The Atacama Pathfinder EXperiment (APEX) operates a 12m submillimeter wavelength telescope in the high Andes in Chile at 5107 m above sea level since 2006<sup>1</sup>. Several steps have been taken to improve the operation efficiency of the facility in the given harsh environmental conditions<sup>2</sup>. The developments in remote control and -sensing allowed in 2017 for the transition to a remote science operations scheme, observing 24/7 from the basecamp control center in San Pedro de Atacama. Also engineering and maintenance is in the transition phase to a similar scheme to minimize presence and activities at the very high site. Instrument control servers allowing remote operation even of heterodyne THz instrumentation, with no compromise on instrument performance, had been developed and proven to reliably work<sup>3</sup>. The transition to full remote science operations required major hardware upgrades on the antenna drive system and a failsafe remote-control system to ensure the safety of the antenna, the Sun Avoidance System (SAS). We report on the layout, the implementation and on the experience of the first year of this new operations model started in April 2017. <p> </p>The engineering tasks also are in a transition phase to a scheme that minimizes the presence at the antenna. Daily engineering work at the high site for preventive and corrective maintenance can be reduced when all critical hardware systems are integrated in a remote monitoring and control system. We have started with this in 2015 and have stepwise introduced this new scheme. This required the introduction of redundancies of systems as well as the extension of sensing points and remote-control interfaces, throughout all levels in the project breakdown structure of the telescope and its auxiliary systems. We present examples of theses implemented systems and discuss the concept of redundancies. <p> </p>The APEX observatory is the smallest ESO site in Chile, incorporated as a department of LPO, the ESO La Silla – Paranal Observatory, within the directorate of Operations (DoO). The work presented will attempt an outline of approaches that can be applied to telescopes exposed to similar environmental conditions as well as to larger and distributed operations such as envisaged for the Paranal Observatory extended by the ELT on Cerro Armazones.
We report on developments of submillimeter heterodyne arrays for high resolution spectroscopy with APEX. Shortly, we will operate
state-of-the-art instruments in all major atmospheric windows accessible from Llano de Chajnantor. CHAMP+, a dual-color 2×7 element heterodyne array for operation in the 450 μm and 350 μm atmospheric windows is in operation since late 2007. With its
state-of-the-art SIS detectors and wide tunable local oscillators, its cold optics with single sideband filters and with 3 GHz of processed IF bandwidth per pixel, CHAMP+ does provide outstanding observing capabilities. The Large APEX sub-Millimeter Array (LAsMA) is in the final design phase, with an installation goal in 2009. The receiver will operate 7 and 19 pixels in the lower submillimeter windows, 285-375 GHz and 385-520 GHz, respectively. The front-ends are served by an array of digital wideband Fast Fourier Transform spectrometers currently processing up to 32×1.5 (optionally 1.8) GHz of bandwidth. For CHAMP+, we process 2.8 GHz of instantaneous bandwidth (in 16.4 k channels) for each of the 14 pixels.
This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI), to be launched onboard of ESA's Herschel Space Observatory, by 2008. It includes the first results from the instrument level tests. The instrument is designed to be electronically tuneable over a wide and continuous frequency range in the Far Infrared, with velocity resolutions better than 0.1 km/s with a high sensitivity. This will enable detailed investigations of a wide variety of astronomical sources, ranging from solar system objects, star formation regions to nuclei of galaxies.
The instrument comprises 5 frequency bands covering 480-1150 GHz with SIS mixers and a sixth dual frequency band, for the 1410-1910 GHz range, with Hot Electron Bolometer Mixers (HEB). The Local Oscillator (LO) subsystem consists of a dedicated Ka-band synthesizer followed by 7 times 2 chains of frequency multipliers, 2 chains for each frequency band. A pair of Auto-Correlators and a pair of Acousto-Optic spectrometers process the two IF signals from the dual-polarization front-ends to provide instantaneous frequency coverage of 4 GHz, with a set of resolutions (140 kHz to 1 MHz), better than < 0.1 km/s. After a successful qualification program, the flight instrument was delivered and entered the testing phase at satellite level. We will also report on the pre-flight test and calibration results together with the expected in-flight performance.
CHAMP<sup>+</sup>, a dual-color 2 × 7 element heterodyne array for operation in the 450 μm and 350 μm atmospheric windows is under development. The instrument, which is currently undergoing final evaluation in the laboratories, will be deployed for commissioning at the APEX telescope in August this year.
With its state-of-the-art SIS detectors and wide tunable local oscillators, its cold optics with SSB filters and with 2 GHz of usable IF bandwidth per pixel, CHAMP<sup>+</sup> will provide unmatched observing capabilities for the APEX community. The optics allows for simultaneous observations in both colors. For both sub-arrays a hexagonal arrangement with closest feasible spacing of the pixels on sky (2×Θmb) was chosen, which, in scanning mode, will provide data sampled with half-beam spacing. The front-end is connected to a flexible autocorrelator array with a total bandwidth of 32 GHz and 32768 spectral channels, subdivided into 32 IF bands of 1 GHz and 1024 channels each.
The Heterodyne Instrument for FIRST is comprised of five SIS receiver channels covering 480 - 1250 GHz and two HEB receiver channels covering parts of 1410 - 1910 GHz and 2400 - 2700 GHz. Two local oscillator sub-bands derived from a common synthesizer will pump each receiver band. The synthesizer, control electronics and frequency distribution will be performed in the spacecraft service module. The service module will be connected in the local oscillator unit on the outside of the cryostat with a WR-28 waveguide for each of the 14 local oscillator sub-bands. the local oscillator unit will be passively cooled and thermally isolated from the cryostat wall. The module is comprised of seven units, one for each receiver band, containing two multiplier chains consisting of a k- to w-band multiplier, a MMIC power amplifier operating in one of five bands between 71 and 113 GHz, the high frequency multipliers, launching optics and electrical distribution. The entire assembly will be cooled to 120 K. The local oscillator system has the two field technical challenge of providing broad band frequency coverage at very high frequencies. This will be achieved through the use of high power GaAs MMIC amplifiers and planar diode multiplier technology in a passively cooled 120 Kelvin environment. The design criteria and the resulting overall system design will be presented along with a programmatic view of the development program and development progress.
A 16-element SIS heterodyne array for operation in the 625 micrometer atmospheric window is under development at the MPIfR. The array consists of 2 X 8 elements with closest feasible spacing of the pixels on the sky ((root)2 (DOT) (Theta) <SUB>mb</SUB>). The L.O. tuning range covers the astronomically important CI and the CO(4-3) transitions, and an IF bandwidth of 2 GHz (1200 kms<SUP>-1</SUP>) will permit mapping of extragalactic systems. For best system sensitivity the design allows for cold optics ( 15K) and single-sideband operation. The frontend will be linked to a flexible autocorrelator, with a maximum bandwidth of 2 GHz (2048 channels) for each of the 16 modules. In the high-resolution mode, 500 MHz of bandwidth can be operated with 8192 channels of 61 kHz spectral resolution. System components are currently undergoing final integration and critical evaluation in our laboratories. First astronomical commissioning is scheduled for later this year. The sensitivity expected with CHAMP, for e.g. carbon studies, will be unparalleled. With the full array in SSB operation the mapping speed will be enhanced by a factor of 50 - 100 compared to current single-pixel detectors.