The GRASP telescope

The GRASP mission Gamma-Ray Astronomy with Spectroscopy and Positioning addresses the scientific goals of fine spectroscopy with imaging and accurate positioning of gamma-ray sources, an unexplored area within gamma-ray astronomy. The assessment of GRASP as a future space astronomy mission in the mid-1990s has led to the design of the instrument outlined in this article. Thus GRASP is a third generation gamma-ray telescope and is designed to operate as a high quality spectral imager in the mid-1990s, when, following the GRO, SIGMA, and GAMMA-1 missions, there will be requirement for a more sophisticated instrument to maintain the momentum of advance in gamma-ray astronomy. The telescope will be capable of locating point sources with a precision of typically 1 arc min, whilst making a fine spectral analysis (E/E 1000) of any gamma-ray line features. The high sensitivity of this instrument and the long (> 2 year) lifetime of the mission will enable a large number ( 1000) of astronomical objects to be studied. The GRASP mission has the potential to move gamma-ray astronomy from an era of basic exploration to one in which detailed and novel measurements can be used to gain a better understanding of many astrophysical problems.     

The gamma-ray telescope Gamma-1

The telescope Gamma-1 is designed to investigate cosmic gamma rays in the energy range from 50 MeV to 5000 MeV. The geometrical sensitive area of the telescope amounts to 1500 cm², the angular resolution in each direction is equal to 1.2° at the energy 300 MeV and is about 20 when including a coded mask in the telescope, the energy resolution changes from 70% at 100 MeV to 35% at 550 MeV. The characteristics of the telescope and its systems have been determined by the Monte-Carlo method as well as by accelerator calibrations. Discrete sources at the intensity level of 10^–7 quanta cm^–2 s^–1 may be recorded in a year of observations with the gamma-ray telescope Gamma-1 with a source location accuracy of 10 arc min.     

Post: Polar stratospheric telescope

The tropopause, typically at 16 to 18 km altitude at the lower latitudes, dips to 8 km in the polar regions. This makes the cold, dry and nonturbulent lower stratosphere accessible to tethered aerostats. Tethered aerostats can fly as high as 12 km and are extremely reliable, lasting for many years. In contrast to free-flying balloons, they can stay on station for weeks at a time, and payloads can be safely recovered for maintenance and adjustment and relaunched in a matter of hours. We propose to use such a platform, located first in the Arctic (near Fairbanks, Alaska) and, potentially, later in the Antarctic, to operate a new technology 6-meter, diluted aperture telescope with diffraction-limited performance in the near infrared. Thanks to the low ambient temperature (220 K), thermal emission from the optics is of the same order as that of the zodiacal light in the 2 to 3 micron band. Since this wavelength interval is the darkest part of the zodiacal light spectrum from optical wavelengths to 100 microns, the combination of high resolution images and a very dark sky make it the spectral region of choice for observing the redshifted light from galaxies and clusters of galaxies at moderate to high redshifts.Affiliated to the Astrophysics Division, Space Science Department, European Space Agency     

Infrared telescope in space: IRTS

The IRTS is a first Japanese infrared satellite mission which will be launched on February of 1995 by HII rocket. The IRTS is one of the mission experiments aboard the small space platform, SFU. The telescope aperture of the IRTS is 15cm, but is cooled by liquid Helium to realize very low background condition. Four instruments are installed on the focal plane which cover wide wavelengths from near infrared to submillimeter regions. The IRTS is optimized to observe the diffuse extended emission, and will survey about 10% of the sky in 20 days of mission life. The IRTS will provide significant information on cosmology, interstellar matter, late type stars, and interplanetary dust.     

Development of a 1m-normal-incidence-EUV telescope

Astrophysical plasmas at temperatures in the range (0.5–5)×10⁵ K that occur e.g. in interstellar space, in the extended atmospheres around stars of essentially all spectral types, including the numerous late-type stars with low photospheric temperatures, and in the atmospheres of highly evolved stars, can best be studied at extreme ultraviolet wavelengths where they release the bulk of their energy. We report here the current development status of a 1m-normal-incidence-EUV-telescope that will be flown on an ARIES rocket to observe the spectra of nearby stars in the 350 – 700 mm range.     

