— Divestiture of Canadian Subsidiary to Reinforce Space Company’s Core
Business Focus and Improve Balance Sheet —

(Dulles, VA 16 April 2001) – Orbital Sciences Corporation (NYSE: ORB)
today that it has signed a definitive agreement to sell 12.35 million shares
that it holds in its MacDonald, Dettwiler and Associates Ltd. subsidiary
MDA) to a Canadian investment group for approximately $111 million. In
addition, Orbital also has the option to sell its remaining 5.65 million
Estimated proceeds from the sale of all 18 million shares would be at least
million. The Canadian investment group includes CAI Capital Partners and
Company II, L.P., British Columbia Investment Management Corporation and the
Ontario Teachers’ Pension Plan Board. The transaction has been approved by
Orbital’s Board of Directors and is subject to certain U.S. and Canadian
regulatory approvals and customary closing conditions.

Under the terms of the agreement, Orbital expects to complete the 12.35
share initial transaction by mid-May. The buyers have until May 31, 2001 to
exercise their option to purchase the remaining 5.65 million shares of MDA.
Orbital plans to use the proceeds from the MDA transaction to reduce debt
boost cash reserves to fund working capital and for other general purposes.

“This agreement is a major step forward in Orbital’s ‘back-to-basics’
that focuses our full attention on the company’s core space technology
and in our campaign to strengthen our financial structure,” stated Mr. David
Thompson, Orbital’s Chairman and Chief Executive Officer.

“Together with last year’s sale of our Fairchild Defense subsidiary and
public offering of MDA’s stock, this divestiture will allow us to
reduce outstanding debt and improve overall liquidity. At the same time,
transaction will broaden MDA’s public investor base in Canada, adding strong
institutional shareholders who can support its continued growth in advanced
information-based systems and products,” he added.

MDA is Canada’s leading space and information systems company and is the
primary supplier of space robotics technology. It employs approximately
people at major facilities in the Vancouver and Toronto areas, as well as at
other Canadian and international locations.

Orbital is one of the world’s leading manufacturers of low-cost space
including satellites, launch vehicles, electronics and sensors, and
ground systems. Orbital is also involved with satellite-based networks that
provide wireless data communications and high-resolution Earth imagery to
customers all around the world.

More information about Orbital can be found at http://www.orbital.com

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