A device for positioning a functional trihedron of a star tracker in a reference trihedron tied to a structure on which the star tracker is mounted comprises: a fixing interface to connect the device to the star tracker, a set of geometric markers configured to, by means of an optical measurement instrument tied to the structure, position a marker tied to the device in the reference marker tied to the structure, an optical simulator comprising a set of optical markers to be measured by the star tracker, making it possible to position the functional trihedron of the star tracker in the trihedron tied to the device, the measurements of position of the functional trihedron in the trihedron tied to the device, and of position of the trihedron tied to the device in the reference trihedron, making it possible to position by calculation the functional trihedron in the reference trihedron.

The present disclosure provides a system and a method for controlling a motion of a spacecraft in a multi-object celestial system while avoiding an unauthorized entry into a keep-away region during a normal and an abnormal operation of the spacecraft. The method includes executing, during the normal operation of the spacecraft, a nominal control law subject to constraints on maintaining a state of the spacecraft within a union of a plurality of control invariant sets of values of the state of the spacecraft. The state of the spacecraft includes a location of the spacecraft and at least one or a combination of a velocity and an acceleration of the spacecraft. The method further includes executing, upon detecting the abnormal operation of the spacecraft, an abort control law associated with the control invariant set including a current state of the spacecraft.

A satellite orbiting in one of a plurality of orbital planes of a satellite constellation system at an altitude range corresponding to low earth orbit includes at least one processor configured to generate satellite state data, and to generate a navigation signal based on the satellite state data. The satellite includes at least one transmitter configured to transmit the navigation signal for receipt by at least one client device on earth. Each of the plurality of orbital planes includes a corresponding one of a plurality of satellite subsets of a plurality of satellites of the satellite constellation system. Each of the plurality of orbital planes is within the altitude range, and the plurality of orbital planes includes a set of inclined orbital planes at a non-polar inclination.

One embodiment is directed towards a method of navigating a body. The method includes determining a respective measured direction of each of a plurality of celestial objects with respect to the body based on an output of one or more star tracking sensors mounted to the body. Calculating an expected direction of at least one of the plurality of celestial objects with respect to the body based on a current navigation solution for the body. Calculating an updated navigation solution for the body based on the expected direction of the at least one celestial object, the measured direction of the plurality of celestial objects, and an output of one or more inertial sensors mounted to the body.

A device for determining an attitude of a satellite is disclosed, the satellite having an attitude control system comprising a gyroscopic actuator including a flywheel mounted so as to be rotatable around an axis of rotation and carried by a gimbal articulated to rotate around an axis of rotation. The device includes an attitude sensor configured to measure the attitude of the satellite, a position sensor configured to measure the angular position of the gimbal around its axis of rotation, a speed sensor configured to measure the rotational speed of the flywheel, and a processing circuit configured to determine the attitude of the satellite by using the measurement of the angular position of the gimbal, the measurement of the rotational speed of the flywheel, and the measurement of the attitude of the satellite.

A satellite in orbit around a planetary body includes a bus and a drag flap coupled to the bus. The drag flap is used to increase the drag torque applied to the satellite. The bus may house sensors and actuators, such as a star tracker, a gyroscope, a reaction wheel, and a global position system (GPS) receiver to monitor the attitude of the satellite in response to the applied drag torque. The measurements from the sensors and actuators may be used to determine the drag torque applied to the satellite. An estimate of the atmospheric density may be then be determined based on the drag torque. Compared to conventional approaches, the satellite and methods described herein estimates the atmospheric density at comparable, if not better, resolution and bandwidth. The atmospheric density estimates may also be acquired in real-time using a cheaper, lighter, and smaller satellite.

Apparatus and methods for controlling a spacecraft for a transfer orbit. The spacecraft includes a momentum subsystem that stores angular momentum relative to a center of mass of the spacecraft, and a propulsion subsystem that includes electric thrusters. A controller identifies a target spin axis for the spacecraft, determines gimbal angles for electric thruster(s) that so that thrust forces from the electric thrusters are parallel to the target spin axis, and initiates a burn of the electric thruster(s) at the gimbal angles. The controller controls the momentum subsystem to compensate for a thruster torque produced by the burn of the electric thrusters. The momentum subsystem is able to produce a target angular momentum about the center of mass, where a coupling between the target angular momentum and an angular velocity of the spacecraft creates an offset torque to counteract the thruster torque.

Apparatus and methods for controlling a spacecraft for a transfer orbit. The spacecraft includes a propulsion subsystem with electric thrusters that are installed with two-axis gimbal assemblies. The spacecraft also includes a controller that identifies a target spin axis for the spacecraft, determines an actual spin axis for the spacecraft during the transfer orbit, determines gimbal angles for the electric thruster(s) that adjust the actual spin axis toward the target spin axis, and initiates a burn of the electric thruster(s) at the gimbal angles.

A modular satellite for converting solar energy to microwave energy and transmitting the microwave energy to the earth to be converted into electricity includes solar panels configured to convert solar energy into direct current; a magnetron operatively connected to the solar panels to receive the direct current and configured to convert the direct current into microwave energy; a planar wave guide antenna operatively connected to the magnetron to receive the microwave energy and direct the microwave energy to a station on earth; and a coupling system for coupling with another satellite to form an array in response to at least one of locking, unlocking, and navigational commands. The satellite has a mass equal to or less than four kilograms, and a volume equal to or less than three liters.

Described are systems and methods for direct sun imaging by a star tracker. Disclosed in a certain example is a direct sun imaging star tracker that includes an imaging sensor and a baffle. The baffle includes a star port, a sun port, and a beam splitter. The star port is configured to image first viewing environment while the sun port is configured to image a second viewing environment that includes the sun. The beam splitter is configured to combine electromagnetic radiation from the star port and the sun port into a combined image. In various examples, the systems and techniques described herein allow a star tracker to simultaneously view both the sun and the stars.