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Important Step Has Taken Towards the Development of Europe's Galileo Global Navigation Satellite System by Successful Launch of GIOVE-B
:: 27 April, 2008
A further step towards the deployment of Europe's Galileo global navigation satellite system was taken tonight, with the successful launch of ESA's second Galileo In-Orbit Validation Element (GIOVE-B) satellite, carrying the most accurate atomic clock ever flown into space.
The GIOVE-B satellite was lofted into a medium altitude orbit around the earth by a Soyuz/Fregat rocket departing from the Baikonur cosmodrome in Kazakhstan by launch operator Starsem. Lift-off occurred at 04:16 local time on 27 April (00:16 Central European Summer Time). The Fregat upper stage performed a series of manoeuvres to reach a circular orbit at an altitude of about 23 200 km, inclined at 56 degrees to the Equator, before safely delivering the satellite into orbit some 3 hours and 45 minutes later. The two solar panels that generate electricity to power the spacecraft deployed correctly and were fully operational by 05:28 CEST.
This 500 kg satellite was built by a European industrial team led by Astrium GmbH, with Thales Alenia Space performing integration and testing in Rome. Two years after the highly successful GIOVE-A mission, this latest satellite will continue the demonstration of critical technologies for the navigation payload of future operational Galileo satellites.
Three high-accuracy space clocks aboard
Like its predecessor, GIOVE-B carries two redundant small-size rubidium atomic clocks, each with a stability of 10 nanoseconds per day. But it also features an even more accurate payload: the Passive Hydrogen Maser (PHM), with stability better than 1 nanosecond per day. The first of its kind ever to be launched into space, this is now the most stable clock operating in earth orbit. Two PHMs will be used as primary clocks onboard operational Galileo satellites, with two rubidium clocks serving as back-up.
GIOVE-B also incorporates a radiation-monitoring payload to characterise the space environment at the altitude of the Galileo constellation, as well as a laser retroreflector for high-accuracy laser ranging.
Signal generation units will provide representative Galileo signals on three separate frequencies broadcast via an L-band phase array antenna designed to entirely cover the visible earth below the satellite.
The satellite is now under the control of Telespazio's spacecraft operations centre in Fucino, Italy, and in-orbit checking-out of the satellite has begun.
Final demonstration before Galileo
In addition to its technology-demonstration mission, GIOVE-B will also take over GIOVE-A's mission to secure the Galileo frequencies, as that first Galileo demonstration satellite launched in December 2005 is now approaching the end of its operational life.
Beyond GIOVE-B, the next step in the Galileo programme will be the launch of four operational satellites, to validate the basic Galileo space and related ground segment, by 2010. Once that In-Orbit Validation (IOV) phase is completed, the remaining satellites will be launched and deployed to reach the Full Operational Capability (FOC), a constellation of 30 identical satellites.
“With the successful launch of GIOVE-B, we are about to complete the demonstration phase for Galileo”, said ESA Director General Jean Jacques Dordain in Fucino while congratulating the ESA and industrial teams. “The strong cooperation between ESA and the European Commission has been instrumental in making progress in a difficult environment over the past few years; and, even with that being so, Galileo has already materialised, with two satellites now in orbit, significant headway made on the next four (already in the construction phase) and a fully qualified EGNOS service (*) - all this designed to serve citizens in Europe and all around the globe. ESA will begin shortly the procurement process for the overall constellation beyond IOV under EC responsibility.”
Galileo will be Europe's very own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civil control. It will be interoperable with the US Global Positioning System (GPS) and Russia's GLONASS, the two other global satellite navigation systems. Galileo will deliver real-time positioning accuracy down to the metre range with unrivalled integrity.
Numerous applications are planned for Galileo, including positioning and derived value-added services for transport by road, rail, air and sea, fisheries and agriculture, oil-prospecting, civil protection, building, public works and telecommunications.
About GIOVE-B
GIOVE, or Galileo In-Orbit Validation Element, is the name for each satellite in a series being built for the European Space Agency (ESA) to test technology in orbit for the Galileo positioning system.
Giove is the Italian word for "Jupiter". The name was chosen as a tribute to Galileo Galilei, who discovered the first four natural satellites of Jupiter, and later discovered that they could be used as a universal clock to obtain the longitude of a point on the Earth's surface.
The GIOVE satellites are exploited by the GIOVE Mission (GIOVE-M) segment in the frame of the risk mitigation for the In Orbit Validation (IOV) of the Galileo positioning system.
This satellite (previously called GSTB-V2/B), has a similar mission, but has greatly improved signal generation hardware. GIOVE-B was originally built by satellite consortium European Satellite Navigation Industries, but following re-organization of the project in 2007, the satellite prime contractor responsibility was passed to Astrium. GIOVE-B also has MEO environment characterization objectives, as well as Signal-In-Space and receiver experimentation objectives. GIOVE-B will also carry three atomic clocks: two rubidium atomic clocks and the first space-qualified passive hydrogen maser atomic clock. The launch has been delayed due to various technical problems, and is now scheduled for 27 April 2008 at 4.16 a.m. (Baikonur time) aboard a Soyuz-FG/Fregat rocket provided by Starsem.
At 4:16 a.m. local time (2216 GMT Saturday) the Soyuz rocket was launched, and placed the Giove-B into its projected orbit after 0200 GMT. The satellite separated from the launcher, the Russian Fregat acceleration unit, making the launch a success, since the satellite "reached its nominal orbit and the orbit's parameters were excellent."
GIOVE-B success technical credits go to the European Industrial consortium (ESNIS) prime of Galileo development until end of last year, when changes at the organizational level put ESA on top in the role of the Galileo prime.
About Global Positioning System
The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 Medium Earth Orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its location, speed, direction, and time. Other similar systems are the Russian GLONASS (incomplete as of 2008), the upcoming European Galileo positioning system, the proposed COMPASS navigation system of China, and IRNSS of India.
Developed by the United States Department of Defense, GPS is officially named NAVSTAR GPS (Contrary to popular belief, NAVSTAR is not an acronym, but simply a name given by John Walsh, a key decision maker when it came to the budget for the GPS program). The satellite constellation is managed by the United States Air Force 50th Space Wing. The cost of maintaining the system is approximately US$750 million per year, including the replacement of aging satellites, and research and development.
Following the shooting down of Korean Air Lines Flight 007 in 1983, President Ronald Reagan issued a directive making the system available for free for civilian use as a common good. Since then, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, and scientific uses. GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks.
A typical GPS receiver calculates its position using the signals from four or more GPS satellites. Four satellites are needed since the process needs a very accurate local time, more accurate than any normal clock can provide, so the receiver internally solves for time as well as position. In other words, the receiver uses four measurements to solve for four variables: x, y, z, and t. These values are then turned into more user-friendly forms, such as latitude/longitude or location on a map, then displayed to the user.
Each GPS satellite has an atomic clock, and continually transmits messages containing the current time at the start of the message, parameters to calculate the location of the satellite (the ephemeris), and the general system health (the almanac). The signals travel at the speed of light through outer space, and slightly slower through the atmosphere. The receiver uses the arrival time to compute the distance to each satellite, from which it determines the position of the receiver using geometry and trigonometry)
Although four satellites are required for normal operation, fewer may be needed in some special cases. If one variable is already known (for example, a sea-going ship knows its altitude is 0), a receiver can determine its position using only three satellites. Also, in practice, receivers use additional clues (doppler shift of satellite signals, last known position, dead reckoning, inertial navigation, and so on) to give degraded answers when fewer than four satellites are visible.
