Under a clear, moonless sky, the 205-foot-tall rocket's hydrogen-fueled RS-68 main engine throttled up at 8:59 p.m. EST, followed five seconds later by ignition of two strap-on solid-fuel boosters.
Trailing a brilliant plume of fiery exhaust visible for miles around, the Delta 4 quickly vaulted away from launch complex 37 at the Cape Canaveral Air Force Station, accelerating to the east with 1.2 million pounds of thrust.
The launching was delayed 19 minutes because of concern about higher-than-allowable levels of solar radiation. But the readings dropped back within limits before the launch window closed, and mission managers cleared the rocket for flight.
The climb out went smoothly, and the solid-fuel boosters burned out and fell away about a minute and 40 seconds after liftoff. The first stage followed suit 2 1/2 minutes later and the rocket continued toward space under the power of a single hydrogen-fueled Pratt & Whitney Rocketdyne RL10B-2 engine.
The second stage engine shut down as expected about 12 minutes and 14 seconds after launch, putting the rocket and its GPS payload into an initial orbit with a high point of around 215 miles and a low point of just 100 miles or so.
Two subsequent engine firings were planned to boost the satellite into the desired 12,500-mile-high circular orbit tilted 55 degrees to the equator.
The Boeing-built Global Positioning System 2F-5 satellite was expected to be released from the Delta 4 second stage three hours and 33 minutes into the mission.
The satellite is the first of three GPS navigation beacons scheduled for launch through July to replace older spacecraft in the constellation. The 2F-5 satellite is the fifth of 12 planned "block 2" spacecraft that make up the core of the current GPS fleet.
Equipped with ultra-accurate atomic clocks, Global Positioning System satellites circle the globe in six orbital planes. Using an active constellation of more than two dozen satellites, at least four GPS spacecraft are visible in the sky from any point on the Earth's surface, transmitting location and timing signals that allow compact receivers to compute position, altitude and velocity.
An encrypted band gives military users position accuracy to within a few feet while an unencrypted public channel provides slightly less precise data to a wide variety of devices, from smart phones to automobile-mounted GPS mapping units.
The block 2F satellites are more accurate than earlier spacecraft and feature new channels to support commercial and civil aviation, more easily upgradeable flight computers and beefed up anti-jamming hardware.
The satellite being replaced by the GPS 2F-5 spacecraft was launched in 1997 and is well past its design life.
"The satellite we are replacing is over 16 years old and its design life was 7.5 years," Col. William Cooley, Global Positioning Systems director, told reporters before launch.
"Sometimes we joke those are getting old enough to vote and some are old enough to drink, and they're well past their design life. The oldest is 23 years. We've gotten remarkable performance out of them, but they are aging."
No comments:
Post a Comment