http://www.esa.int/Our_Activities/Navigation/Galileo/Launching_Galileo/Four_Galileo_satellites_on_one_Ariane_5
Quad satellites see space
8 November 2016
This month, a single Ariane 5 rocket is set to propel four Galileo satellites into orbit for the navigation constellation’s first-ever quadruple launch. Mission controllers are training intensively for the complex space delivery.
On 17 November, an Ariane 5 will use a new payload dispenser to release four identical satellites into orbit in one go.
This will be the eighth Galileo launch, and will bring the number of satellites in space to 18. Once complete, the system will sport 24 operational satellites and a ground network to provide positioning, navigation and timing services.
To date, Soyuz rockets have carried two satellites at a time. This quadruple launch presents several technical challenges, including the new dispenser and the need to establish control over four independent satellites almost simultaneously.
Four times complex mission control
The ascent into the medium-altitude orbit will take three and a half hours. Then, after the satellites separate, a combined team from ESA and France’s CNES space agency will take over, establishing control and shepherding them through their early orbits, lasting nine days for one pair and 13 days for the other.
Galileo control room
“At the time that the four satellites separate two by two, we’ll have two shifts of the mission team working in the control room at the CNES centre in Toulouse, France, each shift managing two satellites – so it will be an intense period,” says Liviu Stefanov, co-flight director from ESA.
“This is the same team who conducted the previous Galileo early orbit phases, so we’re familiar with the satellites themselves,” says Hélène Cottet, lead flight director from CNES.
“What’s different this time is managing four satellites, sometimes in sequence and sometimes in parallel. We have concentrated a lot of effort on planning and training for the first few hours in space.”
Since 2011, the joint team have conducted the Galileo initial flight operations alternately from ESA’s centre in Darmstadt, Germany, and the CNES centre in Toulouse.
Target orbit: 23 200 km
Cut-away foursome
Separation will mark the start of a set of critical activities and manoeuvres to ensure the four are ready for handover to the Galileo Control Centre in Oberpfaffenhofen, Germany for the rest of their mission.
This includes ensuring that each have opened their solar wings and are ‘power positive’, establishing a data link via a set of ground stations, conducting extensive health checks and then switching the craft into a stable Earth-pointing mode, ready for subsequent manoeuvres.
Each must make three engine firings at roughly one-day intervals to get onto their ‘drift’ orbits, after which control will be passed from the joint team to the Galileo Control Centre.
“After a few days, we expect things to settle down, and we’ll be able to concentrate on manoeuvring two satellites while babysitting the other two,” says ESA’s Tom Cowell, one of four spacecraft operations managers.
Teamwork
“After handover of the first pair to Oberpfaffenhofen, we can manoeuvre the other two just as we’ve done for previous dual launches.”
Even after handover, specialists will continue determining the orbits and computing manoeuvres to position the satellites in their final orbits at around 23 200 km, expected early in 2017.
Training, simulating, preparing
Since summer, everyone involved in this Galileo launch has worked through multiple simulations, mostly focused on preparing for if things go wrong.
This week, the training will end with an intensive three-day live simulation in Toulouse.
After a network countdown practice on 14 November, the live network countdown for the actual launch will start a couple of hours after midnight on 17 November, with lift off from the European Spaceport in Kourou, French Guiana, set for the same day at 13:06 GMT (14:06 CET).
“It will be a challenge, but having already taken 14 Galileo satellites into orbit, our joint teams are confident of our abilities and skills,” says Hervé Côme, co-flight director from ESA.
“We know we can rely on teamwork and expertise, and we’re looking forward to a smooth lift off for Galileo’s first quad launch.”
VERSIÓN EN ESPAÑOL :
El vuelo de los Cuatro Fantásticos
Sección del cohete con los cuatro satélites
9 noviembre 2016
Este mes, cuatro satélites del sistema de navegación Galileo serán puestos en órbita a bordo de un cohete Ariane 5, en lo que constituirá el primer envío cuádruple de esta constelación. Los controladores de la misión están preparándose a fondo para este complejo lanzamiento al espacio.
El 17 de noviembre, el Ariane 5 empleará un nuevo dispensador capaz de situar en órbita cuatro satélites idénticos de una sola vez.
Se trata del octavo lanzamiento de Galileo y, con él, serán 18 los satélites en el espacio. Una vez completado, el sistema contará con 24 satélites operativos y una red terrestre para la provisión de servicios de posicionamiento, navegación y determinación de la hora.
Hasta el momento, los satélites se enviaban de dos en dos a bordo de cohetes Soyuz. Este lanzamiento cuádruple presenta varios retos técnicos, incluyendo el nuevo dispensador de la carga útil y la necesidad de establecer el control sobre cuatro satélites independientes casi al mismo tiempo.
