Dawn Mission & Spacecraft
Dawn is part of NASA’s Discovery mission and it was designed to orbit the asteroid Vesta, which is located between Jupiter and Mars. Its secondary trip was to head over to Ceres, and it became the first spacecraft to visit a dwarf planet and orbit two extraterrestrial objects.
Dawn operated between 2007 and 2018, and not only broke several records along the way, but astounded scientists with the incredible volume of information that it sent back to Earth.
Dawn faced a lot of problems along the way. The first difficulty was when it lost three of the four reaction wheels that maintained its orientation in space. Even with this problem, Dawn continued on its primary mission to study both of the extraterrestrial targets in 2016.
By 2018, Dawn hit another roadblock when it ran out of fuel, but officials at NASA said that it will continue for another 50 years in orbiting around Ceres.
Dawn launched in 2007 from Cape Canaveral, Florida and then traveled 1.7 billion mi/2.8 billion km to arrive at its first target in 2011, the asteroid Vesta. Dawn was propelled by ion engines and became the little spacecraft that could!
After arriving at Vesta, Dawn spent a year orbiting and collecting information on the second largest asteroid in the asteroid belt. After the year, it left Vesta and began its trek to the dwarf planet Ceres.
In March, 2015, Dawn entered Ceres’ orbit and began sending back information. Scientists found out that Ceres is the most massive object in the asteroid belt between Jupiter and Mars.
It has a weight of almost 2/3 the total mass of the entire belt. Because of its size and the fact that its round, it qualifies under the description of a dwarf planet.
Dawn found Vesta to be a rocky asteroid and sent back images that let scientists discover that Vesta had a rather exotic and diverse geologic landscape. Researchers made use of the data sent by Dawn to put together the first map of Vesta, which is only 330 mi/530 km wide.
The scientists also discovered that Vesta had a similar layered structure like the one that we have on Earth. It revealed that the core was substantially made up of nickel-iron, like Mercury, Earth and Mars.
The core makes up about 18% of the total mass of Vesta. It has a surface that is entirely basalt, which is a kind of frozen lava. At one point in its history, Vesta had a magnetic field.
Another find was that Vesta is the source of the howardite-eucrite-diogenite (HED) meteorites that are found on both Mars and Earth. The HEDs more than likely occurred due to an impact basin that the team nicknamed “Rheasilvia.”
They believe that the basin formed from a huge collision about 1 billion years ago that ripped away most of the atmosphere from the asteroid’s southern hemisphere.
The basin is around 310 mi/500 km, so Rheasilivia is almost as large as Vesta. This kind of basin depression has led scientists to think that Vesta is fairly close to shattering.
Dawn’s data sent back to Earth has also led researchers to believe that there is ice under the surface. The scientists have used Dawn’s information to fill in the blanks for knowledge about our own solar system. It appears as if Vesta is the survivor from the beginning of the development of the solar system.
Dawn was the first mission to arrive at a dwarf planet, but just barely. NASA’s New Horizons mission was heading to Pluto only a couple of months later. New Horizon’s had launched earlier than Dawn, but Dawn had farther to go. The ion propulsion system took four days to accelerate it from 0-60 mph/0-97 kmh at maximum throttle.
Each of Dawn’s engines only produced about the same amount of force as if you had a single piece of notebook paper pressed against your hand.
It may not sound like much, but in space, over time, the force adds up. In 2010, Dawn had already beaten the record for velocity set by NASA’s Deep Space 1 when it was going 9,600 mph/4.3 km/second.
Once Dawn entered the orbit of Ceres scientists realized that this would be an entirely different exploration. Ceres is icy, and researchers thought that it might be made up of as much as one quarter water that has frozen under the surface.
They made these deductions based on Hubble Space Telescope observations when they saw a cloud of vapor that indicated that Ceres might be releasing its gas.
When Dawn cruised by Ceres, the surface appeared to be somewhat bland. There were only a few craters and a single mountain, Ahuna Mons. Scientists suspected that the mountain was due to cryovolcanic action that releases ice instead of the lava that we have on Earth.
While it is the only mountain that is seen today, there might have been other mountains on Ceres in the past that slowly flowed back so that they became part of the surface.
Scientists are using the data about Ceres as their case for cryovolcanic action. They think that Ahuna Mons is around 200 million years old, and hasn’t had the time to deform.
Later, a study involving ESA, the German Aerospace Center (DLR), NASA’s Jet Propulsion Laboratory (JPL), and Sapnienza Università di Roma, Rome, Italy have resolved the problem of the mountain.
They used gravity measurements from the Dawn mission that showed an ascending plume that was made up of rock from the dwarf planet and salty water.
