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A comprehensive review is presented of worldwide communication programs that range in time from the inception of satellite communications to August 1971. The programs included are: Echo, Courier, West Ford, Telstar, Relay, Syncom, Lincoln experimental satellites, Intelsat, Tacsat, Skynet, Nato system, and Telesat.
Starting with the 1960 Delta launch of the first Echo satellite, NASA's Goddard Space Flight Center (GSFC) became one of the pioneers in satellite communications. Attention is given to the project Syncom, the Applications Technology Satellite (ATS) program, the ATS-6 project, and current GSFC efforts. After the decision announced in January of 1973 that NASA would phase out of communications satellite programs, the communications effort at GSFC concentrates on the operation of ATS spacecraft in orbit, experiments in the 12- to 14 GHz frequency band, and advanced communications research.
The design of a 12/14 GHz wideband two-way ground station compatible with the CTS, PSCS, and SYNCOM 4 satellites is described. Efforts to find a suitable site location in the vicinity of the Denver Network Coordinating Center are related.
Since the beginning of the space age in October 1957, a family of expendable launch vehicles, capable of launching a wide range of payloads, was developed along with the Space Shuttle and a number of upper stages. A brief description is presented of selected orbits which have proved to be most useful for initial or conceptual understanding of space operations, taking into account direct injection and Hohman transfers, and synchronous and sun-synchronous orbits. Early American boosters are discussed along with current expendable launch vehicles, giving attention to the Vanguard, Redstone and Juno, Saturn 1B and Saturn V, Scout, the Atlas booster, Atlas Centaur, Delta, Titan IIIC, and Ariane. Details regarding the Space Shuttle are considered along with PAM-D, PAM-A, PAM-DII, TOS, IUS, Centaur-G, and Syncom-IV and Intelsat-VI.
Problems associated with the in-orbit repair and maintenance of spacecraft systems are examined with reference to experience gained from three servicing missions: in-orbit capture, repair, and reflight of the Solar Maximum Mission satellite, capture and return to earth of the Palapa and Westar communications satellites, and in-orbit repair of Syncom 3. It is then shown how the lessons learned from the three servicing missions are applied to current and future servicing activities. In particular, planned servicing missions for the Hubble Space Telescope, tools and servicing facilities development, and the development of the Explorer Platform are discussed.
The Interim Operational Contamination Monitor (IOCM) is an attached shuttle payload to the Long Duration Exposure Facility (LDEF) that was used on 2 earlier flights to quantify the contamination deposited during the course of the missions. The IOCM can characterize by direct measurement the deposition of molecular and particulate contamination during any phase of flight. Also, the IOCM actively measures the optical property changes of thermal control surfaces by calorimetry, the flux of the ambient atomic oxygen environment, the incident solar flux, and the absolute ambient pressure in the payload bay. The IOCM also provides a structure and sample holders for the exposure of passive material samples to the space environment, e.g., thermal cycling, atomic oxygen, and micrometeoroids and/or debris. Some of the more salient results from the flight suggests that the payload bay was slightly contaminated during both the prelaunch phase of the mission and after the deployment of the SYNCOM IV payload. Measurements during the postflight phases, i.e., ferry flight and deintegration processing, show negligible to very low mass deposition. The results of the data are discussed in depth.
Over 11 hours of three-axis microgravity accelerometer data were successfully measured in the payload bay of Space Shuttle Columbia as part of the Microgravity Disturbances Experiment on STS-32. These data were measured using the High Resolution Accelerometer Package and the Aerodynamic Coefficient Identification Package which were mounted on the Orbiter keel in the aft payload bay. Data were recorded during specific mission events such as Orbiter quiescent periods, crew exercise on the treadmill, and numerous Orbiter engine burns. Orbiter background levels were measured in the 10(exp -5) G range, treadmill operations in the 10(exp -3) G range, and the Orbiter engine burns in the 10(exp -2) G range. Induced acceleration levels resulting from the SYNCOM satellite deploy were in the 10 (exp -2) G range, and operations during the pre-entry Flight Control System checkout were in the 10(exp -2) to 10(exp -1) G range.
Important visual events including launch, Syncom 4 deployment, LDEF retrieval, onboard crew activities, and landing are presented. Air-to-ground transmission between the crew and Mission Control is also included.
Video footage of the post-flight press conference of STS-32 is presented. The footage is narrated by the crew, and it covers the following topics: launch, deployment of Syncom IV-5, retrieval of the Long Duration Exposure Facility, in-orbit activities, and the landing.
This video features scenes, shot by the crew, of onboard activities including Syncom deploy, Long Duration Exposure Facility retrieval, various middeck experiments, and Earth and payload bay views.
The crew (Commander Frederick H. Hauck, Pilot David M. Walker, Mission Specialists Anna L. Fisher, Dale A. Gardner, and Joseph P. Allen) prepares for the 14th shuttle mission. The Canadian communications satellite TELESAT-H (ANIK) is attached to Payload Assist Module-D (PAM-D) and deployed into geosynchronous orbit on flight day two. Defense communications satellite SYNCOM IV-I is deployed on day three. Allan and Gardner retrieve two malfunctioning satellites (PALAPA-B2 and WESTAR-VI). Fisher operates the remote manipulator system, grappling satellites and depositing them in the payload door.
