地基大口径望远镜系统结构技术综述

This paper describes two space science missions tha t could take advantage of the proposed Ares-V heavy lift launch vehicle; the first, a Titan sample return mi ssion, would leverage the Ares-V’s injected mass ca pability and the second, a new large space telescope mission , would leverage its 8-10 meter shroud diameter. A direct trajectory sample return mission is described that features aerocapture at Titan, which is considered a relatively easy destination for aerocapture because of its dense nitrogen atmosphere and its low gravi ty. The Ares-V’s ability to boost 12 mt on a 6 year Titan t rajectory enables this exciting mission. The Advanc ed Technology Large Aperture Space Telescope (ATLAST), placed into Sun-Earth Lagrange Point 2 (SEL2), would take advantage of the Ares-V’s useable payload volume of 860 m, a space big enough to hold 8 school buses, offering significantly greater optical capab ility than the Humble Telescope. The Ares-V could prove to be a national asset, opening the door to many new, flagship high science value exploration missions. I. Introduction A variety of Heavy Lift Launch Vehicle (HLLV) concepts have been proposed over the past 50 years, ofte n, though not exclusively, with an emphasis on the boo st of the elements required for a Lunar or Mars lan ding. Recent analysis of the Ares V and other HLLV concepts (Ares-III, Direct, Sidemount, Shuttle-C, Magnum and Superheavy multi-core EELV’s) are now widely publicized and compared in their ability for Lunar missions. It is t he objective of this paper, however, to show the benefits of an HLLV’s capability to enable science and exploration missions that are otherwise impossible or impractical with the cu rrent fleet of launch vehicles. At its inception, t he Ares-V was conceived to boost 65 mt of payload to Trans-Lunar injection as part of the Constellation Lunar program. New ambitious exploration missions to distant destinati ons are more feasible with vehicles of this class. Another benefit an HLLV would bring would be very large payload volumes; allowing groups of several large payloads in a single launch, or large aeroshells, large mirrors and othe r deployable structures. At the time of this writin g, the Ares V consists of 2 five-and-one-half segment Solid Rocke t Boosters and a core stage with liquid Oxygen (LO2 )/liquid Hydrogen (LH2) engines positioned underneath a modified Shuttle External Tank. A large diameter Earth Departure Stage (EDS), powered by a J-2X LO2/LH2 engine, is located on top of the Core stage. The Ares-V shroud is 10m in diameter, has a usable internal diameter of 8.8 m, a usable cylindrical height of 9.3 m and a useable frustum (below the nose cap) length of 7.5 m, for a total useable length of 17.2 m and usable payload volume of 860 m, 3 big enough to hold 8 school buses. The potential is there for enabling some important science missions; in this p aper two such missions are described ‐ the Titan Sample Return mi ssion and the New Large Space Telescope mission. These missions bound HHLV capability in two ways; throw weight capability for distant destinations and volum e availability for large optical systems. In the firs t row of Table 1, injection energy (C3 km2/2), payl oad (mt) and outbound trip time (years) are listed for the Ares- V Titan mission. For this mission a Delta-IV upper stage is added to the EDS to boost the Titan orbiter and lander cr aft to their required velocity. In the last row, C3 , payload, and trip time for the Space Telescope mission is given; this large telescope is boosted to the Sun-Earth Lagran ge Point 2 (SEL2); an upper stage is not used for this mission .

