SHARAD
Encyclopedia
SHARAD is a subsurface sounding radar
embarked on the Mars Reconnaissance Orbiter
probe. It complements the MARSIS
instrument on Mars 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 to JPL for use on board the Mars Reconnaissance Orbiter
Spacecraft
in the frame of a NASA
/ASI agreement which foresees exploitation of the data by a joint Italian/US team. The INFOCOM dept. of the University of Rome
"La Sapienza" is rensponsible for the whole mission, while Alcatel 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 the Alcatel Alenia Space facilities in the suburbs of Rome
.
surface, providing images of subsurface 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.
ed" signal with a bandwidth of 10 MHz. Pulsewidth is 85 μsec and the nominal Pulse 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 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 the matching network.
The receiver provides amplification, filtering and digital gain control directly at RF, and the digitised using a undersampling
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:
The Engineering Model (EM) of the instrument was delivered to Lockheed Martin Space Systems
in Denver (responsible for the spacecraft) in March 2004, and integrated into the Orbiter Test Bed.
The ProtoFlight Model (PFM) was delivered and integrated on the Mars Reconnaissance Orbiter
Spacecraft
in Denver in September 2004.
Mars Reconnaissance Orbiter
was launched from Cape Canaveral Air Force Station
on August 12, 2005, with an Atlas V
-Centaur
launch vehicle, and reached Mars
orbit
on March 10, 2006. The aerobraking
phase, needed to reach the operational orbit, lasted until August 30, 2006.
On September 17, 2006, the SHARAD antenna was deployed, and the first in-flight test of the radar
was successfully carried out on September 19.
SHARAD has been operational since November 2006.
greater than 300 kilometers thick. Radar results consistent with massive deposits of water ice in middle latitudes support a debris-covered glacier hypothesis.
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
embarked on the Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...
probe. It complements the MARSIS
MARSIS
MARSIS is a low frequency, pulse-limited radar sounder and altimeter used on the ESA Mars Express mission...
instrument on Mars Express
Mars Express
Mars Express is a space exploration mission being conducted by the European Space Agency . The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was...
, 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
Italian Space Agency
The Italian Space Agency is a government agency established in 1988 to fund, regulate and coordinate space exploration activities in Italy...
(ASI, Agenzia Spaziale Italiana), and provided to JPL for use on board the Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...
Spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
in the frame of a NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
/ASI agreement which foresees exploitation of the data by a joint Italian/US team. The INFOCOM dept. of the University of Rome
Rome
Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...
"La Sapienza" is rensponsible for the whole mission, while Alcatel 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 the Alcatel Alenia Space facilities in the suburbs of Rome
Rome
Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...
.
Science objectives
SHARAD is intended to map the first kilometer below the MarsMars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
surface, providing images of subsurface scattering
Subsurface scattering
Subsurface scattering is a mechanism of light transport in which light penetrates the surface of a translucent object, is scattered by interacting with the material, and exits the surface at a different point...
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 "chirpChirp
A chirp is a signal in which the frequency increases or decreases with time. In some sources, the term chirp is used interchangeably with sweep signal. It is commonly used in sonar and radar, but has other applications, such as in spread spectrum communications...
ed" signal with a bandwidth of 10 MHz. Pulsewidth is 85 μsec and the nominal Pulse Repetition Frequency
Pulse repetition frequency
Pulse repetition frequency or Pulse repetition rate is the number of pulses per time unit . It is a measure or specification mostly used within various technical disciplines Pulse repetition frequency (PRF) or Pulse repetition rate (PRR) is the number of pulses per time unit (e.g. Seconds). It...
is 700.28 Hz. Transmitted power is 10 W peak. The antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
is a 10-m dipole.
A synthetic aperture
Synthetic aperture radar
Synthetic-aperture radar is a form of radar whose defining characteristic is its use of relative motion between an antenna and its target region to provide distinctive long-term coherent-signal variations that are exploited to obtain finer spatial resolution than is possible with conventional...
is generated on-ground to reduce the unwanted surface returns from off-nadir
Nadir
The nadir is the direction pointing directly below a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface there. Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous...
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 antennaAntenna (radio)An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
impedance matchingImpedance matchingIn electronics, impedance matching is the practice of designing the input impedance of an electrical load to maximize the power transfer and/or minimize reflections from the load....
network), within a metal frame which acts as thermal radiator for the electronic modules inside (Mars Reconnaissance OrbiterMars Reconnaissance OrbiterMars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...
is an open frame spacecraft, and SHARAD has an autonomous thermal control) - the antennaAntenna (radio)An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
, made by two fiber tubes, folded and stowed in a cradle (covered by thermal insulator to protect it from the heating induced by the aerobrakingAerobrakingAerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit by flying the vehicle through the atmosphere at the low point of the orbit . The resulting drag slows the spacecraft...
