Orbital Sciences Corporation announced today that it is prepared to launch the U.S. Navy'sGEOSAT Follow-On (GFO) satellite and two ORBCOMM communications satellites aboard its Taurus(R) rocket early next week. The GFO/ORBCOMM launch will be the second mission for Orbital's ground-launched Taurus vehicle, which is a four-stage derivative of the company's Pegasus(R) space launcher. The mission will originate from Vandenberg Air Force Base (VAFB), California, and is subject to final preparations and testing, as well as acceptable weather conditions at the launch site.

Orbital also announced that the next launch of its Pegasus rocket,

originally scheduled for late this week, has been delayed by the poor weather

conditions on the West Coast that are forecasted to continue for the next

several days. The combination of the inclement conditions and a busy launch

schedule from VAFB facilities is expected to result in a new Pegasus launch

date after the Taurus mission.

On launch day, the Taurus rocket will be prepared for its mission during a

four-hour countdown procedure. The vehicle will then ignite its first stage

rocket motor, lift off and follow a preprogrammed launch sequence controlled

by its on-board flight computer. Taurus will first deliver the GFO satellite

into its planned polar orbit at an altitude of 779 by 790 kilometers inclined

at 108 degrees. The rocket will then release the two ORBCOMM satellites into

approximately the same orbit. The launch is scheduled to occur at

approximately 7:00 a.m. Pacific time on Monday (February 9), with another

available opportunity at the same time on Tuesday (February 10). The launch

window extends from approximately 5:00 a.m. to 7:35 a.m. on both days. Due to

the trajectory of the Taurus rocket, initial communications with the GFO and

ORBCOMM satellites are not expected to be established for several hours after

their release from the launch vehicle.

The Taurus Launch System

Orbital developed the ground-launched Taurus vehicle to provide a cost-

effective, reliable means of launching satellites weighing up to 3,000 pounds

into low-Earth, or up to 800 pounds into geosynchronous Earth orbit. Taurus

incorporates advanced structural and avionics technology proven on Pegasus and

other operational launch systems and is designed for easy transportability,

offering customers rapid-response launches from a wide range of locations.

The first Taurus launch occurred in March 1994 and placed two U.S.

Department of Defense satellites precisely into their target orbits. Since

then, Orbital has developed an upgraded Taurus vehicle to meet the need for

greater performance and payload volume. The vehicle being used for the

GFO/ORBCOMM mission has several different features compared to the original

Taurus configuration, including a larger payload fairing (92 inch versus 62

inch diameter) and a more powerful first stage, the commercial Castor 120

motor built by Thiokol Corporation [NYSE:TKCnews].

The GFO Satellite

The 813 lb. GFO satellite was built by Ball Aerospace & Technologies Corp.

for the U.S. Navy's Space and Naval Warfare Systems Command. The satellite

will use a radar altimeter and a water vapor radiometer to precisely measure

the subtle differences in sea surface height associated with ocean currents

and eddies. The altimeter will also provide information about wave height and

sea and glacier ice. GFO will transmit this oceanographic information

directly to ships at sea and to Navy facilities on shore. The data from the

mission is intended to enhance the effectiveness of Navy weapon and sensor

systems.

The ORBCOMM Satellites

The two ORBCOMM satellites to be launched aboard Taurus will bring the

total number of satellites in the low-orbit constellation of data

communications satellites to 12. The first two satellites were launched on a

Pegasus rocket in April 1995, followed by a recent launch of eight more on

another Pegasus in December 1997. Twenty-four more ORBCOMM satellites are

currently in production at Orbital's Germantown, Md. satellite manufacturing

facility.

The ORBCOMM satellites are based on Orbital's flight-proven MicroStar(TM)

spacecraft platform. After the first launch in 1995, Orbital took advantage

of the latest technology to make the newer models even more robust and durable

than the original versions. These satellites incorporate improvements that

will increase their on-orbit life as well as expand ORBCOMM's overall system

capacity. At the same time, Orbital's use of new materials and components has

allowed the weight of each satellite to be reduced by 10% to approximately 90

lbs.

Following the launch, the two ORBCOMM satellites will undergo standard

spacecraft checkout procedures to ensure that they are operating as planned,

as well as to make adjustments to their orbital positions using small onboard

thrusters. Like the first two ORBCOMM satellites, which were also launched

into a polar orbit, these satellites will increase total communications system

coverage over the higher latitude regions of the Earth. The satellites are

expected to be placed into commercial service about 90 days after launch.

The ORBCOMM Network

ORBCOMM Global, L.P. is a partnership of Orbital, which owns 50% of the

company, Teleglobe Inc. [NYSE:TGOnews] of Canada and TRI Inc. of Malaysia. ORBCOMM is the

world's first mobile satellite services provider offering two-way data and

messaging communications globally through a network of international service

licensees, covering over 90 countries, and in North America through more than

35 value-added resellers and direct sales channels. It is fully licensed by

the U.S. Federal Communications Commission and is currently providing

communications services in the U.S. and Canada. It has also been granted

spectrum worldwide by the International Telecommunications Union.

Applications for ORBCOMM's data and messaging services include mobile

industrial asset tracking and fixed-site monitoring. With its two operational

satellites that were launched in 1995, ORBCOMM currently offers global data

communications services to customers in the transportation, marine, oil and

gas, utility, heavy equipment and defense-related industries. As more

satellites are deployed and the system's coverage increases, ORBCOMM expects

to develop applications for the two-way personal messaging and paging markets.

ORBCOMM maintains its corporate and administrative offices, as well as its

state-of-the-art Network Control Center, in Dulles, Va., approximately 30

miles outside of Washington, D.C. It currently operates four gateway ground

stations in the U.S., and is constructing and activating additional ground

stations in Europe, Asia, Africa and South America this year.

About Orbital

Orbital is one of the ten largest space-related companies in North

America, with 1997 sales of over $600 million and a work force of 4,000

people. The company is the world's leading manufacturer of low-cost space

systems and products. Through its ORBCOMM and ORBIMAGE subsidiaries, Orbital

is also a pioneering operator of satellite networks that provide

communications and imagery services to customers all around the world.

Since its founding in 1982, Orbital (including several predecessor

companies) has built and launched, or now has on order, nearly 350 small- and

medium-class satellites and small launch vehicles. It has also produced over

15,000 space-related sensors and electronics systems and has installed

satellite ground stations in more than 25 countries.

The company's Magellan subsidiary is the world's premier producer of

mobile satellite access products. Magellan offers the broadest line of

products that use the Global Positioning System (GPS), from hand-held consumer

models that retail for $99 to advanced technology, high-precision units for

industrial and scientific uses. Using GPS and other technologies, Magellan's

PathMaster(TM) is the most popular satellite-based car navigation system in

the U.S., with over 10,000 units installed. In addition, Magellan produces

state-of-the-art satellite communications products, including satellite

telephones and hand-held personal messaging units for the ORBCOMM network.

Finally, Orbital is now building a strong position in the rapidly growing

market for satellite-delivered services. In addition to ORBCOMM's data

communications services, Orbital's ORBIMAGE subsidiary is offering

satellite-based Earth imaging services worldwide with two operational

satellites, OrbView-l and -2, and with the OrbView-3 and -4 high-resolution

digital imaging satellites expected to be in service in 1999 and 2000,

respectively.