The European Space Agency announced Wednesday it has selected two companies to develop a vehicle to transport cargo to the International Space Station by 2028, in a potential first step towards independent missions carrying astronauts.

The agency has recently struggled to find rockets to launch its missions into space, and is following in the footsteps of NASA by purchasing services from firms rather than developing them itself.

In November, the ESA launched a competition allocating up to 75 million euros ($80 million) to a maximum of three firms to build a vehicle to take cargo to the ISS and back.

Out of seven proposals, the ESA selected those from French-German The Exploration Company and French-Italian company Thales Alenia Space, each of which will receive 25 million euros, the agency's chief Josef Aschbacher told AFP.

"The evaluation is still ongoing," he said, adding that the ESA may yet select a third proposal.

The contracts, which run until June 2026, will focus on developing the technology and structure of the vehicles.

Additional funds for the ambitious plan would need to be approved by the ESA's 22 members states in 2025.