a barn door tracker using spare parts he had accumulated from around the space station,[2] permitting sharper high resolution images of city lights at night from the ISS.

By using a second arm to drive the camera platform - making fabrication slightly less simple - tracking accuracy is greatly increased, allowing exposure times of up to one hour.

[4] A basic geometrical analysis of the tangent error shows that it can be fully compensated for by inserting a specially shaped piece between the threaded rod and the top board.

A key modification of the original design is the hinged suspension of the drive rod, which avoids binding, as well as a central tripod mount that can be moved along the supporting truss tubes to better balance for lighter or heavier loads according to their orientation.