Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions

Plasmaspheric density structures have been studied since the discovery of the plasmasphere in the late 1950s. But the advent of the Cluster and Image missions in 2000 has added substantially to our knowledge of density structures, thanks to the new capabilities of those missions: global imaging with Image and four-point in situ measurements with Cluster. The study of plasma sources and losses has given new results on refilling rates and erosion processes. Two-dimensional density images of the plasmasphere have been obtained. The spatial gradient of plasmaspheric density has been computed. The ratios between H⁺, He⁺ and O⁺ have been deduced from different ion measurements. Plasmaspheric plumes have been studied in detail with new tools, which provide information on their morphology, dynamics and occurrence. Density structures at smaller scales have been revealed with those missions, structures that could not be clearly distinguished before the global images from Image and the four-point measurements by Cluster became available. New terms have been given to these structures, like “shoulders”, “channels”, “fingers” and “crenulations”. This paper reviews the most relevant new results about the plasmaspheric plasma obtained since the start of the Cluster and Image missions.     

Evolution of executive branch space policy making

This paper assesses the impacts that changes in the US presidency have had on the civilian space program during the post-Apollo period. It suggests that the White House has lost influence over space issues relative to other interested sectors. The primary factors causing this are a long-term shift to lower priority for these issues, and an inevitable widening of the scope of influence over this sector of activity. Key post-Apollo decisions are discussed for their substantive content and also for what they reveal about the extent to which the president chose to be involved. These findings have implications across all science and technology issue areas as the USA, in the aftermath of the Cold War, reexamines its post-World War II social contract with science.     

Electronics brain design for advanced microspacecraft

A brief history of NASA robotic spacecraft computing architectures is given. Changing needs driving changes in features (10x reduction in cost, various increases in capability, 10x to 100x reduction in power, mass and volume) for spacecraft computing are discussed. An architecture which addresses these changes is proposed. Finally, future directions of exploration for this spacecraft computing architecture are considered.     

Comparison analyses on the 150 × 150 lunar gravity field models by gravity/topography admittance,correlation and precision orbit determination

We analyzed the 150 × 150 lunar gravity field models, LP150Q, GLGM-3 and SGM150, using the power spectrum on the lunar nearside and farside, the lunar global and localized gravity/topography admittance and correlation, and Chang’E-2 precision orbit determination to investigate which model is a more effective tool to estimate geophysical parameters and determine the lunar satellite precision orbit. Results indicate that all gravity field models can be used to estimate the lunar geophysical parameters of the nearside of the Moon. However, SGM150 is better in such computation of the farside. Additionally, SGM150 is shown to be the most useful model for determining the lunar satellite orbit.     

The Effect of Ground Reflections and Scattering on an Interferometer Direction Finder

The azimuth and elevation angles of an airborne beacon transmitter can be determined using a direction finder comprised of two orthogonal interferometers located near the earth's surface. In this paper we consider the reflection of the incident electromagnetic field by the earth's surface and the resultant effect on the direction-finding system. The analysis yields an upper bound or limit to the interferometer phase error and the corresponding error in bearing angle that can result because of specular reflection and diffuse scattering.     

Cancellation of Unwanted Spectral Components in an FM Multivibrator System

The performance of FM multivibrator systems for high quality communications applications is limited by the presence of unwanted spectral components. A theory is presented for an improved system in which unwanted spectral components are cancelled, achieved by generating a cancelling component in a square-law device. The cancelling component tracks the unwanted component in both frequency and amplitude over a wide bandwidth of signal frequencies. Reductions in magnitude of the unwanted components by at least 16 dB are predicted; reductions of better than 14 dB have been achieved in practice.     

是分开月球和火星的时候了

给出了国外对于载人深空探测的另外一个角度的看法，指出必须充分认识到载人火星探测的风险和成本，应优先考虑发展空间能力，解决社会民生问题。     

Electrical Charging of Volcanic Plumes

Many explosive terrestrial volcanic eruptions are accompanied by lightning and other atmospheric electrical phenomena. The plumes produced generate large perturbations in the surface atmospheric electric potential gradient and high charge densities have been measured on falling volcanic ash particles. The complex nature of volcanic plumes (which contain gases, solid particles, and liquid drops) provides several possible charging mechanisms. For plumes rich in solid silicate particles, fractoemission (the ejection of ions and atomic particles during fracture events) is probably the dominant source of charge generation. In other plumes, such as those created when lava enters the sea, different mechanisms, such as boiling, may be important. Further charging mechanisms may also subsequently operate, downwind of the vent. Other solar system bodies also show evidence for volcanism, with activity ongoing on Io. Consequently, volcanic electrification under different planetary scenarios (on Venus, Mars, Io, Moon, Enceladus, Tethys, Dione and Triton) is also discussed.     

The real aerospace plane

In this article reproduced from Aerospace, Spring 1986, James Haggerty reports on the US National Aerospace Plane (NASP) research programme. NASP is a joint Department of Defense/NASA programme to develop and demonstrate the technologies for a revolutionary class of aerospace vehicles, powered by airbreathing engines, that would have the capability to take off from and land horizontally on standard runways, cruise in the atmosphere at hypersonic speeds, or fly into low-Earth orbit. The Air Force has been named executive agency for the programme. NASA is charged with overall technology direction. Other DoD participants include DARPA, the Navy and the Strategic Defense Initiative Organization.

In April 1986, the USAF awarded development contracts to seven aerospace manufacturing firms. Contracts for air-frame design went to Boeing Aerospace Company, Lockheed Advanced Aeronautics Company, General Dynamics Corporation, McDonnell Douglas Corporation and Rockwell International Corporation. General Electric Company and Pratt & Whitney Division of United Technologies were awarded propulsion contracts.