The Goldstone Solar System Radar (GSSR) is a large

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

system used for investigating objects in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

, a field called

radar astronomy Radar astronomy is a technique of observing nearby astronomical objects by reflecting radio waves or microwaves off target objects and analyzing their reflections. Radar astronomy differs from ''radio astronomy'' in that the latter is a passive ob ...

. Located in the desert near

Barstow, California Barstow is a city in San Bernardino County, California, in the Mojave Desert of Southern California. Located in the Inland Empire region of California, the population was 25,415 at the 2020 United States census, 2020 census. Barstow is an impor ...

, it comprises a 500-kW X-band (8500 MHz) transmitter and a low-noise receiver on the 70-m DSS 14 antenna at the

Goldstone Deep Space Communications Complex The Goldstone Deep Space Communications Complex (GDSCC), commonly called the Goldstone Observatory, is a satellite ground station located in Fort Irwin in the U.S. state of California. Operated by NASA's Jet Propulsion Laboratory (JPL), its ...

. It has been used to investigate Mercury,

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

, the

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

s, and moons of

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

and

Saturn Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...

. The solar system radar is only active a small percentage of the time, as the 70 meter antenna is primarily used for tracking and communicating with spacecraft as part of the

NASA Deep Space Network The NASA Deep Space Network (DSN) is a worldwide Telecommunications network, network of spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that supports NASA' ...

Planetary observations

GSSR can work in two different modes. In the monostatic radar mode, GSSR both transmits and receives. In bistatic mode, GSSR transmits and other radio astronomy facilities receive. Although more difficult to schedule, this offers two advantages - the transmitter does not need to turn off to allow the receiver to listen, and it allows the use of

interferometry Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...

to extract more information from the reflected signal. Since the GSSR takes about 5 seconds to switch from transmit to receive, nearby targets must necessarily use bistatic mode. Bodies that have been investigated using GSSR include: *Mercury: In particular, by watching specific reflected features of Mercury sweep across the Earth's surface (using spatially separated receivers), GSSR enables the pole position to be computed quite accurately. The measured

libration In lunar astronomy, libration is the cyclic variation in the apparent position of the Moon that is perceived by observers on the Earth and caused by changes between the orbital and rotational planes of the moon. It causes an observer to see ...

s show Mercury has a liquid core. *Venus *Mars: GSSR was used extensively to characterize sites for Mars landers. *Asteroids: Small asteroids appear only as unresolved points of light in ground-based optical telescopes. Radar, however, can image near-Earth asteroids and comets with a resolution of several meters. For example, the asteroid

4179 Toutatis 4179 Toutatis ( provisional designation ) is an elongated, stony asteroid and slow rotator, classified as a near-Earth object and potentially hazardous asteroid of the Apollo asteroid group, approximately 2.5 kilometers in diameter. Discovere ...

was imaged in 1992, 1996, 2000, 2004, 2008, and 2012. Although spacecraft such as

Dawn Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the diffuse sky radiation, appearance of indirect sunlight being Rayleigh scattering, scattered in Earth's atmosphere, when the centre of the Sun's disc ha ...

can image particular asteroids in much finer detail, radar astronomy can investigate many more asteroids of different characteristics. For example, most existing images of binary asteroids were obtained through radar astronomy. *Moons of Jupiter *Rings and moons of Saturn Toutatis.jpg,

in 1996 Asteroid 1999 JM8.gif, (53319) 1999 JM8 in 1999 2005YU55-20111107.jpg, (308635) 2005 YU55 in 2011 Upcoming asteroid observations can be found online at the Goldstone Asteroid Schedule.

Other scientific uses

*Recovery of the

Solar and Heliospheric Observatory The Solar and Heliospheric Observatory (SOHO) is a European Space Agency (ESA) spacecraft built by a European industrial consortium led by Matra Marconi Space (now Airbus Defence and Space) that was launched on a Lockheed Martin Atlas IIAS la ...

after loss of attitude control. *Investigation of orbital debris around Earth.

Similar facilities

The GSSR is the only planetary radar in current regular operation. Others are or were: * The planetary radar at

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science F ...

, which collapsed in 2020. * The Soviet planetary radar at the Pluton complex, since dismantled. * The Millstone Hill and Haystack radio telescopes of the Haystack Observatory made radar observations from 1958 through at least 1970. * The Yevpatoria RT-70 radio telescope is equipped with a powerful transmitter, and has been used in bi-static radar observations. There are proposals and prototypes for possible additional radars: * The

Green Bank Observatory The Green Bank Observatory (previously National Radio Astronomy Observatory, Green Bank) is an Observatory, astronomical observatory located in the United States National Radio Quiet Zone, National Radio Quiet Zone in Green Bank, West Virginia, G ...

is investigating a Ku-band radar for its 100 meter radio telescope. Its low power prototype has imaged the moon. * China is developing a planetary radar. Their initial phase has imaged the moon.

References

{{Portal bar, California, Astronomy, Stars, Spaceflight, Outer space, Solar System, Education, Science Deep space networks Space radars Mojave Desert Radio telescopes Astronomical observatories in California