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| þ | QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 |
|--------|-----------------------------------------------------------------------------------------|
|   | For the quarterly period ended June 30, 2011                                            |

| o      | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIESEXCHANGE ACT OF 1934 |
|--------|-----------------------------------------------------------------------------------------|
|   | For the transition period from ______ to ______                                         |

| Delaware                               | 06-1209561                           |
|----------------------------------------|--------------------------------------|
| (State of Incorporation of Registrant) | (I.R.S. Employer Identification No.) |

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TABLE OF CONTENTS

|     |                  |                                                                                                  | Page   |
|----------|-----------------------|-------------------------------------------------------------------------------------------------------|--------|
|     |                  |                                                                                                  |   |
| PART I.  | FINANCIAL INFORMATION |                                                                                                  |
|     |                  |                                                                                                  |   |
|     | Item 1.               | Financial Statements                                                                                  |   |
|     |                  |                                                                                                  |   |
|     |                  | Condensed Consolidated Balance Sheets as of June 30, 2011 and December 31, 2010                       | 1      |
|     |                  |                                                                                                  |   |
|     |                  | Condensed Consolidated Income Statements for the Quarters and Six Months Ended June 30, 2011 and 2010 | 2      |
|     |                  |                                                                                                  |   |
|     |                  | Condensed Consolidated Statements of Cash Flows for the Six Months Ended June 30, 2011 and 2010       | 3      |
|     |                  |                                                                                                  |   |
|     |                  | Notes to Condensed Consolidated Financial Statements                                                  | 4      |
|     |                  |                                                                                                  |   |
|     | Item 2.               | Management’s Discussion and Analysis of Financial Condition and Results of Operations           | 16     |
|     |                  |                                                                                                  |   |
|     | Item 3.               | Quantitative and Qualitative Disclosures About Market Risk                                            | 29     |
|     |                  |                                                                                                  |   |
|     | Item 4.               | Controls and Procedures                                                                               | 31     |
|     |                  |                                                                                                  |   |
| PART II. | OTHER INFORMATION     |                                                                                                  |
|     |                  |                                                                                                  |   |
|     | Item 1.               | Legal Proceedings                                                                                     | 32     |
|     |                  |                                                                                                  |   |
|     | Item 1A.              | Risk Factors                                                                                          | 32     |
|     |                  |                                                                                                  |   |
|     | Item 2.               | Unregistered Sales of Equity Securities and Use of Proceeds                                           | 32     |
|     |                  |                                                                                                  |   |
|     | Item 3.               | Defaults Upon Senior Securities                                                                       | 32     |
|     |                  |                                                                                                  |   |
|     | Item 4.               | Removed and Reserved                                                                                  | 32     |
|     |                  |                                                                                                  |   |
|     | Item 5.               | Other Information                                                                                     | 32     |
|     |                  |                                                                                                  |   |
|     | Item 6.               | Exhibits                                                                                              | 33     |
|     |                  |                                                                                                  |   |
|     |                  |                                                                                                  |

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Table of Contents

PART I

|   | ITEM 1.  FINANCIAL STATEMENTS |
|--------|-----------------------------------------|

|   | ORBITAL SCIENCES CORPORATION |
|--------|------------------------------|

CONSOLIDATED BALANCE 

|                                                                            |   | June 30, |      |   | December 31, |   |
|---------------------------------------------------------------------------------|--------|----------|-----------|--------|--------------|--------|
|                                                                            |   | 2011     |      |   | 2010         |   |
| ASSETS                                                                          |   |     |      |   |         |   |
| Current assets:                                                                 |   |     |      |   |         |   |
| Cash and cash equivalents                                                       |   | $        | 286,742   |   |         | $      | 252,415 |   |
| Receivables, net                                                                |   |     | 447,418   |   |         |   | 326,543 |   |
| Inventories                                                                     |   |     | 52,531    |   |         |   | 56,217 |   |
| Deferred income taxes, net                                                      |   |     | 34,260    |   |         |   | 24,348 |   |
| Other current assets                                                            |   |     | 8,067     |   |         |   | 18,111 |   |
| Total current assets                                                            |   |     | 829,018   |   |         |   | 677,634 |   |
| Investments                                                                     |   |     | 9,700     |   |         |   | 8,600 |   |
| Property, plant and equipment, net                                              |   |     | 249,061   |   |         |   | 232,706 |   |
| Goodwill                                                                        |   |     | 75,261    |   |         |   | 74,747 |   |
| Deferred income taxes, net                                                      |   |     | 33,923    |   |         |   | 47,806 |   |
| Other non-current assets                                                        |   |     | 27,294    |   |         |   | 21,043 |   |
| Total assets                                                                    |   | $        | 1,224,257 |   |         | $      | 1,062,536 |   |
|                                                                            |   |     |      |   |         |   |   |   |
| LIABILITIES AND STOCKHOLDERS’ EQUITY                                      |   |     |      |   |         |   |   |   |
| Current liabilities:                                                            |   |     |      |   |         |   |   |   |
| Accounts payable and accrued expenses                                           |   | $        | 298,164   |   |         | $      | 248,835 |   |
| Deferred revenues and customer advances                                         |   |     | 183,960   |   |         |   | 112,182 |   |
| Total current liabilities                                                       |   |     | 482,124   |   |         |   | 361,017 |   |
| Long-term obligations                                                           |   |     | 128,308   |   |         |   | 125,535 |   |
| Other non-current liabilities                                                   |   |     | 5,764     |   |         |   | 7,367 |   |
| Total liabilities                                                               |   |     | 616,196   |   |         |   | 493,919 |   |
| Commitments and contingencies                                                   |   |     |      |   |         |   |   |   |
| Stockholders’ equity:                                                     |   |     |      |   |         |   |   |   |
| Preferred Stock, par value $.01; 10,000,000 shares authorized, none outstanding |   |     | —   |   |         |   | — |   |
| Common Stock, par value $.01; 200,000,000 shares authorized, 58,458,374 and     |   |     |      |   |         |   |   |   |
| 58,239,875 shares outstanding, respectively                                     |   |     | 585       |   |         |   | 582 |   |
| Additional paid-in capital                                                      |   |     | 562,931   |   |         |   | 558,015 |   |
| Accumulated other comprehensive loss                                            |   |     | (1,038    | )      |         |   | (2,011 | ) |
| Retained earnings                                                               |   |     | 45,583    |   |         |   | 12,031 |   |
| Total stockholders’ equity                                                |   |     | 608,061   |   |         |   | 568,617 |   |
| Total liabilities and stockholders’ equity                                |   | $        | 1,224,257 |   |         | $      | 1,062,536 |   |

