It is America's largest
unmanned space booster. Its level of complexity causes engineers to liken it to
launching three rockets at one time. And its fiery blastoffs create a dazzling
yet heart-in-your-throat sight.
Now, the mammoth Delta
4-Heavy has entered
operational service with Saturday night's successful
ascent carrying a critical surveillance satellite.
Towering more than 230 feet
tall and packing nearly two million pounds of thrust from its three
hydrogen-fueled main engines, this rocket is built to loft big payloads. And
the roomy nose cone offers spacious accommodations for exceptionally large
spacecraft.
The Delta 4-Heavy's
characteristics make it well suited for launching a Defense Support Program
(DSP) missile warning satellite into geosynchronous orbit 22,300 miles above
the planet.
But in its lone previous
flight three years ago, the Heavy encountered an unexpected
problem within its fuel lines, causing the engines to snuff out a few
seconds early and leaving the rocket well short of the intended orbit. That December
2004 launch was only a test, an Air Force-financed demonstration flight
designed to uncover the unknown flaws in the system before expensive and vital
national security payloads were entrusted to the big booster.
"It's always better to
find a problem than to have a latent and yet-to-be-discovered (problem). That's
part of why we considered the Heavy demo such a success. It was a very subtle
problem, but we found it and we fixed it," said Col. Jim Planeaux, the
Delta group commander at the Space and Missile Systems Center.
The
test rocket was outfitted with vast amounts of data-collecting sensors to
understand all aspects of the ascent, leading to some other changes before the
first operational launch.
"We took a lot of
readings on accelerations, vibrations, acoustics in the various compartments of
the vehicle. In a few cases (we) determined that they were higher than we
expected and we either modified the hardware slightly or moved some of the
components to a more benign environment. We finished all of those
(modifications) late last year, and we're very comfortable with the vehicle
we've got."
Rocket-maker United Launch
Alliance and the Air Force, both confident that the Heavy was ready for a real
mission, fired off the rocket from Cape Canaveral in Florida at 8:50 p.m. EST
(0150 GMT) Saturday evening.
Hidden inside the long
metallic nose cone rode the Defense
Support Program 23 spacecraft, the last in a series of eye-in-the-sky
satellites designed to spot enemy missile launches and nuclear explosions.
DSP satellites have been
flying since November 1970, rocketing into orbit aboard various versions of
now-retired Titan rockets and the space shuttle. This final one -- DSP 23 --
has been waiting more than two years for the new Heavy to hoist it into space.
The Delta 4-Heavy is
created by taking three Common Booster Cores -- the liquid hydrogen-fueled
motor that forms a Delta 4-Medium's first stage -- and strapping them together
to form a three-wide rocket, and then adding the powerful upper stage.
Each
15-story booster core features a Pratt & Whitney Rocketdyne RS-68 main
engine that generates 650,000 pounds of thrust while burning supercold liquid
hydrogen and liquid oxygen propellants. The cryogenic upper stage has the Pratt
& Whitney Rocketdyne RL10B-2 powerplant.
As the countdown entered
the final seconds, liquid hydrogen rushed through the three RS-68 engines and
then the powerplants roared to ignition. A massive cloud of fire raced up the
rocket, creating a visually awesome but terrifying display. A dozen explosive
bolts holding the vehicle to pad 37B detonated as clocks struck zero to free
the Heavy to begin climbing as three launch pad swing arms pulled back.
Data from the test flight
showed the ignition fireball created hot temperatures around the nose cone,
leading to another change for the DSP satellite launch.
"We've done a lot of
thinking about it since (the test). It does get pretty hot up around even the
payload vents. So to mitigate that, we've added some modifications to this
particular payload fairing to essentially keep the plume out as the vehicle
rises and still allow the payload compartment to vent properly," Planeaux
said.
"When you've got a
payload that's very sensitive to contamination, we had to go through some
fairly elaborate measures to ensure we were well protected there."
The three identical main
engines, the world's largest hydrogen-fueled rocket engine and each capable of
generating 17 million horsepower, propelled the vehicle into a clear night sky
with three distinct red-hot plumes trailing more than 200 feet long.
See our image collections:
About 50 seconds into
flight, the center Common Booster Core's engine was throttled back to its
minimum power level of 57 percent thrust to conserve fuel that became important
later. The starboard and port boosters continued firing at full throttle -- 102
percent thrust -- through the launch's first four minutes before emptying their
liquid hydrogen and liquid oxygen propellant tanks and shutting down the RS-68
engines. The boosters peeled away and plummeted into the Atlantic Ocean.
Once the outer boosters
were shed, the center stage finally throttled back up to 102 percent for more
than a minute of propulsion, consuming that fuel supply saved during the period
of reduced thrust. The stage was jettisoned about five minutes, 40 seconds
after liftoff, leaving the rocket's upper stage and payload to continue the
journey to orbit.
About 13 minutes into
flight, the upper stage completed its first burn to achieve an initial parking
orbit above Earth and entered an hour-long coast mode until it reached the
extreme western Pacific Ocean northeast of Australia. That is where the RL10
engine was re-ignited to reach a geosynchronous transfer orbit with a high
point stretching 22,000 miles at its high point.
The stage then coasted in
this orbit, eventually reaching the apogee where the RL10 engine was fired for
a third time starting at T+plus 6 hours, 10 minutes. The three-minute burn
circularized the orbit over the equator off the western coast of South America.
At 3:09 a.m. EST, the
5,179-pound DSP satellite was released from the Delta 4-Heavy rocket to
complete the launch.
"Last
night's successful countdown and flight culminate a tremendous amount of hard
work by the entire Air Force launch team and our industry partners.
Congratulations to all who made this challenging and spectacular launch of the
DSP 23 satellite a reality," Planeaux said.
"As the first
operational launch of a Delta 4 Heavy Lift Vehicle, it marks a major milestone
accomplishment for the EELV program and for assured access to space."
Bringing the Heavy version
of the Air Force's Evolved Expendable Launch Vehicle family into operational
service, the military has now successfully replaced the retired Titan rocket
fleet for deploying large satellite payloads.
"This success
highlights the continued maturization of our EELV program," said Brig.
Gen. Susan Helms, 45th Space Wing commander at Cape Canaveral.
Another Heavy is next up on
the Delta 4's launch schedule. An April liftoff is planned from Cape Canaveral
to deliver a classified spy satellite into orbit for the U.S. National
Reconnaissance Office.
Officials plan a five-month
gap between Saturday's flight and the subsequent launch while engineers
complete a thorough review of data.
"That has a five-month
standoff to digest all of the analysis and redo all of the loads for the
payload. But we look forward to not taking any more time than that to launch
NROL-26," said Mark Wilkins, United Launch Alliance vice president for
Delta Programs.
Another secret NRO launch
using a Heavy from the Cape is planned in 2009, followed no sooner than 2010
the first Heavy flight from California's Vandenberg Air Force Base with another
NRO payload. Outfitting of that West Coast pad to install equipment for the
larger rocket has begun.
For more on Defense Support
Program 23 satellite launched Saturday night, see our separate story here.
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2007 SpaceflightNow.com, all rights reserved.
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