Exhibit 10.1

October 31, 2011

ViaSat, Inc.

6155 El Camino Real

Carlsbad, California 92009

Attention: Paul Castor, Esq.

Gentlemen:

We refer to that certain Fourth Amended and Restated Revolving Loan Agreement dated as of July 1, 2009 among ViaSat, Inc., a Delaware corporation (the “Borrower”), each lender from time to time party thereto, Union Bank, N.A., as Administrative Agent, Bank of America, N.A., as Syndication Agent, JPMorgan Chase Bank, N.A., Compass Bank and Wells Fargo Bank, National Association, as Co-Documentation Agents, Credit Suisse AG, Cayman Islands Branch and Bank of the West, as Co-Agents, Merrill Lynch, Pierce, Fenner & Smith Incorporated and Union Bank, N.A., as Joint Lead Arrangers and Joint Book Runners, and Union Bank, N.A., as Collateral Agent (as amended, modified or supplemented from time to time, the “Credit Agreement”). Capitalized terms used herein and not defined shall have the meanings assigned to them in the Credit Agreement.

The Borrower has requested, and the Requisite Lenders have agreed, effective as of September 30, 2011, to amend the Credit Agreement in certain respects in accordance with the terms of this Amendment. Accordingly, the Credit Agreement is amended so that the definition of “EBITDA” is amended and restated in its entirety to read as follows:

“EBITDA” means the sum of (a) Net Income plus (b) to the extent deducted in determining Net Income, (i) Interest Expense, (ii) expense for taxes paid or accrued, (iii) depreciation, (iv) amortization, (v) non-cash losses as a result of the disposition of customer premises equipment, (vi) any extraordinary non-cash or nonrecurring non-cash charges or losses, (vii) any non-cash charges arising from compensation expense as a result of the adoption of Financial Accounting Standards Board Statement 123 (Revised 2004), “Share-Based Payment”, which requires certain stock-based compensation to be recorded as expense within the Borrower’s consolidated statement of operations, (viii) non-recurring expenses for professional services, regulatory clearances and filings, transfer fees, severance payments and other similar closing costs (to the extent such expenses are not capitalized by the Borrower) incurred in connection with Permitted Acquisitions and reasonably approved by the Administrative Agent and (ix) with respect to the operating costs related to the ViaSat-1 Project, (A) up to $300,000 incurred during Borrower’s Fiscal Quarter ended April 1, 2011, (B) up to $5,650,000 incurred during Borrower’s Fiscal Quarter ended July 1, 2011, (C) up to $5,650,000 incurred during Borrower’s Fiscal Quarter ended September 30, 2011 and (D) up to $7,500,000 incurred

during Borrower’s Fiscal Quarter ended December 30, 2011; minus (c) to the extent included in Net Income, (i) non-cash gains as a result of the disposition of customer premises equipment, (ii) any extraordinary non-cash or nonrecurring non-cash gains, (iii) the amount of any subsequent cash payments in respect of any non-cash charges described in the preceding clause (b)(vii), and (iv) Interest income; all calculated for the Borrower and its Subsidiaries on a consolidated basis.

The governing law and venue provisions of Section 11.17 of the Credit Agreement are incorporated herein by this reference mutatis mutandis. This letter amendment may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one instrument. Delivery of an executed counterpart hereof by facsimile or electronic transmission shall be effective as delivery of a manually executed counterpart. Except as amended hereby, all of the provisions of the Credit Agreement and the other Loan Documents shall remain unmodified and in full force and effect except that each reference to the “Agreement”, or words of like import in any Loan Document, shall mean and be a reference to the Credit Agreement as amended hereby. This letter amendment shall be deemed a “Loan Document” as defined in the Credit Agreement.

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If you are in agreement with the foregoing, please execute this letter in the space provided below.

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