The size of what Elon Musk's Space Exploration Technologies Corp. plans in Bastrop County, east of Austin, is coming into focus — and it appears to be massive.

The company wants to construct a 521,521-square-foot "shell building," according to an Aug. 31 filing with the Texas Department of Licensing and Regulation. An estimated project cost of $43 million was given, along with an expected completion date of July 2023.

To put the size into perspective, it would be larger than the footprint of half-a-dozen typical H-E-B grocery stores.

The details in TDLR filings often change. But this represents one of the very few glimpses into what Musk's rocket company plans to do in the rural area since Austin Business Journal first reported in June that SpaceX had taken control of dozens of acres.

The filing does not list SpaceX by name but uses the address for the company's test facility in McGregor, southwest of Waco.

Representatives with SpaceX did not respond to a request for comment. Other entities listed on the filing, including West Lake Hills-based architecture firm TAG International LLP, also did not respond to requests for comments.

The facility, named "Project Echo," was previously detailed in a June 6 filing with the Texas Commission on Environmental Quality. At the time, SpaceX was approved to construct a warehouse on 29.5 acres at 816 FM 1209. The project was estimated to start June 6 and be completed by the end of March 2023. The permit allowed for stormwater dumping into the adjacent Colorado River.

This is not the first time SpaceX has been connected to the Austin area but is more concrete evidence that Musk's company is setting up shop in the metro. SpaceX now has four job listings on its website for the Austin area, up from two a couple of months ago: one for a facilities engineer, one for a senior application software engineer, one for a development test engineer and one for a site reliability engineer.

The action east of Austin marks the continued investment by Musk in Central Texas. Recently, much of that has been in Bastrop County, which had a population of 102,058 in 2021, up from 74,171 in 2010, according to the U.S. Census Bureau.

The most active of Musk's companies has been The Boring Co., a tunneling startup, which has been buying large tracts of land in Bastrop County in the past year. County property records show that Gapped Bass LLC — an entity tied to Pflugerville-based Boring Co. — has grown its land holdings to more than 250 acres along FM 1209.

On June 9, a 46.5-acre tract along FM 1209 was transferred from Gapped Bass to SpaceX, according to the records. That's the site of the proposed warehouse.

Boring has not publicly detailed what work is being done in Bastrop County but the company wants to dig transit tunnels in urban areas across the United States, aiming to alleviate traffic and free up real estate traditionally dedicated to surface roads.

Some Bastrop County neighbors have lamented a lack of transparency about the facility and additional traffic in the rural region.

TCEQ had received three complaints about wastewater and concrete production at the site and launched a pair of investigations, though the issues have since been resolved. And Bloomberg in June detailed a spat with the Texas Department of Transportation.

Meanwhile, just east of Austin, Tesla Inc. (Nasdaq: TSLA) is producing vehicles at its 4-million-square-foot "gigafactory." The site is considered the company's headquarters and is expected to employ thousands.

Musk's Neuralink Corp. — a startup focused on creating brain implants to treat neurological issues such as paralysis — also appears to still be hiring in the Austin area. It lists dozens of job openings online, for roles from engineering to manufacturing to animal care specialists.