RBSP (x2) - Atlas V 401 - Canaveral SLC-41 - 30.08.2012 08:05 UTC

[Salo]

http://ria.ru/science/20130725/952144580.html

Зонды RBSP нашли источник электронов в радиационных поясах Земли

22:21 25.07.2013



МОСКВА, 25 июл — РИА Новости. Наблюдения зондов RBSP показали, что большая часть электронов высокой энергии в радиационных поясах Земли, разгоняются до околосветовых скоростей внутри них, а не в других частях околоземного пространства, как считали некоторые ученые, заявляют планетологи в статье, опубликованной в журнале Science.

Радиационные пояса Земли, заполненные частицами высокой энергии, были открыты американским астрофизиком Джеймсом Ван Алленом в 1958 году. Наблюдения в последующие годы показали, что электроны и другие частицы в этих областях разогнаны до околосветовых скоростей. На сегодняшний день существует две основных теории, объясняющих такие скорости. Первая предполагает, что электроны попадают в эти пояса из околоземного пространства уже разогнанными, а вторая говорит о разгоне частиц внутри самих поясов.

Джеффри Ривз (Geoffrey Reeves) из Национальной лаборатории Лос-Аламос (США) и его коллеги выяснили, что вторая теория больше соответствует действительности, проанализировав данные, собранные парой спутников RBSP с момента их выхода на орбиту в августе 2012 года. Сравнивая число "разогнанных" электронов, их плотность и скорость в разных частях поясов Ван Аллена в спокойные периоды времени и во время геомагнитных бурь, ученые пытались понять, откуда берутся эти частицы.

Ученые выяснили, что наибольшее число ускоренных электронов наблюдалось не по краям пояса, как это предсказывает теория "космического" разгона частиц, а в его середине. Данный факт, по их словам, позволяет говорить о том, что электроны ускоряются внутри самих поясов под действием магнитного поля Земли и других сил, существующих внутри "радиационного щита" нашей планеты.

Таким образом, Ривзу и его коллегам удалось решить одну из загадок радиационных поясов Земли. Пока не понятно, разгоняются ли электроны схожим образом в третьем поясе Ван Аллена, об открытии которого ученые заявили в феврале 2013 года. По всей видимости, для ответа на данный вопрос потребуются дальнейшие наблюдения на RBSP.

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Salo пишет:
 http://ria.ru/science/20130725/952144580.html

Зонды RBSP нашли источник электронов в радиационных поясах Земли

22:21 25.07.2013

http://www.nasa.gov/content/goddard/van-allen-probes-find-source-of-fast-particles/index.html

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Van Allen Probes Mark First Anniversary with New Discoveries and New Investigations
http://www.nasa.gov/content/goddard/van-allen-probes-mark-first-anniversary/

[Liss]

От НИИЯФ МГУ ( http://www.sinp.msu.ru/ru/post/13909 ):

Объяснено происхождение третьего радиационного пояса Земли
            
 25 Сен 2013, 17:15, автор: Васильева Анна Людвиговна
 
    Физики России, в числе которых сотрудники НИИЯФ МГУ - Александр Дроздов и Ксения Орлова, совместно с коллегами из Канады и США объяснили происхождение третьего радиационного пояса Земли, открытого в феврале 2013 года. Исследование опубликовано в журнале Nature Physics, кратко его содержание приводится в PhysOrg.
Почти полвека считалось, что Землю окружают два радиационных пояса: внутренний (на высоте от 1600 до 13000 км), состоящий из протонов, и внешний (на высоте от 19000 до 40000 км), состоящий из электронов. Третий был недавно обнаружен на внутреннем крае внешнего пояса на высоте от 19 100 до 22 300 километров от Земли, а состоит он исключительно из самых энергичных (проще говоря, самых «скоростных»), ультрарелятивистских электронов, обладающих максимальной проникающей способностью.
«Пояса Ван Аллена могут представлять серьёзную угрозу для спутников и космических кораблей, это может быть как незначительный сбой аппаратуры, так и полный его выход их строя. Лучшее понимание природы излучения в пространстве поможет защитить людей и аппаратуру от неприятностей», - сообщил руководитель Международной группы учёных, выпускник МФТИ, профессор Сколковского института науки и технологий Юрий Шприц.
Для изучения природы третьего радиационного пояса Земли Международная группа учёных создала модель околоземных радиационных поясов за период с конца августа 2012 года по начало октября 2012 года. Моделирование проводилось на основе данных об ультрарелятивистских электронах, которые были получены с помощью запущенных в августе 2012 года двух идентичных спутников Van Allen Probes.
В результате, учёные выявили, что 1 сентября 2012 года плазменные волны, порождённые ионами, выхватили и выбросили ультрарелятивистские электроны с внешнего радиационного пояса к его внутреннему краю, сформировав тонкое кольцо - третий радиационный пояс.
После бури пузырь холодной плазмы вокруг Земли расширился и тем самым защитил ультрарелятивистские электроны от ионных волн, позволяя существовать третьему радиационному поясу долгое время.
Также ультрарелятивистские электроны были разогнаны до столь высоких энергий, что практически не давало им возможности войти во взаимодействие с плазменными волнами, обычно рассеивающими электроны более низких энергий. Именно ещё и поэтому ультрарелятивистские электроны не распались мгновенно после прекращения бури и смогли остаться на орбите в течение четырёх недель.
«Я думаю, что этим исследованием мы приоткрыли лишь верхушку айсберга, — сказал Юрий Шприц. — Нам всё ещё осталось в полной мере понять, как именно эти электроны ускоряются до таких скоростей, откуда они приходят и как различается динамика радиационных поясов в различных типах бурь в околоземном пространстве».
    

