Dawn on Vesta

Dawn Spacecraft
Dawn Spacecraft
Image Credit: NASA
The Dawn mission seeks to answer questions about the origins of planets in the Solar System. What are the roles that the size of a body and the amount of water held by the body play in the evolution of bodies in the Solar System? Vesta and Ceres are two bodies that contain clues to these questions. These baby planets were interrupted by the formation of Jupiter, which scooped up a lot of material that might have been accreted by these two bodies. Vesta turned out evolved and dry, while Ceres turned out wet and primitive.

Ceres and Pluto are the two dwarf planets that have been observed in enough detail to qualify them as dwarf planets based on their having enough mass to be rounded by their own gravity, but have not cleared their neighbouring region of planetesimals and are not a satellite.

Vesta, on the other hand, is classified as a Small Solar System Body. These objects do not posses enough mass to be rounded. They are not in hydrostatic equilibrium.

Dawn’s mission is to visit these bodies and see what makes them tick. What are their current properties, where did they form, of what are they composed.

Dawn Mission Timeline:

  • Launch – 27 September 2007
  • Mars gravity assist – February 2009
  • Arrival at Vesta – July 2011
  • Departure from Vesta – July 2012
  • Arrival at Ceres – February 2015
  • End of primary mission – July 2015

It has been suggested by many that Ceres, with its supply of water, might well become the “gas station” of the Solar System economy. Water can be broken down into Hydrogen and Oxygen. Hydrogen and Oxygen can be burned as fuel and oxidizer to propel spacecraft. Hydrogen can be used with carbon sources to produce methane and other hydrocarbons, useful as chemical feedstock for plastics and other products.

Vesta, Ceres and the Moon
Comparison of Vesta, Ceres and the Earth’s Moon
Credit: Wikipedia
Dawn Spacecraft Schematic
Schematic of the Dawn Spacecraft
Image Credit: NASA
One of the strong points of Dawn is that it makes use of components proven on other successful spacecraft.

These include: the ion propulsion system, based on the design validated on Deep Space 1, Flight proven attitude control system used on Orbview, TOPEX/Poseidon ocean topography mission, and Far Ultraviolet Spectroscopic Explorer, Simple hydrazine reaction control subsystem with two sets of six 0.9 N engines used on the Indostar spacecraft, Command and data handling uses off the shelf components and Modular flight software based on design used on Orbview.

KEY

  • HGA – High Gain Antenna
  • LGA – Low Gain Antenna
  • CSS – Coarse Sun Sensors
  • GRaND – Gamma Ray and Neutron Detector
  • IPS Thrusters – Ion Propulsion Thrusters
  • RCS Thrusters – Reaction Control System Thrusters
  • VIR – Visible and Infrared Mapping Spectrometer
  • FC – Framing Camera
Once Dawn was launched by the 76th consecutive successful launch of a Delta II (read this interesting blog post on the event), the spacecraft began using its ion propulsion to get the additional velocity needed to reach Vesta.

Dawn’s engines have a specific impulse of 3100 s and a thrust of 90mN. While a chemical rocket on a spacecraft might have a thrust of up to 500 Newtons, Dawn’s much smaller engine achieves an equivalent trajectory change by firing over a much longer period of time.

Dawn will then use the ion engine to lower its altitude to Vesta, where it will begin its exploration (pdf).

The science payload consists of two cameras, a visible and infrared mapping spectrometer to reveal the surface minerals, and a gamma ray and neutron spectrometer to determine the elements that make up the outer parts of the asteroids. The spacecraft also will be used to measure the gravity field, thereby revealing details of these asteroids’ interiors.

Ion Engine on the Dawn Spacecraft
The Ion Engine on the Dawn Spacecraft
Image Credit: NASA / JPL
Dawn Trajectory
Dawn Trajectory
Image Credit: NASA
Dawn will use the ion engine to leave Vesta and cruise to Ceres. It will spiral to a low altitude orbit at Ceres. Ion propulsion makes efficient use of the onboard fuel by accelerating it to a velocity ten times that of chemical rockets.

A great list of Frequently Asked Questions (FAQ) about the mission can be found here.

The current status of the mission can be viewed here. Click on the images to see a larger view—images are updated hourly.

Currently, Dawn is a year away from Vesta.

Let us know what you think. What do you want to know about? Post a comment.