The Advanced L-band Phased Array Camera for Astronomy (ALPACA) will be a fully cryogenic phased array feed instrument operating from 1.3-1.7 GHz, providing an unmatched combination of sensitivity, wide bandwidth, and large instantaneous field of view. The instrument was originally targeted for installation at the Arecibo Radio Telescope but the tragic loss of the Gregorian platform in 2020 has led to a proposal to deploy ALPACA at the prime focus of the Green Bank Telescope. Here, we will report on the design and implementation of the antenna array, cryogenic vacuum vessel, signal transport and the digital back end.
KEYWORDS: Satellites, Space operations, Global Positioning System, Telescopes, Radio telescopes, Solar cells, Meteorological satellites, Contamination, Observatories, Earth observing sensors
Remote detection of spacecraft arcing is important for the satellite operators in order to properly respond for anomalies caused by spacecraft charging due to the space weather conditions. Satellites operating at geosynchronous orbit (GEO) are prone to spacecraft charging due to fluxes of high energy electrons onto and beneath their surfaces, usually coincident with geomagnetic storms. Thus, satellite surfaces can charge thousands of volts with respect to each other whereas entire satellites can charge tens of thousands of volts negative of their surrounding space plasma. The ensuing electric fields can cause local discharges (arcs), endangering the normal operation of the satellite. It has been shown that the most probable cause of the excess power loss of the global positioning system (GPS) satellites is radiationinduced arcing observed on the solar arrays coverglass and producing its contamination. In this paper, we used a new 327 MHz feed system installed on the Arecibo 305 m radio telescope for the remote arc detection of two low-inclination GEO satellites, namely, SES-10 and AMC- 3, and compare it to the standard 327 MHz feed system observations of the high-inclination GEO satellite ASTRA 1-D. Statistical analysis of arcing data revealed a high arcing rate for both SES-10 and AMC-3, but SES-10 arcs less often than AMC-3. On the other hand, ASTRA 1-D observations show no significant evidence that scans of the satellite within view of the telescope (“on-source”) are any different than those with the satellite outside of it (“off-source”), suggesting no-arcing behavior of this satellite. It is believed that the design of the ASTRA 1-D satellite’s solar arrays precludes arcing.
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