In order to test the feasibility of the system, the case of a meter-scale sail was examined. For example, to focus the light beam on a 4mX4m sail across an acceleration distance of 2x10⁶ km requires a focusing angle of 2 nano-radians (0.4 milliarcseconds), which is the diffraction limit for a kilometer-scale light beamer operating at a wavelength of 1 micron.

Interferometry with the Event Horizon Telescope has already been demonstrated across the Earth, achieving sub-nano-radian precision at a 1mm wavelength. This is an encouraging benchmark on the way to achieving the required precision of the optical system for a kilometer-scale array on the ground.

Research:

• http://www.eventhorizontelescope.org/technology/building_a_larger_array.html
• Lu et al., “Resolving the Inner Jet Structure of 1924-292 with the Event Horizon Telescope”, ApJ, 757, 14 (2012)