ExoMars 2016 -- Протон-М/Бриз-М -- Байконур -- 14.03.2016, 12:31 ДМВ

Автор Space Alien, 18.06.2015 10:07:45

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Цитироватьzandr пишет:
если Вы сумеете доказать
Это ничего не изменит, орбиты все равно будут эволюционировать не так как Вы себе придумали
Не надо греть кислород!
Я не против многоразовых ракет, я за одноразовые!

PIN

Я совсем не баллистик, но многое имею возможность наблюдать. И, так понимаю, стратегию снижения выбирали (DEIMOS отвечал за анализ вариантов и выбор подхода) давно и аккуратно, с учетом всех ограничений по операциям, о которых широкая публика обычно и не задумывается.
Одна из поздних статей http://issfd.org/ISSFD_2012/ISSFD23_GC_3.pdf
В деталях, скорее всего, устарела - финальные решения по результатам моделирования на ATB были приняты на этой неделе.

zandr

#2222
SOE, Спасибо!  :D  
Всё они предусмотрели и запланировали, а не так, как написано на сайте Роскосмоса!
ЦитироватьThe last phase of the aerobraking includes several pericenter raising maneuvers. They will gradually decrease the aerobraking effect until the final target apocenter is reached. This phase is characterized by a large numbers of aerobraking passes and each of them with a high duration. To ensure the safety of the spacecraft, short turn-around time for operations is considered, with an optimization of one maneuver each time.
И перицентр будут поднимать постепенно, как я предположил, учитывая увеличение эффективности аэродинамического торможения и не допуская перегрева аппарата во время прохождения через атмосферу (до этого - не додумал). И корректировать, по необходимости, процесс снижения каждые два дня, с учётом возможности срыва очередной коррекции - всё под контролем!
ЦитироватьThe main phase is based by several maneuvers, performed on the apocenter, which control the pericenter high. From the ESOC requirements, each maneuver shall assure:
   Not to violate any aerodynamic constraint until the next maneuver + 48h.
   Not to decrease the apocenter height below 350 km until the next maneuver + 48h.
 Due to the survivability requirement, the worst case to be analyzed is when the spacecraft enters in safe mode at the moment to perform a pericenter control maneuver (PCM) and no autonomous pericenter raising maneuver is performed. Then, the previous maneuver has to assure 48h without violating any aerodynamic constraint and also assure the apocenter height remains above 350 km.
 Two strategies are analyzed:
   One PCM at approximately every 2 days.
   One PCM at approximately every day.
 One simulation including maneuvers every 2 days without considering the safety policy of a potential failure of maneuvers is performed. This is done only to show the effect of the survivability requirement, but it is not considered a valid operational approach.
Графики снижения апоцентра

и изменения перицентра!

(даты условные - рассчитывали прилететь раньше)

tnt22

Вроде только недавно - и на тебе - Целый год в космосе! С днюхой, ExoMars 2016!
Цитировать ESA‏Подлинная учетная запись @esa 42 мин. назад
 
A new image of #Mars to mark @ESA_TGO's first year in space - @esascience #IOTW #ExoMars http://www.esa.int/spaceinimages/Images/2017/03/Noctis_Labyrinthus_stereo_pair ...
 

tnt22


tnt22

Цитировать @ESA_ExoMars‏Подлинная учетная запись @ESA_ExoMars 47 мин назад
 
Wrap-up of latest @ESA_TGO science instrument tests, plus we're go for aerobraking! http://ow.ly/FFWH309XCnA
 
 
http://www.esa.int/Our_Activities/Space_Science/ExoMars/ExoMars_science_checkout_completed_and_aerobraking_begins
ЦитироватьExoMars: science checkout completed and aerobraking begins
 
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Flying over Mellish crater
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16 March 2017
 The ExoMars Trace Gas Orbiter has completed another set of important science calibration tests before a year of aerobraking gets underway.
 
The mission was launched a year ago this week, and has been orbiting the Red Planet since 19 October. During two dedicated orbits in late November, the science instruments made their first calibration measurements since arriving at Mars.
 
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The latest tests were carried out 5–7 March fr om a different orbit, and included checking procedures associated with taking images and collecting data on the planet's atmosphere.

For example, the Nadir and Occultation for Mars Discovery (NOMAD) instrument made test observations to help determine the best settings to make future measurements of trace gases in the atmosphere.

 Methane in particular is of high interest. On Earth it is produced primarily by biological activity, and to a smaller extent by geological processes, such as some hydrothermal reactions. Understanding how the Red Planet's methane is produced therefore has extremely exciting implications.
 
NOMAD also had the opportunity to test joint measurements with the Atmospheric Chemistry Suite, which together will take highly sensitive measurements of the atmosphere to determine its constituents.
 
