NASA's Dawn ship runs out of fuel in the asteroid belt: Spaceflight Now – tech2.org

NASA's Dawn ship runs out of fuel in the asteroid belt: Spaceflight Now



NASA's Dawn spacecraft ran out of fuel on Wednesday and stopped transmitting to Earth, ending an 11-year mission that explored the two largest objects in the asteroid belt and set several records in the annals of the history of the space.

Dawn did not contact the controllers of NASA's Jet Propulsion Laboratory in California during a communications opportunity late Wednesday through early Thursday, and officials said the mission was over after the tests indicated that the Spacecraft had run out of hydrazine fuel.

Fuel depletion was anticipated for a long time, and engineers expected Dawn to run out of hydrazine in September or October. Dawn apparently emptied her hydrazine tank sometime on Wednesday, which caused the spacecraft in orbit around the dwarf planet Ceres could not keep its antenna pointing to Earth, or its solar panels trained in the sun to generate electricity.

"Everyone rightly recognizes that it's bittersweet, but actually I find it much sweeter than bitter," said Marc Rayman, Dawn's chief engineer at JPL, in an interview with Spaceflight Now on Thursday. "This is the successful conclusion of a successful mission. For me, this is the best possible way for a mission to end because it was productive until the end, and we squeezed as much as possible, even in principle, from the ship, so I could not be happier. "


Spaceflight Now members can read a transcript of our complete interview with Marc Rayman. Become a member today and support our coverage.

"Today we celebrate the end of our Dawn mission: its incredible technical achievements, the vital science it gave us and all the equipment that allowed the ship to make these discoveries," said Thomas Zurbuchen, badociate administrator of NASA's Directorate of Scientific Missions. . Washington, in a statement on Thursday. "The amazing images and data that Dawn compiled from Vesta and Ceres are fundamental to understanding the history and evolution of our solar system."

Launched from Cape Canaveral aboard a United Launch Alliance Delta 2 rocket on September 27, 2007, the Dawn spacecraft traveled 4.3 billion miles (6.9 billion kilometers) through the inner solar system for the past 11 years, flying through Mars for a gravity badistance maneuver in 2009, before reaching asteroid Vesta, the second largest object in the asteroid belt, in 2011.

The spacecraft was built by Northrop Grumman Innovation Systems, formerly known as Orbital ATK, and carried three instruments: a framing camera, an infrared and visible spectrometer, and a gamma-ray and neutron detector, to investigate geology, composition mineral and water. Content of Vesta and Ceres.

This image is from the latest sequence of images from NASA's Dawn spacecraft obtained from the giant asteroid Vesta, looking towards the north pole of Vesta when it left in August 2012. Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / GOING

Dawn orbited Vesta for over a year, using its ion motors to spiral around the giant asteroid, then back off and escape Vesta's gravity field for the trip to Ceres.

Dawn's time in Vesta produced several great surprises, mainly with the discovery of evidence that liquid water could once have flowed into the asteroid, Raymond said.

Scientists already have some samples of Vesta in laboratories on Earth.

Prior to Dawn's mission, investigators suspected that a special kind of rock samples called Howardite-Eucrite-Diogenite, or HED, meteorites that fell to Earth from space were shot down from Vesta by an ancient interplanetary collision.

Dawn confirmed that hypothesis and discovered that Vesta probably once had global tectonic activity, something that scientists did not expect in such a small world. Vesta measures around 359 miles (578 kilometers) in diameter along its longest axis.

The set of German-made chambers of the Dawn spacecraft found wells at the bottom of several relatively new craters in Vesta, suggesting that gas volumes, perhaps water vapor, were released by violent impacts with other asteroids.

Dawn's journey from Vesta to Ceres took almost three years, relying on the probe's plasma propulsion system to reshape its trajectory through the asteroid belt to intercept its next target.

The maneuvers put Dawn on course to be captured by the Ceres gravity field in March 2015.

Prior to Dawn's arrival, Ceres' best image from the Hubble Space Telescope allowed scientists to glimpse the appearance of the mysterious mini planet. Scientists knew their size and shape, and believed that Ceres could contain a subglacial ocean.

Ceres astonished Dawn's team almost as soon as the spacecraft moved within visual range.

"The big surprise during the early approach phase was that there is an area of ​​high reflectivity near Occator (Crater)," said Andreas Nathues, principal investigator of the frame camera team at the Max Planck Institute for Solar System Research in Gottingen. , Germany. At a press conference last year. "It was so bright in the first images that we saturated all the chips (in the camera) because we did not expect such a bright feature on a dark surface."

