ESA’s New CebrerosStation Ready toSupport VenusExpress

ESA’s New CebrerosE S A’s N e w Ce b re ro sStation Ready toS t a t i o n R e a d y toSupport VenusS u p p o rt Ve n u sExpress

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Cebreros Station

Manfred Warhaut, Rolf Martin & Valeriano ClarosESA Directorate of Operations andInfrastructure, ESOC, Darmstadt, Germany

E SA’s new deep-space radio antenna atCebreros (near Avila) in Spain was

officially inaugurated on 28 September. Thenew 35 metre antenna is the Agency’s secondfacility devoted to communications withspacecraft on interplanetary missions or in verydistant orbits; the first is at New Norcia inWestern Australia. Cebreros’s first task is thetracking of ESA’s Venus Express spacecraft,launched on 9 November.

IntroductionThe construction of ESA's deep-space

antenna at Cebreros was completed inrecord time. The site-selection processbegan in April 2002, the procurementactivities began in February 2003, and thebuilding work began in Spring 2004 on thesite of a former NASA ground station.After successful assembly of the antennastructure in November 2004 and the almostflawless acceptance testing of the variousinfrastructure elements and the radio-frequency components, the new antennawas completed in August 2005, whichprovided just sufficient time for finaltesting before being used for the first timeto support Venus Express.

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Infrastructure

Technical Specifications of the Cebreros Antenna

REFLECTOR DISHDiameter: 35 metresDepth: 8 metresSurface contour: shaped parabolaNumber of panels: 304 on 7 ringsSurface accuracy: 0.3 mm rmsWeight: 100 tons

ANTENNA PEDESTALHeight: 40 metresWeight movable part: 500 tonsTotal weight: 620 tons

OPERATING ENVIRONMENTTemperature: -20°C to + 50°CRelative humidity: 0 – 100% including condensation Wind: up to 50 km/h constant, gusting to 70 km/hRain: up to 35 mm/hSolar heat: up to 1200 W/m2

MECHANICAL PERFORMANCESlew range:

Azimuth 0 to 540 degElevation 0 to 90 deg

Slew rate:Both axes 1.0 deg/s max.

Acceleration:Both axes 0.4 deg/s2 max.

Pointing error: 0.006 deg

RF PERFORMANCE• X-band (8 GHz) transmission/reception with right- and left-hand polarisations• Ka-band reception• Beam-waveguide concept• G/T at 10 deg elevation ! 50.8 dB/K at X-band• G/T at 10 deg elevation ! 55.8.0 dB/K at Ka-band • Transmit EIRP >107 dBW at X-band

SPECIAL FEATURES• Temperature-measuring system incorporating 230 sensors on antenna structure• Compensation of pointing errors• Steerable sub-reflector • Helium-cooled amplifiers (LNAs) with very low noise temperature• 20 kW de-ionised water-cooled primary high-power amplifier• 2 kW air-cooled secondary low-power amplifier• Fully digitised receive system with ranging function• Hydrogen-maser timing system with very high accuracy• Designed for unmanned and full remote-controlled operation• Completely power self-contained with back-up power diesel generators.

The novel Cebreros antenna feed concept

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Cebreros Station

Cebreros was chosen as the site onwhich to build ESA’s second deep-spaceantenna for several reasons. To achieve therequired coverage, this antenna had to bepositioned 120 degrees East or West of theantenna in Australia and an ideal locationwould have been ESA’s European SpaceAstronomy Centre (ESAC) at Villafrancanear Madrid. However, active urbandevelopment in the surroundings of ESACcould be a source of interference. TheCebreros location is equally good from atechnical point of view and is also wellaway from densely-populated areas, butstill sufficiently close to ESAC forpurposes of operating efficiency. Like allother ground stations within ESA’sESTRACK network, Cebreros will beremotely operated from ESOC inDarmstadt, Germany, and will only bemanned during especially critical missionphases, such as launches.

The entire antenna-carrying structure is40 metres high and weighs about 630 tons,making it one of the World’s largest TT&Cantennas. It has been built by an industrialconsortium led by the Canadian companySED Systems. The Spanish firms Esteycoand Necso built the antenna-towerinfrastructure, and LV Salamanca wasresponsible for the building refurbishment.

Novel Features of CebrerosFuture deep-space missions will transmitincreasing amounts of data from positionshundreds of millions of kilometres fromEarth and require higher frequencies to

increase data return. ESA's new Cebrerosground station therefore features a Ka-band reception capability, significantlyenhancing the performance of the ESAStation Tracking Network (ESTRACK).

The Cebreros antenna incorporates thelatest technology, which provides someadvantages compared to the New Norciafacility. For instance, the Cebreros dataacquisition capacity is higher, due to thefact that it will receive signals in the Ka-band (31.8 – 32.3 GHz). Cebreros also hasa higher pointing accuracy, with a state-of-the-art pointing/calibration system with amaximum error of 6 milli-degrees, which isten times better than a standard ESA 15 metre antenna. This exceptionalmechanical accuracy is required due to thehigher frequencies of the Ka-bandcompared to X- or S-band. It is achievedthrough the combination of a very stiffmechanical structure and 250 temperature

sensors mounted throughout the antennastructure to automatically compensate forexpansion and contraction due totemperature changes. Cebreros offersenhanced wind resistance compared withthe New Norcia dish, can operate over awider temperature range, and can rotatefurther in azimuth and at a higher speed.

The heart of Cebreros' antenna is thebeam waveguide concept and the Ka-bandreception capability featuring a 1.2 m x 1.1 m dichroic mirror. This mirror is just7.9 mm thick but contains several thousandrectangular holes drilled to an accuracy of10 microns. It therefore reflects radiosignals in the X-band (7.1 and 8.5 GHz)and allows those in the Ka-band to passthrough its surface, thereby channellingthe signals of different wavelengthreceived by the main antenna dish to thecorrect receivers. Like New Norcia,Cebreros relies on Low-Noise Amplifierscooled to 15K (-258°C) to reduce thesystem noise temperature to facilitate thereception of faint signals, and 20 kWamplifiers are used to transmit instructionsand commands.

ConclusionCebreros and New Norcia are the first twoof ESA's three planned 35 metre deep-spaceantennas. The third is likely to be built laterin the decade and will be sited at anAmerican longitude. As an integral part of anine-station ESTRACK ground-stationnetwork, these three ground stations located120° apart will be able to providecontinuous coverage for any ESA missiondespite the Earth's rotation.

In addition to being the dedicatedground station for Venus Express,Cebreros is also providing back-up supportfor the Mars Express and Rosetta missions.In the coming years, it will also beinvolved in tracking the Herschel/Planck,Lisa Pathfinder and Gaia spacecraft, aswell as BepiColombo, ESA's first missionto Mercury. r

The supporting structure of the Cebreros antenna

The novel dichroic mirror used in the Cebreros antenna