Debris swarms seen by SMEI

The large 3° × 60° fields-of-view of the Solar Mass Ejection Imager (SMEI) instruments are oriented on the stabilized Coriolis satellite to image most of the sky each Sun-synchronous orbit. Besides observing coronal mass ejections, the SMEI mission objective, SMEI also has detected a plethora of Earth-orbiting satellites (resident space objects or RSOs) brighter than ∼8th magnitude at a rate of about 1 per minute. Occasionally, SMEI sees an RSO swarm: a sudden onset of a large number of RSOs, many more than the nominal rate, upto dozens detected in a 4-s frame. These swarms usually last for a few minutes. A sample of six such RSO ensembles is analyzed in this paper in which the distance and the direction of the velocity vector for individual objects are estimated. We present the observational evidence indicating that the swarms must be near-field objects traveling in orbits near that of Coriolis, and that the relatively speeds between the objects and Coriolis are low. Further, analyses indicate that the RSOs are quite close (<20 m) and are generally moving radially away from the satellite. The predicted encounter geometries for Coriolis passing through or near a small debris cloud is, generally, quite inconsistent with the observations. The most likely explanation consistent with the observations is that SMEI is seeing debris being ejected from the Coriolis spacecraft itself. An analysis of distance and brightness for a subset of the RSOs indicates that the median diameter of the debris particles is ∼80 μm.     

Optimal Digital Beam Splitting for Radar Beacon Systems

Beam splitting for a radar beacon system that scans in azimuth is investigated from a theoretical viewpoint. The video output is quantized into two levels corresponding to a detection and no detection. Further, the antenna sensitivity profile is described by sin ?/?. For this system, a digital method of beam splitting that minimizes angular error is developed. Prior information about the probable location of targets can be included. Both Bayesian and minimax approaches are developed. The minimax estimate of the target azimuth is the average of the angles at which beacon signals are detected. The antenna beam can be interpolated by a factor of 10 when the signal power is 3 dB above the noise and without prior azimuth information The interaction of beam splitting and detection is discussed.     

Attitude and orbit control systems for the LISA Pathfinder mission

The main purpose of the LISA Pathfinder mission is to provide in-orbit validation of the critical technologies necessary for LISA (Laser Interferometer Space Antenna), aiming at detecting gravitational waves generated by very massive objects such as black holes. The spacecraft consists of a Science Module (SCM) and a Propulsion Module (PRM). The former performs the science experiment, and the later provides the propulsive capability to raise the spacecraft from the injection orbit to the operational orbit at around L1 and is then separated from the former. The Spacecraft Attitude and Orbit Control System (AOCS) is actually composed of three distinct systems to fulfill the needs of the whole mission: – Composite AOCS, used to reach L1, aims at raising the Perigee through a succession of about 10 boosts performed with high thrust chemical propulsion; – Micro-propulsion AOCS takes over once the separation of the SCM from PRM has occurred and is based on micro-propulsion systems (micro-Newton electrical thrusters); – Drag-Free Attitude Control System (DFACS) is then used to perform science experiments. This article provides a comprehensive overview of the AOCS architecture, requirements, selected sensors and actuators, system design & evolution, and achieved performances. It focuses in particular on the Composite AOCS and the Micro-propulsion AOCS and will analyze the challenges of using micro-Newton electric propulsion.     

On the nature of coronal loops above the quiet sun network

The structure and dynamics of a box in a stellar corona can be modeled employing a 3D MHD model for different levels of magnetic activity. Depending on the magnetic flux through the surface the nature of the resulting coronal structures can be quite different. We investigate a model of an active region for two sunspots surrounded by magnetic field patches comparable in magnetic flux to the sunspots. The model results in emission from the model corona being concentrated in loop structures. In Gudiksen and Nordlund (2005) the loops seen in EUV and X-ray emission outline the magnetic field, following the general paradigm. However, in our model, where the magnetic field is far from a force-free state, the loops seen in X-ray emission do not follow the magnetic field lines. This result is of interest especially for loops as found in areas where the magnetic field emerging from active regions interacts with the surrounding network.     

