DAWN Capture Into Vesta Orbit

Dawn was scheduled to enter Vesta's orbit by 1 a.m. EDT Saturday, July 16th, 2001. That made DAWN the first to enter orbit around a minor planet! The spacecraft was to spiral gently into orbit around the asteroid as by approximately 9,900 miles (16,000 km) from Vesta, the asteroid's gravity was to capture the spacecraft in orbit. DAWN was to have gently slow down to about 75 mph as the minor planet will lied by 117 million miles (188 million kilometers) away from Earth. After DAWN enters Vesta's orbit, engineers expected to hear from the spacecraft and confirm that it performed as planned during a scheduled communications pass that started at approximately 2:30 a.m. EDT Sunday, July 17. They were to need a few days to determine the exact time of capture as unlike other missions where a dramatic insertion burn results in orbit DAWN ion propulsion engine is not able to that and a, until Dawn nears Vesta and makes accurate measurements, the asteroid's mass and gravity keep only be estimates. DAWN spacecraft had reached its official approach phase by May 3rd, 2011 to last three months beginning by 752,000 miles (1.21 million km) from Vesta, or about three times the distance between Earth. By Mar. 21, 2011, DAWN had got out of a hibernation of about six months. DAWN's three instruments were all functioning and appear to be properly calibrated before encounter

That image, as seen from 96,000 miles (155,000 kilometers) away was taken on June 20th, 2011 and is about twice as sharp as the best images of Vesta taken through the Hubble Space Telescope. A previous, June 2011 video loop from images obtained for navigation purposes from a distance of about 300,000 miles (483,000 kilometers) already showed such a jagged, irregular shape, as a enormous crater known to exist at Vesta's south pole is also now well seen. courtesy site 'Amateur Astronomy' from a picture NASA/JPL-Caltech/UCLA/MPS/DLR/PSI and NASA/ESA/STScI/UMd

DAWN spacecraft on Saturday, July 16th, 2011 became the first probe ever to enter orbit around a minor planet in the main asteroid belt between Mars and Jupiter. The spacecraft relayed information to confirm it entered Vesta's orbit. The time of DAWN's capture depended on Vesta's mass and gravity, which only has been estimated until now. The asteroid's mass determines the strength of its gravitational pull. If Vesta is more massive, its gravity is stronger, meaning it pulled DAWN into orbit sooner. If the asteroid is less massive, its gravity is weaker and it would have taken the spacecraft longer to achieve orbit. Ensuing data allowed to determine a tentative definition of the exact time that Dawn entered Vesta's orbit, which is 12:47 a.m. EDT, July 16, 2011

To improving imaging plans mission engineers have built in 2011 a digital best guess terrain of Vesta as data taken by the mission will equal best global topography maps of Earth made by NASA's Shuttle Radar Topography mission. Dawn however experienced a loss of thrust on June 27 and got into safe mode after a computer glitch. Engineers were able to return the spacecraft to a normal configuration and restart the spacecraft's thrusting on June 30 by switching to a second digital control and interface unit with equivalent capabilities. In an unrelated event, the visible and infrared mapping spectrometer on Dawn reset itself on June 29. At the time of the reset, the instrument was gathering calibration data during the spacecraft's approach to the giant asteroid Vesta. Some of its planned observations were completed successfully before automatic sensors turned the instrument off. On June 30, Dawn team members were able to trace the reset to an internal error in the instrument's central processing unit, though they don't yet know why the internal error occurred. They powered the instrument back off, as originally planned for this time. Team members were working to determine when they will turn it back on again