 
Water vapour
 
 Meanwhile, the FREND detector continued to collect more on the flow of neutrons from the surface. Eventually, these data will be used to identify sites wh ere water or ice might be hidden just below the surface.

 The high-resolution Colour and Stereo Surface Imaging System was commanded to take a number of images, including star calibrations, and several pointing at Mars.
 
An example is presented here, taken just as the orbiter was crossing the boundary between day and night, over the southern hemisphere.
 
"These dress rehearsals enable our science teams to fine-tune their data acquisition techniques including pointing commands, iron out any software bugs, and get used to working with the data, well in advance of the start of the main mission starting next year," says Håkan Svedhem, ESA's project scientist. "What we're seeing so far is really promising for our science goals."
 
 
Carbon dioxide
 
 Starting next year, the craft will make its observations from a near-circular 400 km-altitude orbit, circling the planet every two hours.
 
It is currently in a one-day, 200 x 33 000 km orbit but will use the atmosphere to adjust the orbit gradually by 'aerobraking'. It will repeatedly surf in and out of the atmosphere at closest approach, pulling down its furthest point over the course of the year.
 
 Earlier this week, the first commands for aerobraking were uploaded, ready to be executed starting yesterday. Over the next few weeks it will make seven engine burns that will adjust its orbit as part of a 'walk-in' period before the main aerobraking. This will first see the closest point of the orbit reduced to about 113 km.
 
 
Neutron detections
 
 "It's not ESA's first experience with aerobraking, but it is the first time we've used this technique to achieve a planned science orbit, repeating it for such a long duration," says flight director Michel Denis.
 
"The mission controllers have worked intensively with our flight dynamics experts to prepare for this challenging phase – we're go for aerobraking.
 
"We'll closely monitor the solar array temperature and the acceleration of the spacecraft, not only during the first few passages through the atmosphere but throughout the rest of 2017, and adjust the trajectory as needed."
 
The final orbit is also designed for relay and communications with rovers and landers on the surface. In particular it will act as a relay for the 2020 ExoMars mission of a stationary surface platform and a rover.
 
ExoMars is a joint endeavour between ESA and Roscosmos.
 
 For further information, please contact:
 Håkan Svedhem
 ESA ExoMars TGO Project Scientist
Email: hakan.svedhem@esa.int
 Markus Bauer








 ESA Science and Robotic Exploration Communication Officer









 Tel: +31 71 565 6799









 Mob: +31 61 594 3 954









Email: markus.bauer@esa.int
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tnt22


tnt22

Цитировать РОСКОСМОС‏Подлинная учетная запись @roscosmos 9 мин. назад

#ExoMars2016: начались операции по выходу аппарата на круговую орбиту https://www.roscosmos.ru/23326/ 
 
https://www.roscosmos.ru/23326/
ЦитироватьЭКЗОМАРС. НАЧАЛИСЬ ОПЕРАЦИИ ПО ВЫХОДУ АППАРАТА НА КРУГОВУЮ ОРБИТУ
16.03.2017 13:14

 
15 марта 2017 года, через один год и один день после запуска миссии «ЭкзоМарс-2016», начались операции по торможению аппарата с помощью атмосферы. Сейчас орбитальный модуль Trace Gas Orbiter (TGO) находится на высокоэллиптической орбите с апоцентром 33 000 км и перицентром 200 км.
    
В течение следующих недель с помощью двигателей космического аппарата начнутся маневры по ещё большему снижению перицентра (до 113 км над поверхностью). Затем начнётся основная фаза торможения, которая продлится почти год. В итоге аппарат должен выйти на рабочую круговую орбиту высотой около 400 км.
    
В соответствии с программой операций по выходу на рабочую круговую атмосферного торможения во время прохождения перицентра - ближайшей к поверхности точке орбиты – TGO будет «задевать» верхние слои атмосферы и таким образом понемногу снижать скорость и, как следствие, апоцентр орбиты.
    
Проект «ЭкзоМарс» — совместный проект РОСКОСМОСА и Европейского космического агентства по исследованию Марса, его поверхности, атмосферы и климата с орбиты и на поверхности планеты. Он откроет новый этап исследования космоса для Европы и России.

zandr

https://www.roscosmos.ru/23327/
ЦитироватьЭКЗОМАРС. ПОДВЕДЕНЫ ИТОГИ РАБОТЫ НАУЧНЫХ ПРИБОРОВ НА БОРТУ TGO
Завершена вторая тестовая кампания по включению научных приборов на борту аппарата Trace Gas Orbiter миссии «ЭкзоМарс-2016». Четыре научных прибора, в их числе — два российских, провели тестовые измерения и калибровки во время нахождения на однодневной высокоэллиптической орбите вокруг планеты. 15 марта начался этап торможения с помощью атмосферы (так называемый «аэробрейкинг»), в результате которого TGO будет выведен на рабочую круговую орбиту с высотой около 400 км над поверхностью.
    