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Еще от НИИЯФ МГУ:

http://www.sinp.msu.ru/ru/post/13988

Интервью с сотрудниками НИИЯФ МГУ, объяснившими происхождение третьего радиационного пояса

14 Окт 2013, 11:37, автор: Васильева Анна Людвиговна

Соавторы статьи о происхождении третьего радиационного пояса Земли, опубликованной в журнале Nature Physics, физики НИИЯФ МГУ, к.ф.-м.н. Александр Дроздов и к.ф.-м.н. Ксения Орлова рассказали о сложностях написания статьи для Nature Physics, о личном вкладе и о своих планах.

Корр.: НИИЯФ МГУ сердечно вас поздравляет с успешной работой! Что вы испытали после публикации статьи в одном из самых престижных журналов - Nature Physics?

Александр Дроздов: Конечно же, мы испытали радость, гордость, а так же некоторое облегчение, потому что публикация в таком журнале требует достаточно серьёзной выдержки. Обычно до публикации статья проходит несколько этапов. Сначала статью одобряет технический редактор. Затем назначают рецензентов. После идёт долгое общение с рецензентами, ответы на их многочисленные вопросы и комментарии.

Корр.: Расскажите, пожалуйста, подробнее о том, как готовилась статья?

Ксения Орлова: Руководитель нашей группы Юрий Шприц написал нам по электронной почте: «Давайте попробуем опубликоваться в Nature Physics, у нас теоретически всё сходится». И мы приступили к работе над ней. Каждый из нас внёс свой вклад. Александр анализировал данные. Многие из числа нашей группы занимались созданием модели. Кто-то смотрел на параметры волн и т.д. И когда мы провели моделирование, наши начальные представления о происхождении третьего радиационного пояса Земли подтвердились.

Далее был этап написания статьи. Это достаточно сложный процесс. Мы привыкли писать статьи в научном стиле, а для Nature Physics статья должна быть в научно-популярном. Здесь мы не можем использовать свою терминологию без пояснений. Если мы приводим какой-то термин, то его нужно обязательно раскрыть. Статья должна быть понятной не только учёным, но и широкому кругу читателей. Кроме того, текст необходимо изложить на простом языке и достаточно ёмко.

Александр Дроздов: Для подробностей, которые не могут войти в основную статью, есть приложение «Дополнительные материалы» (Supplementary materials). Если наша основная статья состоит из четырёх с половиной страниц, то приложение - из 11-ти.

Ксения Орлова: Действительно, в «Дополнительных материалах» более подробно даётся описание модели и параметров, которые используем. Приложение рассчитано на более узкий круг специалистов, которые занимаются радиационными поясами.

Александр Дроздов: Относительно сроков добавлю, что наша статья поступила в редакцию журнала в марте этого года. Была опубликована online в конце сентября.

Корр.: Поделитесь, в чём заключалась непосредственно ваша работа по исследованию третьего радиационного пояса Земли?

Александр Дроздов: Я работал над анализом спутниковых данных для того, чтобы интегрировать их в модель. Поясню, есть первичные данные, получаемые с аппарата, такие данные являются «сырыми» и требуют расшифровки. Сложность заключается не только в их декодировании, но и в понимании того, насколько полученные в результате физические величины соответствуют действительности. Кроме прочего, я принимал непосредственное участие в обсуждении модели с Дмитрием Субботиным, а конкретно - граничных условий.

Ксения Орлова: Моя работа заключалась в подготовке диффузионных коэффициентов для модели. Рассматривалось резонансное взаимодействие электронов с различными типами плазменных волн. К примеру, в статье приведены времена потерь электронов, полученных на основе диффузионных коэффициентов. Также в статье наглядно показано на каких широтах выполняется резонансное соотношение взаимодействия волн с частицами.

