SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

For Annual and Transition Reports

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Commission file number 1-14279

ORBITAL SCIENCES CORPORATION

(Exact name of registrant as specified in charter)

Registrant’s telephone number, including area code:

(703) 406-5000

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.     Yes þ     No o

     Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.     o

     Indicate by check mark whether the registrant is an accelerated filer (as defined in Exchange Act Rule 12b-2).     Yes þ     No o

     The aggregate market value of the voting common equity held by non-affiliates of the registrant based on the closing sales price of the registrant’s Common Stock as reported on The New York Stock Exchange on June 30, 2004 was approximately $669,900,000. The registrant has no non-voting common equity.

     As of March 1, 2005, 55,523,954 shares of the registrant’s Common Stock were outstanding.

     Portions of the registrant’s definitive proxy statement to be filed on or about March 22, 2005 are incorporated by reference in Part III of this report.

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TABLE OF CONTENTS

Pegasus is a registered trademark and service mark of Orbital Sciences Corporation; Taurus is a registered trademark of Orbital Sciences Corporation; Orbital is a trademark of Orbital Sciences Corporation.

PART I

General

   We design, develop, manufacture and operate small rockets and space systems for the U.S. Department of Defense (“DoD”) and other U.S. government agencies and for global commercial and scientific customers. We define small rockets and space systems to include the following major product lines:

   Orbital was incorporated in Delaware in 1987 to consolidate the assets, liabilities and operations of two entities established in 1982 and 1983.

   It has been our general strategy to develop and expand a core integrated business of space systems technologies and products, focusing on the design and manufacturing of affordable lightweight rockets, small satellites and other space systems in order to establish and expand positions in niche markets that have not typically been emphasized by our larger competitors. It is also part of our strategy to seek contracts that will fund the development of enhancements to our existing launch vehicle and space systems product lines. As a result of our capabilities and experience in designing, developing, manufacturing and operating a broad range of small rockets and space systems, we believe we are well positioned to capitalize on the demand for small space-technology systems in missile defense, spaced-based military and intelligence operations, and commercial satellite communications programs, and to take advantage of continuing government-sponsored initiatives for space-based scientific research and lunar and planetary exploration initiatives.

   Our executive offices are located at 21839 Atlantic Boulevard, Dulles, Virginia 20166 and our telephone number is (703) 406-5000.

Available Information

   We maintain an Internet website at www.orbital.com. In addition to news and other information about our company, we make available on or through the Investor Information section of our website our annual report on Form 10-K, our quarterly reports on Form 10-Q, our current reports on Form 8-K and all amendments to these reports as soon as reasonably practicable after we electronically file this material with, or furnish it to, the Securities and Exchange Commission.

   At the Investor Information section of our website, we have a Corporate Governance page that includes, among other things, copies of our Code of Business Conduct and Ethics, our Corporate Governance Guidelines and the charters for each standing committee of the Board of Directors, including the Audit and Finance Committee, the Corporate Governance and Nominating Committee and the Human Resources and Compensation Committee.

   Printed copies of all of the above-referenced reports and documents may be requested by contacting our Investor Relations Department either by mail at our corporate headquarters, by

telephone at (703) 406-5543 or by e-mail at investor.relations@orbital.com. All of the above-referenced reports and documents are available free of charge.

Description of Orbital’s Products and Services

   Our products and services are grouped into three reportable segments that are described more fully below: launch vehicles (formerly launch vehicles and advanced programs), satellites and related space systems and transportation management systems. Our business is not seasonal. Customers that accounted for 10% or more of our consolidated revenues in 2004 were The Boeing Company (“Boeing”), DoD and the National Aeronautics and Space Administration (“NASA”).

   Launch Vehicles. Our launch vehicles segment is involved in developing and producing interceptor launch vehicles, suborbital launch vehicles and space launch vehicles, and designing and demonstrating launch vehicle technologies for advanced space and suborbital programs.

   Interceptor Launch Vehicles. We develop and produce interceptor launchers that boost “kill vehicles” to intercept hostile ballistic missiles and targets. Pursuant to a contract with Boeing, we are the primary supplier of operational and test interceptor boosters for the U.S. Missile Defense Agency’s (“MDA”) Ground-based Midcourse Defense (“GMD”) program, for which our interceptor boost vehicle, a modified version of our Pegasus rocket, is being used as a major operational element in the U.S. national missile defense system. We have also been awarded a contract to develop and produce a boost vehicle for MDA’s Kinetic Energy Interceptor (“KEI”) program. During 2004, we had one successful GMD interceptor flight test and delivered 10 GMD interceptors, including eight operational vehicles.

