Locations of Atmospheric Photoelectron Energy Peaks Within the Mars Environment

By identifying peaks in the photoelectron spectrum produced by photoionization of CO₂ in the Martian atmosphere, we have conducted a pilot study to determine the locations of these photoelectrons in the space around Mars. The significant result of this study is that these photoelectrons populate a region around Mars bounded externally by the magnetic pileup boundary, and internally by the lowest altitude of our measurements (∼250 km) on the dayside and by a cylinder of approximately the planetary radius on the nightside. It is particularly noteworthy that the photoelectrons on the nightside are observed from the terminator plane tailward to a distance of ∼3 R _M, the Mars Express apoapsis. The presence of the atmospherically generated photoelectrons on the nightside of Mars may be explained by direct magnetic field line connection between the nightside observation locations and the Martian dayside ionosphere. Thus the characteristic photoelectron peaks may be used as tracers of magnetic field lines for the study of the magnetic field configuration and particle transport in the Martian environment.     

The Geophysics of Mercury: Current Status and Anticipated Insights from the MESSENGER Mission

Current geophysical knowledge of the planet Mercury is based upon observations from ground-based astronomy and flybys of the Mariner 10 spacecraft, along with theoretical and computational studies. Mercury has the highest uncompressed density of the terrestrial planets and by implication has a metallic core with a radius approximately 75% of the planetary radius. Mercury’s spin rate is stably locked at 1.5 times the orbital mean motion. Capture into this state is the natural result of tidal evolution if this is the only dissipative process affecting the spin, but the capture probability is enhanced if Mercury’s core were molten at the time of capture. The discovery of Mercury’s magnetic field by Mariner 10 suggests the possibility that the core is partially molten to the present, a result that is surprising given the planet’s size and a surface crater density indicative of early cessation of significant volcanic activity. A present-day liquid outer core within Mercury would require either a core sulfur content of at least several weight percent or an unusual history of heat loss from the planet’s core and silicate fraction. A crustal remanent contribution to Mercury’s observed magnetic field cannot be ruled out on the basis of current knowledge. Measurements from the MESSENGER orbiter, in combination with continued ground-based observations, hold the promise of setting on a firmer basis our understanding of the structure and evolution of Mercury’s interior and the relationship of that evolution to the planet’s geological history.     

Launch and Early Operation of the MESSENGER Mission

On August 3, 2004, at 2:15 a.m. EST, the MESSENGER mission to Mercury began with liftoff of the Delta II 7925H launch vehicle and 1,107-kg spacecraft including seven instruments. MESSENGER is the seventh in the series of NASA Discovery missions, the third to be built and operated by The Johns Hopkins University Applied Physics Laboratory (JHU/APL) following the Near Earth Asteroid Rendezvous (NEAR) Shoemaker and Comet Nucleus Tour (CONTOUR) missions. The MESSENGER team at JHU/APL is using efficient operations approaches developed in support of the low-cost NEAR and CONTOUR operations while incorporating improved approaches for reducing total mission risk. This paper provides an overview of the designs and operational practices implemented to conduct the MESSENGER mission safely and effectively. These practices include proven approaches used on past JHU/APL operations and new improvements implemented to reduce risk, including adherence to time-proven standards of conduct in the planning and implementation of the mission. This paper also discusses the unique challenges of operating in orbit around Mercury, the closest planet to the Sun, and what specific measures are being taken to address those challenges.     

应用绿色半导体量子点进行乳腺癌原位成像

乳腺癌是癌症中引起妇女死亡的首要因素。本文采用绿色量子点作为荧光显色材料，建立了一种用于早期乳腺癌诊断的原位成像技术。利用生物素标记的抗HER2／neu抗体与乳腺癌细胞表面表达的HER2结合的特点，然后用偶联绿色量子点的链霉亲和素作为荧光检测标记物，与HER2抗原抗体复合物中的生物素发生特异结合，检测出乳腺癌细胞的存在。结果表明，在荧光显微镜下用绿色量子点原位显色的乳腺癌细胞，相对有机染料组显色亮度增强，故检测灵敏度有所提高。     

Sandwich module prototype progress for space solar power

Space solar power (SSP) has been broadly defined as the collection of solar energy in space and its wireless transmission for use on earth. This approach potentially gives the benefit of provision of baseload power while avoiding the losses due to the day/night cycle and tropospheric effects that are associated with terrestrial solar power. Proponents have contended that the implementation of such systems could offer energy security, environmental, and technological advantages to those who would undertake their development. Among recent implementations commonly proposed for SSP, the modular symmetrical concentrator (MSC) and other modular concepts have received considerable attention. Each employs an array of modules for performing conversion of concentrated sunlight into microwaves or laser beams for transmission to earth. While prototypes of such modules have been designed and developed previously by several groups, none have been subjected to the challenging conditions inherent to the space environment and the possible solar concentration levels in which an array of modules might be required to operate. The research described herein details our team's efforts in the development of photovoltaic arrays, power electronics, microwave conversion electronics, and antennas for microwave-based “sandwich” module prototypes. The implementation status and testing results of the prototypes are reviewed.     

