Spaceflight Insider

ULA set to launch GPS IIF-7 atop Atlas V

GPS IIF-7 satellite sitting atop a ULA Atlas V rocket, ready to launch. Photo Credit: Mike Howard / SpaceFlight Insider

CAPE CANAVERAL, Fla. — So far this year, there has been an influx of GPS satellites launched to orbit. With United Launch Alliance’s (ULA) GPS IIF-7 launch marking the third of these spacecraft to be sent to orbit since February. Tonight, at approximately 11:23 p.m. EDT (0323 GMT), an Atlas V 401 rocket is set to be launched from Space Launch Complex 41 (SLC-41).

Atlas V with GPS IIF-7 satellite prior to pad roll out. Photo Credit: ULA

Atlas V with GPS IIF-7 satellite prior to pad roll out. Photo Credit: ULA

“Almost everyone has been touched by GPS today in one way or another,” said the U.S. Air Force Space Command’s General William Shelton. “Your smartphone, financial transaction, high-speed network you may have used that uses GPS timing. It literally serves the world.”

Tonight’s launch marks the seventh of Boeing’s planned twelve Block IIF spacecraft to be launched. These satellites will provide the bulk of the GPS network for the foreseeable future.

People rely on the GPS satellites continuous signals to find their positions, as well as measure time. GPS receivers record the length of the time delay (how long it takes the signal to reach the receiver), which will indicate the apparent range to the satellite. Measurements collected from a cluster of four satellites are incredibly accurate, able to tell users their location within feet, speed within a fraction of a mile per hour and even time within a second.

So far this year, two different Delta IV launch vehicles have delivered GPS satellites into orbit in February (GPS IIF-5) and May (GPS IIF-6), dubbed Canopus and Rigel. Tonight, an Atlas V rocket will be doing the lifting, launching GPS IIF-7, or Capella, into orbit. Capella, or the “goat star” is the third brightest star in the celestial Northern hemisphere. Atlas is also slated for another launch in October with the next satellite in the series, GPS IIF-8.

The Block IIF Satellites are based on the AS-4000 Satellite Bus and built by Boeing. Each satellite has a liftoff mass of 3,593 lbs (1,630 kilograms), and come equipped with two three-panel solar arrays that will be deployed for power generation. Together, the two solar arrays will supply the satellite with 1,900 Watts of power which will stored in NiH2 rechargeable batteries for use during night passes. The GPS IIF class of satellites are stabilized with a three-axis zero momentum system, allowing the vehicles to fly with their nadir pointed at the Sun, in an Earth-oriented position.

The Vertical Assembly Building adjacent from Space Launch Complex 41 played host to the Atlas V with the GPS IIF-7 satellite up until only yesterday. Photo Credit: U.S. Air Force

The Vertical Assembly Building adjacent from Space Launch Complex 41 played host to the Atlas V with the GPS IIF-7 satellite up until only yesterday. Photo Credit: U.S. Air Force

Each satellite provides navigation data via Earth and Sun sensors and use reaction wheels for attitude control. They have a 16 Hydrazine thruster propulsion system perfect for any orbit adjustments. Thermal control is regulated with blankets, thermal coatings, radiators and electric heaters. The vehicle launches with 320 lbs (145 kg) of propellant and twelve 4.5-Newton and four 22.2-Newton Rocket Engine Assemblies.

Accurate navigation signals are provided by two high-stability Rubidium clocks and a single Caesium atomic clock. The IIF satellite signals are twice as accurate as previous models. Each satellite has the ability to supply M-Code Signals, which are secure, jam-resistant signals needed for military operations. The Block IIF satellites contain the L5 ‘Safety of Life’ Signal and RH32 reprogrammable central processors, capable of receiving in-orbit software updates.

GPS IFF block satellite. Image Credit: NOAA

GPS IFF block satellite. Image Credit: NOAA

GPS IIF-7 will take the place of GPS 2R-2, launched in July 1997 atop a Delta 245, in Slot 3 of Plane F. This swap is part of a constellation reshuffling upgrade, to strengthen the network. With the launch of GPS IIF-8 in October, this will be the first time since 1993 that four satellites have been launched in the same year. Once GPS IIF-7 is in place, GPS 2R-2 will be able to relocate to another portion of the F Plane to replace one of the longest serving GPS satellites, GPS 2A-14. This 22 year-old satellite has served since its launch aboard Delta 211 (a Delta II rocket) in July of 1992.

The GPS fleet is composed of six orbital planes, each containing at least four satellites, totaling the minimum 24 satellites required for the network to perform as expected. The use of a global positioning system (GPS) dates back to the 1970s when Atlas rockets carried the first satellites into orbit. From February 1978 to October 1985, Atlas rockets were used to launch 11 of the Block 1 series satellites from California’s Vandenberg Air Force Base.

Schematic of the Atlas V 401 configuration. Image Credit: ULA

Schematic of the Atlas V 401 configuration. Image Credit: ULA

In 1989, the Delta family of rockets began carrying GPS satellites into orbit for civilians and military alike to rely on. With last year’s launch of GPS IIF-4, Atlas carried an upgraded, modernized Boeing satellite with enhanced internal atomic clocks, for increased accuracy and improved anti-jam resistance as well as a civil signal for commercial aviation into orbit.

The Atlas V rocket will be flying in the commonly-used 401 configuration, which features a two-stage vehicle with no strap-on solid rocket boosters and a four-meter-wide nose cone.

The 401 configuration of ULA’s Atlas V rocket has two stages. When fully assembled and vertical on the launch pad, the rocket stands approximately 189 ft tall (58 meters). The main Atlas V booster is 12.5 feet (4 meters) in diameter, 106.5 ft (32.5 meters) in length and constructed out of spun-formed aluminum domes with isogrid aluminum barrels making up the fuel tank. The vehicle’s Russian-made RD-180 engine will produce 860,200 pounds of thrust and is fueled by liquid oxygen and controlled by a Centaur avionics system.

The second stage is composed of a cryogenic-fueled Centaur and powered by liquid hydrogen and liquid oxygen propellant. An RL-10A Centaur upper engine, produced by Aerojet Rocketdyne, will ignite after Atlas’ fuel has been used and will propel the spacecraft into orbit with its 22,300 pounds of thrust.

 

For the latest launch info as well as a live webcast be sure to tune into our Live Mission Monitor and follow along on social media.

 

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