Completed · full success Flyby 2007

Dawn

NASA's Dawn mission used a gravity assist flyby of Mars in February 2009 to modify its trajectory toward the asteroids Vesta and Ceres. After completing its primary objectives in the main belt, the mission concluded in November 2018 due to propellant exhaustion.

Agency NASA
Launch SOL 3 OF QUIRINO OF YEAR 28 · 23:47 MTC
Arrival at Mars SOL 16 OF LUNO OF YEAR 29 · 21:28 MTC
Mission End SOL 10 OF OLYMPO OF YEAR 34 · 13:37 MTC
of travel 509 days · ~495 sols
Cruise to Mars510 days
Operations3,543 days

Trajectory to Mars

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Technical Analysis of the Dawn Mission (Mars Flyby)

  • Mission Designation: Dawn (Discovery 9)
  • COSPAR Designation: 2007-047A
  • Operating Agency: NASA / Jet Propulsion Laboratory (JPL)
  • Launch Date: September 27, 2007 11:34 UTC
  • Mars Flyby Date: February 18, 2009 00:27:58 UTC
  • Launch Vehicle: Delta II 7925H D-327 rocket
  • Launch Site: Space Launch Complex 17B (SLC-17B), Cape Canaveral, USA
  • Mission Status: Mission Accomplished

1. Historical Context and Detailed Objectives

The Dawn mission represented a high-risk technological demonstration by employing xenon ion propulsion to orbit two distinct bodies in the main asteroid belt (Vesta and Ceres). The scientific gap it aimed to fill focused on understanding the primordial conditions and processes of the solar system by studying two intact protoplanets. Primary objectives centered on providing a gravity assist at Mars to modify the probe's trajectory, simultaneously utilizing the Martian encounter to calibrate onboard scientific instruments before studying Vesta and Ceres.

Main Objectives:

  • Execute a gravity assist maneuver at Mars to increase the spacecraft's heliocentric velocity.
  • Calibrate optical and spectrometric scientific instruments during the hyperbolic flyby.
  • Study the composition, internal structure, and geological evolution of the protoplanets Vesta and Ceres.

2. Vehicle Architecture and Main Subsystems

The launch (wet) mass of the Dawn probe was 1,217.7 kg, including 425 kg of xenon propellant and 45.6 kg of hydrazine, with a dry mass of 747.1 kg. Its structural dimensions were 1.64 m in length, 1.27 m in width, and 1.77 m in height, reaching a span of 19.7 m with solar panels deployed. The power system consisted of two large photovoltaic solar arrays providing more than 10 kW at Earth distance (1 AU) and 1.3 kW in the asteroid belt (3 AU), backed by a 35 Ah nickel-hydrogen rechargeable battery. Communications were carried out via a 1.52 m diameter high-gain antenna linked to NASA's Deep Space Network (DSN). Its main propulsion system operated with three xenon ion engines (NSTAR type) and lacked atmospheric or surface mobility.

3. Payload and Scientific Instrumentation

To fulfill scientific and calibration tasks, the probe incorporated the following instrumentation:

  • FC (Framing Camera): Multispectral optical framing and cartography camera (equipped with one clear filter and seven bandpass filters) provided by the German Aerospace Center (DLR).
  • VIR (Visible and Infrared Mapping Spectrometer): Visible and infrared mapping spectrometer to analyze surface mineralogy, contributed by the Italian Space Agency (ASI).
  • GRaND (Gamma Ray and Neutron Detector): Gamma ray and neutron detector (nuclear spectrometer) to determine the elemental composition of the surface, built by Los Alamos National Laboratory (LANL).
  • Telecommunications Subsystem and DSN Network: Used jointly to perform radiometry and gravity measurements of the visited celestial bodies.

4. Launch Vehicle and Trajectory

Dawn lifted off on September 27, 2007 at 11:34 UTC aboard a Delta II 7925H D-327 rocket from Space Launch Complex 17B at Cape Canaveral. After a long journey in the interplanetary medium, the spacecraft executed a hyperbolic gravity assist flyby of Mars on February 18, 2009 at 00:27:58 UTC, reaching a periapsis point at 542 km altitude and obtaining an effective heliocentric velocity increase of approximately 2.6 km/s. Subsequently, the probe arrived at asteroid Vesta on July 16, 2011, continued toward dwarf planet Ceres with arrival on March 6, 2015, and ended operations on November 1, 2018.

5. Results and Discoveries

During its passage by Mars, Dawn successfully calibrated its scientific instruments (FC and GRaND) and validated its navigation subsystems. In later stages of its main belt mission, it discovered that Vesta possesses a dense core, a gigantic impact crater with a colossal central mountain, and a differentiated geological history. At Ceres, it confirmed the presence of highly reflective sodium carbonate deposits (bright spots) in Occator crater, in addition to evidence of cryovolcanic activity and underground water-rich brine reservoirs.

6. Legacy and Mission Importance

The mission formally concluded on November 1, 2018 due to the total exhaustion of the hydrazine supply required for attitude control and antenna orientation toward Earth. Dawn successfully demonstrated the performance of high-efficiency solar electric propulsion in Discovery-class missions, revolutionizing knowledge about protoplanet formation at the dawn of the solar system. The spacecraft currently rests inactive in a stable and permanent orbit around Ceres.

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