外海上璀璨的明珠

在赫尔辛基外海的一串小岛上,芬兰城堡静静地矗立着。一眼望去,她无疑是外海上璀璨的明珠......芬兰城堡建于250多年前,是现存于世的海防军事要塞之一,且在规模上令人惊叹。1991年,芬兰城堡已经被联合国教科文组织列入了世界遗产名录。     

Investigation Into Cost-Effective Propulsion System Options for Small Satellites

The paper summarizes research into cost-effective propulsion system options for small satellites. Research into the primary cost drivers for propulsion systems is discussed and a process for resolving them is advanced. From this analysis, a new paradigm for understanding the total cost of propulsion systems is defined that encompasses nine dimensions – mass, volume, time, power, system price, integration, logistics, safety and technical risk. This paradigm is used to characterize all near-term propulsion technology options. From this effort, hybrid rockets emerges as a promising but underdeveloped technology with great potential for cost-effective application. A dedicated research program was completed to characterize this potential. This research demonstrated that hybrid rockets offer a safe, reliable upper stage option that is a versatile, cost-effective alternative to solid rocket motors. Finally, an innovative technique was derived to parametrically combine the diverse cost dimensions into a useful, quantifiable figure of merit for mission and research planning. Overall, it is shown that the most cost-effective solution is found by weighing all options along the nine dimensions of the cost paradigm within the context of a specific mission.     

Radiative damping of gravity waves in the solar atmosphere

The nonlocal character of the radiation field sianificantly modifies the radiative damping of perturbations in the solar photosphere. Gravity waves are not usually considered to exist in the solar photosphere because the radiative damping time, when based on the Newtonian approximation, is too short. However, this restriction does not apply to low order gravity waves. In fact, with the inclusion of nonlocal effects, the radiative damping for low order gravity waves becomes negative for some region in the photosphere and thus acts as a driving mechanism for gravity waves there.     

The Mercury Laser Altimeter Instrument for the MESSENGER Mission

The Mercury Laser Altimeter (MLA) is one of the payload science instruments on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, which launched on August 3, 2004. The altimeter will measure the round-trip time of flight of transmitted laser pulses reflected from the surface of the planet that, in combination with the spacecraft orbit position and pointing data, gives a high-precision measurement of surface topography referenced to Mercury’s center of mass. MLA will sample the planet’s surface to within a 1-m range error when the line-of-sight range to Mercury is less than 1,200 km under spacecraft nadir pointing or the slant range is less than 800 km. The altimeter measurements will be used to determine the planet’s forced physical librations by tracking the motion of large-scale topographic features as a function of time. MLA’s laser pulse energy monitor and the echo pulse energy estimate will provide an active measurement of the surface reflectivity at 1,064 nm. This paper describes the instrument design, prelaunch testing, calibration, and results of postlaunch testing.     

Nitrous oxide as a rocket propellant

Nitrous oxide is introduced as a multi-purpose propellant for spacecraft. Potential space applications of this propellant are given. Based on comparison to conventional systems, a multi-mode nitrous oxide propulsion concept is expected to deliver higher performance. Main features of a self-pressurising, nitrous oxide storage system are described. A nitrous oxide catalytic decomposition technique is suggested for restartable spacecraft propulsion. Up-to-date experimental results are presented. A conclusion describes the long-term feasibility of novel nitrous oxide propulsion option concepts.     

Design and Performance of the ICON EUV Spectrograph

We present the design, implementation, and on-ground performance measurements of the Ionospheric Connection Explorer EUV spectrometer, ICON EUV, a wide field (\(17^{\circ}\times 12^{\circ}\)) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54–88 nm, are the Oii emission lines at 61.6 nm and 83.4 nm. Its design, using a single optical element, permits a $0\stackrel{{}^{°}}{.}26$ imaging resolution perpendicular to the spectral dispersion direction with a large (\(12^{\circ} \)) acceptance parallel to the dispersion direction while providing a slit-width dominated spectral resolution of \(R\sim25\) at 58.4 nm. Pre-flight calibration shows that the instrument has met all of the science performance requirements.