Abstract: Provided herein are various enhanced systems, apparatuses, and techniques for optical communication among a constellation of satellites. One example includes establishing an initial cross-connect configuration comprising optical communication links among a constellation of satellites. In the initial cross-connect configuration, the satellites can optically communicate with both adjacently positioned and non-adjacently positioned satellites in the constellation. The satellites obtain angular states of the optical communication links resultant from orbital motion of the satellites. When angular states of a portion of the optical communication links reach an exclusion range, the satellites establish a subsequent cross-connect configuration to avoid optically communicating within the exclusion range.

Abstract: A modular spacecraft is provided. The modular spacecraft includes a bus module and a payload module. The bus module provides additional thermal radiative capacity for the payload module by including a bus-panel payload thermal zone that couples operational components of the payload module to a radiator panel in the bus module. The bus module also includes its own operational components that are thermally coupled to the radiator panel but that are thermally isolated from the payload module and the bus-panel payload thermal zone.

Abstract: Systems and methods of the present disclosure can be utilized to provide an improved propulsion system that uses multiple high efficiency engines to provide fault-tolerant and scalable high thrust for orbit transfer and maneuvering over life. An exemplary spacecraft includes a base panel, a cylindrical core member mounted to the base panel, multiple DV thrusters mounted within the cylindrical core member, and multiple reaction engine assemblies mounted to the base panel outside the cylindrical core member. Each of the DV thrusters has a thrust level that is greater than a thrust level of each of the reaction engine assemblies. The multiple DV thrusters are operated for velocity control, with attitude control being performed by off-pulsing at least one of the multiple DV thrusters.

Abstract: Method of and system for on-board substantially autonomous control for transferring a spacecraft from an initial orbit to a final geosynchronous orbit, by a trajectory that minimizes remaining transfer time and orbit transfer fuel. The spacecraft determines its orbit using a GPS-based system to determine the spacecraft orbital elements. Based on the measured orbit error, corrected co-state parameters are calculated and used to generate an updated thrust trajectory. The corrections are calculated using an innovative numerical procedure, carried out repetitively at a fixed interval until the target geosynchronous orbit is achieved.

Abstract: One embodiment of the present invention relates to a system for correcting spacecraft thermal distortion pointing errors. The system comprises one or more spacecraft sensors located at positions on a spacecraft and which are adapted to measure spacecraft parameters at those positions. The system also includes a spacecraft distortion prediction module, which is adapted to generate expected spacecraft thermal distortion parameter values and expected antenna thermal distortion pointing errors. Further, the system includes a spacecraft parameter processing module adapted to generate measured spacecraft thermal distortion parameter values from the measured spacecraft parameters, and an antenna pointing error calculation module adapted to calculate antenna pointing error correction commands. Finally, the system includes an antenna pointing control module adapted to receive the antenna pointing correction commands and control the adjustment of the antenna pointing using the correction commands.

Abstract: A sparing system for space vehicle constellations. A plurality of space vehicles arranged in at least one mission orbit plane. The number of space vehicles is at least one greater than a minimum number necessary to provide at least a minimum level of service necessary to carry out a constellation mission. If one of the space vehicles fails the remaining space vehicles are repositioned in the mission orbit plane to provide the minimum level of service necessary to carry out a constellation mission.

Abstract: A velocity change (?V) thruster is operated on a spacecraft, which unavoidably causes attitude error. A reaction wheel (RWA) corrects the attitude. At the beginning of the thruster maneuver, the total attitude control momentum required to at least correct for the ?V thruster attitude errors over the duration of the entire maneuver is determined, and the RWA momentum may also be determined. Attitude control thrusters (REAs) are operated. The REAs are operated to correct at least the net ?V thruster induced attitude error, and preferably also to reset the RWA to its nominal momentum. The maneuver may be stationkeeping.

Abstract: A method for increasing the roll offset operating range for a spacecraft using an earth sensor operating in single scan mode includes the steps of moving the spacecraft to a first roll position, which has a roll angle that will cause the earth sensor to have a desired standard chord, switching the earth sensor to single scan mode by deselecting one of the earth sensor scans, whereby switching the earth sensor to a single scan mode, the earth sensor standard chord is locked at or near the desired standard chord. After the desired standard chord is set, the spacecraft is moved to a second roll position, which is a desired roll offset operating position for the spacecraft, and the earth sensor roll output (generated by using the single scan mode) is used to calculate the spacecraft roll at the roll offset operating position.

Abstract: In general, a constellation of spacecraft is used to broadcast to a particular region with high angles of view in order to reduce blockage or shadowing. A constellation of a plurality of spacecraft is placed in 24-hour orbits having inclination of about 55°, eccentricity of about 0.32, semi-major axis of about 42,000 km, longitude of the ascending node of about 43° East, argument of perigee of about 270°, and longitude of the ground track at maximum latitude of about 7° East. The preferred number of spacecraft ranges from three to six. In a particular application of Digital Audio Broadcast to Europe in some embodiments, the most populous cities are provided with service from no more than about 10° from vertical, and broadcast takes place when the spacecraft are above at least 35° North latitude. The broadcast power is reduced during those portions of the orbit in which the ground track lies in the Southern hemisphere.

Abstract: The present invention relates generally to systems and methods for transferring a spacecraft from a first orbit to a second orbit. In accordance with one embodiment of the invention, the method comprises calculating thruster-off regions within an orbit transfer in which it is efficient to turn-off spacecraft thrusters, and in those thruster-off regions, turning off the spacecraft thrusters.