Upstream of Saturn and Titan

The formation of Titan??s induced magnetosphere is a unique and important example in the solar system of a plasma-moon interaction where the moon has a substantial atmosphere. The field and particle conditions upstream of Titan are important in controlling the interaction and also play a strong role in modulating the chemistry of the ionosphere. In this paper we review Titan??s plasma interaction to identify important upstream parameters and review the physics of Saturn??s magnetosphere near Titan??s orbit to highlight how these upstream parameters may vary. We discuss the conditions upstream of Saturn in the solar wind and the conditions found in Saturn??s magnetosheath. Statistical work on Titan??s upstream magnetospheric fields and particles are discussed. Finally, various classification schemes are presented and combined into a single list of Cassini Titan encounter classes which is also used to highlight differences between these classification schemes.     

The dynamics and control of the CubeSail mission: A solar sailing demonstration

The CubeSail mission is a low-cost demonstration of the UltraSail solar sailing concept (, ,  and ), using two near-identical CubeSat satellites to deploy a 260 m-long, 20 m² reflecting film. The two satellites are launched as a unit, detumbled, and separated, with the film unwinding symmetrically from motorized reels. The conformity to the CubeSat specification allows for reduction in launch costs as a secondary payload and utilization of the University of Illinois-developed spacecraft bus. The CubeSail demonstration is the first in a series of increasingly-complex missions aimed at validating several spacecraft subsystems, including attitude determination and control, the separation release unit, reel-based film deployment, as well as the dynamical behavior of the sail and on-orbit solar propulsion. The presented work describes dynamical behavior and control methods used during three main phases of the mission. The three phases include initial detumbling and stabilization using magnetic torque actuators, gravity-gradient-based deployment of the film, and steady-state film deformations in low Earth orbit in the presence of external forces of solar radiation pressure, aerodynamic drag, and gravity-gradient.     

Low-Cost Operation of the ORBCOMM Satellite Constellation

Financial pressures are forcing organizations to minimize operations costs. Although the easiest way to achieve this goal is simply to reduce operational requirements, often this is not possible. Therefore, automation must be employed. This paper discusses the system trade-offs that must be performed to maximize the impact of automation efforts. The discussion begins with the development of generic automation guidelines. Since many automation issues are program-specific, the paper addresses the application of these principles to operation of the ORBCOMM satellite constellation. This example demonstrates how automation can be used to produce a highly efficient satellite operations system.     

Mars Global MHD Predictions of Magnetic Connectivity Between the Dayside Ionosphere and the Magnetospheric Flanks

Atmospheric photoelectrons have been observed well above the ionosphere of Mars by the ASPERA-3 ELS instrument on Mars Express. To systematically interpret these observations, field lines from two global MHD simulations were analyzed for connectivity to the dayside ionosphere (allowing photoelectron escape). It is found that there is a hollow cylinder behind the planet from 1–2 R _M away from the Mars-Sun line that has a high probability of containing magnetic field lines with connectivity to the dayside ionosphere. These results are in complete agreement with the ELS statistics. It is concluded that the high-altitude photoelectrons are the result of direct magnetic connectivity to the dayside at the moment of the measurement, and no extra trapping or bouncing mechanisms are needed to explain the data.     

Degradation of cyanobacterial biosignatures by ionizing radiation

Primitive photosynthetic microorganisms, either dormant or dead, may remain today on the martian surface, akin to terrestrial cyanobacteria surviving endolithically in martian analog sites on Earth such as the Antarctic Dry Valleys and the Atacama Desert. Potential markers of martian photoautotrophs include the red edge of chlorophyll reflectance spectra or fluorescence emission from systems of light-harvesting pigments. Such biosignatures, however, would be modified and degraded by long-term exposure to ionizing radiation from the unshielded cosmic ray flux onto the martian surface. In this initial study into this issue, three analytical techniques--absorbance, reflectance, and fluorescence spectroscopy--were employed to determine the progression of the radiolytic destruction of cyanobacteria. The pattern of signal loss for chlorophyll reflection and fluorescence from several biomolecules is characterized and quantified after increasing exposures to ionizing gamma radiation. This allows estimation of the degradation rates of cyanobacterial biosignatures on the martian surface and the identification of promising detectable fluorescent break-down products.