   Suborbital Launch Vehicles. We design and produce suborbital launch vehicles that place payloads into a variety of high-altitude trajectories, but unlike space launch vehicles, do not place payloads into orbit around the Earth. Our suborbital launch products include suborbital rockets and their principal subsystems, as well as payloads carried by such vehicles.

   Various branches and agencies of the U.S. military, including MDA, also use our suborbital launch vehicles as targets for defense-related applications such as ballistic missile interceptor testing and related experiments. These rockets are programmed to simulate incoming enemy missiles, offering an affordable and reliable means to test advanced missile defense systems. Our family of targets extends from long-range target launch vehicles, which include the primary targets for testing the MDA’s GMD system, to medium- and short-range target vehicles designed to simulate threats to U.S. and allied military forces deployed in overseas theaters. We have also developed a short-range supersonic sea-skimming target that flies just above the ocean’s surface and is currently being tested by the U.S. Navy.

   Since 1982, we have performed a total of 127 interceptor and major suborbital target launch missions, including five successful missions in 2004 and one successful mission so far in 2005.

   Space Launch Vehicles. We developed and produce the Pegasus, Taurus and Minotaur space launch vehicles that are used by commercial, civil government and military customers to launch small- and medium-class satellites into low-Earth orbit. Our Pegasus launch vehicle is launched from our L-1011 carrier aircraft to deploy relatively lightweight satellites into low-Earth orbit. The Taurus launch vehicle is a ground-launched derivative of the Pegasus vehicle that can carry heavier payloads to orbit. The ground-launched Minotaur launch vehicle combines Minuteman II and Peacekeeper ballistic missile rocket motors with our Pegasus and Taurus technology. Since 1990, the Pegasus, Taurus and Minotaur rockets have performed a total of 46 launches. Pursuant to a contract with the U.S. Air Force, we are developing a new class of Minotaur rockets that can carry heavier payloads

than the Taurus. We carried out one successful Taurus mission in 2004. We did not conduct any Pegasus or Minotaur missions in 2004.

   Our launch vehicle technology has also been the basis for several other advanced space and suborbital programs, including supporting efforts to develop technologies that could be applied to reusable launch vehicles, space maneuvering vehicles, hypersonic aircraft and missiles, and missile defense systems. For example, we are developing for NASA a demonstration vehicle intended to validate technology that will allow spacecraft to rendezvous with other spacecraft without human intervention. Also, during 2004, we successfully launched two Pegasus-derived Hyper-X hypersonic research launchers for NASA.

   Customers that accounted for 10% or more of our launch vehicles segment revenues in 2004 were Boeing, DoD and NASA.

   Satellites and Related Space Systems. We design and manufacture spacecraft, including LEO and GEO satellites and planetary (or “deep space”) spacecraft for communications, remote sensing, scientific, military and technology demonstration missions. Since 1982, we have built and delivered 92 satellites for various commercial and governmental customers for a wide range of communications, broadcasting, remote imaging, scientific and national security applications. In 2004, we had 18 spacecraft in various stages of design, production and/or delivery, including 11 LEO satellites, six GEO satellites and one planetary spacecraft.

   We design and manufacture various other advanced space systems, including satellite command and data handling, attitude control and structural subsystems for a variety of government and commercial customers. In addition, we provide a broad range of space-related technical services, including specialized space-related analytical, engineering and production services for U.S. government agencies such as NASA, the Jet Propulsion Laboratory, the Naval Research Laboratory and the U.S. Department of Energy. Since 1982, we have supplied such systems and services on 24 major space missions and over 100 smaller missions.

   Customers that accounted for 10% or more of our satellites and related space systems segment revenues in 2004 were DoD, NASA and Optus Networks Pty. Limited.

   Transportation Management Systems. Our transportation management systems division develops and produces fleet management systems that are used primarily by metropolitan mass transit operators in the United States. We combine global positioning satellite vehicle tracking technology with terrestrial wireless communications to help transit agencies manage public bus and public works systems. Major customers for our transportation management systems include the metropolitan mass transit authorities in Los Angeles, Philadelphia, Phoenix, San Diego, and a number of other state and municipal transit systems and private vehicle fleet operators. In addition, we have a contract to provide a system to a mass transit service in Singapore. We do not consider this product line to be core to our business.

Competition

   We believe that competition for sales of our products and services is based on performance, other technical features, reliability, price, scheduling and customization, and we believe that we compete favorably on the basis of these factors. The table below identifies our primary competitors for each major product line.

   Many of our competitors are larger and have substantially greater resources than we do. Furthermore, it is possible that other domestic or foreign companies or governments, some with greater experience in the space and defense industry and many with greater financial resources than we possess, will seek to provide products or services that compete with our products or services. Any such foreign competitor could benefit from subsidies from or other protective measures by its home country.