Commander Henry W. Hartsfield, STS 41-D mission by listing the following firsts: (a) first Discovery flight; (b) first flight for a commercial payload specialist; (c) first SYNCOM satellite deployed from an orbiter; and (d.) first to deploy 3 satellites. This was also the heaviest stack at lift-off and the heaviest payload. The footage concludes with a film of the mission highlights.
The crew, Commander Henry W. Hartsfield, Jr., Pilot Michael L. Coats, Mission Specialists Judith A. Resnik, Steven A. Hawley, and Richard M. Mullane, and Payload Specialist Charles D. Walker are seen participating a panel discussion. Live footage of the Press Conference begins with a brief introduction of all the crew, followed by highlights of the flight, a selection of slides and still pictures, and ends with a question and answer segment. The highlights consist of the astronauts walk out to the Astro-Van, panoramic views of the Discovery on the launch pad, main engine start, ignition of the solid rocket boosters, liftoff, and separation of the boosters. Images of the opening of the sun shield and the deployment of the three communication satellites (Satellite Business System (SBS-D), SYNCOM IV-2, and TELSTAR) are also seen. The crew is seen working on experiments, dumping the wastewater, eating supper, and sleeping. Concluding the live footage are slides, and stills of various areas around the world, including the Libyan Desert, Angola, Namibia, and Australia. The Press Conference ends with questions from Houston, NASA Headquarter, Kennedy Space Center, and Marshall Space Flight Center.
Significance In natural environments, plants establish intimate interactions with a wide diversity of microbes. It is unknown, however, how microbiota composed of commensal bacteria colonize roots in the face of a sophisticated plant immune system that evolved to recognize microbial-associated molecular patterns. We investigate the interaction between plant immune system function and the root microbiota. We report that root-associated commensal bacteria actively suppress the host immune response in the context of a community. Suppressors and nonsuppressors co-occur in the root microbiome and the presence of the former can enhance the colonization ability of the latter. We highlight the role of a specific sector of the plant immune system and its suppression in gating microbial access to the roots.
Bacteria are recognized for their diverse metabolic capabilities, yet the impact of microbe-microbe interactions on multispecies community structure and dynamics is poorly understood. Cell-to-cell signaling in the form of quorum sensing (QS) often regulates secondary metabolite production and microbial interactions. Here, we examine how acylhomoserine lactone (AHL)-mediated QS impacts microbial community structure in a 10-member synthetic community of isolates from Populus deltoides . To explore the role of QS in microbial community structure and dynamics, we disrupted AHL signaling by exogenous addition of AiiA-lactonase, an enzyme that cleaves the lactone ring. Microbial community structure resulting from signal inactivation, as measured by 16S rRNA amplicon sequencing and secondary metabolite production, was assessed after successive passaging of the community. Further, we investigated the impact of quorum quenching on specific microbe-microbe interactions using pairwise inhibition assays. Our results indicate that AHL inactivation alters the relative abundance of dominant community members at later passages but does not impact the overall membership in the community. Quorum quenching significantly alters the metabolic profile in lactonase-treated communities. This metabolic alteration impacts microbe-microbe interactions through decreased inhibition of other community members. Together, these results indicate that QS impacts microbial community structure through the regulation of secondary metabolites in dominant members and that the membership of microbial communities can be relatively stable despite changes in metabolic profiles.
During prolonged resource limitation, bacterial cells can persist in metabolically active states of non-growth. These maintenance periods, such as those experienced in stationary phase, can include upregulation of secondary metabolism and release of exometabolites into the local environment. As resource limitation is common in many environmental microbial habitats, we hypothesized that neighboring bacterial populations employ exometabolites to compete or cooperate during maintenance and that these exometabolite-facilitated interactions can drive community outcomes. Here, we evaluated the consequences of exometabolite interactions over the stationary phase among three environmental strains: Burkholderia thailandensis E264, Chromobacterium subtsugae ATCC 31532, and Pseudomonas syringae pv. tomato DC3000. We assembled them into synthetic communities that only permitted chemical interactions. We compared the responses (transcripts) and outputs (exometabolites) of each member with and without neighbors. We found that transcriptional dynamics were changed with different neighbors and that some of these changes were coordinated between members. The dominant competitor B. thailandensis consistently upregulated biosynthetic gene clusters to produce bioactive exometabolites for both exploitative and interference competition. These results demonstrate that competition strategies during maintenance can contribute to community-level outcomes. It also suggests that the traditional concept of defining competitiveness by growth outcomes may be narrow and that maintenance competition could be an additional or alternative measure.
Major communications satellite systems and evaluation of problems encountered in their establishment
High gain antenna beam geometry calculations for communications satellites in synchronous orbits