The first SETI observations with the Allen telescope array

The Search for ExtraTerrestrial Intelligence (SETI) finally has its own full-time telescope. The Allen telescope array (ATA) in Northern California was dedicated on October 11, 2007. This array, which will eventually be composed of 350 small radio antennas, each 6.1 m in diameter, is being built as a partnership between the SETI Institute and the University of California Radio Astronomy Laboratory. Last October, Paul G. Allen (who provided the funds for the technology development and the first phase of array construction) pushed a silver button and all 42 antennas of the current ATA-42 slewed to point in the direction of the distant galaxy M81. Specialized electronic backend detectors attached to the ATA began making a radio map of that galaxy and simultaneously began SETI observations of HIP48573, a G5V star near M81 on the sky and a distance of 264 light years from Earth. The Allen telescope array will greatly improve the speed of conducting SETI searches over the next few decades, and it will allow a suite of different search strategies to be undertaken. This paper summarizes some of the earliest SETI observations from the array, and describes the search strategies currently being planned.     

Design concepts for the first 40 km a key step for the space elevator

The Marine Node for the Space Elevator Infrastructure is the base for all activities to load and unload the cargo and climbers. As the basic design of the space elevator power system is solar power only, the first 40 km is hazardous to operations and demands enclosed packaging of fragile tether climbers. A significant question is: how do we place a full-up tether climber, driven by solar power, above the atmosphere? Two approaches, starting at the Marine Node, allow the tether climber to initiate the climb with solar energy above the atmosphere. The third viable approach is to provide a platform at altitude for initiation of tether climb. These approaches would enable solar power to be the source of energy for climbing. The three approaches are:     

NaK release model for MASTER-2009

Sodium–potassium droplets from the primary coolant loop of Russian orbital reactors have been released into space. These droplets are called NaK droplets. Sixteen nuclear powered satellites of the type RORSAT launched between 1980 and 1988 activated a reactor core ejection system, mostly between 900 and 950 km altitude. The core ejection causes an opening of the primary coolant loop. The liquid coolant consists of eutectic sodium–potassium alloy and has been released into space during these core ejections. The NaK coolant has been forming droplets up to a diameter of 5.5 cm. NaK droplets have been modeled before in ESA's MASTER Debris and Meteoroid Environment Model. The approach is currently revised for the MASTER-2009 upgrade. A mathematical improvement is introduced by substituting the current size distribution function by the modified Rosin–Rammler equation. A bimodal size distribution is derived which is based on the modified mass based Rosin–Rammler equation. The equation is modified by truncating the size range and normalizing over the finite range between the size limits of the smallest and the biggest droplet. The parameters of the model are introduced and discussed. For the validation of the NaK release model, sixteen release events are simulated. The resulting size distribution is compared with radar measurement data. The size distribution model fits well with revised published measurement data of radar observations. Results of orbit propagation simulation runs are presented in terms of spatial density.     

Spacecraft detumbling using movable telescoping appendages

The dynamics of detumbling a randomly spinning spacecraft using externally mounted, movable telescoping appendages are studied both analytically and numerically. Two types of telescoping appendages are considered: (a) where an end mass is mounted at the end of an (assumed) massless boom; and (b) where the appendage is assumed to consist of a uniformly distributed homogeneous mass throughout its length. From an application of Lyapunov's second method, boom extension maneuvers can be determined to approach either of two desired final states: close to a zero inertial angular velocity state and a final spin rate about only one of the principal axes. Recovery dynamics are evaluated analytically for the case of symmetrical deployment. Numerical examination of other asymmetrical cases verifies the practicality of using movable appendages to recover a randomly tumbling spacecraft.     