Research and Development

   We invest in product-related research and development to conceive and develop new products and to enhance existing products. Our research and development expenses totaled approximately $6.3 million, $7.8 million and $4.7 million for the years ended December 31, 2004, 2003 and 2002, respectively. In addition, a large portion of our total new product development and enhancement programs is funded under customer contracts.

Patents

   We rely, in part, on patents, trade secrets and know-how to develop and maintain our competitive position and technological advantage, particularly with respect to our launch vehicle and satellite products. We hold U.S. and foreign patents relating to the Pegasus vehicle, certain of our satellites and other systems and products. The majority of our U.S. patents relating to the Pegasus vehicle expire between 2007 and 2016, and most of our U.S. patents relating to our satellites expire beginning in 2013.

Components, Raw Materials and Carrier Aircraft

   We purchase a significant percentage of our product components, structural assemblies and certain key satellite components and instruments from third parties. We also occasionally obtain from the U.S. government parts and equipment that are used in the production of our products or in the provision of our services. Generally, we have not experienced material difficulty in obtaining product components or necessary parts and equipment and we believe that alternatives to our existing sources of supply are available, although increased costs and possible delays could be incurred in securing alternative sources of supply. We rely upon a sole source supplier for motors used on all our launch vehicles. While alternative sources would be available, the inability of such supplier to provide us with motors could result in significant delays, expenses and loss of revenues. Our ability to launch our Pegasus vehicle depends on the availability of an aircraft with the capability of carrying and launching such space launch vehicle. We own a modified Lockheed L-1011 carrier aircraft that is used to launch the Pegasus vehicle. In the event that our L-1011 carrier aircraft were to be unavailable, we would experience significant delays, expenses and loss of revenues as a result of having to acquire and modify a new carrier aircraft.

U.S. Government Contracts

   During 2004, 2003 and 2002, approximately 80%, 67% and 58%, respectively, of our total annual revenues were derived from contracts with the U.S. government and its agencies or from subcontracts with other U.S. government prime contractors. Most of our U.S. government contracts are funded incrementally on a year-to-year basis.

   Our major contracts with the U.S. government primarily fall into two categories: cost-reimbursable contracts and fixed-price contracts. Approximately 90% and 10% of revenues from U. S. government contracts in 2004 were derived from cost-reimbursable contracts and fixed-price contracts, respectively. Under a cost-reimbursable contract, we recover our actual allowable costs incurred, allocable overhead costs and a fee consisting of a base amount that is fixed at the inception of the contract and/or an award amount that is based on the customer’s evaluation of our performance in terms of the criteria stated in the contract. Our fixed-price contracts include firm fixed-price and fixed-price incentive fee contracts. Under firm fixed-price contracts, work performed and products shipped are paid for at a fixed price without adjustment for actual costs incurred in connection with the contract. Therefore, we bear the risk of loss due to increased cost, although some of this risk

may be passed on to subcontractors. Fixed-price incentive fee contracts provide for sharing by us and the customer of unexpected costs incurred or savings realized within specified limits, and may provide for adjustments in price depending on actual contract performance other than costs. Costs in excess of the negotiated maximum (ceiling) price and the risk of loss by reason of such excess costs are borne by us, although some of this risk may be passed on to subcontractors.

   All our U.S. government contracts and, in general, our subcontracts with other U.S. government prime contractors provide that such contracts may be terminated for convenience by the U.S. government or the prime contractor, respectively. Furthermore, any of these contracts may become subject to a government-issued stop work order under which we would be required to suspend production. In the event of a termination for convenience, contractors generally are entitled to receive the purchase price for delivered items, reimbursement for allowable costs for work in process and an allowance for reasonable profit thereon or adjustment for loss if completion of performance would have resulted in a loss. For a more detailed description of risks relating to the U.S. government contract industry, see “Risks Related to Our Business and Industry.” We derive a significant portion of our revenues from U.S. government contracts, which are dependent on continued political support and funding and are subject to termination by the U.S. government at any time.

   A portion of our business is classified for national security purposes by the U.S. government and cannot be specifically described. The operating results of these classified programs are included in our consolidated financial statements. The business risks associated with classified programs, as a general matter, do not differ materially from those of our other U. S. government programs and products.

Regulation

   Our ability to pursue our business activities is regulated by various agencies and departments of the U.S. government and, in certain circumstances, the governments of other countries. Commercial space launches require licenses from the U.S. Department of Transportation (“DoT”) and operation of our L-1011 aircraft requires licenses from certain agencies of the DoT, including the Federal Aviation Administration. Our classified programs require that we and certain employees maintain appropriate security clearances. We also require licenses from the U.S. Department of State (“DoS”) and the U.S. Department of Commerce (“DoC”) with respect to work we do for foreign customers or with foreign subcontractors.

