|
|
|
|
|
Delta 4-Heavy rocket takes its place atop launch pad BY JUSTIN RAY SPACEFLIGHT NOW Posted: January 4, 2007 A massive Delta 4-Heavy rocket stood up on its Cape Canaveral launch pad Thursday morning to begin a three-month campaign of testing and preparations for blastoff carrying a critical military surveillance spacecraft.
Technicians then got to work readying the rocket to be raised vertically. The cradle-like pallets upon which the rocket rested were tied down to the erector platform on the pad's surface. The diesel-powered transporter used to haul the rocket to the pad then disengaged from the pallets and pulled away. The erector, with its two hydraulic pistons, began lifting the rocket at about 11:07 a.m. EST. News media invited to cover the spectacle watched as the orange and white booster gracefully rose up and pointed skyward within a remarkably quick 15 minutes. The mobile service tower stood by to become a cocoon for the rocket. The structure provides workers full 360-degree access during the pre-flight checkout process. The pallets will be unhooked from the booster and the erector lowered back to the ground. The transporter then returns to retrieve the pallets, completing the rocket's pad delivery. Must-see photo galleries are available: Countdown rehearsals are planned for next week and again in early February. A complete launch day simulation that includes fueling the rocket's eight cryogenic propellant tanks is expected in mid-February. The rocket's payload, the 23rd and final in the Defense Support Program (DSP) satellite series, will arrive at the launch pad in early March for attachment. Officials are eyeing an April 1 liftoff during a four-hour launch window opening around 12 noon EDT (1600 GMT). The rocket will fly directly into geostationary orbit 22,000 miles above Earth -- a trip lasting about six hours and featuring three firings by the upper stage -- to deploy the DSP spacecraft for its mission to detect enemy missile launches and nuclear weapon detonations. The Northrop Grumman-built DSP satellites use infrared telescopes to spot the heat from missile and booster plumes against the Earth's background, giving the U.S. and allies early warning of impending attacks. The craft also detect nuclear explosions. Recent DSP satellites rode aboard Titan 4 rockets. But that vehicle family has been retired in favor of the new-generation Atlas 5 and Delta 4 Evolved Expendable Launch Vehicles. The Delta 4-Heavy is created by taking three hydrogen-fueled Common Booster Core stages and strapping them together, then adding a powerful upper stage to form a launcher capable of delivering hefty amounts of cargo into space. It is the biggest unmanned rocket available in the U.S. inventory today.
That decision proved wise. The rocket suffered premature engine shutdowns on all three of its core boosters because of a condition in the liquid oxygen plumbing called cavitation. The phenomenon saw the super-cold oxidizer change from liquid to vapor within the feedlines running from the rocket's tanks to engines. The bubbles fooled internal sensors into believing the boosters had run out of liquid oxygen and the engines were told to shut down several seconds early. That left the rocket with an underspeed too great for the upper stage to overcome, resulting in a final orbit far lower than planned. "Analyses show that the cavitation originated at the entrance of the propellant feedline, where a filtration screen and turning elbow restrict the propellant flow as it accelerates leaving the tank. This feedline restriction has been present in all previous Delta 4 flights, but the unique combination of vehicle acceleration, liquid level in the tank, and propellant flow rate for this mission, reduced the fluid pressure enough to enable the creation of gaseous oxygen at this location as the tanks emptied," the Air Force said in a report about the launch.
Relieved that the incident occurred during the test flight and didn't jeopardize a real satellite payload, officials ordered corrective measures to prevent the problem from repeating in the future. The Delta 4 rocket fleet, including Medium and Heavy rocket configurations, underwent updating with hardware and computer software changes aimed at increasing the pressure in the liquid oxygen tank to remove the potential of bubbles forming. Also, the time in which the onboard computer would begin accepting "dry" readings from the fuel-level sensors was moved later. The changes were incorporated into the two Delta 4 rockets successfully flown last year from Vandenberg Air Force Base, California. The upcoming DSP 23 launch will be the 8th for a Delta 4 vehicle and the first since Boeing and Lockheed Martin merged the Delta and Atlas programs into the United Launch Alliance joint venture. Following the April flight, the team will ready another Delta 4-Heavy rocket to loft a classified spy satellite payload for the National Reconnaissance Office. Officials expect that booster to fly from Cape Canaveral approximately five months after the DSP mission. |
|
|
|
 |
|||||||||||||||||||||||||
Check out amazing footage from the video cameras mounted on the twin solid rocket boosters during space shuttle Discovery's nighttime launch.
Relive space shuttle Discovery's STS-116 mission to the International Space Station. We have nearly 200 movie clips from the December flight that installed a new truss segment and retracted a stubborn solar wing.
It was a beautiful sunrise blastoff for the Orbital Sciences Minotaur rocket from Wallops Flight Facility carrying the Air Force's TacSat 2 spacecraft and NASA's GeneSat 1.
The first United Launch Alliance Delta 2 rocket blasts off from California's Vandenberg Air Force Base carrying a classified payload for the National Reconnaissance Office.
Mars Global Surveyor has found bright new deposits in two gullies that suggest water may have spurted on the surface during the past few years. The images are presented by scientists in this news briefing presentation.
