The next launch of a Global Positioning System satellite is back on track after engineers gained fresh insight into the circumstances surrounding a previous GPS flight and its low-thrust condition on the upper stage.
The Delta 4 rocket is aiming for a Feb. 20 launch of the GPS 2F-5 navigation satellite. The evening launch window at Cape Canaveral extends from 8:40 to 8:59 p.m. EST.
Engineers have been studying the situation since the October 2012 flight, even continuing to investigate after putting in place vehicle modifications that allowed three high-profile launches to go forward in 2013.
Rocket-operator United Launch Alliance and the Air Force were preparing to launch GPS 2F-5 in October 2013 when work was halted.
"The cause for delaying the GPS 2F-5 launch was not a new observation, but rather a potential new understanding the dynamic signatures that were measured during the October 2012 launch, along with the need to assess whether this could result in any change in previous flight clearance assessment," officials said.
"The investigation had previously determined that a fuel leak occurred within the engine system and that this fuel leak caused the low thrust. The ongoing Phase II investigation included very detailed characterization and reconstructions of the instrumentation signatures obtained from the October 2012 launch. These efforts resulted in some updated preliminary conclusions last October that perhaps low-frequency dynamic responses occurred on the engine system during the first engine start event."
By taking the flight telemetry from 2012, teams were able to replicate the charateristics in ground testing over the past few months.
"It was new ground testing of the launch vehicle instrumentation system that led to the preliminary conclusion that there may have been low-frequency dynamic responses during the first engine start," officials said.
During the 2012 flight, a fuel leak started as the engine was lit for the first time. That dropped the thrust level down five percent.
Two subsequent burns of the upper stage also experienced five percent drops as well, but the flight did achieve the planned orbit successfully.
"Over the past few months, the investigation team has conducted additional high-fidelity dynamic testing and analysis related to the hardware system structural and telemetry system characteristics," officials said.
"[I]t has been reconfirmed that the mitigations/system improvements previous implemented were appropriate. The flight constraint that was imposed last October has been removed."
Those mitigations included extra inspections, officials said, looked for any signs of existing damage or foreign objects within the engine that could impact the mission.
In addition, Delta 4 launches now include in-flight helium purges to critical areas of the engine system and changes how the engine is thermally conditioned during ascent to prepare for its initial ignition after first stage separation.
During the Oct. 4, 2012 launch, a small fuel leak began at the moment the engine was ignited, robbing the rocket of its expected top-level thrust settings and forcing the vehicle to improvise to overcome the anomaly during the flight.
The first stage and its strap-on boosters had done their jobs during the morning blastoff, separating to leave the cryogenic upper stage to perform three firings to lob the 3,400-pound bird into an orbit 11,000 nautical miles up.
But as the RL10B-2 engine was ignited for the initial time and reached its peak chamber pressure, a leak started above the narrow throat portion of the thrust chamber, officials revealed in December 2012.
The situation reduced the engine thrust output below the expected 25,000 pounds, causing the powerplant to burn longer to compensate and still achieve the proper orbit targets on its circuitous route into the GPS constellation.
It could have doomed some launches, but the coupling of the relatively light-weight GPS and the generous fuel margins on the Delta 4 allowed the flight to persevere.
Fed with supercold liquid hydrogen and liquid oxygen, the Aerojet Rocketdyne RL10B-2 is the latest in a long line of upper stage engines dating back a half-century. The original version of the RL10 debuted successfully on an Atlas rocket in 1963 and has been part of Centaur for more than 200 space missions.
The RL10 has dispatched robotic expeditions to every planet in our solar system, plus multiple missions to the moon and countless military spacecraft and commercial communications satellites in orbits around Earth.
This latest RL10 variant was introduced in 1998 as part of Boeing's Delta 3 program, which served as a stepping-stone to the Delta 4 rocket and development of its cryogenic upper stage.
The engine design has been fired in space 26 times to date.
Quelle: ULA / SN
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Launch of Delta IV with payload GPS IIF-5
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Launch of GPS IIF-5 on a Delta IV rocket from Cape Canaveral AFB, FL launch complex LC-37B
Launch scheduled for 21 Feb 14 1:40:00 GMT
Local Time : 20 Feb 14 20:40:00 EST
The next GPS Satellite to be added to the constellation is sitting on top of a ULA Delta IV rocket waiting to be launched on Thursday. GPS IIF-5 is scheduled to lift off sometime between 8:40 and 8:59pm EST on the 20st February from Launch Complex 37B at Cape Canaveral Air Force Station in Florida.
This will be the return to flight for this configuration of the Delta IV after a problem with the second stage of the GPS IIF-3 mission on the Delta IV rocket. Back in October 2012 there was a thrust problem with the upper stage and the engineers had to create a longer than planned burn to compensate. The GPS Satellite was placed in the correct orbit and is now functioning add part of the GPS constellation.
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Mission Live Updates Feb 21 - Delta IV : GPS IIF-5 Launch site Cape Canaveral AFB, FL
Launch Date Feb 21
From Launch Pad LC-37B
Launch Window : 8:40pm to 8:59pm EST 20th ( 1:40 - 1:59am 21st GMT)
The next GPS Satellite to be added to the constellation is sitting on top of a ULA Delta IV rocket waiting to be launched on Thursday. GPS IIF-5 is scheduled to lift off sometime between 8:40 and 8:59pm EST on the 20st February from Launch Complex 37B at Cape Canaveral Air Force Station in Florida.
This will be the return to flight for this configuration of the Delta IV after a problem with the second stage of the GPS IIF-3 mission on the Delta IV rocket. Back in October 2012 there was a thrust problem with the upper stage and the engineers had to create a longer than planned burn to compensate. The GPS Satellite was placed in the correct orbit and is now functioning add part of the GPS constellation.
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Update: 17.02.2014
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Update: 19.02.2014
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Weather looks promising for Thursday night Delta IV rocket launch
Launch teams today will determine if a Delta IV rocket and Global Positioning System satellite are ready to begin counting down to an 8:40 p.m. Thursday lift off from Cape Canaveral.
If they give a “go” to proceed, on Thursday morning the 330-foot, 9 million-pound service tower at Launch Complex 37 will roll backward to reveal the 206-foot United Launch Alliance rocket and spacecraft inside its protective fairing.
The weather forecast is excellent, with a 20 percent chance that cumulus clouds or solar activity could present problems during the 19-minute launch window.
The Air Force is attempting to launch the fifth in a new generation of Boeing-built GPS satellites used by both the military and civilians for precise position, navigation and timing information.
The new satellite, called GPS IIF-5, will replace an aging member of a constellation that has 31 operational spacecraft orbiting more than 11,000 miles above the Earth.
A mission dress rehearsal was completed Tuesday.
The launch would be ULA’s second of the year and 25th by a Delta IV, which began flying in 2002.
Quelle: Florida Today
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Update: 20.02.2014
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After Four-Month Delay, 25th Delta IV Primed for Thursday Launch of GPS IIF-5
Satellite
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Update: 21.02.2014
Erfolgreicher Start von Delta-4 mit GPS 2F-3 Satelliten
Quelle: ULA
