An Ariane 5 launcher uniquely modified to loft four of Europe’s Galileo navigation satellites on one flight has received its payload for liftoff next week in French Guiana.
The satellite quartet will boost the size of the Galileo fleet to 18 spacecraft. Officials say 24 satellites are needed for the European navigation network to provide global positioning and timing services independent of U.S. or Russian navigation fleets.
Liftoff is set for Nov. 17 at 1306:48 GMT (8:06:48 a.m. EST), or 10:06 a.m. local time at the European-run space base in Kourou, French Guiana.
The launch is a rare morning flight for the Ariane 5, which typically blasts off with large telecommunications satellites with evening launch windows. Next week’s mission is timed for the Ariane 5 to deploy the four new Galileo craft into a specific part of the growing navigation fleet, aiming for one of three orbital planes making up the constellation.
Owned and managed by the European Commission with technical support from the European Space Agency, the Galileo program has launched its 14 existing satellites two at a time aboard Russian-made Soyuz boosters from French Guiana.
The Ariane 5 launch next week is the first of at least three flights by the heavy-duty European-made rocket set to send up four Galileo satellites per mission.
The Galileo satellites will ride aboard a specially-modified version of the Ariane 5 ES with a new dispenser developed by Airbus Defense and Space to accommodate four spacecraft bolted together.
The launcher version designed for Galileo missions also features a shortened nose cone enclosing the satellites, and a lightened Vehicle Equipment Bay structure compared to previous Ariane 5 ES flights, which carried heavy 20-ton Automated Transfer Vehicles on cargo runs to the International Space Station.
The Galileo satellites, manufactured in Germany by OHB System and outfitted with British-made navigation payloads from SSTL, are lighter and put less of a load on the Ariane 5’s structure.
Engineers also introduced electrical and thermal modifications to allow the Ariane 5’s upper stage to coast for more than three hours between engine burns, a requirement to inject the Galileo satellites close to their final operational orbits more than 14,000 miles (about 23,000 kilometers) above Earth.
The Ariane 5 ES configuration replaces the Ariane 5’s more commonly-used cryogenic upper stage, powered by a hydrogen-fueled HM7B engine, with an upper stage fitted with a hydrazine-burning Aestus engine. The key difference is the HM7B engine is only designed to fire one time in flight, while the Aestus is capable of multiple starts on the same mission.
Two upper stage burns are necessary for the Nov. 17 launch, but instead of coating for less than an hour between firings as with previous flights of the Ariane 5 ES variant, the Aestus engine will switch off and coast for more than three hours as the rocket climbs to the 14,000-mile-high altitude of the Galileo fleet for the final injection maneuver.
The critical upper stage burns will come after the Ariane 5’s main stage Vulcain 2 engine and twin solid rocket boosters propel the launcher off the pad in French Guiana. The 165-foot (50-meter) rocket will turn northeast from the Guiana Space Center, and let go of its two strap-on boosters at about T+plus 2 minutes, 19 seconds.
The Vulcain 2 engine, consuming a mix of liquid hydrogen and liquid oxygen, will fire for around nine minutes, then the upper stage’s Aestus powerplant will take over for the first of its two burns.
Separation of the first pair of Galileo satellites is expected at T+plus 3 hours, 35 minutes. The other two spacecraft will deploy from the rocket 20 minutes later.
Each Galileo satellite weighs about 1,580 pounds (717 kilograms) with a full load of fuel, according to a launch information kit released by Arianespace, the Ariane 5’s commercial operator.
Next week’s launch will mark the sixth Ariane 5 flight of the year, and the 89th overall. It will also be the ninth launch by Arianespace so far in 2016.
Technicians working inside the Guiana Space Center’s final assembly building topped off the 16-story rocket last week with the addition of the four satellites mounted on their dispenser Nov. 2. Workers lowered the rocket’s payload fairing, made in Switzerland by Ruag Space, over the satellites the next day.
The satellites set to go up Nov. 17 are nicknamed Antonianna, Lisa, Kimberley and Tijmen after the winners of a European children’s drawing contest.
Plans call for the Ariane 5 to roll out of the final assembly building for the 1.7-mile (2.7-kilometer) trip to the launch pad Nov. 15, with the final countdown commencing late Nov. 16.
More photos of the Galileo satellites, and their stacking atop the Ariane 5 rocket, are shown below.
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