Александр Дроздов: Кстати, наша статья вызвала широкий резонанс в СМИ. К сожалению, кое-где не обошлось без ошибок и неточностей. На будущее – хотелось бы, чтобы текст заметок согласовывали с авторами.

Корр.: Расскажите о своей научной деятельности в целом: с начала пути и до сегодняшнего дня.

Александр Дроздов: В 2007 году я поступил на работу в НИИЯФ МГУ на должность младшего научного сотрудника, где числюсь по сей день. В нашей статье в Nature Рhysics аффилиация НИИЯФ МГУ стоит как у меня, так и у Ксении. В конце 2007 года поступил в аспирантуру. При этом оставался на полставки в НИИЯФ МГУ. Успешно окончил аспирантуру, защитив диссертацию в 2011 году. До приезда в Калифорнийский университет в Лос-Анджелесе (UCLA) я занимался проблемами генерации грозовых нейтронов в атмосфере и возможностью их детектирования как на Земле, так и на орбитальных высотах. Тематика была мною раскрыта, нужно было выходить на эксперимент. НИИЯФ МГУ дал мне хорошую школу в области знаний радиации околоземного пространства, в том числе и поэтому изменить тематику было не сложно. Замечу, что в современном научном сообществе смена деятельности достаточно распространена. Учёный всегда должен раздвигать горизонты своих познаний.

В конце 2012 года в UCLA в группе Юрия Шприца начал заниматься исследованием радиационных поясов. Сейчас я активно работаю с данными новых спутников Van Allens Probes в тесном сотрудничестве с их командой. Уже было несколько случаев исправления расшифровки данных с наводки нашей группы. Кроме того, я работаю над моделированием посредством диффузионного кода, разработанного в нашей группе. В ближайшее время подам в журнал статью, которая покажет важность моделирования радиационных поясов на высоких энергиях. В статье будет кратко и понятно отражена вся моя деятельность за последний год.

Ксения Орлова: Я поступила на физический факультет МГУ в 2003 году. Дипломную работу выполнила под началом прекрасного научного руководителя из НИИЯФ МГУ, профессора Антоновой Елизаветы Евгеньевны и сотрудника института Бахаревой Маргариты Фёдоровны. Тема работы заключалась в исследовании взаимодействия волн с частицами в радиационных поясах Земли, чем и занимаюсь и по сей день. Поступила в аспирантуру на кафедру физики космоса и в 2012 году успешно защитила кандидатскую диссертацию, в которой основной задачей было изучение влияния недипольного магнитного поля Земли на процессы взаимодействия волн и частиц. Я показала, что на ночной стороне магнитосферы Земли темпы ускорения и потерь энергичных электронов очень сильно зависят от вытянутости магнитных силовых линий.

В данный момент, как и Александр, я являюсь сотрудником НИИЯФ МГУ и UCLA. Продолжаю заниматься исследованием процессов взаимодействия волна-частица. Интересной работы много в связи с запуском в прошлом году двух спутников, о которых упоминал Александр. Впереди ещё новые спутники - «Ломоносов», «РЭЛЕК», «Резонанс». Будем открывать новое! Как сказал один знакомый учёный: «Как же вам повезло! Вы попали в нужное время, только-только запустили новые спутники, изучающие сердце радиационных поясов. Поле для деятельности сейчас у вас открытое и широкое». Это действительно так. Мы сможем многое понять из анализа новых данных, усовершенствовать наши модели. Думаю, что мы приблизимся к ответу на главный вопрос, который мучает, пожалуй, если не всех, то многих учёных нашей области: когда и какие механизмы ускорения и потерь частиц доминируют. После этого мы сможем не только понимать происходящее в радиационных поясах, но и прогнозировать их динамику.

Александр Дроздов: Стоит отметить, что мы сможем подойти к вопросу радиационной безопасности полётов около Земли с большим багажом знаний. Радиационные пояса вкупе с солнечными вспышками оказывают негативное влияние не только на человека, но и на наземное и космическое электронное оборудование. Яркий пример: в 80-ых годах из-за мощной солнечной вспышки половина Америки осталась без электричества, что привело к многомиллиардным потерям в финансовом и инфраструктурном плане. Никто не ожидал, что такое может случится. Посмотрим, что будет дальше, конечно, исключительно в надежде на лучшее.

Корр.: Желаем вам дальнейших успехов!

Александр Дроздов и Ксения Орлова: Спасибо большое!

