Attitude and direction sensor using GPS carrier phase data

We present a prototype attitude sensor based on Real Time GPS interferometry, suitable for navigation on the Earth surface or for platforms in Low Earth Orbit (LEO). The sensor is designed to measure both the attitude angles and the change in length of the baselines between the antennas. Our breadboard consists of three NovAtel/CMC single frequency SmartAntennas with 5Hz sampling rate. The antennas form a baseline of 1m length with an intermediate antenna 0.2m far from one of the baseline end-sides. We have developed a real time software to log data from the receivers and to compute and interpret the phase differences between pairs of receivers. We demonstrated that the data processing from this antenna set, at each epoch, leads to the baseline orientation angles with r.m.s. (root mean square) repeatability of 0.3 degrees for horizontal angles and of 0.5 degrees for vertical angles. The precision of this result is limited mainly by multipath. The effect of multipath can be mitigated using a calibration signal optimised for the structures surrounding the GPS interferometric attitude sensor, if they maintain a fixed geometry with time.