Electron beam charging of Space Shuttle thermal protection system tiles

Six space shuttle reusable surface insulation tiles were tested in the NASA Lewis Research Center's electron bombardment test facility. The 30-cm-square specimens were assembled by using the same materials and techniques used to apply the tiles to the space shuttle and were composed to 15-cm- and 20-cm-square tiles and pieces on 0.6-cm-thick aluminum substrates. There were two specimens of each of three thicknesses. One specimen of each thickness had gaps of less than 0.1 cm between tiles, and the other had gaps of approximately 0.15 cm. The specimens were exposed to monoenergetic electron beams (2 to 25 keV) with nominal fluxes of 0.1 and 1 nA/sq. cm. Tests were conducted with both grounded and floating substrates. The data presented include charging rates, equilibrium potentials, and substrate currents. There is evidence that discharging occurred

Testing of a spacecraft model in a combined environment simulator

A scale model of a satellite was tested in a large vacuum facility under electron bombardment and vacuum ultraviolet radiation to investigate the charging of dielectric materials on curved surfaces. The model was tested both stationary and rotating relative to the electron sources as well as grounded through one megohm and floating relative to the chamber. Surface potential measurements are presented and compared with the predictions of computer modelling of the stationary tests. Discharge activity observed during the stationary tests is discussed and signals from sensing devices located inside and outside of the model are presented

Charging of flexible solar array substrates in kilovolt electron beams

A series of survey tests were conducted to evaluate samples of flexible solar arrays. The samples used woven carbon fibers and/or coatings to increase the surface conductivity of the KAPTON substrate and thereby reduce surface charging. Four different samples were evaluated by exposing them to monoenergetic electron beams of 2 to 20 KeV at a current density of 1 nA sq cm. Simulated eclipse tests were also conducted. The results were as expected; the more continuous the conductive pattern, the lower the surface charging

Test program for transmitter experiment package and heat pipe system for the communications technology satellite

The test program is described for the 200 watt transmitter experiment package and the variable conductance heat pipe system which are components of the high-power transponder aboard the Communications Technology Satellite. The program includes qualification tests to demonstrate design adequacy, acceptance tests to expose latent defects in flight hardware, and development tests to integrate the components into the transponder system and to demonstrate compatibility

Testing of typical spacecraft materials in a simulated substorm environment

The test specimens were spacecraft paints, silvered Teflon, thermal blankets, and solar array segments. The samples, ranging in size from 300 to 1000 sq cm were exposed to monoenergetic electron energies from 2 to 20 keV at a current density of 1 NA/sq cm. The samples generally behaved as capacitors with strong voltage gradient at their edges. The charging characteristics of the silvered Teflon, Kapton, and solar cell covers were controlled by the secondary emission characteristics. Insulators that did not discharge were the spacecraft paints and the quartz fiber cloth thermal blanket sample. All other samples did experience discharges when the surface voltage reached -8 to -16kV. The discharges were photographed. The breakdown voltage for each sample was determined and the average energy lost in the discharge was computed

Investigation of high voltage spacecraft system interactions with plasma environments

An experimental investigation was undertaken for insulator and conductor test surfaces biased up to + or - 1kV in a simulated low earth orbit charged particle environment. It was found that these interactions are controlled by the insulator surfaces surrounding the biased conductors. For positive applied voltages the electron current collection can be enhanced by the insulators. For negative applied voltages the insulator surface confines the voltage to the conductor region. Understanding these interactions and the technology to control their impact on system operation is essential to the design of solar cell arrays for ion drive propulsion applications that use direct drive power processing

First results of material charging in the space environment

A satellite experiment, designed to measure potential charging of typical thermal control materials at near geosynchronous altitude, was flown as part of the SCATHA program. Direct observations of charging of typical satellite materials in a natural charging event ( 5 keV) are presented. The results show some features which differ significantly from previous laboratory simulations of the environment

Risk factors for high anti-HHV-8 antibody titers (≥1:51,200) in black, HIV-1 negative South African cancer patients: a case control study

