WASHINGTON — A NASA spacecraft that visited two of the largest objects in the solar system’s main asteroid belt has run out of fuel, ending its mission, NASA announced Nov. 1.
NASA announced that the Dawn spacecraft was silent during two communications sessions on the Deep Space Network Oct. 31 and Nov. 1. After eliminating other possible causes for the lack of transmissions, managers concluded that the spacecraft had run out of hydrazine fuel for its attitude control thrusters, preventing it from maneuvering to orient its main antenna towards the Earth or its solar panels towards the sun.
That lack of maneuverability ends the spacecraft’s mission, as expected. Project officials had warned for months that the mission would likely end this fall based on estimates of the remaining hydrazine on the spacecraft.
“To within our current uncertainty, there’s zero usable hydrazine remaining,” said Marc Rayman, chief engineer and mission director for Dawn at the Jet Propulsion Laboratory, during a presentation Oct. 4 at the International Astronautical Congress in Bremen, Germany. At the time he said the spacecraft would likely run out of fuel in the middle of October.
Dawn, built by Orbital Sciences Corp. (now Northrop Grumman Innovation Systems), launched in 2007 as part of NASA’s Discovery program of lower-cost planetary science missions. The spacecraft, propelled by electric thrusters, entered orbit around the large main belt asteroid Vesta in July 2011. After leaving Vesta in September 2012, Dawn entered orbit around Ceres, the dwarf planet that is the largest object in the main asteroid belt, in March 2015.
Dawn remained in orbit around Ceres for the rest of its mission, although mission managers proposed at one point leaving orbit to fly by another asteroid. NASA elected to keep Dawn at Ceres and fly in different orbits around it, including its final orbit that brought the spacecraft to within 35 kilometers of the planet’s surface.
The data collected by Dawn helped scientists better understand the two worlds, as well as broader questions about the formation and evolution of the solar system. Observations of Ceres in particular indicated that it might once had, and could still have today, a subsurface ocean of liquid water.
“Dawn’s data sets will be deeply mined by scientists working on how planets grow and differentiate, and when and where life could have formed in our solar system,” said Carol Raymond, principal investigator for Dawn at JPL, in a statement. “Ceres and Vesta are important to the study of distant planetary systems, too, as they provide a glimpse of the conditions that may exist around young stars.”
With its hydrazine depleted, Dawn will remain in orbit for decades before eventually crashing to the surface of Ceres. NASA said that there is a more than 99 percent chance the spacecraft will remain in orbit for at least 50 years.
“The demands we put on Dawn were tremendous, but it met the challenge every time,” Rayman said in the statement. “It’s hard to say goodbye to this amazing spaceship, but it’s time.”
The end of the Dawn mission comes two days after NASA announced the end of another mission, Kepler. Both spacecraft ended their missions because they ran out of hydrazine fuel needed for attitude control, and both had suffered failures of reaction control wheels earlier in their missions that made them rely on their thrusters more than originally planned.
Despite the similarities, there was little in the way of interaction between the two missions as their spacecraft used up their last of their hydrazine. “Our needs for fuel were different than theirs,” said Charlie Sobeck, project system engineer for Kepler at NASA’s Ames Research Center, during an Oct. 30 briefing about the end of that mission. “We had more communication with Dawn about reaction wheels than we did about fuel.”