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 CONSOLIDATED 

|                                         |   | Quarters Ended June 30, |    |   | Six Months Ended June 30, |   |
|----------------------------------------------|--------|-------------------------|---------|--------|---------------------------|--------|
|                                         |   | 2011                    |    |   | 2010                      |   |   | 2011 |   |   | 2010 |   |
| Revenues                                     |   | $                       | 350,599 |   |                      | $      | 337,726 |   |   | $ | 668,302 |   |   | $ | 633,916 |   |
| Cost of revenues                             |   |                    | 282,758 |   |                      |   | 271,297 |   |   |   | 553,798 |   |   |   | 499,199 |   |
| Research and development expenses            |   |                    | 23,432  |   |                      |   | 30,268 |   |   |   | 40,567 |   |   |   | 60,431 |   |
| Selling, general and administrative expenses |   |                    | 21,602  |   |                      |   | 23,933 |   |   |   | 41,013 |   |   |   | 44,693 |   |
| Income from operations                       |   |                    | 22,807  |   |                      |   | 12,228 |   |   |   | 32,924 |   |   |   | 29,593 |   |
| Interest income and other                    |   |                    | 703     |   |                      |   | 408 |   |   |   | 12,192 |   |   |   | 746 |   |
| Interest expense                             |   |                    | (2,804  | )      |                      |   | (2,341 | ) |   |   | (5,337 | ) |   |   | (4,702 | ) |
| Income before income taxes                   |   |                    | 20,706  |   |                      |   | 10,295 |   |   |   | 39,779 |   |   |   | 25,637 |   |
| Income tax benefit (provision)               |   |                    | 511     |   |                      |   | (3,950 | ) |   |   | (6,227 | ) |   |   | (10,024 | ) |
| Net income                                   |   | $                       | 21,217  |   |                      | $      | 6,345 |   |   | $ | 33,552 |   |   | $ | 15,613 |   |
|                                         |   |                    |    |   |                      |   |   |   |   |   |   |   |   |   |   |   |
| Basic income per share                       |   | $                       | 0.36    |   |                      | $      | 0.11 |   |   | $ | 0.57 |   |   | $ | 0.27 |   |
|                                         |   |                    |    |   |                      |   |   |   |   |   |   |   |   |   |   |   |
| Diluted income per share                     |   | $                       | 0.36    |   |                      | $      | 0.11 |   |   | $ | 0.56 |   |   | $ | 0.27 |   |

