All imaging systems from space are affected by disturbances originating in the spacecraft in the form of mechanical noise from thruster and reaction/momentum wheels, and sensor noise. A drag-free system is truly unaffected by any disturbances, as it is in pure freefall. Hence, leveraging drag-free technology can provide a quantum leap in improvement for spaceborne imaging systems.
Image stabilization techniques used to reduce blurring associated with the motion of a camera during exposure attempt to compensate for pan and tilt (angular movement, equivalent to yaw and pitch) of a camera or other imaging device. Such techniques are used in image-stabilized binoculars, still and video cameras, and astronomical telescopes. With still cameras, camera shake is particularly problematic at slow shutter speeds or with long-focal-length (telephoto) lenses. With video cameras, camera shake causes visible frame-to-frame jitter in the recorded video.
In order to dramatically improve the image resolution achievable from space with widely separated cameras onboard satellites, a technique alternative to those used in commercial cameras for image stabilization is needed in which the imaging focal plane on each spacecraft is in freefall, hence undisturbed. Combined with large-aperture synthesis solutions, such as those relying on formation flying, the drag-free imaging system has the capability of providing both extremely high levels of disturbance reduction and high imaging resolution, both in remote science and astrophysics applications.
In practice, this system is realized by a retaining mechanism for an instrument/camera that is set in freefall inside an enclosed cavity onboard a host spacecraft. The camera is released to its freefall state during image acquisition and, after the images have been taken, it is recaptured and repositioned. Since the cavity is within the spacecraft, during the image acquisition phase, the camera is shielded from external perturbations such as drag and solar radiation pressure, with its orbit determined only by gravity. Although the only external disturbing forces that can act on the camera arise from the enclosing spacecraft itself (vehicle gravity, and stray electric and magnetic fields) or from any external perturbations that can possibly penetrate it, these effects are not expected to affect the quality of the images captured by using the technique, and preliminary analyses indicate more than 10× potential improvement in focal plane stability. Multiple drag-free imaging systems could be installed at different locations on a single spacecraft (or on separated formation spacecraft) in order to achieve a high imaging resolution by synthesizing a large virtual aperture.