Microwave landing system: a pilots point of view

The author describes the MLS installation on runway 19L at Mid-Continent Airport, Wichita, Kansas, which has been operational since mid-1987. He describes the MLS equipment installation in his aircraft, which is one of a number of aircraft in the Wichita area that have been equipped with MLS equipment and routinely utilize the system. He summarizes his operational experience with the system. He reports complete satisfaction and increased versatility as a result of the guidance information provided     

Angle of arrival estimation of coherent signals using an arraydoublet in motion

Shown here is how the estimation of signal parameters via relational invariance techniques (ESPRIT) algorithm may be used with a single pair of antennas in motion to estimate angles of arrival (AOA) for coherent signals. The approach exploits the Doppler frequency shifts caused by the doubler in motion. With this estimator, the number of signals that can be handled is not limited by the size of the array, as in the usual ESPRIT application, but by an adjustable parameter. A theoretical performance analysis of the estimator and typical examples showing the use of this estimator are given     

Radioactive satellites: Intact reentry and breakup by debris impact

There is a substantial mass of radioactive material in nuclear reactors or radioisotope thermal generators (RTGs) in orbit about the earth. This paper examines the reentry of intact nuclear fuel cores and RTGs and the fragmentation and subsequent radioactive debris cloud deposition and evolution resulting from the impact of orbital debris upon an orbiting reactor, fuel core, or RTG. To assess the intact reentry, decay rates and a predicted decay date using historical and projected orbital decay data, are estimated. The current NASA debris environment model is utilized to estimate impact rates and debris cloud evolution of a fragmentation event. Results of these analyses are compared and concepts are tendered which would tend to minimize the radiological debris hazard to personnel and structures both on the earth's surface and in low earth orbit.     

NASA力促国际合作共建月球基地

最近,NASA 公布了建设月球基地的初步方案和一个《全球探索战略》。《全球探索战略》的目的是鼓励世界各国参与未来的美国的月球探索和其他航天计划,以有效利用全球可用的知识和资源,推动人类对太空的发现和探索。力促国际合作NASA 对邀请国际伙伴和商业组织参与重返月球计划采取了一种开放态度,并希望它的这种态度可以最终导致在近地轨道之外的载人航天活动中形成一种广泛的合作形式。     

Networks of low-Earth orbit store-and-forward satellites

A slotted multiaccess protocol is proposed for networks of low-Earth orbit store-and-forward communications satellites. Networks of this type would provide communication between low cost geographically distributed Earth stations, and would be particularly attractive in areas where conventional terrestrial communications systems were not available. Applications of this type include data acquisition and remote process monitoring. The proposed protocol incorporates time division multiplexing (TDM) on the downlink, slotted Aloha with collision resolution on the uplink, and an automatic repeat request (ARQ) algorithm. Since the network connectivity is intermittent, analysis of networks of this type is difficult. Nevertheless, relationships among the performance parameters for a general network are deduced, and performance of three particular network configurations is studied via simulation     

EDISON: The next generation infrared space observatory

EDISON, a large-aperture, radiatively-cooled telescope, is proposed as the major international mission to follow the current generation of cryogenically-cooled infrared space telescopes. It is being studied at present as a 2.5–3.5 m mixed radiatively- and mechanically-cooled facility optimized to investigate the wavelength range 3–100+ m. This paper outlines the status of the project, discusses some aspects of a smaller-aperture precursor mission, and describes a portion of the baseline science mission.     

Fluctuating magnetic fields in the magnetosphere

The study of ULF waves in space has been in progress for about 12 years. However, because of numerous observational difficulties the properties of the waves in this frequency band (10^-3 to 1 Hz) are poorly known. These difficulties include the nature of satellite orbits, telemetry limitations on magnetometer frequency response and compromises between dynamic range and resolution. Despite the paucity of information, there is increasing recognition of the importance of these measurements in magnetospheric processes. A number of recent theoretical papers point out the roles such waves play in the dynamic behavior of radiation belt particles.At the present time the existing satellite observations of ULF waves suggest that the level of geomagnetic activity controls the types of waves which occur within the magnetosphere. Consequently, we consider separately quiet times, times of magnetospheric substorms and times of magnetic storms. Within each of these categories there are distinctly different wave modes distinguished by their polarization: either transverse or parallel to the ambient field. In addition, these wave phenomena occur in distinct frequency bands. In terms of the standard nomenclature of ground micropulsation studies ULF wave types observed in the magnetosphere include quiet time transverse — Pc 1, Pc 3, Pc 4, Pc 5 quiet time compressional — Pc 1 and Pi 1; substorm compressional Pi 1 and Pi 2; storm transverse — Pc 1; storm compressional Pc 4, 5. The satellite observations are not yet sufficient to determine whether the various bands identified in the ground data are equally appropriate in space.Publication No. 982. Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Calif. 90024.     

Data on and methodology for calculating space shuttle programme costs

This report presents data on the annual and total costs of NASA's Space Shuttle programme through fiscal year (FY) 1993. The total cost of the programme through FY 1993 is found to be $83.7 billion in 1992 dollars. This information has significance for pending policy decisions on the future of the Shuttle programme, its possible successors, and interrelated programmes, such as the Space Station.     

The USA and the 1985 space WARC

This article considers the US policy objectives at the forthcoming WARC-ORB 85 Conference, and argues that with US willingness to modify its position the Conference seems for the first time to provide a good basis for a dialogue between the USA and those countries that feel the existing system is not equitable. Two main problems still need to be considered: the role of common user organizations such as INTELSAT, and the relationship between the Federal Communications Commission and other actors involved in the US international telecommunication decision-making process. Failure to reach agreement at the conference could lead to the USA being the country which suffers most.     

The Orbiting Astronomical Observatories

A review is presented of the Orbiting Astronomical Observatories Program together with a detailed of the OAO spacecraft and the four astronomical instruments currently being developed for the first three observations.