Вторая тестовая кампания по калибровке научных приборов на однодневной эллиптической орбите (сокращение MCO-2 от Mars Capture Orbit) прошла 28 февраля и 1 марта, а также 5–7 марта.
    
В состав научной аппаратуры на борту аппарата Trace Gas Orbiter (TGO) входят четыре прибора, из них два представляют российский вклад в проект и были созданы в Институте космических исследований РАН.
    
Российский нейтронный детектор ФРЕНД был включен раньше: в период с 24 февраля по 2 марта и 5–7 марта. В общей сложности удалось получить данные во время восьми прохождений района перицентра.
    
Они дополняют информацию, полученную при прохождении перицентров во время первой тестовой кампании по калибровке научных приборов (MCO-1) в ноябре 2016 года. В совокупности они представляют калибровочные данные, по которым можно оценить собственный фон аппарата и уровень нейтронного сигнала от Марса. ФРЕНД отработал штатно, и для сохранности устройства на время аэродинамического торможения включения не предусматриваются. Таким образом, полноценные измерения начнутся только в следующем году.
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Временной профиль отсчетов нейтронов, полученных прибором ФРЕНД во время второй тестовой кампании по включению научных приборов миссии «ЭкзоМарс-2016». Цветом обозначены данные, полученные тремя различными счетчиками в составе прибора (с) РОСКОСМОС/ESA/ЭкзоМарс/ФРЕНД/ИКИ
 
В рамках проверочных включений 28 февраля - 7 марта 2017 прибор ТИРВИМ в составе спектрометрического комплекса АЦС успешно отработал всю намеченную программу. Она включала в себя наблюдения лимба Марса на подлёте к перицентру, несколько специальных режимов работы в перицентральной части орбиты, а также измерения рассогласования осей спектрометров по наблюдениям Солнца.
    
Один из ста тысяч спектров Марса, полученных прибором ТИРВИМ в составе спектрометрического комплекса АЦС. Слева: в единицах спектральной яркости; справа — то же самое в пересчёте на яркостную температуру. По горизонтальной оси — волновое число. Углекислый газ, основной компонент марсианской атмосферы, даёт глубокую и широкую спектральную полосу с центром на 667 см-1. В центре этой полосы мы «видим» верхние слои атмосферы (и измеряем их температуру), в её крыльях — нижние слои. Таким образом вычисляется температурный профиль атмосферы, необходимый для расчёта моделей глобальной циркуляции атмосферы Марса (с) РОСКОСМОС/ESA/ЭкзоМарс/АЦС/ИКИ
 
В ходе тестовых включений были также получены изображения Марса с помощью камер комплекса CaSSIS и спектры атмосферы планеты спектрометра NOMAD.
    Во время кампании MCO-2 наземный научный комплекс (ННК) проекта «ЭкзоМарс» работал в штатном режиме. В течение сеансов связи с орбитальным модулем TGO в Институт космических исследований поступали данные, принимаемые на наземных станциях ESA системы ESTRACK в Маларгуэ (Аргентина) и Нью-Норсиа (Австралия). Сеансы связи длительность около 8 часов проводились до двух раз в сутки, при этом информация, принимаемая на станциях, поступала в ННК через Европейский центр космической астрономии ESAC (Мадрид, Испания) и Европейский Центр управления полётом ESOC (Дармштадт, Германия).
    
Поступающая в ННК информация обрабатывалась для выделения значений ключевых параметров, обеспечивающих контроль функционирования бортовой научной аппаратуры. Одновременно с этим научные и технологические данные становились доступны разработчикам научных приборов для дальнейшей обработки.
Графики температур, токов потребления и других параметров работы российских приборов во время MCO-2 (с) РОСКОСМОС/ESA/ЭкзоМарс
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ZOOR

ЦитироватьКалибровка научного оборудования аппарата миссии «Экзомарс» завершена

Орбитальный марсианский аппарат Trace Gas Orbiter миссии «ЭкзоМарс» завершил ещё одну важную серию мероприятий по настройке научного оборудования, предшествующую этапу аэродинамического торможения аппарата, который согласно плану миссии будет продолжаться в течение примерно одного года.

Эта миссия была отправлена к Красной планете примерно один год назад, и прибыла к орбите вокруг планеты 19 октября. Первая калибровка научных инструментов миссии была проведена в конце ноября в течение двух специально выделенных для этой цели недель в конце ноября.