Digital LQR control scheme to maintain the separation distance of the NASA benchmark tetrahedron constellation

In previous papers, the authors developed an active control scheme based on the linear quadratic regulator (LQR) to maintain the separation distance constraints of the NASA benchmark tetrahedron constellation. Two different active control schemes were used to maintain the separation distance constraints, but one control scheme applied to every eccentricity of the NASA benchmark problem. Through this paper, the digital LQR strategy will be developed with this active control scheme to maintain the separation distance conditions of the tetrahedron constellation. The motion of a pair of satellites in an elliptical orbit about the Earth is defined by the linearized Tschauner–Hempel (TH) equations. These equations will be defined discretely in the true anomaly angle for the development of the digital control scheme. In summary, the digital LQR approach will be implemented and studied to determine how this active control scheme maintains the separation distance constraints for different specific sizes of the NASA benchmark tetrahedron constellation.     

Influence of solar-geomagnetic disturbances on SABER measurements of 4.3 μm emission and the retrieval of kinetic temperature and carbon dioxide

Thermospheric infrared radiance at 4.3 μm is susceptible to the influence of solar-geomagnetic disturbances. Ionization processes followed by ion-neutral chemical reactions lead to vibrationally excited NO⁺ (i.e., NO⁺(v)) and subsequent 4.3 μm emission in the ionospheric E-region. Large enhancements of nighttime 4.3 μm emission were observed by the TIMED/SABER instrument during the April 2002 and October–November 2003 solar storms. Global measurements of infrared 4.3 μm emission provide an excellent proxy to observe the nighttime E-region response to auroral dosing and to conduct a detailed study of E-region ion-neutral chemistry and energy transfer mechanisms. Furthermore, we find that photoionization processes followed by ion-neutral reactions during quiescent, daytime conditions increase the NO⁺ concentration enough to introduce biases in the TIMED/SABER operational processing of kinetic temperature and CO₂ data, with the largest effect at summer solstice. In this paper, we discuss solar storm enhancements of 4.3 μm emission observed from SABER and assess the impact of NO⁺(v) 4.3 μm emission on quiescent, daytime retrievals of Tk/CO₂ from the SABER instrument.     

Aerodynamics of cross-flow fans and their application to aircraft propulsion and flow control

Cross-flow fans offer unique opportunities for distributed propulsion and flow control due to their potential for spanwise integration in aircraft wings. The fan may be fully or partially embedded within the wing using a variety of possible configurations. Its inlet may be used to ingest the boundary-layer flow, and its high-energy exhaust flow may be injected into the wake at the wing trailing edge for drag reduction or vectored thrust. Cross-flow fans are high-pressure coefficient machines, so they can be diametrically compact. However, their efficiency is fundamentally limited by unavoidable recirculation flows within the impeller at all flight speeds, and by additional compressibility losses at high speeds. This article reviews the fundamental aerodynamics and flow regions of cross-flow fans using a simple mean-line analysis to examine the basic energy transfer and loss processes. Experimental data for fans intended for aircraft application are then reviewed and compared to calculations using unsteady Navier–Stokes methods, showing the state-of-the art in flow field and performance prediction capability. Alternative prediction methods where blade action is modeled in terms of body-force or vortex elements are discussed, including challenges in handling arbitrary non-uniform, unsteady blade flows for various design configurations. The article concludes with a review of cross-flow fan propulsion and flow control concepts that have been investigated by various researchers, and with discussions on future challenges in their application.     

Observations of Climate Variability – Discussion Session 3a

Space Science Reviews -     

The Theory of Gamma-Ray Bursts

This chapter gives a brief review on the theory of gamma-ray bursts (GRBs), including the models of multi-messengers (e.g., prompt multiwavelength electromagnetic emissions, high-energy neutrinos, ultra-high-energy cosmic rays, and gravitational waves) and central engines (in particular, mergers of binary neutron stars for short GRBs). For detailed reviews, please see (Piran in Phys. Rep. 314:575, 1999; Rev. Mod. Phys. 76:1143, 2004; Mészáros in Annu. Rev. Astron. Astrophys. 40:137, 2002; Rep. Prog. Phys. 69:2259, 2006; Zhang and Mészáros in Int. J. Mod. Phys. A 19:2385, 2004; Zhang in Chin. J. Astron. Astrophys. 7:1, 2007; Nakar in Phys. Rep. 442:166, 2007; Kumar and Zhang in Phys. Rep. 561:1, 2015).