Carolyn Atkins

Toward Large-Area Sub-Arcsecond X-Ray Telescopes

The future of x-ray astronomy depends upon development of x-ray telescopes with larger aperture areas (≈ 3 m2) and fine angular resolution (≈ 1″). Combined with the special requirements of nested grazing-incidence optics, the mass and envelope constraints of space-borne telescopes render such advances technologically and programmatically challenging. Achieving this goal will require precision fabrication, alignment, mounting, and assembly of large areas (≈ 600 m2) of lightweight (≈ 1 kg/m2 areal density) high-quality mirrors at an acceptable cost (≈ 1 M

Development of mirror modules for the ART-XC instrument aboard the Spectrum-Roentgen-Gamma mission

/m2 of mirror surface area). This paper reviews relevant technological and programmatic issues, as well as possible approaches for addressing these issues—including active (in-space adjustable) alignment and figure correction.

Toward Active X-ray Telescopes II

The Marshall Space Flight Center (MSFC) is developing x-ray mirror modules for the ART-XC instrument on board the Spectrum-Roentgen Gamma Mission. Four of those modules are being fabricated under a Reimbursable Agreement between NASA and the Russian Space Research Institute (IKI.) An additional three flight modules and one spare for the ART-XC Instrument are produced under a Cooperative Agreement between NASA and IKI. The instrument will consist of seven co-aligned x-ray mirror modules with seven corresponding CdTe focal plane detectors. Each module consists of 28 nested thin Ni/Co shells giving an effective area of 65 cm2 at 8 keV, response out to 30 keV, and an angular resolution of 45 arcsec or better HPD. Delivery of the first four modules is scheduled for November 2013, while the remaining three modules will be delivered to IKI in January 2014. We present a status of the ART x-ray module development at MSFC.

X-ray optic developments at NASA's MSFC

In the half century since the initial discovery of an astronomical (non-solar) x-ray source, the observation time required to achieve a given sensitivity has decreased by eight orders of magnitude. Largely responsible for this dramatic progress has been the refinement of the (grazing-incidence) focusing x-ray telescope, culminating with the exquisite subarcsecond imaging performance of the Chandra X-ray Observatory. The future of x-ray astronomy relies upon the development of x-ray telescopes with larger aperture areas (< 1 m2) and comparable or finer angular resolution (< 1″). Combined with the special requirements of grazing-incidence optics, the mass and envelope constraints of space-borne telescopes render such advances technologically challenging—requiring precision fabrication, alignment, and assembly of large areas (< 200 m2) of lightweight (≈ 1 kg m-2 areal density) mirrors. Achieving precise and stable alignment and figure control may entail active (in-space adjustable) x-ray optics. This paper discusses relevant programmatic and technological issues and summarizes current progress toward active x-ray telescopes.

ART-XC/SRG: status of the x-ray optics development

NASAs Marshall Space Flight Center (MSFC) has a successful history of fabricating optics for astronomical x-ray telescopes. In recent years optics have been created using electroforming replication for missions such as the balloon payload HERO (High energy replicated optics) and the rocket payload FOXSI (Focusing Optics x-ray Solar Imager). The same replication process is currently being used in the creation seven x-ray mirror modules (one module comprising of 28 nested shells) for the Russian ART-XC (Astronomical Rontgen Telescope) instrument aboard the Spectrum-Roentgen-Gamma mission and for large-diameter mirror shells for the Micro-X rocket payload. In addition to MSFCs optics fabrication, there are also several areas of research and development to create the high resolution light weight optics which are required by future x-ray telescopes. Differential deposition is one technique which aims to improve the angular resolution of lightweight optics through depositing a filler material to smooth out fabrication imperfections. Following on from proof of concept studies, two new purpose built coating chambers are being assembled to apply this deposition technique to astronomical x-ray optics. Furthermore, MSFC aims to broaden its optics fabrication through the recent acquisition of a Zeeko IRP 600 robotic polishing machine. This paper will provide a summary of the current missions and research and development being undertaken at NASAs MSFC.