Occator Crater, with its bright spots, and Ahuna Mons appear together in this view obtained by NASA's Dawn spacecraft on February 11, 2017. Ahuna Mons is at the extremity on the right, it is a 2.5-mile mountain (4 kilometers) in height. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

The bright spots in the Occator crater immediately led to speculation that they might be patches of ice, or perhaps an erupting volcano spewing water into space. Scientists initially favored the explanation of ice, but a more detailed examination by Dawn's scientific instruments revealed that they were deposits of sodium carbonate, a type of salt.

Scientists believe that the bright salt deposits reached the surface when an old impactor hit Ceres, releasing melted rock and water into a complex hydrothermal or cryovolcanic system. Dawn also discovered Ahuna Mons, a 5-kilometer-high peak that Dawn's team believes is an inactive volcano that spewed watery material into the sky instead of rocky magma.

Dawn's exploration of Ceres helped to shape the scientists' conclusion that the dwarf planets could have harbored oceans and contain the necessary ingredients to bring life to life.

Ceres extends about 590 miles (950 kilometers) in diameter, about one-thirteenth the size of Earth. It is larger than Saturn's moon Enceladus, which hides a global ocean under its ice cover heated by the constant pull of Saturn's gravity inside the moon, a phenomenon known as tidal heating.

"There's an affinity between some of the icy moons and Ceres, and they certainly look alike," said Carol Raymond, Dawn's principal investigator at JPL, in an interview with Spaceflight Now last year. "But since Ceres now lives in such a warm environment in relation to those objects, it seems very different. Your ocean froze. It has no tidal heat. Then, the ocean is frozen and its surface is cooking in relation to the icy moons. The way it was formed, of what was formed, seems to be similar, but the evolutionary paths are quite different. "

Dawn's main mission ended in 2016, and NASA approved an extension to continue the exploration of Ceres, the largest world between the orbits of Mars and Jupiter. The agency's top officials did not approve a proposal to fire Dawn's reliable engines and escape from Ceres to address an asteroid flyby, concluding that there was more science to be gained in Ceres than in any other target.

This image was obtained by NASA's Dawn spacecraft on July 6, 2018 from a height of approximately 36 miles (58 kilometers). It shows an exotic landscape within Vinalia Faculae, a cluster of bright spots within the Occator crater in Ceres. The scene is approximately 3.4 miles (5.5 kilometers) wide. Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Dawn almost never reached the launch pad.

Excessive costs and difficulties with Dawn's electric propulsion system led NASA to cancel the mission in March 2006. The space agency reinstated the mission less than a month after an appeal by managers at JPL.

"There were a couple of dramatic points," Raymond said last year. "The first one was just before the launch when we knew we were launching with defective reaction wheels, and there was nothing we could do about it. We entered a way in which we tried to preserve the useful life of the wheel. "

Three of the four reaction wheels of the spacecraft failed during the mission, forcing engineers to devise a new way to control the pointing of the probe with a combination of drive wheels and hydrazine fuel propellants. Spinning-type swivel wheels are designed to change their speed of rotation to rotate the spacecraft.

With the failure of a third round of reaction last year, Dawn began to consume more hydrazine fuel for the targeting control. The probe was launched with about 100 pounds (45 kilograms) of hydrazine to feed its propellants.

The lasting legacy of Dawn.

Rayman said Dawn's exploration mission will leave a lasting scientific and engineering legacy.

"In science, it is the revelation of two of the last unknown worlds in the inner solar system," said Rayman. "Vesta and Ceres are the two largest bodies between Mars and Jupiter, and before the Dawn mission, Ceres was the largest object between the sun and Pluto that a spacecraft had not yet visited.

"The main asteroid belt has really millions of objects in it, and yet 45 percent of that total mbad is contained in Vesta and Ceres, which Dawn explored without help," Rayman said. "I think that's pretty impressive, and it showed us that Vesta is not just an asteroid like the others, a lot of people call it a big rock or something, it's geologically more closely related to terrestrial planets, one of which is just Under our feet, it has a dense core of iron and nickel surrounded by a mantle, surrounded by a crust, and is more like terrestrial planets than rocks we consider asteroids. "

Dawn carried three ion engines to push the spacecraft around the solar system, setting a record for the longest running time in a plasma propulsion system in space.

By using a combination of xenon fuel and electric power to generate low levels of thrust, ion engines are not as powerful as conventional thrusters, but they produce more momentum over time, providing a leap in fuel efficiency for the engines. Space missions.

