A NOVEL, RUGGED AND ROBUST LONGITUDINAL RANGE FINDING METHOD FOR FORMATION FLYING MISSIONS

摘要

An optical metrology measurement system is being developed for the Proba-3 formation flying mission to measure the longitudinal separation of the satellites. Based on current experimental breadboard performance, it is anticipated that the inter-satellite spacing will be unambiguously determined to ≤10 microns resolution at ranges from metres to hundred of metres and at update rates of at least 10 Hz, thus meeting or exceeding the Proba-3 optical metrology requirements. The metrology technique employed is believed to be unique in that it is based on a variable frequency optical pulse source, with the optical pulse repetition rate varied to find the exact parameters which provide a null in the phase difference between a reference pulse train and the return pulses from the outlying satellite. The unambiguous measurement range is limited only by the coherence length of the laser, and therefore the system will be appropriate for future formation flying missions requiring longitudinal range measurements over many kilometres. Range accuracies are limited only by the stability of an electronic reference frequency which governs the repetition rate of the optical pulses. Every system component of this new metrology system already exists as either a military or space qualified version, allowing rapid prototyping of a mission ready system. An important system feature is its ability to switch between pulsed and continuous laser operation, thus enabling variations in the satellite formation spacing to be tracked with interferometric resolution following initial range determination.