The COmet Nucleus TOUR (CONTOUR) was a NASA Discovery-class space probe that failed shortly after its July 2002 launch. It had as its primary objective close flybys of two comet nuclei with the possibility of a flyby of a third known comet or an as-yet-undiscovered comet.
The two comets scheduled to be visited were Encke and Schwassmann-Wachmann-3, and the third target was d'Arrest. It was hoped that a new comet would have been discovered in the inner solar system between 2006 and 2008, in which case the spacecraft trajectory would have been changed if possible to rendezvous with the new comet. Scientific objectives included imaging the nuclei at resolutions of up to 4 metres (13 ft), performing spectral mapping of the nuclei at resolutions of up to 100 metres (330 ft), and obtaining detailed compositional data on gas and dust in the near-nucleus environment, with the goal of improving knowledge of the characteristics of comet nuclei.
After the solid rocket motor intended to inject the spacecraft into solar orbit was ignited on August 15, 2002, contact with the probe could not be re-established. Ground-based telescopes later found three objects along the course of the satellite, leading to the speculation that it had disintegrated. Attempts to contact the probe were ended on December 20, 2002. The probe thus accomplished none of its primary scientific objectives, but did prove some spaceflight technologies, such as the APL-developed non-coherent spacecraft navigation technique, which was later used on the New Horizons spacecraft.
The CONTOUR spacecraft had a total fueled mass of 775 kg, including 70 kg of hydrazine fuel and a Star 30BP booster with a mass of 377 kg. Power was provided by a body-mounted solar array designed for operation at distances between 0.75 and 1.5 AU from the Sun. It was three-axis stabilized for encounters and spin-stabilized during cruise mode between encounters.
COUNTOUR's Command/Data-handling and Guidance/Control computers both used the Mongoose-V microprocessor. Communications were through a fixed 0.45 m diameter high-gain antenna designed to support data rates greater than 100 kbit/s at encounters. Data and images were stored on two 3.3 Gbit solid-state recorders with a capacity of 600 images.
The spacecraft was equipped with four primary science instruments: the Contour Remote Imager/Spectrograph (CRISP), the Contour Aft Imager (CAI), the Dust Analyzer (CIDA), and the Neutral Gas Ion Mass Spectrometer (NGIMS).
CONTOUR launched on a Delta 7425 (a Delta II Lite launch vehicle with four strap-on solid-rocket boosters and a Star 27 third stage) on July 3, 2002, at 6:47:41 UT (2:47:41 a.m. EDT) from Cape Canaveral Air Force Station. It was launched into a high-apogee Earth orbit with a period of 5.5 days. Following a series of phasing orbits, the Star 30 solid rocket motor was used to perform an injection maneuver on August 15, 2002, to put CONTOUR in the proper trajectory for an Earth flyby in August 2003 followed by an encounter with comet Encke on November 12, 2003, at a distance of 100 to 160 km and a flyby speed of 28.2 km/s, 1.07 AU from the Sun and 0.27 AU from Earth. During the August 2002 injection maneuver, the probe was lost.
Three more Earth flybys would have followed, in August 2004, February 2005, and February 2006. On June 18, 2006, CONTOUR would have encountered comet Schwassmann-Wachmann-3 at 14 km/s, 0.95 AU from the Sun and 0.33 AU from Earth. Two more Earth flybys were scheduled in February 2007 and 2008, and a flyby of comet d'Arrest might have occurred on 16 August 2008 at a relative velocity of 11.8 km/s, 1.35 AU from the Sun and 0.36 AU from Earth. All flybys would have had a closest encounter distance of about 100 km and would have occurred near the period of maximum activity for each comet. After the comet Encke encounter, CONTOUR might have been retargeted towards a new comet if one was discovered with the desired characteristics (e.g. active, brighter than absolute magnitude 10, perihelion within 1.5 AU).
According to NASA: "An investigation board concluded that the most likely cause of the mishap was structural failure of the spacecraft due to plume heating during the solid-rocket motor burn. Alternate possible but less likely causes determined were catastrophic failure of the solid rocket motor, collision with space debris, and loss of dynamic control of the spacecraft."
After the loss of CONTOUR, a replacement spacecraft – CONTOUR 2 – was proposed, scheduled for launch in 2006. However, the replacement did not ultimately materialize.
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