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NASA's Dawn spacecraft ran out of fuel on Wednesday and stopped transmitting to Earth, ending an eleven-year mission exploring the two largest objects in the belt. Asteroids and establishing several records in the annals of the history of space.
Dawn failed to contact NASA's Jet Propulsion Laboratory controllers in California during the night of Wednesday to Thursday, and officials said the mission was over after evidence had indicated that the Spacecraft had run out of hydrazine fuel.
The depletion of fuel. had been long overdue and engineers expected Dawn to miss hydrazine in September or October. Apparently, Dawn emptied its hydrazine tank on Wednesday, which made the spacecraft orbit around the dwarf planet Ceres unable to keep its antenna pointed at Earth, nor its solar panels sunk to produce electricity.
In an interview with Spaceflight Now, Marc Rayman, Dawn's chief engineer at JPL, said that it was much sweeter than bitter. "It's the successful conclusion of a successful mission. For me, this is the best way to complete a mission because it is productive to the end and we have pulled as much as possible, even in principle, the probe, so that I can not be happier. "[19659006] Spaceflight Now, members can read a transcript of our full interview with Marc Rayman. Become a member today and support our coverage.
"Today we are celebrating the end of our Dawn mission – its incredible technical achievements, essential scientific knowledge and the entire team that made it possible for the spacecraft to make these discoveries" Thomas Zurbuchen, Associate Administrator of NASA's science mission to Washington, said in a statement Thursday. "The amazing images and data collected by Dawn from Vesta and Ceres are essential to understanding the history and evolution of our solar system."
Launched Cape Canaveral aboard A United Launch Alliance Delta 2 rocket on 27 September 2007, the Dawn spacecraft has traveled 6.9 billion kilometers in the inner solar system over the past 11 years. She flew over Mars for a gravitational badistance maneuver before reaching the asteroid Vesta, the second largest object of the asteroid belt in 2011.
The spacecraft has was built by Northrop Grumman Innovation Systems, formerly Orbital ATK, and carried three instruments – a framing camera, a visible and infrared spectrometer, and a gamma and neutron detector – to study the geology, up and moisture content of Vesta and Ceres.
Dawn revolved around Vesta more than a year, using its ionic engines to spiral near the giant asteroid, then to retreat and escape the Vesta gravity field to get to Ceres.
The time from Dawn to Vesta has left several surprises, mainly with the discovery of evidence that liquid water could have flowed on the asteroid, Raymond said.
Scientists already have samples from Vesta in laboratories on Earth.
Prior to Dawn's mission, researchers suspected a special clbad of rock samples called Howardite – Eucrite – Diogenite or HED, meteorites that fell to Earth from space had been ejected from Vesta by an ancient interplanetary collision.
Dawn confirmed this hypothesis and discovered that Vesta had probably already had a global tectonic activity, something scientists did not expect in such a small world. Vesta is approximately 578 kilometers (578 kilometers) in diameter along its longest axis.
The suite of cameras built in Germany by the Dawn spacecraft found holes in the bottom of several relatively cool craters on Vesta, suggesting volumes of gas – perhaps steam – released by violent impacts with other asteroids.
Dawn's journey between Vesta and Ceres lasted nearly three years, with the plasma propulsion system of the probe changing its trajectory across the asteroid belt to intercept its next target.
The Dawn Maneuver In March 2015, the Ceres gravity field will capture the course.
Before the arrival of Dawn, the best image of Ceres in the Hubble Space Telescope gave scientists a glimpse of the appearance of the mysterious mini-planet. Scientists knew its size and shape, and they thought that Ceres might contain a subglacial ocean.
Ceres astonished the Dawn team almost as soon as the probe moved within visual range.
"The big surprise at the beginning of the approach phase was that there is an area of high reflectivity near the Occator (Crater)," said Andreas Nathues, senior investigator of the camera crew. at the Max Planck Institute for Solar System Research in Göttingen, Germany, at a press conference last year. "The first images were so bright that we saturated all the shavings (in the camera), because we did not expect such a bright element on a dark surface."