Abstract: One embodiment of the present invention relates to a method for increasing the roll offset operating range for a spacecraft using an earth sensor operating in a single scan mode. In accordance with this embodiment, the method comprises moving the spacecraft to a first roll position, which has a roll angle that will cause the earth sensor to have a desired standard chord. Next, the earth sensor is switched to single scan mode by deselecting one of the earth sensor scans. By switching the earth sensor to a single scan mode, the earth sensor standard chord is locked at or near the desired standard chord. After the desired standard chord is set, the spacecraft is moved to a second roll position, which is a desired roll offset operating position for the spacecraft. Finally, the earth sensor roll output (generating using the single scan mode) is used to calculate the spacecraft roll at the roll offset operating position.

Abstract: A velocity change (&Dgr;V) thruster is operated on a spacecraft, which unavoidably causes attitude error. A reaction wheel (RWA) corrects the attitude. At the beginning of the thruster maneuver, the total attitude control momentum required to at least correct for the &Dgr;V thruster attitude errors over the duration of the entire maneuver is determined, and the RWA momentum may also be determined. Attitude control thrusters (REAs) are operated. The REAs are operated to correct at least the net &Dgr;V thruster induced attitude error, and preferably also to reset the RWA to its nominal momentum. The maneuver may be stationkeeping.

Abstract: A sparing system for space vehicle constellations. A plurality of space vehicles arranged in at least one mission orbit plane. The number of space vehicles is at least one greater than a minimum number necessary to provide at least a minimum level of service necessary to carry out a constellation mission. If one of the space vehicles fails the remaining space vehicles are repositioned in the mission orbit plane to provide the minimum level of service necessary to carry out a constellation mission.

Abstract: A fault tolerant attitude control system for a zero momentum spacecraft. A zero momentum attitude control system is operable to control spacecraft attitude utilizing data received from an earth sensor, a sun sensor, and the inertial measurement unit. A gyroless attitude control system is operable to control spacecraft attitude without receiving data from the inertial measurement unit. A redundancy management system is operable to monitor an inertial measurement unit to detect faults and to reconfigure the inertial measurement unit if a fault is detected and operable to determine when an inertial measurement unit fault is resolved. A controller is operable to automatically switch the spacecraft from the zero momentum attitude control to the gyroless attitude control when a fault in the inertial measurement unit is detected and is operable to automatically switch the spacecraft from the gyroless attitude control to the zero momentum control upon resolution of the fault.

Abstract: An attitude control system for a spacecraft that includes a north side, a south side, an east side, a west side, an earth facing side, and an anti-earth facing side. The attitude control system includes a plurality of gimbaled thrusters interconnected with the spacecraft and arranged to produce thrust in a direction parallel to a roll-pitch plane of the spacecraft.

Abstract: A method for correcting differences in measurements between sensors. Misalignment of a roll error of a sun sensor alignment is estimated with respect to a reference roll value measured by an earth sensor. Sun sensor assembly elevation angle residual is calculated utilizing the estimated sun sensor assembly roll misalignment. A yaw attitude of the spacecraft is updated based upon the calculated sun sensor assembly elevation residual.

Abstract: A method for controlling a geosynchronous spacecraft. A yaw axis and a roll axis of the spacecraft are oriented parallel to the earth equatorial plane. A coordinate frame of a payload is rotated about a minus roll axis of the spacecraft at an angle equivalent to an orbit inclination of the spacecraft, thereby maintaining elements of a payload pointing toward a desired region on the earth. A spacecraft attitude is corrected to maintain the payload elements pointing at the desired region on the earth.

Abstract: In general, a constellation of spacecraft is used to broadcast to a particular region with high angles of view in order to reduce blockage or shadowing. A constellation of a plurality of spacecraft is placed in 24-hour orbits having inclination of about 55°, eccentricity of about 0.32, semi-major axis of about 42,000 km, longitude of the ascending node of about 43° East, argument of perigee of about 270°, and longitude of the ground track at maximum latitude of about 7° East. The preferred number of spacecraft ranges from three to six. In a particular application of Digital Audio Broadcast to Europe in some embodiments, the most populous cities are provided with service from no more than about 10° from vertical, and broadcast takes place when the spacecraft are above at least 35° North latitude. The broadcast power is reduced during those portions of the orbit in which the ground track lies in the Southern hemisphere.

Abstract: A method for maintaining three axis control of a geosynchronous spacecraft without body rate measurements using reaction wheel assemblies. Earth sensor assembly angle measurements are utilized for high-bandwidth roll and pitch control. A positive pitch momentum bias is stored in the reaction wheel assemblies. A gyroscopic feedforward torque is applied to rotate reaction wheel assembly momentum in a yaw/roll plane of the spacecraft at orbit rate. A dynamic mode that couples yaw and roll axes and that results from applying the gyroscopic feedforward torque and the high-bandwidth roll control is damped based on earth sensor assembly roll measurements.

Abstract: A method for controlling spacecraft velocity. A thruster torque gimbal angle command is calculated to provide a desired thruster torque demand command including a desired momentum adjust torque and a desired attitude control torque. A velocity change error between a commanded velocity change and an actual velocity change, a commanded force vector based on the error to cause the actual velocity change to approach a commanded velocity change, and force gimbal angle commands and force thrust commands to achieve the commanded force vector are calculated; and/or an error between gimbal angles and thrust levels and reference gimbal angles and thrust levels, reference gimbal angle commands and reference thrust commands to drive actual gimbal angles and thrust levels toward reference gimbal angles and reference thrust levels are calculated. A total gimbal angle command is calculated by adding the torque gimbal command with at least one of the force gimbal angle command and the reference gimbal angle command.