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TEMENTS

|                                                                                        |   | Six Months Ended June 30, |    |
|---------------------------------------------------------------------------------------------|--------|---------------------------|---------|
|                                                                                        |   | 2011                      |    |   | 2010 |   |
| Operating Activities:                                                                       |   |                      |    |   |   |   |
| Net income                                                                                  |   | $                         | 33,552  |   |   | $ | 15,613 |   |
| Adjustments to reconcile net income to net cash provided by (used in) operating activities: |   |                      |    |   |   |   |   |   |
| Depreciation and amortization expense                                                       |   |                      | 16,476  |   |   |   | 11,393 |   |
| Deferred income taxes                                                                       |   |                      | 4,055   |   |   |   | 7,170 |   |
| Stock-based compensation and other                                                          |   |                      | 7,102   |   |   |   | 6,188 |   |
| Changes in assets and liabilities, net of effect of acquisition                             |   |                      | 6,777   |   |   |   | (93,584 | ) |
| Net cash provided by (used in) operating activities                                         |   |                      | 67,962  |   |   |   | (53,220 | ) |
|                                                                                        |   |                      |    |   |   |   |   |   |
| Investing Activities:                                                                       |   |                      |    |   |   |   |   |   |
| Capital expenditures                                                                        |   |                      | (32,774 | ) |   |   | (33,591 | ) |
| Payment for business acquisition                                                            |   |                      | — |   |   |   | (55,000 | ) |
| Net cash used in investing activities                                                       |   |                      | (32,774 | ) |   |   | (88,591 | ) |
|                                                                                        |   |                      |    |   |   |   |   |   |
| Financing Activities:                                                                       |   |                      |    |   |   |   |   |   |
| Net proceeds from issuances of common stock                                                 |   |                      | 1,364   |   |   |   | 10,311 |   |
| Debt issuance costs                                                                         |   |                      | (2,938  | ) |   |   | — |   |
| Tax benefit of stock-based compensation                                                     |   |                      | 713     |   |   |   | 1,958 |   |
| Net cash (used in) provided by financing activities                                         |   |                      | (861    | ) |   |   | 12,269 |   |
|                                                                                        |   |                      |    |   |   |   |   |   |
| Net increase (decrease) in cash and cash equivalents                                        |   |                      | 34,327  |   |   |   | (129,542 | ) |
| Cash and cash equivalents, beginning of period                                              |   |                      | 252,415 |   |   |   | 372,986 |   |
| Cash and cash equivalents, end of period                                                    |   | $                         | 286,742 |   |   | $ | 243,444 |   |

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NOTES TO CONDENSED 

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|   | • | Launch Vehicles - Rockets that are used as small- and medium-class space launch vehicles that place satellites into Earth orbit and escape trajectories, interceptor and target vehicles for missile defense systems and suborbital launch vehicles that place payloads into a variety of high-altitude trajectories. |
|--------|---------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|   | • | Satellites and Space Systems - Small- and medium-class satellites that are used to enable global and regional communications and broadcasting, conduct space-related scientific research, collect imagery and other remotely-sensed data about the Earth, carry out interplanetary and other deep-space exploration missions and demonstrate new space technologies. |
|--------|---------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|   | • | Advanced Space Programs - Human-rated space systems for Earth-orbit and deep-space exploration, and small- and medium-class satellites primarily used for national security space programs and to demonstrate new space technologies. |
|--------|---------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

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|                          | Quarters Ended June 30, |    | Six Months Ended June 30, |            |
|-------------------------------|-------------------------|---------|---------------------------|-----------------|
|                          | 2011                    |    |                      | 2010            |   | 2011 |   |   | 2010 |   |
| Launch Vehicles:              |                    |    |                      |            |   |   |   |   |   |   |
| Revenues(1)                   |  $131,367          |    |                      | $95,702         |   |  $236,640 |   |   | $196,044 |   |
| Operating income              |  6,870             |    |                      |  3,469     |   |  1,821 |   |   |  8,000 |   |
| Identifiable assets           |  200,116           |    |                      |  212,360   |  (2) |  200,116 |   |   |  212,360 |  (2) |
| Capital expenditures          |  10,184            |    |                      |  12,209    |   |  20,696 |   |   |  22,425 |   |
| Depreciation and amortization |  3,952             |    |                      |  1,808     |   |  7,272 |   |   |  3,614 |   |
| Satellites and Space Systems: |                    |    |                      |            |   |   |   |   |   |   |
| Revenues(1)                   |  $138,174          |    |                      | $139,423        |   |  $290,833 |   |   | $239,944 |   |
| Operating income              |  8,474             |    |                      |  7,512     |   |  18,784 |   |   |  15,219 |   |
| Identifiable assets           |  293,661           |    |                      |  268,804   |  (2) |  293,661 |   |   |  268,804 |  (2) |
| Capital expenditures          |  2,016             |    |                      |  1,797     |   |  3,845 |   |   |  3,327 |   |
| Depreciation and amortization |  2,805             |    |                      |  2,515     |   |  5,516 |   |   |  4,780 |   |
| Advanced Space Programs:      |                    |    |                      |            |   |   |   |   |   |   |
| Revenues(1)                   |  $103,188          |    |                      | $120,926        |   |  $195,898 |   |   | $228,469 |   |
| Operating income              |  7,463             |    |                      |  2,867     |   |  12,319 |   |   |  7,994 |   |
| Identifiable assets           |  307,228           |    |                      |  188,184   |  (2) |  307,228 |   |   |  188,184 |  (2) |
| Capital expenditures          |  2,480             |    |                      |  3,672     |   |  7,196 |   |   |  6,182 |   |
| Depreciation and amortization |  118               |    |                      |  116       |   |  235 |   |   |  119 |   |
| Corporate and Other:          |                    |    |                      |            |   |   |   |   |   |   |
| Revenues(1)                   |  $(22,130          | )  |                      | $(18,325        | )  |  $(55,069 | )  |   | $(30,541) |   |
| Operating loss                |  —           |    |                      |  (1,620    | ) (3) |  — |   |   |  (1,620 | ) (3) |
| Identifiable assets           |  423,252           |    |                      |  393,188   |  (2) |  423,252 |   |   |  393,188 |  (2) |
| Capital expenditures          |  778               |    |                      |  816       |   |  1,037 |   |   |  1,657 |   |
| Depreciation and amortization |  1,754             |    |                      |  1,711     |   |  3,453 |   |   |  2,880 |   |
| Consolidated:                 |                    |    |                      |            |   |   |   |   |   |   |
| Revenues                      |  $350,599          |    |                      | $337,726        |   |  $668,302 |   |   | $633,916 |   |
| Operating income              |  22,807            |    |                      |  12,228    |   |  32,924 |   |   |  29,593 |   |
| Identifiable assets           |  1,224,257         |    |                      |  1,062,536 |  (2) |  1,224,257 |   |   |  1,062,536 |  (2) |
| Capital expenditures          |  15,458            |    |                      |  18,494    |   |  32,774 |   |   |  33,591 |   |
| Depreciation and amortization |  8,629             |    |                      |  6,150     |   |  16,476 |   |   |  11,393 |   |