Теперь эти новые тесты оборудования были проведены 5-7 марта, когда аппарат находился уже совсем на другой орбите, и включали процедуры контроля, связанные с получением изображений и сбором научных данных об атмосфере планеты.



Например, инструмент Nadir and Occultation for Mars Discovery (NOMAD) провел пробные наблюдения (на фото), в ходе которых были установлены наилучшие настройки для будущих измерений следовых количеств газов в атмосфере планеты.

Начиная со следующего года, космический аппарат будет проводить наблюдения с орбиты высотой 400 километров, по форме близкой к круговой и с периодом примерно 2 часа.
Я зуб даю за то что в первом пуске Ангары с Восточного полетит ГВМ Пингвина. © Старый
Если болит сердце за народные деньги - можно пойти в депутаты. © Neru - Старому

Salo

#2230
О TGO в середине ролика:
https://youtu.be/yAAyAqwx5YM
https://youtu.be/yAAyAqwx5YM
"Были когда-то и мы рысаками!!!"


tnt22

#2232
Цитировать ESA Operations‏Подлинная учетная запись @esaoperations 2 ч. назад

#Hang10 #FeelTheBurn News from @ESA_TGO mission control: 1st of 7 lowering manoeuvres A-OK. Next is tmrrow #ExoMars http://blogs.esa.int/rocketscience/2017/03/17/tgo_feels_the_burn/ ...
 
http://blogs.esa.int/rocketscience/2017/03/17/tgo_feels_the_burn/
Цитировать
Posted on 17 March 2017 by Daniel
TGO feels the burn

 Mars atmosphere grabs our spacecraft
 
Got an update on TGO aerobraking progress at mid-day today from Silvia Sangiorgi, our deputy spacecraft operations manager here at ESOC. She wrote:
 

ExoMars/TGO Deputy Spacecraft Operations Manager Silvia Sangiorgi seen in the Main Control Room at ESOC during launch in March 2016. Credit: ESA/J. Mai

 PLM 1 [on 15 March] was nominal. [Since then] we have already had two percienter (= periapsis – point of closest approach above Mars) passes at 150 km height; they gave us, respectively, 11 and 10 mm/sec of delta V.  All is nominal and working fine for the moment  :)    PLM 2 will be tomorrow at 11:45 UTC (12:45 CET); it will bring us a further 10 km down. Flight dynamics are producing the commands now – these will be uplinked tonight. Ciao, Silvia

Tomorrow's burn is planned to provide a delta-v (change in velocity) of 58 cm/sec and targets a pericenter hight of 140 km.

If the team are already seeing 'changes in velocity' due to the atmosphere on the order of 10 to 11 mm/second, then TGO is already 'feeling the burn'.

PLM refers to 'pericentre lowering manoeuvre' – how the engineers on the TGO team refer to the seven (planned) thruster burns that are slowing TGO, allowing it to sink, step-wise, lower in its orbit until atmospheric drag reaches a certain load. Then we'll be in aerobraking proper!

The seven manoeuvres are planned for:
 
    [/li]
  • March: 15, 18, 21, 24 and 27
  • April: 1 and 6
Read yesterday's blog post Hang 10 over Mars for full background.
 
Note that pericentre and periapsis, and apocentre and apoapsis are, when referring to Mars, often used interchangeably.

ZOOR

Цитироватьtnt22 пишет:
ЦитироватьESA Operations ‏Подлинная учетная запись @ esaoperations 6 ч. назад

Channel your inner flight engineer! Evolution of @ ESA_TGO apoapsis altitude during # aerobraking # hang10 # mars http://blogs.esa.int/rocketscience/2017/03/16/hanging-10-over-mars/ ...
 
А зачем "полочка" летом 2017?
Я зуб даю за то что в первом пуске Ангары с Восточного полетит ГВМ Пингвина. © Старый
Если болит сердце за народные деньги - можно пойти в депутаты. © Neru - Старому

tnt22

ЦитироватьZOOR пишет:
А зачем "полочка" летом 2017?
Видимо, зря я не стал здесь приводить статью ESA "Hang 10 over Mars"
Цитировать...
Break in aerobraking

The aerobraking phase will have to be interrupted for about two months due to the solar conjunction when Mars is behind the Sun as seen from Earthradio 'noise' from the Sun will interfere with the radio-frequency signal between TGO and Earth [conjunction season is also known as 'low-bit-rate season' - Ed.].

A key element in this pause is that the TGO periapsis will be deliberately raised (by a manoeuvre) so that it stays above the atmosphere for these two months – so the spacecraft is safe even if not controlled as tightly as atmospheric passes require.

