Updated May 24 to clarify role of Evolution Space.

WASHINGTON — Two companies have demonstrated the ability to conduct launches from a floating platform in U.S. territorial waters, a concept that could help address congestion at terrestrial launch sites.

The Spaceport Company announced May 23 it hosted four sounding rocket launches with the support of Evolution Space on May 22 from a platform in the Gulf of Mexico. The launches were part of a proof-of-concept test of the ability to conduct launches from an offshore platform.

“This demonstration provided numerous lessons which will be incorporated into our next project: building a sea-based spaceport capable of orbital operations,” Tom Marotta, chief executive and founder of The Spaceport Company, said in a statement.

The launches, the company said, were intended to exercise the procedures needed to conduct an orbital launch from such a platform. That included getting approvals from the Federal Aviation Administration and U.S. Coast Guard, clearing airspace and waters to allow for a safe launch and remotely launching the rocket.

The companies did not disclose the specific location of the launches. The FAA did have airspace closures in place May 22 for “space operations” in a small area of the Gulf of Mexico just south of Gulfport, Mississippi, an area where such airspace closures typically do not take place.

The launches used propulsion systems supplied by Evolution Space, a Mojave, California-based company working on solid-propellant launch vehicles for defense and space applications. The company conducted its first launch that passed the 100-kilometer Kármán Line April 22 from the California desert, reaching a peak altitude of 124.5 kilometers.

“We’re proud and grateful to be involved in what The Spaceport Company is doing,” Steve Heller, chief executive and founder of Evolution Space, said in a company statement. The company later said that the rockets were provided by Rick Maschek, an experienced small rocket builder and launch operator who was brought in by The Spaceport Company.

The Spaceport Company plans to develop floating launch platforms based on a ship design called a liftboat. The platform can sail to a designed location and then extend legs to anchor itself to the seafloor and raise the platform out of the water.

The launch platforms would not require any land-based infrastructure and would be easier to develop and operate than traditional launch sites on land. That includes facilities like Cape Canaveral Space Force Station and the neighboring Kennedy Space Center, which have seen growing launch activity that is straining the range’s infrastructure.

“It’s a lot easier to build more ships to meet more launch demand than it is to go find 100 acres on the coast somewhere,” Marotta said at a conference in February.

Those platforms would be able to accommodate small launch vehicles with payload capacities of up to about one ton to low Earth orbit. Marotta said in February the company was working on a funding round to support work on those platforms that he said would be helped by both the demonstration launches and partnerships with launch providers. The company announced in April a partnership with Vaya Space, a small launch vehicle developer previously known as Rocket Crafters, to host launches of that company’s vehicles as soon as 2025.

Floating launch platforms have been used on a larger scale, notably by the former multinational Sea Launch venture, which launched Zenit-3SL rockets from a converted oil rig on the Equator in the Pacific Ocean. SpaceX has also considered using offshore platforms for its Starship vehicle, but the company said in February it was scrapping two oil rigs it had planned to convert into launch pads after concluding they were not the right platforms.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...