John H. Goebel

The Gravity Probe B test of general relativity

The Gravity Probe B mission provided two new quantitative tests of Einsteins theory of gravity, general relativity (GR), by cryogenic gyroscopes in Earths orbit. Data from four gyroscopes gave a geodetic drift-rate of −6601.8 ± 18.3 marc-s yr−1 and a frame-dragging of −37.2 ± 7.2 marc-s yr−1, to be compared with GR predictions of −6606.1 and −39.2 marc-s yr−1 (1 marc-s = 4.848 × 10−9 radians). The present paper introduces the science, engineering, data analysis, and heritage of Gravity Probe B, detailed in the accompanying 20 CQG papers.

UV LED operation lifetime and radiation hardness qualification for space flights

We report measurements of ultraviolet light emitting diode (UV LED) performance under conditions simulating operation in an orbiting satellite. UV LED light output maintained within less than 3% observational uncertainty, over more than 19,000 hours of operation in a nitrogen atmosphere, and over 8,000 hours operation at a pressure of less than 10-7 torr vacuum. In addition, irradiation with 63 MeV protons to a total fluence of 2×1012 protons/cm2 does not degrade the UV light output. Spectrally, the emissive center-wavelength and spectral shape are unchanged after proton irradiation within the precision of our measurement. These results qualify the UV LED operation lifetime and radiation hardness for space flights

Modular gravitational reference sensor development

The Modular Gravitational Reference Sensor (MGRS) is targeted as a next generation core instrument for both space gravitational wave detection and an array of other precision gravitational experiments in space. The objectives of the NASA funded program are to gain a system perspective of the MGRS, to develop key component technologies, and to establish important test platforms. Our original program was very aggressive in proposing ten areas of research and development. Significant advancements have been made in these areas, and we have met or exceeded the goals for the program set in 2007-2008. Additionally, we have initiated research projects for innovative technologies beyond the original plan. In this paper we will give a balanced overview of progress in MGRS technologies: the two layer sensing and control scheme, trade-off studies of GRS configurations, multiple optical sensor signal processing, optical displacement and angular sensors, differential optical shadow sensing, diffractive optics, proof mass center of mass and moment of inertia measurement, UV LED charge management, proof mass fabrication, thermal control and sensor development, characterization for various proof mass shapes, and alternative charge manage techniques.

Liquid helium-cooled MOSFET preamplifier for use with astronomical bolometer

A liquid helium‐cooled p‐channel enhancement mode MOSFET, the 3N167, is found to have sufficiently low noise for use as a preamplifier with helium‐cooled bolometers that are used in infrared astronomy. Its characteristics at 300, 77, and 4.2 K are presented. It is also shown to have useful application with certain photoconductive and photovoltaic infrared detectors.

Infrared charge-injection-device array performance at low background.

Low-background tests of a 1 x 32 Si:Bi charge-injection-device (CID) IR detector array were carried out to evaluate its feasibility for space-based astronomical observations. Optimum performance was obtained at a temperature of 11 K. The device showed a peak responsivity of 4.4 A/W, an average noise level of ~670 electrons, and a minimum noise equivalent power of 3 x 10(-17) W/[equation] for 1-sec integration time. This sensitivity compares well with that of discrete extrinsic silicon photoconductors. The measured sensitivity, plus the apparent absence of anomalous effects, make extrinsic silicon CID arrays very promising for astronomical applications.

Hydrogenated Amorphous Carbon (α:C-H) in the Planetary Nebula NGC 7027

A spectroscopic identification of the infrared continuum radiation is proposed for the planetary nebula NGC 7027. Hydrogenated amorphous carbon (α:C-H) is shown to account for the undulating spectrum between 5 and 15μm. The unidentified infrared emission bands lie at the peaks in the α:C-H spectrum, pointing to their association with a carbon polymorph, possibly α:C-H or polycyclic aromatic hydrocarbon molecules (PAHs). Except for atomic emission lines, all the infrared emission from NGC 7027 comes from one or another polymorph of carbon.

Characterization of direct readout Si:Sb and Si:Ga infrared detector arrays for space-based astronomy

Preliminary test results from the evaluation of Si:Sb and Si:Ga 58 x 62 element infrared detector arrays are presented. These devices are being characterized under background conditions and readout rates representative of operation in orbiting cryogenically-cooled infrared observatories. The arrays are hybridized to silicon direct readout multiplexers which allow random-access and non-destructive readout. Array performance optimization is being conducted with a flexible microcomputer-based drive and readout electronics system. Preliminary Si:Sb measurements indicate a sense node capacitance of 0.06 pF, peak (28 μm) responsivity >3 A/W at 2V bias, read noise of 130 rms e-, dark current ~10 e-/s, and a well capacity >105e-. The limited test data available on the performance of the Si:Ga array are also discussed.

Detector arrays for low-background space infrared astronomy

The status of development and characterization tests of integrated infrared detector array technology for astronomical applications is described. The devices under development include intrinsic, extrinsic silicon, and extrinsic germanium detectors, with hybrid silicon multiplexers. Laboratory test results and successful astronomical imagery have established the usefulness of integrated arrays in low-background astronomical applications.

Narrow Band Imagery In The 8-14 Micron Spectral Region

The problem of deconvolution of the point source response function (PSF) for two dimensional imaging infrared arrays is addressed. A variety of phenomena can lead to PSF degradation ranging from atmospheric turbulence to the array itself. The maximum entropy (MEM) algorithm is used to demonstrate that substantial image quality improvements are possible in the case of a PSF which is degraded by electronic rather than optical smearing. This result implies that IR arrays need not have perfect or even very good pixel-pixel crosstalk rejection ratios for use in astronomy.

Charge-injection-device 2 × 64 element infrared array performance

Three 2 × 64 element Si:Bi accumulation-mode charge-injection-device (CID) arrays were tested at low and moderate background to evaluate their usefulness for space-based astronomical observations. Testing was conducted both in the laboratory and in ground-based telescope IR observations. The devices showed an average readout noise level below 200 equivalent electrons, a peak responsivity of 4 A/W, and a noise equivalent power of 3 × 10−17 W/Hz1/2. This sensitivity compares well with that of nonintegrating discrete extrinsic silicon photoconductors. The array well capacity was significantly smaller than predicted. The measured sensitivity makes extrinsic silicon CID arrays useful for certain astronomical applications. However, their readout efficiency and frequency response represent serious limitations in low-background applications.