{"id":14529,"date":"2017-06-17T19:05:54","date_gmt":"2017-06-17T11:05:54","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/dawn-mission-managers-await-nasa-decision-on-spacecrafts-future\/"},"modified":"2017-06-17T19:05:54","modified_gmt":"2017-06-17T11:05:54","slug":"dawn-mission-managers-await-nasa-decision-on-spacecrafts-future","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/dawn-mission-managers-await-nasa-decision-on-spacecrafts-future\/","title":{"rendered":"Dawn mission managers await NASA decision on spacecraft\u2019s future"},"content":{"rendered":"
\"\"
Artist\u2019s concept of the Dawn spacecraft with one of its ion engines firing. Credit: NASA\/JPL-Caltech<\/figcaption><\/figure>\n

The future of NASA\u2019s Dawn spacecraft, running low on hydrazine fuel and now flying around the dwarf planet Ceres without the help of internal pointing wheels, will be decided in the coming weeks by top space agency managers.<\/p>\n

Scientists have not ruled out sending Dawn on a journey across the solar system to another destination, a voyage that counterintuitively might burn less of the craft\u2019s remaining hydrazine propellant than if Dawn stayed in orbit around Ceres, where it has resided since March 2015.<\/p>\n

Dawn\u2019s primary mission ended in June 2016, and NASA officials approved a one-year extension that expires June 30. The fate of Dawn after June 30 remains uncertain, but senior managers at NASA Headquarters are expected to soon decide whether the spacecraft should be turned off, continue exploring Ceres, or depart the dwarf planet and perhaps fly by an asteroid.<\/p>\n

Officials are expected to consider the financial cost of Dawn\u2019s operations and the scientific payoff of continuing the mission, either at Ceres or another destination.<\/p>\n

\u201cWe are in the process of assessing with NASA options for a second extended mission,\u201d said Carol Raymond, Dawn\u2019s deputy principal investigator at NASA\u2019s Jet Propulsion Laboratory.<\/p>\n

Raymond said Tuesday at a meeting of NASA\u2019s Small Bodies Assessment Group, a community of asteroid and comet scientists, that one option for Dawn\u2019s future could be to send the probe away from Ceres to encounter an asteroid.<\/p>\n

Otherwise, Dawn could remain at Ceres for further exploration of the previously-unvisited world, a dwarf planet with a diameter matching Texas\u2019s, and the largest object in the asteroid belt.<\/p>\n

The gray landscape of Ceres is scattered with impact craters, some of which contain salt deposits in the form of bright spots that greeted scientists with mystery as Dawn arrived in early 2015.<\/p>\n

Dawn also found evidence of an ice-rich later in Ceres\u2019s crust just below the world\u2019s charcoal-colored surface, and scientists believe Ceres harbored an underground ocean in the past.<\/p>\n

The mission also discovered a tenuous, temporary atmosphere containing water vapor around Ceres, and scientists have linked its fluctuations to the intensity of the solar wind.<\/p>\n

Ceres was Dawn\u2019s second destination after the craft orbited the giant asteroid Vesta in 2011 and 2012.<\/p>\n

\"\"
Occator Crater, measuring 57 miles (92 kilometers) across and 2.5 miles (4 kilometers) deep, contains the brightest area on Ceres. This region has been the subject of intense interest since Dawn\u2019s approach to the dwarf planet in early 2015. Dawn\u2019s close-up view reveals a dome in a smooth-walled pit in the bright center of the crater. Numerous linear features and fractures crisscross the top and flanks of this dome. Prominent fractures also surround the dome and run through smaller, bright regions found within the crater. This image shows the bright spots in a mosaic of two Dawn images taken using a shorter exposure time. The shorter exposure reveals details within the bright features that are overexposed, or nearly so, in the full mosaic. The images used to make these mosaics were taken from Dawn\u2019s low-altitude mapping orbit (LAMO), 240 miles (385 kilometers) above Ceres. Credit: NASA\/JPL-Caltech\/UCLA\/MPS\/DLR\/IDA\/PSI<\/figcaption><\/figure>\n

The solar-powered spacecraft, fitted with solar array wings spanning 65 feet (19.7 meters) tip-to-tip, was built by Orbital ATK and launched from Cape Canaveral aboard a United Launch Alliance Delta 2 rocket in September 2007.<\/p>\n

The mission has exceeded all of its scientific objectives, and the last year of bonus operations at Ceres included extra imaging of the dwarf planet, and a unique \u201copposition\u201d observation in late April that positioned the Dawn spacecraft directly between the sun and Occator Crater.<\/p>\n

Scientists hoped the favorable sun angle would yield new insights about the bright salt material inside Occator.<\/p>\n

Dawn lost the third of its four reaction wheels \u2014 spinning devices similar to gyroscopes which use momentum to control the craft\u2019s pointing \u2014 April 23, less than a week before the opposition observation opportunity.<\/p>\n

The science campaign went ahead as planned after ground controllers restored Dawn to its regular flight mode, but using hydrazine-fueled rocket thrusters instead of reaction wheels.<\/p>\n

Dawn\u2019s first reaction wheel failed in 2010, before it reached Vesta. A second wheel stopped working in 2012 as the craft\u2019s ion propulsion system drove Dawn away from Vesta for the trip to Ceres.<\/p>\n

Engineers designed Dawn to control its attitude, or orientation, in space with three reaction wheels, one for each pointing axis. A spare fourth reaction wheel was added for redundancy.<\/p>\n

