The Dawn spacecraft is scheduled for launch on July 7 from Cape Canaveral. Its eight-year mission, managed by JPL in La Cañada Flintridge, will explore the asteroid Vesta and dwarf planet Ceres and look into the very beginning of the solar system.
A press conference was held last week where an update on the mission was released. The mission has a brief launch time window of July 7 to 11, due in part to other missions that are scheduled for launch including the space shuttle.
The mission has had its trials and tribulations. The mission was announced in December of 2001 with an original launch date in June of the same year. It was put on hold that October and then reinstated in March 2006. Throughout the years there had been many reviews with criticism from technical problems to cost overruns. The current cost of the mission is $449 million; if there is a delay that price could go up another $25 million.
"Every one of these missions has its quirks. This one does too," said Bill Robel of NASA launch services.
Throughout its long journey to launch, the science of the mission has not been in question. The Vesta and Ceres were chosen because they developed into two different kids of bodies. Vesta is dry, with a surface that shows signs of resurfacing that resembles the rocky bodies of the inner solar system including Earth. In contrast, Ceres has a primitive surface containing water-bearing minerals and may possess a weak atmosphere. By studying this contrast, the Dawn mission hopes to compare the different evolutionary path each took and to open a wider window of understanding the origin of the universe in general.
In addition to unique science, the fuel used to make the 3-billion-mile journey is also of great interest and not only to science fiction fans. The science fiction term "ion propulsion" is now true science. With ion propulsion the Dawn spacecraft will have more propulsion capability than any previous spacecraft; without it the mission would not be able to reach its targeted asteroids. Instead of gas being heated up or energy resulting in great pressure, the ion system thrusters uses an electrical charge to accelerate ions from xenon fuel to speed ten times that of normal chemical engines. Electric charges are shot out of the spacecraft and push it forward. Engineers at JPL were part of the ion propulsion development team.
Because ion propulsion needs less fuel to cover more space, the Dawn spacecraft can remain small. The system has been used before on NASA's Deep Space 1 mission, which also journeyed to an asteroid and a comet. The spacecraft has three ion propulsion engines, with only one thruster operating at a time.
If the launch window is missed it will be delayed for two years as it waits for another launch time.
Waiting for the Dawn is something JPL engineers and scientists are used to.