"From the end of August, aerobraking will be started again by repeating the step-wise descent into the atmosphere that we are just doing now," says Flight Director Michel Denis.
...
Коротко, соединение Земли, Марса и Солнца (когда Марс для Земли за Солнцем) вызывает существенные радиопомехи в канале связи Земля-TGO => временный перекур на два месяца, пока Марс не выйдет из-за Солнца снова в августе.

tnt22

http://blogs.esa.int/rocketscience/2017/03/16/hanging-10-over-mars/
ЦитироватьHang 10 over Mars

 TGO begins the 'walk-in' phase for aerobraking


Hanging Ten is a surfing maneuver. It means to perform a stunt on a longboard in which a surfer moves to the front of the board and rides with ten toes extended out over the nose, after positioning the board so the back of it is covered and held in place by a wave. #hang10 #aeb #aerobraking
 
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Scene fr om 2010 All-Girl Cayucos Pier Classic Surf Contest, 20 March 2010, Cayucos, CA. Credit: Mike Baird CC BY 2.0
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Following months of extremely hard work by the mission control team at ESOC, the science team at ESAC, the ExoMars project team at ESTEC and industry, the Big Day has finally arrived!

At 11:56 UTC (12:56 CET) yesterday, the ExoMars Trace Gas orbiter (TGO) executed the first of a series of seven thruster burns that will lower its orbit, step-wise, until it starts 'feeling' the wispy faint drag (see Notes below) due to the atmosphere of Mars.

The burns are taking place between 15 March and 6 April. Yesterday's was the biggest, delivering a planned 'delta-v' (change in velocity) of about 3 m/sec.

The effect of the first manoeuvre will be to take the periapsis – the point of closet approach above the surface – altitude down to about 150 km above the surface; the rest of the burns will be smaller.

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Walking in fr om up above

"The first manoeuvre can be likened to 'testing the water'," says Michael Khan from the Mission Analysis team at ESOC.

"The resulting atmospheric passes, one per day, go in deep enough to let the spacecraft experience some real air drag, so the mission team can see how the spacecraft stands up to actual aerobraking conditions."

"However, at a minimum altitude of 150 km, the heating and forces will not be strong enough to cause any risk of damage even if the spacecraft does not behave as planned."

If the first three days go as expected, there will be another manoeuvre to lower the periapsis altitude to 140 km, on 18 March.
 

Illustration of the highly elliptical orbit at start of aerobraking. Periapsis is the red arrow at left; apoapsis is the TGO spacecraft at right. The aim is to make this round, at about 400 km altitude. Credit: ESA

 That will significantly up the ante, exposing the spacecraft to notably higher aerodynamic loads. If that, too, goes well, three days later the periapsis will be again lowered by 10 km. After that, the lowering will happen in smaller increments.

The currently foreseen periapsis altitude at the end of the walk-in phase on 6 April, i.e., when aerobraking will be in full swing, is 113 km, but this may well change subject to what TGO experiences during the walk-in.

Aerobraking begins

So, as of 6 April, the craft will begin the critical, year-long 'aerobraking' phase proper, using the faint drag of the very upper reaches of the Martian atmosphere to slow the craft, lowering its orbit.
 

Venus Express aerobraking in 2014 Credit: ESA

 In the aerobraking technique, the ever-so-faint drag the craft experiences at periapsis slows it such that the height of its apoapsis – the point one-half orbit later when it makes its highest passage over the surface – is steadily reduced.

If all goes well, by early 2018, the orbit will have been transformed from its current highly elliptical shape, at 33 000 km x 200 km with one revolution per 24 hours, to a circular orbit at about 400 km x 400 km with one revolution in about two hours.

This will be the routine orbit for the main science phase, and is optimised both for science data-gathering and to enable TGO to serve as a radio relay platform, transmitting signals from surface assets like rovers to Earth.

"It's a great technique for saving fuel, which means our spacecraft could be designed, built and launched without needing to lug along hundreds of kilogrammes of extra fuel [we saved about 600 kg – Ed.] to conduct the long engine burns that would otherwise be necessary," says Spacecraft Operations Manager Peter Schmitz.

Double, double toil and (not) trouble

But aerobraking means that, for most of a year, the mission control teams at ESOC in Darmstadt, Germany, will have to work very intensively, monitoring and assessing the spacecraft's progress very closely and making tiny adjustments to the orbit by firing the thrusters if needed.
 

Spacecraft Operations Manager Peter Schmitz seen sitting in the Main Control Room at ESOC, at left, in discussion with ESA's Head of Mission Operations, Paolo Ferri, just after ExoMars/TGO launch in March 2016. Deputy Operations Manager Silvia Sangiorgi sits on console at right. Credit: ESA/P. Shlyaev.

 "If the drag is too gentle, we need to get lower; if the drag is too high, we need to get higher," says Peter.

