A special thanks to Jean-Claude, Rolf and Francois for their support.
I - MSG PLATFORM DESIGN
What does "platform" means?
A spacecraft is normally made of two main elements; The platform which comprises all the support subsystems and the payload (SEVIRI and GERB for MSG) that will provide the mission data.The MSG platform design comprises the following subsystems:
- Data Handling Subsystem (DHSS) + Software (SW)
- Electrical power Subsystem (EPS): 8 Solar Arrays, 2 Batteries, Power conditioning and distribution Units (PCU and PDU), and Pyrothechnic Release Unit (PRU)
- Attitude and Orbit Control Subsystem (AOCS). This comprises Control Electronic units (AOCE), Sun and Earth Sensor Units (SSU and ESU) and the passive nutation Dampers. The AOCS directly commands the UPS.
- Unified propulsion System (UPS). The UPS is a Bi-propellant system including the Liquid Apogee Motors (LAMs), the Reaction Control thrusters (RCTs), the pressurant and propellant tanks, all necessary valves, filters, pressure regulators and transducers and the Ultrasonic Gauge sensors (UGS)
- The Telemetry, Tracking and Command Subsystem (TT & C). This is supported by the Mission Communication Package (MCP) with all antennas and electronic units.
- The Thermal Control Subsystem (TCS), mainly insulation blanket (MLI) and optical sun reflectors (OSR).
- The Structure Subsystem, mechanisms and Pyrotechnic devices
Where can I find a good description of the MSG-3 spacecraft platform functions?
About satellite architecture.
About Communications.
About propulsion: to be filled later
About MSG facts and figures
Why MSG has a cylindrical shape?
Because the spacecraft is designed to rotate around its vertical axis during its mission at an angular speed of 100 rounds per minutes. The spinning increases the moment of inertia and therefore the gyroscopic stabilisation. It simplifies the the design of the attitude control sub-system compared to a 3 axis stabilised spacecrafts.
Why MSG is spinning and what are the general benefits of spinning satellites?
MSG
rotation is 100 round per minute around its vertical inertial axis. It
belongs then to the spin-stabilised satellite family. The main benefit
is the
attitude stabilisation by mean of the gyroscopic effect which makes the
design
of the attitude control much more simpler than a 3 axis stabilised
spacecraft.
The attitude stability is an essential parameter to get a sharp image by
a
“camera” at 36.000kms distance from Earth. At the time MSG programme was
started
in the seventies, the 3 axis technology was not able to meet the mission
requirements. This new technology will appear on the third generation
of Meteosat spacecraft (MTG) by end of the decade.
Why the SEVIRI solar array is slightly longer than the other ones?
- to determine the spacecraft attitude when S/C, sun and earth are not to close from alignment (i.e. angle between S/C earth direction and S/C sun direction is above ca 15 deg and below ca 165 deg)
- to measure the spacecraft spin rate (function done by the sun sensor unit only)
- to elaborate a reference pulse used a) for synchronising the image taking by SEVIRI and GERB with the S/C rotation (ie to determine when the instrument is exactly facing the Earth), b) for synchronising the radial thrusters in order to deliver a radial force in a given direction (as the S/C is permanently spun)
- to synchronise the electronically despun antenna (which counteract the S/C spin in order to ensure permanent pointing of this antenna towards the earth.
An
Electronically Despun Antenna (EDA) is mounted on the top of the
cylindrical MSG-3 spacecraft. The EDA purpose is to have the antenna
continuously pointing at Earth whilst the spacecraft is rotating.
How MSG communicates with Earth?
This function is performed by the Mission Communication Package.
to be filled later
to be filled later
What are the propellants used on board MSG-3?
MSG propulsion is achieved by a classical bi-propellant system, i.e. the combustion of two components: a liquid fuel with a liquid oxidizer.
MSG system uses Monomethylhydrazine (MMH) as liquid fuel and Mixed Oxides of Nitrogen (MON) as liquid oxidizer.
II - PAYLOAD
What is the main instrument mounted on MSG-3?The main payload is called SEVIRI (Spinning Enhanced Visible and InfraRed Imager). This is an imager able to provide a picture of Earth every 15 minutes.
From its position, once in geostationary orbit, MSG covers Western Europe and North Africa .
Here under is a sketch of the SEVIRI:
Credits: EUMETSAT/ESA
MSG-3 spacecraft rotates on its inertial vertical axis. A complete 360 degrees rotation is completed in 600 milliseconds. The SEVIRI imager which is made of a radiometer telescope and a mirror faces the Earth for a period of 30 millisecond (18o sweeping angle). During the 570 millisecond left for completing the rest of the 360o, the imager looks at the deep space. This time is used to modify the tilt angle of the mirror in order that at the next sweep, a contiguous band of the Earth ground but slightly higher is seen by the imager. This is repeated till the full scan of the globe image is achieved. This takes 12 minutes and 30 seconds. The next 2 minutes and 30 seconds are used for repositioning the mirror in its initial configuration and calibrate the detectors. With a repetition of such process MSG-3 sends to Earth a full image of the globe every 15 minutes. Put in sequence, this succession of images provides short movie which can be seen on TV in the weather forecast programme every day.
What are the other payloads/services of the MSG mission?
-GERB is the second payload on board MSG. It stands for Global Earth Radiation Budget. The purpose is to measure the terrestrial Albedo. With simple words, Albedo is a coefficient (expressed in percentage) of the reflected radiation from an incident radiation upon it. GERB will be used to visualize differences of heat radiation over the Earth surface.
-DCP (Data Collection Platform). This is a service relaying data from Data Collection Platform, such as buoys, in support to the Tsunami Warning System for the Indian Ocean (Wikipedia)
- SRSP ( Search and Rescue Signal Processor) also called S&R (Search and Rescue). This is a service capable of detecting 406Mhz distress signal from signal radiobeacons (Wikipedia).
