Observations of stars with the Hopkins Ultraviolet Telescope

The Hopkins Ultraviolet Telescope (HUT) was flown aboard the space shuttle Columbia as part of the Astro-1 mission during December 1990. During the nine-day flight, HUT carried out 3 Å resolution spectrophotometry of a wide variety of astronomical objects, including a number of stellar targets, in the 912–1860 Å range of the far ultraviolet. A few nearby stars were observed in the 415–912 Å range of the extreme ultraviolet as well. For nearly all of these targets, the spectra obtained by HUT are the first ever obtained in the spectroscopically rich region between Lyman (1216 Å) and the Lyman limit (912 Å). Here, we present highlights of the results obtained by HUT in a variety of areas of stellar astronomy.     

Periodic components in Cyg X-3

Hard X-ray observations of Cyg X-3 in the energy range 20–100 keV were made with a Balloon-borne telescope using two large area proportional counters. The source was seen with a total significance of 20.

A 121 s periodicity was seen during Fourier analysis of the data. The phenomenon can be interpreted as due to transient pulsation since no other peak was seen in our data. Quasi-periodic oscillation in the range 0.06–20 mHz have been observed from Cyg X-3 at lower energies. Interestingly, most of the reported periods are multiple of the present measurements. The observed pulsation at high energies indicate the occasional unstable behaviour of the inner parts of the accretion disk connected with the basic rotation period of the compact object.

The 4.8^h modulation, characteristic of the orbital period of the binary system was seen in the data, with a broad maximum between the phase 0.3 to 0.7.     

卫星:所有通信业务发展的必由之路

1　概述□□未来航天活动的特点是,建造卫星星座,开展新业务及新应用,增强运载火箭推力。还应当考虑为地面通信网开发有关技术,满足用户不断增长的需求。为了对上述变化作好准备,乃至采取未雨绸缪的行动,阿尔卡特航天公司(AlcatelSpace)已经对其组织结构进行了变动。1998年,阿尔卡特公司卫星业务部和法国宇航公司及汤姆逊-CSF公司合并,组建了拥有近6000名员工的AlcatelSpace。目前,这家世界主要的卫星制造商从事两种主要的活动:1制造由阿尔卡特航天工业公司(AlcatelSpaceIndustries)负责;2运行和业务由阿尔卡特空间通信公司(AlcatelSpa…     

Recursive temporal-spatial information fusion with applications totarget identification

Centralized/distributed recursive algorithms for temporal-spatial information integration using the Dempster-Shafer technique are developed. Compared with the Bayesian approach, the Dempster-Shafer technique has the strong capability of handling information uncertainties, which are particularly desirable in many applications. In the centralized integration algorithm, all information is pooled into the central processor and integrated. In contrast, the distributed integration algorithm shares the computational burden among the local processors, which increases the computational efficiency. The developed algorithms are effectively applied to a target identification problem with three sensors: identification of friend-foe-neutral (IFFN), electronic support measurement (ESM), and infrared search and track (IRST)     

Improved bolometric corrections for WR stars

Evolutionary models allow an assignment of both a mass and a luminosity to a Wolf-Rayet (WR) star in a cluster, and hence allow a determination of the Bolometric Correction (B.C.). The B.C.'s derived for WN stars range from –4.0 to –6.0 with the expected trend of larger values (in absolute values) for stars with higher excitation spectra. For WC stars, there is little evidence for a similar trend; most observations presented here are consistent with B.C.=–4.5, as found by Smith and Maeder (1989). The convergence of B.C. values derived from evolutionary and atmospheric models is extremely satisfactory, giving increased confidence in both methods.     

Is it a plane?

An international colloquium on the Spaceplane and the Law was organized by the French Society for Air and and Space Law, with the help of the European Space Agency, the French Civil Aviation Authority, the Centre National d'Etudes Spatiales (CNES) and Air France, and had ICAO, Eurocontrol and the French Ministries of Foreign Affairs, Transport, PTT and Research as its patrons. The purpose of the colloquium was to create awareness of the legal problems that may arise when spaceplanes become reality, and to propose solutions to those problems. The colloquium was held in Paris on 14–15 May 1991.     

Deriving the spin rate/orientation from the quiescent spacecraft ABRIXAS using optical observations

With the loss of the battery system of ABRIXAS shortly after launch and consequent absence of telemetry, there was urgent need to determine ABRIXAS' spin rate and orientation in order to assess the possibility of re-establishing telemetry during periods of full-Sun orbits. We, therefore, conducted optical and video observations of ABRIXAS passages with a 1-second time resolution, and later simulated the optical appearance of ABRIXAS for several passages based on a three-dimensional model of the reflectivity properties of the 2.5m × 1.8m × 1.2m size-satellite. Here we present the results of the comparison of our grid of light curve models with the observations and show (i) how the spin rate of ABRIXAS slowed down between June and December 1999 and (ii) what information can be deduced on the temporal change of the orientation of the spin axis. We conclude with discussing the benefit of using ground based optical observation as a cost effective way to develop information about the orientation of a satellite when there is no telemetry.     

Implications of previous space commercialization experiences for the reusable launch vehicle

In evaluating the prospects for the development of a commercially viable RLV, it may be useful to examine ’lessons learned‘ from previous space commercialization efforts– both those that succeeded and those that did not. It can be argued that several distinct streams of market and technological development may have to converge for successful commercialization of space systems to occur. Factors influencing the prospects for commercialization include the size and growth rate of the potential customer base, the extent to which a governmental customer exists to underpin the market, the development of associated ’value-added‘ markets, the stability of governmental policies, the availability of enabling or enhancing infrastructure, the levels of technological and business risk, and the degree to which competitive markets exist. This paper examines two previous space commercialization experiences, evaluates the relative importance of the various factors that influence the prospects for success of commercialization efforts, and assesses the implications of those factors for the commercial viability of the proposed RLV.     

Position Location from Sensors with Position Uncertainty

A statistical analysis of a mixed-mode position-location system with sensors position uncertainty is described. Expressions for the maximum likelihood estimator and its error statistics, under ?small errors? assumption, are derived.