Darell Engelhaupt

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.

Development of Wolter I x-ray optics by diamond turning and electrochemical replication

Abstract Demonstration x-ray optics have been produced by diamond turning and replication techniques that could revolutionize the fabrication of advanced mirror assemblies. The prototype optics were developed as part of the Advanced X-ray Astrophysics Facility—Spectrographic program (AXAF-S). The initial part of the project was aimed at developing and testing the replication technique so that it could potentially be used for the production of the entire mirror array. This assembly will ultimately be comprised of up to 50 nested mirror shells. The mirrors are produced by electroforming a thin shell optic with a conical mandrel. The mandrel is diamond-turned electroless nickel over an aluminum substrate. The initial goal was to produce a surface finish on the replicated mirror shell of less than 10 A rms (measured with a WYKO 3D at 20X). The electroformed mirror shell is made from pure nickel deposited in a state of minimum stress. A cryogenic separation technique is used to remove the finished mirror from the mandrel. The replication technology for the mirror components has the potential to revolutionize the fabrication of precision components. The extremely high precision required of x-ray optics may lead to advances in manufacturing techniques that could be utilized in the fabrication of other precision components. The key procedures of the fabrication process are presented with the appropriate testing results.

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.

Effect of Pulse Plating Parameters on the Composition of Alumina/Nickel Composite

Nickel/aluminum oxide composite was electroformed in a sulfamate bath with 50 g/L of 0.05 μm aluminum oxide powder. Different plating methods, including direct current plating, periodic pulse plating, and periodic reversepulse plating, were used. With conventional direct current plating, the maximum particle inclusion in the nickel matrix remains about 2 wt %. However, much higher percentile particle inclusions were achieved when a specific pulse reversal plating technique was applied. The particle incorporation approaches the theoretical maximum when the deposit thickness per cycle approaches the particle diameter size at lower duty cycle. The highest particle incorporation achieved is 23% (by weight). Conceptual models interpreting the dramatic differences in the results of these plating methods are proposed.

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.

Calibration results for the AXAF flight contamination monitor

The Advanced X-ray Astrophysics Facility (AXAF) ground calibration program, easily the most extensive in the history of high energy astrophysics, requires careful attention to the verification of its validity for on-orbit operations of the observatory. The purpose of the Flight Contamination Monitor (FCM) is to verify the transfer of the AXAF absolute flux scale calibration from ground to on-orbit operations and to measure or bound any changes in molecular contamination on the AXAF mirrors. This paper reports the current status of the analysis of FCM measurements taken during ground calibration. The FCM measurements during the AXAF activation phase will be the first look at the on-orbit AXAF performance.

Autonomous long-range open area fire detection and reporting

Approximately 5 billion dollars in US revenue was lost in 2003 due to open area fires. In addition many lives are lost annually. Early detection of open area fires is typically performed by manned observatories, random reporting and aerial surveillance. Optical IR flame detectors have been developed previously. They typically have experienced high false alarms and low flame detection sensitivity due to interference from solar and other causes. Recently a combination of IR detectors has been used in a two or three color mode to reduce false alarms from solar, or background sources. A combination of ultra-violet C (UVC) and near infra-red (NIR) detectors has also been developed recently for flame discrimination. Relatively solar-blind basic detectors are now available but typically detect at only a few tens of meters at ~ 1 square meter fuel flame. We quantify the range and solar issues for IR and visible detectors and qualitatively define UV sensor requirements in terms of the mode of operation, collection area issues and flame signal output by combustion photochemistry. We describe innovative flame signal collection optics for multiple wavelengths using UV and IR as low false alarm detection of open area fires at long range (8-10 km/m2) in daylight (or darkness). A circular array detector and UV-IR reflective and refractive devices including cylindrical or toroidal lens elements for the IR are described. The dispersion in a refractive cylindrical IR lens characterizes the fire and allows a stationary line or circle generator to locate the direction and different flame IR “colors” from a wide FOV. The line generator will produce spots along the line corresponding to the fire which can be discriminated with a linear detector. We demonstrate prototype autonomous sensors with RF digital reporting from various sites.

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.