A precision bearing gimbal system for the Teal Ruby program

A precision bearing gimbal system designed to allow a spaceborne infrared sensor to stare at points on the Earth while in orbit is described. The problems encountered, analytical tools and test methods used, and data applicable to users of similar systems are presented. Assembly procedures, bearing preload effects, moisture control, structural analysis, and noise control are specifically examined

Mechanics of liquid helium in a partially filled rotating dewar in low gravity with application to Gravity Probe-B

The Gravity Probe-B spacecraft is composed largely of a liquid helium dewar containing an experiment package. It is shown that an unsymmetric liquid helium distribution in the dewar can cause unacceptably high forces, gravitational and gravity gradient forces, at the experiment location. It is further shown that for the planned spacecraft configuration and operational parameters, it is very likely that the liquid helium distribution in the dewar will be unsymmetric. The required symmetry can be attained by using higher operational spacecraft rotation rates

The nucleus of 103P/Hartley 2, target of the EPOXI mission

103P/Hartley 2 was selected as the target comet for the Deep Impact extended mission, EPOXI, in October 2007. There have been no direct optical observations of the nucleus of this comet, as it has always been highly active when previously observed. We aimed to recover the comet near to aphelion, to a) confirm that it had not broken up and was in the predicted position, b) to provide astrometry and brightness information for mission planning, and c) to continue the characterisation of the nucleus. We observed the comet at heliocentric distances between 5.7 and 5.5 AU, using FORS2 at the VLT, at 4 epochs between May and July 2008. We performed VRI photometry on deep stacked images to look for activity and measure the absolute magnitude and therefore estimate the size of the nucleus. We recovered the comet near the expected position, with a magnitude of m_R = 23.74 \pm 0.06 at the first epoch. The comet had no visible coma, although comparison of the profile with a stellar one showed that there was faint activity, or possibly a contribution to the flux from the dust trail from previous activity. This activity appears to fade at further epochs, implying that this is a continuation of activity past aphelion from the previous apparition rather than an early start to activity before the next perihelion. Our data imply a nucleus radius of \le 1 km for an assumed 4% albedo; we estimate a ~6% albedo. We measure a colour of (V-R) = 0. 26 \pm 0.09.Comment: 5 pages, 4 figures, accepted for publication in A&

Photometry of cometary nuclei: Rotation rates, colours and a comparison with Kuiper Belt Objects

We present time-series data on Jupiter Family Comets (JFCs) 17P/Holmes, 47P/Ashbrook-Jackson and 137P/Shoemaker-Levy 2. In addition we also present results from `snap-shot' observations of comets 43P/Wolf-Harrington, 44P/Reinmuth 2, 103P/Hartley 2 and 104P/Kowal 2 taken during the same run. The comets were at heliocentric distances of between 3 and 7 AU at this time. We present measurements of size and activity levels for the snap-shot targets. The time-series data allow us to constrain rotation periods and shapes, and thus bulk densities. We also measure colour indices (V-R) and (R-I) and reliable radii for these comets. We compare all of our findings to date with similar results for other comets and Kuiper Belt Objects (KBOs). We find that the rotational properties of nuclei and KBOs are very similar, that there is evidence for a cut-off in bulk densities at ~ 0.6 g cm^{-3} in both populations, and the colours of the two populations show similar correlations. For JFCs there is no observational evidence for the optical colours being dependant on either position in the orbit or on orbital parameters.Comment: 15 pages, 19 figures, accepted for publication in MNRA

Optical observations of 23 distant Jupiter Family Comets, including 36P/Whipple at multiple phase angles