). 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
PRF
PRF is an acronym and can stand for:* Platelet Rich Fibrin, A combination of platelets and fibrin used to regenerate tissue* PRF-3, the call letters of the now defunct TV Tupi, Brazil's first television station* Pain Relief Foundation...
(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
Signal processing
Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...
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
Chirp
A chirp is a signal in which the frequency increases or decreases with time. In some sources, the term chirp is used interchangeably with sweep signal. It is commonly used in sonar and radar, but has other applications, such as in spread spectrum communications...
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 the matching network.
The receiver provides amplification, filtering and digital gain control directly at RF, and the digitised using a undersampling
Undersampling
In signal processing, undersampling or bandpass sampling is a technique where one samples a bandpass filtered signal at a sample rate below the usual Nyquist rate In signal processing, undersampling or bandpass sampling is a technique where one samples a bandpass filtered signal at a sample rate...
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 (RomeRomeRome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...
plant) - DES (Digital electronics subsystem): Alcatel Alenia Space Italia (MilanMilanMilan is the second-largest city in Italy and the capital city of the region of Lombardy and of the province of Milan. The city proper has a population of about 1.3 million, while its urban area, roughly coinciding with its administrative province and the bordering Province of Monza and Brianza ,...
plant - formerly Laben) - Chirp Generator, Receiver: Alcatel Alenia Space Italia (RomeRomeRome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...
/L'AquilaL'AquilaL'Aquila is a city and comune in central Italy, both the capital city of the Abruzzo region and of the Province of L'Aquila. , it has a population of 73,150 inhabitants, but has a daily presence in the territory of 100,000 people for study, tertiary activities, jobs and tourism...
plants) - Transmitter, matching network: Galileo Avionica (MilanMilanMilan is the second-largest city in Italy and the capital city of the region of Lombardy and of the province of Milan. The city proper has a population of about 1.3 million, while its urban area, roughly coinciding with its administrative province and the bordering Province of Monza and Brianza ,...
, 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
Lockheed Martin Space Systems
Lockheed Martin Space Systems Company is one of the four major business divisions of Lockheed Martin. It is headquartered in Denver, Colorado with additional sites in Sunnyvale, California; Newtown, Pennsylvania; Huntsville, Alabama; and elsewhere in the US and UK...
in Denver (responsible for the spacecraft) in March 2004, and integrated into the Orbiter Test Bed.
The ProtoFlight Model (PFM) was delivered and integrated on the Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...
Spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
in Denver in September 2004.
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...
was launched from Cape Canaveral Air Force Station
Cape Canaveral Air Force Station
Cape Canaveral Air Force Station is an installation of the United States Air Force Space Command's 45th Space Wing, headquartered at nearby Patrick Air Force Base. Located on Cape Canaveral in the state of Florida, CCAFS is the primary launch head of America's Eastern Range with four launch pads...
on August 12, 2005, with an Atlas V
Atlas V
Atlas V is an active expendable launch system in the Atlas rocket family. Atlas V was formerly operated by Lockheed Martin, and is now operated by the Lockheed Martin-Boeing joint venture United Launch Alliance...
-Centaur
Centaur (rocket stage)
Centaur is a rocket stage designed for use as the upper stage of space launch vehicles. Centaur boosts its satellite payload to geosynchronous orbit or, in the case of an interplanetary space probe, to or near to escape velocity...
launch vehicle, and reached Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
on March 10, 2006. The aerobraking
Aerobraking
Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit by flying the vehicle through the atmosphere at the low point of the orbit . The resulting drag slows the spacecraft...
phase, needed to reach the operational orbit, lasted until August 30, 2006.
On September 17, 2006, the SHARAD antenna was deployed, and the first in-flight test of the radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
was successfully carried out on September 19.
SHARAD has been operational since November 2006.
Findings
The SHARAD radar penetrated the north polar layered ice deposits of Mars and revealed a relatively small (about 100 meter) maximum deflection of the underlying rock, which suggests a strong lithosphereLithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
greater than 300 kilometers thick. Radar results consistent with massive deposits of water ice in middle latitudes support a debris-covered glacier hypothesis.