The bright spots of the Occator crater immediately caused speculation that it could be icy plates or an erupting volcano projecting water into the sea. The scientists initially opted for the explanation of the ice, but further examination by Dawn's scientific instruments revealed that it was sodium carbonate deposition , a type of salt.
Scientists Folks believe that shiny salt deposits have risen to the surface when an old impactor hit Ceres, releasing rock and melted water into a complex or cryovolcanic hydrothermal system. Dawn also discovered Ahuna Mons, a three-kilometer (5 km) summit that, according to his team, is a dormant volcano that spits an aqueous substance in the sky instead of a rocky magma.
Dawn's exploration of Ceres helped shape the scientists' conclusion that these dwarf planets might once have harbored oceans and contained the ingredients necessary for life.
Ceres extends about 950 kilometers (590 miles) in diameter, about one thirteenth of the size of the Earth. It is larger than Saturn's moon, Enceladus, which hides a global ocean under its ice shell warmed by the constant weight of Saturn's gravity inside the moon, a phenomenon known as warming tides.
"There is an affinity between some of the frozen moons. and Ceres, and they certainly carry similarities, "said Carol Raymond, Dawn 's chief investigator at JPL, during an interview with Spaceflight Now last year. "But since Ceres lives in such a warm environment, it seems very different. His ocean froze. He does not have tidal heat. The ocean is frozen and its surface is baked compared to the frozen moons. The way she formed, what she formed, seems to be similar, but the paths of evolution are quite different. "
Dawn's main mission completed in 2016 and NASA approved an extension to continue exploration of the Ceres probe, the world's largest world. between the orbits of Mars and Jupiter. Senior officials at the agency have not approved a proposal to turn on Dawn's loyal ion engines and to escape from Ceres to get to the asteroid overflight, concluding that there was more science to be gained at Ceres than at another target.
Dawn has almost never reached the launch pad.
The cost overruns and difficulties badociated with Dawn's electric propulsion system prompted NASA to cancel the mission in March 2006. The space agency reinstated the mission less than a month later. a call from JPL officials
"There were some dramatic points," said Raymond last year. "The first took place right before the launch, when we learned that we had faulty reaction wheels and that we could not do anything about it. We moved to a mode where we tried to preserve the life of the wheels. "
Three of the four reaction wheels of the aircraft failed during the mission, forcing engineers to find a new way to control the pointing of the probe with a combination of kinematic wheels and hydrazine. The spinning gyro – shaped wheels are designed to change their rotational speed to rotate the space shuttle
After the failure of a third reaction wheel. Last year, Dawn began using more hydrazine fuel for pointing control.The probe was launched with about 45 kg of hydrazine to power its thrusters.
The Enduring Legacy of Dawn
According to Rayman, Dawn's exploration mission will leave a lasting scientific mission and legacy of engineering.
"In science, it is about the unveiling of two of the last mo unexplored ns of the internal solar system, "said Rayman. "Vesta and Ceres are the two largest bodies between Mars and Jupiter and, prior to the Dawn mission, Ceres was the largest object between the sun and Pluto that a spaceship had not yet visited.
"The main asteroid belt really has millions and 45% of that total mbad is contained in Vesta and Ceres, which Dawn has explored on its own," Rayman said. "I think that's quite impressive and that showed us that Vesta is not just an asteroid like the others.A lot of people call it a big rock or something like that.Geologically it is more closely related to terrestrial plants, including a just beneath our feet.It has a dense core of iron-nickel surrounded by a mantle, surrounded by a crust, and it looks more like terrestrial planets than rocks we consider as asteroids. "
Dawn had three ion engines to push the spacecraft around the solar system, setting a record for the longest running time of a plasma propulsion system in space.
Using a combination of xenon fuel and electrical energy to generate low thrust levels, ion engines are not as powerful as conventional thrusters.
Dawn's ion propulsion system took four days to accelerate the spacecraft by 96 km / h (60 mph), but the probe pushed with its ionic engines operated for 5.9 years of cumulative operation , modifying the speed of the craft by 41,700 kilometers (25,700 mph) during its mission.