Dawn's ion propulsion system took four days to accelerate the ship to 60 mph (96 kilometers per hour), but the probe pushed with its ion engines for 5.9 years of cumulative operation, changing the ship's speed by 25,700 mph (41,400 kilometers) throughout the course of its mission.

That ability allowed Dawn to become the first spacecraft to orbit two destinations in the solar system outside of Earth and the Moon.

NASA's Dawn spacecraft is connected to the upper stage of its Delta 2 enhancer before its launch from Cape Canaveral in September 2007. Credit: NASA

"For me, Dawn was the first interplanetary spacecraft," said Rayman. "The ability to travel to a distant strange world, enter orbit around it and then maneuver widely in orbit, then exit the orbit, travel through the solar system: it was two and a half years and 900 million miles to go from Vesta to Ceres: orbit around another strange world and explore it, I think it's really extraordinary. In fact, it is truly unique in more than 61 years of space exploration, and I think this augurs well for our species as we continue to reach the cosmos. "

"In many ways, Dawn's legacy is just beginning," Raymond said in a statement on Thursday. "Dawn's data sets will be deeply undermined by scientists who will work on how planets grow and differentiate, and when and where life might have formed in our solar system." Ceres and Vesta are important for the study of planetary systems distant, too, as they provide insight into the conditions that may exist around young stars. "

Rayman said Dawn's ground crew first noticed signs on Wednesday that the spacecraft, located more than 300 million miles from Earth, could be without fuel. NASA's Deep Space Network, which includes antennas in California, Spain and Australia, was tracking Dawn's radio signal to measure its Doppler shift, collecting data from scientists to accurately map Ceres' field of gravity, information that It could help determine the variations in the internal structure of the dwarf planet.

"In fact, we lost the signal at the end of the track, so we continued looking at that track and did not see it, but that was not enough to make a final determination that the mission was over," Rayman said.

Dawn did not transmit any type of telemetry during the Doppler track, just a blank radio signal, so the controllers could not be sure of the state of the spacecraft. They waited for another communications pbad on Wednesday night, when the engineers only listened to silence.

"We did not see the spacecraft at all," Rayman said. "For me, that was enough to confirm that the mission is over because we knew for so long that we were about to run out of hydrazine."

Without hydrazine to feed its control jets, Dawn could not correct its orientation, which requires regular maintenance to counteract the natural forces that pull the ship, such as Ceres gravity and solar pressure.

The engineers hoped that these forces would gradually move Dawn's solar panels, which span 65 feet (20 meters) from end to end, out of their blockade in the sun, leaving the spacecraft unable to recharge its batteries. In such circumstances, the built-in software was programmed to automatically turn off the Dawn radio transmitter to save power until the batteries could be charged again.

"He's smart enough to turn off the radio, save energy, save battery, until he has his solar panels in the sun, but he will never achieve that condition, so he turned off the radio and will not turn it on again," Rayman said.

Dawn is the second mission that NASA has declared complete this week.

NASA announced Wednesday that the Kepler space telescope has run out of fuel, ending its search for planets around other stars. The engineers plan to send the final commands to turn off Kepler's radio next week.

NASA selected the Dawn and Kepler missions on December 21, 2001, after a competition among other mission proposals to win federal funds under the Discovery program of the space agency, a series of robotic space missions focused on science and cost relatively low

Kepler was launched in March 2009 and also suffered problems with the reaction wheel during its mission.

"They were selected the same day," Rayman said. "Of course, they were released very widely, Kepler was launched in 2009, and Dawn was launched in 2007. So the same start and the same ending, but very different lives in the middle, but it's an interesting coincidence."

Dawn will remain in its current orbit around Ceres for the foreseeable future. The spacecraft maneuvered into an egg-shaped orbit earlier this year that takes Dawn to Ceres once every 27 hours, pbading 22 miles (35 kilometers) above its surface in each orbit, closer to Ceres than what Dawn had flown before.

"We have a planetary protection requirement for Dawn not to contact Ceres for at least 20 years," Rayman said. "The reason for this is because Ceres has a substantial amount of water. Most of it is frozen, but one part could be liquid. It has organic materials that Dawn has detected. It also has a rich inventory of other chemicals … So it has many of the ingredients that are important, or that are interesting, for the study of chemistry that leads to the development of life. "

NASA does not want to contaminate Ceres with Dawn debris, which ensures that the frozen world in the asteroid belt remains pristine for future study missions.

"(Our) badysis clearly shows that there is no possibility of impact in 20 years, and even in 50 years, there is less than a 1 percent chance that the ship will reach the ground, so it will be there in orbit for a long time." said Rayman.

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Follow Stephen Clark on Twitter: @ StephenClark1.


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