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Dawn

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Dawn

Status: Operational 2007. First Launch: 2007-09-27. Last Launch: 2007-09-27. Number: 1 . Thrust: 0.27 N (0.06 lbf). Gross mass: 1,218 kg (2,685 lb). Unfuelled mass: 793 kg (1,748 lb). Height: 1.64 m (5.38 ft). Diameter: 1.27 m (4.16 ft). Span: 20.00 m (65.00 ft).

The ninth NASA Discovery mission, and a follow-on to the Deep Space 1 technology mission, it was equipped with three NSTAR xenon ion engines. The spacecraft used the Orbital/Dulles Star-2-derived bus. The three main instruments were a Framing Cameras, a VIR visible/IR mapping spectrometer, and the GRaND gamma ray and neutron spectrometer. Using its ion engines and a Mars flyby in February 2009, Dawn was scheduled to reach Vesta in 2011 and Ceres in 2015.

Mission profile:

• Mars flyby and gravity assist: 4 February 4, 2009. Dawn will fly within 500 kilometers of Mars and have completed slightly under one orbit of the sun. During the flyby, Dawn may use its science instruments to make observations of the planet. Main purpose of the flyby is to use Mars' gravity to torque Dawn's orbit out of the ecliptic plane, towards Vesta. The flyby will give Dawn a heliocentric delta-V of 1.12 km/sec.
• Vesta arrival: 14 August 2011. Dawn's ion propulsion system will be used to spiral out towards Vesta, and then match its flight path to that of the asteroid. The slow approach ensures there are no time-critical thruster firings. As it approaches, Dawn will conduct a survey of the region around the asteroid for any possible natural satellites, dust and debris. It will then use ion propulsion to brake itself into a polar mapping orbit around Vesta. By the time it reaches the asteroid, Dawn will have accumulated about 1,000 days of ion engine operation. During nine months of Vesta orbit operations, the ion engine will be used to ensure a changing series of circular near-polar orbits, allowing Dawn to study the entire surface of the asteroid. The highest orbit will be roughly 2,500 kilometers altitude, the lowest under 200 kilometers.
• Ceres arrival: 1 February 2015. After leaving Vesta, the spacecraft will spend nearly three years en route to Ceres, making about three-fourths of one orbit around the sun as it spirals outward toward the dwarf planet. Dawn will use its ion propulsion to make a slow approach to and drop into orbit around Ceres. As at Vesta, Dawn will enter a series of circular near-polar orbits that will provide vantage points for studying nearly the entire surface of the dwarf planet.
• End of mission: July 2015. At the planned end of Dawn's primary mission, the spacecraft was to be in a quarantine orbit around Ceres at an altitude of 700 kilometers. This orbit ensured that the decommissioned spacecraft would not impact Ceres for 50 years, supposedly allowing time for action in case some kind of life was detected. Total days of ion engine thrusting during the entire mission were to be 2,000

Development Cost $: 281.700 million. Cost Notes: $357.5 total, including $75.8 m mission operations. RCS Coarse No x Thrust: 12 MR-103G x 0.9 N. RCS Propellants: 46 kg (101 lb). Electric System: 10.00 kWh.

NASA NSSDC Master Catalog Description

Dawn is a mission designed to rendezvous and orbit the asteroids 4 Vesta and 1 Ceres. The scientific objectives of the mission are to characterize the asteroids' internal structure, density, shape, size, composition and mass and to return data on surface morphology, cratering, and magnetism. These measurements will help determine the thermal history, size of the core, role of water in asteroid evolution and what meteorites found on Earth come from these bodies, with the ultimate goal of understanding the conditions and processes present at the solar system's earliest epoch and the role of water content and size in planetary evolution. The data returned will include, for both asteroids, full surface imagery, full surface spectrometric mapping, elemental abundances, topographic profiles, gravity fields, and mapping of remnant magnetism, if any.