And there won't be much time available to react in case anything unexpected happens.

"Aerobraking will be especially demanding for our flight dynamics experts, who must conduct regular and frequent orbit determinations so that we know exactly wh ere the spacecraft is, which is necessary for things like planning ground station communication passes," says Peter.

The unpredictability of the aerobraking effect during each orbit – and the resulting uncertainty in attitude and orientation – will also affect the star trackers, which might be temporarily be blinded if they are pointed at any part of the Mars limb during or after an aerobraking pass.

"It's hard to overstate the demanding amount of planning, careful assessment and regular, time-limited command cycles that will be required during aerobraking," says Peter.

Gone surf'in

One of the big factors the team will have to accommodate is the unpredictability of the Martian atmosphere.

The Mars atmosphere, comprising mainly carbon dioxide, is very thin in comparison to Earth, and its density is highly changeable.
 

TGO - typical aerobraking orbit. The drag pass happens at periapsis, at left. Credit: ESA

Close to the surface, its temperature and density are affected by variables such as the weather, dust storms, sunlight and hard-to-predict (in real-time) effects such as solar heating of the surface (causing convection currents).

At the very upper altitudes, around 113 km wh ere TGO will begin aerobraking orbits, it is extremely thin, with a density on the order of just 10^-7 Kg/m3, and solar activity and dust storms can have a big effect on density.

The net result is that the amount of slowing due to atmospheric drag during each aerobraking passage (the segment of the orbit around periapsis) can vary unpredictably, and teams will have to watch carefully to asses actual braking results.

Heat and pressure

Further, the spacecraft is designed to handle certain maximum levels of heat and dynamic pressure, and teams will have to watch carefully to see that these are not exceeded.

For example, the temperature due to frictional drag on the specially designed solar arrays should not exceed 145 C.

"With current plans, we only expect to see around 70 C on the arrays, and a few degrees more would be no problem," says Spacecraft Operations Engineer Chris White.

"If the temperature goes above 145 C, or if any one of several other 'trigger' conditions are encountered, the spacecraft is programmed to autonomously conduct a 'pop-up manoeuvre,' firing its engine at the next apoapsis passage so that it raises the periapsis height back up, so as to reduce the temperature and pressure due to drag."
 

TGO aerobraking attitude, seen in elevation/profile. Direction of flight is from right to left. Credit: ESA

 This is also why the spacecraft is being lowered step-wise through the seven thruster burns during the 'walk-in' phase taking place now, so that aerobraking only begins when the craft starts to experience a certain target atmospheric density, and not more or less.

"The atmospheric models aren't perfect, so we have to 'feel' our way down to the start of aerobraking proper," says Chris.

Note that when going through each aerobraking pass at periapsis, TGO will be out of contact with ground stations due to the spacecraft's special attitude (pointing engine-first in the direction of flight, tilted slightly 'up' – see diagram at right), which means the high-gain antenna will be off-pointed away from Earth.

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TGO is a tough cookie

Engineers have spent months planning for aerobraking, which will use atmospheric drag to lower the spacecraft into its final ca. 400 x 400 km routine science orbit. When it comes to the heat and pressure of aerobraking, here are some of the physical limitations of the spacecraft – which are being applied with a 150% safety margin!

•   Peak heat flux: 1120 W/m2 (but TGO can take 2.5x that without degradation)
 •    Heat load per pass: 100 kJ/m2 (but TGO can take 2.5x that without degradation)
 •    Peak dynamic pressure: 0.175 N/m2 – but simulations say we'll hit one of the thermal limits first
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Break in aerobraking

The aerobraking phase will have to be interrupted for about two months due to the solar conjunction when Mars is behind the Sun as seen from Earth – radio 'noise' from the Sun will interfere with the radio-frequency signal between TGO and Earth [conjunction season is also known as 'low-bit-rate season' - Ed.].

A key element in this pause is that the TGO periapsis will be deliberately raised (by a manoeuvre) so that it stays above the atmosphere for these two months – so the spacecraft is safe even if not controlled as tightly as atmospheric passes require.

"From the end of August, aerobraking will be started again by repeating the step-wise descent into the atmosphere that we are just doing now," says Flight Director Michel Denis.
 

TGO aerobraking apoapsis altitude evolution. Flat plateau indicates the pause in aerobraking due to conjunction season. Credit: ESA

 During these weeks, even with not too much happening with the spacecraft itself, the mission control team will be extremely busy with reviews, assessing results, bench testing, software validation and preparation for the next, final phase of aerobraking and much else. 

"During this intense activity, the team will also take advantage of conjunction period to book some leave," says Peter Schmitz.

