Abstract: A sourceless orientation sensor having an azimuthal sensor which determines the azimuthal orientation relative to a planetary magnetic field, and a tilt sensor which determines the direction and magnitude of the displacement from vertical using the planetary gravitational field. The tilt sensor includes a transparent gas and a transparent viscous fluid in a spherical shell, a light emitting diode (LED) mounted at the top of the shell, and four photodetectors mounted at the bottom of the shell. As the tilt sensor is rotated the path of the light cone emanating from the LED and refracting at the gas/fluid interface is altered, thereby altering the intensity of light incident on the photodetectors. The magnitude of the light incident on the photodetectors is processed to provide the tilt angles. A thin transparent disk floats at the gas/fluid interface to damp surface waves caused by reorientation of the device.