We discuss both the theoretical reasons for considering a non-circular format for the Large Deployable Reflector, and a potentially realizable concept for such a device. The optimum systems for diffraction limited telescopes with incoherent detection have either a single filled aperture, or two such aperatures as an interferometer to synthesize a larger aperture. For a single aperture of limited area, a reflector in the form of a slot can be used to give increased angular resolution. We show how a 20 x 8 meter telescope can be configured to fit the space shuttle bay, and deployed with relatively simple operations. We discuss the relationship between the sunshield design and the inclination of the orbit. We conclude by discussing the possible use of the LDP as a basic module to permit the construction of supergiant space telescopes and interferometers both for IR/submm studies and for the entire ultraviolet through mm wave spectral region.
We describe the experiences in coaligning and phasing the MMT, together with studies in setting up radio telescopes. We discuss these experiences and on the basis of them, we suggest schemes for coaligning and phasing four large future telescopes with complex pri-mary mirror systems. These telescopes are MT2, a 15m equivalent MMT, The University of California Ten Meter Telescope, the 10m sub-mm wave telescope of the University of Arizona and the Max Planck Institute for Radioastronomy, and the Large Deployable Reflector, a future space telescope for far IR and sub-mm waves.
There is historically a gap between the technologies of optical systems and of radio frequency antennas. The gap is, of course, man made because the electromagnetic spectrum is a continuum. The recent attention of radio frequency users to large apertures and small wavelengths and of optical instrument users to the infrared regime has erased the gap. One of the results is that some of the advanced concepts for large antennas in space become useful for infrared telescopes.
A procedure was developed to generate point spread functions for a segmented mirror system for a deployable reflector for submillimeter astronomy. These point spread functions were generated using ACCOS V and special purpose software. This procedure allows tilt and piston sensitivities to be evaluated. Point spread functions with tilt and piston errors are discussed.
A method has been developed for comparing the tilt and phase of segments of a collimated wavefront using a multiple-order radial-grating shearing interferometer. Here the extension of this technique to segmented primary mirror tilt and phase alignment is considered. A configuration for the interferometer and a method of unambiguously measuring a two-dimensional array of segments is presented.
Boresighting of laterally separated optical systems or lines of sight may require the lateral transfer of a collimated alignment beam without the introduction of error into the look angle represented by the alignment beam. An extended retro of some sort (e.g., cube corner) is commonly used for transfer of the look angle reference. One major error source that degrades the accuracy of the extended retro is bending of the "tube" connecting the retroreflector input and output optics. Control of this bending requires that the retro-reflector be well isolated from environmental stress such as vibration or thermal gradients across the tube. Alternatively, the bend of the tube may be monitored. This paper describes some of the techniques used in the accurate lateral transfer of alignment beams. Several approaches which are functionally equivalent to an extended retroreflector are discussed. The five-surface retroreflector concept (using empty pentaprisms) is modified into an "Alignment Reference Transfer System" (ARTS), which to first order is insensitive to tube bends. Several optical configurations of the ARTS concept are shown, and the tradeoffs leading to the selection of the baseline design are described. The error sources in the baseline are pointed out. The coupling of ARTS input beam misalignment to tube bend produces an ARTS error which is the product of the two. A brief discussion of the application of the ARTS in the boresight of two apertures is also included.
Lengths of glass tubing are used as the starting point of a new method to make light-weight glass honeycomb. The tubes are packed together and filled with free flowing refrac-tory sand. On heating to the softening point of the glass the sand pressure forces the tubes into contact. Close packed round tubes yield hexagonal glass honeycomb. Face plates can be incorporated in the same fusion step. The method has been demonstrated for borosilicate glass, but should be applicable also to fused silica. A method for accurate repli-cation of borosilicate glass off a fused silica master has also been demonstrated. It is shown that gold is an effective parting layer, and small scale replicas have been measured to have about 1μ FMS accuracy. It is suggested that honeycomb panels made by the sand fusion method and replicated off fused silica may make ideal panels for precision deployable reflectors like LDR.
A holographic technique for sensing the optical figure of a deformable mirror is described. This technique uses the coherent summation of subaperture zone plate to achieve full aperture interferograms. As such, it is inherently scalable to arbitrarily large mirrors. Experimental confirmation of feasibility is presented.
The Active Control of Space Structures (ACOSS) program of the Defense Advanced Research Projects Agency has identified problems in active vibration control of structural modes in extremely flexible space structures and in precisely pointed optics. The Air Force Wright Aeronautical Laboratories programs are an outgrowth of the ACOSS program. They are aimed at the problems of sensors, actuators, and their dynamic interactions with the structure to be controlled, and at the problem of system identification by one-g laboratory experiments. The VCOSS-1 and VCOSS-2 programs (Vibration Control of Space Structures) address the dynamic interactions of the sensor-actuator-structure; the Benchless Laser program and the Airborne Laser Mirror-Control program address the active control of HEL mirrors; the Experimental Modal Analysis and Component Synthesis and the Large Space Structure Dynamics programs address the problems of system identification and testing. Closer coordination with NASA and DARPA is being sought in support of on-orbit dynamic testing using the Space Shuttle and in the development of a national facility for one-g dynamics testing of large space structures.
In the last year, the Air Force Office of Scientific Research (AFOSR) has undertaken some bold initiatives to intensify the Air Force Basic Research program in certain areas of science and technology which promise to potentially impact in a major way projected future space systems. This initiative effort has involved the total Basic Research community from the in-house researchers at the participating Air Force laboratories to the extramural players in industry and in academia. Ongoing tasks in a number of areas have been refocussed on issues related to space systems and operations, and critical areas of technology and science have been augmented in funding.
The NASA's long range goal in space research and technology is to maintain a strong technology base to insure continued U.S. space leadership. Therefore a principal objective is to strengthen NASA's space R&T program to insure the timely provision of new concepts and advanced technologies for the U.S. civil and military space activities. A program is in place at NASA for the development of active control technology to support major initiatives such as space station and advanced spacecraft. A number of key control technology needs are cited as required for these and other future NASA missions together with an integrated control/structures technology flight experiment to demonstrate and validate technology for large flexible structures.
Research progress in the area of structural dynamics and control using the flexible beam facility at the NASA Langley Research Center is reviewed. Particular attention is placed on the progress in adaptive control and reliability improvements using advanced control concepts. Both theoretical and experimental results are given to indicate the nature of the work being undertaken. In the adaptive control area, emphasis is placed on parameter and system identification and in comparison of competing on-line algorithms. Also, results are presented for on-line modal control laws that are interfaced to a parameter identification scheme. This provides an on-line distributed adaptive control system. In the reliability area, a design process is outlined that incorporates reliability over the design mission life.