Isabelle Domken

XMM flight mirror modules with reflection grating assembly and x-ray baffle testing

In the frame of the XMM project, several test campaigns are accomplished to qualify the optical elements of the mission. The test described in this paper are performed on a XMM flight model mirror module added with a reflection grating assembly (RGA). The mirror module contains 58 x-ray optical quality shells, an x-ray baffle (XRB) to reduce the straylight. This complete XMM flight model mirror assembly (MA) is tested in a vertical configuration at CSL, in a full aperture or partial EUV collimated beam illumination, and with an x-ray pencil beam. One of the advantages of the EUV collimated beam is to verify the correct position of the RGA when integrated in flight configuration on the mirror module structure. This is not possible in x-ray with a finite source distance. The partial EUV illumination is performed to verify the correct integration of the RGA grating stacks. The pencil beam allows to make an accurate metrology of the XRB position, and to verify the positions of the 0, 1 and 2 diffraction order foci. In this paper, the tested module is first exposed, and the approach to qualify the instrument is described. The analysis of the results achieved over the different test configurations is presented. The impact of the environmental test on the reflection grating box is also diagnosed.

X-ray baffle of the XMM telescope: development and results

The high throughput x-ray spectroscopy mission XMM is the second cornerstone project in the European Space Agency (ESA) long-term program for space science. This observatory has at its heart three large x-ray telescopes, which will provide a large collection area with a spatial resolution around 15 arcsec. Five flight models of the XMM x-ray telescope have been delivered to ESA in 1998. They show optical performance, which is far better than the specifications, especially in terms of optical and x-ray stray light reduction. The low level of x-ray stray light will be an important benefit for the observation of the extended faint sources such as super nova remnants or clusters of active galaxies. This reduction of x-ray stray light is due, in particular, to the implementation of a very complex and accurate x-ray baffle mounted at the entrance of the telescope. In this paper, we present first the need, the design, the manufacturing and the integration of the x-ray baffle. Then, we concentrate on the verification of the performance of the baffle at the Centre Spatial de Liege. Finally, we will present the excellent results obtained with these baffles.

Lessons learned from the development of the XMM optics

The high throughput x-ray spectroscopy mission XMM is the second cornerstone project in the European Space Agency (ESA) long-term program for space science. This observatory has at its heart three large x-ray telescopes, which will provide a large collecting area with a spatial resolution better than 15 arcsec. In 1998, the three Flight Models and the two spare models of the x-ray telescope have been delivered to ESA, after verification and calibration at the Centre Spatial de Liege and at the Max Planck Institute near Munich. They show mechanical and optical performances much better than the specification. Their performance will undoubtedly bring an important benefit for the astronomers. The most challenging part of the development of these telescopes was the design, the manufacturing and the testing of the x-ray mirrors, during four intensive years. In this paper, we will first summarize the development and the excellent results of the mirrors. Then, we will discuss the lessons learned during this development, mainly in terms of management and technical aspects, including design, manufacturing and testing. These lessons will be drawn in perspective of the future x-ray missions such as Constellation X, Xeus and ASTRO-F.

Alignment and calibration of the ICON-FUV instrument: Development of a vacuum UV facility

The optical calibration of the ICON-FUV instrument requires designing specific ground support equipment (GSE). The ICON-FUV instrument is a spectrographic imager that operates on two specific wavelengths in the UV (135.6 nm and 157 nm). All the operations have to be performed under vacuum UV light. The optical setup is based on a VUV monochromator coupled with a collimator that illuminates the FUV entrance slit. The instrument is placed on a manipulator providing fields pointing. Image quality and spectral properties can be then characterized for each field. OGSE, MGSE, optical calibration plan and vacuum alignment of the instrument are described.

VUV optical ground system equipment and its application to the ICON FUV flight grating characterization and selection

ICON FUV is a two channel spectrographic imager that measures intensity and spatial distribution of oxygen (135.6 nm) and molecular nitrogen (157 nm) of the ionosphere. As those wavelengths are strongly absorbed by the atmosphere, the optical elements of the system have to be tested inside vacuum chambers. Prior to the instrument alignment and calibration, two 3600 gr/mm gratings were characterized. The primary focus is the measurement of the diffraction efficiencies; while the second objective is to select the best grating and to define which is the flight and the spare. A dedicated setup has been developed to assess the grating optical performances under vacuum. A 1 cm diameter collimated beam is generated using an off-axis parabola and a UV source at its focal point. The grating is placed at the center of two rotation stages collinearly aligned. One detector is placed on a rotating arm, deported from its rotation center. A PMT detector records diffracted light intensity with respect to its angular position and its wavelength. Angular incidence on the grating is tuned with the help of the second rotation stage. The grating efficiency homogeneity and scattering properties are measured through a Y-X scan.