(DULLES, VA 5 OCTOBER 1998) – Orbital Sciences Corporation (NYSE: ORB) announced that its Taurus^® rocket successfully launched an advanced experimental satellite for the U.S. National Reconnaissance Office on Saturday, October 3, in a mission that originated from Vandenberg Air Force Base, California. This mission was the third flight of the company’s ground-launched Taurus rocket, all of which were successful. It also marked the third successful space launch mission that Orbital has conducted in the past two months.

Lift-off of the Taurus rocket occurred at 3:04 a.m. Pacific time (6:04 a.m. Eastern time), when the vehicle’s first stage ignited, commencing its flight into low-Earth orbit. After an approximate 13-minute flight following a pre-programmed launch sequence controlled by Taurus’ on-board flight computer, the NRO’s Space Technology Experiment (STEX) satellite separated from the final stage of the Taurus rocket over Antarctica. Preliminary information gathered following the launch indicates that the Taurus rocket performed as planned, accurately delivering the STEX satellite into an orbit approximately 665 kilometers (370 nautical miles) above the Earth, inclined at 85 degrees to the equator.

“We are very pleased to add this mission to Taurus’ perfect launch record,” said Mr. James R. Thompson, Orbital’s Executive Vice President and General Manager of its Launch Systems Group. “Throughout 1998, Orbital has continued to build on its enviable record of successes for our full line of launchers, including our suborbital rockets and our Pegasus^® and Taurus space launch vehicles. Today’s mission was our sixth successful space launch mission this year.”

The four-stage Taurus rocket used for this mission consisted of a U.S. Government-supplied Peacekeeper first stage and three Pegasus-derived upper stages. The vehicle stood 89 feet tall and weighed approximately 151,000 pounds at lift-off. Orbital developed the ground-launched Taurus vehicle to provide a reliable and cost-effective means of launching satellites weighing up to 3,000 pounds into low-Earth orbit, or up to 800 pounds into geosynchronous orbit. Taurus incorporates advanced structural and avionics technology flight-proven on Pegasus and other operational launch systems. The STEX mission was the second Taurus launch in 1998, and the third in the rocket program’s history. Earlier this year, Orbital successfully launched the GeoSat Follow-on (GFO) satellite for the U.S. Navy, together with two ORBCOMM data communications satellites, on its second Taurus vehicle. The maiden flight of Taurus occurred in 1994, when Orbital successfully carried out a mission for the U.S. Government’s Defense Advanced Research Projects Agency.

The STEX satellite is a 1,523-pound experimental spacecraft built by Lockheed Martin Corporation that will be operated by the NRO. Over its two-year design life, the spacecraft will demonstrate 29 new technologies that may result in lower cost and higher performance spacecraft for future missions.

Orbital is a space and information systems company with 1997 revenues in excess of $600 million. The company employs over 4,200 people and has operations in eight states and several international locations. Headquartered in Dulles, VA, the company designs, manufactures, operates and markets a broad range of affordable space infrastructure systems, satellite access products and satellite services. These include satellites, launch vehicles, sensors and electronics, satellite ground systems and software, satellite-based navigation and communications products, and satellite-delivered fixed and mobile communications and Earth imaging services.