Modeling technique for the Hubble Space Telescope wave-front deformation

Images from the Hubble Space Telescope suffer from an overcorrected spherical aberration that is due to a conic-constant error in the primary mirror. Within the program known as the corrective optics space telescope axial replacement (COSTAR) simulators have been built to provide the point-spread function (PSF) of the telescope alone and of the telescope with the faint-object camera F/96. It was found that the experimental PSF's were identical to those in orbit, which was not the case when the PSF's were calculated with commonly used optical software. We explain this discrepancy and propose a modeling method that is based on the determination of the wave-front error at the exit-pupil level that gives results that are consistent with observations.     

Hubble Space Telescope Faint Object Camera calculated point-spread functions

A set of observed noisy Hubble Space Telescope Faint Object Camera point-spread functions is used to recover the combined Hubble and Faint Object Camera wave-front error. The low-spatial-frequency wave-front error is parameterized in terms of a set of 32 annular Zernike polynomials. The midlevel and higher spatial frequencies are parameterized in terms of set of 891 polar-Fourier polynomials. The parameterized wave-front error is used to generate accurate calculated point-spread functions, both pre- and post-COSTAR (corrective optics space telescope axial replacement), suitable for image restoration at arbitrary wavelengths. We describe the phase-retrieval-based recovery process and the phase parameterization. Resultant calculated precorrection and postcorrection point-spread functions are shown along with an estimate of both pre- and post-COSTAR spherical aberration.     

HST image restoration developments at the ST-ECF

When spherical aberration was found to be degrading the performance of the Hubble Space Telescope (HST), great interest in image restoration methods arose in the astronomical community. The Richardson-Lucy (RL) method became the preferred tool for restoring such data which typically has Poisson noise characteristics and a low signal-to-noise ratio. Subsequently, corrective optics were inserted into the telescope which is now operating close to the original specifications. However, generalized RL methods and some new techniques based on projections onto convex sets have proved useful both for the present HST data, which are often insufficiently sampled, and also for many other classes of astronomical images. The ST-ECF staff have worked extensively in this and related areas, and some of these developments and their application to real data are described.     

Astrometry with reconstructed hubble space telescope planetary camera (WF/PC 1) images

The effect of image reconstruction on the astrometric precision of the Hubble Space Telescope Planetary Camera (WF/PC 1) has been investigated. Depending on the crowded nature and exposure of the stellar images, the reconstruction process may provide benefits for the image centering, especially in terms of the number of stars which can be detected. Unfortunately, there is also evidence that the positions derived from reconstructed images are biased toward the center of individual pixels, an astrometrically unacceptable condition.     

Illustration of the use of multimode deformable plane mirrors to record high-resolution concave gratings: results for the Cosmic Origins Spectrograph gratings of the Hubble Space Telescope

To illustrate the efficiency of using a deformable plane mirror to record holographic gratings, we have computed the three gratings for the Cosmic Origins Spectrograph. Their working conditions are severe, since they have to correct the residual spherical aberration of the Hubble Space Telescope. Nevertheless, all images obtained are largely diffraction limited with regard to the resolution.     

Universal method for holographic grating recording: multimode deformable mirrors generating Clebsch-Zernike polynomials

Recording methods for making aberration-corrected holographic gratings are greatly simplified by use of a plane multimode deformable mirror (MDM) upon one of the two recording beams. It is shown that MDM compensators easily provide the superposition of many interesting active optics modes, which we have named Clebsch-Zernike modes. When we apply only a uniform loading or no loading at all onto the rear side of the MDM clear aperture, the available Clebsch-Zernike modes are made to belong to a subclass of the Zernike modes that includes the three modes of the third-order aberration theory as well as a well-defined part of the Zernike higher-order modes. Such a recording method is considered to be universal, since it does not require the use of a sophisticated optical system such as a compensator. Active optics 12-arm MDM's in the vase form have been designed from the elasticity theory. The design of six-arm MDM's is currently carried out with theoretical results. As an example of the method, the recording of three holographic gratings of the Hubble Space Telescope Cosmic Origins Spectrograph has been investigated. Substantial improvements in image quality have been found by use of a six-arm MDM as recording compensator. The result is that aberrations of much higher order can simultaneously be corrected so that the residual blur images of the spectra occupy areas approximately 10 (direction of dispersion) x 3 (cross dispersion) = 30 times smaller-also in terms of pixel number-than those obtained by our American colleagues. Therefore the active optics recording method appears to provide substantial gains in resolving power and in sensitivity: (i) For all three gratings the spectral resolution would be increased by a factor of 10, and (ii), in addition, for the two higher dispersion gratings, the limiting magnitude on the sky appears to be increased by a magnitude of approximately 1-1.2.     

