Encountered comet Halley March 13, 1986. The Giotto mission was designed to study Comet P/Halley, and also studied Comet P/Grigg-Skjellerup during its extended mission. The spacecraft encountered Halley on March 13, 1986, at a distance of 0.89 AU from the sun and 0.98 AU from the Earth and an angle of 107 degrees from the comet-sun line. The actual closest approach was measured at 596 km. All experiments performed well and returned a wealth of new scientific results, of which perhaps the most important was the clear identification of the cometary nucleus. Fourteen seconds before closest approach, Giotto was hit by a `large' dust particle. The impact caused the spacecraft angular momentum vector to shift 0.9 degrees. Scientific data were received intermittently for the next 32 minutes. Some experiment sensors suffered damage during this 32-minute interval. Other experiments (the camera baffle and deflecting mirror, the dust detector sensors on the front sheet of the bumper shield, and most experiment apertures) were exposed to dust particles regardless of the accident and also suffered damage. Many of the sensors survived the encounter with little or no damage. Questionable or partially damaged sensors included the camera (later proved to not be functional) and one of the plasma analyzers (RPA). Inoperable experiments included the neutral and ion mass spectrometers and one sensor each on the dust detector and the other plasma analyzer (JPA). During the Giotto extended mission, the spacecraft successfully encountered Comet P/Grigg-Skjellerup on July 10, 1992. The closest approach was approximately 200 km. The heliocentric distance of the spacecraft was 1.01 AU, and the geocentric distance, 1.43 AU at the time of the encounter. The payload was switched-on in the evening of July 9. Eight experiments were operated and provided a surprising wealth of data. The Johnstone Plasma Analyser detected the first presence of cometary ions 600,000 km from the nucleus at 12 hours before the closest approach. The Dust Impact Detectors reported the first impact of a fairly large particle at 15:30:56. Bow shocks/waves and acceleration regions were also detected. After the P/Grigg-Skjellerup encounter operation were terminated on 23 July 1992. The spacecraft will fly by the Earth on 1 July 1999.

Stardust was to fly within 100 km of comet 81P/Wild-2 in January 2004 and recover cometary material using an aerogel substance. A return capsule would land on a lake bed in Utah in January 2006, returning the material to earth. The launch went as planned. The second stage ignited at 21:08 GMT and its first burn put the vehicle into a 185 km x 185 km x 28 degree parking orbit at 21:14 GMT. The second stage second burn at 21:25 changed the orbit to planned values of 178 km x 7184 km x 28.5 degrees. The Star 37FM solid third stage ignited at 21:29 GMT and placed the spacecraft into a 2 year period solar orbit. The spacecraft separated at 21:31 GMT. Meanwhile, the Delta 266 second stage burned a third time on its own, until its propellants were depleted, entering a final orbit of 294 km x 6818 km x 22.5 degrees. The Stardust probe flew past Earth at a distance of 3706 km at 1115 GMT on January 15, 2001, and flew near the Moon at a distance of 98000 km at around 0200 GMT on January 16. The gravity assist flyby changed Stardust's heliocentric orbit from 0.956 x 2.216 AU x 0.0 deg to 0.983 x 2.285 AU x 3.7 deg.

Launch delayed from July 1st. The latest NASA Discovery mission was successfully launched on Jul 3. The CONTOUR (Comet Nucleus Tour) probe, built and operated by the Johns Hopkins University's Applied Physics Laboratory (APL), began its five year mission to explore three comets, using repeated encounters with the earth to modify its orbit in order to reach each target. The first burn of the second stage completed at 0659 UTC putting the spacecraft in a 185 x 197 km x 29.7 deg parking orbit. At 0746 UTC the second stage restarted for a short 4s burn to 185 x 309 km x 29.7 deg, and then separated once the PAM-D (ATK Star 48B) solid third stage was spun up. The 1.5 minute burn of the third stage motor at 0748 UTC put it and CONTOUR in a 90 x 106689 km x 30.5 deg phasing orbit. By July 8 CONTOUR's orbit was 214 x 106686 km x 29.8 deg. CONTOUR stayed in this phasing orbit until August 15, when it was injected into solar orbit using its internal ATK Star 30 solid motor. Flyby of the first target, comet 2P/Encke, was scheduled for Nov 2003.

Launched into a 0.981 AU x 1.628 AU solar orbit inclined 0.6 deg to the ecliptic. Deep Impact was to fly by Comet 9P/Tempel-1 on 3 July 2005. An impacter it released was to hit the comet on 4 July at 10.2 km/s, producing a crater and ejecta plume that would allow the flyby spacecraft to determine the composition and structure of the comet's nucleus.