| (1)   | Corporate and other revenues are comprised solely of the elimination of intersegment revenues summarized as follows (in millions): |
|-----------------|------------------------------------------------------------------------------------------------------------------------------------|

|                         |   | Quarters Ended June 30, |   |   | Six Months Ended June 30, |   |
|------------------------------|--------|-------------------------|--------|--------|---------------------------|--------|
|                         |   | 2011                    |   |   | 2010                      |   |   | 2011 |   |   | 2010 |   |
| Launch Vehicles              |   | $                       | 20.3   |   |                      | $      | 16.5 |   |   | $ | 51.7 |   |   | $ | 27.0 |   |
| Satellites and Space Systems |   |                    | 1.3    |   |                      |   | 1.5 |   |   |   | 2.5 |   |   |   | 2.8 |   |
| Advanced Space Programs      |   |                    | 0.5    |   |                      |   | 0.3 |   |   |   | 0.9 |   |   |   | 0.7 |   |
| Total intersegment revenues  |   | $                       | 22.1   |   |                      | $      | 18.3 |   |   | $ | 55.1 |   |   | $ | 30.5 |   |

|   | (3) | The corporate and other operating loss in 2010 is comprised solely of transaction expenses incurred in connection with a business acquisition (see Note 2). |
|--------|-----|-------------------------------------------------------------------------------------------------------------------------------------------------------------|

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|                      |   |                                                  |                                                               | Quarters Ended June 30, |   |   | Six Months Ended June 30, |   |
|---------------------------|--------|-------------------------------------------------------|--------------------------------------------------------------------|-------------------------|--------|--------|---------------------------|--------|
| Numerator                 |   | 2011                                                  |                                                               |                    | 2010   |   |                      | 2011   |   |   | 2010 |   |
|                      |   | Net income                                            |                                                               | $                       | 21,217 |   |                      | $      | 6,345 |   |   | $ | 33,552 |   |   | $ | 15,613 |   |
|                      |   | Percentage allocated to shareholders (1)              |                                                               |                    | 98.9   | %      |                      |   | 99.2 | % |   |   | 98.9 | % |   |   | 99.2 | % |
|                      |   | Numerator for basic and diluted earnings per share    |                                                               | $                       | 20,984 |   |                      | $      | 6,294 |   |   | $ | 33,183 |   |   | $ | 15,488 |   |
|                      |   |                                                  |                                                               |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
| Denominator               |   |                                                  |                                                               |                    |   |   |                      |   |   |   |   |   |   |   |   |   |
|                      |   | Denominator for basic earnings per share -            |                                                               |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
|                      |   |    weighted-average shares outstanding |                                                               |                    | 58,422 |   |                      |   | 57,682 |   |   |   | 58,361 |   |   |   | 57,373 |   |
|                      |   | Dilutive effect of stock options                      |                                                               |                    | 454    |   |                      |   | 667 |   |   |   | 472 |   |   |   | 729 |   |
|                      |   | Denominator for diluted earnings per share            |                                                               |                    | 58,876 |   |                      |   | 58,349 |   |   |   | 58,833 |   |   |   | 58,102 |   |
|                      |   |                                                  |                                                               |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
| Per share income          |   |                                                  |                                                               |                    |   |   |                      |   |   |   |   |   |   |   |   |   |
|                      |   | Basic                                                 |                                                               | $                       | 0.36   |   |                      | $      | 0.11 |   |   | $ | 0.57 |   |   | $ | 0.27 |   |
|                      |   | Diluted                                               |                                                               |                    | 0.36   |   |                      |   | 0.11 |   |   |   | 0.56 |   |   |   | 0.27 |   |
| _________________________ |   |                                                  |                                                               |                    |   |   |                      |   |   |   |   |   |   |   |   |   |
|                      |   |                                                  |                                                               |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
|                      |   |  (1)                                             | Basic weighted-average shares outstanding                          |                    |   | 58,422 |                      |   |   | 57,682 |   |   |   | 58,361 |   |   |   | 57,373 |   |
|                      |   |                                                  | Basic weighted-average shares outstanding and                      |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |   |
|                      |   |                                                  |    unvested restricted share units expected to vest |                    |   | 59,096 |                      |   |   | 58,155 |   |   |   | 59,039 |   |   |   | 57,847 |   |
|                      |   |                                                  | Percentage allocated to shareholders                               |                    |   | 98.9   | %                         |   |   | 99.2 | % |   |   | 98.9 | % |   |   | 99.2 | % |

