Abstract: A spacecraft according to the invention includes a pair of propellant tanks, with the nominal center of mass of the spacecraft located therebetween. Propellant is coupled from the tanks to a velocity-change-inducing thruster by a controllable coupling arrangement. Unwanted torques may occur which tend to perturb the attitude. An attitude control arrangement generates an error signal in response to deviations of the attitude from the desired attitude. The error signal is processed to control the propellant coupling arrangement, to cause propellant to be used preferentially from at least one of the tanks in a manner which tends to move the actual center of mass relative to the axis of thrust or line of action of the thruster. In one embodiment of the invention, the controllable coupling arrangement includes a manifold for coupling propellant from the tanks to the thruster, a tank of pressurizing gas, and a controllable manifold coupling the tank of pressurizing gas to the propellant tanks.

Abstract: A spacecraft-based cellular communications system includes a spacecraft with transmit and receive antennas, each of which produces a plurality of spot beams which, together, provide coverage of the region served. In order to control the pointing of the spacecraft antennas, four mutually adjacent spot beams are centered over a particular "beacon" location, so that the beacon location lies between a pair of North and South spot beams, and between a pair of East and West spot beams. The transmit antenna is controlled by transmitting a beacon signal in time sequence over each of the four spot beams surrounding the beacon location, and decoding or desequencing the time-sequential signal received at the beacon location. The decoded signal is processed to provide a signal indicating the pointing error of the transmit antenna, and the error signal is used to control a gimbal which controls the pointing of the transmit antenna.

Abstract: An RF amplifier includes a FET output stage and a driver. The FET is subject to long-term degradation in multiple-carrier use if its average gate current often exceeds a predetermined value. The random superposition of signal peaks of the multicarrier signal may cause such peaks to occur. The driver stage is selected to provide a range of four dB or less between the single-signal 1 dB compression point and the hard compression point, as measured by driver input signal level. This prevents application of excessive input signal to the output stage in a multicarrier situation, and prevents degradation of the FETs of the output stage. In one embodiment, a predistortion equalizer or linearizer is placed before the driver stage, to tend to linearize the characteristic of the driver and output stage combination at signal levels below those at which the driver is limited.

Abstract: A three-axis stabilized spacecraft is subject to a velocity change in a desired direction by a thruster. Unavoidable alignment errors cause a body torque, which tends to slew the body away from the attitude which orients the thrust axis in the direction. The attitude control system eventually corrects the attitude, but the thrust during the attitude transient results in an error in the direction of the velocity change. This error in the direction accumulates during the attitude transient. When the attitude transient passes, no further pointing error occurs. A control system, operating without an accelerometer, determines the total error accumulated during the attitude transient, and processes the error signal to generate a supplemental torque demand signal, which is added to the torque demand signal produced by the attitude control system, to cause an oppositely-directed attitude transient to thereby cancel the original velocity change direction error.

Abstract: A two-way light amplitude divider includes a light rotator (18) with first (18.sub.1), second (18.sub.2) and third (18.sub.3) ports. The second port is coupled to a port of a controllable Fabry-Perot etalon (22). The etalon can take on a state in which a particular .lambda. of light is passed, and others are reflected. Light at .lambda..sub.1 applied to the first port (18.sub.1) of the rotator (18) passes through the etalon (22) to a port (22.sub.2) when the etalon (22) is in its first state, and the light is reflected by the etalon (22) in its second state, and flows to the third port (18.sub.3) of the rotator (18). Thus, the arrangement (10) acts as a single-pole, double throw switch, depending upon the state of the etalon. The arrangement can be cascaded in a manner which operates as a multiplexer (700) or demultiplexer (600).

Abstract: A spacecraft carries a deployable active antenna array panel(s) and a deployable solar array panel(s). In the stowed condition, the antenna array panel(s) is sandwiched between a side of the body of the spacecraft and the solar array panel(s). This stowed state prevents the antenna panels from becoming too cold by radiation, or too hot by insolation, in an intermediate orbit. The outermost solar panel preferably has its active surface facing outward, so that it can generate electricity in the intermediate orbit.

Abstract: A communication system (10) includes a plurality of fixed terrestrial gateway terminals (14) and fixed village terminals (18), and also includes a plurality of mobile user terminals (16). The system includes a first satellite (12m) which provides communication in a bent-pipe manner between user terminals (16) lying in spot-beams of the first satellite's antenna and gateway terminals (18) lying in a broad antenna beam. The system also includes a second satellite which provides communications in a bent-pipe manner between or among the gateways/village terminals. The village terminals differ from the gateways in that the village terminals do not include the subscriber of user home or visitor registers. The village terminal includes a wireless local communication system such as a WLL, for communicating with user terminals (16) lying within its range. The user terminals (16) are dual-mode.

Abstract: In a multi-cell battery, an open-circuit failure of any one cell renders the entire battery unusable. An automatic electronic bypass switch is connected across each battery cell to provide a low-resistance conductive path around such battery cell should it fail. Contrary to conventional usage in which a fuse is employed to "clear" or "open" a short-circuit condition, the electronic switch of the present invention employs a fuse to activate a highly conductive path, which ideally would approach a short circuit, around an open-circuit condition. The electronic switch includes a field-effect transistor connected across the battery cell and a fuse to hold the field-effect transistor in the "off" condition.

Abstract: An array antenna (12atf) particularly useful for a spacecraft includes a plurality of antenna elements (310). Each of the elements includes a conductive hexagonal cup (408) having sides (410a, 410b, 410c, . . .) which are thirteen twentieths of a wavelength long at the center frequency, and have a height above the bottom (412) which is a little more than one-third wavelength. A crossed dipole (420) includes two dipoles (420V, 420H), the first (421, 422) having elements approximately one quarter wavelength long, and the second (420H) having elements (423, 424) about three twentieths of a wavelength long. The plane of the crossed dipole is about one quarter wavelength above the bottom of the cup. A first director ring (512) has a diameter of about one quarter wavelength, and is spaced about nine tenths of a wavelength above the bottom. A second director ring (514) has a like diameter, and is spaced about seven tenths of a wavelength above the bottom of the cup.