Observing the material after it erupted they found that it formed a mountain 2.5 mi/4 km high and since Ceres has extremely cold temperatures, it froze.
Dawn may have now run out of fuel, but scientists indicated that it will continue for another 20 years to orbit Ceres. The planetary-protection rules don’t allow it to crash into Ceres for fear of contamination so the Dawn team will set the spacecraft into orbit that will keep it in space for at least 50 years.
- The spacecraft has a box-like shape that measures 1.64m c 1.27 m x 1.77 m. Dawn is constructed of aluminum and graphite composites. The center of the spacecraft is a cylinder made of graphite, with xenon and titanium hydrazine tanks that are inside mounted. Access panels are made of an aluminum core with aluminum face sheets. Without fuel it weighs 747.1 kg and with fuel prior to launch it weighed 1217.7 kg.
- Dawn has three ion thrusters for the ion propulsion system, which was taken from the Deep 1 spacecraft ion drive design. It uses xenon which is ionized and accelerated by electrodes.
- Dawn also has a solar panel array. When extended it measures 19.7 m. The solar generated energy is for the electronic components of the spacecraft and power is stored in a 35 Ah NiH2 battery.
- The payload for Dawn is state of the art science and includes: Framing Camera (FC), Visible & Infrared Spectrometer (VIS), Gamma Ray and Neutron Detector (GRaND) along with a memory chip containing the names of 360,000 space enthusiasts, a laser altimeter and star trackers. X-band communications are used for uplink (7.8 b/s – 2.0 kb/s) and downlink (10 b/s – 124 kb/s) transmissions. A RAD6000 processor, 8 Gb mass memory and a Mil-Std-1553B data bus deals with all the data handling operations.
- The xenon tank has a capacity of 425g of propellant at launch time. The hydrazine tank holds 45.6 g of propellant at launch.
- 2007: Launch
- 2009: Mars Gravity Assist
- 2011: Arrives at Vesta
- 2012: Leaves Vesta
- 2015: Arrives at Ceres
- 2016: Ends the prime mission
- 2016: Begins the first mission extension
- 2017: Begins the second mission extension
Key Mission Findings:
During the orbit of Vesta, which lasted over a year, Dawn confirmed that Vesta is the parent of the HED meteorites which have been found on terrestrial planets. The information from Dawn connected the location of the HED meteorites to the south polar basin.
Vesta is around the same size as Saturn’s moon Enceladus. It is deeply scarred by the Rhesasilvia impact that launched the HED’s. Dawn found carbon rich and hydrated material on its surface that was the result of the impactors.
Once Dawn began its orbit around Ceres it discovered that the dwarf planet was an ocean world where the ammonia and water reacted with the silicate rocks. When the ocean was freezing, salts and other minerals concentrated into deposits that are all over Ceres’ surface. Dawn also found several locations on the surface that had organics.
Some of Dawn’s Major Achievements:
First spacecraft mission to orbit 2 destinations.
Broke records in the use of solar-electric propulsion of any prior spacecraft.
Active powered flight for 5.9 years.
Dawn found that Ceres had carbonites that indicated an interior process that alters chemistry.
The formation of Ahuna Mons made up of flowing ice suggests the presence of salts and an ancient ocean that was once underneath the crust of Ceres.
Scientists are unsure whether the information that Dawn sent indicates that the ocean under Ceres surface is continuing to be active today.
Dawn sent data that showed researchers that Ceres has ammonia-rich clays.
The results sent by Dawn demonstrates that Ceres is an evolving world.
- Dawn is the first spacecraft that has ever successful orbited two extraterrestrial locations. (Vesta and then Ceres)
- Once dawn left Vesta and arrived at Ceres it then became the first spacecraft to orbit in the main asteroid belt.
- Dawn became the first spacecraft to visit a dwarf planet. New Horizons became the second spacecraft, arriving at Pluto only a few months later.
- The information sent back from Dawn showed that location is one of the important keys for the organization and evolution of the early solar system.
- Dawn validated the fact that dwarf planets could have been host to oceans during a major part of their history and possibly might still be host to oceans.
- The organics that Dawn found on Ceres have left scientists wanting to know more information about the dwarf planet.
- In the move “Star Wars,” the TIE fighters stood for “twin ion engine.” Dawn had its own ion engines.
- Previously, scientists thought that Vesta was just a boring space rock. Dawn discovered that Vesta is a lot more varied than researchers thought.
- Dawn showed scientists that Ceres is geologically active or was very recently active.
- Dawn didn’t stop collecting data and continued until its fuel ran out.