Background: Infection with human herpesvirus 8 (HHV-8) is the necessary causal agent in the development of Kaposi's sarcoma (KS). Infection with HIV-1, male gender and older age all increase risk for KS. However, the geographic distribution of HHV-8 and KS both prior to the HIV/AIDS epidemic and with HIV/AIDS suggest the presence of an additional co-factor in the development of KS. Methods: Between January 1994 and October 1997, we interviewed 2576 black in-patients with cancer in Johannesburg and Soweto, South Africa. Blood was tested for antibodies against HIV-1 and HHV-8 and the study was restricted to 2191 HIV-1 negative patients. Antibodies against the latent nuclear antigen of HHV-8 encoded by orf73 were detected with an indirect immunofluorescence assay. We examined the relationship between high anti-HHV-8 antibody titers (≥1:51,200) and sociodemographic and behavioral factors using unconditional logistic regression models. Variables that were significant at p = 0.10 were included in multivariate analysis. Results: Of the 2191 HIV-1 negative patients who did not have Kaposi's sarcoma, 854 (39.0%) were positive for antibodies against HHV-8 according to the immunofluorescent assay. Among those seropositive for HHV-8, 530 (62.1%) had low titers (1:200), 227 (26.6%) had medium titers (1:51,200) and 97 (11.4%) had highest titers (1:204,800). Among the 2191 HIV-1 negative patients, the prevalence of high anti-HHV-8 antibody titers (≥1:51,200) was independently associated with increasing age (ptrend = 0.04), having a marital status of separated or divorced (p = 0.003), using wood, coal or charcoal as fuel for cooking 20 years ago instead of electricity (p = 0.02) and consuming traditional maize beer more than one time a week (p = 0.02; p-trend for increasing consumption = 0.05) although this may be due to chance given the large number of predictors considered in this analysis. Conclusions: Among HIV-negative subjects, patients with high anti-HHV-8 antibody titers are characterized by older age. Other associations that may be factors in the development of high anti- HHV-8 titers include exposure to poverty or a low socioeconomic status environment and consumption of traditional maize beer. The relationship between these variables and high anti- HHV-8 titers requires further, prospective study

Valganciclovir for suppression of human herpesvirus-8 replication: a randomized, double-blind, placebo-controlled, crossover trial.

BACKGROUND: Human herpesvirus-8 (HHV-8) replication is critical in the induction and maintenance of Kaposi sarcoma, primary effusion lymphoma, and some cases of Castleman disease. In vitro and observational studies suggest that ganciclovir inhibits HHV-8 replication, but no randomized clinical trials have been conducted. METHODS: A total of 26 men infected with HHV-8 were randomized to receive 8 weeks of valganciclovir administered orally (900 mg once per day) or 8 weeks of placebo administered orally. After a 2-week washout period, participants in each group received the study drug they had not yet taken (either valganciclovir or placebo), for 8 additional weeks. Oral swab samples were collected daily during the study, and HHV-8 and CMV DNA were quantified by real-time PCR. RESULTS: A total of 16 human immunodeficiency virus (HIV)-positive men and 10 HIV-negative men enrolled in and completed the study. Of the 3,439 swab samples that participants had been expected to provide, 3029 (88%) were available for analysis. HHV-8 was detected on 44% of swabs collected from participants who were receiving placebo, compared with 23% of swabs collected from participants who were receiving valganciclovir (relative risk [RR], 0.54 [95% confidence interval {CI}, 0.33-0.90]; P = .02). Valganciclovir reduced oropharyngeal shedding of cytomegalovirus by 80% (RR, 0.20 [95% CI, 0.08-0.48]; P < .001). Shedding of HHV-8 and shedding of cytomegalovirus were independent. Hematologic, renal, or hepatic toxicities were no more common among participants who received the active drug, compared with those who received placebo, though participants who received valganciclovir reported more days of diarrhea. CONCLUSIONS: Valganciclovir administered orally once per day is well tolerated and significantly reduces the frequency and quantity of HHV-8 replication

Cancers associated with Kaposi's sarcoma (KS) in AIDS: a link between KS herpesvirus and immunoblastic lymphoma

Kaposi's sarcoma (KS), common among persons with acquired immunodeficiency syndrome (AIDS), is caused by KS herpesvirus (KSHV) but whether KSHV causes other malignancies is uncertain. Using linked United States AIDS and cancer registries, we measured the incidence of specific malignancies in persons with AIDS (4–27 months after AIDS onset). We identified associations with KSHV by calculating a relative risk: cancer incidence in persons with KS (all were KSHV-infected) divided by incidence in persons without KS. Using Poisson regression, relative risks were adjusted for human immunodeficiency virus risk group, gender, age, race, and calendar year. We included 189 159 subjects (26 972 with KS). Immunoblastic lymphoma was significantly associated with KS (506 cases; relative risks: unadjusted 2.44, 95%CI 2.00–2.96, adjusted 1.58, 95%CI 1.29–1.93). Only one immunoblastic lymphoma had pleura as primary site. None of 37 other specified malignancies (other non-Hodgkin lymphomas, haematological malignancies, solid tumours) was significantly associated with KS. In summary, the association of immunoblastic lymphoma with KS was specific among examined malignancies and remained significant after statistical adjustment. Our findings, and the previously demonstrated presence of KSHV in the histologically related primary effusion lymphoma, suggest that KSHV is involved in the pathogenesis of some immunoblastic lymphomas. © 2001 Cancer Research Campaig