A Space Station (SS) attached Payload Pointing System (PPS) was designed and analyzed. The PPS is responsible for maintaining inertially fixed payload pointing in the presence of disturbances applied to the SS. The payload considered in this analysis, the Solar Optical Telescope (SOT), was attached to the SS via a 3-axis gimbal system. NASTRAN structural models were developed assuming the SS to be a flexible structure while the gimbal mechanism and SOT were assumed to be rigid bodies, and a state space description of the plant (SS + Gimbal + SOT) was formulated. A digital controller was designed and a linear stability analysis of the overall control loop was performed. Finally, system performance was evaluated via digital time simulations by applying various disturbance forces to the SS including crew motions, centrifuge, thruster firing, and Space Shuttle docking. The PPS met the SS articulated pointing requirement for all disturbances except Shuttle docking and some centrifuge cases.

The Spacelab Instrument Pointing System (IPS) is a three axes gimbal system providing pointing and stabilization in the arcsec range to a variety of space experiments with a mass of up to 7000 kg. The IPS demonstrated a high performance and versatility in operations during its maiden flight, the Spacelab 2 mission onboard Challenger in July 1985. The mature mechanical design of the IPS together with the growth in processor and sensor technology revealed a considerable potential for further improvements at moderate effort. By incorporating advanced sensors, computers and software, the IPS pointing performance is improved and the range of IPS applications is widened. In order to achieve a high degree of IPS autonomy and automation, a new computer and software architecture has been conceived, yielding high independence from external services, automation of operational procedures and thus a simpler man-machine interface. The improved IPS is capable to perform closed loop tracking of moving objects. The IPS simulator PERFSIM demonstrates a tracking accuracy and stability being close to the inertial pointing performance. Taking full advantage of the IPS automation and autonomy features, the ultimate goal is to achieve full platform autonomy, that is to use the improved IPS as a self-contained tracking and pointing system on the Space Staion or other free-flying platforms.

The Goddard Space Flight Center (GSFC) is planning a series of space communication experiments to validate laser technology for future NASA missions. Requirements include sevelal hundred MBPS data relay in the near earth environment and approximately one MBPS over the deep space to earth link. A key element in this program is a Shuttle-based laser system called the Laser Technology Experiments Facility (LTEF). This Facility will be designed to communicate with a cooperative laser system under development for the Advanced Communication Technology Satellite (ACTS) and will conduct a comprehensive set of acquisition, tracking and communication experiments. This report presents the results of the initial study of this Facility with particular emphasis on the challenges associated with LTEF acquisition of the ACTS downlink beacon laser.

Some of the strategic-initiative-type threats that may face the population include an attack by a large number of very similar objects, such as missiles surrounded by an even larger number of decoys. The feasibility of discriminating among two different classes of objects that have no difference in appearance and no intrinsic signature is investigated. In the direct imaging approach, a decoy will appear to be identical to a missile. Therefore, imaging is eliminated as the approach to separating real threat objects from simulated objects. Another discrimination approach is based on the agile illumination concept. Agile illumination consists of a two-aperture illumination with a coherent light (such as laser), diffraction of light due to propagation, and the resulting interference on the object surface. A scanning two-beam interference pattern illuminates one object at a time. After the propagation time delay, the light reflected from the object is collected and analyzed for amount and temporal dependence. Depending on the shape, momentum, spinning, and tumbling characteristics of the interrogated object, different temporal signatures will be obtained for different classes of objects. The study shows that even for identical objects with no intrinsic signature, agile illumination can be used to discriminate between objects. Their different physical and dynamic characteristics are expected to differentiate the decoys from the threat objects.

Many current and future electro-optical systems employ acquisition, tracking, and pointing subsystems. The functions of these subsystems and their relationships are defined, and typical components are identified. Theoretical performance equations are presented in a tutorial fashion. Current performance levels are reviewed for ground-based, airborne, and space-based applications.

