Design and performance testing of the 5 degree of freedom formation flying sensor

Formation flying of spacecraft nowadays is acknowledged to be an important technology for many future space missions. TNO underlines the importance and has therefore designed and tested a general use sensor system that is modular and can be used and adapted to the specific needs of a variety of missions. The sensor system is designed to be operated complementary to an interferometric distances measurement system. It replaces the interferometer retro reflector and uses a small part of its laser light. This light then is used to measure lateral displacement in two directions, pitch, yaw and roll. The lateral displacement accuracy is to the micrometer level and the pitch yaw and roll accuracies are to the arcsecond level. The basis for this system was created by the successful ESA HPOM-project, where TNO developed and tested Fine Lateral displacement Sensor (FLS), with a few cm range and with sub-micron accuracies. At this stage the technology was aimed at the SMART 2 mission, which is very similar to the presently initiated PROBA 3. After including tilt, yaw and roll measurements the system has become a very versatile robust piece of formation flying metrology. This paper treats the development of the sensor system as well as the experiments performed on the first prototype. This prototype consists of all the required optics and sensors assembled in a robust housing. As a result of the first experiments, the design was improved on some aspects. Although the experiments have yet only proven the Technology Readiness Level 4 for the tilt measurements and TRL 6 for the lateral displacement, no difficulties are foreseen for the further development of the sensor system. All potentially critical elements have flown before.