<strong>12.1 Introduction</strong> Astronomers require larger and larger radiation-gathering apertures for their telescopes to penetrate farther into the mysteries of the universe. Large telescopes collect more photons and thus see fainter objects. These large apertures also increase the angular resolution across the object, as we saw in Chapter 10. For practical reasons such as telescope mass and thermal inertia, astronomers who build ground-based telescopes now partition primary mirrors greater than about 8 m into smaller segments, with each segment aligned so that its surfaces fall on the desired concave surface of the larger mirror. Large space- and ground-based telescopes are often divided into two stages. Stage 1 is the large collector, which forms an imperfect image in complex amplitude and phase. Before an image is detected, stage 2 of the optical system takes this imperfect image and removes wavefront aberrations using WFSC. This principle was discussed in Chapter 11. In Chapter 5 we learned that the number of reflections in the optical system needs to be small in order to minimize the power that is absorbed by the mirrors and that does not reach the focal plane. Consequently, rather than correcting the wavefront at an image of the telescope pupil, many telescopes correct the wavefront at the secondary mirror of the astronomical telescope before the primary focus. Correcting the wavefront at the secondary limits the FOV of the telescope that can be corrected. However, most astronomical applications today use a narrow FOV (limited by the expensive digital array detector size or by atmospheric turbulence), so wavefront control (WFC) at the secondary is sufficient. Frequently, the optical system for large telescopes is divided into three parts: the large precision telescope radiation collector, a metrology and WFSC system (see Chapter 11), and the instrument that analyzes the radiation. The motivation behind this configuration is to reduce the cost of the telescope system. For ground-based telescopes, the two expensive subsystems are the dome and the very stiff massive mechanical structure required to hold the mirror, the secondary, and its supports.

We report on the performance of FLAMINGOS, the world's first fully cryogenic near-IR multi-object spectrometer. FLAMINGOS has a fast all refractive optical system, which can be used at telescopes slower than f/7.5. This makes FLAMINGOS a very efficient wide-field imager when used on fast small aperture telescopes and a high AW spectrometer using laser machined aperture masks for MOS spectroscopy. FLAMINGOS uses a 2048x2048 HgCdTe HAWAII-2 array by the Rockwell Science Center. The array is readout through 32 amplifiers, which results in low overheads for observations. We describe both the operating characteristics of the HAWAII-2 array and of the array controller and data acquisition system. FLAMINGOS has been in operation for about 1.5 years and is now in routine use on four telescopes: The Kitt Peak 4-m and 2.1-m, The 6.5-m MMT and the 8-m Gemini South Telescope. We will describe the operating characteristics of FLAMINGOS on each of these telescopes that deliver fields-of-view from 21x21 arcminutes to 2.7x2.7 arcminutes and pixels from 0.6 arcseconds to 0.08 arcseconds. While providing a large AW product for fast telescopes (i.e. f/8), FLAMINGOS becomes progressively less efficient on slower telescopes. Since nearly all large telescopes have fairly slow optical systems (f/12 or slower) the combination of large aperture and slow optical systems makes FLAMINGOS ill suited for optimal performance on current large aperture telescopes. Thus, we are beginning construction of FLAMINGOS-2, which will be optimized for performance on the f/16 Gemini South 8-m telescope. Similar to FLAMINGOS, FLAMINGOS-2 will be fully refractive using grisms, laser machined aperture masks and a 2048x2048 HgCdTe HAWAII-2 array. FLAMINGOS-2 will provide a 6.1 arcminute field-of-view with 0.18 arcsecond pixels. FLAMINGOS-2 will also be designed to except an f/32 beam from the Gemini South MCAO system.

This paper developed the internal model PID control for large telescope control system considerations in more parameters adjustment in servo control loop at present. The large electro-optic telescope system belongs to a big inertia system. This simplifies the debug process; the feasibility and robustability are also verified by the analyses and simulation results that satisfy the high precision demand. The practicability of this algorithm is verified in an actual project that only two parameters need adjusted. The application shows that this system runs stably with high accuracy. The technology and methods adopted in the system are practical and worthy of using abroad.

Space telescopes are widely used nowadays with the development of space optics and manufacture technologies. Large aperture of telescope means better resolution and observation. However, due to the carrying capacity and outline dimension of rocket, the aperture of telescope cannot be too large. In order to get the large telescope, more and more scientists and engineers are coming to a new idea that assembling the large space telescope on orbit. First of all, the paper makes an introduction about the concepts and types of on-orbit assembly for telescope. Then paper presents some projects which are being conducted and takes one project as an example to introduce specific implementation methods of on-orbit assembly. What’s more, high precision robots are needed in this process. Therefore, paper also introduces technologies about the robots for space assembly. At last, the paper summarizes the features and technical difficulties in on-orbit assembly of large space telescope. Furthermore, the paper points out the development directions about on-orbit assembly telescope in the future, which can give some help or guidance to engineers.

