NASA spacecraft Dawn ran out of fuel on Wednesday and ended transmission to Earth. An eleven-year mission ended in exploring the two largest objects in the asteroid belt and setting several records in the history of space history
Dawn could not navigate the jet propulsion controls during late night Wednesday to early Thursday communication NASA's California Laboratory, and officials said the mission was over after evidence proved that the spacecraft was out of hydrazine fuel.
The fuel shortage Lange was expected, and engineers expected Dawn to run out of hydrazine sometime in September or October. Dawn evidently emptied his hydrazine tank sometime Wednesday and did not allow the spacecraft in orbit around the dwarf planet Ceres to hold its antenna to Earth, or its solar panels trained on the sun to generate electricity.
"Everyone rightfully recognizes that it's bittersweet, but I actually find it sweeter than bitter," said Marc Rayman, Dawn's chief engineer at JPL, in an interview with Spaceflight Now on Thursday. "This is the successful completion of a successful mission. For me, this is the best way for a mission to end because it was productive to the end and we pushed ourselves as far as possible from the spaceship, so I could not be happier. " Space members can now read a transcript of our full interview with Marc Rayman. Become a member today and support our coverage.
"Today we are celebrating the demise of our Dawn mission – their incredible technical achievements, the vital science they have given us, and the entire team that has enabled the spaceship to make these discoveries." said Thomas Zurbuchen, deputy administrator of NASA's Science Mission Directorate in Washington, in a statement on Thursday. "The amazing images and data Dawn has collected from Vesta and Ceres are critical 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 has flown 4.3 billion kilometers (6.9 billion kilometers) through the inner solar system over the past 11 years In 2009, he flew to Mars for gravity maneuvers before reaching the asteroid Vesta in 2011, the second largest object in the asteroid belt.
The spacecraft was built by Northrop Grumman Innovation Systems, formerly known as Orbital ATK, and carried three instruments – a framing camera, a visible and an infrared spectrometer as well as a gamma ray and neutron detector – to ascend the geology, minerals and water content of Vesta and Ceres.
Dawn circled Vesta for more than a year, using her ion engines to move near the Giant asteroid, then retreating and escaping Vestas Gravity field for the journey to Ceres.
Dawn's time in Vesta brought some big surprises, especially through the discovery of evidence that once liquid water could have flowed on the asteroid, Raymond said. Scientists already have some samples of Vesta in laboratories on Earth.
Prior to Dawn's mission, researchers suspected a special class of rock samples called Howardite-Eucrite Diogenite or HED. Meteorites that fell from space to Earth were shot down by an ancient interplanetary collision of Vesta
Dawn confirmed this hypothesis, noting that Vesta probably once had global tectonic activity, something that scientists do not do in such a small world had expected. Vesta has a diameter of about 578 km along its longest axis.
The Dawn probe camera suite built in Germany found in Vesta pits in the soil of some relatively fresh craters, suggesting gas levels – possibly water vapor – released by violent collisions with other asteroids.
Dawn's journey from Vesta to Ceres took almost three years to lean on the probe's plasma propulsion system to reshape its trajectory through the asteroid belt and intercept the next target.
The maneuvers put Dawn on track, to be captured by Ceres & # 39; gravity field in March 2015.
Prior to Dawn's arrival, Ceres's best-of-Hubble Space Telescope image gave scientists an insight into the planet's mysterious appearance. The scientists knew the size and shape, and they thought Ceres might contain a sub-oceanic ocean.
Ceres almost surprised Dawn's team as soon as the spacecraft was in sight.
"The big surprise in the early approach phase was that there is a high reflectivity area near Occator (Crater)," said Andreas Nathues, senior investigator of the Framing Camera team at the Max Planck Institute for Solar System Research in New York Göttingen, last year at a press conference. "It was so bright on the first pictures that we saturated all the chips (in the camera) because we did not expect such a bright feature on a dark surface."