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NASA declares Mission Success for Van Allen Probes
http://www.spaceflight101.com/rbsp-mission-updates.html

NASA has officially declared the Van Allen Probes mission a success in March – one year and seven months into the planned two-year mission. The Van Allen Probes have achieved and surpassed all mission objectives and requirements for mission success. Over the course of their mission, the twin spacecraft circling Earth in an highly elliptical orbit have found a transient third radiation belt not known before, discovered a massive electron acceleration process in the belts, measured double layers that seed particle population and provided data for the improvement of space weather models.

"All of these fundamental findings are, in very real ways, changing much of what we thought we knew about the radiation belts and plasma physics," said Barry Mauk of the Johns Hopkins University Applied Physics Laboratory, Van Allen Probes project scientist.

"It's very gratifying to be able to have these incredibly accurate and sensitive instruments in orbit, and use them to produce these results. The declaration by NASA of mission success at this early stage of the mission is another laurel for all of the teams."

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Johns Hopkins APL‏Подлинная учетная запись @JHUAPL 17 ч. назад

Today one of the twin Van Allen Probes begins 3/5 de-orbit maneuvers, bringing spacecraft A fr om about 372 miles to 161 miles closer to Earth. The final burn will be this Friday, March 22nd, 2019. #FinalCountdown #spaceweather @NASASun http://bit.ly/jhuapl-vap 

http://vanallenprobes.jhuapl.edu/News-Center/newsArticles/article.php?id=20190210

February 10, 2019
Radiation Belts Revealed and Conquered, NASA's Van Allen Probes Begin Final Phase of Exploration


Launched on August 31, 2012, the twin Van Allen Probes carried identical suites of five instruments to explore the Van Allen radiation belts above Earth. The instruments measure the particles, magnetic and electric fields, and waves in this harsh radiation environment, giving researchers insights into the belts and space weather. In 2019, the mission begins a de-orbit maneuver that will allow the spacecraft to safely burn up in the Earth's atmosphere in about 15 years. Credit: NASA/Johns Hopkins APL/Steve Gribben

Two tough, resilient NASA spacecraft have been orbiting Earth for the past six and a half years, flying repeatedly through a hazardous zone of charged particles known as the Van Allen radiation belts. Designed to study these areas above our planet, previously thought to be stable and well-understood, the twin Van Allen Probes – launched in August 2012 – have confirmed scientific theories and revealed new structures, compositions, and processes at work in these dynamic regions.


This chart shows the change in the orbit of the Van Allen Probes that will occur after de-orbit maneuvers in February and March 2019. The spacecrafts' highly elliptical orbits will gradually tighten over the next 15-25 years as the Van Allen Probes begin to experience atmospheric drag at their perigee, or lowest point of orbit. The drag will pull the elliptical orbit into a circular one as early as 2034, at which time the spacecraft will begin to enter the atmosphere and safely disintegrate. Credit: Johns Hopkins APL

On February 12, the Van Allen Probes mission operations team at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland – where the probes were designed and built – will begin a series of orbit descent maneuvers that will last into March. These changes will change the lowest point of orbit, or perigee, of both spacecraft some 161 miles (260 km) in order to position them for an eventual re-entry into Earth's atmosphere, in approximately 15 years. "In order for the Van Allen Probes to have a controlled re-entry within a reasonable amount of time, we need to lower the perigee," said Nelli Mosavi, project manager for the Van Allen Probes at the Johns Hopkins Applied Physics Laboratory, or APL, in Laurel, Maryland. "At the new altitude, aerodynamic drag will bring down the satellites and eventually burn them up in the upper atmosphere. Our mission is to obtain great science data, and also to ensure that we prevent more space debris so the next generations have the opportunity to explore the space as well."

Спойлер

Originally designated as a two-year mission – based on predictions that no spacecraft could survive much longer operating in the harsh radiation belts – these rugged spacecraft have operated without incident since 2012, and continue to enable groundbreaking discoveries about the Van Allen Belts. "The spacecraft and instruments have given us incredible insight into spacecraft operations in a high-radiation environment," Mosavi said. "Everyone on the mission feels a real sense of pride and accomplishment in the work we've done and the science we've provided to the world – even as we begin the de-orbiting maneuvers."

The Van Allen Radiation Belts

"The radiation belts are doughnut-shaped bands of energized particles – protons and electrons – trapped around, and endlessly circling, the Earth at distances above the planet's surface, ranging from several hundred miles to a tenth of the distance to the Moon," explained mission scientist David Sibeck, of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"We know that other planets in our solar system with magnetic fields have radiation belts," said project scientist Sasha Ukhorskiy of APL, "and we can assume that other bodies throughout the universe do too. By studying the belts and the physics associated with them here at Earth, and using our world as a natural laboratory, we can learn about how these structures function around other objects in the universe with magnetic fields."

Earth's radiation belts – and the twin spacecraft that study them – are named for James Van Allen, whose work in space science and exploration, particularly with the 1958 Explorer I spacecraft, led to some of the earliest detailed study and definition of these regions of space.