Backlog

   Our firm backlog was approximately $1.17 billion at December 31, 2004 and approximately $995 million at December 31, 2003. We expect to convert approximately $535 million of the 2004 year-end firm backlog into revenues during 2005.

   Our firm backlog as of December 31, 2004 included approximately $1.05 billion of contracts with the U.S. government and its agencies or from subcontracts with prime contractors of the U.S. government, of which approximately $615 million is related to contracts for GMD and KEI interceptor launch vehicles. Most of our government contracts are funded incrementally on a year-to-year basis. Firm backlog from government contracts at December 31, 2004 included total funded orders of $135 million and orders not yet funded of $915 million. Changes in government policies, priorities or funding levels through agency or program budget reductions by the U.S. Congress or executive agencies could materially adversely affect our financial condition and results of operations. Furthermore, contracts with the U.S. government may be terminated or suspended by the U.S.

government at any time, with or without cause. Such contract suspensions or terminations could result in unreimbursable expenses or charges or otherwise adversely affect our business.

   Total backlog was approximately $2.31 billion at December 31, 2004. Total backlog includes firm backlog in addition to unexercised options, indefinite-quantity contracts and undefinitized orders and contract award selections. Backlog at December 31, 2004 does not give effect to new orders received or any terminations or cancellations since that date.

Employees

   As of February 1, 2005, Orbital had approximately 2,450 permanent employees. None of our employees is subject to collective bargaining agreements. We believe our employee relations are good.

* * *

   Financial information about our products and services, domestic and foreign operations and export sales is included in “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and the notes to our consolidated financial statements, and is incorporated herein by reference.

Special Note Regarding Forward-Looking Statements

   All statements other than those of historical facts included in this Form 10-K, including those related to our financial outlook, liquidity, goals, business strategy, projected plans and objectives of management for future operating results, are forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. These forward-looking statements are subject to numerous assumptions, risks and uncertainties, including the risks set forth below, and are based on our current expectations and projections about future events. Our actual results, performance or achievements could be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Although we believe the expectations reflected in these forward-looking statements are based on reasonable assumptions, there is a risk that these expectations will not be attained and that any deviations will be material. We disclaim any obligation or undertaking to disseminate any updates or revisions to any forward-looking statement contained in this Form 10-K to reflect any changes in our expectations or any change in events, conditions or circumstances on which any statement is based.

Risks Related to Our Business and Industry

   Investors should carefully consider, among other factors, the risks listed below.

We derive a significant portion of our revenues from U.S. government contracts, which are dependent on continued political support and funding and are subject to termination by the U.S. government at any time.

   A substantial majority of our revenues and firm backlog is derived from U. S. government contracts. Most of our U.S. government contracts are funded incrementally on a year-to-year basis and are subject to uncertain future funding levels. Furthermore, our direct and indirect contracts with the U.S. government may be terminated or suspended by the U.S. government or its prime contractors at any time, with or without cause. There can be no assurance that government contracts will not be terminated or suspended in the future, or that contract suspensions or terminations will not result in unreimbursable expenses or charges or other adverse effects on our financial condition.

A decline in U.S. government support and funding for key missile defense and space programs could materially adversely affect our financial condition and results of operations.

   We are also subject to laws and regulations regulating the formation, administration and performance of, and accounting for, U.S. government contracts. With respect to such contracts, any failure to comply with applicable laws could result in contract termination, price or fee reductions, or suspension or debarment from contracting with the U.S. government.

Our U.S. government contracts are subject to audits that could result in a material adverse effect on our financial condition and results of operations if a material adjustment is required.

   The accuracy and appropriateness of our direct and indirect costs and expenses under our contracts with the U.S. government are subject to extensive regulation and audit by the Defense Contract Audit Agency, or by other agencies of the U.S. government. These agencies have the right to audit our cost estimates and/or allowable cost allocations with respect to certain contracts. From time to time we have in the past made and may in the future be required to make adjustments and reimbursements as a result of these audits. Responding to governmental audits, inquiries or investigations may involve significant expense and divert management attention. Also, an adverse finding in any such audit, inquiry or investigation could involve fines, injunctions or other sanctions.

Termination of our backlog of orders could negatively impact our revenues.

