Engineering topics
Publications and source records attributed to Armstrong, John T..
In this paper we present a systematic study of how intra-spacecraft wireless communication can be adopted to various subsystems of the spacecraft including C&DH (Command & Data Handling), Telecom, Power, Propulsion, and Payloads, and the interconnects between them. We discuss the advantages of intra-spacecraft wireless communication and the disadvantages and challenges and a proposal to address them.
The refractory inclusions embedded in the matrix of many carbonaceous and some ordinary or enstatite chondrites exhibit mineralogical and bulk composition characteristics which correlate with the first, or highest-temperature, condensation products that have been predicted to form from a hot, but cooling, solar nebula. These inclusions' isotopic compositions indicate presolar nucleosynthetic processes that have contributed to the production of the elements from which the solar system was formed; subsequently, the inclusions experienced melting, recrystallization, and alteration histories that have obscured the formation processes.
A detailed petrographic and chemical study of Zelda (a gigantic sulfide-rich Fremdling from the Allende Ca-rich inclusion, CAI, Egg 6) and its contact with the host was conducted using analytical SEM and electron-microprobe techniques, and the results were compared with those obtained on other sulfide-rich and oxide-rich Fremdlinge. Strong evidence is presented that Zelda, a type-example of sulfide-rich Fremdlinge, has been formed from a preexisting Ur-Fremdling, similar by composition to Willy, by closed-system sulfidization of magnetite and metal. At least two different sulfidization mechanisms appear to have occurred in altering Fremdlinge: one producing compositionally homogeneous equigranular objects such as Zelda, the other producing compositionally and texturally heterogeneous objects.
This paper presents the first isotopic measurements, made with an ion microprobe, of Mg, Fe, Mo, Ru, and W in Fremdlinge and refractory metal nuggets from Allende meteorite. No non-mass-dependent deviations exceeding 1 percent from normal solar isotopic abundances were found for any of the elements analyzed, despite the unusual mineralogy of Fremdlinge and the extreme enrichment in refractory siderophile elements. It is concluded that the chemical, petrologic, and isotopic data on Fremdlinge are most plausibly interpreted in terms of the origin of Fremdlinge within the solar nebula.