Progress in Differential Deposition for Improving the Figures of Full-Shell Astronomical Grazing Incidence X-Ray Optics

The Astronomical Roentgen Telescope (ART) instrument is a hard-x-ray instrument with energy response up to 30 keV that is to be launched on board of the Spectrum Roentgen Gamma (SRG) Mission. The instrument consists of seven identical mirror modules coupled with seven CdTe strip focal-plane detectors. The mirror modules are being developed at the Marshall Space Flight Center (MSFC.) Each module has ~65 sq. cm effective area and an on-axis angular resolution of 30 arcseconds half power diameter (HPD) at 8 keV. The current status of the mirror module development and testing will be presented.

X-Ray Optics at NASA Marshall Space Flight Center

One of the developments at MSFC that is underway to meet the demand of high-resolution X-ray optics for future X-ray astronomy missions is the ‘differential deposition’ technique. This process corrects the axial figure profile of optics by selectively depositing material onto the mirror’s reflective surface. The process relies on accurate metrology achieved using a long trace profiler whose slope resolution is better than 1μrad. From these metrology data an error map is generated that shows the profile of material to be deposited to correct the optic’s figure. A computer-controlled, deposition system then applies this corrective coating. Simulations show that a substantial improvement in angular resolution is possible with this approach after multiple correction ‘cycles’. To assess this, custom coating systems have been developed and corrections of full-shell optics are underway. To date, a factor of < 2 improvement in the imaging quality of the optics has been demonstrated in x-ray tests after a single stage of correction.

Development of a Direct Fabrication Technique for Full-Shell X-Ray Optics

NASAs Marshall Space Flight Center (MSFC) engages in research, development, design, fabrication, coating, assembly, and testing of grazing-incidence optics (primarily) for x-ray telescope systems. Over the past two decades, MSFC has refined processes for electroformed-nickel replication of grazing-incidence optics, in order to produce highstrength, thin-walled, full-cylinder x-ray mirrors. In recent years, MSFC has used this technology to fabricate numerous x-ray mirror assemblies for several flight (balloon, rocket, and satellite) programs. Additionally, MSFC has demonstrated the suitability of this technology for ground-based laboratory applications—namely, x-ray microscopes and cold-neutron microscopes and concentrators. This mature technology enables the production, at moderately low cost, of reasonably lightweight x-ray telescopes with good (15–30 arcsecond) angular resolution. However, achieving arcsecond imaging for a lightweight x-ray telescope likely requires development of other technologies. Accordingly, MSFC is conducting a multi-faceted research program toward enabling cost-effective production of lightweight high-resolution x-ray mirror assemblies. Relevant research topics currently under investigation include differential deposition for post-fabrication figure correction, in-situ monitoring and control of coating stress, and direct fabrication of thin-walled full-cylinder grazing-incidence mirrors.

Differential Deposition Correction of Segmented Glass X-Ray Optics

Future astrophysical missions will require fabrication technology capable of producing high angular resolution x-ray optics. A full-shell direct fabrication approach using modern robotic polishing machines has the potential for producing high resolution, light-weight and affordable x-ray mirrors that can be nested to produce large collecting area. This approach to mirror fabrication, based on the use of the metal substrates coated with nickel phosphorous alloy, is being pursued at MSFC. A model of the wear pattern as a function of numerous physical parameters is developed and verified using a mandrel sample. The results of the polishing experiments are presented.

Active figure control effects on mounting strategy for x-ray optics

One of the challenges faced within the astronomical X-ray community is how to produce lightweight high angular resolution optics for a future X-ray mission capable of probing the early X-ray universe. To this end, the differential deposition project at NASA Marshall Space flight Center (MSFC) is looking to improve current X-ray optic technology by applying a corrective coating with a goal of achieving arc-second-level resolution. This paper will focus on the correction of segmented glass optics fabricated at NASA Goddard Space Flight Center (GSFC) and the paper will highlight: the design of the vacuum chamber and internal mechanics; the algorithm used to perform the correction; metrology of the glass segments; and the improvement post correction that has been achieved to date.