   All of our direct and indirect contracts with the U.S. government or its prime contractors may be terminated or suspended at any time, with or without cause, for the convenience of the government. Our contract with Boeing to provide interceptor boosters for MDA’s GMD program is material, and the program’s termination could have an adverse impact on our liquidity and operations. From time to time, certain of our commercial contracts have also given the customer the right to unilaterally terminate the contracts. For these reasons, we cannot assure you that our backlog will ultimately result in revenues.

The majority of our contracts are long-term contracts, and our revenue recognition and profitability under such contracts may be adversely affected to the extent that actual costs exceed estimates or that there are delays in completing such contracts.

   The majority of our contracts are long-term contracts. We generally recognize revenues on long-term contracts using the percentage-of-completion method of accounting, whereby revenue, and therefore profit, is recognized based on actual costs incurred in relation to total estimated costs to complete the contract. Revenue recognition and our profitability, if any, from a particular contract may be adversely affected to the extent that original cost estimates, estimated costs to complete or incentive or award fee estimates are revised, delivery schedules are delayed or progress under a contract is otherwise impeded.

We may not receive full payment for our satellites or launch services in the event of a failure, and we could incur penalties if our satellites are not delivered or our rockets are not launched on schedule.

   Some of our satellite contracts provide for performance-based payments to be made to us after the satellite is on-orbit. Additionally, some contracts also require us to refund a percentage of payments made prior to launch if performance-based incentives are not achieved. Launch contracts may also have payments contingent upon a successful launch. While we generally intend to procure insurance to compensate us for incentive payments that are not made in the event of a launch or on-orbit failure, insurance may not be available on economical terms, if at all. In addition, some of our satellite and launch contracts require us to pay penalties in the event that satellites are not delivered, or the launch does not occur, on a timely basis. Our failure to receive incentive payments, or a

requirement that we refund amounts previously received or pay delay penalties, could adversely affect revenue recognition, profitability and our liquidity.

Our fixed-price and cost-reimbursable contracts could subject us to losses and impair our liquidity if we experience cost overruns.

   We provide our products and services primarily through fixed-price and cost-reimbursable contracts. Cost overruns may result in losses and, if the magnitude of an overrun or overruns is significant, could impair our liquidity position:

Our success depends on our ability to penetrate and retain markets for our existing products and to continue to conceive, design, manufacture and market new products on a cost-effective and timely basis.

   We anticipate that we will continue to incur expenses to design and develop new products. There can be no assurance that we will be able to achieve the technological advances necessary to remain competitive and profitable, that new products will be developed and manufactured on schedule or on a cost-effective basis or that our existing products will not become technologically obsolete. Our failure to predict accurately the needs of our customers and prospective customers, and to develop products or product enhancements that address those needs, may result in the loss of current customers or the inability to secure new customers. The development of new or enhanced products is a complex and uncertain process that requires the accurate anticipation of technological and market trends and can take a significant amount of time to complete. We may experience design, manufacturing, marketing and other difficulties that could delay or prevent the development, introduction or acceptance of new products and enhancements.

There can be no assurance that our products will be successfully developed or manufactured or that they will perform as intended.

   Most of the products we develop and manufacture are technologically advanced and sometimes include novel systems that must function under highly demanding operating conditions and are subject to significant technological change and innovation. We have in the past experienced product failures, cost overruns in developing and manufacturing our products, delays in delivery and other operational problems. We may experience some product and service failures, schedule delays and other problems in connection with our launch vehicles, satellites, transportation management systems and other products in the future. Some of our satellite and launch services contracts impose penalties on us for delays, which could be significant. In addition to any costs resulting from product

warranties or required remedial action, product failures or significant delays may result in increased costs or loss of revenues due to postponement or cancellation of subsequently scheduled operations or product deliveries and claims against performance bonds. Negative publicity from product failures may also impair our ability to win new contracts.

Several years of low demand and overcapacity in the commercial satellite market have resulted in slow growth in demand for our small GEO satellites.

   The commercial satellite market has experienced pricing pressures due to excess capacity in the telecommunications industry and weakened demand over the past several years. Satellite demand also has been impacted by the business difficulties encountered by some companies in the commercial satellite services industry, which have resulted in reduced revenues and/or access to capital and a reduction in the total market size in the near term. In addition, our competitors tend to be larger satellite manufacturers who are able to provide aggressive pricing terms. We did not win any new commercial GEO satellite contracts in 2004. While the market appears to be making a recovery, we may continue to experience slow growth in the demand for our small GEO satellites.

If our key suppliers fail to perform as expected, our reputation may be damaged, we may experience delays and lose customers and our revenues, profitability and cash flow may decline.