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|     |   | June 30, |    |   | December 31, |   |
|----------|--------|----------|---------|--------|--------------|--------|
|     |   | 2011     |    |   | 2010         |   |
| Billed   |   | $        | 61,774  |   |         | $      | 56,035 |   |
| Unbilled |   |     | 385,644 |   |         |   | 270,508 |   |
| Total    |   | $        | 447,418 |   |         | $      | 326,543 |   |

|      |   | June 30, 2011          |   |   | December 31, 2010          |   |
|-----------|--------|------------------------|--------|--------|----------------------------|--------|
|      |   | Cost or Amortized Cost |   |   | Net Unrealized Gain (Loss) |   |   | Fair Value |   |   | Cost or Amortized Cost |   |   | Net Unrealized Gain (Loss) |   |   | Fair Value |   |
| Debt      |   | $                      | 7,150  |   |                       | $      | (250 | ) |   | $ | 6,900 |   |   | $ | 7,150 |   |   | $ | (450 | ) |   | $ | 6,700 |   |
| Equity(1) |   |                   | 2,000  |   |                       |   | 800 |   |   |   | 2,800 |   |   |   | 2,000 |   |   |   | (100 | ) |   |   | 1,900 |   |
| Total     |   | $                      | 9,150  |   |                       | $      | 550 |   |   | $ | 9,700 |   |   | $ | 9,150 |   |   | $ | (550 | ) |   | $ | 8,600 |   |
|      |   |                   |   |   |                       |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |

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|                                        |   | Quarters Ended June 30, |   |   | Six Months Ended June 30, |   |
|---------------------------------------------|--------|-------------------------|--------|--------|---------------------------|--------|
|                                        |   | 2011                    |   |   | 2010                      |   |   | 2011 |   |   | 2010 |   |
| Debt Securities                        |   |                    |   |   |                      |   |   |   |   |   |   |   |
| Fair value at beginning of period           |   | $                       | 6,800  |   |                      | $      | 10,500 |   |   | $ | 6,700 |   |   | $ | 10,900 |   |
| Temporary impairment credits (charges), net |   |                    | 100    |   |                      |   | — |   |   |   | 200 |   |   |   | (400 | ) |
| Fair value at end of period                 |   | $                       | 6,900  |   |                      | $      | 10,500 |   |   | $ | 6,900 |   |   | $ | 10,500 |   |
|                                        |   |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
|                                        |   |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
| Equity Securities                           |   |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
| Fair value at beginning of period           |   | $                       | 2,400  |   |                      | $      | 2,100 |   |   | $ | 1,900 |   |   | $ | 2,200 |   |
| Temporary impairment credits (charges), net |   |                    | 400    |   |                      |   | — |   |   |   | 900 |   |   |   | (100 | ) |
| Fair value at end of period                 |   | $                       | 2,800  |   |                      | $      | 2,100 |   |   | $ | 2,800 |   |   | $ | 2,100 |   |
|                                        |   |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
|                                        |   |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
| Total                                       |   |                    |   |   |                      |   |   |   |   |   |   |   |   |   |   |   |
| Fair value at beginning of period           |   | $                       | 9,200  |   |                      | $      | 12,600 |   |   | $ | 8,600 |   |   | $ | 13,100 |   |
| Temporary impairment credits (charges), net |   |                    | 500    |   |                      |   | — |   |   |   | 1,100 |   |   |   | (500 | ) |
| Fair value at end of period                 |   | $                       | 9,700  |   |                      | $      | 12,600 |   |   | $ | 9,700 |   |   | $ | 12,600 |   |

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|                                  |   | Quarters Ended June 30, |   |   | Six Months Ended June 30, |   |
|---------------------------------------|--------|-------------------------|--------|--------|---------------------------|--------|
|                                  |   | 2011                    |   |   | 2010                      |   |   | 2011 |   |   | 2010 |   |
| Net income                            |   | $                       | 21,217 |   |                      | $      | 6,345 |   |   | $ | 33,552 |   |   | $ | 15,613 |   |
| Unrealized gain (loss) on investments |   |                    | 500    |   |                      |   | — |   |   |   | 1,100 |   |   |   | (500 | ) |
| Defined benefit plans, net of tax     |   |                    | (155   | )      |                      |   | (447 | ) |   |   | (127 | ) |   |   | (281 | ) |
| Total comprehensive income            |   | $                       | 21,562 |   |                      | $      | 5,898 |   |   | $ | 34,525 |   |   | $ | 14,832 |   |

