Following the use of the James Webb Space Telescope (JWST), there will be a need for space telescopes or interferometers of increasing size and, later, of increasing aperture. Looking ahead to the known problems of the next decade allows a modest extrapolation from JWST to address the currently interesting science. Increasing telescope sizes will also allow exploration with higher angular resolution. Eventually, the telescope/interferometer sizes will be so large that they must be constructed in space.

Recent advances in astronomical research have led to a much-improved understanding of the evolution of the physical Universe. Recent advances in biology and genetics have led to a much-improved understanding of our biological Universe. Scientists now believe that we have the research tools to begin to answer one of man’s two most compelling research questions: Are we alone? and How did we get here? This paper reviews the requirements and challenges we face to engineer and build the large space-based systems of interferometers and innovative single-aperture telescopes to detect and characterize in detail earth type planets around stars other than our sun.

With the selection completed of the industrial partners for the James Webb Space Telescope (JWST) and subsequent replanning concluded, several groups and NASA have begun to consider options for subsequent major space astronomy missions. Active interest includes scientific justification for even larger space observatories, the technologies necessary to enable such missions, supporting infrastructure and facilities, system designs, and the political environment that would be receptive to the sustained funding necessary for such major missions. This paper discusses each of these issues in turn and concludes similarly to the recommendations of the NASA Exploration Team (NEXT) that a human-occupied gateway at the Earth-Moon L1 point offers several attractive opportunities for NASA and the scientific community, including primarily the capability to support very large aperture science facilities, as well as a publicly appealing option for human exploration beyond low-Earth orbit.

Conventional telescopes whether for ground or space feature a highly accurate primary mirror coupled to a secondary and other mirrors using a stiff metering structure. In the last decade, significant progress has been made in aperture size (8 to 10-meters on the ground) and 2.4-meters in space. It is our position that highly active components made using revolutionary new materials will enable the reduction of mass, provide Angstrom level wavefront control, and enable highly integrated compact space telescope designs. It is the intent of this paper to discuss a roadmap on a component basis that can serve as a building block for future telescope systems having lower areal density, larger mirror apertures, and greater resolution and bandwidth. Precision actuators under computer control are being developed that enable Angstrom level control of the telescope structure. Structural materials such as silicon carbide provide the ability to make mirrors with an order of magnitude lower areal density while retaining dimensional stability, high natural resonance, and excellent optical quality. Highly active primary mirror configurations that combine the relative merits of control actuators and silicon carbide will provide an order of magnitude increase in control authority. Deformable mirrors having 10,000+ actuator channels offer the potential to field coronagraphic instruments that can image planets about distant stars. Multi-functional optics that integrates both tilt and fine phase control functions in a single device enable wavefront control in a very compact package. Low power, vacuum compatible drive electronics designed specific to the actuator operating mode are being developed in a hybrid microelectronics package. Material processing on the nanoscale provides the basis for a new class of functional hybrid materials that feature the scaling of polymers, the dimensional stability of ceramics, and the structural strength of metals.

Decisions about structural architecture for future large space observatories will influence how overall optical stability scales with observatory size. This is examined using basic structural design analyses that relate overall stability requirements to telescope structural modal frequency and damping ratio. In this way, the influence of certain system level architectural choices on the performance can be assessed. In particular, trades between structural depth and optical correction requirements is examined, and compared against other design parameters such as the material specific modulus. For representative configurations and loads, the required optical correction increases with dimension to the fourth power, but reduces with the square of the structural depth and in proportion to the material specific modulus; areal density has no direct affect. This means that, unless the structural architecture improves with dimension, the optical error produced in a 6-meter telescope might increase by a factor of 123:1 for a 20-meter telescope and 77000:1 for a 100-meter telescope. If the structural depth, however, increases in proportion to telescope dimension, these requirements can be reduced by two orders of magnitude. Architectural options for achieving these benefits are discussed, with particular emphasis on considerations of the deployment or assembly scheme.

The sole purpose of a mirror is to maintain a reflecting surface within specified (wavelength dependent) tolerances for figure and finish. Recent work is now enabling the use of separate approaches to figure and finish, in particular for space telescope mirrors. This approach may eventually yield a mirror with optical performance equal to the best that can be provided by glass, but offering other characteristics that may in fact be enabling for advanced telescope systems not only in space, but also on the ground and airborne. These system enabling characteristics include lower areal densities, rapid and repeatable manufacturing capability, new and more extensive fabrication and production infrastructures, and (possibly) new performance capabilities.