The bright spots in the Occator crater immediately triggered speculation that they might be icy spots or a volcano erupting that spits water into space , The scientists initially preferred the explanation of the ice, but a closer examination by Dawn's scientific instruments showed that it is sodium carbonate deposits, a type of salt.
Scientists believe that the bright salt deposits came to the surface when an ancient impact body hit Ceres and released rocks and water melted in a complex hydrothermal or cryovolcanic system. Dawn also spotted Ahuna Mons, a three-kilometer (5-kilometer) peak that Dawn's team believes is a dormant volcano that used to spit watery material into the sky instead of rocky magma.
Dawn's Exploration of Ceres Helped Scientists' Conclusion These dwarf planets could once have housed oceans and contain the necessary ingredients to create life.
Ceres has a diameter of about 950 kilometers, about a thirteenth of the Earth. It's bigger than the Saturn moon Enceladus, which hides a global ocean beneath its icy shell, which is heated by the constant pull of Saturn's gravity inside the Moon, a phenomenon known as tidal heating.
"There is an affinity and ceres between some of the icy moons, and they certainly have similarities," said Carol Raymond, Dawn's principal investigator at JPL, in an interview with Spaceflight Now last year. "But since Ceres now lives in a relatively warm environment to these objects, it looks quite different. His sea froze. It has no tidal heat. The ocean is thus frozen and its surface is baked relative to the icy moons. The way it has formed seems to be similar, but the development paths are quite different.
Dawn's main mission ended in 2016, and NASA approved an expansion to continue the exploration of Ceres, the world's largest probe, between the orbits of Mars and Jupiter. High officials at the agency did not agree to a proposal to fire Dawn's trusted ion engines and flee Ceres to fly an asteroid, concluding that more science was to be gained in Ceres than any other destination.
Dawn has almost never made it to the launch pad.
Cost overruns and difficulties with Dawn's electric propulsion system prompted NASA to abandon the mission in March 2006. The space agency resumed its mission less than a month later, after being asked by the JPL managers.
"There were a few dramatic points," Raymond said last year. "The first one was about to start when we learned we were starting with defective reaction wheels and we could not help it. We went into a mode where we wanted to preserve the life of the wheels. "
Three of the four reaction wheels of the probe failed during the mission and forced the engineers to find a new way to control the alignment of the probe with a combination of flywheels and hydrazine – powered engines Rate of rotation changed to pivot the spacecraft.
After a third reaction wheel failed last year, Dawn began to consume more hydrazine fuel for directional control. The probe launched around 45 kilograms of hydrazine to feed its engines.
Dawn's Enduring Legacy
Rayman said Dawn's research mission would leave a lasting legacy and technical heritage.
"In science, these are the discovery of two of the last unexplored 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 Sun and Pluto that had not yet visited a starship."
"The asteroid belt really has millions of objects in it, and yet 45 percent of that total is contained in Vesta and Ceres, which Dawn explored on his own," Rayman said. "I think that's pretty impressive and it's shown us that Vesta is not just an asteroid like the others, many people call it a big stone or something like that, and geologically it's more closely connected to terrestrial plants, one of which is right under our feet, with a dense iron-nickel core which is surrounded by a mantle and surrounded by a crust, and it resembles the terrestrial planets more than the rock we call an asteroid. "
Spacecraft around the solar system, record for the longest lifetime of a plasma propulsion system in space
Combining xenon fuel and electrical energy to produce low thrust forces, ion motors are not as powerful as h powerful engines, but they generate more momentum over time and fuel the jump in fuel efficiency for space missions.
Dawn's ion propulsion system took four days to accelerate the spacecraft by 96 km / h, but the probe crashed. Its ion engines are cumulative for 5.9 years and change the speed of the aircraft by 41,400 kilometers during its mission ,
This ability allowed Dawn to become the first spacecraft to put two sol into orbit. A target system outside the Earth and the Moon.