   We purchase a significant percentage of our product components, structural assemblies and some key satellite components and instruments from third parties. We also occasionally obtain from the U.S. government parts and equipment used in the production of our products or the provision of our services. In addition, we have a sole source for the rocket motors we use on our Pegasus and Taurus launch vehicles and the interceptor boost vehicles that we are developing and producing for MDA under our contract with Boeing. If our subcontractors fail to perform as expected or encounter financial difficulties, we may have difficulty replacing them in a timely or cost effective manner. As a result, we may experience performance delays that could result in additional program costs, a customer terminating our contract for default, or damage to our customer relationships, causing our revenues, profitability and cash flow to decline. In addition, negative publicity from any failure of one of our products as a result of a failure by a key supplier could damage our reputation and prevent us from winning new contracts.

Our international business is subject to risks. Political and economic instability in foreign markets may have a material adverse effect on our operating results.

   For the years ended December 31, 2004, 2003 and 2002, direct sales to non-U.S. customers comprised approximately 15%, 19% and 12%, respectively, of our consolidated revenues. Further, as of December 31, 2004, approximately 7% of our firm backlog was derived from non-U.S. customers. International contracts are subject to numerous risks, including:

We operate in a regulated industry, and our inability to secure or maintain the licenses, clearances or approvals necessary to operate our business could have a material adverse effect on our financial condition and results of operations.

   Our ability to pursue our business activities is regulated by various agencies and departments of the U.S. government and, in certain circumstances, the governments of other countries. Commercial space launches require licenses from the DoT, and operation of our L-1011 aircraft requires licenses from certain agencies of the DoT, including the Federal Aviation Administration. Our classified programs require that we and certain employees maintain appropriate security clearances. There can be no assurance that we will be successful in our future efforts to secure and maintain necessary licenses, clearances or regulatory approvals. Exports of our products, services and technical information frequently require licenses from the DoS or from the DoC. We have a number of international customers and subcontractors. Our inability to secure or maintain any necessary licenses or approvals or significant delays in obtaining such licenses or approvals could negatively impact our ability to compete successfully in international markets, and could result in an event of default under certain of our international contracts.

We face significant competition in each of our lines of business and many of our competitors possess significantly more resources than we do.

   Many of our competitors are larger and have substantially greater resources than we do. Furthermore, it is possible that other domestic or foreign companies or governments, some with greater experience in the space industry and many with greater financial resources than we possess, could seek to produce products or services that compete with our products or services, including new launch vehicles using new technology which could render our launch vehicles less competitively viable. Some of our foreign competitors currently benefit from, and others may benefit in the future from, subsidies from or other protective measures by their home countries.

Our financial covenants may restrict our operating activities.

   Our revolving credit facility and the indenture governing our 9% senior notes contain certain financial and operating covenants, including, among other things, certain coverage ratios, as well as limitations on our ability to incur debt, make dividend payments, make investments, sell all or substantially all of our assets and engage in mergers and consolidations and certain acquisitions. These covenants may restrict our ability to pursue certain business initiatives or certain acquisition transactions. In addition, failure to meet any of the financial covenants in our credit facility could cause an event of default under and/or accelerate some or all of our indebtedness, which would have a material adverse effect on us.

The loss of executive officers and our inability to retain other key personnel could adversely affect our operations.

   Our inability to retain our executive officers and other key employees, including personnel with security clearances required for classified work and highly skilled engineers, could have an adverse effect on our operations.

The anticipated benefits of future acquisitions may not be realized.

   From time to time we may evaluate potential acquisitions that we believe would enhance our business. Were we to complete any acquisition transaction, the anticipated benefits may not be fully realized if we are unable to successfully integrate the acquired operations, technologies and personnel into our organization.

We are subject to environmental regulations.

   We are subject to various federal, state and local environmental laws and regulations relating to the operation of our business, including those governing pollution, the handling, storage and disposal of hazardous substances and the ownership and operation of real property. Such laws may result in significant liabilities and costs. We do not believe that compliance with or liability under environmental laws and regulations has had a material impact on our operations to date, but there can be no assurance that such laws and regulations will not have a material adverse effect on us in the future.

Our restated certificate of incorporation, our amended and restated bylaws, our stockholder rights plan and Delaware law contain anti-takeover provisions that may adversely affect the rights of our stockholders.

   Our Board of Directors has the authority to issue up to 10 million shares of our preferred stock, $0.01 par value per share, and to determine the price, rights, preferences and privileges of those shares without any further vote or action by the stockholders. The rights of the holders of our common stock will be subject to, and may be adversely affected by, the rights of the holders of any preferred stock that may be issued in the future. The issuance of preferred stock, while providing desirable flexibility in connection with possible acquisitions and other corporate purposes, could have the effect of making it more difficult for a third party to acquire a majority of our outstanding voting stock.