Spacecraft and Subsystems

The Dawn spacecraft is generally box-shaped (1.64 x 1.27 x 1.77 m) and made of aluminum and graphite composite with a dry mass of 747.1 kg and a fueled launch mass of 1217.7 kg. The spacecraft core is a graphite composite cylinder, with the titanium hydrazine and xenon tanks mounted inside. Mounting, access, and other panels are aluminum core with aluminum facesheets. Two solar panel wings extend 19.7 m tip-to-tip and are mounted on opposite sides of the spacecraft. A parabolic fixed 1.52 m high gain dish antenna is mounted on one side of the spacecraft in the same plane as the solar arrays. Three low gain antennas are also mounted on the spacecraft. A 5 m long magnetometer boom extends from the top panel of the spacecraft. Also mounted on the top panel is the instrument bench, holding the cameras, mapping spectrometer, laser altimeter, and star trackers. A gamma ray / neutron spectrometer is mounted on the top panel as well.

The two 2.3 x 8.3 meter solar arrays, composed of InGaP/InGaAs/Ge triple-junction cells, provide 10.3 kW at 1 AU (1.3 kW at end-of-life at 3 AU) to drive the spacecraft (22-35 V) and the solar electric ion propulsion system (80-140 V). Power is stored in a 35 Ah NiH2 battery. The ion propulsion consists of three ion thrusters and is based on the Deep Space 1 spacecraft ion drive, using xenon which is ionized and accelerated by electrodes. The xenon ion engines have a maximum thrust at 2.6 kW input power of 92 mN and a specific impulse of 3200 to 1900 s. The 30-cm diameter thrusters are two-axis gimbal mounted at the base of the spacecraft. The xenon tank held 425 kg of propellant at launch.

Attitude control is maintained by reaction wheels and twelve 0.9 N hydrazine engines placed around the spacecraft. The hydrazine tank holds 45.6 kg propellant at launch. The hydrazine thrusters can also be used to help orbit insertion maneuvers. Attitude knowledge is provided by star trackers and gyros The thermal control system consists of ammonia-based heat pipes and louvers, and requires roughly 200 W at 3 AU. Communications are in X-band for both uplink and downlink, through the body-fixed high and medium gain antennas and a low gain omnidirectional antenna, utilizing a 100 W traveling wave tube amplifier. The command and data handling system utilizes a RAD6000 processor, 8 Gb mass memory, and a Mil-Std-1553B data bus. Uplink data rates range from 7.8 b/s to 2.0 kb/s and downlink rates from 10 b/s to 124 kb/s.

Mission Profile

Launch from Cape Canaveral on a Delta 2 (7925-H) took place on 27 September at 11:34 UT (7:34 a.m.. EDT). Transfer into a trajectory towards the asteroid belt took place approximately 1 hour later. After a four year heliocentric cruise including a Mars flyby to within 542 km of the surface and gravity assist on 18 February 2009 at 00:27:58 UT. Dawn reached Vesta on 16 July 2011 and went into orbit. Dawn spiraled down to a high survey orbit at 2750 km altitude with a period of 69 hours on 2 August, followed by a 12.3 hour mapping orbit at 680 km on 27 September and then a lower (210 km, 4.3 hour) mapping orbit on 8 December. Dawn departed Vesta on 5 September 2012 at 06:26 UT and entered initial orbit around Ceres on 6 March 2015 at 12:29 UT. It reshaped the orbit to its first science orbit, circular with an altitude of 13500 km, reaching this on April 23. It is now spiraling down into lower orbits, and finally to a 375 km altitude circular science orbit, achieving this in December of 2015. The end of the primary mission takes place in June 2016. After the end of the mission Dawn will remain in orbit around Ceres. The final orbit will be stable with a lifetime of several hundred years. The hydrazine thrusters were used for orbit capture.

The total cost for the mission is estimated to be $446 million.

Photo Gallery

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Dawn Credit: Manufacturer Image

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• Dawn - . Mass: 1,218 kg (2,685 lb). Nation: USA. Agency: Martin. Class: Surveillance. Type: Civilian surveillance satellite. Spacecraft: Dawn. USAF Sat Cat: 32249 . COSPAR: 2007-043A.

  Asteroid belt unmanned probe designed to first orbit and survey the asteroid Vesta, and then fly on to the largest asteroid, Ceres. The Delta upper stage boosted the spacecraft and PAM-D solid third stage to 9.01 km/sec and a 185 km x 6835 km orbit. The PAM-D fired at 12:29 GMT and released Dawn after accelerating it to 11.50 km/sec and sending it into a 1.00 AU x 1.62 AU x 0.5 deg solar orbit. The ion engines were ignited on 6 October. Using its ion engines and a Mars flyby in February 2009, Dawn was scheduled to reach Vesta in 2011 and Ceres in 2015.