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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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<SEC-DOCUMENT>0001140361-10-030748.txt : 20100729
<SEC-HEADER>0001140361-10-030748.hdr.sgml : 20100729
<ACCEPTANCE-DATETIME>20100729154307
ACCESSION NUMBER:		0001140361-10-030748
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100728
FILED AS OF DATE:		20100729
DATE AS OF CHANGE:		20100729

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ORBITAL SCIENCES CORP /DE/
		CENTRAL INDEX KEY:			0000820736
		STANDARD INDUSTRIAL CLASSIFICATION:	RADIO & TV BROADCASTING & COMMUNICATIONS EQUIPMENT [3663]
		IRS NUMBER:				061209561
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1204

	BUSINESS ADDRESS:	
		STREET 1:		21839 ATLANTIC BLVD
		CITY:			DULLES
		STATE:			VA
		ZIP:			20166
		BUSINESS PHONE:		703 406 5524

	MAIL ADDRESS:	
		STREET 1:		21839 ATLANTIC BLVD
		STREET 2:		21839 ATLANTIC BLVD
		CITY:			DULLES
		STATE:			VA
		ZIP:			20166

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ORBITAL SCIENCES CORP II
		DATE OF NAME CHANGE:	19900212

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			ELIAS ANTONIO L
		CENTRAL INDEX KEY:			0001045847
		STANDARD INDUSTRIAL CLASSIFICATION:	SEARCH, DETECTION, NAVIGATION, GUIDANCE, AERONAUTICAL SYS [3812]
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-14279
		FILM NUMBER:		10977797

	MAIL ADDRESS:	
		STREET 1:		21700 ATLANTIC BLVD
		STREET 2:		ORBITAL SCIENCES CORP
		CITY:			DULLES
		STATE:			VA
		ZIP:			20166
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-07-28</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000820736</issuerCik>
        <issuerName>ORBITAL SCIENCES CORP /DE/</issuerName>
        <issuerTradingSymbol>ORB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001045847</rptOwnerCik>
            <rptOwnerName>ELIAS ANTONIO L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>21839 ATLANTIC BLVD.</rptOwnerStreet1>
            <rptOwnerStreet2>C/O ORBITAL SCIENCES CORP</rptOwnerStreet2>
            <rptOwnerCity>DULLES</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>20166</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP and GM</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2010-07-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>12000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>85142</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Grant of Restricted Stock Units under the issuer's 2005 Stock Incentive Plan.</footnote>
        <footnote id="F2">The reporting person received the Restricted Stock Units as a grant for no consideration.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Antonio L. Elias by Vanessa T. Hoang Attorney-in-Fact</signatureName>
        <signatureDate>2010-07-29</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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