Of Doresa and Milena: ESA’s Galileo spacecraft primed for flight atop Soyuz ST-B rocket
The last stages of functional testing for the European Space Agency’s (ESA ) twin Galileo navigation satellites has concluded at Europe’s Spaceport located at Kourou, French Guiana. With these last tests completed, the twin spacecraft now stand ready for a launch currently scheduled to take place on Thursday, 21 August at 14:31:14 CEST (12:31:14 UTC).
Both spacecraft were fueled on Aug. 7-8. This propellant will allow them maintain the proper altitude as well as to maintain the proper orbit to carry out their mission. Unlike your automobile, these vehicles cannot be refueled, therefore the satellites have to carry enough propellant to last them throughout the course of their operational lives – which are estimated at some 12 years.
More importantly, for engineers, is that safety requirements be maintained as they fuel the two navigation satellites. Prior to the fueling of the duo, engineers dressed themselves in what is known as Self Contained Atmospheric Protective Ensemble or “SCAPE.” This is a requirement as the fuel which the Galileo spacecraft uses, hydrazine, is incredibly toxic.
Three days after fueling, on Aug. 11, the two satellites were installed together on the flight dispenser which mounts them to the Fregat upper stage of the Soyuz ST-B booster, the rocket which has been tasked with flying the duo to orbit. ESA wanted to give a more personal face to Soyuz’s current cargo – and worked to provide them with that three years ago.
There was a drawing contest held in 2011. Children scribbled their best – and the two satellites which are about ready for their big day – were given their names by the budding artists. The names – Doresa and Milena.
Once arriving at their orbital destination, they will join four other Galileo satellites which were launched in October of 2011, with two more following in October of 2012. These particular spacecraft were also launched atop the venerable Soyuz launcher, the Soyuz-2-1b Fregat-MT. These satellites however, were not the first to be flown to validate various aspects of this system’s design.
GIOVE-A was launched in 2005, with GIOVE-B taking flight three years later in 2008. Both missions were tasked with testing out systems that were to be used on Galileo as well as to secure frequencies which would fly on the constellation with the International Telecommunications Union.
The first four spacecraft, were less about providing navigational services, and more about proving that this particular system would work. With these two spacecraft at “Full Operational Capability” – the first of the core Galileo constellation will be sent aloft.
With the In-Orbit Validation or “IOV” phase completed by the first four satellites sent to orbit and with the first two operational spacecraft poised for liftoff – Galileo stands ready to move on to the Initial Operational Capability (IOC). If everything proceeds apace – IOC should take place around the middle of this decade.
“IOV was required to demonstrate that the future performance that we want to meet when the system is deployed is effectively reachable,” ESA’s Galileo Ground Segment Manager Sylvain Loddo, said. “It was an intermediate step with a reduced part of the system to effectively give evidence that we are on track.”
Once the IOC has been completed, the constellation of satellites will be increased and new services will be checked out and brought online for consumers to use. This will mark another transition, one toward what has been dubbed Full Operational Capability (FOC).
Galileo, like the U.S.’ GPS and Russian GLONASS systems, is designed to provide navigational services to users on the ground. Galileo is designed to be inter-operable with both of these systems and is described as: “Europe’s own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control.”
Galileo is designed to provide services on two frequencies and should deliver real-time positioning – down to a distance of approximately three feet (1 meter). Users will be forewarned of any satellite failure before hand. This makes the system capable of supporting efforts that are viewed as “safety-critical” – those relating to the directing of cars, trains and aircraft.
Galileo is also designed to serve as a global Search and Rescue or “SAR” resource. The system is based off of the Cospas-Sarsat system and therein are equipped with transponders. This enables these spacecraft to relay distress signals from users’ transmitters to local rescue centers. Another signal will also be sent to the user, letting them know that their signal has been detected – and that help should be on the way. According to statements appearing on ESA websites, this is a service not currently provided by existing systems.
Galileo is described as the first, complete, civil positioning system, different than the military-based navigational systems that have preceded it.
Fully-equipped, the fleet should consist of 30 satellites, 27 of which will be active with the remaining three serving as spares. The satellites will operate in medium-Earth-orbit (MEO) in three circular orbits at an orbital inclination of 56 degrees. Galileo will provide services at latitudes of about 75 degrees north. This means the most northern tip of Europe, Norway’s North Cape, will be encompassed under this new service.
Over the course of the next few years, two additional Galileo spacecraft will be sent to orbit via Soyuz rockets and four more via Arianespace’s powerful Ariane 5 booster. The Ariane 5 which will carry out this mission is currently being prepared for flight.
The “Full Operational Capability” phase is managed and funded by the European Commission, they, along with ESA, have entered into an agreement wherein the European Space Agency serves to design the spacecraft as well as acquire the needed components to build the fleet.
To support this growing system Europe has established two Galileo Control Centres (GCCs ). These will control the spacecraft as well as perform navigational mission management. The data that is produced by the network of Galileo Sensor Stations, which stretches across the world, will be relayed back to the GCCs via uplink stations. This information will be used to synchronize ground station clocks.
The elements which will generate the navigational signals back to the ground were built by Surrey Satellite Technology Ltd., located in the United Kingdom. The primary structures of the satellites themselves were built by OHB in Germany.
On Aug. 15, the assembled payload fairing, which included the two spacecraft and their dispenser was attached to the booster’s upper stage. The payload fairing, which shields the delicate cargo through Earth’s turbulent atmosphere was then affixed around the two satellites.
In European space circles, this mini stack is known as the “space head.” This combined structure was then added to the Soyuz ST-B just a few days prior to this week’s planned Aug. 21 lunch date.
If everything goes according to plan, three hours 47 minutes and 57 seconds into the flight, the two satellites will be deployed from Fregat courtesy of the dispenser’s pyrotechnic separation system. When all is said and done? The two spacecraft will be orbiting at a distance of some 14,429 miles (23,222 km).
Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology, Space.com, The Mars Society and Universe Today.