Orbital Successfully Launches Minotaur Rocket Carrying U.S. AirForce's XSS-11 Satellite

Contact: Barron Beneski, (703) 406-5000,

Orbital Successfully Launches Minotaur Rocket Carrying U.S. Air Force's
XSS-11 Satellite
Flight Is the First of Up To Four Minotaur Launch Vehicle Missions Planned
in 2005

(Dulles, VA 12 April 2005) - Orbital Sciences Corporation (NYSE: ORB)
announced that it successfully launched the U.S. Air Force's Experimental
Small Satellite Number 11 (XSS-11) satellite aboard a company-built Minotaur
I rocket. The mission originated on Monday, April 11, 2005, at 9:35 a.m.
(EDT) from Vandenberg Air Force Base, CA (VAFB) when the Minotaur rocket
ignited its first stage motor and lifted-off from its West Coast launch
site. Approximately 12 minutes after launch, the XSS-11 satellite was
inserted into its targeted orbit of approximately 850 kilometers above the
Earth. Yesterday's mission was the third flight the Minotaur I space launch
vehicle, all of which have been successful.

Since the program's first flight in 2000, the Minotaur family of space and
suborbital launch vehicles has carried out eight launches with 100% success.
Over the next three years, Minotaur rockets are scheduled to conduct another
nine launches, including the first flights of the larger Peacekeeper-based
vehicles.

About Orbital's Minotaur Product Line

The Minotaur I space launch vehicle used in yesterday's successful launch of
the XSS-11 satellite is the first in Orbital's Minotaur product line, which
includes both space launch vehicles as well as long-range missile defense
targets and other suborbital vehicles. The rockets are derived from U.S.
Government-supplied Minuteman and Peacekeeper rocket motors. The space
launch configurations combine commercial rocket motors, avionics and other
elements with the government-supplied stages to create responsive, reliable
and low-cost launch systems for U.S. government payloads.

The Minotaur I configuration includes Minuteman rocket motors that serve as
the vehicle's first and second stages, efficiently reusing motors that have
been previously decommissioned. Its third and fourth stages, structures and
payload fairing are common with Orbital's highly reliable Pegasus XL rocket.
The Minotaur I space launch vehicle made its inaugural flight in January
2000, successfully delivering a number of small military and university
satellites into orbit and marking the first-ever use of residual U.S.
Government Minuteman boosters in a space launch vehicle. Its second mission
was carried out less than six months later, in July 2000, with the launch of
a technology demonstration satellite for the U.S. Air Force Research
Laboratory.

In addition to the Minotaur I space booster, Orbital's Minotaur product line
also includes:

· Minotaur II - A Minuteman-based three-stage suborbital rocket, used as a
target vehicle for testing U.S. missile defense systems and related
missions.

· Minotaur III - A Peacekeeper-based three-stage suborbital rocket, also
used as a target vehicle for testing U.S. missile defense systems and
similar missions.

· Minotaur IV - A heavier-lift Peacekeeper-based four-stage space launch
vehicle, used to place U.S. Government-sponsored satellites weighing up to
3,800 lbs. into low-altitude orbit. Orbital was recently awarded its first
contract by the U.S. Air Force to launch the Space-Based Surveillance System
(SBSS) satellite.

· Minotaur V - An enhanced-performance version of the Minotaur IV space
launch vehicle, that may be used to launch government satellites into
higher-energy orbits for missions related to space exploration and other
activities beyond low-Earth orbit.

About Orbital
Orbital is one of the world's leading developers and manufacturers of
affordable space systems for commercial, civil government and military
customers. The company's primary products are satellites and launch
vehicles, including geostationary and low-orbit spacecraft for
communications, remote sensing and scientific missions; ground- and
air-launched rockets that deliver satellites into orbit; and missile defense
boosters that are used as interceptor and target vehicles. Orbital also
offers space-related technical services to government agencies and develops
and builds satellite-based transportation management systems for public
transit agencies and private vehicle fleet operators.

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Note to editors: A high-resolution photo of the Minotaur I rocket that
launched the XSS-11 satellite is available on Orbital's web site at:
http://www.orbital.com/images/high/Minotaur_pad_HR.jpg


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Jacques :-)

www.spacepatches.info