Simultaneous satellite laser ranging and intercomparison of ranging were performed by three NASA tracking stations, in support of NASA Crustal Dynamics Project, to determine accuracy in laser ranging to earth bound satellites. The satellite used in this experiment is LAGEOS (laser geodynamic satellite) which is equipped with retroreflectors and is at a distance of 6000km in a near circular earth orbit. All three stations went through major hardware upgrades and have demonstrated single shot satellite ranging precision of 8mm, 14mm, 30mm respectively with a stability better than 3mm; the difference in precision emerging from the photoelectron statistics as well as the time of flight measurement devices used. The data was taken with all three stations in close proximity (<40meter) to each other and performance comparison accomplished through data processing software such as POLYQUICK (using pure geometry) and GEODYN (using orbital techniques) which are capable of providing comparison at the mm level. Since the POLYQUICK program is very sensitive to the accuracy of the telescope pointing angle, refinement of the predicted angle was performed via integrating the IRV( inter range vector) using the actual range data and using this data for analysis. Results indicate consistent agreement in satellite ranging among these stations under lcm. Details are discussed.

lhis report demonstrates the use of a grating in a lateral heterodyne interferometer to make high resolution angular measurements at high speed. Depending on choice of grating, various range, resolution, and speed tradeoffs can be made. Details of two systems will be shown which use gratings with a pitch of 25 microns and 2 microns. The system using a 25 micron grating can track a 20 cm. shaft at 25 rad/sec with 284 nanoradian resolution, and the 2 micron system the same shaft at 2 rad/sec and 36 nanoradian resolution.

A docking/berthing sensor can support operations for NSTS orbiter retrieval of satellites or free-flyers, space station rendezvous with OMV and NSTS orbiter, and orbiter/lander docking for interplanetary missions. A laser docking sensor (LDS) has the capability to fulfill these missions due to its ability to optically resolve the target for measurement of target attitude in conjunction with the inherent compactness, low power consumption and high reliability of all-semiconductor optoelectronics. An LDS design is presented using a laser diode rangefinder, CCD array with active laser diode illumination, and multi-target video tracker.

Many precision pointing systems for the coming decade will require subarcsecond stability in the presence of base motion. Satellite vibration data from various sources indicates that there is base motion between 30 and 150 urad in the frequency range from 1 to 300 Hz on most vehicles, and that there may be significant motion near 1000 Hz. In many applications, optical tracking sensor data is not available with sufficient band-width to allow rejection of base motion. Such line-of-sight (LOS) stabilization systems, therefore, require inertial sensors with signal noise levels in the submicroradian range and signal bandwidths of several hundred hertz. This paper discusses inertial LOS stabilization concepts having the potential for this accuracy. We present a configuration that illustrates the performance achievable using highly linear fine-steering mirrors (FSM), star trackers with high and long-term accuracy, and accelerometers with bandwidths approaching 1000 Hz. Simulation results are included for performance prediction.

A compact and robust focus drive mechanism was developed for the International Ultra-violet Explorer (IUE) scientific instrument. The design philosophies and detail design features of this mechanism are discussed. The mechanism design is based on a novel planetary-type drive which converts angular increments of a permanent magnet stepping motor into simultaneous linear displacements of three ball screws which support the secondary mirror. The design produces significant torque margins while providing an exceptionally smooth and reliable operation. Materials selections, driven by bearing and ball screw requirements, are also discussed. A summary of performance capabilities is included.

A high bandwidth, sub-arc second, two degree of freedom image motion compensator has been developed to enhance pointing stability of shuttle based optical telescope experiments. The mechanism design includes a gimbal-type flex pivot suspension, a novel ironless two axis forcer and a differential capacitive tilt sensor system capable of sub-arcsecond performance. The image motion compensator was developed to permit the Ultraviolet Imaging Telescope sensor, part of the Astro-1 scientific instrument cluster, to maintain stringent pointing requirements for extended integration intervals while experiencing perturbations typical of those expected from a manned orbiter background. The servo control system, which encompasses other sensors and pointing capabilities, is briefly discussed.

