CONTOUR

The Comet Nucleus Tour (CONTOUR) was a Discovery class space mission. It had as its primary objective close fly-bys of two comet nuclei with the possibility of a fly-by 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 that will be 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 include imaging the nuclei at resolutions of 4 m, performing spectral mapping of the nuclei at resolutions of 100-200 m, and obtaining detailed compositional data on gas and dust in the near-nucleus environment, with the goal of improving our knowledge of the characteristics of comet nuclei.

During an course correction engine firing on August 15, 2003, contact with the probe was lost. Ground-based telescopes later found three objects along the course of the satellite, leading to the speculation that it had been destroyed. Attempts to contact the probe were December 20, 2003. The probe accomplished none of its objectives.

Spacecraft design

The CONTOUR spacecraft had a total fueled mass of 775 kg, including a Star 27 SRM booster with a mass of 377 kg and 70 kg of hydrazine fuel. 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. Communications were through a fixed 0.45 m diameter high-gain antenna which will support data rates greater than 100 kbit/sec 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).

Mission

CONTOUR launched on a Delta 7325 (a Delta II Lite launch vehicle with three 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) into a high-apogee Earth orbit with a period of 5.5 days from Cape Canaveral Air Force Station. Following a series of phasing orbits, the Star 27 solid rocket motor was used to perform an injection maneuver on August 15, 2002 to put CONTOUR in the proper trajectory for an Earth fly-by in August 2003 followed by an encounter with comet Encke on 12 November 2003 at a distance of 100 to 160 km and a fly-by speed of 28.2 km/sec, 1.07 AU from the Sun and 0.27 AU from Earth. During the manuever the probe was lost. Three more Earth fly-bys would have followed, in August 2004, February 2005, and February 2006. On 18 June 2006 CONTOUR would have encountered comet Schwassmann-Wachmann-3 at 14 km/sec, 0.95 AU from the Sun and 0.33 AU from Earth. Two more Earth fly-bys were scheduled in February of 2007 and 2008, and a fly-by of comet d'Arrest might have occurred on 16 August 2008 at a relative velocity of 11.8 km/sec, 1.35 AU from the Sun and 0.36 AU from Earth. All fly-bys 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 is discovered with the desired characteristics (e.g. active, brighter than absolute magnitude 10, perihelion within 1.5 AU).