A fresh look is taken at how light propagates through the atmosphere and how atmospheric turbulence affects images formed by large ground-based telescopes. Telescopes with fixed and adaptive optics are considered. The approach is based on a layered model of the atmosphere. It is shown that the atmosphere can be represented by an equivalent phase screen for the two quantities that determine most of the important image properties—the atmospheric modulation transfer function and the spectral correlation function. Techniques are described for measuring the parameters that define the equivalent phase screen. Expressions are given in terms of screen parameters for a number of image properties. Many of these properties are different from those in the conventional literature. Diffraction-limited cores in star images are discussed. An optimum wavelength at which resolution is maximized is also discussed. Resolution of the order of 0.05 arcsec is possible at this wavelength, but only if the telescope is near diffraction limited. The optimum wavelength can be used to produce maximum energy density at the focus of a ground-based laser beam directed at a target in space.

The CMB Stage 4 (CMB-S4) experiment is a next-generation, ground-based experiment that will measure the cosmic microwave background (CMB) polarization to unprecedented accuracy, probing the signature of inflation, the nature of cosmic neutrinos, relativistic thermal relics in the early universe, and the evolution of the universe. CMB-S4 will consist of O(500,000) photon-noise-limited detectors that cover a wide range of angular scales in order to probe the cosmological signatures from both the early and late universe. It will measure a wide range of microwave frequencies to cleanly separate the CMB signals from galactic and extra-galactic foregrounds. To advance the progress towards designing the instrument for CMB-S4, we have established a framework to optimize the instrumental configuration to maximize its scientific output. The framework combines cost and instrumental models with a cosmology forecasting tool, and evaluates the scientific sensitivity as a function of various instrumental parameters. The cost model also allows us to perform the analysis under a fixed-cost constraint, optimizing for the scientific output of the experiment given finite resources. In this paper, we report our first results from this framework, using simplified instrumental and cost models. We have primarily studied two classes of instrumental configurations: arrays of large-aperture telescopes with diameters ranging from 2–10 m, and hybrid arrays that combine small-aperture telescopes (0.5-m diameter) with large-aperture telescopes. We explore performance as a function of telescope aperture size, distribution of the detectors into different microwave frequencies, survey strategy and survey area, low-frequency noise performance, and balance between small and large aperture telescopes for hybrid configurations. Both types of configurations must cover both large (∼ degree) and small (∼ arcmin) angular scales, and the performance depends on assumptions for performance vs. angular scale. The configurations with large-aperture telescopes have a shallow optimum around 4–6 m in aperture diameter, assuming that large telescopes can achieve good performance for low-frequency noise. We explore some of the uncertainties of the instrumental model and cost parameters, and we find that the optimum has a weak dependence on these parameters. The hybrid configuration shows an even broader optimum, spanning a range of 4–10 m in aperture for the large telescopes. We also present two strawperson configurations as an outcome of this optimization study, and we discuss some ideas for improving our simple cost and instrumental models used here. There are several areas of this analysis that deserve further improvement. In our forecasting framework, we adopt a simple two-component foreground model with spatially varying power-law spectral indices. We estimate de-lensing performance statistically and ignore non-idealities such as anisotropic mode coverage, boundary effect, and possible foreground residual. Instrumental systematics, which is not accounted for in our analyses, may also influence the conceptual design. Further study of the instrumental and cost models will be one of the main areas of study by the entire CMB-S4 community. We hope that our framework will be useful for estimating the influence of these improvements in the future, and we will incorporate them in order to further improve the optimization.