III - MISSION
What is the main mission objective of MSG-3?The MSG spacecraft, under EUMETSAT operations, offers a wide range of meteorological services. The most visible one for European citizens is the weather forecast map broadcasted daily by most of TV programs.
Live MSG picture of the sky over Europe is given by the folloing link:
http://www.wetterzentrale.de/pics/D2u.jpg
MET9 means that the picture is coming from MSG-2
What is the foreseen life time of the MSG-3 missions?
The MSG is designed for a nominal mission of 7 years in space. In fact the review of past missions shows that this nominal life time has always been extended which proves the robust MSG design. The oldest spacecraft of the MSG family is Meteosat-7 still working today 15 years after its launch in 1997.
IV - LAUNCH AND LAUNCHER
Which rockets are used to launch MSG spacecrafts?
MSG-1 was launched by an Ariane 5G, V155, (Atlantic Hotbird-1/Meteosat-8) on 28/08/2000 @23:22 (UTC)MSG-2 was launched by an Ariane 5GS, V169, (INSAT-4A/Meteosat-9) on 21/12/2005 @22:33 (UTC)
MSG-3 will be launched by an Ariane 5 ECA (Echostar-17/Meteosat-10) planned mid June 2012.
Why MSG is launched with a co-passenger?
Because the MSG mass, about 1,3 tons, is far to low to fill the Ariane 5 launch capacity in geostationary transfer orbit (GTO). Ariane 5G and GS are able to transfer respectively 6,2 and 6,1 tons in GTO whilst Ariane 5 ECA has a capacity go 10.5 Tones. Therefore Arianespace arrange dual launches to optimize launches according to the launcher used.
What does SYLDA means?
SYLDA stands for SYstem de Lancement Double Ariane (Ariane Dual Launch System). This is a cylinder shaped device which enables to accommodate two separates payloads inside the Ariane 5 fairing. The first one inside the SYLDA in lower position (MSG-3) and the other one the top of the SYLDA, (Echostar-17) in upper position.
Why MSG-3 is in lower position inside the Ariane fairing?
The main reason is because at this place there are less shocks when the fairing separates from the launcher under the effects of the pyro activation. Due to the MSG lower tolerance to shocks ,Two shocks absorbers have been designed: PSAD (Passive Shock Attenuator device) and MFD (Modular Fitting Dummy) . En passant, these devices PSAD and MFD cost a lot in term of mass.
The second reason is that MSG-3 fits perfectly well by its size and mass inside the SYLDA.
The third reason is that, being injected into orbit in second position, a higher spin can be provided by the third stage of the launcher.
Does the launcher gives an initial spin to MSG-s after separation?
Yes, 5 round per minutes.
Is there an optimum launch window for MSG-3?
Yes (to be completed later)
V - FROM KOUROU TO GEO ORBIT
Why it is so favorable to launch MSG from Kourou?
The Centre Spatial Guyanais (CSG), located in Kourou, is in the vicinity of the equator (5o09’35’’N). At this quasi equator latitude, Earth’s rotation gives an additional velocity of 460m/sec (1700km/h) known in French as “effet de fronde” to the launcher when the launch trajectory heads eastward . This is precisely the case for MSG-3 before being injected into the transfer orbit. Energywise, for such an orbit, the benefit of the Kourou equatorial location compared to other launch bases located more in the North is about 15%.
Other Kourou assets: launches can be made in the sea direction, low density of population, no earthquake zone, no cyclones…
What is the geostationary transfer orbit?
Before reaching its final position in Geostationary orbit, MSG-3 will be injected into a transfer orbit with an inclination of 6 degrees. It is a temporary elliptical orbit with an perigee of 251,5 km and an apogee of 35.852 kms. The transition from the transfer to the geostationary orbit will be achieved with the LAM (Liquid Apogee Motor) built-on the spacecraft. By means of impulsions at the perigee, the transfer orbit will be progressively become circular to circa 36.000 kms radius around the Earth.
This manoeuver will be completed roughly 10 days after launch, will necessitate four AMFs (Apogee Motor Firing) and will consume roughly 820 kgs of the 970 kgs of propellant stored on-bard the MSG-3 spacecraft at launch.
Why MSG orbit is a geostationary orbit (GEO)?
The geostationary orbit allows to have a fixed view on Earth from space. It is a specific orbit where the MSG spacecraft will rotate with the same angular speed than Earth. It is then a perfect position to look a specific portion of the globe from space. For MSG-3, the location will be such that the spacecraft will be permanently looking at Europe and Africa. This is illustrated by the first colour image acquired by MSG-2 on 25/01/2006 below.
Credit ESA/EUMETSAT
VI - GROUND SEGMENT
What is the purpose of the Ground Segment?The MSG system is made of the Space Segment (the MSG spacecraft) and the Ground Segment. The Ground Segment comprises all the facilities and staff on ground needed to track, operate the spacecraft and collect/distribute the data.The Agency Operating MSG after the LEOP (see below) is EUMETSAT located in Darmstadt, Germany
What LEOP means?
LEOP means Launch and Early Operation Phase. During this two week phase, MSG will be transferred from the orbit where it has been injected by the launcher (transfer orbit) to its final orbit, the Geostationary orbit (GEO, see above). Once in GEO, the MSG-3 commissioning phase will start.
What commissioning means?
The commissioning phase lasts about 6 months. This phase aims at checking all the platform subsystems and Payload. After commissioning, MSG spacecraft enters the MSG system which delivers all the expected operational services.
C O N G R A T U L A T I O N S !!!!!!!!!
ReplyDeleteErnesto.Lopez@uv.es