Una sala de control cuatro veces más compleja
El ascenso hasta la órbita circular intermedia durará tres horas y media. A continuación, una vez separados los satélites, un equipo formado por personal de la ESA y de la agencia espacial francesa CNES asumirá su control y los guiará por sus órbitas tempranas. Esta fase se prolongará durante nueve días en el caso de la primera pareja de satélites, mientras que su duración para los otros dos será de 13 días.
Sala de control de Galileo
“En el momento en que los cuatro satélites se separen por parejas, el equipo de la misión se dividirá en dos turnos para trabajar desde la sala de control del CNES en Toulouse, Francia. Cada uno de estos turnos se encargará de dos satélites, por lo que el trabajo será intenso”, explica Liviu Stefanov, codirector de vuelos de la ESA.
Como reconoce Hélène Cottet, directora principal de vuelos del CNES: “Se trata del mismo equipo que llevó a cabo las anteriores fases de órbita temprana de Galileo, por lo que conocemos bien los satélites”.
“La diferencia esta vez está en que hay que gestionar cuatro satélites, a veces en secuencia y a veces en paralelo. Así, hemos invertido mucho esfuerzo en planificación y entrenamiento de cara a las primeras horas en el espacio”.
Desde 2011, este equipo conjunto ha dirigido las operaciones de vuelo iniciales de Galileo alternando el trabajo desde el centro de la ESA en Darmstadt, Alemania, y el del CNES de Toulouse.
Órbita objetivo: 23.200 km
Llegada de los cuatro satélites al espacio
La separación marcará el comienzo de una serie de actividades y maniobras críticas para garantizar que los cuatro satélites estén listos para su traspaso al Centro de Control de Galileo en Oberpfaffenhofen, Alemania, por el resto de la misión.
Entre otras cuestiones, se comprobará que cada uno de ellos ha desplegado sus paneles solares y recibe energía; además, habrá que establecer un enlace de datos mediante una serie de estaciones terrestres, llevar a cabo amplias comprobaciones de funcionamiento y, a continuación, poner los módulos en un modo estable orientados hacia la Tierra, quedando así listos para posteriores maniobras.
ENGLISH VERSION:
Four Galileo satellites on one Ariane 5
Fairing lowered onto Galileo satellites
11 November 2016
Europe’s next four Galileo navigation satellites are together on their dispenser atop the Ariane 5 launcher due to launch them next Thursday from Europe’s Spaceport in French Guiana.
Having been attached to their dispenser as a combined ‘upper composite’, the four 715 kg satellites were transported to the final assembly building on 31 October.
The next step saw them put on top of the upper stage of their customised launcher. Finally, on 3 November, the quartet was enclosed within a protective fairing – the last time they were seen by human eyes – to protect them from the onrushing atmosphere during ascent.
In the following week, the rocket was prepared for takeoff, including filling its cryogenic upper stage, in preparation for the move to the launch pad on Tuesday, 15 November.
Galileos atop Ariane 5
In development since 2012, this new Ariane variant has evolved from the version used to place ESA’s 20 t Automated Transfer Vehicle vehicle into low orbit. The new launcher has to carry a lighter payload but needs to take it up to the much higher altitude of 22 900 km.
The target orbit is actually 300 km under the Galileo constellation’s final working altitude. This leaves Ariane’s upper stage in a stable ‘graveyard orbit’, while the four Galileos manoeuvre themselves up to their final set height.
The decision to proceed with this launch was taken after in-depth analysis of two recent anomalies occurring in rubidium atomic clocks aboard Galileo satellites in orbit.
Galileos meet Ariane 5
Highly accurate timing is core to satellite navigation. Each Galileo carries four atomic clocks to ensure quadruple redundancy of the timing subsystem: two Passive Hydrogen Maser clocks plus two Rubidium Atomic Frequency Standard (RAFS) clock.
Investigations jointly conducted by ESA and industry point to a short circuit in these two RAFS units. The ultimate objective of the fourfold redundancy on each satellite is to ensure operations over their planned lifetime.
Taking into account the redundancy and considering that the upcoming launch will increase the constellation’s overall robustness,it has been decided to maintain the mid-November launch date.
Quad satellites see space
Once this latest flight is complete, there will be 18 Galileo satellites in orbit – the single largest increase of any navigation satellite constellation from a single launch.
This will mark the first time that ESA deploys four satellites simultaneously. Usually, simply shepherding a spacecraft through the first critical days in orbit is a demanding enough task. A combined team from ESA and France’s CNES space agency based in Toulouse, France, will make contact, establish control and then see the quartet through its initial, critical, activities.
Two further Ariane 5 flights are planned for Galileo during the next two years, one each for the constellation’s remaining orbital planes.
ESA
Guillermo Gonzalo Sánchez Achutegui
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