"For me, Dawn was the first interplanetary spaceship," Rayman said. "The ability to travel to a distant alien world, go into orbit and then maneuver in orbit, then break orbit, travel through the solar system – it was two and a half years and 900 million miles from Vesta to Ceres get into orbit around another alien world and explore it. I think that's really extraordinary. In fact, in the more than 61 years of space exploration it is truly unique, and I think that this is a good sign for our species as we move further into the cosmos. "
" In many ways, Dawn's legacy just begins, Raymond said in a statement on Thursday. "Dawn's datasets are deeply researched by scientists working on how planets grow and different, and when and where life could have formed in our solar system. Ceres and Vesta are also important for the study of distant planetary systems, as they give an insight into the conditions for young stars.
Rayman said Dawn's ground crew noticed signs of fuel leaching on Wednesday for the first time that the spacecraft was located more than 300 million miles from Earth. NASA's Deep Space Network, which includes antennas in California, Spain, and Australia, tracked Dawn's radio signal to measure its Doppler shift, and collected data for scientists to accurately map the Ceres gravitational field. This information could help to determine differences in the inner structure of the dwarf planet.
"We did not lose the signal until late in the track, so we went on and did not see that route, but that was not enough to make a final decision that the mission was over," Rayman said.
Dawn did not transmit telemetry during the Doppler track – just a blank radio signal – so the controllers could not know the status of the spacecraft. They waited for another communication pass on late Wednesday when the engineers only heard silence.
"We have not seen the spacecraft at all," Rayman said. "For me, that was enough to confirm that the mission was over because we had known for so long that we were about to leave the hydrazine."
Without hydrazine to fuel his control jets, Dawn Do not Correct It Alignment requires regular maintenance to counteract the spacecraft's natural forces, such as gravity and sun pressure from Ceres.
Engineers expected these forces to gradually pull Dawn's solar arrays, which tilt 20 feet (20 meters). Up, from the sun, and the spaceship can not charge its batteries. In such circumstances, the on-board software has been programmed to automatically turn off Dawn's radio station to save power until the batteries can be recharged.
"It's smart enough to turn off the radio, save power, conserve the battery's solar arrays on the sun, but it will never reach that state, so it turned off the radio and it will not turn it back on," said Rayman.
Dawn is NASA's second mission to be completed this week.
NASA announced Wednesday that the Kepler Space Telescope has run out of fuel and the search for planets for others The engineers are planning to call the final orders to turn off Kepler's radio from next week.
NASA has selected the Dawn and Kepler missions on December 21, 2001, after refraining from other mission proposals competing for federal funding Space Agency had fought Discovery's program, a series of relatively inexpensive, science-oriented robotic space missions.
Kepler started in March 2009 and also suffered from problems with the reaction wheel during his mission.
"They were selected the same day," Rayman said. "Of course, they started far apart. Kepler started in 2009 and Dawn in 2007. So the same beginning and the same end, but completely different lives, but it's an interesting coincidence. "
Dawn will remain in its current orbit around Ceres for the foreseeable future. The spaceship maneuvered into an egg-shaped orbit earlier this year, in which Dawn rode around Ceres once every 27 hours, passing over its surface in each orbit closer than 22 miles (35 kilometers), closer to Ceres than Dawn had previously. [19659003"WirhabendieForderungnacheinemPlanetenschutzdasssichDawnnichtmindestens20JahremitCeresinVerbindungsetzt"sagteRayman"DerGrunddafüristdassCeresvielWasserhatDasmeisteistgefrorenabereinTeildavonkönntenochflüssigseinEshatorganischeMaterialiendieDawnentdeckthatEshataucheinreichhaltigesInventarananderenChemikalienEshatalsovieleZutatendiefürdasStudiumderChemiediezurEntwicklungdesLebensführtwichtigoderinteressantsind"
NASA will not contaminate Ceres with ruins of Dawn, to ensure that the icy world remains untouched in the asteroid belt for future study visits this.
"(Our) analysis clearly shows that there is no effect in 20 years and even 50 years The likelihood of the spaceship touching the ground is less than 1 percent. So it will be in orbit for a very long time, "said Rayman.
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