Since 1996, a team at the University of Arizona has been designing and fabricating lightweight, active space mirrors. These glass/composite mirrors use a thin flexible substrate for the optical surface and an actuated composite structure for support. We present a design method that yields the best figure correction for the lightest mass by assuming that the substrate's material properties are the limiting parameters. The results are such that the designer decides on a total mass budget and an aperture area, and the algorithm provides the substrate thickness, number of support points, and the mass distribution between the substrate and actuators.

This paper presents modeling and simulation results pertaining to the wave front correction performance of the recently developed large aperture deformable mirror concept using the novel flexure-hinged substrate. The modeling addresses the potential of this new concept to significantly alleviate the CTE mismatch problems, thereby opening the door to greatly relaxed fabrication, thermal and operational requirements of telescopes. The large aperture deformable mirror consists of an ultra-lightweight nanolaminate face sheet supported by actuated flexure-hinged lightweight substrate. The mirror system is modeled using a combination of Matlab and NASTRAN codes. Using this model, mirror responses to severe thermal loads and the corrections of the resulting deformations through the actuated substrate, are studied. These results represent an important first step in advancing this new concept towards eventual laboratory tests.

The concept of a Sun occulting screen alows a large space telescope to be shielded from solar UV, visible, and IR radiation. Telescope operation in the screen's shadow reduces background radiation from scattering off telescope structures, and reduces expansion and contraction of the telescopes physical dimensions due to changes in solar heating. It is possible to design a non-conducting Sun occulting screen that travels in tandem with a large space telescope such that both the screen and the telescope travel in Sun synchronous orbits that do not cross. The constant separation distance between the screen and the telescope is on the order of 10 Km (far enough from the screen to minimize any radiated IR from the warm screen). The focus of the space telescope's elliptical (or circular) orbit lies at the Earth's center. However, the focus of the screen's orbit will lie at a point displaced toward the Sun, from the Earth's center, by the screen/telescope separation distance. It will be shown that by passing a small photoelectric current through a few turns of wire surrounding the screen, a Lorentz force can be generated that is sufficient to maintain the position of the screen's shifted orbital focal point.

The ultimate limiter of mission lifetime for current space systems is onboard propellant supply. In the past, propellant usage once on-orbit was primarily for station keeping, requiring only a modest amount of mass. However, the increased interest in flying spacecraft in formations that evolve in some prescribed way over time has greatly increased the potential amount of propellant needed over a mission lifetime. For cluster missions that are insensitive to their center of mass location this constraint can be lifted by using internally generated electromagnetic forces between vehicles as an alternative method of formation control. Such missions include rendezvous and docking applications and sparsely distributed apertures for interferometry. The dipole nature of the electromagnetic force allows for full control of the relative degrees of freedom, position and orientation, provided reaction wheels are used for angular momentum storage and control. This paper briefly presents the current research in this area at the MIT Space Systems Laboratory (SSL), and develops the theory behind electromagnetic formation flight under the far field approximation, specifically addressing the operation of clusters within the Earth's magnetic field. Discussion of the hardware technology associated with Electromagnetic Formation Flight (EMFF) and the testbed currently under development at the SSL is also provided.

We present the baseline telescope design for the telescope for the SuperNova/Acceleration Probe (SNAP) space mission. SNAP’s purpose is to determine expansion history of the Universe by measuring the redshifts, magnitudes, and spectral classifications of thousands of supernovae with unprecedented accuracy. Discovering and measuring these supernovae demand both a wide optical field and a high sensitivity throughout the visible and near IR wavebands. We have adopted the annular-field three-mirror anastigmat (TMA) telescope configuration, whose classical aberrations (including chromatic) are zero. We show a preliminary optmechanical design that includes important features for stray light control and on-orbit adjustment and alignment of the optics. We briefly discuss stray light and tolerance issues, and present a preliminary wavefront error budget for the SNAP Telescope. We conclude by describing some of the design tasks being carried out during the current SNAP research and development phase.