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Since 2012, the Van Allen Probes have traveled in an elliptical orbit around the Earth, through the inner region of the Earth's geomagnetic field.

In this region, many of the magnetic field lines intersect the surface of the Earth in the north and south. This means that lower energy ions and electrons, some 'boiled off' the Earth's ionosphere by solar ultraviolet radiation, can be trapped along these field lines. The charged particles spend their time bouncing between the 'mirror points' in the Earth's magnetic field. This trapped population forms the radiation belts around the Earth. The radiation created by this charged particle population can be hazardous to satellites and astronauts so it is important to understand their characteristics.

"These areas of trapped radiation were the first scientific discovery of humanity's pioneering spacecraft missions in the late 1950s," said Ukhorskiy. "After more than fifty years of study, we understand that the near-Earth radiation region is a complex and dynamic environment. But profound mysteries remained that called for designing a new mission – the Van Allen Probes – with uniquely capable scientific instrumentation that can capture all particle populations in the radiation belts and resolve the processes that drive and guide them."

Since their launch from Cape Canaveral Air Force Station, Florida on Aug. 30, 2012, the twin Van Allen Probes have delivered to scientists an unprecedented look into the make-up and processes within the belts. The spacecrafts' orbits are highly eccentric: at perigee, they swoop to within about 373 miles (600 km) of the planet's surface, then out to an apogee of more than 19,417 miles (31,250 km). Twin spacecraft provide their instruments with the opportunity to deliver different (in time and space) looks at the same features of the belts, giving scientists a detailed image of how particle and wave events begin and change.

"Everything that happens in the radiation belts begins with the Sun," said Sibeck. "The Sun periodically sends out blasts of plasma that batter our own Earth's magnetic field." The magnetic field creates a bubble known as the magnetosphere, which protects our planet from these plasma blasts – but it also serves to capture the particles within them, eventually settling these high-energy particle populations into the radiation belts around the Earth.

Some of these particles are moving at speeds approaching that of the speed of light – over 670 million miles an hour. They are accelerated to those speeds by a complex chain of processes that occur in the near-Earth space, a region which acts like a giant particle accelerator. The highly energized particles in the radiation belts can pose a number of hazards to space operations, as the they can damage sensitive electronics.

During solar storms, conditions worsen, and the belts can swell in size, threatening nearby spacecraft. "Our magnetic field does a pretty good job of shielding us from these solar blasts," said Sibeck, "but some of their energy penetrates deep into the Earth's field and, through a variety of mechanisms, powers up the radiation belts. When that happens, spacecraft in the belts had better look out. Trouble lies ahead in the form of short circuits, disrupted computer memory, and instrument failure."

The Van Allen Probes were designed and built to be resilient to this harsh environment.

"Over the past six and a half years, the Van Allen Probes have completed three full circuits around the magnetosphere, and measured more than 100 geomagnetic storms," said Ukhorskiy. "The Van Allen Probes verified and quantified previously suggested theories, discovered new mechanisms that can sculpt near-Earth energetic particle populations, and used uniquely capable instruments to unveil unexpected features that were all but invisible to previous sensors."

The information on particles and waves delivered by the Van Allen Probes has proven to be a treasure trove for space physics research. Findings and observations include multiple belt structures, including a third belt observed shortly after launch; definitive answers about particle acceleration processes; and the discovery of a nearly impenetrable barrier region that prevents the fastest and most energetic electrons from reaching Earth.

"The data from the Van Allen Probes has led to more than 560 articles published in peer-reviewed science journals since the launch of the mission," he continued. "Most of these articles are led by the authors not directly affiliated with the mission's science teams. And the publication rate has steadily grown since the mission launch; every four days, a new article is published in an international peer-reviewed journal."

Built to Survive


In this late 2010 photo, engineers at the Johns Hopkins Applied Physics Laboratory in Laurel, Md., prepare to place Van Allen Probes spacecraft "B" in a thermal-vacuum chamber, wh ere the propulsion system was tested to ensure it would stand up to the range of hot, cold and airless conditions the spacecraft would face in outer space. Beginning in February 2019, the Van Allen Probes will begin a de-orbit maneuver that will lower both spacecraft nearly 161 miles. In approximately 15 years, the new orbits will cause enough atmospheric drag to re-enter the spacecraft and safely burn them up, preventing further space junk from orbiting Earth. Credit: NASA/Johns Hopkins APL/Ed Whitman

The Van Allen Probes – known as spacecraft A and B – were the first spacecraft designed to spend years operating within and studying the radiation belts, a region around our planet that most spacecraft missions avoid due to the damage hazards of the environment. The ionizing radiation in the belts – strong enough to blast electrons off of molecules – can physically harm electronics, cause faults in programming and operations known as single event effects, and disrupt operations.