   In addition to our ability to issue preferred stock without stockholder approval, our charter documents contain other provisions which could have an anti-takeover effect, including:

   In 1998, we adopted a stockholder rights plan which is intended to deter coercive or unfair takeover tactics. Under the rights plan, a preferred share purchase right, which is attached to each share of our common stock, generally will be triggered upon the acquisition, or actions that would result in the acquisition, of 15% or more of our common stock by any person or group. If triggered, these rights would entitle our stockholders (other than the acquirer) to purchase, for the exercise price, shares of Orbital’s common stock having a market value of two times the exercise price. The exercise price, which is subject to certain adjustments, is $210 per right. The stock purchase rights would cause substantial dilution to a person or group that attempts to acquire us on terms not approved by our Board of Directors.

   In addition, we are subject to the anti-takeover provisions of Section 203 of the Delaware General Corporation Law, which restricts the ability of current stockholders holding more than 15% of our voting shares to acquire us without the approval of 66²/3% of the other stockholders. These provisions could discourage potential acquisition proposals and could delay or prevent a change in control transaction. They could also have the effect of discouraging others from making tender offers for our common stock. As a result, these provisions may prevent our stock price from increasing

substantially in response to actual or rumored takeover attempts. These provisions may also prevent changes in our management.

We may not have the ability to raise the funds necessary to finance the repurchase offer required by the indenture governing our senior notes in the event of a change of control, which may prevent us from entering into or consummating a change of control transaction otherwise in the best interests of our stockholders.

   In the event of a change of control, under the terms of the indenture governing the terms of our $126.4 million aggregate principal amount of our 9% senior notes due 2011, we are required to offer to repurchase the notes at a premium. If a change of control were to occur, there can be no assurance that we would have sufficient financial resources, or would be able to arrange financing, to pay the purchase price for all notes tendered by holders thereof. In addition, our repurchase of the notes as a result of a change of control may be prohibited or limited by, or constitute an event of default under, the terms of our credit facility or the terms of other agreements which we may enter into from time to time. Because our failure to repurchase the notes would constitute an event of default under the indenture, we may not be able to consummate a change of control transaction, even if the transaction may be in the best interests of our stockholders.

Item 2. Properties

   We lease approximately one million square feet of office, engineering and manufacturing space in various locations in the United States, as summarized in the table below:

   We also own a 125,000 square foot state-of-the-art space systems manufacturing facility that primarily houses our satellite manufacturing, assembly and testing activities in Dulles, Virginia.

   We believe that our existing facilities are adequate for our requirements for the foreseeable future.

Item 3. Legal Proceedings

   We are party to certain litigation or proceedings arising in the ordinary course of business. In the opinion of management, the probability is remote that the outcome of any such litigation or proceedings would have a material adverse effect on our results of operations or financial condition.

Item 4. Submission of Matters to a Vote of Security Holders

   There was no matter submitted to a vote of our security holders during the fourth quarter of 2004.

Item 4A. Executive Officers of the Registrant

   The following table sets forth the name, age and position of each of the executive officers of Orbital as of February 25, 2005. All executive officers are elected annually and serve at the discretion of the Board of Directors.

   David W. Thompson is a co-founder of Orbital and has been Chairman of the Board and Chief Executive Officer of Orbital since 1982. From 1982 until October 1999, he also served as our President. Prior to founding Orbital, Mr. Thompson was employed by Hughes Electronics Corporation as special assistant to the President of its Missile Systems Group and by NASA at the Marshall Space Flight Center as a project manager and engineer, and also worked on the Space Shuttle’s autopilot design at the Charles Stark Draper Laboratory. Mr. Thompson is a Fellow of the American Institute of Aeronautics and Astronautics, the American Astronautical Society and the Royal Aeronautical Society, and is a member of the U.S. National Academy of Engineering.

   James R. Thompson (who is not related to David W. Thompson), has been Vice Chairman, President and Chief Operating Officer since April 2002, and was President and Chief Operating Officer since October 1999. He has been a director of the Company since 1992. He was Acting General Manager of our Transportation Management Systems Group from 2001 until August 2003. From 1993 until October 1999, Mr. Thompson served as Executive Vice President and General Manager, Launch Systems Group. Mr. Thompson was Executive Vice President and Chief Technical Officer of Orbital from 1991 to 1993. He was Deputy Administrator of NASA from 1989 to 1991. From 1986 until 1989, Mr. Thompson was Director of the Marshall Space Flight Center at NASA. Mr. Thompson was Deputy Director for Technical Operations at Princeton University’s Plasma Physics Laboratory from 1983 through 1986. Before that, he had a 20-year career with NASA at the Marshall Space Flight Center. He is a director of SPACEHAB Incorporated.