A 2-meter by 4-meter aperture DART (dual anamorphic reflector telescope) system has been designed and fabricated using thin stretched mesh reflectors. The system concept consists of a pair of single curvature reflectors with curvature in orthogonal directions relative to each other and is being developed for future ultra-lightweight space applications. The current design is an extension of a 1-meter aperture system previously prototyped and successfully tested in the FarIR. The 2m x 4m system is a laboratory prototype with areal density of less than 10kg/m² for each reflector. The new design demonstrates the advantageous scaling properties of the single curvature reflector concept. The 2m x 4m system was configured and tested in the RF over several frequencies from 5.8 - 8.2 GHz. This paper documents the structural configuration, test preparation, test results, and analysis correlation. Test results show the DART system to be a high directivity antenna (46.5 dB), very low cross-polarization (-33 dB), and good off-axis properties. Test results were in good agreement with analytical predictions of the performance. Generally, the DART system easily achieves the surface accuracy requirements at 8.2 GHz.

High energy cosmic rays and neutrinos may be detected by observing the fluorescence showers induced after interaction with Earth's atmosphere. A high energy cosmic rays observatory would benefit from being lifted into space as a larger portion of atmosphere will be observable. Such a system should have a better performance than existing and future ground based observatories, detecting up to 10³ - 10⁴ events per year. However, only a system with large field of view, and large collecting aperture can achieve the requested high sensitivity and acceptable event statistics. Several optical designs for the optics of a cosmic ray space observatory have been proposed so far. Amongst them, the Schmidt telescope, one of the best known reflectors, well matches both those characteristics, and appears as an appropriate solution to solve the problem.

The Delft Testbed Interferometer (DTI) will be presented. The basics of homothetic mapping will be explained together with the method of fulfilling the requirements as chosen in the DTI setup. The optical layout incorporates a novel tracking concept enabling the use of homothetic mapping in real telescope systems for observations on the sky. The requirements for homothetic mapping and the choices made in the DTI setup will be discussed. Finally the planned experiments will be discussed.

Diffractive lenses offer two potential advantages for very large aperture space telescopes; very loose surface-figure tolerances and physical implementation as thin, flat optical elements. In order to actually realize these advantages one must be able to build large diffractive lenses with adequate optical precision and also to compactly stow the lens for launch and then fully deploy it in space. We will discuss the recent fabrication and assembly demonstration of a 5m glass diffractive Fresnel lens at LLNL. Optical performance data from smaller full telescopes with diffractive lens and corrective optics show diffraction limited performance with broad bandwidths. A systems design for a 20m space telescope will be presented. The primary optic can be rolled to fit inside of the standard fairings of the Delta IV vehicle. This configuration has a simple deployment and requires no orbital assembly. A twenty meter visible telescope could have a significant impact in conventional astronomy with eight times the resolution of Hubble and over sixty times the light gathering capacity. If the light scattering is made acceptable, this telescope could also be used in the search for terrestrial planets.

Advances in the fabrication of adaptive ceramic modules result in compact components that can be adapted to a variety of applications. The adaptive tertiary is a unique component that can provide a variety of functions. Individual modules integrated with a tip/tilt stage can provide auxiliary phasing control of future large segmented telescopes. In addition, each module can contain hundreds of individual actuators allowing the devices to also act as high-spatial frequency deformable mirrors. Measurements have shown that pathfinder devices can be assembled well within the capture range of the devices. This demonstrates the overall feasibility of the concept.

Large optics for space will undergo a revolutionary change in the early 21st century. Conventional discrete manufacturing technology will be replaced by an integrated materials approach conducted on the mesoscale level. Integrated Zonal Meniscus is a revolutionary design and manufacturing approach for ultra-lightweight active mirrors that departs radically from the prevailing composite mirror designs and optical processing methods. The integration of actuators, sensors and electronics directly into a silicon carbide thin meniscus mirror substrate has decided advantages over conventional passive and active mirror configurations. The mirror is given the ability to compensate for optical wavefront errors in a configuration that reduces the overall areal density below 10 kg/m². Our design and manufacturing approach are scaleable to 8-meter class mirrors and beyond.