Experimental and numerical research on the aerodynamics of unsteady moving aircraft

For the experimental determination of the dynamic wind tunnel data, a new combined motion test capability was developed at the German–Dutch Wind Tunnels DNW for their 3 m Low Speed Wind Tunnel NWB in Braunschweig, Germany, using a unique six degree-of-freedom test rig called ‘Model Positioning Mechanism’ (MPM) as an improved successor to the older systems. With that cutting-edge device, several transport aircraft configurations including a blended wing body configuration were tested in different modes of oscillatory motions roll, pitch and yaw as well as delta-wing geometries like X-31 equipped with remote controlled rudders and flaps to be able to simulate realistic flight maneuvers, e.g., a Dutch Roll. This paper describes the motivation behind these tests and the test setup and in addition gives a short introduction into time accurate maneuver-testing capabilities incorporating models with remote controlled control surfaces. Furthermore, the adaptation of numerical methods for the prediction of dynamic derivatives is described and some examples with the DLR-F12 configuration will be given. The calculations are based on RANS-solution using the finite volume parallel solution algorithm with an unstructured discretization concept (DLR TAU-code).     

Estimation of Galactic Cosmic Ray exposure inside and outside the Earth’s magnetosphere during the recent solar minimum between solar cycles 23 and 24

The evidently low solar activity observed between solar cycles 23 and 24 during the years 2008–2010 led to a substantial increase in the Galactic Cosmic Ray (GCR) intensity in comparison with preceding solar minima. As the GCRs consist of highly-ionizing charged particles having the potential to cause biological damage, they are a subject of concern for manned missions to space. With the enhanced particle fluxes observed between 2008 and 2010, it is reasonable to assume that the radiation exposure from GCR must have also increased to unusually high levels. In this paper, the GCR exposure outside and inside the Earth’s magnetosphere is numerically calculated for time periods starting from 1970 to the end of 2011 in order to investigate the increase in dose levels during the years 2008–2010 in comparison with the last three solar minima. The dose rates were calculated in a water sphere, used as a surrogate for the human body, either unshielded or surrounded by aluminium shielding of 0.3, 10 or 40 g/cm².     

An experimental study of elastic properties of dragonfly-like flapping wings for use in biomimetic micro air vehicles (BMAVs)

This article studies the elastic properties of several biomimetic micro air vehicle (BMAV) wings that are based on a dragonfly wing. BMAVs are a new class of unmanned micro-sized air vehicles that mimic the flapping wing motion of flying biological organisms (e.g., insects, birds, and bats). Three structurally identical wings were fabricated using different materials: acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and acrylic. Simplified wing frame structures were fabricated from these materials and then a nanocomposite film was adhered to them which mimics the membrane of an actual dragonfly. These wings were then attached to an electromagnetic actu-ator and passively flapped at frequencies of 10–250 Hz. A three-dimensional high frame rate imag-ing system was used to capture the flapping motions of these wings at a resolution of 320 pixels × 240 pixels and 35000 frames per second. The maximum bending angle, maximum wing tip deflection, maximum wing tip twist angle, and wing tip twist speed of each wing were measured and compared to each other and the actual dragonfly wing. The results show that the ABS wing has considerable flexibility in the chordwise direction, whereas the PLA and acrylic wings show better conformity to an actual dragonfly wing in the spanwise direction. Past studies have shown that the aerodynamic performance of a BMAV flapping wing is enhanced if its chordwise flexibility is increased and its spanwise flexibility is reduced. Therefore, the ABS wing (fabricated using a 3D printer) shows the most promising results for future applications.     

Search for the OH (X(2)Pi) Meinel band emission in meteors as a tracer of mineral water in comets: detection of N(2)(+) (A-X)

We report the discovery of the N(2)(+) A-X Meinel band in the 780-840 nm meteor emission from two Leonid meteoroids that were ejected less than 1000 years ago by comet 55P/Tempel-Tuttle. Our analysis indicates that the N(2)(+) molecule is at least an order of magnitude less abundant than expected, possibly as a result of charge transfer reactions with meteoric metal atoms. This new band was found while searching for rovibrational transitions in the X(2)Pi electronic ground state of OH (the OH Meinel band), a potential tracer of water bound to minerals in cometary matter. The electronic A-X transition of OH has been identified in other Leonid meteors. We did not detect this OH Meinel band, which implies that the excited A state is not populated by thermal excitation but by a mechanism that directly produces OH in low vibrational levels of the excited A(2)Sigma state. Ultraviolet dissociation of atmospheric or meteoric water vapor is such a mechanism, as is the possible combustion of meteoric organics.     

Bumpy ride back to space

Plans for U.S. return to the International Space Station via STS-114 are described with emphasis on safety of flight hardware and safety of the space station and the space shuttle.