This report is a general introduction on Chinese large telescope projects. It includes the ongoing project Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST),and three projects which have reviewed by Chinese government recently: Five-hundred-meter Aperture Spherical (radio) Telescope (FAST); Space Solar Telescope (SST); Hard X-ray Modulation Telescope (HXMT). These three projects have finished their feasibility studies and development of key technologies. They are very likely to be approved by the Chinese government in 2006. Besides these large telescope projects, the site survey in Western China for large telescopes in optical, infrared, sub-millimeter and millimeter astronomy, the preliminary study on Chinese future giant optical/infrared telescopes, and a future extremely large wide field telescope are also briefly introduced.

Firstly,Power Spectral Density( PSD) is proposed for mirror surface figure evaluation in the large aperture telescope system as for some difficulties for Root Mean Square( RMS) in the evaluation of large scale variety and disadvantage of robust for rigid body displacement. Then,the decomposition arithmetic of PSD is analyzed with Zernike polynomial,and Zernike polynomial spectrum energy distribution is analyzed in some order. The algorithm has been used in the surface figure evaluation of a Φ 500 mm mirror,and energy distribution in the frequency domain of the actual mirror surface has been obtained. The experimental results indicate that the evaluation of PSD is more practical when used in large aperture mirror for their manufacture and testing and for the error budget allocation in telescope system. Finally,a kind of noncorrelative sub-aperture stitching method for evaluation of reflective mirror shape based on PSD is proposed which can be used in the large aperture telescope.

We report on the collaborative effort of the European Southern Observatory (ESO) and the National Institute of Standards and Technology (NIST) to establish—through laboratory measurements—wavelength standards in the near-infrared (IR) emission line spectrum of a low current Th–Ar hollow cathode lamp. These standards are now routinely used for the wavelength calibration of the cryogenic infrared echelle spectrograph (CRIRES) operated at one of the unit telescopes of the very large telescope (VLT) at ESO's La Silla Paranal Observatory in Chile. The availability of highly accurate wavelength standards from a commercially available calibration source permits a shift to a new operational paradigm for high-resolution IR spectroscopy. Wavelength calibration no longer has to rely on atmospheric features but can make use of laboratory traceable reference data as is normally done in the ultraviolet and visible regions. This opens the door for more quantitative spectroscopic work in the near-IR. To illustrate the potential impact of this development, we briefly review the current state of affairs in IR astronomy and its projected future. With the advent of the next generation of extremely large ground-based telescopes the IR region will become the most powerful window on the universe within the next 10–15 years. We conclude with a short outlook on the contribution atomic physics can make to this evolution.

The utilization of a telescope with a large single aperture is limited by the manufacturing technique, cost, volume and weight of a monolithic mirror. In order to solve these problems, the technology of the segmented synthetic aperture was introduced. The primary mirror of a large segmented synthetic aperture telescope consists of several segmented mirrors, whose misalignment errors make the wavefront change drastically and influence the MTF of the optical system badly. The wavefront coding technology (WFC) is an innovative technology that joints the optical design and digital image processing together. By adding a phase mask close to the pupil of an optical system and modulating the wavefront, the WFC system becomes very insensitive to defocus and other aberrations based on defocus. The theoretical analysis of characteristics of the WFC system was done in the form of PSF. The application of WFC to a segmented three mirror anastigmat (TMA) was presented. A space telescope with an effective focal length as 40m, a F number as 10, a field of view as 0.5°x0.05° was designed, whose primary mirror consisted of seven segmented mirrors. The influence of defocus and misalignment errors on the telescope was discussed. The imaging process of the WFC system and following image restoration were simulated. As a result, sharp images were obtained and the large segmented synthetic aperture telescope had looser misalignment tolerance and extended depth of focus.

As a non-expert in computers and their uses, my aims in this paper are not to explore any subject in detail, but rather to survey the subject of large ground-based telescopes along with some of their present and future demands on computing and data-analysis facilities, and to try to stimulate discussion from experts as to how these needs can be met.