自适应光学在空间光学遥感器上的应用

阐述了在空间光学遥感器上应用自适应光学技术的必要性,介绍了国外的ＳＴ－ＭＴ,ＬＤＲ和Ｈｕｂｂｌｅ等几种空间光学遥感器应用自适应光学技术的情况,论述了轻小型和集成化的星载自适应光学系统的技术现状和发展趋势。进行了星载相机主镜温度变形的自适应光学校正实验,改善系数大于１０。这说明,对大口径、高分辨率空间相机采用自适应光学技术校正主镜由于温度场变化而产生的变莆,可以有效地改善波前质量。     

High-precision measurement of pixel positions in a charge-coupled device

The high level of spatial uniformity in modern CCD's makes them excellent devices for astrometric instruments. However, at the level of accuracy envisioned by the more ambitious projects such as the Astrometric Imaging Telescope, current technology produces CCD's with significant pixel registration errors. We describe a technique for making high-precision measurements of relative pixel positions. We measured CCD's manufactured for the Wide Field Planetary Camera II installed in the Hubble Space Telescope. These CCD's are shown to have significant step-and-repeat errors of 0.033 pixel along every 34th row, as well as a 0.003-pixel curvature along 34-pixel stripes. The source of these errors is described. Our experiments achieved a per-pixel accuracy of 0.011 pixel. The ultimate shot-noise limited precision of the method is less than 0.001 pixel.     

Hypervelocity impacts on solar cells — observations, experiments, and empirical scaling laws

The recent retrieval of the EURECA satellite and one solar array from the Hubble Space Telescope initiated meteoroid and debris impact investigations on these surfaces. This paper gives an overview of observations of impact sites found on retrieved spacecraft surfaces, hypervelocity test programs performed as part of the European Space Agency (ESA) post-flight investigation programs (PFIP), and develops empirical scaling laws for various geometric parameters. These empirical scaling laws are intended to relate particle parameters to crater dimensions to support the modeling of the microparticle environment in near-Earth space.     

Theory and computation of three cosmic origin spectrograph aspheric gratings recorded with a multimode deformable mirror

The theory of three Cosmic Origin Spectrograph holographic gratings recorded with a deformable plane mirror is presented. Their working conditions are severe, since they have to correct the strong spherical aberration and the field astigmatism of the Hubble Space Telescope. Recorded on aspherized substrates, the gratings produce images that are diffraction limited with regard to spectral resolution.     

Analogies and differences between quasi-static indentation and hypervelocity impact morphologies on thin solar cells

Morphologies produced by quasi-static indentation on thin Hubble Space Telescope (HST) solar cells show remarkable similarities to much of the hypervelocity damage sustained by the HST solar array whilst in orbit. Quasi-static indentation tests carried out with blunt and sharp indentors reveal analogies between static and dynamic (hypervelocity) indentation indicating similar fracture mechanics processes over the energy range evaluated. Understanding the static case assists to characterise better the dynamic process and bridge the intervening gap.     

Laboratory studies of alkali metal filter deposition, ultraviolet transmission, and visible blocking

Far-ultraviolet alkali metal or Wood's filters have been produced and tested supporting the production of a flight filter for the Wide Field Planetary Camera 2 on the Hubble Space Telescope. Sodium layers 0.5-1-mum thick transmit up to 40% in the ultraviolet while efficiently blocking visible wavelengths. The prevention of visible pinholes is assisted by a clean, sleek-free surface and a cooled substrate during deposition. The coatings are stabilized efficiently by a bismuth overcoating whose transmission spectrum is presented. We also report for the first time, to our knowledge, the first demonstrated long-wavelength cutoff from a lithium filter, with a shorter cutoff wavelength than sodium and potentially higher stability for astronomical imaging.     

Developments in Turbo Brayton technology for low temperature applications

A single stage reverse Brayton cryocooler using miniature high-speed turbomachines recently completed a successful space shuttle test flight demonstrating its capabilities for use in cooling the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope (HST). The NICMOS CryoCooler (NCC) is designed for a cooling load of about 8 W at 65 K, and comprises a closed loop cryocooler coupled to an independent cryogenic circulating loop. Future space applications involve instruments that will require 5–200 mW of cooling at temperatures between 4 and 10 K. This paper discusses the extension of Turbo Brayton technology to meet these requirements.     

Multilayer resonant subwavelength gratings: effects of waveguide modes and real groove profiles

The boundary integral equation code PCGrate-S(X) is used to analyze diffraction on Hubble Space Telescope Cosmic Origins Spectrograph gratings at different boundary shapes and layer thicknesses. An effect of resonance anomalies excited in nonconformal dielectric layers overcoated on the surface of metallic grating on the efficiency is studied for the first time to our knowledge. Refractive indices (RIs) for bulk MgF2 taken from well-known references are found to be not suitable for thin optical layers at wavelengths between 115 and 170 nm. A method based on scale fitting of calculated and measured grating efficiencies is outlined for derivation of thin-film optical constants at hard to measure wavelengths. The calculated efficiency based on real boundary profiles and derived RIs of the G185M subwavelength grating is shown to fit within 9.6% or better to the measured data.     