"Designing the spacecraft and instruments to withstand a very harsh radiation environment was the toughest challenge for Van Allen Probes during design and development," said Rick Fitzgerald of APL, who served as the mission's project manager from 2007 to 2012. "Radiation can cause damage to electronics, leading to erratic behavior or outright failure. We lowered the risk of failure through a rigorous design review process, careful selection of electronics parts, and extensive parts and materials testing."

To protect the spacecrafts' sensitive electronics, the team created two of the toughest spacecraft ever built. "Additional shielding was used around the electronic boxes to prevent localized accumulation of electrical charges and reduce the overall charging dose," said APL's Kristin Fretz, mission system engineer from 2013 to 2018. "All integrated circuits were designed to survive in the belts, and the spacecraft has a fault management and autonomy system, which mitigates the effects of the environment by resetting electronics in response to single event effects."

The design has proven itself up to the challenge. "We have had very few momentary errors or 'upsets' of our electronics on orbit, and no electronics box failures to date," said Fitzgerald. "This is the true validation of all the hard work put into the design and test program prior to launch."

The longevity and resilience of the spacecraft and instruments mean that not only are they still delivering high volumes of data to Earth, they are also teaching spacecraft engineers about operations in the belts. "The Van Allen Probes have essentially become a live test facility for understanding how electronics and materials can survive harsh radiation," Fitzgerald said. "The six and a half years on orbit provides new data to be used in the models that determine how to manufacture, how to select, and how to predict performance of parts and materials on orbit."

Thanks to constant work and iterations by the mission operations team, data download rates for the five instrument suites – the Energetic Particle, Composition, and Thermal Plasma Suite (ECT), the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS), the Electric Field and Waves Suite (EFW), the Relativistic Proton Spectrometer (RPS), and the Radiation Belt Storm Probes Ion Composition Experiment (RBPICE) – soared to three times the required rates during the mission.

Final Maneuvers

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This animation shows the twin Van Allen Probes spacecraft above Earth shortly after their August 30, 2012 launch as the twin spacecraft deploy spin plane booms. Credit: NASA/Johns Hopkins APL/Steve Gribben

The spacecraft continue to operate optimally, and their propellant supplies are plentiful. However, NASA regulations require the controlled de-orbit and removal from orbit of all spacecraft after a period of 25 years from the end of the mission . To meet this requirement, the Van Allen Probes team in 2017 began planning how to lower the spacecraft into orbits that would eventually decay and lead to the re-entry through the atmosphere, safely disintegrating them.

"If we didn't do these maneuvers, the Van Allen Probes would continue orbiting for hundreds or thousands of years, presenting a potential problem to future satellite activities," said APL's Justin Atchison, Van Allen Probes mission designer.

The APL mission operations team has made several orbit changes during the life of the mission, but none this large. To lower the spacecraft, they knew they had to perform the maneuvers at a very specific point in the orbit; that they had to do the operation in stages, rather than one long engine burn; and they knew they had to do it at a certain time of year.

"We need to maneuver when the satellites are at their highest orbit point away from the Earth, or what's known as apogee," said Atchison. "Ideally, we'd do all of the orbit change in a single maneuver on a single day. However, we're limited by the capability of the thrusters, which are typically only used for very small maneuvers to slightly adjust the orbit or the pointing. So we have to divide the maneuver up into smaller segments to achieve the goal."

Each spacecraft will be moved to a lower perigee of about 200 miles through a series of five two-hour engine burns during February 12 to 22 (spacecraft B) and March 11 to 22 (spacecraft A). The engine burns will each use about 4.4 pounds (2 kilograms) of propellant.

"We'll perform the burns at apogee over the course of two weeks," said Madeline Fosbury of APL, current Van Allen Probes mission system engineer. "The challenge of doing all these burns in quick succession is that we don't have as much time to analyze the effect of each burn and then optimize the next one. Because of the rapid cadence, we need to design and perform the first four burns with our best estimates, then tailor the last one to ensure we hit our specific perigee target."

"The Van Allen Probes are spinning spacecraft," explained Atchison. "Their spin axis points at the Sun, so that they have sunlight to power their solar arrays. We have to conduct our maneuvers along this spin axis. In order to lower the perigee, we need to maneuver in a particular direction at a particular time in the orbit. The geometry occurs only occasionally, for a few weeks once or twice per year. This February and March just happen to be the right times for the two satellites."

The team has been rehearsing and practicing the perigee-lowering campaign, and is ready to begin this new stage of the mission's life. "We're all excited to begin, and we're looking forward to unlocking even more science data during this time," said Mosavi. "We'll continue to operate and obtain new science in our new orbit until we are out of fuel, at which point we won't be able to point our solar panels at the Sun to power the spacecraft systems."

