<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-06-08</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000756502</issuerCik>
        <issuerName>SKYTERRA COMMUNICATIONS INC</issuerName>
        <issuerTradingSymbol>SKYT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001256239</rptOwnerCik>
            <rptOwnerName>AFRICK ANDREW</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O APOLLO MANAGEMENT LP</rptOwnerStreet1>
            <rptOwnerStreet2>TWO MANHATTANVILLE ROAD</rptOwnerStreet2>
            <rptOwnerCity>PURCHASE</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10577</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>No Securities Beneficially Owned</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Option to Purchase</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>29.45</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-06-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>7500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2015-06-08</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>7500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>50000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Mr. Africk is associated with Apollo Management IV, L.P. (&quot;Management&quot;) and its affiliated investment managers. Management serves as the day-to-day manager of Apollo Investment Fund IV, L.P., Apollo Overseas Partners IV, L.P., AIF IV/RRRR LLC and AP/RM Acquisition LLC (the &quot;Apollo Funds&quot;), which are each record holders of certain shares of common stock and Series A Preferred Stock of SkyTerra Communications, Inc. Mr. Africk disclaims beneficial ownership of all securities of SkyTerra Communications, Inc. that may be deemed beneficially owned by Management, the Apollo Funds or Apollo Advisors IV, L.P. (the general partner of each of the Apollo Funds). This report shall not be deemed an admission that Mr. Africk is the beneficial owner of, or has any pecuniary interest in, such securities for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose.</footnote>
        <footnote id="F2">The option is exercisable as to one-third of the underlying shares on each of 6/8/06, 6/8/07 and 6/8/08, and acceleration upon Mr. Africk ceasing to be renominated to an additional term of the Board of Directors.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Andrew Africk</signatureName>
        <signatureDate>2005-07-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