The resolved history of galaxy evolution

We briefly review the study of the evolution of galaxies from an observational point of view, with particular emphasis on the role of the Hubble Space Telescope in probing the evolution of the different morphological types of galaxy. We show how using the stellar mass of galaxies as a tracer of evolution can improve our understanding of the physical process taking place before turning our eyes towards the future and giving an overview of what we can expect from future advances in technology.     

Material damage in space from microparticle impact

A large variety of materials have now been recovered from long term exposure to the space environment. The authors have investigated samples which have spent several years in space on various satellites, including: the NASA satellite ‘Long Duration Exposure Facility’, the Franco–Russian ‘Aragatz’ mision experiment on MIR and the Hubble Space Telescope. The samples come mainly from experiments devoted to the study of meteoroids and orbital debris and the damage that these can cause to spacecraft materials. In this paper some interesting impact features have been selected to demonstrate the different types of damage sustained on different materials. This revised version was published online in November 2006 with corrections to the Cover Date.     

静止轨道高分辨率光学遥感探索

为了实现地球静止轨道高分辨率光学遥感,研究了在运载的动力学环境上与低轨的差异。分析了主动飞行段时间长、力学环境差、在成像方法上采用面阵成像、轨道高等原因使相机体积增大的问题。对静止轨道21.5m分辨率模拟相机进行了研究,开展了动力学模拟试验,得到了相机关键部位的测试参数,证明了地球静止轨道高分辨率光学遥感的核心环节即有效载荷研制的可行性。     

The terrestrial particulate environment and its future evolution

In this paper an overview over the current space debris situation is given. With the help of ESA's new Meteoroid And Space Debris Terrestrial Environment Reference (MASTER) model, the spatial density of space debris is calculated as function of altitude and latitude. Statistical information about collision risk and collision velocities is presented. In order to estimate the ratio of debris to meteoroid impacts on the surfaces of returned hardware from space (LDEF, Hubble Space Telescope solar array and EuReCa) a state-of-the-art meteoroid model is required. At the Max-Planck-Institute in Heidelberg the meteoroid model of Neil Divine was enhanced and implemented in a software programme used at ESOC for meteoroid flux predictions on satellite surfaces. Finally, using the models of the current environment as initial conditions an attempt is made to predict the future evolution of the space debris environment. Two models using different approaches are considered: CHAINEE, a particle-in-the-box model and SDM, a semi-deterministic model. Both models are used to study the effectiveness of debris mitigation measures.     

Measurement of large cryogenic structures using a spatially phase-shifted digital speckle pattern interferometer

The James Webb Space Telescope (JWST) Backplane Stability Test Article (BSTA) was developed to demonstrate large precision cryogenic structures' technology readiness for use in the JWST. The thermal stability of the BSTA was measured at cryogenic temperatures at the Marshall Space Flight Center (MSFC) X-Ray Calibration Facility (XRCF) and included nearly continuous measurements over a six-week period in the summer of 2006 covering the temperature range from ambient down to 30 Kusing a spatially phase-shifted digital speckle pattern interferometer (SPS-DSPI). The BSTA is a full size, one-sixth section of the JWST primary mirror backplane assembly (PMBA). The BSTA, measuring almost 3 m across, contains most of the prominent structural elements of the backplane and is to our knowledge the largest structure ever measured with SPS-DSPI at cryogenic conditions. The SPS-DSPI measured rigid body motion and deformations of BSTA to nanometer-level accuracy. The SPS-DSPI was developed specifically for the purposes of this test and other tests of large cryogenic structures for JWST.     

Wide-field-of-view polarization interference imaging spectrometer

A wide-field-of-view polarization interference imaging spectrometer (WPIIS) based on a modified Savart polariscope, without moving parts, and with a narrow slit has been designed. The primary feature of this device is for use with a large angle of incidence, and the target image as well as the interferogram can be obtained at the same time in the spatial domain and are recorded by a two-dimensional CCD camera. Under compensation, the field of view of the WPIIS will extend 3-5 times as large as a common interference imaging spectrometer, and throughput will raise 1-2 orders of magnitude. The developed optics is 20 x 8 cm ? in size. The spectral resolution of the prototype system is 86.8 cm(-1) between 22222.2 and 11111.1 cm(-1). This system has the advantages of being static and ultracompact with wide field of view and a very high throughput. The optics system and especially the wide-field-of-view compensation principle are described, and the experimental result of the interference imaging spectrum is shown.