Quantum Strings and the AdS4/CFT3 Interpolating Function

The existence of a nontrivial interpolating function h(\lambda) is one of the novel features of the new AdS4/CFT3 correspondence involving ABJM theory. At strong coupling, most of the investigation of semiclassical effects so far has been for strings in the AdS4 sector. Several cutoff prescriptions have been proposed, leading to different predictions for the constant term in the expansion h(\lambda)=\sqrt{\lambda/2} + c + ... . We calculate quantum corrections for giant magnons, using the algebraic curve, and show by comparing to the dispersion relation that the same prescriptions lead to the same values of c in this CP3 sector. We then turn to finite-J effects, where a comparison with the Luescher F-term correction shows a mismatch for one of the three sum prescriptions. We also compute some dyonic and higher F-terms for future comparisons.Comment: 30 pages, 1 figure, 1 table. v2 has minor improvements to the text, and extra references. v3 has further textual changes, version to appear in JHE

Power density of a bare electrodynamic tether generator

The maximum performance of bare electrodynamic tethers as power generating systems under OML-theory is analyzed. Results show that best performance in terms of power density is achieved by designing the tether in such a way to increase ohmic impedance with respect to plasma contact impedance, hence favoring longer and thinner tethers. In such condition the corresponding optimal value of the load impedance is seen to approach the ohmic impedance of the conducting tether. At the other extreme, when plasma contact impedance dominates (which is not optimal but can be relevant for some applications) optimum power generation is found by matching the load impedance with an effective tether-plasma contact impedance whose expression is derived

Optimal 3D orbit corrections in curvilinear coordinates

The minimum-time, constant-thrust orbit correction between two close non-coplanar circular orbits is studied using a relative motion formulation in curvilinear coordinates. The associated optimal control problem in the thrust orientation is tackled using the direct method to numerically solve a diverse set of problems for varying orbital radius and inclination. Additionally, an analytical estimate for the minimum-time inclination change maneuver is obtained. Fundamental changes in the structure of the solution and objective function are high-lighted depending on the relation between the required radial displacement, inclination change and available thrust

Low-thrust trajectory optimization in Dromo variables

The Dromo orbital propagator was recently introduced by Peldez et al., and has been under active development. It has proven to be an excellent propagation tool, both in terms of accuracy and computational cost. In this article, we explore its applicability to the solution of optimal control problem in low-thrust missions. To this end, an optimal control formulation based in Dromo and a direct transcription method is used to solve several LEO-GEO and escape from Earth problems; the obtained results clearly show the suitability of this orbital propagator for such purposes

Optimal low thrust orbit correction in curvilinear coordinates

The minimum-time, constant-thrust transfer between two close, coplanar, quasi-circular orbits is studied using a novel non-linear formulation of relative motion in curvilinear coordinates. The Optimal Control Problem in the thrust orientation angle is treated from a quantitative and qualitative point of view, using the direct and indirect methods respectively. The former yields numerical solutions for a wide range of thrust parameters, while a better understanding of the physics is achieved seeking for an approximate solution of the latter. Fundamental changes in the structure of the solution with the thrust parameter are identified

Participation in the Analysis of the Far-Infrared/Submillimeter Interferometer

We have contributed to the development of the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) by analyzing various aspects related to the tethers that connect the spacecraft of this space interferometer. We have focused our analysis on key topics as follows: (a) helping in the configuration selection; (b) computing the system eigenfrequencies as a function of baseline length; (c) developing techniques and conceptual design of devices for damping the tether oscillations; (d) carrying out numerical simulations of tethered formation to assess the effects of environmental perturbations upon the baseline length variation; (e) devising control laws for fast retargeting of the interferometer at moderate baseline lengths; (f) estimating the survivability to micrometeoroid impacts of a tether at L2; and (g) developing a conceptual design of a high-strength and survivable tether

Real and Virtual Bound States in L\"uscher Corrections for CP3 Magnons

We study classical and quantum finite-size corrections to giant magnons in AdS_4 x CP^3 using generalised L\"uscher formulae. L\"uscher F-terms are organised in powers of the exponential suppression factor exp(-Delta/2h)^m, and we calculate all terms in this series, matching one-loop algebraic curve results from our previous paper arXiv:1006.2174. Starting with the second term, the structure of these terms is different to those in AdS_5 x S^5 thanks to the appearance of heavy modes in the loop, which can here be interpreted as two-particle bound states in the mirror theory. By contrast, physical bound states can represent dyonic giant magnons, and we also calculate F-terms for these solutions. L\"uscher mu-terms, suppressed by exp(-Delta/E), instead give at leading order the classical finite-size correction. For an elementary dyonic giant magnon, we recover the correction given by arXiv:0903.3365. We then extend this to calculate the next term in 1/h, giving a one-loop prediction. Finally we also calculate F-terms for the various composite giant magnons, RP^3 and `big', again finding agreement to all orders.Comment: 33 pages and 3 figures. v3 adds new section treating F-terms of all orders; version to appear in J. Phys.

Accurate analytical approximation of asteroid deflection with constant tangential thrust

We present analytical formulas to estimate the variation of achieved deflection for an Earth-impacting asteroid following a continuous tangential low-thrust deflection strategy. Relatively simple analytical expressions are obtained with the aid of asymptotic theory and the use of Peláez orbital elements set, an approach that is particularly suitable to the asteroid deflection problem and is not limited to small eccentricities. The accuracy of the proposed formulas is evaluated numerically showing negligible error for both early and late deflection campaigns. The results will be of aid in planning future low-thrust asteroid deflection mission