SpaceX has filed an application with the Federal Communications Commission to begin ground testing of a satellite communications system between its facilities in Redmond, Wash., as early as this month.

Redmond is the base of operations for SpaceX’s multibillion-dollar effort to create a 4,425-satellite constellation in low Earth orbit for global broadband internet access and remote imaging. This week’s filing suggests that the company is getting closer to deploying its first prototype satellites.

The filing first came to light on Reddit’s SpaceX discussion forum.

SpaceX’s application covers the time frame from Oct. 24 to April 24, 2018, and refers to “antenna testing at the SpaceX Redmond Facility for SpaceX Mission 1400.” The equipment to be tested includes experimental rigs built by SpaceX, plus standard components from Texas-based Fairview Microwave.

“All tests will be short duration, and will only be performed once,” SpaceX said. The filing says the purpose of the operation is to test satellite communications links as well as telemetry, tracking and control systems for a “commercial payload prior to flight.”

No high-flying spacecraft would be involved in the tests described in the FCC application.

Sharp-eyed SpaceX fans on Reddit checked out the GPS coordinates listed in the document and figured out that the antenna system would be deployed at SpaceX’s recently acquired lab at Redmond Ridge Corporate Center. The other end of the communications link would be located about three miles away, in the vicinity of SpaceX’s satellite development offices on Northeast 68th Street in Redmond.

SpaceX’s plan calls for the first operational satellites of the constellation to be launched in 2019, to support a commercial service that may be called StarLink.

In May, a SpaceX executive told lawmakers on Capitol Hill that a prototype satellite could be launched for testing by the end of this year — and the company hasn’t yet publicly ruled out that possibility.

In a separate application, SpaceX is seeking FCC authorization to communicate with a launch vehicle for a mission during a time frame running from Nov. 10 to April 10. That mission has a different designation, listed as SpaceX Mission 1390.

Although SpaceX hasn’t yet announced what the payload for Mission 1390 will be, the favored view is that it’s a spy satellite or a military payload.