(Dulles, VA 23 DECEMBER 1999) — Orbital Sciences Corporation (NYSE: ORB) announced today that the National Aeronautics and Space
Administration (NASA) has selected the company’s Pegasus® rocket to launch the Solar Radiation and Climate Experiment (SORCE) and SCISAT-1
satellites on two separate missions in 2002. The SORCE mission will originate from Cape Canaveral Air Station, Florida and is scheduled for launch in
July 2002. The SCISAT-1 mission will originate from Vandenberg Air Force Base, California and is scheduled for launch in the second quarter of 2002.
Orbital has now been awarded four of the 16 potential missions that may be awarded by NASA’s Kennedy Space Center under the Small Expendable
Launch Vehicle Services (SELVS) contract, which is valued at up to $400 million.

“With the addition of these two missions, Orbital’s Pegasus rocket was again confirmed as the world’s workhorse vehicle in the market for reliable
launches of small scientific, remote sensing and communications satellites,” said Mr. Ronald J. Grabe, Orbital’s Executive Vice President and General
Manager of its Launch Systems Group. “As always, we look forward to working with the NASA-led teams and are proud of our role in providing
dependable, low-cost access to space to help to further space science studies.”

In addition to being selected to launch the SORCE satellite, the company’s Space Systems Group is also building the spacecraft for NASA under contract
to the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder, Colorado. The SORCE satellite will carry four instruments
to study and measure solar irradiance, the main source of energy in the Earth’s atmosphere. The SORCE program merges two previous efforts: the
Solar-Stellar Irradiance Comparison Experiment/Solar Atmospheric Variability Explorer (SOLSTICE/SAVE) mission and the Total Solar Irradiance
Mission (TSIM).

The primary objective of the NASA-sponsored SCISAT-1 mission is to study the chemical and dynamic processes that control the distribution of ozone in
the upper troposphere and stratosphere. The SCISAT-1 satellite is being built by Bristol Aerospace Limited of Winnipeg, Canada with cooperation from
the Canadian Space Agency.

Orbital’s three-stage Pegasus rocket sets the standard in the small launch market, carrying satellites weighing up to 1,000 pounds into low-Earth orbit.
Pegasus is carried aloft by the company-owned “Stargazer” L-1011 aircraft to an altitude approximately 40,000 feet over open ocean, where it is released
and then free-falls in a horizontal position for five seconds before igniting its first stage rocket motor. This patented air-launch system has enabled Orbital
to conduct launches from five separate sites, including four sites in the United States and one in Europe, the first time a space launch vehicle has provided
such operational flexibility. Pegasus recently completed its 28th mission with the successful launch of seven ORBCOMM data communications satellites
on December 4, 1999.

Orbital is one of the largest space technology and satellite services companies in the world, with 1999 revenues targeted to exceed $900 million. The
company, which is headquartered in Dulles, Virginia, employs over 5,200 people at its major facilities in the United States, Canada and several overseas
locations. Orbital is the world’s leading manufacturer of low-cost space systems and products, including satellites, launch vehicles, electronics and
sensors, satellite ground systems and software, and satellite-based navigation and communications products. Through its ORBCOMM and ORBIMAGE
affiliates and ORBNAV subsidiary, Orbital is also a pioneering operator of satellite-based networks that provide data communications, high-resolution
imagery and automotive information services to customers all around the world.