SEATAC, Wash. - The Port of Seattle officially broke ground Friday on a near doubling of the north satellite, from 12 to 20 gates.

The 201,000 square-foot expansion also doubles options for dining and retail. The satellite, reached by underground train from the main terminal, is the home for most flights by SeaTac-based Alaska Airlines.

In 2015, Sea-Tac was the fastest growing airport in the country at 12.8 percent. 2016 saw slowing to a dull road at 8 percent, still causing the airport to become the 9th busiest in the country according to Port calculations. Sea-Tac is located between Seattle and Tacoma.

This year, the expectation is still expected to fall between 4 and 5 percent growth, but that's hardly a crawl. Airport Director Lance Lyttle said that will still result in an additional 2 million more passenger trips in 2017.

The north satellite, or North Star expansion, will cost $550 million, paid for primarily by the Passenger Facility Charge and landing fees, not from Port levied taxes in King County.

That represents one-fourth of the port's planned work that includes an all new baggage system and replacing a patchwork of different systems out of sight to most passengers. The new International Arrivals Hall, as well as runway work is already complete.

The newly expanded and renovated north satellite is due to open during the second quarter of 2019.