1803.11181
The Americal space exploration narrative from the Cold War through the Obama Administration
Holland, Burns
Document how the narrative and the policies of space exploration in the US have changed over the past 50 years. First examine the history of the US space exploration program and also assess 3 current conditions of space exploration including: (1) the increasing role of the private sector, (2) the influence of global politics, and (3) the focus on a human mission to Mars. Identify 5 rhetorical themes: competition, prestige, collaboration, leadership, and a new paradigm. These themes are then used to analyze the content of 40 documents from 8 presidential administration. The historical narrative and content analysis together suggest that space exploration has developed from a discourse about a bipolar world composed of the US and USSR into a complicated field that encompass many new players. Make 3 observations: (1) there is a disconnect between stated US policy goals and the implementation of those goals, (2) the US communicates mixed messages regarding its intent to be both the dominant leader in space exploration and also a committed participant in international collaborations, and (3) the US cannot remain a true pioneer in space exploration if it does not embrace the realities of globalization and the changing dynamics within space exploration. Conclude with 3 suggestions: (1) the US government and NASA should critically examine space exploration priorities and commit to implementing a program that will further realistic policy and goals, (2) the US should reexamine its intention to play a dominant leadership role in space exploration and consider emphasizing a commitment toward active participation in international collaboration in space, and (3) the US should fully embrace the new paradigm of space exploration by lowering barriers that hinder competitiveness.
Stellar disc strams as probes of the Galactic potential and satellite impacts
Laporte, et al
Stars aligned in thin stream-line features (feathers), with widths of delta~1-10 deg and lengths as large as Delta ell~180 deg, have been observed towards the Anticenter of our Galaxy and their properties mapped in abundances and phase-space. Study their origin by analyzing similar features arising in an N-body simulations of a Galactic disc interacting with a Sagittarius-like dwarf spheroidal galaxy (Sgr). By following the orbits of the particles identified as contributing to feathers backwards in time, trace their excitation to one of Sgr's previous peri centric passages. These particles initially span a large range of phase-angles but a tight range of radii, suggesting they provide a probe of populations in distinct annuli in the outer Galactic disc. The structures are long lived and persist after multiple passages on timescales of ~4 Gyrs. On the sky, they exhibit oscillatory motion that can be traced with a single orbit mapped over much of their full length and with amplitudes and gradients similar to those observed. Demonstrate how these properties of feathers may be exploited to measure the potential, its flattening, as well as infer the strength of recent potential perturbations.
1803.11526
Tensions between direct measurements of the lens power spectrum from Planck data
Motloch, Hu
Apply a recently developed method to directly measure the gravitational lensing power spectrum from CMB power spectra to the Planck satellite data. This method allows analysis of the tension between the temperature power spectrum and lens reconstruction in a model independent way. Even when allowing for arbitrary variations in the lensing power spectrum, the tension remains at the 2.4 sigma level. By separating the lensing and unlensed high redshift information in the CMB power spectra, also show that under LCDM the two are in tension at a similar level whereas the unlensed information is consistent with lensing reconstruction. These anomalies are driven by the smoother acoustic peaks relative to LCDM at ell~1250-1500. Both tensions relax slightly when polarization data are considered. This technique also isolates the one aspect of the lensing power spectrum that the Planck CMB power spectra currently constrain and can be straightforwardly generalized to future data when CMB power spectra constrain multiple aspects of lensing which are themselves correlated with lensing reconstruction.
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