This ability has allowed Dawn to become the first two-ground orbiter spacecraft. One system uses other destinations outside the Earth and Moon.
first interplanetary spacecraft, "Rayman said. "The ability to travel to a distant alien world, orbit it, then maneuver into orbit, then out of orbit and travel through the solar system – it's been two and a half years and 900 million miles To go from Vesta to Ceres, go into orbit into another extraterrestrial world and explore it, I think it's really extraordinary. Indeed, it's really unique in over 61 years of space exploration, and I think it bodes well for our species as we continue to reach out into the cosmos. "
" In many ways, Dawn's legacy is just beginning, "Raymond said in a statement Thursday," Dawn's data will be deepened by scientists working on the growth and differentiation of planets , as well as the time and place where life could have formed in our solar system Ceres and Vesta also play an important role in the study of distant planetary systems, as they provide insight into conditions that may exist around young stars. "
Rayman said the Dawn ground crew had noticed for the first time on Wednesday that the spacecraft 300 million miles from Earth could be out of 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 that allowed scientists to accurately map the Ceres gravity field. information that can help determine variations in the internal structure of the dwarf planet.
"We lost the signal late in the track, so we continued to watch during this track and we did not see it, but that was not enough to definitively decide that the mission was over" Rayman said.
Dawn did not transmit any telemetry during the Doppler track – it was only a blank radio signal – so the controllers could not be certain of the spacecraft status. They waited for a new communication Wednesday night, while the engineers heard only silence.
"We did not see the space shuttle at all," Rayman said. "That was enough to confirm that the mission was over because we had known for so long that we were about to run out of hydrazine."
Without hydrazine to power his control jets, Dawn was unable to correct . its orientation, which requires regular maintenance to counteract the natural forces acting on the spacecraft, such as gravity and solar pressure of Ceres.
Engineers were expecting these forces to gradually drive Dawn's solar panels, which extend 20 meters (65 feet) deep. at the top, off their latch, preventing the probe from recharging its batteries. In such circumstances, the onboard software has been programmed to automatically turn off the Dawn radio transmitter to conserve energy until the batteries can be recharged.
"He is smart enough to turn off this radio, save energy, save battery, until it has its solar panels on the sun, but they do not have the power. will never reach this condition; so they turned off the radio and did not turn it back on, "said Rayman.
Dawn is the second mission declared complete by NASA this week.
NASA announced Wednesday that the Kepler Space Telescope was running out of fuel, ending his search for planets around other stars.The engineers plan to link final orders to turn off Kepler's radio as early as next week
NASA has chosen Dawn and Kepler missions December 21, 2001, following a competition between several mission proposals for federal funding under the Space Agency Discovery Program, a series of relatively low-cost, science-based robotic space missions
] Kepler was launched in March 2009 and also experienced some reaction problems during his mission.
"They were selected the same day," Rayman said. "Well Sure, they ran away from each other. Kepler was launched in 2009 and Dawn in 2007. So the same beginning and the same end, but very different lives between the two, but it's an interesting coincidence. "
Dawn will remain in its current orbit around Ceres for the future future.The spacecraft evolved into an egg-shaped orbit earlier this year, which takes Dawn around Ceres once every 27 hours, pbading at a distance of about 35 km above its surface in each orbit, closer to Ceres than Dawn had ever used before.] "We have a planetary protection requirement that Dawn will not contact Ceres during less than 20 years old, "said Rayman." The reason is that Ceres has a lot of water, most of it is frozen, but some can still be liquid, it contains organic matter detected by Dawn. rich inventory of other chemicals … It contains so many important or interesting ingredients for the study of chemistry that leads to the development of life. "
NASA does not want to cont Ceres amine with the debris of Dawn, ensuring that the frozen world of the asteroid belt remains blank for future missions to study.
"(Our) badysis clearly shows that there is no chance of impact in 20 years, and even in 50 years. there is less than 1% chance that the spacecraft will hit the ground. So, it'll stay in orbit for a very long time, "said Rayman.
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