Once Earth and Mars continue in their orbits so that Mars has moved more than ~10° away from the Sun as seen from the ground, normal communication passes can restart and aerobraking can recommence.
 

TGO aerobraking periapsis altitude evolution (altitude with respect to Mars sphere, R=3397 km). Flat, raised plateau indicates the pause in aerobraking due to conjunction season. Credit: ESA

 End of the beginning

If all goes well, by early 2018, TGO will be pretty close to a ca. 120 x 400 km orbit, and, in principle, will need only a short boost or two to circularise the orbit to 400 x 400 km.

But ending aerobraking won't be quite that simple for the operations team.

One big factor will be that, by this time, the orbital period will be down to just two or so hours. This is a factor because the craft has to slew using its reaction wheels into a specific attitude for each aerobraking passage, then slew back into an Earth-pointing attitude to conduct the subsequent communication pass.

"Our reaction wheels, while reliable, are somewhat small, and TGO is somewhat massive, so slewing is slow, and we may find that there is insufficient time margin to conduct the required slews during each orbit when each orbit only lasts two hours," says Peter.

"One solution may lie in the fact that the high-gain antenna is steerable, so we're looking at options that take advantage of this. The precise operations strategy for this phase is still being worked out, but we'll be ready."

Challenging interplanetary techniques

While this is the first time we've used aerobraking to achieve an operational orbit around another planet, this is not the first experience with the technique for teams at ESA.

A few years back, in 2014, Venus Express conducted a lengthy aerobraking campaign at the end of its mission, using the technique to lower itself steadily into the Venusian atmosphere to gather valuable science data from previously unexplored altitudes.

NASA have also used aerobraking at Mars – to bring the Mars Reconnaissance Orbiter and other spacecraft into low orbit at Mars.

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Notes:
    [/li]
  • In fact, the spacecraft is already feeling the 'wispy fainties' now, with its periapsis still firmly outside the real atmosphere at 200 km. ESA teams 'see' the drag effects in spacecraft Doppler data – detected by analysing the communication signals transmitted by TGO – and they see it in unplanned attitude changes.
  • Many thanks to Peter Schmitz, Michael Khan and Chris White for their inputs and review of this post.
  • Here is a great animation showing the development of TGO's orbit throughout the aerobraking campaign:
https://www.youtube.com/watch?v=oOcrznm629Q
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ОАЯ

#2236
Описан триллер по выживанию. Здесь и температура от разогрева об атмосферу, цейтнот компьютеров и маленькие колеса, что бы развернуть массивный аппарат и отсутствие перерывов на обед по КЗОТу...

145 градусов , это предел для СБ. В полете достигли 70 градусов. Остались 145-70=жалких 75 градусов на разогрев 2 киллограмов песка и алюминия за минут пять (если учитывать, что 120 минут полный оборот по орбите.).  Вот интересно ПО «Союза» сотню раз опускались в атмосферу Земли. Какой реальный график нарастания температуры у СБ ПО «Союз». И что наступает раньше – механическое разрушение от набегающего потока или температурный шок? По времени «Союз» находится в атмосфере дольше, чем вышеописанный агрегат в марсианской атмосфере.

tnt22

https://spaceflightnow.com/2017/03/20/europes-exomars-craft-begins-lowering-its-orbit/
ЦитироватьEurope's ExoMars spacecraft begins lowering its orbit
 March 20, 2017 Stephen Clark

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Artist's concept of the ExoMars Trace Gas Orbiter. Credit: ESA/ATG medialab
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The ExoMars Trace Gas Orbiter, a Russian-launched, European-built spacecraft that arrived at Mars in October, is starting to dip into the upper reaches of the red planet's atmosphere in a year-long "aerobraking" campaign place the observatory in the right position to hunt for methane, an indicator of potential biological activity.

The effort to reshape the craft's course around Mars uses aerodynamic drag from repeated dips into the upper atmosphere to gradually drag down the high point of the probe's orbit from its current altitude of 20,500 miles (33,000 kilometers) to a planned perch 250 miles (400 kilometers) above the Martian surface.

Ground controllers at the European Space Operations Center in Darmstadt, Germany, are overseeing a series of seven thruster burns to nudge the low point of the spacecraft's orbit from an altitude of 120 miles (200 kilometers) down to 70 miles (113 kilometers).

The Trace Gas Orbiter completed the first two burns Wednesday and Saturday, according to Håkan Svedhem, TGO's project scientist at the European Space Agency. He said the orbit's low point was at an altitude of 87 miles (140 kilometers), as of Monday.

