Wavefront sensing and control in space-based coronagraph instruments using Zernike’s phase-contrast method

Future space telescopes with coronagraph instruments will use a wavefront sensor (WFS) to measure and correct for phase errors and stabilize the stellar intensity in high-contrast images. The HabEx and LUVOIR mission concepts baseline a Zernike wavefront sensor (ZWFS), which uses Zernike’s phase contrast method to convert phase in the pupil into intensity at the WFS detector. In preparation for these potential future missions, we experimentally demonstrate a ZWFS in a coronagraph instrument on the Decadal Survey Testbed in the High Contrast Imaging Testbed facility at NASA’s Jet Propulsion Laboratory. We validate that the ZWFS can measure low- and mid-spatial frequency aberrations up to the control limit of the deformable mirror (DM), with surface height sensitivity as small as 1 pm, using a configuration similar to the HabEx and LUVOIR concepts. Furthermore, we demonstrate closed-loop control, resolving an individual DM actuator, with residuals consistent with theoretical models. In addition, we predict the expected performance of a ZWFS on future space telescopes using natural starlight from a variety of spectral types. The most challenging scenarios require ∼1  h of integration time to achieve picometer sensitivity. This timescale may be drastically reduced by using internal or external laser sources for sensing purposes. The experimental results and theoretical predictions presented here advance the WFS technology in the context of the next generation of space telescopes with coronagraph instruments

Richard Wright's Globalism

This essay takes a long view of Wright’s work, arguing that his racial consciousness always extended beyond national boundaries and was forged from a globalist perspective. This outlook is not, as some critics have maintained, a late-stage development in Wright’s career, but rather the predominant theme that unites his oeuvre with a single continuous thread. Wright’s work—including his fiction, essays, journalism, poetry, letters, and unpublished pieces spanning from the beginning of his career in the mid-1930s to his deathbed writings of 1960—crystallizes his globalist imagination even as it shifts registers: from an anti-fascist political solidarity framed by Marxist internationalism to an affective kinship among formerly colonized peoples expressed through existentialist proto-postcolonialism, and finally a transcendent poetics in search of universal humanism

Political Demands, Political Opportunities: Explaining the Differential Success of Left-Libertarian Parties

Using qualitative comparative analysis, we examine why left-libertarian parties, associated with environmental and other "new social movements," have been relatively successful in some western democracies but not others. We conceptualize the parties as products of new citizen demands on the one hand, and of political opportunity structures, which govern party supply, on the other. We show that supply-side factors, such as a strong left and the existence of proportional representation, tend to work together to facilitate party innovation. A strong left appears more likely to downplay left-libertarian issues and push new-left activists to form separate parties, while proportional representation eases entry into the party system. Demand-side factors play a significant but lesser role. The theoretical and methodological strategies employed here have the potential to help political sociologists explain the variable success of other types of party innovators.Sociolog

Enabling Space Telescope Technologies : OPTIIX Technology Feed-Forward

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