Orbital Sciences Pegasus
Orbital Sciences Corporation, (OSC: http://www.orbital.com/),
developed the Pegasus launch vehicle to provide their customers
the lowest cost per pound to place a 1,000 LB payload into
low Earth orbit. The Pegasus launch vehicle consists of
three solid rocket motor stages with a wing and fins for
lift and attitude control of the first stage and gimbaled
rocket nozzles on the second and third stages. The vehicle
is carried aloft horizontally and dropped from a carrier
aircraft at approximately 40,000 ft and .8 Mach. Upon motor
ignition, the vehicle accelerates to a velocity of 8,300
fps (8.3 Mach) and performs a 2.5 g positive pull up to
the correct trajectory angle. The 2nd and 3rd stages are
then fired sequentially to place the payload into orbit.
Scaled Composites worked very closely with
the OSC personnel from the beginning of the program. Significant
flight loads and thermal stresses would have to be supported
by the wing and control fins during the launch. Scaled engineering
personnel carefully examined the launch profile and developed
a composite structure that would meet the OSC performance
goals in a cost-effective manner.
The wing structure is primarily graphite/epoxy
skins over Rohacell foam cores. An aluminum structural box
is used in the center of the wing to accommodate the 4-point
carriage loads, which optimizes the structural weight of
the wing. Scaled has also performed a block structural upgrade
of the wing in order to carry heavier launch loads. The
upgrade, called the "XL" uses higher performance
IM-8 roving in the spars instead of IM-7, which allowed
the upgrade to be accomplished without a change in tooling
or schedule. The finished wing weighs approximately 630
LB and will lift, at pull-up, the equivalent weight of a
fully loaded Boeing 717 airliner.
Scaled is also responsible for the fabrication and test
of the Pegasus tail fins (a graphite/foam sandwich structure
over a reinforced urethane core - years before the X-45),
the wing-body fairing, and other on-demand special structural
components.
All of the Pegasus components are manufactured
under a customized quality assurance program which includes
full proof loadings before delivery to OSC. The QA program
embraces the key principles of Mil-I-45208. The wing and
fins contain internal strain gauges and thermocouples to
verify performance during proof testing as well as flight
loads and temperatures. The data gathered during the launch
and flight conditions are used to continually monitor the
performance and operating conditions for theses structures.
The Scaled-built structures have not had any failures or
any modifications after many successful launches.
One example of Scaled's dedicated support
for the Pegasus program occurred when the pylon adapter
used to fit the Pegasus vehicle to the B-52 launch vehicle
failed its qualification inspection. Scaled reviewed the
existing structure , conducted a CDR for an all composite
pylon adapter two days later and delivered the new pylon
adapter, for testing, 14 days after program start. When
in production, Scaled builds the Pegasus components at the
rate of one shipset per month.
For the latest Pegasus program news, visit Orbital
Sciences web page.
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