CAESAR Project Summary

Y. Porat, M. Sedero, N. Leshem, H. Amar, I. Cohen, N. Leiter, N. Bavli, O. Marfogel
Jacob Herscovitz
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Project objectives: To design a cost-effective system capable of autonomously locating people in distress in oceanic surroundings and relaying their distress signal and location immediately to rescue forces.

The system consists of a user segment (beacon) and ground segment (control station) (out of the scope of the project) and of a space segment consisting of a constellation of nano-satellites.
The space segment includes 48 Cubesat nano-satellites in a Walker Constellation pattern, spread out in 6 orbital planes at an altitude of 710 km and inclination of 45⁰. Each orbital plane consists of 8 satellites divided to 4 formations, each formation consisting of 2 satellites – Leader and Follower.
The formations were designed to be kept at a nominal distance of 200 km between the leader and the follower by a relative control method, thus allowing the geo-location of a user by means of TDOA algorithm.
The TDOA geo-location algorithm, combined with an Extended Kalman Filter (EKF), allows us to geo-locate users with a minimum of 2 satellites per formation with accuracy better than 1 km, for more than 97% of the incidents in less than 15 minutes from the moment of signal transmission by the user.
The specific pattern of our constellation allows us to use our own satellites as relay satellites capable of broadcasting a distress signal from one satellite to another and to one of the 9 ground stations scattered around the world, instead of using geo-stationary relay satellites.
An original cold gas propulsion subsystem has been designed specifically for the project’s needs allowing the maneuver of the satellites as required.
A unique control algorithm has been designed, allowing full 3-axis attitude stabilization using only Magneto-Torquers as actuators and magnetic sensors and self-designed analog sun sensors as attitude determination sensors.
The electric power system consists of a specialized EPS unit, a battery and 25 photo-voltaic cells capable of producing a sufficient average of approximately 7 Wh per cycle.
The communication system is comprised of 2 dipole antennas for communication between satellites and telemetry and control with ground stations, and one patch antenna which is in fact the satellite’s payload which is responsible for the communication with the user segment.
The entire mission reliability was found to be 0.76, and the entire project’s cost estimation (excluding launch costs) was calculated to be: ~ 6 M$