Mikhail V. Gubarev

The Development of Hard-X-Ray Optics at MSFC

We have developed the electroformed-nickel replication process to enable us to fabricate light-weight, high-quality mirrors for the hard-x-ray region. Two projects currently utilizing this technology are the production of 240 mirror shells, of diameters ranging from 50 to 94 mm, for our HERO balloon payload, and 150- and 230-mm-diameter shells for a prototype Constellation-X hard-x-ray telescope module. The challenge for the former is to fabricate, mount, align and fly a large number of high-resolution mirrors within the constraints of a modest budget. For the latter, the challenge is to maintain high angular resolution despite weight-budget-driven mirror shell thicknesses (100 μm) which make the shells extremely sensitive to fabrication and handling stresses, and to ensure that the replication process does not degrade the ultra-smooth surface finish (~3Å) required for eventual multilayer coatings. We present a progress report on these two programs.

Development of a Prototype Nickel Optic for the Constellation-X Hard-X-Ray Telescope

The Constellation-X mission planned for launch in 2015-2020 timeframe, will feature an array of Hard X-ray telescopes (HXT) with a total collecting area greater than 1500 cm at 40 keV. Two technologies are being investigated for the optics of these telescopes, one of which is multilayer-coated Electroformed-Nickel-Replicated (ENR) shells. The attraction of the ENR process is that the resulting full-shell optics are inherently stable and offer the prospect of better angular resolution which results in lower background and higher instrument sensitivity. We are building a prototype HXT mirror module using an ENR process to fabricate the individual shells.This prototype consists of 5 shells with diameters ranging from 15 cm to 28 cm with a length of 42.6 cm. The innermost of these will be coated with iridium, while the remainder will be coated with graded d-spaced W/Si multilayers. The assembly structure has been completed and last year we reported on full beam illumination results from the first test shell mounted in this structure. We have now fabricated and coated two (15 cm and 23 cm diameter) 100 micron thick shells which have been aligned and mounted. This paper presents the results of full beam illumination X-ray tests, taken at MPE-Panter. The HEW of the individual shells will be discussed, in addition to results from the full two shell optic test.

Alignment, assembly, and testing of high-energy x-ray optics

We are developing grazing incidence x-ray imaging optics for a balloon-borne hard x-ray telescope (HERO). The HERO payload, scheduled for launch in May 2006, consists of 8 mirror modules with 12 mirror shells each fabricated using electroform-nickel replication off super polished cylindrical mandrels. An optical system for alignment and assembly of the shells into their modules will be described together with an assessment of the systematic errors associated with this process. Full details of the assembly procedures and results of the on-ground x-ray testing of the HERO modules will be provided.

X-ray testing Constellation-X optics at MSFC's 100-m facility

As NASA’s next facility-class x-ray mission, Constellation X will provide high-throughput, high-resolution spectroscopy for addressing fundamental astrophysical and cosmological questions. Key to the Constellation-X mission is the development of lightweight grazing-incidence optics for its Spectroscopy X-ray Telescopes (SXT) and for its Hard X-ray Telescopes (HXT). In preparation for x-ray testing Constellation-X SXT and HXT development and demonstration optics, Marshall Space Flight Center (MSFC) is upgrading its 100-m x-ray test facility, including development of a five degree-of-freedom (5-DoF) mount for translating and tilting test articles within the facility’s large vacuum chamber. To support development of alignment and assembly procedures for lightweight x-ray optics, Goddard Space Flight Center (GSFC) has prepared the Optical Alignment Pathfinder Two (OAP2), which will serve as a surrogate optic for developing and rehearsing x-ray test procedures. In order to minimize thermal distortion of the mirrors during x-ray testing, the Harvard-Smithsonian Center for Astrophysics (CfA) has designed and implemented a thermal control and monitoring system for the OAP2. CfA has also built an aperture wheel for masking and sub-aperture sampling of the OAP2 to aid in characterizing x-ray performance of test optics.

Gas scintillation proportional counters for high-energy x-ray astronomy

A focal plane array of high-pressure gas scintillation proportional counters (GSPC) for a balloon-borne hard-x-ray telescope is under development at the Marshall Space Flight Center. These detectors have an active area of ~ 20 cm2, and are filled with a high pressure (106 Pa) xenon-helium mixture. Imaging is via crossed-grid position-sensitive phototubes sensitive in the UV region. The performance of the GSPC is well matched to that of the telescopes x-ray optics which have response to 75 keV and a focal spot size of ~ 500 μm. The detector’s energy resolution, 4% FWHM at 60 keV, is adequate for resolving the broad spectral lines of astrophysical importance and for accurate continuum measurements. Full details of the instrument and its performance will be provided.

Constellation-X Mirror Technology Development

As NASAs next major space X-ray observatory, the Constellation-X mission (Bookbinder et al. 2008) requires mirror assemblies with unprecedented characteristics that cannot be provided by existing optical technologies. In the past several years, the project has supported a vigorous mirror technology development program. This program includes the fabrication of lightweight mirror segments by slumping commercially available thin glass sheets, the support and mounting of these thin mirror segments for accurate metrology, the mounting and attachment of these mirror segments for the purpose of X-ray tests, and development of methods for aligning and integrating these mirror segments into mirror assemblies. This paper describes our efforts and developments in these areas.

Technology development for high-energy x-ray optics

We are developing hard-x-ray optics using an electroformed-nickel-replication process off superpolished mandrels. To date, we have fabricated over 100 shells for our HERO balloon payload with typical angular resolutions in the 13-15 arcsec range. This paper discusses the factors currently limiting this resolution and various developments geared towards the production of higher-resolution optics.

Hard x-ray telescope concentrator for astrophysical mission Spectrum-X-Gamma

The hard X-ray telescope-concentrator ART-XC on board the Spectrum-X-Gamma X-ray astrophysical observatory (launching in 2011) is one of the main instruments of the mission. The instrument will be used for an all-sky survey and then for pointed observations which are planned for the first four and the next three years of the Mission, respectively. ART-XC will be sensitive in the 4-30 keV energy range and will have an effective area of several hundred square centimeters at 10 keV. It will have a field of view of about ~28 arcmin, angular resolution better than 1 arcmin and will be an order of magnitude more sensitive than the current generation of collimated instruments and coded mask telescopes in the survey mode and a two or three orders of magnitude more sensitive in the pointing mode. With its high sensitivity in the hard X-ray band and good imaging capabilities, ART-XC will extend the operating energy range of the observatory (complementing the capabilities of the primary science instrument eROSITA), thus significantly enhancing the mission both in the all-sky survey over the energy band 4-10 keV and, especially, in pointed observations over the energy band 4-30 keV. During the 4-year survey, this ART-XC would detect more than ~104 sources over 4-10 keV. For a 105 second pointed observation, the telescope will provide better than 10 microCrab sensitivity in the 4-20 keV energy range.

Figure Measurements of High-Energy-X-Ray Replicated Optics

We are developing grazing incidence x-ray optics for a balloon-borne hard-x-ray telescope (HERO). The HERO mirror shells are fabricated using electroform-nickel replication off super-polished cylindrical mandrels. One of the sources for mirror resolution error is departure of the shell figure from prescription. We have modified a Vertical-scan Long Trace Profilometer (VLTP) in order to measure the figure of the inner surface of the HERO mirror shells for diameters as small as 74 mm. Metrology of the figure, the microroughness, tilt angle, the circularity for the shell mirrors and the mandrels, as well as alignment procedures are discussed. Comparison of metrology of the mandrel and the shells is presented together with results from x-ray tests.