Spaceflight Now Delta



The Mission




Rocket: Delta 2 (7925)
Payload: GPS 2R-M1
Date: Sept. 25, 2005
Window: 11:37 p.m.-12:05 a.m. EDT
Site: SLC-17A, Cape Canaveral, Florida
Satellite feed: AMC 3, Transponder 14, C-band, 87° West

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Launch of modernized GPS satellite set for this week
BY JUSTIN RAY
SPACEFLIGHT NOW

Posted: September 18, 2005

Editor's note: Launch was delayed after this story was published. The new launch date is Sunday, Sept. 25.

The first modernized Global Positioning System satellite featuring additional navigation signals to benefit military and civilian users around the world will be launched Wednesday night aboard a Boeing Delta 2 rocket.


A Delta 2 rocket will launch the first modernized GPS 2R satellite. Photo: Carleton Bailie/Boeing
 
Liftoff from pad 17A at the Cape Canaveral spaceport is scheduled for 11:53 p.m. EDT, the opening of a 28-minute window that extends past midnight to 12:21 a.m. EDT (0353-0421 GMT).

The Lockheed Martin-built GPS 2R-M1 spacecraft has spent seven months undergoing launch testing and preparations at the Cape, twice as long as originally envisioned. Concerns about internal components on the satellite and delays building Range Safety batteries for the Delta booster postponed the mission from May.

The early weather forecast is calling for a 40 percent chance of clouds and rain interfering with Wednesday's launch attempt. See the full forecast here.

It will take just over 24 minutes for the three-stage Delta 2 vehicle to propel the $75 million payload into a highly elliptical transfer orbit looping from 150 miles at its closest point from Earth to nearly 11,000 miles at the farthest. From there, the spacecraft will use its onboard kick motor to reach the GPS constellation by raising the low point to circularize the orbit and increase the orbital inclination to 55 degrees above and below the equator.

The spaceborne network features 24 primary and several backup satellites flying in six orbital groupings. The Air Force continues to launch new satellites as replacements to keep the critical navigation system in good health. There are 28 functioning GPS satellites today, according to the military.

GPS 2R-M1 will assume the Plane C, Slot 4 position, taking over for the GPS 2A-20 craft launched in May 1993. The aging satellite, although still operational, will be repositioned within the GPS constellation for the remainder of its life. The new slot for the old spacecraft will be determined later.

The satellites send continuous navigation signals that enable users virtually anywhere on the planet to find their position in latitude, longitude and altitude and determine time. The information is so accurate that time can be figured to less than a millionth of a second, speed within a fraction of a mile per hour and pinpoint location within a matter of feet.

The military's orbiting GPS constellation began to take shape in 1989. To replace the original satellites as they age, Lockheed Martin built 21 so-called "replenishment" satellites. Dubbed the "2R" series, this current generation of GPS spacecraft has seen 13 flown since 1997, although the first one was lost in a launch explosion. Now, the remaining 8 are being retrofitted with upgrades to provide additional capabilities once deployed in space.

Carrying the re-titled name GPS 2R-M, for Modernized, these upcoming satellites increase the power for existing signals and offer two new military signals as well as a second civilian signal.

The changes fit within the existing GPS 2R satellite design. The Modernized spacecraft, which will weigh 4,545 pounds at launch, only 60 pounds heavier than the earlier model, have a redesigned external antenna panel; and higher-power, more-efficient transmitters highlight the internal changes.

The navigation payload is built for Lockheed Martin by ITT Industries.

The improvements will provide greater accuracy, added resistance to interference and enhanced performance for all users, according to the Air Force. The advancements for the military will provide warfighters with a more robust jam-resistant signal and enable better targeting of GPS-guided weapons in hostile environments, while the new civilian signal removes ionospheric errors and improves accuracy, officials say.

Once circling the Earth, ground controllers will perform a multi-month test program to examine the new 2R-M satellite's performance and users' reception before proceeding with the next launch. If all goes well, the 2R-M2 satellite could lift off in January or February.

Lockheed Martin has set aside several of the GPS 2R satellites that have not yet been upgraded in case a problem develops in space and the military needs to launch the proven design on short notice. The others are undergoing the overhaul process now.

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