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|                             |   | Restricted Stock Units |    | Stock Options    |
|----------------------------------|--------|------------------------|---------|------------------|
|                             |   |                   |    | Weighted Average |   |   |   | Weighted Average |
|                             |   | Number of              |    | Measurement      |   | Number of |   | Exercise |
|                             |   | Units                  |    | Date Fair Value  |   | Options |   | Price |
| Outstanding at December 31, 2010 |   |                   | 684,674 |             |   | $ | 16.38 |   |   |   | 1,226,582 |   |   | $ | 6.46 |   |
| Granted (1)                      |   |                   | 26,860  |             |   |   | 17.47 |   |   |   | — |   |   |   | — |   |
| Exercised                        |   |                   | — |             |   |   | — |   |   |   | (135,971 | ) |   |   | 4.60 |   |
| Vested                           |   |                   | (35,107 | )                |   |   | 16.59 |   |   |   | — |   |   |   | — |   |
| Forfeited                        |   |                   | (8,145  | )                |   |   | 16.73 |   |   |   | — |   |   |   | — |   |
| Expired                          |   |                   | — |             |   |   | — |   |   |   | (5,648 | ) |   |   | 4.14 |   |
| Outstanding at June 30, 2011     |   |                   | 668,282 |             |   | $ | 16.41 |   |   |   | 1,084,963 |  (2) |   | $ | 6.70 |   |

| (1)   | The fair value of restricted stock unit grants is determined based on the closing market price of Orbital’s common stock on the date of grant.  Such value is recognized as expense over the service period, net of estimated forfeitures. |
|-----------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (2)   |   The weighted average remaining contractual term is 1.85 years. |
|-----------------|----------------------------------------------------------------------------|

|                                                                                      |   | Quarters Ended June 30,   |
|-------------------------------------------------------------------------------------------|--------|---------------------------|
| (in millions)                                                                             |   | 2011                      |   | 2010 |
| Stock-based compensation expense                                                          |   | $                         | 1.5 |   |   | $ | 1.7 |   |
| Income tax benefit related to stock-based compensation expense                            |   |                      |  0.5 |   |   |   |  0.7 |   |
| Intrinsic value of options exercised computed as the market                               |   |                      |   |   |   |   |   |   |
|     price on the exercise date less the price paid to exercise the options |   |                      |  0.5 |   |   |   |  1.2 |   |
| Cash received from exercise of options                                                    |   |                      |  0.1 |   |   |   |  2.2 |   |
| Tax benefit recorded as credits to additional paid-in capital related                     |   |                      |   |   |   |   |   |   |
|     to stock-based compensation transactions                               |   |                      |  0.2 |   |   |   |  0.4 |   |
|                                                                                      |   |                      |   |   |   |   |   |   |
|                                                                                      |   |                      |   |   |   |   |   |   |
|                                                                                      |   | Six Months Ended June 30, |
| (in millions)                                                                             |   | 2011                      |   | 2010 |
| Stock-based compensation expense                                                          |   | $                         | 2.9 |   |   | $ | 3.5 |   |
| Income tax benefit related to stock-based compensation expense                            |   |                      |  0.9 |   |   |   |  1.4 |   |
| Intrinsic value of options exercised computed as the market                               |   |                      |   |   |   |   |   |   |
|     price on the exercise date less the price paid to exercise the options |   |                      |  1.8 |   |   |   |  5.4 |   |
| Cash received from exercise of options                                                    |   |                      |  0.6 |   |   |   |  9.7 |   |
| Tax benefit recorded as credits to additional paid-in capital related                     |   |                      |   |   |   |   |   |   |
|     to stock-based compensation transactions                               |   |                      |  0.7 |   |   |   |  2.0 |   |

|                                                                                        |   | As of         |   |
|---------------------------------------------------------------------------------------------|--------|---------------|--------|
| (in millions)                                                                               |   | June 30, 2011 |   |
| Shares of common stock available for grant under stock-based incentive plans                |   |          | 1.3    |   |
| Aggregate intrinsic value of restricted stock units that are expected to vest               |   | $             | 11.3   |   |
| Unrecognized compensation expense related to non-vested restricted stock units, expected to |   |          |   |   |
| be recognized over a weighted-average period of 1.80 years                                  |   |          | 6.1    |   |
| Aggregate intrinsic value of stock options outstanding, all fully vested                    |   |          | 11.0   |   |

