Chet Speegle

First Images from HERO: A Hard-X-Ray Focusing Telescope

We are developing a balloon-borne hard X-ray telescope that utilizes grazing-incidence optics. Termed HERO, for High-Energy Replicated Optics, the instrument will provide unprecedented sensitivity in the hard X-ray region and will achieve millicrab-level sensitivity in a typical 3 hr balloon-flight observation and 50 μcrab sensitivity on ultralong-duration flights. A recent proof-of-concept flight, featuring a small number of mirror shells, captured the first focused hard X-ray images of galactic X-ray sources. Full details of the payload, its expected future performance, and its recent measurements are provided.

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.

HERO: high-energy replicated optics for a hard-x-ray balloon payload

We are developing high-energy grazing-incidence optics for a balloon-borne hard-x-ray telescope. When completed the instrument, termed HERO for High Energy Replicated Optics, will have 200 cm2 effective collecting area at 40 keV and <EQ 30 arcsec angular resolution. The payload will offer unprecedented sensitivity in the hard-x-ray region, with milliCrab level sensitivity on a one-day balloon flight and 100 microCrab on an ultra-long-duration flight. While the full science payload is scheduled for flight in 2002, an engineering/proving flight is currently awaiting launch. This flight, consisting of just two mirror modules, each containing three nested shells above a pair of gas scintillation proportional counter focal plane detectors, is intended to test a newly designed gondola pointing and aspect system and to examine the stability of optical bench designs. This paper provides an overview of the HERO program.

Development of hard x-ray optics at MSFC

We are fabricating optics for the hard-x-ray region using electroform nickel replication. The attraction of this process, which has been widely used elsewhere, is that the resulting full shell optics are inherently stable and thus can have very good angular resolution. The challenge with this process is to develop lightweight optics, and to keep down the costs of mandrel fabrication. We accomplished the former through the development of high-strength, low-stress nickel alloys that permit very thin, stable, shells without fabrication- and handling-induced deformations. For the latter, we have utilized inexpensive grinding and diamond turning to figure the mandrels and then purpose-built polishing machines to finish the surface. In-house plating tanks and a simple water-bath separation system complete the process. To date we have built shells ranging in size from 5 cm diameter to 50 cm, and with thickness down to 100 micron. For our HERO balloon program, we are fabricating over 200 iridium-coated shells, 250 microns thick, for hard-x-ray imaging up to 75 keV. Early test results on these have indicated half-power-diameters of 15 arcsec. The status of these developments will be reviewed.

HERO program: high-energy replicated optics for a hard-x-ray balloon payload

We are developing high-energy replicated optics for a balloon-borne hard-x-ray telescope. When completed, the telescope will have around 130 cm2 of effective collecting area at 60 keV, and an angular resolution of <EQ 30 arc seconds, half power diameter. With an array of gas scintillation proportional counters in the focal plane the payload will provide unprecedented sensitivity for pointed observations in the hard-x-ray band. We present an overview of the HERO program, together with test data from the first mirror shell. The overall sensitivity of the full payload is given for planned long- and ultra-long-duration balloon flights.

Metrology for the Development of High Energy X-Ray Optics

We are developing grazing-incidence x-ray optics for a balloon-borne hard-x-ray telescope (HERO). The instrument will have 200 cm2 effective collecting area at 40 keV and an angular resolution goal of 15 arcsec. The HERO mirror shells are fabricated using electroformed-nickel replication off super-polished cylindrical mandrels. The angular resolution goal puts stringent requirements on the quality of the x-ray mirrors and, hence, on mandrel quality. We used metrology in an iterative approach to monitor and refine the x-ray mirror fabrication process. Comparison of axial slope measurements of the mandrel and the shells will be presented together with results from x-ray tests.

HERO: program status and first images from a balloon-borne focusing hard x-ray telescope

HERO is a balloon payload featuring shallow-graze angle replicated optics for hard-x-ray imaging. When completed, the instrument will offer unprecedented sensitivity in the hard-x-ray region, giving thousands of sources to choose from for detailed study on long flights. A recent proof-of-concept flight captured the first hard-x-ray focused images of the Crab Nebula, Cygnus X-1 and GRS 1915+105. Full details of the HERO program are presented, including the design and performance of the optics, the detectors and the gondola. Results from the recent proving flight are discussed together with expected future performance when the full science payload is completed.

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.

Computer-controlled cylindrical polishing process for development of grazing incidence optics for the hard x-ray region

The focusing performance of shell optics for the hard X-ray region strongly depends on their axial mid-spatialfrequency- range figure errors. This paper presents the development of a deterministic computer-controlled polishing process to minimize these axial figure errors on cylindrical shaped mandrels from which the mirror shells are replicated. A mathematical model has been developed to simulate the residual surface figure errors due to the polishing process parameters and the polishing tools used, along with their non-conformance to the mandrel. We present design considerations of a large-size polishing lap where the experimentally determined process variables have been used for optimizing the lap configuration and the machine operational parameters. Furthermore, the developed model is capable of generating a corrective polishing sequence for a known surface error profile. Practical polishing experiments have been performed to verify the model and to determine its ability to correct known axial figure errors through polishing machine control.