Active wavefront correction of a space telescope provides a technology path for extremely high contrast imaging astronomy at levels well beyond the capabilities of current telescope systems. A precision deformable mirror technology intended specifically for wavefront correction in a visible/near-infrared space telescope has been developed at Xinetics and extensively tested at JPL over the past several years. Active wavefront phase correction has been demonstrated to 1-Angstrom rms over the spatial frequency range accessible to a mirror with an array of actuators on a 1-mm pitch. High density deformable mirror technology is based on a modular actuator arrays that are scalable to 1000s of actuator elements coupled to the surface of a thin mirror facesheet. Precision actuator control is done by using a low-power, vacuum compatible multiplexed driver system. Mirror surface figure, actuator influence function, and dimensional stability will be given in the context of the Eclipse point design for a coronagraphic space telescope.

The importance of research in optical nano-engineering today is comparable to that of research in semiconductors 60 years ago. Biologically inspired photoactive isomers are being engineered and incorporated into substrates to construct optically addressable nanomachine “laser controlled molecular actuators” which will provide non-contact active figure control, allowing a robust response of lightweight optics to pointing slewing, thermal perturbations, and misalignment. The ability of photoactive molecules to change structure within a matrix in response to light has application to minimizing optical element mass while drastically improving control authority of active optics. Ongoing experiments are providing a foundation for applications in the development of novel optically addressable light-activated shape control of deformable mirrors, as well as addressing issues like damping vibrations after re-pointing large space telescopes. Several types of systems are being studied. The goal is to design and then synthesize materials, generate a picture of molecular scale mechanical forces, bulk geometric distortions, and then to optimize the systems for active optical elements. This requires the design and synthesis of novel photoactive materials. Understanding the molecular-scale motion of photomechanical nano-machines require chemical studies, novel synthesis and fabrication techniques, spectroscopy, imaging molecular-scale mechanical responses and surfaces, optical metrology, and development of novel control techniques. After synthesizing appropriate photoactive substances, active substrates will be produced. A test apparatus is being developed to quantify control authority. Once the chemistry has evolved, a down selection will occur, and new substrates will be fabricated and tested. This talk will report results of this effort.

Significant advances have been achieved in manufacturing optical quality membrane materials with surface quality suitable for use as first surface mirrors. These materials have been used to fabricate test articles demonstrating diffraction limited performance in the laboratory environment. These mirrors are supported using heavy rigid fixtures and pressure forces to tension the membrane. A lighter weight system is required to transition the membrane mirror technology to space hardware applications. Using electrostatic forces to tension and figure the membrane is one promising approach to developing a flight weight membrane mirror system. This paper discusses the design and testing of an experimental membrane mirror system that was developed to evaluate the potential areal density, figure accuracy and stability of a lightweight electrostatically figured mirror manufactured from precision cast optical quality membrane material.

Xinetics has been investigating ferroelectric actuator materials to meet the greater amplitude and higher bandwidth operation for the large mirror actuators of the 21^st Century. This class of actuators features precision displacement control in terms of set-point accuracy and resolution, exhibits excellent dynamic response in terms of bandwidth and temporal response and feature thermal stability in terms of low power dissipation and low thermal expansion. High strain single crystal Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) actuators exhibit strains 3 times greater than the current ferroelectric PMN-based ceramic formulation. In addition, the lower dielectric constant of the single crystal material enables increased bandwidth operation. The major limitation to bringing single crystal multilayer devices to production levels is assembly cost and high operating voltages. A new technology in which the grains in the ceramic material are oriented - Nanotextured Ceramics - offers a technology to achieve near single crystal performance in a low cost, low voltage cofired multilayer actuator device. In this paper, we will discuss Xinetics’ solid state actuator development from randomly oriented ceramic to single crystal oriented materials.

In this work we present an introduction to photonic crystals by discussing the basic concepts and principles behind these artificial materials, as well as their abilities to control light and enable unusual optical phenomena. We will focus on specific examples including (1) negative refraction of light, (2) the superprism effect (anomalous electromagnetic dispersion), and (3) the possibility of superlensing (subwavelength focusing). These are very general results based on direct solutions of Maxwell’s equations, and can consequently be of relevance to many areas of science and technology.

