Near Earth Asteroid Rendezvous (NEAR) mission was the first of NASA's Discovery missions, a series of small-scale spacecraft designed to proceed from development to flight in under three years for a cost of less than $150 million. The spacecraft's mission was to rendezvous with and achieve orbit around the asteroid Eros in January 1999, and study the asteroid for one year. However as it flew by the Earth on 23 January 1998, a problem caused an abort of the first encounter burn. The mission had to be rescoped for a later encounter but successfully entered orbit around Eros on Valentine's Day 2000 and ended the mission by gently landing on its surface on 12 February 2001.

The primary mission of Deep Space 1 probe was to test new technology for future interplanetary spacecraft, the main experiment being an ion propulsion engine using xenon propellant. It had an initial mass of 486.3 kg, including 81.5 kg of Xenon and 31.1 kg of hydrazine propellants. The Delta 7326 used three Alliant GEM-40 solid strap-on motors, the standard Delta II core vehicle, and a Thiokol Star 37FM solid motor as the third stage. The Delta second stage entered a 185 km parking orbit, then fired again to enter a 174 km x 2744 km x 28.5 degree orbit. The Star 37FM then separated and accelerated to place Deep Space 1 to escape velocity. Deep Space 1 successfully started its ion engine on November 24 after an initial attempt failed after four minutes on November 10. From its initial solar orbit of 0.99 AU x 1.32 AU x 0.4 degree, Deep Space 1 was to fly past the 3 km diameter asteroid 1992 KD at its perihelion of 1.33 AU. The spacecraft then flew past the nucleus of comet 19P/Borrelly at a distance of 2200 km at 2230 GMT on Sep 22 2001. It survived the encounter in good shape, sending back photos of the comet. At the encounter DS1 was in a 1.3 x 1.5 AU x 0 deg (ecliptic) solar orbit; Borrelly's orbit was 1.3 x 5.9 AU.