טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentDavid Tsur
SubjectUsing Satellite Formation for Local Positioning
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Guelman Mauricio
Full Thesis textFull thesis text - English Version


Abstract

This work examines a navigation application using satellites in formation. This system is comprised of a leader satellite in geo-synchronous orbit and at least three other follower satellites in a bounded relative motion around it. Since the leader satellite is in geo-synchronous orbit, the proposed system enables navigation for limited geographical areas. Global or larger coverage can be achieved though, using more formations and clusters of satellites in different orbits.

The satellites broadcast a simultaneous signal to Earth. Since the distances between the user and each satellite are different, the signal arrives at different times to the user's receiver. The receiver combines these Time Difference Of Arrival (TDOA) readings to produce an estimate of the user's position. In a similar fashion, the Frequency Difference Of Arrival (FDOA) can be measured, yielding an estimate of the user's velocity.

This formulation of a TDOA mechanism is reverse to the one generally used - locating emitter point sources using passive sensor arrays.   

The satellites in this formation, unlike the GPS satellites, achieve their goals of navigation without using precise atomic clocks onboard, i.e. no knowledge of the absolute time is required. The leader satellite is responsible for the synchronization of the formation and for maintaining the follower satellites in their desired relative positions.

The results of the preliminary analysis conducted in this work show that a formation of this sort can achieve a position accuracy of approx. 5 [m] and a velocity accuracy of 30 [cm/s], assuming a synchronization of 1 [ns] between the satellites.