Lunar mission aerobrake performance study

Nine lunar mission scenarios were developed to show the transfer vehicle performance benefits of aerobraking into low Earth orbit (LEO) upon Earth return as opposed to an all-propulsive maneuver. The initial mass in LEO (IMLEO) of the lunar transfer vehicle is considered the measure of vehicle performance. Four types of mission profiles in conjunction with two vehicle concepts were used to construct the scenarios. These nine scenarios were designed to represent a broad range of possible lunar missions so that a general knowledge base of aerobraking and lunar transfer vehicle performance levels could be obtained. Also discussed are the mass sensitivities of each transfer vehicle to changes in the selected design parameters: Isp, crew module mass, payload to surface, and aerobrake mass fraction. A parametric study was performed on two of the mission scenarios to help quantify the performance benefits by adding a set of drop tanks to the vehicle. The parametric study also provides partial derivatives which show the sensitivities of IMLEO to the four design parameters listed. A ranking is given based on vehicle performance

NAFTA and the changing pattern of state exports

The trade liberalization associated with NAFTA has affected the pattern of state exports by altering the origin as well as the destination of merchandise exports. We find that NAFTA has increased US merchandise exports to Mexico and Canada by just over 15 percent, and has increased total US merchandise exports by nearly 8 percent. We also find that although many states have seen large increases in exports to both Mexico and Canada, others have seen large decreases. NAFTA has also affected states’ exports to non-NAFTA regions of the world, tending to decrease exports to Europe and Latin America and increase exports to Asia. States in the northeast regions of the United States have seen the smallest increases in exports in the wake of NAFTA.North American Free Trade Agreement ; International trade

Ethnic networks and trade: intensive vs. extensive margins

Ethnic networks?as proxies for information networks?have been associated with higher levels of international trade. Previous research has not differentiated between the roles of these networks on the extensive and intensive margins. The present paper does so using a model with fixed effects, finding that ethnic networks increase trade on the intensive margin but not on the extensive margin.International trade ; Exports

Modeling Multi-Wavelength Stellar Astrometry. III. Determination of the Absolute Masses of Exoplanets and Their Host Stars

Astrometric measurements of stellar systems are becoming significantly more precise and common, with many ground and space-based instruments and missions approaching 1 microarcsecond precision. We examine the multi-wavelength astrometric orbits of exoplanetary systems via both analytical formulae and numerical modeling. Exoplanets have a combination of reflected and thermally emitted light that cause the photocenter of the system to shift increasingly farther away from the host star with increasing wavelength. We find that, if observed at long enough wavelengths, the planet can dominate the astrometric motion of the system, and thus it is possible to directly measure the orbits of both the planet and star, and thus directly determine the physical masses of the star and planet, using multi-wavelength astrometry. In general, this technique works best for, though is certainly not limited to, systems that have large, high-mass stars and large, low-mass planets, which is a unique parameter space not covered by other exoplanet characterization techniques. Exoplanets that happen to transit their host star present unique cases where the physical radii of the planet and star can be directly determined via astrometry alone. Planetary albedos and day-night contrast ratios may also be probed via this technique due to the unique signature they impart on the observed astrometric orbits. We develop a tool to examine the prospects for near-term detection of this effect, and give examples of some exoplanets that appear to be good targets for detection in the K to N infrared observing bands, if the required precision can be achieved.Comment: Accepted to the Astrophysical Journal. 9 pages, 6 figures, 1 table in emulateapj forma

Ethnic networks and U.S. exports

This paper provides new estimates of the effects of ethnic networks on U.S. exports. In line with recent research, our dataset is a panel of exports from U.S. states to 29 foreign countries. Our analysis departs from the literature in two ways, both of which show that previous estimates of the ethnic-network elasticity of trade are sensitive to the restrictions imposed on the estimated models. Our first departure is to control for unobserved heterogeneity with properly specified fixed effects, which we can do because our dataset contains a time dimension absent from previous studies. Our second departure is to remove the restriction that the network effect is the same for all ethnicities. We find that ethnic-network effects are much larger than has been estimated previously, although they are important only for a subset of countries.Exports ; Regional economics