The next orbit-lowering maneuver is scheduled for Tuesday, followed by more burns March 24, March 27, April 1 and April 6.
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"It's not ESA's first experience with aerobraking, but it is the first time we've used this technique to achieve a planned science orbit, repeating it for such a long duration," said Michel Denis, ESA's ExoMars flight director. "The mission controllers have worked intensively with our flight dynamics experts to prepare for this challenging phase – we're go for aerobraking."

The gradual step-down into TGO's aerobraking orbit allows ground controllers to monitor pressures and temperatures on the spacecraft.

"The atmospheric models aren't perfect, so we have to 'feel' our way down to the start of aerobraking proper," said Chris White, an ExoMars spacecraft operations engineer, in an ESA blog post describing the aerobraking procedures.

 
This illustration shows TGO's current orbit. The aerobraking campaign will tighten the orbit to a circular perch just 250 miles (400 kilometers) from Mars. Credit: ESA

The orbiter will fly in a special orientation as it slices through the rarefied upper layers of the atmosphere, preventing direct communications with Earth at the most critical point of each orbit. As the spacecraft encounters air particles, friction will cause temperatures to rise outside the probe. Models predict the temperatures should be around 158 degrees Fahrenheit (70 degrees Celsius) on the craft's two power-generating solar arrays during each passage.

If the temperatures reach 293 degrees Fahrenheit (145 degrees Celsius), or if other temperature and pressure redlines are exceeded, the spacecraft will automatically fire its thrusters to raise its orbit in a "pop-up" maneuver to avoid such extreme conditions on the next orbit, according to ESA.

"We'll closely monitor the solar array temperature and the acceleration of the spacecraft, not only during the first few passages through the atmosphere but throughout the rest of 2017, and adjust the trajectory as needed," Denis said in an ESA statement.

Changes in the density of the upper atmosphere caused by dust storms and solar activity make each TGO close approach unpredictable.

ESA's Venus Express spacecraft flew deeper into the atmosphere of Venus during its final year of operations in 2014, gathering data about the planet's thick, toxic atmosphere and giving European engineers experience with aerobraking techniques needed on future missions, starting with TGO.

NASA has conducted aerobraking maneuvers the red planet with the Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter missions.

The technique saves fuel, reducing the mass of a spacecraft at launch. In TGO's case, the tradeoff saved around 1,300 pounds (600 kilograms) of fuel, according to ESA.

The aerobraking campaign will take a two-month hiatus in July and August, when Mars is behind the sun as seen from Earth. The conjunction disrupts normal communications with spacecraft at the red planet, so managers want to temporarily raise TGO's orbit to a safer altitude before resuming aerobraking at the end of August.

By early 2018, the repeated passes through the Martian atmosphere should pull TGO's peak altitude to around 250 miles. Another rocket burn will raise the low point of the orbit to the same altitude, placing the spacecraft in a circular perch to begin regular scientific observations.

The circular orbit also allows TGO to act as a data relay satellite between Earth and landers and rovers on the Martian surface. ESA and Roscosmos, the Russian space agency, plan to send a stationary landing platform and rover to the red planet in 2020, and TGO will be critical to enable communications for the mission.

 
Close-up of the rim of a large unnamed crater north of a crater named Da Vinci, situated near the Mars equator, as viewed by the CaSSIS camera aboard the ExoMars Trace Gas Orbiter on Nov. 22, 2016. Credit: ESA/Roscosmos/ExoMars/CaSSIS/UniBE
 
The aerobraking maneuvers come after thruster burns in January and February and tilted the angle of TGO's orbit from a path hugging the Martian equator to one circling at an angle of 74 degrees, permitting greater coverage of the planet.

TGO's four science instruments have collected initial data since the spacecraft arrived at Mars on Oct. 19, but the meat of the mission will wait for 2018.

"These dress rehearsals enable our science teams to fine-tune their data acquisition techniques including pointing commands, iron out any software bugs, and get used to working with the data, well in advance of the start of the main mission starting next year," Svedhem said in a press release. "What we're seeing so far is really promising for our science goals."

TGO's camera has taken several test images of Mars, and the orbiter's two atmospheric measurement suites also completed successful demos. The Russian-made FREND neutron detector, designed to look for signs of water just below the top layer of Martian soil, is also working as expected.

Svedhem said the science team has no observations planned during the year-long aerobraking campaign, but there may be opportunities to turn on the science payload to test new instrument modes.

TGO flew to Mars with the Schiaparelli lander, a demonstrator designed to test European entry, descent and landing technologies for the 2020 rover. The lander crashed after prematurely releasing its parachute and turning off its braking rockets due to incorrect altitude data fed to the craft's computer.

The orbiter's chief objective is to tease out the trace constituents of the Martian atmosphere, particularly methane, a gas detected intermittently over the last decade that scientists think could be produced by microbes or undiscovered ongoing geological activity.
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