Dawn (spacecraft)

Dawn (spacecraft)
Name	Dawn
Mission type	Asteroid orbiter
Operator	NASA / Jet Propulsion Laboratory
COSPAR ID	2007-043A
SATCAT	32249
Mission duration	Planned: 9 years, Final: 11 years, 1 month, 5 days
Spacecraft	Dawn
Manufacturer	Orbital Sciences Corporation
Launch mass	1,217.7 kg (2,685 lb)
Power	10 kW at 1 AU, 1.3 kW at 3 AU
Launch date	September 27, 2007, 11:34 UTC
Launch rocket	Delta II 7925H
Launch site	Cape Canaveral SLC-17B
End of mission	November 1, 2018
Last contact	October 31, 2018
Orbit reference	Vesta and Ceres
Apsis	helion

Dawn (spacecraft) was a pioneering NASA mission that became the first to orbit two extraterrestrial destinations, the protoplanet Vesta and the dwarf planet Ceres. Launched in 2007, it was the first purely scientific mission to use ion propulsion for primary interplanetary travel, allowing for unprecedented orbital flexibility. Managed by the Jet Propulsion Laboratory and built by Orbital Sciences Corporation, its mission concluded in 2018 after vastly expanding our understanding of the early Solar System.

Spacecraft Design and Development

The spacecraft's design was centered around its revolutionary ion thruster system, which utilized xenon propellant and solar-derived electrical power to achieve high efficiency over its long-duration mission. Its primary scientific payload consisted of three instruments: the Framing Camera provided by the Max Planck Institute for Solar System Research, a Visible and Infrared Spectrometer from the Italian Space Agency, and a Gamma Ray and Neutron Detector from the Los Alamos National Laboratory. The Orbital Sciences Corporation constructed the bus, which featured large solar arrays to power the ion engines and instruments in the dim light of the asteroid belt. The development faced significant technical and budgetary challenges, including a cancellation and reinstatement by NASA in 2006, before its successful launch.

Mission Overview

Launched atop a Delta II rocket from Cape Canaveral SLC-17B on September 27, 2007, Dawn began a complex interplanetary cruise. Its trajectory included a gravity-assist flyby of Mars in 2009 to boost its velocity toward the asteroid belt. The mission's defining characteristic was its use of ion propulsion to spiral into and out of orbit around its two targets, a capability impossible with conventional chemical rockets. After studying Vesta in 2011-2012, Dawn departed and traveled to Ceres, entering orbit in 2015 to commence an extended investigation that lasted until its fuel was exhausted.

Scientific Objectives

The core scientific goal was to characterize the conditions and processes of the early Solar System by studying these two intact protoplanets, which are remnants from the epoch of planetary formation. By comparing the geologically evolved, dry Vesta with the water-rich, potentially ocean-world Ceres, scientists aimed to understand the role of water in planetary evolution. Specific objectives included determining the shape, internal structure, and elemental composition of each body, mapping their surface geology, and investigating the nature of bright, reflective deposits on Ceres.

Orbital and Landing Phases

Dawn did not land but conducted extensive orbital operations. At Vesta, it occupied several science orbits, including a low-altitude mapping orbit (LAMO) at about 210 km, providing high-resolution data. After over a year in residence, it used its ion thrusters to depart. At Ceres, it achieved a series of progressively lower orbits, culminating in a final, ultra-close orbit at less than 35 km from the surface. This final phase, ending in 2018, provided the highest-resolution measurements of Ceres's gravity field and surface composition before the spacecraft's hydrazine fuel for attitude control was depleted.

Discoveries and Observations

At Vesta, Dawn confirmed it as the source of the HED meteorites, revealed a heavily cratered surface with a massive impact basin at its south pole named Rheasilvia, and detected a dense iron core. At Ceres, its findings were transformative, identifying numerous localized bright areas now known to be deposits of sodium carbonate, suggesting recent geologic activity. It discovered the prominent, isolated mountain Ahuna Mons and, critically, detected widespread phyllosilicates and a significant reservoir of briny water in the form of a subsurface ocean or deep brine reservoirs. These results positioned Ceres as an ocean world.

Current Status

The mission ended on November 1, 2018, when the spacecraft exhausted its hydrazine fuel and could no longer point its antenna toward Earth or its solar arrays at the Sun. Per NASA's planetary protection protocols, Dawn was placed in a long-term stable orbit around Ceres, where it will remain for at least 20 years to prevent contamination of the dwarf planet. The spacecraft is now a silent monument in the asteroid belt, having completed one of the most ambitious and successful missions in the history of planetary science.

Category:NASA probes Category:Asteroid spacecraft Category:2007 in spaceflight