Cost data for ground-based telescopes of the last century are analyzed for trends in the relationship between aperture size and cost. We find that for apertures built prior to 1980, costs scaled as aperture size to the 2.8 power, which is consistent with the previous finding of Meinel (1978). After 1980, 'traditional' monolithic mirror telescope costs have scaled as aperture to the 2.5 power. The large multiple mirror telescopes built or in construction during this time period (Keck, LBT, GTC) appear to deviate from this relationship with significant cost savings as a result, although it is unclear what power law such structures follow. We discuss the implications of the current cost-aperture size data on the proposed large telescope projects of the next ten to twenty years. Structures that naturally tend towards the 2.0 power in the cost-aperture relationship will be the favorable choice for future extremely large apertures; our expectation is that space-based structures will ultimately gain economic advantage over ground-based ones.

The disks of disk galaxies contain a substantial fraction of their baryonic matter and angular momentum, and much of the evolutionary activity in these galaxies, such as the formation of stars, spiral arms, bars and rings, and the various forms of secular evolution, takes place in their disks. The formation and evolution of galactic disks are therefore particularly important for understanding how galaxies form and evolve and the cause of the variety in which they appear to us. Ongoing large surveys, made possible by new instrumentation at wavelengths from the UV (Galaxy Evolution Explorer), via optical (Hubble Space Telescope and large groundbased telescopes) and IR (Spitzer Space Telescope), to the radio are providing much new information about disk galaxies over a wide range of redshift. Although progress has been made, the dynamics and structure of stellar disks, including their truncations, are still not well understood. We do now have plausible estimates of disk mass-to-light ratios, and estimates of Toomre's Q parameter show that they are just locally stable. Disks are mostly very flat and sometimes very thin, and they have a range in surface brightness from canonical disks with a central surface brightness of about 21.5 B-mag arcsec−2down to very low surface brightnesses. It appears that galaxy disks are not maximal, except possibly in the largest systems. Their Hi layers display warps whenever Hi can be detected beyond the stellar disk, with low-level star formation going on out to large radii. Stellar disks display abundance gradients that flatten at larger radii and sometimes even reverse. The existence of a well-defined baryonic (stellar + Hi) Tully-Fisher relation hints at an approximately uniform baryonic to dark matter ratio. Thick disks are common in disk galaxies, and their existence appears unrelated to the presence of a bulge component; they are old, but their formation is not yet understood. Disk formation was already advanced at redshifts of ∼2, but at that epoch disks were not yet quiescent and in full rotational equilibrium. Downsizing (the gradual reduction with time in the mass of the most actively star-forming galaxies) is now well-established. The formation and history of star formation in S0s are still not fully understood.

Ly{alpha} photons that escape the interstellar medium of star-forming galaxies may be resonantly scattered by neutral hydrogen atoms in the circumgalactic and intergalactic media, thereby increasing the angular extent of the galaxy's Ly{alpha} emission. We present predictions of this extended, low surface brightness Ly{alpha} emission based on radiative transfer modeling in a cosmological reionization simulation. The extended emission can be detected from stacked narrowband images of Ly{alpha} emitters (LAEs) or of Lyman break galaxies (LBGs). Its average surface brightness profile has a central cusp, then flattens to an approximate plateau beginning at an inner characteristic scale below {approx}0.2 Mpc (comoving), then steepens again beyond an outer characteristic scale of {approx}1 Mpc. The inner scale marks the transition from scattered light of the central source to emission from clustered sources, while the outer scale marks the spatial extent of scattered emission from these clustered sources. Both scales tend to increase with halo mass, UV luminosity, and observed Ly{alpha} luminosity. The extended emission predicted by our simulation is already within reach of deep narrowband photometry using large ground-based telescopes. Such observations would test radiative transfer models of emission from LAEs and LBGs, and they would open a new window on the circumgalacticmore » environment of high-redshift star-forming galaxies.« less