Experts from JPL and Orbital ATK devised a hybrid method of controlling Dawn\u2019s attitude with the two remaining reaction wheels and hydrazine thrusters, the spacecraft now must fully rely on its rocket jets, wrote Marc Rayman, Dawn\u2019s chief engineer at JPL, in a mission update posted on a NASA website.<\/p>\n

\u201cWith the third wheel failure, we can be grateful that each wheel provided as much benefit as it did,\u201d Rayman wrote. \u201cThe wheels allowed Dawn to conduct extremely valuable work while using the hydrazine very sparingly.\u201d<\/p>\n

Raymond said Tuesday that the third reaction wheel failure was \u201ccertainly not a mission-ending event, but it does reduce our lifetime because we have to use the hydrazine at a faster rate.\u201d<\/p>\n

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NASA\u2019s Dawn spacecraft successfully observed Ceres at opposition on April 29, 2017, taking images from a position exactly between the sun and Ceres\u2019 surface. This movie shows these opposition images, with contrast enhanced to highlight brightness differences. The bright spots of Occator stand out particularly well on an otherwise relatively bland surface. Dawn took these images from an altitude of about 12,000 miles (20,000 kilometers). Credit: NASA\/JPL-Caltech\/UCLA\/MPS\/DLR\/IDA<\/figcaption><\/figure>\n

Dawn will use more hydrazine to maintain its attitude when it is closer to Ceres, but spiraling the probe away from the dwarf planet with its three xenon-fueled ion engines would require even less of the hydrazine maneuvering propellant.<\/p>\n

\u201cThe amount of hydrazine Dawn uses depends on its activities,\u201d Rayman wrote last month. \u201cWhenever it fires an ion engine, the engine controls two of the three axes, significantly reducing the consumption of hydrazine.<\/p>\n

\u201cIn orbit around Vesta and Ceres, the probe often trains its sensors on the alien landscapes beneath it. The lower the orbital altitude, the faster the orbital velocity, so Dawn needs to turn faster to keep the ground in its sights,\u201d Rayman wrote. \u201cAlso, the gravitational attraction of these massive worlds tends to tug on the unusually large solar arrays in a way that would turn the ship in an unwanted direction. That force is stronger at lower altitude, so Dawn needs to work harder to counter it.<\/p>\n

\u201cThe consequence is that Dawn uses more hydrazine in orbit around Vesta and Ceres than when it is journeying between worlds, orbiting the sun and maneuvering with its ion engine. And it uses more hydrazine in lower orbits than in higher ones,\u201d Rayman wrote.<\/p>\n

There is plenty of xenon gas left aboard Dawn, officials said.<\/p>\n

Raymond said Dawn is currently in an egg-shaped orbit around Ceres that ranges in distance between 12,000 miles (20,000 kilometers) and 30,000 miles (50,000 kilometers). The probe traveled as close as 240 miles (385 kilometers) to Ceres last year.<\/p>\n

\u201cWe have enough resources, hydrazine and xenon, to support operations through at least the end of 2018,\u201d Raymond said. \u201cThat will be depending the decision at (NASA) Headquarters what we will do with those resources.\u201d<\/p>\n

That lifetime prediction depends on Dawn remaining far away from Ceres.<\/p>\n

\u201cOne day at our low-altitude mapping orbit, which was at 385 kilometers, would be equivalent to about 18 days (of hydrazine fuel) at higher altitude, which is what we\u2019re in now,\u201d Raymond said.<\/p>\n

\u201cLifetime at a lower altitude would likely be limited to weeks at this point,\u201d she said.<\/p>\n

A decision on Dawn\u2019s future in the coming weeks \u2014 whether it will stay at Ceres or head elsewhere \u2014 echoes a similar stay or go choice that faced NASA managers last June.<\/p>\n

Dawn\u2019s science team last year proposed dispatching Dawn toward asteroid Adeona, a primitive, carbon-rich remnant from a collision that destroyed a much larger body, for a relatively slow-speed flyby in May 2019, but NASA officials decided keeping the probe in orbit around Ceres would yield a greater scientific return.<\/p>\n

One possible fate has been ruled out.<\/p>\n

Scientists don\u2019t want Dawn to collide with Ceres and potentially spoil future exploration of the airless world.<\/p>\n

\u201cWhen our planetary protection requirements were negotiated, (scientists) already made the prediction that Ceres was an ocean world in the past, and could possibly be an ocean world today,\u201d Raymond said. \u201cWe\u2019ve been vindicated, so our planetary protection requirement was don\u2019t land, don\u2019t crash.\u201d<\/p>\n

Before shutting off Dawn for good, navigators will ensure the spacecraft is on a \u201cquarantine\u201d trajectory that avoids impacting Ceres, she said.<\/p>\n

Email the author.<\/i><\/b><\/p>\n

Follow Stephen Clark on Twitter: @StephenClark1.<\/strong><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

Artist\u2019s concept of the Dawn spacecraft with one of its ion engines firing. Credit: NASA\/JPL-Caltech The future of NASA\u2019s Dawn spacecraft, running low on hydrazine fuel and now flying around the dwarf planet Ceres without the help of internal pointing wheels, will be decided in the coming weeks by top space agency managers. Scientists have […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[2837,1519,2838,2839,2840,1183,2899,1561],"class_list":["post-14529","post","type-post","status-publish","format-standard","hentry","category-news","tag-asteroid-belt","tag-asteroids","tag-ceres","tag-dawn","tag-dwarf-planets","tag-jet-propulsion-laboratory","tag-orbital-atk","tag-planetary-science"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/14529"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=14529"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/14529\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=14529"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=14529"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=14529"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}