Concepts are presented for using negative refractive index (NRI) materials to design parabolic reflector telescopes and antennas with resolutions significantly better than the diffractions limit. The main question we are attempting to answer is can negative refractive material be used to improve performance of parabolic systems even when the signal or light source is far away and no evanescent fields are present when they arrive at the parabolic reflector. The main approach is to take advantage of any knowledge that we have to recreate the evanescent fields. Fields are then adapted to improve a performance measure such a sharper focus or antenna rejection of interference. A negative refraction index lens is placed between the conventional reflector and focal plane to shape the point spread function. To produce telescope resolutions that are better than the diffraction limit, evanescent fields created by the reflection off of the parabolic surface are amplified and modified to generate fields that sharpen the focus. A second approach use available knowledge of an emitting aperture to synthesize a field at a distance that matches as closely as possible the field of the emitting aperture. The yet unproven conclusion is that techniques can be developed that will improve antenna and telescopes resolution that is better than the diffraction limit.

The mass-strength ratio is of exceptional importance for space application. The critical parts of both shuttle vehicles and satellites depends on strength and toughness of the materials they are made of, while strict limitations on the weight of the different components are placed by the launch technology. Single wall carbon nanotubes (SWNT) present significant potential as the basic material for the space applications. Exceptional mechanical properties of single wall carbon nanotubes (SWNT) have prompted intensive studies of SWNT composites. These qualities can also be used in a variety of other technologies from automotive to military and medical. However, the present composites have shown only a moderate strength enhancement when compared to other hybrid materials. Although substantial advances have been made, mechanical characteristics of SWNT-doped polymers are noticeably below their highly anticipated potential. Pristine SWNTs are well known for poor solubilization, which leads to phase segregation of composites. Severe structural inhomogeneities result in the premature failure of the hybrid SWNT/polymer materials. The connectivity with and uniform distribution within the matrix are essential structural requirements for the strong SWNT composites. Here we show that a new processing approach based on sequential layering of chemically-modified nanotubes and polyelectrolytes can greatly diminish the phase segregation and render SWNT composite highly homogeneous. Combined with chemical cross-linking, this processing leads to drastically improved mechanical properties. Tensile strength of the composites is several times higher than that of SWNT composites made via mixing; it approaches values seen for hard ceramics. The universality of the layering approach applicable to a wide range of functional materials makes possible successful incorporation of SWNT into a variety of composites imparting them required mechanical properties. The thin film membranes that are obtained in the result of the layer-by-layer process can be used as an intermediate or as a component of ultrastrong laminates. At the same time, the prepared membranes can also be utilized in the as-prepared form for the large area space telescopes (both radio and optical) because the combine the strength and multiple functionality of the SWNT membranes with the ease of deployment.

Research and development in multi-component composites demonstrated new material and fabrication concepts for mirrors for space-based optics. Cornerstone Research Group, Inc., effort, conducted under contract to the Air Force Research Laboratory, developed new organic and inorganic composite materials and investigated their potential for application as light-weight, low-cost alternatives mitigating the drawbacks of conventional materials (glass and metals) and fabrication processes for space-based mirrors. This development demonstrated the feasibility of multi-component organic composites integrating cyanate ester resin with several reinforcements, especially carbon fabric and nanofibers. It demonstrated feasibility of high-quality cyanate ester-based syntactic composite (structural foam composed of microspheres embedded in resin). The development also demonstrated initial feasibility of multi-component inorganic composites integrating a proprietary inorganic resin with particulate and nanofiber reinforcements. These new materials (both organic and inorganic composites) show strong potential for achieving major reduction in mirror areal density (compared with current operational mirrors) while achieving strength, stiffness, and thermal properties required for space applications. Finally, this project demonstrated feasibility of a replication approach to mirror fabrication. With this fabrication technology, a composite mirror is cast directly to net figure and finish. This dramatically simplifies the mirror fabrication process, thereby enabling less expensive tooling than conventional practice for glass or metal mirrors. In production lots of identical mirrors (e.g., spacecraft constellations), the replication approach will provide radical reduction in mirror costs by eliminating the lengthy, expensive grinding and polishing processes for individual units.