"The Van Allen Probes mission has done a tremendous job in characterizing the radiation belts and providing us with the comprehensive information needed to deduce what is going on in them," said NASA's Sibeck. "More than six years of non-stop excitement and discoveries that provide us with the information needed to ensure that spacecraft can survive in the some of the harshest environments known to humanity. In fact, the very survival of these spacecraft and all their instruments, virtually unscathed, after all these years is an accomplishment and a lesson learned on how to design spacecraft."

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The Van Allen Probes Begin Final De-Orbit Maneuvers

JHU Applied Physics Laboratory

Опубликовано: 19 мар. 2019 г.

The twin Van Allen Probes have spent more than six and a half years operating in the most hazardous environment around Earth - the radiation belts. Now, after making new scientific discoveries and providing insights into how to protect spacecraft from space weather, the mission is making its final major orbit maneuver to prepare it for eventual re-entry into the atmosphere.

NASA's Van Allen Probes: Exploring Earth's radiation belts and the extremes of space weather since August 30, 2012.

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Johns Hopkins APL‏Подлинная учетная запись @JHUAPL 2 ч. назад

The Van Allen Probes team are preparing to perform the final maneuver tomorrow, March 22nd, 2019 (4:30pm ET). Join #JHUAPL and @NASASun LIVE during the final burn. https://www.facebook.com/NASASunScience/videos/383710538880201/ ...

20:30 UTC

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Orbiting in the Danger Zone - Behind the Scenes of the Van Allen Probes' Final Maneuver

NASA Video

Опубликовано: 22 мар. 2019 г.

The Van Allen Probes have spent more than six years exploring the harshest environment of near-Earth space: the radiation belts. This is an intense region of charged particles trapped in Earth's magnetic field that can interfere with satellite electronics and could even pose a threat to astronauts who pass through them on interplanetary journeys. On March 22, the mission team performs the final adjustment to the orbits of the twin spacecraft to ensure that they will eventually de-orbit and disintegrate in Earth's atmosphere. Join us to get a live look inside mission control at the Johns Hopkins Applied Physics Laboratory as the Van Allen Probes perform the final orbital maneuver of their mission. Hear from NASA and APL experts about the mission, what we've learned and what we hope to discover during the Van Allen Probes' final phase of exploration.

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https://www.nasa.gov/feature/goddard/2019/ten-highlights-from-nasa-s-van-allen-probes-mission

Oct. 17, 2019

Ten Highlights Fr om NASA's Van Allen Probes Mission

After seven years of operations, and upon finally running out of propellant, the second of the twin Van Allen Probes spacecraft will be retired on Friday, Oct. 18, 2019. Spacecraft A of the Van Allen Probes mission will be shut down by operators at the Johns Hopkins University Applied Physics Lab in Laurel, Maryland. The command follows one three months previously that terminated operations for spacecraft B, the second spacecraft of the mission.

"This mission spent seven years in the radiation belts, and broke all the records for a spacecraft to tolerate and operate in that hazardous region, all with no interruptions," said Nelofar Mosavi, Van Allen Probes project manager at Johns Hopkins APL. "This mission was about resiliency against the harshest space environment."

Originally slated for a two-year mission, the spacecraft flew through the Van Allen belts — rings of charged particles trapped by Earth's magnetic field — to understand how particles were gained and lost by the belts. The spacecraft made major discoveries that revolutionized how we understand our near-Earth environment.

https://www.youtube.com/embed/CKUNT2Qshk4
The Van Allen Probes flew through Earth's geomagnetic field and radiation belts.
Credits: NASA's Goddard Space Flight Center
Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

"Van Allen Probe observations have been the subject of over 600 publications to date in refereed journals, and over 55 Ph.D. theses have used Van Allen Probe observations," said David Sibeck, Van Allen Probes mission scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

With instruments measuring electromagnetic fields and charged particles, the Van Allen Probes explored the invisible phenomena shepherding particles in and around the belts. It made discoveries about the architecture of the belts and the forces shaping them. Just as ocean storms on Earth can create giant waves, space weather, caused by the Sun, can create plasma waves, wh ere seas of particles are tossed by electromagnetic fields. The Van Allen Probes pioneered new explorations into the dynamics of these waves and their effects on our near-Earth environment.

"The Van Allen Probes rewrote the textbook on radiation belt physics," said Sasha Ukhorskiy, Van Allen Probes project scientist at Johns Hopkins APL, which also designed and built the spacecraft. "The spacecraft used uniquely capable instruments to unveil radiation belt features that were all but invisible to previous sensors, and discovered many new physical mechanisms of radiation belt acceleration and loss."

