CONTOUR

The Comet Nucleus Tour (CONTOUR) Discovery class mission has 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 to be visited are Encke[?] and Schwassmann-Wachmann-3[?], and the third target is d'Arrest[?]. It is hoped that a new comet will be discovered that will be in the inner solar system between 2006 and 2008, in which case the spacecraft trajectory will be 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.

Spacecraft design

The CONTOUR spacecraft has 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 is provided by a body-mounted solar array designed for operation at distances between 0.75 and 1.5 AU from the Sun. It is three-axis stabilized for encounters and spin-stabilized during cruise mode between encounters. Communications are 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 are stored on two 3.3 Gbit solid-state recorders with a capacity of 600 images. The spacecraft is 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 will be 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. Three more Earth fly-bys follow, in August 2004, February 2005, and February 2006. On 18 June 2006 CONTOUR encounters 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 are scheduled in February of 2007 and 2008, and a fly-by of comet d'Arrest may occur 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 will have a closest encounter distance of about 100 km and will occur near the period of maximum activity for each comet. After the comet Encke encounter, CONTOUR may be 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).