NASA's Dawn Spacecraft: Visiting Vesta and Ceres

Artist's concept of Dawn at Ceres. Credit: NASA/JPL-Caltech

 

• Launch Date: September 27, 2007
• Launch Site: Launch Complex 17B at Cape Canaveral Florida, United States
• Launch Vehicle: Delta II
• Mission Type: Orbiter
• Targets: Vesta & Ceres
• Dimensions: 1.64 Meters by 1.27 Meters by 1.77 Meters
• Mass: 747.1 Kilograms

Dawn was the first spacecraft to orbit two different celestial bodies in one mission. Its first target was the protoplanet Vesta, which is a very large asteroid. Its second target was Ceres, which at the time of launch was recently reclassified as a dwarf planet by the International Astronomical Union. The probe had a rocky start getting funded, and was delayed many times before it could launch. 

Target One: Vesta

Vesta was one of the first asteroids discovered, because of its large size and relative brightness. It is one of the few objects in the solar system that meteorites have been traced back to. HED (howardite, eucrite, and diogenite) meteorites are believed to come from Vesta because of a similarity in their composition.

 

Dawn launched on a Delta II rocket on September 27, 2007. In October, Dawn started testing its novel ion propulsion system. Ion engines work by ionizing Noble Gases, usually Xenon because of its mass. Once ionized, the gas is shot out the back of the thruster with an electric current. This creates a tiny amount of thrust, far less than that of a chemical rocket. This means that the maneuver burns are really long. The reason ion engines are considered feasible is because of their incredible fuel efficiency. 

In December, Dawn began its interplanetary cruise phase. On Febuary 17, 2009 Dawn made a flyby of Mars on its way to the asteroid belt. Dawn made its orbital insertion around Vesta from July 15-16, 2011. This made it the first spacecraft to orbit a main belt asteroid. Over a period of 14 Months, Dawn imaged Vesta, and analysed its properties. The closest Dawn got to Vesta was an altitude of 210 kilometres.

Features on Vesta imaged by Dawn. Credit: NASA/JPL/Caltech

Target Two: Ceres

Ceres was the first asteroid to be discovered, back in 1801 by Guiseppe Piazzi. It was originally hailed as a new planet, but many similar objects where soon discovered in the same region, including Pallas and Vesta. These objects were dubbed asteroids, meaning "star-like." In 2006 Ceres was reclassified again to a dwarf planet along with Pluto. Most people still consider it an asteroid however, and it has a dual classification in many circles. After its 14 months at Vesta, Dawn departed on September 4, 2012. 

Features on Ceres Imaged by Dawn. Credit NASA/JPL/Caltech

For almost three years, Dawn slowly maneuvered around the asteroid belt on its way to Ceres. It was able to enter orbit around Ceres on March 6, 2015. This made it the first spacecraft to explore a dwarf planet, beating New Horizons at Pluto by a couple months. Dawn's primary science campaign begain on April 23, after some orbital adjustments. Dawn continued to image Ceres, and gather scientific data until it ran out of fuel on November 1, 2018.

The Targets

Mosaic of Vesta from Dawn data. Credit: NASA/JPL/Caltech

• Date Discovered: April 29, 1807
• Designation: 4 Vesta (A807 FA)
• Class: Main-Belt Protoplanet
• Radius: 262.7 Kilometres
• Rotational Period: 5.34 Hours
• Orbital Period: 1325.86 Days (3.63 Years)

Ceres in true colour from Dawn. Credit: NASA/JPL/Caltech

• Date Discovered: January 1, 1801
• Designation: 1 Ceres (A801 AA)
• Class: Dwarf Planet/Main Belt Asteroid
• Radius: 469.7 Kilometres
• Rotational Period: 9.07 Hours
• Orbital Period: 1681.4 Days (4.6 Years)