How Did the Dawn Mission End?
NASA’s Dawn mission to Vesta and Ceres, the two largest bodies in the main asteroid belt, ended its extended mission when a key fuel ran low. Hydrazine was used to control the spacecraft’s orientation in space. And Dawn only had as much as it carried from Earth. When Dawn ran out of hydrazine, it was no longer be able to point its antennas toward Earth for communication. Once communication was lost, mission managers attempted communicating for a limited period—a couple of days—to verify that there was not an unexpected problem. When there was no response, they will officially end Dawn’s mission on Nov. 1, 2018.
Science ‘til the End
Dawn continued to gather science data about Ceres and return it to Earth, right up until the it could no longer do so. The spacecraft collected high-resolution gamma ray and neutron data, images, infrared spectra and gravity data from an altitude as low as 22 miles (35 kilometers). These observations focused on a region that contains Occator Crater and a diversity of geological terrains. The main goal was to understand the evolution of the dwarf planet and the origin of the bright regions in the famous crater.
When Did Dawn Run Out of Fuel?
Mission managers could not predict exactly when Dawn would run out of fuel. There is no real-time gauge for hydrazine levels. Engineers regularly adjusted their calculations of the fuel available. The fuel lasted until the last week of October and mission managers made the official end of mission announcement on Nov. 1, 2018.
How Did We Know Dawn was Out of Hydrazine?
Dawn gave mission controllers no heads-up that it was getting low on hydrazine. Performance will go along the same as it has been, then all of a sudden, Dawn will have expended its last puff of hydrazine.
What happened is that Dawn wasl no longer able to control its orientation with its reaction control thrusters. It started rotating very slowly. Dawn’s solar arrays no longer pointed to the Sun; its camera and other sensors no longer pointed at Ceres. Its main and low-gain antennas could not point toward Earth.
Within a few days of Dawn losing its ability to point, it became clear to Dawn mission managers that the chances of recovering communications with Dawn were very low. They attempted contact through different Deep Space Network stations. The Dawn project manager at JPL determined those communications should cease and alerted NASA managers. NASA shared the news, publicly signaling Dawn’s official end of mission.
Dawn will simply remain a new “moon” of Ceres in orbit around the object it has been studying since 2015.
Because Ceres has conditions of interest to scientists who study chemistry that leads to the development of life, NASA follows strict planetary protection protocols for the disposal of the Dawn spacecraft at the end of the mission. Engineers put the spacecraft in an orbit that guarantees it will not crash for at least 20 years—and likely for decades longer.