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|                                        |   | Second Quarter |   |   | First Six Months |   |   | Inception |   |
|---------------------------------------------|--------|----------------|--------|--------|------------------|--------|--------|-----------|--------|
|                                        |   | 2011           |   |   | 2010             |   |   | 2011      |   |   | 2010 |   |   | To Date |   |
| Research and development costs incurred (1) |   | $              | 36.5   |   |             | $      | 38.9   |      |   | $ | 78.4 |   |   | $ | 67.2 |   |   | $ | 337.5 |   |
| Less - amounts funded by NASA               |   |           | 25.2   |   |             |   | 18.1   |      |   |   | 59.3 |   |   |   | 33.1 |   |   |   | 211.6 |   |
| Net research and development expenses       |   | $              | 11.3   |   |             | $      | 20.8   |      |   | $ | 19.1 |   |   | $ | 34.1 |   |   | $ | 125.9 |   |

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ITEM 2.  

| ·   | Launch Vehicles - Rockets that are used as small- and medium-class space launch vehicles that place satellites into Earth orbit and escape trajectories, interceptor and target vehicles for missile defense systems and suborbital launch vehicles that place payloads into a variety of high-altitude trajectories. |
|--------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| ·   | Satellites and Space Systems - Small- and medium-class satellites that are used to enable global and regional communications and broadcasting, conduct space-related scientific research, collect imagery and other remotely-sensed data about the Earth, carry out interplanetary and other deep-space exploration missions and demonstrate new space technologies. |
|--------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| ·   | Advanced Space Programs - Human-rated space systems for Earth-orbit and deep-space exploration, and small- and medium-class satellites primarily used for national security space programs and to demonstrate new space technologies. |
|--------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

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|                                        |   | Second Quarter |   |   | First Six Months |   |   | Inception |   |
|---------------------------------------------|--------|----------------|--------|--------|------------------|--------|--------|-----------|--------|
|                                        |   | 2011           |   |   | 2010             |   |   | 2011      |   |   | 2010 |   |   | To Date |   |
| Research and development costs incurred (1) |   | $              | 36.5   |   |             | $      | 38.9   |      |   | $ | 78.4 |   |   | $ | 67.2 |   |   | $ | 337.5 |   |
| Less - amounts funded by NASA               |   |           | 25.2   |   |             |   | 18.1   |      |   |   | 59.3 |   |   |   | 33.1 |   |   |   | 211.6 |   |
| Net research and development expenses       |   | $              | 11.3   |   |             | $      | 20.8   |      |   | $ | 19.1 |   |   | $ | 34.1 |   |   | $ | 125.9 |   |

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|             |   | Second Quarter |    |   | First Six Months |   |
|------------------|--------|----------------|---------|--------|------------------|--------|
| ($ in thousands) |   | 2011           |    |   | 2010             |   |   | % Change |   |   | 2011 |   |   | 2010 |   |   | % Change |   |
| Revenues         |   | $              | 131,367 |   |             | $      | 95,702 |   |   |   | 37% |   |   | $ | 236,640 |   |   | $ | 196,044 |   |   |   | 21% |   |
| Operating income |   |           | 6,870   |   |             |   | 3,469 |   |   |   | 98% |   |   |   | 1,821 |   |   |   | 8,000 |   |   |   | (77% | ) |
| Operating margin |   |           | 5.2%    |   |             |   | 3.6% |   |   |   |   |   |   |   | 0.8% |   |   |   | 4.1% |   |   |   |   |   |

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|             |   | Second Quarter |    |   | First Six Months |   |
|------------------|--------|----------------|---------|--------|------------------|--------|
| ($ in thousands) |   | 2011           |    |   | 2010             |   |   | % Change |   |   | 2011 |   |   | 2010 |   |   | % Change |   |
| Revenues         |   | $              | 138,174 |   |             | $      | 139,423 |   |   |   | (1% | ) |   | $ | 290,833 |   |   | $ | 239,944 |   |   |   | 21% |   |
| Operating income |   |           | 8,474   |   |             |   | 7,512 |   |   |   | 13% |   |   |   | 18,784 |   |   |   | 15,219 |   |   |   | 23% |   |
| Operating margin |   |           | 6.1%    |   |             |   | 5.4% |   |   |   |   |   |   |   | 6.5% |   |   |   | 6.3% |   |   |   |   |   |
|             |   |           |    |   |             |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |

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|             |   | Second Quarter |    |   | First Six Months |   |
|------------------|--------|----------------|---------|--------|------------------|--------|
| ($ in thousands) |   | 2011           |    |   | 2010             |   |   | % Change |   |   | 2011 |   |   | 2010 |   |   | % Change |   |
| Revenues         |   | $              | 103,188 |   |             | $      | 120,926 |   |   |   | (15% | ) |   | $ | 195,898 |   |   | $ | 228,469 |   |   |   | (14% | ) |
| Operating income |   |           | 7,463   |   |             |   | 2,867 |   |   |   | 160% |   |   |   | 12,319 |   |   |   | 7,994 |   |   |   | 54% |   |
| Operating margin |   |           | 7.2%    |   |             |   | 2.4% |   |   |   |   |   |   |   | 6.3% |   |   |   | 3.5% |   |   |   |   |   |

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ITEM 3.  