   Garrett E. Pierce has been Vice Chairman and Chief Financial Officer since April 2002, and was Executive Vice President and Chief Financial Officer since August 2000. He has been a director of the Company since August 2000. From 1996 until August 2000, he was Executive Vice President

and Chief Financial Officer of Sensormatic Electronics Corp., a supplier of electronic security systems, where he was also named Chief Administrative Officer in July 1998. Prior to joining Sensormatic, Mr. Pierce was the Executive Vice President and Chief Financial Officer of California Microwave, Inc., a supplier of microwave, radio frequency and satellite systems and products for communications and wireless networks. From 1980 to 1993, Mr. Pierce was with Materials Research Corporation, a provider of thin film equipment and high purity materials to the semiconductor, telecommunications and media storage industries, where he progressed from Chief Financial Officer to President and Chief Executive Officer. Materials Research Corporation was acquired by Sony Corporation as a wholly owned subsidiary in 1989. From 1972 to 1980, Mr. Pierce held various management positions with The Signal Companies.

   Ronald J. Grabe has been Executive Vice President and General Manager, Launch Systems Group since 1999. From 1996 to 1999, he was Senior Vice President and Assistant General Manager of the Launch Systems Group, and Senior Vice President of the Launch Systems Group since 1995. From 1994 to 1995, Mr. Grabe served as Vice President for Business Development in the Launch Systems Group. From 1980 to 1993, Mr. Grabe was a NASA astronaut during which time he flew four Space Shuttle missions and was lead astronaut for development of the International Space Station.

   John M. Danko has been Executive Vice President and General Manager, Space Systems Group since 2003. He served as Senior Vice President and Acting General Manager, Space Systems Group during 2002. From 1998 until the end of 2001, he served as Deputy General Manager, Space Systems Group. He previously was in charge of our Technical Services Division, a position he had held since 1989 at one of our predecessor companies. Mr. Danko held various positions with OAO Corporation from 1975 until 1989, including General Manager of the Aerospace Division when it was formed in 1980.

   Antonio L. Elias has been Executive Vice President and General Manager, Advanced Programs Group since October 2001, and was Senior Vice President and General Manager, Advanced Programs Group since August 1997. From January 1996 until August 1997, Dr. Elias served as Senior Vice President and Chief Technical Officer of Orbital. From May 1993 through December 1995, he was Senior Vice President for Advanced Projects, and was Senior Vice President, Space Systems Division from 1990 to April 1993. He was Vice President, Engineering of Orbital from 1989 to 1990 and was Chief Engineer from 1986 to 1989. From 1980 to 1986, Dr. Elias was an Assistant Professor of Aeronautics and Astronautics at Massachusetts Institute of Technology. He was elected to the National Academy of Engineering in 2001.

   Leo Millstein has been Senior Vice President, General Counsel and Corporate Secretary since August 2003. From 2002 until 2003, Mr. Millstein worked as a consultant on software and telecommunications matters. From 2000 to 2002, Mr. Millstein was Vice President, General Counsel and Corporate Secretary of MERANT plc, a software company listed on the London Stock Exchange and NASDAQ. From 1989 to 2000, Mr. Millstein held a variety of senior management and legal positions at the International Telecommunications Satellite Organization (INTELSAT), including Director of Corporate Restructuring from 1999 to 2000, Deputy General Counsel from 1995 to 1999, and Assistant General Counsel from 1989 to 1995. From 1984 to 1989, he was a partner of Dyer, Ellis, Joseph & Mills, a Washington, D.C. based law firm. From 1974 to 1984, Mr. Millstein held various legal positions with the Communications Satellite Corporation (COMSAT).

PART II

   On February 25, 2005, there were 2,055 Orbital common stockholders of record.

   Our common stock trades on the New York Stock Exchange (“NYSE”) under the symbol ORB. The range of high and low sales prices of Orbital common stock, as reported on the NYSE, was as follows:

   We have never paid any cash dividends on our common stock, nor do we anticipate paying cash dividends on our common stock at any time in the foreseeable future. Moreover, our credit facility and our indenture governing our 9% senior notes contain covenants limiting our ability to pay cash dividends. See “Management’s Discussion and Analysis of Financial Condition and Results of Operations — Liquidity and Capital Resources.”

   The transfer agent for our common stock is:

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Selected Consolidated Financial Data

   The selected consolidated financial data of the company for the years ended December 31, 2004, 2003, 2002, 2001 and 2000 have been derived from our audited consolidated financial statements. This information should be read in conjunction with the 2004, 2003 and 2002 consolidated financial statements and the related notes thereto appearing elsewhere in this Annual Report on Form 10-K.