We present photometry on 23 Jupiter Family Comets (JFCs) observed at large heliocentric distance, primarily using the 2.5m Isaac Newton Telescope (INT). Snap-shot images were taken of 17 comets, of which 5 were not detected, 3 were active and 9 were unresolved and apparently inactive. These include 103P/Hartley 2, the target of the NASA Deep Impact extended mission, EPOXI. For 6 comets we obtained time-series photometry and use this to constrain the shape and rotation period of these nuclei. The data are not of sufficient quantity or quality to measure precise rotation periods, but the time-series do allow us to measure accurate effective radii and surface colours. Of the comets observed over an extended period, 40P/Vaisala 1, 47P/Ashbrook-Jackson and P/2004 H2 (Larsen) showed faint activity which limited the study of the nucleus. Light-curves for 94P/Russell 4 and 121P/Shoemaker-Holt 2 reveal rotation periods of around 33 and 10 hours respectively, although in both cases these are not unique solutions. 94P was observed to have a large range in magnitudes implying that it is one of the most elongated nuclei known, with an axial ratio a/b \ge 3. 36P/Whipple was observed at 5 different epochs, with the INT and ESO's 3.6m NTT, primarily in an attempt to confirm the preliminary short rotation period apparent in the first data set. The combined data set shows that the rotation period is actually longer than 24 hours. A measurement of the phase function of 36P's nucleus gives a relatively steep \beta = 0.060 \pm 0.019. Finally, we discuss the distribution of surface colours observed in JFC nuclei, and show that it is possible to trace the evolution of colours from the Kuiper Belt Object (KBO) population to the JFC population by applying a 'de-reddening' function to the KBO colour distribution.Comment: 21 pages, 29 figures (1 colour), accepted for publication in MNRA

Opto-mechanical noise cancellation

The experiments presented in this thesis investigate the interaction between radiation and an optical cavity, in which one mirror of the cavity is mounted on a flexure which could be moved by radiation pressure. The cavity was shown to exhibit non-linear behaviour with high input power. The radiation pressure force was shown to change the mechanical resonance frequency of the moveable mirror. Motion was induced through amplitude modulation of a high power input beam and the extent of this motion measured using the cavity control loop. To demonstrate the way quantum correlations could be used to beat the SQL, the laser light incident on the cavity was prepared, using classical modulation techniques, with classical correlations between the quadratures that cause shot noise and radiation pressure noise. A level of modulation much higher than the quantum level was used to make the cancellation effects more visible. The effect of radiation pressure induced motion was cancelled by the addition of correlated frequency modulation. The input amplitude was then modulated by a white noise source. The resulting noise was partially cancelled when the same white noise source was used to drive the frequency modulator with a dierent phase. This cancellation demonstrably improved the signal to noise ratio of a signal injected into the system

Federal campaign committees vary in their reliance on highincome, high education, urban, and highly partisan districts forcontributions

Recent election cycles in the U.S. have seen a massive increase in fundraising by political campaign committees. In new research, Robert C. Lowry finds that these committees do not all raise money from the same kinds of communities. Studying itemized contributions by individuals to campaign committees, he writes that competitive districts generate more contributions to local candidates running in those districts, but there are fewer predicted contributions to many other kinds of committee. He also finds that the contributions made can be greatly affected by the district’s levels of income, education and urbanization

The Influence of Dual-Recycling on Parametric Instabilities at Advanced LIGO

Laser interferometers with high circulating power and suspended optics, such as the LIGO gravitational wave detectors, experience an optomechanical coupling effect known as a parametric instability: the runaway excitation of a mechanical resonance in a mirror driven by the optical field. This can saturate the interferometer sensing and control systems and limit the observation time of the detector. Current mitigation techniques at the LIGO sites are successfully suppressing all observed parametric instabilities, and focus on the behaviour of the instabilities in the Fabry-Perot arm cavities of the interferometer, where the instabilities are first generated. In this paper we model the full dual-recycled Advanced LIGO design with inherent imperfections. We find that the addition of the power- and signal-recycling cavities shapes the interferometer response to mechanical modes, resulting in up to four times as many peaks. Changes to the accumulated phase or Gouy phase in the signal-recycling cavity have a significant impact on the parametric gain, and therefore which modes require suppression.Comment: 9 pages, 11 figures, 2 ancillary file