Dawn Bound for Asteroid Belt With an Assist From Mars
NASA's Dawn spacecraft began its journey to two of the largest bodies in the asteroid belt, Vesta and Ceres, with a September 2007 launch that sent it speeding through space at 25,600 mph (11,444 m/s). Fast? Yes. But that speed was not quite fast enough to approach Mars at the right time, location and angle.

An artist's rendition of Dawn spacecraft flying near Mars

The Dawn spacecraft was launched on Sept. 27, 2007. Image Credit: McREL

What Does Mars Have to Do With Dawn?

Sending a spacecraft to study two objects more than 200 million miles from Earth is no easy task. Success requires not only an initial launch that gets the spacecraft going in the right direction, but also slight adjustments of the spacecraft’s trajectory as it travels toward its desired destinations.

From December 2007 through October 2008, a special onboard propulsion system gradually increased Dawn's speed by a total of 4,050 mph. That speed put the spacecraft on just the right pace and track to fly close to Mars in February 2009.

Dawn used the gravitational pull of Mars to tweak its direction and speed of travel. Known as a "gravity assist," this maneuver helped put Dawn on course to reach Vesta in August 2011. After orbiting Vesta for nine months, Dawn will continue on toward a February 2015 rendezvous with Ceres.

The asteroid Vesta

After a gravity-assist maneuver near Mars, the Dawn spacecraft will travel to the asteroid Vesta. Image Credit: Ben Zellner (Georgia Southern University), Peter Thomas (Cornell University and NASA)

Why Study Vesta and Ceres?

The asteroid belt consists of rocky objects in space whose growth was stunted before they could become planets. Vesta is one of the largest asteroids in the asteroid belt. Ceres, the largest body in the belt, was recently classified as a "dwarf planet." Scientists believe Vesta and Ceres hold clues as to how planets formed and how different planets developed in different ways.

Dawn's instruments will snap detailed images of Vesta and Ceres, gather data about their minerals and elements, and measure their gravity, mass and density. Using this information, scientists will try to answer the following questions:
  • What makes up the insides of Vesta and Ceres?
  • How big are their cores?
  • What is their geologic history?
  • What processes are changing their surfaces?
  • Does Vesta or Ceres contain water?
  • How did size affect the evolution of planets?
  • What role did water play in planet formation?
Dawn is a partnership between the University of California, Los Angeles, and NASA's Jet Propulsion Laboratory in Pasadena, Calif., along with other universities, laboratories, and companies in the United States, Germany and Italy.

Related Resources
Dawn Mission Trajectory   →
Structure and Properties of Matter: Ion Propulsion   →

Dan Stillman, Institute for Global Environmental Strategies