Company Supports Extended Lifetime of the FUSE Mission with Enhanced Command and Control Software

Orbital Sciences Corporation (NYSE: ORB)
announced today that it has completed the in-orbit delivery and initial
checkout of its new gyroless software for the Far Ultraviolet Spectroscopic
Explorer (FUSE) satellite for its customer, the Johns Hopkins University
(JHU). Based on the company’s MidStar spacecraft bus, FUSE was launched in
June 1999 and last year completed its three-year primary mission. The
satellite is now operating in an extended mission lifetime, which the new
gyroless software will significantly enhance.

With the success and importance of the FUSE science, extended mission
operations are highly desirable. Given that the FUSE satellite’s Inertial
Reference Unit’s have life-limiting elements, the FUSE program team embarked
upon a software development program to produce a new system to enable
gyroless control of the satellite in order to extend the space science
mission should the spacecraft encounter future gyro failures. Orbital
integrated a new "safe mode," developed by NASA’s Goddard Space Flight
Center, with the Orbital-developed coarse and fine pointing gyroless
software to provide a substantially enhanced capability to the FUSE
spacecraft and maintain its sub- arcsecond pointing capability. This new
operations scheme also required significant changes to the instrument’s
software and the Fine Error Sensor’s software, which were modified by the
JHU and the Canadian Space Agency, respectively.

"We are thrilled that we are able to provide the scientific community with
assurance of extended mission capability and continuity with the
implementation of this new software" said Mr. Michael Miller, Orbital’s Vice
President of Science and Technology Satellite Programs.

The new gyroless software provides FUSE with better stability than the
original design with only a minor impact to observational efficiency. A
significant amount of new Fault Detection and Correction software was also
added and modified to provide for autonomous "fail operational"

paths associated with the new operations and to speed up recovery back to
the science timeline in the event of anomalies. Combined with the changes
made to the instrument’s software, this new system will allow the extended
mission operations to be handled with fewer operations staff through greater

Mr. Brian Class, Orbital’s lead designer of the original control system and
the new gyroless upgrade, said, "The ground testing of this new system,
prior to implementation aboard the satellite, posed a significant challenge
to the FUSE team. We developed a virtual interface that connected the JHU
test laboratory in Baltimore. Maryland with the Orbital test laboratory in
Dulles, Virginia. The telemetry and command interface was then linked with
the Spacecraft Control Center in Baltimore and the Orbital’s Dulles test
laboratory. This methodology allowed us to perform closed-loop testing of
the Attitude Control Subsystem and the Instrument Data System software and
to test scripts with the new Spacecraft Control Center databases and
displays in a very realistic way, thereby significantly reducing the risk
associated with these major modifications."

Mr. Class concluded, stating, "The FUSE gyroless control software is
Orbital’s second operational system to provide full gyroless capability to a
science mission. Earlier this year we launched NASA’s Solar Radiation and
Climate Experiment spacecraft for the University of Colorado’s Laboratory
for Atmospheric and Space Physics, which we designed and built without
gyroscopes. The FUSE system, however, is significantly more complex due to
the finer pointing requirements and the need to incorporate data from the
FUSE Fine Error Sensor."

Orbital develops and manufactures small space and missile systems for
commercial, civil government and military customers. The company’s primary
products are satellites and launch vehicles, including low-orbit,
geostationary and planetary satellites 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.