An analytical description of the scattered light from a 10 meter diameter Diffractive Optical Element lens-based telescope operating at 1 micron wavelength has been formulated. The specifics of the grating and blaze as well as physical manufacturing constraints were made a part of the problem to be solved. A major simplifying approximation made is that a 1 dimensional lens was assumed for the calculations. This simplified model still serves to illustrate the important effects and limitations of a high performance lens used as a telescope. Focal plane light scattering has been rigorously determined for simplified cases.

We present a new instrument for wide-field, narrow-band imaging of the O VI doublet at 1032, 1038 Å. This doublet constitutes the brightest astrophysical line emission from diffuse gas at 300,000 degrees K. Gases at this temperature are primarily formed by supernova blast waves, and are key in understanding the energy budget of the galaxy. We use a conventional Gregorian telescope design to provide excellent zero-order imaging, in conjunction with aberration-corrected holography to yield high-resolution images of O VI in first order. This instrument design uses only two reflective elements and no transmissions, minimizing the light lost due to the poor reflectivity and transmissivity of materials in the far ultraviolet. The holographic recording solution provides 4-9 arcsecond imaging over a 0.5 degree field of view. This instrument demonstrates the versatility of the holographic telescope concept by expanding is applicability to larger fields of view. We are developing a sounding rocket payload to demonstrate the power of this wide field holographic telescope design, particularly as a means of mapping shocked gas in the interstellar medium, at temperatures intermediate to those sampled in optical and X-ray emission. We present the optical design, instrument performance, image reconstruction techniques, and relevant scientific simulations.

The present topic discusses the shape control of gossamer apertures. Once the aperture is deployed on orbit, final shape refinement has to be done to achieve the desired surface. This shape refinement could be achieved through active seams incorporating active elements like shape memory alloys and piezoelectric polymers like PVDF. Numerical simulation of the shape refinement of the gores of the aperture through active seam is reported. Experimental investigation of extensional PVDF actuators is presented. The theoretical extension of PVDF actuators is compared with the experimental values and the effect of seam adhesive is discussed. A simple prototype of an active seam is also presented.

The AstroMesh antenna is an example of a mesh reflector with perimeter truss for use as a large aperture space antenna. A quarter model of such an antenna, with the original mesh supplemented with a continuous membrane, was analyzed in nonlinear finite element code ABAQUS. In particular, we investigated requirements for maintaining the initial parabolic shape under thermal perturbation. An RMS error was calculated for different thermal loadings as a measurement of deviation of the perturbed surface from a reference parabolic shape. Thermal contraction or expansion of the membrane boundary springs was found to offer reduced RMS error, but at the cost of higher spring reaction force. Electrostatic pressure was also applied to different membrane regions to acheive better RMS error with minimized spring reactions.

Nickel Titanium (NiTi) film shape memory alloy (SMA) is integrated with space-qualified polymer and mesh materials for potential use as deployment mechanisms and actuation of flexible space apertures. SMA thin film is successfully applied to Astromesh metal mesh, Kapton, Upilex, and CP-1 polymer films. Sputter deposition of NiTi onto the substrate is used to validate the material system process and demonstrate the NiTi deployment capability. Although successful, the relatively high processing temperatures required to crystallize NiTi onto the substrates requires care. A second approach is demonstrated that deposits NiTi onto a silicon substrate, followed by coating the NiTi with the desired polymer, e.g. CP-1. Micro-electro-mechanical (MEMS) processing steps are then used to remove the silicon substrate beneath the NiTi, thus freeing up the composite membrane (i.e. NiTi + CP-1). Using MEMS fabrication techniques, a hot-shaped small dome shape structure is shaped into the NiTi before deposition of the CP-1 polymer. Activation of the integrated SMA/CP-1 produces deformation of this composite structure without damage. The test articles demonstrate the feasibility to both grossly deploy and locally actuate space-qualified polymer materials.

We will present a new approach to enable very large aperture telescopes in space. The approach is to autonomously assemble a segmented filled aperture telescope in space using components which may be launched into orbit using multiple launches. Autonomous assembly is a technology that can break the 10 m barrier in space optics imposed by launch vehicle limitations. The autonomously assembled space telescope (AAST) will follow the lead of Hubble telescope which uses monolithic optics, and JWST, which will implement deployable optics. An autonomously assembled space telescope of greater than 10 m diameter can significantly enhance the resolution and detection limit for imaging and space science, as well as enable formation of cost effective telescope constellations in space.