A pseedo random mask telescope tor Spacelab

A pair of pseudo-random mask telescopes is being constructed for Spacelab 2, mainly to observe the emission from galaxy clusters at energies from 2.5 to 25 keV. The main features and expected performance of the telescopes is described.     

Topology optimization of support structure of telescope skin based on bit-matrix representation NSGA-II

Non-dominated sorting genetic algorithm II（NSGA-II）with multiple constraints handling is employed for multi-objective optimization of the topological structure of telescope skin,in which a bit-matrix is used as the representation of a chromosome,and genetic algorithm（GA）operators are introduced based on the matrix.Objectives including mass,in-plane performance,and out-of-plane load-bearing ability of the individuals are obtained by fnite element analysis（FEA）using ANSYS,and the matrix-based optimization algorithm is realized in MATLAB by handling multiple constraints such as structural connectivity and in-plane strain requirements.Feasible confgurations of the support structure are achieved.The results confrm that the matrix-based NSGA-II with multiple constraints handling provides an effective method for two-dimensional multi-objective topology optimization.     

Optics of the far infra-red and submillimetre space telescope

Some of the considerations in the design of the telescope for FIRST are discussed. It is pointed out that instruments that operate at submillimetre wavelengths need to be analyzed with techniques derived from both the Radio and Optical/IR traditions. The issue of emissivity of reflector surfaces is also discussed.     

Determination of the characteristics of the gamma-ray telescope Gamma-1

The Gamma-1 telescope has been developed through a collaboration of scientists in the USSR and France in order to conduct -ray astronomical observations within the energy range from 50 to 5000 MeV. The major characteristics of the telescope were established by Monte-Carlo simulations and calibrations made with the aid of electron and tagged -ray beams produced by an accelerator, and these have been found to be as follows: the effective area for photons coming along the instrument's axis varies from about 50 cm² at E = 50 MeV to approximately 230 cm² at E 300 MeV; the angular resolution (half opening of the cone embracing 68% events) is equal to 2.7° at E = 100 MeV, and 1.8° at E = 300 MeV; the energy resolution (FWHM) varies from 70% to 35% as the energy of the detected photons increases from 100 to 550 MeV; the telescope's field-of-view at the half-sensitivity level is 300–450 square degrees depending upon the spectrum of the detected radiation, and the event selection logic. Proceeding from the thus obtained characteristics it is demonstrated that a point source producing a photon flux J (E 100 MeV) = 3 × 10^-7 cm^-2 s^-1, can be detected with a 5 significance by observing it during 10⁶ s at the level of the Cygnus background, and a source having intensity J (E 100 MeV) = 10^-6 cm^-2 s^-1 can be detected to within a mean square positional accuracy of about 15.     

AGATE: A high energy gamma-ray telescope using drift chambers

The exciting results from the highly successful Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory (CGRO) has contributed significantly to increasing our understanding of high energy gamma-ray astronomy. A follow-on mission to EGRET is needed to continue these scientific advances as well as to address the several new scientific questions raised by EGRET. Here we describe the work being done on the development of the Advanced Gamma-Ray Astronomy Telescope Experiment (AGATE), visualized as the successor to EGRET. In order to achieve the scientific goals, AGATE will have higher sensitivity than EGRET in the energy range 30 MeV to 30 GeV, larger effective area, better angular resolution, and an extended low and high energy range. In its design, AGATE will follow the tradition of the earlier gamma-ray telescopes, SAS-2, COS B, and EGRET, and will have the same four basic components of an anticoincidence system, directional coincidence system, track imaging, and energy measurement systems. However, due to its much larger size, AGATE will use drift chambers as its track imaging system rather than the spark chambers used by EGRET. Drift chambers are an obvious choice as they have less deadtime per event, better spatial resolution, and are relatively easy and inexpensive to build. Drift chambers have low power requirements, so that many layers of drift chambers can be included. To test the feasibility of using drift chambers, we have constructed a prototype instrument consisting of a stack of sixteen 1/2m × 1/2m drift chambers and have measured the spatial resolution using atmospheric muons. The results on the drift chamber performance in the laboratory are presented here.