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The CloudSat mission was selected under NASA's
Earth System Science Pathfinder program in 1999.
Overseen by NASA's Science Mission Directorate,
the Earth System Science Pathfinder Program
sponsors missions designed to address unique,
specific, highly focused scientific issues, and to
provide measurements required to support Earth
science research. Missions selected in this
program are small- to- medium-sized and are
capable of being built, tested, and launched
quickly. They support a variety of scientific
objectives related to Earth science, including
studies of the atmosphere, oceans, land surface,
polar ice regions, and solid Earth.
CloudSat's primary mission is scheduled to
continue for 22 months after launch in 2006, in
order to allow more than one seasonal cycle to be
observed, although radar lifetime data indicates
that the radar is expected to operate for three
years with a 99 percent probability.
Launch Site and Vehicle
CloudSat and CALIPSO were launched together
from Space Launch Complex 2W at Vandenberg Air
Force Base, California, on a two-stage Delta
7420-10C launch vehicle with a dual payload
attachment fitting (DPAF). The Delta II launch
vehicle has a history of more than 300 successful
launches, with a 98 percent success rate. Delta II
payload capabilities range from 2.7 to 5.8 metric
tons (6,020 to 12,820 pounds) to low Earth
orbit.
The Delta launch vehicle features a
liquid-fueled first stage with four strap-on solid
fuel boosters and a second-stage liquid-fueled
engine. With its payloads, the vehicle stood 39
meters (128 feet) tall.
The first stage of the Delta II uses a
Rocketdyne RS-27A main engine. The engine provides
nearly 920,782 newtons (207,000 pounds) of thrust
by reacting RP-1 fuel (thermally stable kerosene)
with liquid oxygen. The four solid rocket motors
are 102 centimeters (40 inches) in diameter and
fueled with enough hydroxyl-terminated
polybutadiene solid propellant to provide about
431,478 newtons (97,000 pounds) of thrust
each.
The Delta's second stage is powered by a
restartable Aerojet AJ10-118K engine, which
produces about 42,703 newtons (9,600 pounds) of
thrust. The engine uses a fuel called Aerozine 50,
which is a mixture of hydrazine and dimethyl
hydrazine, reacted with nitrogen tetroxide as an
oxidizer.
Launch TimingUnlike spacecraft sent to
other planets, comets or asteroids, the launches
of Earth-orbiting satellites such as CloudSat and
CALIPSO do not need to be timed based on the
alignment of the planets. The launch date is based
only on the readiness of the satellites, the Delta
launch vehicle, and the launch range at Vandenberg
Air Force Base.
Earth-orbiting satellites do, however, need to
be launched during particular windows within any
given 24-hour day in order to get into the proper
orbit around Earth. CloudSat and CALIPSO were
launched into a sun-synchronous orbit flying close
to Earth's north and south poles. In order to
achieve this orbit, the satellite could only be
launched during a daily near-instantaneous launch
window. On the actual launch date (28 April 2006),
launch occurred at 3:02:16.721 AM PDT
(10:02:16.721 UTC).
Launch Sequence
When the Delta II launches, its first-stage
engine and its four strap-on boosters ignite at
the moment of liftoff and the rocket rises
vertically from the launch pad and then heads
south over the Pacific Ocean. Sixty-four seconds
after liftoff the strap-on boosters burn out and
their spent casings are jettisoned approximately
83 seconds after liftoff.
About four minutes and 24 seconds into the
flight, the main engine cuts off. About 14 seconds
later, the second stage ignites, and five seconds
later, the nose cone, or 'fairing' falls away. At
about 11 minutes and 10 seconds after liftoff, the
second-stage engine temporarily stops firing.
At about 59 minutes and 56 seconds after
liftoff, the second stage restarts, burning 11
seconds before shutting down. At this point, the
spacecraft with the second stage of the Delta
still attached is in a circular parking orbit 695
kilometers (375 nautical miles) above Earth.
CALIPSO spacecraft separation occurs approximately
62 minutes after liftoff, and CloudSat separates
approximately 97 minutes after liftoff.
After separation, CloudSat deployed its solar
arrays and pointed its mission instruments at
Earth using three-axis attitude control. All
sensors and units were checked, and about 34 days
after launch, CloudSat was maneuvered into its
operational circular, sun-synchronous orbit about
705 kilometers (438 miles) above Earth.
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