Many electro-optical systems rely on a pointable line-of-sight for their operation. Thirty-one pointed optics are described along with their associated characteristics. The design impact of these characteristics is discussed qualitatively to provide some guidance in selection of an appropriate gimbal type. Each of the gimbals described is illustrated to show the general configuration.

The most stressing requirements for acquisition, pointing, and tracking (ATP) operation in a Strategic Defense Initiative (SDI) environment are precision tracking and pointing, rapid retargeting, and target low-level signature detection. The ATP device-to-target ranges are extremely large and not only must active vibration isolation and jitter suppression be employed but so must active wavefront control of HEL (High Energy Laser) illuminator/tracking/ranging lasers that are combined with extremely accurate alignment systems. The system incorporates high-technology subsystems-level hardware in the areas of optics, electro-optics, and electro-mechanics that stress the state of the art. The ATP consists of a coarse and a precision-passive IR acquisition and tracking sensor coupled to a precision-active UV tracker that references boresight, range, and target motion to an NPB-pointing control system. This paper introduces the subject with an overall ATP system diagram outlining optical and electro-optic signal paths for trackers,pointers, alignment, beam steering and control, and target handover. The requirements for tracking and pointing accuracy/precision exceed the capability of current inertial attitude sensors; therefore, boresight calibration for closed-loop precision tracking with respect to (WRT) a local body frame is considered. The inertial reference frame is utilized for large-angle slews, target acquisition on a tracker sensor, and slew settling. Once the target is acquired, the inertial frame is transitioned to the local body frame for tracking control where a stable boresight alignment reference is maintained between the inertial and local body frame. The subject of vibration isolation and jitter suppression WRT sensors, actuators, lasers, and structures is addressed by identifying the fundamental error sources that impact pointing precision and methods for compensation or attenuation. Logical system requirement flowdown and breakout of details are provided to support the rationale for the concept and feasibility of design approach. Finally, alignment system and tracker system relationships are addressed with a brief description of control for boresight alignment (local body WRT inertial frame), alignment relay transfer and beam steering (local body frame), track error (local body frame), pointing error (local body frame), and target handback (inertial frame).

A joint Itek and Kodak project to process the Lode Advanced Mirror Program* (LAMP) mirror facesheets was Kodak's first experience with shaping, measuring, polishing, and handling extremely flexible mirrors. The segmented LAMP mirror has been assembled by Itek containing a center section polished by Kodak using the full-size tool Area Compensated Tool (ACT) process.

Auxiliary inertial instrument, properly applied, can lead to significant improvements in both static and dynamic performance parameters in large pointing and tracking systems. This paper discusses the application of a particular class of inertial sensors, the performance results obtained, and the practical aspects of their use.

The performance of precision stabilization systems for electro-optical sensors is often limited by the friction disturbance torques. This tutorial paper describes the classical design technique for minimizing the line-of-sight (LOS) motion due to friction coupling of the base dynamics. A specific design example with measured data is presented. The potential for improved performance by using additional state feedback techniques is discussed.

The servo model, design methodology, and performance prediction of the W. M. Keck Telescope is discussed. The tracking/slewing requirements are stringent compared with other telescopes in order to take full advantage of the improved technology in mirror fabri-cation. The combination of stringent requirements and large size makes the Keck Telescope servo design interesting to other servo designers.

Communications via optical cross-link between two satellite stations require reciprocal spatial beam tracking. This tracking is achieved by a quadrant detector, which attempts to align the received beam Airy disc on the quadrant cross hairs. Errors due to offset images on the quadrant detector are used to continually realign the gyros so as to aim the pointing optics directly at the received beacon direction. The error voltages at one receiving satellite station depend also on both the pointing errors and the antenna gain pattern at the other transmitting station at the line of transmission. The steady state joint tracking errors of two direct-detection cooperative beam tracking systems are analyzed. In particular, the stable steady state angular pointing errors at both ends are found for constant relative angular motions. Curves of steady state tracking errors will be shown to relate the key system parameters and the type of angular motions. Two of the most important functions for determining steady state stability regions are transmitting aperture functions and the tracking loop S curves. Both first and second order tracking loops at each end of the system are considered.