- SHARAD
SHARAD (
Mars SHAllow RADar sounder) is a subsurface soundingradar embarked on theMars Reconnaissance Orbiter probe. It complements theMARSIS instrument onMars Express , providing lower penetration capabilities (some hundred meters) but much finer resolution (15 metres - untapered - in free space).SHARAD is developed under the responsibility of the
Italian Space Agency (ASI, Agenzia Spaziale Italiana), and provided toJPL for use on board theMars Reconnaissance Orbiter Spacecraft in the frame of aNASA /ASI agreement which foresees exploitation of the data by a joint Italian/US team. The INFOCOM dept. of the University ofRome "La Sapienza " is rensponsible for the whole mission, whileAlcatel Alenia Space Italia (formerly Alenia Spazio) designed and build the instrument.SHARAD operations are managed by INFOCOM from the SHARAD Operation Centre (SHOC), located within theAlcatel Alenia Space facilities in the suburbs ofRome .Science objectives
SHARAD is intended to map the first kilometer below the
Mars surface, providing images ofsubsurface scattering layers with high vertical resolution (15 m), with the intent to locate water/ice/ deposits and to map the vertical structure of the upper subsurface layers.Characteristics
SHARAD operates on a carrier frequency of 20 MHz, transmitting a "
chirp ed" signal with a bandwidth of 10 MHz. Pulsewidth is 85 μsec and the nominalPulse Repetition Frequency is 700.28 Hz. Transmitted power is 10 W peak. The antenna is a 10-m dipole.A synthetic aperture is generated on-ground to reduce the unwanted surface returns from off-nadir scatterers at the same range of the subsurface echoes.SHARAD is physically divided into two elements:
* the SEB (SHARAD electronic box), which contains all the electronics (instrument controller, transmitter, receiver and antennaimpedance matching network), within a metal frame which acts as thermal radiator for the electronic modules inside (Mars Reconnaissance Orbiter is an open frame spacecraft, and SHARAD has an autonomous thermal control)
* the antenna, made by two fiber tubes, folded and stowed in a cradle (covered by thermal insulator to protect it from the heating induced by theaerobraking ). Once released, the antenna extends into position thanks only to the elastic property of the material. A metal wire running inside the non-conductive tubes represents the real radiating element of the antenna.The instrument operates at fixed
PRF (700.28 Hz) and the echo is received in rank 1 (i.e., after the second transmitted pulse). Two alternate (higher and lower) PRF are available to deal with the extended mission orbit range. An open-loop tracking system, based on a priori knowledge of the surface topography, is the nominal means to position the 135 μsec receive window on the expected echo position (a closed-loop tracker is available as backup).The instrument on-board
signal processing is minimal, and consists in a coherent presuming of the received echoes (programmable between 1 and 32 in power of 2 steps) to reduce the generated data rate, with programmable number of bits (8, 6, 4).The
chirp signal is generated directly on the 20 MHz carrier by a digital chirp generator, and fed to the power amplifier, followed by a Transmit/Receive switch and thematching network .The receiver provides amplification, filtering and digital gain control directly at RF, and the digitised using aundersampling technique at a rate of 26.6 MHz.A single DSP processor provides both the control and processing function.The instrument industrial team is composed as follows:
* Instrument design, integration and test: Alcatel Alenia Space Italia (Rome plant)
* DES (Digital electronics subsystem): Alcatel Alenia Space Italia (Milan plant - formerly Laben)
* Chirp Generator, Receiver: Alcatel Alenia Space Italia (Rome /L'Aquila plants)
* Transmitter, matching network: Galileo Avionica (Milan , Italy)
* Antenna: Astro Aerospace (Carpinteria , CA, USA)History
While the initial studies date back to 2001, full-scale development was released only in February 2003.The Engineering Model (EM) of the instrument was delivered to
Lockheed Martin Space Systems inDenver (responsible for the spacecraft) in March 2004, and integrated into the Orbiter Test Bed.The ProtoFlight Model (PFM) was delivered and integrated on theMars Reconnaissance Orbiter Spacecraft inDenver in September 2004.Mars Reconnaissance Orbiter was launched fromCape Canaveral Air Force Station onAugust 12 ,2005 , with anAtlas V -Centaur launch vehicle, and reachedMars orbit onMarch 10 ,2006 . Theaerobraking phase, needed to reach the operational orbit, lasted untilAugust 30 ,2006 .OnSeptember 17 ,2006 , the SHARAD antenna was deployed, and the first in-flight test of theradar was successfully carried out onSeptember 19 .SHARAD has been operational since November 2006.References
# - R. Croci et al. - "SHARAD Design and Operation" - IGARSS 2007 Proceedings, Barcelona, 2007.
External links
* [http://mars.jpl.nasa.gov/mro/ MRO Home Page]
* [http://mars.jpl.nasa.gov/mro/mission/sc_instru_sharad.html SHARAD Page on the MRO Site]
* [http://www.sharad.org/ Official SHARAD Site]
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