Adjusted EBITDA from the Earth Intelligence segment decreased to $131 million from $146 million, or by $15 million, for the three months ended June 30, 2021, compared to the same period of 2020. The decrease was primarily driven by a decrease in the recognition of deferred revenue related to the EnhancedView Contract as mentioned above. The decrease was also driven by an increase in service costs and selling, general and administrative costs for the three months ended June 30, 2021, as compared to the same period of 2020. These decreases were partially offset by growth on contracts with international defense and intelligence customers and the U.S. government.

Space Infrastructure

Changes in revenues from year to year are influenced by the size, timing and number of satellite contracts awarded in the current and preceding years and the length of the construction period for satellite contracts awarded. Revenues on satellite contracts are recognized using the cost-to-cost method of accounting to determine the percentage of completion over the construction period, which typically ranges between 20 to 36 months and up to 48 months in certain situations. Adjusted EBITDA margins can vary from quarter to quarter due to the mix of our revenues and changes in our estimated costs to complete as our risks are retired and as our estimated costs to complete are increased or decreased based on contract performance.