The Society of Photo-Optical Instrumentation Engineers is to be commended for the very fine program of this seminar. The topics covered are all timely and the invited speakers are outstanding in the field.
Space astronomy, the observation of the heavens through telescopes which are above the atmosphere, is now well under way. It began with balloon and rocket flights, and progressed to satellites capable of long steady observation. The most successful of these has been 0A0-2, which is now in its third year of operation, gathering data continuously and adding richly to scientific knowledge of the universe (Ref. 1). 0A0-3 failed to reach orbit in Nov. 1970 due to launch vehicle malfunction, but 0A0-4 is scheduled for launch in late 1971.
A new five-gate, automatic acquisition tracker has been constructed for tracking stars and satellites with a standard video signal from either a vidicon or image orthicon. In order to operate at usual video signal-to-noise ratios, the tracker uses line-to-line correlation to reject random noise. The angular resolution of the tracker is one-half of one percent of the field of view down to a signal-to-noise ratio of about two to one. Laboratory data oper-ating with both image orthicons and vidicons will be presented.
The Sylvania Precision Aircraft Tracking System (PATS) is a precision laser radar system designed for tracking and position determination of cooperative targets which can be mounted with a retroreflector. The reflector provides a very strong laser pulse return which can be detected above the ambient illumination. During operation, the system accurately measures azimuth, elevation, and range of the target at sample rates up to 100 measurement sets per second. These data are available for recording on magnetic tape or realtime computer processing.
With the fast development of anti-ballistic missiles, capable of accelerations beyond 150 G's, it has become a problem for many missile ranges to utilize existing photo-optical tracking devices at reasonably short slant ranges. In order to track such superfast missiles, angular accelerations beyond 10 radians per second squared are required at the tracker's axes. This is about ten times better than what present-day theodolites and tracking mounts can achieve.
Image intensifiers include a wide variety of electronoptical devices having diverse capabilities including color conversion, image deflection, shuttering, image scanning, and recording with linear re-sponse. They also differ greatly in their ability to intensify images. A criterion can be defined in terms of image information for comparing realistically the gain of one intensifier with another or for specifying a true gain over unaided Photography. This criterion depends in certain respects on the type of image being recorded.
This paper constitutes a current status report on the automatic laser tracker being used at Sandia Laboratories' Sled Track Facility. A short review of the need and system description will, be covered, followed by a description of problem areas. Most of the paper will deal with the modifications completed and the results thereof.
High resolution photography from aerospace vehicles requires that there be no relative motion between the film and the image of the scene being photographed during the time of exposure. Such image motion occurs as a result of translation and angular rotation of the vehicle relative to the scene being photographed. Present generation aerospace camera systems employ a two part solution to the problem of image stabilization. A stabilized mount is used to provide isolation from attitude changes, while the effects of forward travel of the vehicle are corrected by a forward motion compensation (FMC) system. A system may provide FMC in any one of several ways, such as movement of the entire camera optical system, movement of a mirror sit-uated in front of the camera lens, or movement of the film relative to the lens system.
The telescope of the most common form of gimbaled star tracker is aimed to encompass a target star within its field of view, and then servo-controlled to point its optical axis precisely at the star. The servo error signals, representing angular separation between telescope optical axis and star line of sight, must be reduced to negligible values before star coordinate data can be extracted.
Present day accumulation of data by range instrumentation is predicated upon the angle of its pointing axis relative to the mis-sile trajectory and its ability to follow the flight of the missile. The general types of flight performance data requires keeping the vehicle within the field of view of various types of photographic, ER sensors, and micro-wave instrumentation. The geographic location of the tracking instrumentation relative to vehicle launch and flight path, vehicle velocity and acceleration, determines how stringent a tracking system is required.
Since World War II, interest in manual control as a design problem has steadily increased. Perhaps no area of man-machine research has produced more scientific literature. However, the rather diverse assortment of manual control equipment in operation today is strongly suggestive of a general failure to utilize empirical findings during the design process. That is, many designs appear to be based onrationale which might be best described as "intuition". Moreover, seldom are parametric studies conducted to determine whether a new design is any better, or worse, than existing equipment. Thus, evaluations of such designs are not, in effect, evaluations at all.
Current and projected requirements for increased angle readout accuracy on photo-optical instrumentation mounts create new demands on the angle encoding systems used to instrument the mount axes. In most modern system requirements, an output is required in real time digital form. In two basic applications, the mount angle readouts are 1. recorded (correlated to real time) as the instrument tracks a target, for the purpose of reconstructing the target trajectory. 2. used in real time as the position feedback reference to a digital position control loop which drives the mount along a specific tra-jectory so that a high resolution optical record of the object can be obtained. In addition to high static accuracy and fine resolution requirements, the above applications require high dynam-ic accuracy of the encoding system. In addition, the angle encoder system must be rugged enough to withstand field environment stresses, and reliable enough to cause negligible system downtime. Inductosyn plates, when correctly adapted to the instrument axis and when properly matched to the right set of electronics, satisfies the current and projected accuracy and resolution re-quirements. An electronic system for converting the Inductosyn* plate out-puts into digital form is discussed, following a pattern in which various alternate schemes are discussed, thus developing the rational for the chosen configuration.Error analyses, considering both static and dynamic conditions, are presented for the entire conversion process for the Inductosyn* plate to the digital output; the error analysis shows that the FSD angle encoder system, using an Inductosyn* plate, produces static and dynamic errors of + 1 arc sec, 1 arc sec/rad/sec, and 1 arc sec/rad/sec2, with resolution as fine as 0.15 arc sec. Techniques are described or mechanically coupling Inductosyn plates to the mount axes, with considerations depending on the mount bearing accuracies and overall system accuracy require-ments. Finally, static and dynamic test results are shown which depict angle readout error curves for a system using the FSD angle encoding systems, demonstrating the accuracy achieved. Several methods of performing accuracy tests are pre sented, emphasizing the care required to achieve consistent test results.
Although the image dissector was probably the first all-electronic optical scanning device to be used (Ref. 1) for generating a video television signal, its first reported use (Ref. 2) as an optical tracking device did not occur until 1960. Since that date it has enjoyed a steadily increasing popularity as a specialized optical scanning device, especially for tracking stars (Ref. 3) and laser (Ref. 4, 10) images.
The Mapping Camera Subsystem provides
precision metric photography of the lunar
surface as well as time correlated stellar
photography used for post-flight camera
system attitude determination. A multiple
camera system, such as the Lunar Mapper,
requires the need for precise stellar calibration
to assure maximum usability of its
photography in subsequent photogrammetric
data reduction. The pertinent parameters
of the Lunar Mapping Camera Subsystem,
as well as the plans and techniques for performing
the overall stellar calibration task
are summarized. Included is a review of
stellar calibration plans for site selection,
site development, logistics, mission observation, and date reduction.
A transportable laser system for lunar ranging is described. It can be used at any astronomical observatory where a 1.5-m telescope is available. Since this telescope is used for the returned signal only, its use for other purposes is not affected significantly. The transportable system uses a high-energy, single-mode, neodymium-glass laser whose frequency-doubled wavelength is 530 nm. Because the laser's divergence is very low, an atmospherically limited beam-width can be achieved with optics only 0.2 m in diameter. An initial phase of the program, con-cerned with ranging to near-earth satellites, will be described. For this application, a 5-cm coude system is used to point the laser beam. There is also a separate 12-cm receiving telescope.