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ITEM 4.  

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PART II

ITEM 1.

ITEM 1A.

ITEM 2.

|         (a) | None. |
|------------------------------------------------|-------|
|         (b) | None. |
|         (c) | None. |

ITEM 3.

ITEM 4. 

ITEM 5.

ITEM 6.   

|         (a) | Exhibits – A complete listing of exhibits required is given in the Exhibit Index. |
|-----------------------------------------------------|-----------------------------------------------------------------------------------------|

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|                            | ORBITAL SCIENCES CORPORATION |
|---------------------------------|------------------------------|
|                            |                         |   |
|                            |                         |   |
| DATED:  July 29, 2011 | By:                          | /s/ David W. Thompson |
|                            |                         | David W. Thompson |
|                            |                         | Chairman, President and Chief Executive Officer |
|                            |                         |   |
|                            |                         |   |
| DATED:  July 29, 2011 | By:                          | /s/ Garrett E. Pierce |
|                            |                         | Garrett E. Pierce |
|                            |                         | Vice Chairman and Chief Financial Officer |

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| Exhibit No. | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|-------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| 3.1         | Restated Certificate of Incorporation (incorporated by reference to Exhibit 4.1 to the company’s Registration Statement on Form S-3 (File Number 333-08769) filed and effective on July 25, 1996).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| 3.2         | Amended and Restated Bylaws (incorporated by reference to Exhibit 3.2 to the company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2005).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| 3.3         | Certificate of Amendment to Restated Certificate of Incorporation, dated April 29, 1997 (incorporated by reference to Exhibit 3.3 to the company’s Annual Report on Form 10-K for the fiscal year ended December 31, 1998).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| 3.4         | Certificate of Amendment to Restated Certificate of Incorporation, dated April 30, 2003 (incorporated by reference to Exhibit 3.4 to the company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2003).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 4.1         | Form of Certificate of Common Stock (incorporated by reference to Exhibit 4.1 to the company’s Registration Statement on Form S-1 (File Number 33-33453) filed on February 9, 1990 and effective on April 24, 1990).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| 4.2         | Indenture dated as of December 13, 2006, by and between Orbital Sciences Corporation and The Bank of New York, as Trustee (incorporated by reference to Exhibit 4.1 to the company’s Current Report on Form 8-K filed on December 13, 2006).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 4.3         | Form of 2.4375% Convertible Senior Subordinated Note due 2027 (incorporated by reference to Exhibit 4.2 to the company’s Current Report on Form 8-K filed on December 13, 2006).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| 10.1        | Credit Agreement, dated as of June 7, 2011, by and among Orbital Sciences Corporation, as Borrower, the subsidiaries of the Borrower party thereto as Guarantors, the Lenders party thereto, and Wells Fargo Bank, National Association, as Administrative Agent, Swingline Lender and Issuing Lender,  Wells Fargo Securities LLC, Citigroup Global  Markets Inc. and Merrill Lynch, Pierce, Fenner & Smith Incorporated as Joint Lead Arrangers and Joint Bookrunners, Citibank, N.A. and Bank of America, N.A. as Co-Syndication Agents and PNC Bank, N.A. and Sovereign Bank as Co-Documentation Agents (incorporated by reference to Exhibit 10.1 to the company’s Current Report on Form 8-K filed on June 10, 2011).  |

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| 10.2 | Security and Pledge Agreement, dated as of June 7, 2011, between Orbital Sciences Corporation, the other obligors party thereto, and Wells Fargo Bank, National Association, as Administrative Agent (incorporated by reference to Exhibit 10.2 to the company’s Current Report on Form 8-K filed on June 10, 2011).                                                                                                                                                                                              |
|------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| 31.1 | Certification of Chairman, President and Chief Executive Officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 (18 U.S.C. Section 1350) (transmitted herewith).                                                                                                                                                                                                                                                                                                                                             |
| 31.2 | Certification of Vice Chairman and Chief Financial Officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 (18 U.S.C. Section 1350) (transmitted herewith).                                                                                                                                                                                                                                                                                                                                                   |
| 32.1 | Written Statement of Chairman, President and Chief Executive Officerpursuant to Section 906 of the Sarbanes-Oxley Act of 2002 (18 U.S.C. Section 1350) (transmitted herewith).                                                                                                                                                                                                                                                                                                                                          |
| 32.2 | Written Statement of Vice Chairman and Chief Financial Officerpursuant to Section 906 of the Sarbanes-Oxley Act of 2002 (18 U.S.C. Section 1350) (transmitted herewith).                                                                                                                                                                                                                                                                                                                                                |
| 101  | The following financial information from the company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2011, formatted in XBRL (eXtensible Business Reporting Language): (i) Condensed Consolidated Balance Sheets as of June 30, 2011 and December 31, 2010;  (ii) Condensed Consolidated Income Statements for the quarters and six months ended June 30, 2011 and 2010 and (iii) Condensed Consolidated Statements of Cash Flows for the six months ended June 30, 2011 and 2010.* |

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