In celebration of the mission's success, here are ten sel ect discoveries, listed in chronological order, made by the Van Allen Probes.

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• The Van Allen belts were first discovered in 1958 and for decades scientists thought there were only two concentric belts. But days after the Van Allen Probes launched, scientists discovered that during times of intense solar activity, a third belt can form.
  

Van Allen Probes image showing three radiation belts first seen around Earth in 2012.
Credits: NASA's Goddard Space Flight Center/Johns Hopkins University, Applied Physics Laboratory

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• The belts, which are composed of charged particles and electromagnetic fields, can be energized by different types of plasma waves. One type, called electrostatic double layers, appear as short blips of enhanced electric field. During one observing period, Probe B saw 7,000 such blips repeatedly pass over the spacecraft in a single minute. These individually small events added up to one million volts over six minutes, capable of accelerating electrons up toward the relativistic energies commonly seen in radiation belt particles.
  

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• During big space weather storms, which are ultimately caused by activity on the Sun, ions — electrically charged atoms or molecules — can be pushed deep into Earth's magnetosphere in a series of impulsive events. These particles carry electromagnetic currents that circle around the planet and can dramatically distort Earth's magnetic field.
  

https://www.youtube.com/embed/CKlho5eXuLQ
On March 17, 2015, Van Allen Probe A detected a pulse of high energy electrons in the radiation belts, generated by the impact of a recent coronal mass ejection striking Earth's magnetosphere. The gradient drift speed of the electron pulse was high enough, that it propagated completely around Earth and was detected by the spacecraft again as the pulse spread out in the radiation belt. Because the particles have a range of energies, the pulse spread out as it moved around Earth, generating a weaker signal the next time it hit the spacecraft.
Credits: NASA's Goddard Space Flight Center
Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

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• Across space, fluctuating electric and magnetic fields can create what are known as plasma waves. These waves intensify during space weather storms and can accelerate particles to relativistic speeds. The Van Allen Probes found that one type of plasma wave known as hiss can contribute greatly to the loss of electrons from the belts.
  

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• The Van Allen belts are composed of electrons and ions with a range of energies. In 2015, research from the Van Allen Probes found that, unlike the outer belt, there were no electrons with energies greater than a million electron volts in the inner belt.
  

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• Plasma waves known as whistler chorus waves are also common in our near-Earth environment. These waves can travel parallel or at an angle to the local magnetic field. The Van Allen Probes demonstrated the two types of waves cannot be present simultaneously, resulting in greater radiation belt particle scattering in certain areas.
  

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• Very low frequency chorus waves, another variety of plasma waves, can pump up the energy of electrons to millions of electron volts. During storm conditions, the Van Allen Probes found these waves can hugely increase the energy of particles in the belts in just a few hours. 
  

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• Scientists often use computer simulation models to understand the physics behind certain phenomena. A model simulating particles in the Van Allen belts helped scientists understand how particles can be lost, replenished and trapped by the Earth's magnetic field.
  

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• The Van Allen Probes observed several cases of extremely energetic ions speeding toward Earth. Research found that these ions' acceleration was connected to their electric charge and not to their mass.
  

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• The Sun emits faster and slower gusts of charged particles called the solar wind. Since the Sun rotates, these gusts — the fast wind — reach Earth periodically. Changes in these gusts cause the extent of region of cold ionized gas around Earth — the plasmasphere — to shrink. Data fr om the Van Allen Probes showed that such changes in the plasmasphere fluctuated at the same rate as the solar rotation ­— every 27 days.
  

By Mara Johnson-Groh
NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: Oct. 17, 2019
Editor: Rob Garner

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The Van Allen Probes: Seven Years of Science in Space

 JHU Applied Physics Laboratory

18 окт. 2019 г.

Originally slated for a two-year mission, the second of the twin Van Allen Probes spacecraft will be retired just prior to running out of propellant, more than seven years after launch.

On October 18, 2019, at about 12:30 p.m. EDT, spacecraft A of the Van Allen Probes mission will be shut down by operators at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. The command — the 4,781st sent to spacecraft A — is of the same type sent four months previously that terminated operations for spacecraft B, the second spacecraft of the mission.

In February, the spacecraft were placed in a lower orbit that will eventually decay, letting the twin Van Allen Probes reenter and burn up in Earth's atmosphere.

These two spacecraft — designed, built and operated for NASA by Johns Hopkins APL — flew through the rings of charged particles trapped by Earth's magnetic field known as the Van Allen belts to understand how particles were gained and lost by the belts. The spacecraft made major discoveries that revolutionized how we understand our near-Earth environment.

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https://www.youtube.com/embed/sbcs755JCOY (2:02)