CONTOUR
The Comet Nucleus Tour was a NASA Discovery-class space probe that failed shortly after its July 2002 launch. It was the only Discovery mission to fail.
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, performing spectral mapping of the nuclei at resolutions of up to, 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 Doppler tracking spacecraft navigation technique, which was later used on the New Horizons spacecraft.
Spacecraft
Design and construction
The CONTOUR spacecraft was constructed in-house at the Johns Hopkins University Applied Physics Laboratory. CONTOUR was shaped as an octagonal prism, measuring at tall and long, had a total fueled mass of at launch, not including the mass of the Star 30 booster it was attached to, during the launch phase of the mission. The spacecraft was fitted with a whipple shield, similar to the one used on Stardust, on its leading face, designed with four layers of nextel fabric and seven layers of kevlar. The shield was built to allow the spacecraft to withstand the respective 28.2 and 14 km/s velocity flybys of comets Encke and Schwassmann-Wachmann-3, where the spacecraft would be subjected to numerous particles ejecting from the nuclei of the comets. Although mission scientists predicted that the spacecraft would take no significant damage during the Encke and Schwassmann-Wachmann-3 encounters, the shield and its prototypes were tested vigorously during the construction of the spacecraft, including one where a shield prototype was shot at with surrogate nylon particles from a two stage light-gas gun. The results of the earlier tests allowed mission planners to determine a safe distance from which the CONTOUR would pass by comets targeted on the mission. Three of the four scientific instruments aboard the spacecraft were embedded within this shield.Spacecraft subsystems
Power
Power for CONTOUR derives from solar cells, which are mounted onto the spacecraft, decorating the sides and rear and generating up to 670 watts of power. A nickel–cadmium battery designed to last up to nine ampere hours was also installed aboard the spacecraft in the event that the solar cell system fails, or does not provide enough power for the spacecraft or its instruments to function.Communications and data
Propulsion and guidance
Unlike many interplanetary missions, CONTOUR was not designed to be propelled beyond Earth orbit by the rocket that launched it, instead it exited Earth orbit using a STAR-30 solid rocket booster built into the spacecraft. This STAR-30 engine provided 1,922 meters per second of delta-v. The firing of this engine is the reason the CONTOUR spacecraft was destroyed. In addition, there were 16 hydrazine thrusters for normal propulsion and course corrections. These thrusters were divided into four clusters of four.Scientific payload
- CIDA
- CRISP
- CAI
- '''NGIMS'''
Mission
Three more Earth flybys would have followed, on August 14, 2004, February 10, 2005, and February 10, 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.