Question: Radar observations of 101 Helena were made from the Arecibo Observatory in what year?
Context: 101 Helena is a rocky main-belt asteroid.  It was discovered by Canadian-American astronomer J. C. Watson on August 15, 1868, and was named after Helen of Troy in Greek mythology.  Radar observations were made of this object on Oct 7 and 19, 2001 from the Arecibo Observatory.  Analysis of the data gave an estimated ellipsoidal diameter of 71×63×63 ± 16% km.  The diameter estimated from IRAS infrared measurements is 66 km.  It is classified as an S-type asteroid in the Tholen system. The Goldstone Solar System Radar, or GSSR, is a large radar system used for investigating objects in the Solar system.  Located in the desert near Barstow, California, 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.  It has been used to investigate Mercury, Venus, Mars, the asteroids, and moons of Jupiter and Saturn.  The most comparable facility is the radar at Arecibo Observatory. The ALFALFA research project is located at the Arecibo Observatory and started on February 4 2005.  It is still ongoing (April 2013).  The name is the abbreviation of Arecibo Legacy Fast ALFA.  ALFA is the abbreviation of Arecibo L-Band Feed Array. Debussy is a rayed impact crater on Mercury, which was discovered in 1969 by low resolution ground based radar observations obtained by the Goldstone Observatory.  Later in 1990–2005 it was imaged in more detail by the Arecibo Observatory.  The crater was initially known as the feature A.  The bright appearance of rays in the radar images indicates that the crater is geologically young, because fresh and rough surfaces of young impact craters are good scatterers of radio waves. A radar tracker is a component of a radar system, or an associated command and control (C2) system, that associates consecutive radar observations of the same target into tracks.  It is particularly useful when the radar system is reporting data from several different targets or when it is necessary to combine the data from several different radars or other sensors. Steven Jeffrey Ostro (March 9, 1946 – December 15, 2008) was an American scientist specializing in radar astronomy.  He worked at NASA's Jet Propulsion Laboratory.  Ostro led radar observations of numerous asteroids, as well as the moons of Jupiter and Saturn, Saturn's rings, and Mars and its satellites.  As of May 2008, Ostro and his collaborators had detected 222 near-Earth asteroids (including 130 potentially hazardous objects and 24 binaries) and 118 main belt objects with radar.  He died December 15, 2008 due to complications related to cancer.  He has been remembered fondly by his colleagues for both his personal and professional contributions. Hokusai is a rayed impact crater on Mercury, which was discovered in 1991 by ground-based radar observations conducted at Goldstone Observatory.  The crater was initially known as feature B. Its appearance was so dissimilar to other impact craters that it was once thought to be a shield volcano.  However improved radar images by the Arecibo Observatory obtained later in 2000–2005 clearly showed that feature B is an impact crater with an extensive ray system.  The bright appearance of rays in the radio images indicates that the crater is geologically young; fresh impact ejecta has a rough surface, which leads to strong scattering of radio waves. Arecibo Catena (Arecibo Vallis until March 2013) is a catena on Mercury.  It is located at latitude 27.5 S, longitude 28.4 W, in the hilly and chaotic terrain antipodal to Caloris Basin.  It is named after Arecibo Observatory. The Arecibo Observatory is a radio telescope in the municipality of Arecibo, Puerto Rico.  This observatory is operated by SRI International, USRA and UMET, under cooperative agreement with the National Science Foundation (NSF).  The observatory is the sole facility of the National Astronomy and Ionosphere Center (NAIC), which refers to the observatory, and the staff that operates it.  From its construction in the 1960s until 2011, the observatory was managed by Cornell University. Donald B. Campbell is an Australian-born astronomer and Professor of Astronomy at Cornell University.  Prior to joining the Cornell faculty he was Director of the Arecibo Observatory in Puerto Rico for seven years.  Campbell's research work is in the general area of planetary studies with a concentration on the radio-wavelength-scattering properties of planets, planetary satellites, and small bodies.  His work includes studies of Venus, the Moon, the Galilean satellites of Jupiter, Titan, as well as comets and asteroids.  Campbell observed near-Earth asteroid 433 Eros, which was the first asteroid detected by the Arecibo Observatory radar system.
Answer: 2001